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ATOLL RESEARCH BULLETIN NOS. 399-414

RESEARCH

BULLETIN

ECOLOGY AND GEOMORPHOLOGY OF THE COCOS

(KEELING) ISLANDS

Issued by

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D.C. U.S.A.

SMITHSONIAN

WASHINGTON,

FEBRUARY 1994

ATOLL RESEARCH BULLETIN

NOS. 399-414

ECOLOGY AND GEOMORPHOLOGY OF THE COCOS
(KEELING) ISLANDS

EDITED BY

COLIN D. WOODROFFE

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

ATOLL RESEARCH BULLETIN

NOS. 399-414

NO. 399. SCIENTIFIC STUDIES IN THE COCOS (KEELING) ISLANDS:
AN INTRODUCTION
BY C.D. WOODROFFE AND P.F. BERRY

NO. 400. CLIMATE, HYDROLOGY AND WATER RESOURCES OF THE
COCOS (KEELING) ISLANDS
BY A.C. FALKLAND

NO. 401. LATE QUATERNARY MORPHOLOGY OF THE COCOS
(KEELING) ISLANDS
BY D.E. SEARLE

NO. 402. GEOMORPHOLOGY OF THE COCOS (KEELING) ISLANDS
BY C.D. WOODROFFE, R.F. McLEAN AND E. WALLENSKY

NO. 403. REEF ISLANDS OF THE COCOS (KEELING) ISLANDS
BY C.D. WOODROFFE AND R.F McLEAN

NO. 404. VEGETATION AND FLORA OF THE COCOS (KEELING)
ISLANDS
BY D.G. WILLIAMS

‘NO. 405. AN UPDATE OF BIRDS OF THE COCOS (KEELING)
ISLANDS
BY T. STOKES

NO. 406. MARINE HABITATS OF THE COCOS (KEELING) ISLANDS
BY D.G. WILLIAMS

NO. 407. SEDIMENT FACIES OF THE COCOS (KEELING) ISLANDS
LAGOON
BY S.G. SMITHERS

NO. 408. HYDRODYNAMIC OBSERVATIONS OF THE COCOS
(KEELING) ISLANDS LAGOON
BY P. KENCH

NO. 409. HERMATYPIC CORALS OF THE COCOS (KEELING)
ISLANDS: A SUMMARY
BY J.E.N. VERON

NO.

NO.

NO.

NO.

NO.

410.

411.

412.

413.

414.

MARINE MOLLUSCS OF THE COCOS (KEELING) ISLANDS
BY F.E. WELLS

ECHINODERMS OF THE COCOS (KEELING) ISLANDS
BY L.M. MARSH ,

FISHES OF THE COCOS (KEELING) ISLANDS
BY G.R. ALLEN AND W.F. SMITH-VANIZ

BARNACLES OF THE COCOS (KEELING) ISLANDS
BY D.S. JONES

DECAPOD CRUSTACEANS OF THE COCOS (KEELING)
ISLANDS
BY G.J. MORGAN

(Manuscripts received 15 March 1993; Revised 8 December 1993)

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

ACKNOWLEDGMENT

The Atoll Research Bulletin is issued by the Smithsonian Institution to
provide an outlet for information on the biota of tropical islands and reefs
and on the environment that supports the biota. The Bulletin is supported by
the National Museum of Natural History and is produced by the Smithsonian
Press. This special issue is financed and distributed with funds from the
Department of the Environment, Sport and Territories, Canberra, Australia, the
Australian Nature Conservation Agency, Directorate for Northern Australia, and
Atoll Research Bulletin readers.

The Bulletin was founded in 1951 and the first 117 numbers were issued by
Pacific Science Board, National Academy of Sciences, with financial support
from the Office of Naval Research. Its pages were devoted largely to reports
resulting from the Pacific Science Board’s Coral Atoll Program.

All statements made in papers published in the Atoll Research Bulletin
are the sole responsibility of the authors and do not necessarily represent
the views of the Smithsonian nor of the editors of the Bulletin.

Articles submitted for publication in the Atoll Research Bulletin should
be original papers in a format similar to that found in recent issues of the
Bulletin. First drafts of manuscripts should be typewritten double spaced and
can be sent to any of the editors. After the manuscript has been reviewed and
accepted, the author will be provided with a page format with which to prepare
a single-spaced camera-ready copy of the manuscript.

COORDINATING EDITOR

Ian G. Macintyre National Museum of Natural History
MRC-125
Smithsonian Institution
Washington, D.C. 20560

EDITORIAL BOARD

Stephen D. Cairns (MRC-163) National Museum of Natural History
Brian F. Kensley (MRC-163) (Insert appropriate MRC code)

Mark M. Littler (MRC-166) Smithsonian Institution

Wayne N. Mathis (MRC-169) Washington, D.C. 20560

Victor G. Springer (MRC-159)

Joshua I. Tracey, Jr. (MRC-137)

Warren L. Wagner (MRC-166)

Roger B. Clapp (MRC-111) National Museum of Natural History

National Biological Survey
Smithsonian Institution
Washington, D.C. 20560

David R. Stoddart Department of Geography
501 Earth Sciences Building
University of California
Berkeley, CA 94720

Bernard M. Salvat Laboratoire de Biologie & Ecologie
Tropicale et Méditerranéenne
Ecole Pratique des Hautes Etudes
Labo. Biologie Marine et Malacologie
Université de Perpignan
66025 Perpignan Cedex, France

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ATOLL RESEARCH BULLETIN

NO. 399

CHAPTER 1

SCIENTIFIC STUDIES IN THE COCOS (KEELING) ISLANDS:
AN INTRODUCTION

BY

C.D. WOODROFFE AND P.F. BERRY

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

96°49 96°50'E -. 96°55

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West Is.

ISLANDS

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CHAPTER 1
SCIENTIFIC STUDIES IN THE COCOS
(KEELING) ISLANDS: AN INTRODUCTION.
BY
C.D. WOODROFFE *
AND
P.F. BERRY **

INTRODUCTION

The Cocos (Keeling) Islands are a particularly isolated group of islands in the
eastern Indian Ocean (Fig. 1). They comprise a southern group, the South Keeling Islands
(12° 12' S, 96° 54’ E), which form a coral atoll with a shallow lagoon fringed by a series
of reef islands. A single horseshoe-shaped island (atollon), North Keeling (11° 50' S, 96°
49' E) is located 26 km to the north of the main group. They lie 900 km west of
Christmas Island and 1000 km southwest of Java Head.

DISCOVERY AND SETTLEMENT

The group is named after the coconut (Cocos nucifera), which grew there in
profusion, even before deliberate planting of all of the southern atoll as a part of the
Clunies Ross estate, and Captain William Keeling. Keeling is believed to have been the
first European to sight the islands in 1609 on his return from Bantam, on behalf of the East
India Company, though there is no record of that sighting. The islands are not shown in
the 1606 edition of Ortelius Theatrum Orbis Terrarum, but do appear in Blaeu's appendix
to the third edition produced about 1631. They are recorded with the name Cocos
Eylanden in a manuscript map drawn by Hessel Gerritsz in 1622, and on Dudley's Arcano
del Mare (1646) on which it says that they were discovered by the English. On a Dutch
chart produced in Amsterdam in 1659 they are called the Cocos Islands; though around this
time they were also called the Triangular Islands. The English hydrographer Thornton
used the name Kelling Island in his Oriental Navigation of 1703. Captain Ekeberg from
Sweden visited North Keeling in 1740. There is an account of the islands in van Keulen's
Zeefakkel, (6th edition, 1753), with a map attributed to the Dutch navigator, Jan de Marre
(1729).

In his sailing directory for this region of the Indian Ocean, compiled in 1805, the
British hydrographer, James Horsburgh, called them the Cocos-Keeling Islands, and
named one of the islands after himself. After settlement the early inhabitants called them
the Borneo Coral Reefs after the supply vessel the Borneo, owned by John and Joseph
Hare and Co, and captained by John Clunies Ross. They were also known as the Keeling-
Cocos Islands, and after 1955 they became officially the Cocos (Keeling) Islands.

Despite knowledge of the islands for 200 years or more, it was not until the early
nineteenth century that they were settled and an interest was taken in them because they lay

‘ Department of Geography, University of Wollongong, Northfields Avenue,
Wollongong, New South Wales, 2522.
ee Western Australian Museum, Francis Street, Perth, Western Australia, 6000.

on a trade route from Europe to the Far East. The first settlement was accidental, Captain
Le Cour and the crew of the brig Mauritius lived on Direction Island for several weeks
after their ship was wrecked on the reef. Captain Driscoll in the Lonach went ashore on 24
November 1825, shortly after the men were rescued, and noted the wreck of the Mauritius.
Shortly thereafter, on 6 December 1825, Captain John Clunies Ross, a Scottisl trader
sailing the Borneo for Alexander Hare's company, made a brief landing on the islands.
During his visit he sounded the main channel, cleared an area on Horsburgh and Direction
Islands, and planted cereals and vegetables.

In the following year a settlement was established by Alexander Hare, a somewhat
discredited trader and associate of Ross, who brought with him a crew of largely Sumatran
and Javanese seamen and an entourage of women of various nationalities, on the
Hippomenes. John Clunies Ross and his family returned on 16 February 1827 (this is the
date given by Ackrill 1984; several other authors state that he returned on 27 November
1827, i.e. Hughes 1950; this error appears to have been perpetuated since an account in
Gleanings in Science, Anon 1830; the correct dates are given by Gibson-Hill 1952), with
the intention of commencing a settlement on the islands. Ross expressed surprise at
finding Hare and a large group of people there, although it would seem that he should have
known that Hare might already be there, since he had not found him at Cape Town on the
outward journey. Relations between Ross and Hare deteriorated; Hare initially lived on
Home Island, though with some occupation of West Island, Direction Island, and
Horsburgh Island. Ross initially settled on Pulu Gangsa, just to the north of Home Island
(presently joined onto Home Island, and the site of the cemetery); but he soon moved his
house down to the central part of South Island. Hare, on the other hand, eventually moved
from Home Island, to Prison Island, according to poorly substantiated reports because the
women of his party were being molested. It appears that he maintained a party of
womenfolk, and most of the children, under close supervision in the lower storey of his
house. Rear Admiral Sir Edward Owen noted in a letter of 10 July 1830, that Hare
engaged in unrestricted intercourse with such females of his establishment as he (might)
deem worthy of his attentions’. The history of this time is particularly colourful, although
it has also been subject to a lot of misrepresentation (Gibson-Hill 1947, Ackrill 1984). In
part this results because the only records that survive reflect Ross' view of the
circumstances, and his objectives and those of Hare differed. Ross endeavoured to
establish a successful settlement, aspiring to a great trading 'entrepot'’. Hare, on the other
hand, sought obscurity and his behaviour, according to Ross, became increasingly
unbalanced and debauched. Initially both claimed ownership of the islands, but in 1831
Hare finally left the atoll, and he died in Batavia in the following year. The Malay
workers, who joined with Ross, are the ancestors of many of the Cocos Malays there
today, and the Clunies Ross family, who became known as 'Kings of the Cocos’, reigned
over the islands for more than 150 years (Hughes 1950).

John Clunies Ross died in 1854. He was succeeded by his son John George
Clunies Ross until 1871. After his death in 1871 George Clunies-Ross took possession
until 1910. John Sydney Clunies-Ross ruled from 1910 to 1944, and John Cecil Clunies-
Ross thereafter. The papers of the Clunies-Ross family contain much useful information
on the islands. The early papers of John Clunies Ross are particularly valuable for their
description of the islands, although some were lost in a fire.

In 1857 the islands were declared a part of the British Dominions by Captain
Fremantle who arrived aboard H.M.S. Juno, having misread his directions which
instructed that he annex Cocos in the Andaman Islands (Gibson-Hill 1947).
Responsibility for supervision of the islands was transferred over the years to the
Governments of Ceylon (1878), the Straits Settlements (1886), Singapore (1903) and

Ceylon again (1939-1945). In 1886 Queen Victoria granted all of the islands, under
certain provisions, to John George Clunies Ross, in perpetuity. They became a Territory
of the Commonwealth of Australia in 1955, and in 1978 Australia purchased all of the
lands, excepting the family home, from the Clunies Ross family for Aus$ 6.25 million. In
1984 the Malay population voted to become a part of Australia. Initially the Territory was
administered by the Commonwealth government, but it is now being transferred to the
responsibility of the state government of Western Australia.

Today the islands are inhabited by the descendants of the original (Malay) settlers,
though there have been several additional intakes of workers from various parts of
Southeast Asia. There are about 400 Malays living in the kampong on Home Island. The
Great House of the Clunies Ross family, Oceania House, is also on Home Island, set
amongst 5 ha of grounds. Across the lagoon on West Island more than 200 people,
associated with various departments of the Australian Government, live alongside the
airfield, which was used as an important refueling stop on commercial air routes between
Europe and Australia until the advent of larger aircraft in the 1950s allowed Cocos to be
by-passed.

NATURAL HISTORY AND SCIENTIFIC DESCRIPTION OF THE
ISLANDS

The Cocos (Keeling) Islands have held a special place in the literature on coral
atolls because they represent the only atoll that Charles Darwin visited, and they played a
central role in his discussion of his theory of coral reef development. The natural history
of the islands was, in fact, uncharacteristically well-known by the turn of the century,
because of the visits of a number of naturalists in addition to Darwin. It is interesting to
note that rather than confirming Darwin's observations and interpretations of the atoll,
many of the works of subsequent naturalists lead them into conflict with Darwin's views,
and that Cocos was also subject to interpretations completely contrary to Darwin's. Thus,
Guppy (Guppy 1889, 1890a, 1890b) subscribed, at least in part to the views of John
Murray, who funded his visit. Wood-Jones put forward an entirely alternative view to
Darwin's, in his book Coral and Atolls (Wood-Jones 1912). However, the strongest
criticism of Darwin came from John Clunies Ross himself, who was absent at the time of
Darwin's visit. His review of Darwin's book, published posthumously, was a bitter,
vitriolic attack on Darwin's ideas (Ross 1855).

Early accounts of the nature of the islands (Anonymous 1830) include a paper on
the formation of the islands by Ross (1836), and descriptions from short visits. Owen's
description (1831) appears to be based upon observations by Captain Sandilands who
visited in February 1830 in the Comet (Owen, 1831), and the account in Holman (1840),
is based largely on the accounts of Keating who left the atoll in November 1829 after less
than a year there with Hare, and those of Captain Mangles. Van der Jagt (1831) visited
and mapped the islands in 1829 in the Blora.

H.M.S. Beagle called into the Cocos (Keeling) Islands on its way home, in its
third year at sea, arriving off the islands on 1 April, and leaving on 12 April 1836 (Darwin
1842, 1845, Fitzroy, 1839). The visit lasted only ten days, and for much of that time
Captain Fitzroy and the crew of the H.M.S. Beagle were engaged in survey work; this
forming the basis of many of the subsequent charts. A more thorough hydrographic
survey was undertaken in June and July 1983 by RAN Moresby. Darwin's visit has been
analysed in detail by Armstrong (1991).

The islands were subsequently visited by Henry Forbes, who arrived at around 17
January 1879, and left on 9 February 1879. Forbes speculated on the origin of the
islands, and devoted two chapters (chapters ii and 111) to Cocos in his book on the Eastern
Archipelago (Forbes 1879, 1885).

Henry Brougham Guppy visited the Cocos (Keeling) Islands in 1888, his visit
being funded by John Murray. Murray had examined a series of rock specimens collected
from Christmas Island (Indian Ocean) by Captain Pelham Aldrich who had been there in
H.M.S. Egeria in 1887, and had found some that were rich in phosphate. He sent
Guppy to visit Christmas Island for a further examination. Guppy needed fine weather
for a landing on Christmas Island, and took passage on the Clunies Ross vessels as the
only way to get there. The weather was apparently not calm enough within the period that
Guppy could stay to get to Christmas, and Guppy spent 10 weeks on Cocos waiting,
before returning to Europe without getting to Christmas. Gibson-Hill (1947) suggests,
however, that during the 5 months that Guppy endeavoured to get to Christmas, George
Clunies-Ross' brother managed to visit the island and establish a settlement of a group of
Malays in Flying Fish Cove. As a consequence of that settlement, the Clunies-Rosses
began with about half of the shares (with John Murray) of the Christmas Island Phosphate
Company when that commenced in the 1890s. Guppy meanwhile undertook an extremely
detailed account of the Cocos (Keeling) Islands, with extensive observations on the nature
and rate of operation of geological processes (Guppy 1889, 1890a, 1890b).

There were other visits and accounts during this time; W.E. Birch, with Rev E.C.
Spicer as naturalist, was on Cocos 20-28 August 1885 (Birch 1866). The lone round-the-
world sailor Joshua Slocum arrived on 17 July 1897 in the Spray, and considered that ‘if
there is a paradise on this earth it is the Keeling-Cocos' (Slocum 1899).

Wood-Jones was the medical doctor at the Cable Station on Direction Island, and
was on Cocos from June 1905 to September 1906. This afforded him ample opportunity
to look around the atoll. He revisited Cocos briefly in 1907 as a guest of George Clunies-
Ross, and subsequently married one of his daughters. He wrote a book, Coral and Atolls,
incorporating his observations. However, the book suffered 'in parts from a considerable
carelessness, and an over-optimistic acceptance of unconfirmed visual records’ (Gibson-
Hill 1947 p.159). His view of the mode of formation of the reef differed both from that of
Darwin, and that of Murray which received some modification from Guppy.

The detailed observations of Wood-Jones are surpassed only by those of Gibson-
Hill. Gibson-Hill was medical officer on Direction Island from 20 December 1940 until 10
November 1941. He made various collections of organisms, some material of which
disappeared from the Raffles Museum during the Japanese occupation of Malaya in the
World War II. Nevertheless his fascination with Cocos persisted, and Gibson-Hill
published a series of notes on the islands, including both his own observations and
collections (Gibson-Hill, 1947, 1948, 1949, 1950a, 1950b, 1950c, 1950d, 1950e, 1950f,
1950g), and his reprinting of earlier literature on the atoll (Gibson-Hill 1953).

Since Gibson-Hill's reviews of Cocos natural history, there have been expeditions
by the Academy of Natural Sciences of Philadelphia (1963 and 1974) and the Western
Australian Museum (Berry 1989), as well as some visits from individual naturalists (e.g.
Alfred 1961). Williams has produced an annotated bibliography of the natural history of
the islands, which appears in a recent Atoll Research Bulletin (Williams 1990). A
summary of major collections on Cocos is given in Table 1.

BIOGEOGRAPHICAL RELATIONSHIPS OF THE COCOS
(KEELING) ISLANDS BIOTA

The Cocos (Keeling) Islands are not only extremely isolated, but they also lie at the
western extension of the Western Pacific marine biogeographic province. For many
species Cocos represents their western limit of distribution. The biota is derived,
therefore, primarily from that of the tropical Indo-West Pacific; taxa from the western
Indian Ocean are poorly represented. The plants contain a large component of drift-
dispersed pantropical species, found throughout the Indian and Pacific Oceans, but the
major source is western Java (Guppy 1890a). Similarly, in the case of the marine biota,
the most likely source of larval recruitment is also the Indonesian and eastern Indian Ocean
region.

For all groups covered of marine biota described in subsequent chapters in this
volume, significant additions have been made to existing knowledge of taxa occurring at
Cocos (Table 1). Total numbers of taxa in the groups discussed in this volume are
summarised in Table 2. The level of collecting now undertaken at Cocos means that the
terrestrial ecology is relatively well-known, and in the marine groups is such that
significant numbers of additional taxa are unlikely to be added. On this basis several
generalised conclusions can be drawn regarding the biogeographical relationships of the
Cocos (Keeling) Islands.

There is almost no endemism in the Cocos biota. The Buff-banded Rail, Rallus
philippensis andrewsi, is considered an endemic subspecies, restricted to North Keeling,
and the rat on Direction Island, Rattus rattus keelingensis, has been accorded subspecies
status, and was considered by Wallace (1902) to be an example of rapid divergence; it can
be traced back to the Mauritius which was wrecked in 1825. The angelfish Centropyge
joculator is recorded only from Christmas and the Cocos (Keeling) Islands. The Cocos
subspecies of Pandanus tectorius, which is only localised in occurrence, is also considered
endemic (Williams 1990, this volume).

This lack of endemism may reflect the effect of rapidly oscillating sea levels during
the late Quaternary, and the pattern of development of coral atolls, whereby the limestone
plateau which was exposed at the last glacial maximum perhaps resembling the modern-
day Christmas Island, was rapidly flooded during postglacial sea-level rise and all land
was submerged in the early Holocene (10,000-8,000 years ago). The present reef islands
appear to be no more than 4000 years old (Woodroffe et al. 1990a, 1990b). This implies
that all the terrestrial biota must have recolonised the atoll in the last few thousand years.
These sea-level fluctuations would also have had substantial implications for shallow-water
ca biota, as the nature of the habitats must have altered drastically over that period
also.

Some taxa which might be expected are conspicuously absent from Cocos. Guppy
(1890a) has drawn attention to the absence of mangroves and Nypa palm, despite the
arrival of propagules on the shore (The stand of mangroves on the northern end of
Horsburgh Island can be attributed to planting by John George Clunies Ross). Some
shallow marine taxa usually common on coral reefs are conspicuously absent in apparently
suitable habitat (i.e. there are no benthic skates or rays in the lagoon). Marine taxa must
either be pelagic as adults or have long-lived larvae or juveniles to reach Cocos.

Christmas Island is the nearest island to Cocos, and there is less similarity than
might at first be expected between the biota found at Cocos and that at Christmas (Table
2). Undoubtedly this results from the contrasting physiography of the two islands.

Christmas Island is an uplifted (and apparently still uplifting) limestone island with
outcrops of volcanic rocks on it. It reaches a maximum elevation of 361 m, and has
probably been above water since the Eocene. It is covered by dense forest, and has only
poorly-developed reef fringing its cliffed coastline. There are not the extensive reef flats or
shallow lagoonal sandy or muddy areas which are found on Cocos. _

In addition to the very different late Quaternary history, and the great contrast in the
time available for establishment of terrestrial biota, the Cocos (Keeling) Islands are
probably more subject to periodic catastrophic influences on the biota. The atoll has
experienced several devastating tropical cyclones, which tend to have an impact all over the
restricted land area of Cocos, as well as in shallow parts of the lagoon and reefs. There
have been a series of coral and fish kills in the lagoon. Darwin (1842) noted an extensive
area of dead coral in the southeastern corner of the lagoon. He speculated initially that this
might have been due to slight emergence of the atoll, but then attributed it to the closure of
a series of interisland passages through South Island and more resticted circulation in this
part of the lagoon. Forbes recorded that in 1876, inky and foul smelling water had spread
through the lagoon from the islands on the eastern rim (Forbes 1885). A similiar fish and
coral kill has recurred, most noticeably in 1983, but also in intervening years. Its cause is
still unclear. Forbes considered that the 1876 event may have been caused as a result of an
earth tremor. The 1983 event was correlated with E] Nino in an incisive, but unpublished
account of it by Blake and Blake, who attributed it to an ‘algal bloom’ (red tide). An
alternative explanation, considered more likely by members of the Western Australian
Museum expedition (Berry 1989), is that it was caused by mass coral spawning at a time
of poor circulaton as has been described by Simpson et al. (in press) on the Western
Australian coast. It is significant that the mortalities at Cocos and Western Australia both
occurred in March and this hypothesis for the cause of mass mortality of corals and other
organisms in the Cocos lagoon would be further supported if it could be established that
coral spawning occurs there in March. A minor episode of fish kill was also observed in
1992 (J. Tranter, pers. comm.). Infestations of Acanthaster have been reported from the
reefs (Colin 1977), and are reviewed in more detail by Marsh (this volume).

Present diversity and abundance of reef organisms closely associated with living
corals may have been reduced by the reduction of coral abundance and diversity on the reef
slopes and in the lagoon as a result of these events. In view of the isolation of Cocos and
the distance to be covered by propagules, if species are lost from the atoll as a result of
such events, they are likely to be slow to recolonise.

Human impact on the Cocos (Keeling) Islands has been most devastating on the
South Keeling Islands (the southern atoll), where the vegetation has been almost totally
altered to coconut plantation. The birds which once characterised the atoll have all but
disappeared, and it is the absence of large numbers of seabirds, which strikes one as the
most conspicuous difference between North Keeling and the southern atoll. There have
also been impacts on marine organisms which are eaten, Tridacna gigas, Lambis lambis
(gong gong), Birgus latro and the palinurid lobsters, though it is to be hoped that
management measures prevent the total elimination of any more of these species. At the
same time occupation of the atoll has resulted in an influx of new species to the Cocos
(Keeling) Islands. These vary from ornamental and food plants, and deliberate animal
introductions, such for instance as the Green Jungle Fowl on West Island. Sheep, cattle,
alpacas and black rhinoceroses and other animals have been temporarily contained within
the Quarantine Station on West Island. Accidental releases, include the rats and the lone
King Parrot on West Island. In addition there are numerous insects which have been
introduced, and a large number of insect pests (Gibson-Hill 1950f, Holloway 1982).

STUDIES IN THIS VOLUME

The frequent visits of naturalists, and the detailed studies that they undertook,
ensured that the Cocos (Keeling) Islands were perhaps the best-known, and certainly the
most hotly debated group of reefs in the world, by the end of the nineteenth century. This
continued in the first half of the twentieth century. Since the overviews of Gibson-Hill,
however, there has been relatively little extension of knowledge about the islands. The
terrestrial ecology of the South Keeling Islands has changed markedly since settlement as
large areas have had their natural vegetation replaced by coconut plantation (now sadly
largely overgrown), and as birds and other food resources have been exploited.

It is now possible to look in greater detail at the geological history of the atoll, and
the marine ecology of its reefs and lagoon as the result of the development of several new
techniques. Radiometric dating allows a new insight into the age of formation of coral
limestones. Subsurface drilling, seismic profiling and dating allow geomorphological
insight into those questions which intrigued the early naturalists to study Cocos. In the
case of marine ecology, the development of more sophisticated underwater research
methods, and particularly the use of SCUBA, has enabled the extension of collections into
water depths that were previously only examinable by dredge, or not at all. It is thus in the
areas of geological investigations, and in terms of the numbers of marine species on the
atoll that the greatest advances in knowledge have been made in recent years.

This volume brings together a series of recent studies on the Cocos (Keeling)
Islands. A preliminary examination of the birds of Cocos was undertaken by T. Stokes of
the Australian National Parks and Wildlife Service (ANPWS) and others in 1982. Since
that time ANPWS has carried out a number of studies of birds, particularly at North
Keeling. Vegetation and marine habitats of the atoll have been mapped by D. Williams,
who was seconded as Environmental Resource adviser to the Territory of the Cocos
(Keeling) Islands in 1986-7. Mapping was undertaken using SPOT satellite imagery,
aerial photographs and ground survey on a habitat data sheet, used by Williams and
ANPWS staff.

A field survey of the inshore marine fauna and habitats of the Cocos (Keeling)
Islands was undertaken 7-28 February 1989 by the Western Australian Museum under the
leadership of P. Berry, sponsored by the Australian National Parks and Wildlife Service.
During that fieldtrip a total of 37 stations was occupied (some more than once), in order to
sample the major marine habitats (Fig. 2), which had been partly described and mapped by
D. Williams. The survey of marine fauna involved SCUBA, snorkelling and reef walking,
as well as the use of an ichthyocide and a small hand spear in the case of fishes and the
photographing of habitats. Specimens have been lodged in the Western Australian
Museum. Accounts of the corals, collected and identified by J.E.N. Veron, and of marine
molluscs by F. Wells, echinoderms by L. Marsh, fishes by G. Allen and W. Smith-Vaniz,
barnacles by D. Jones, and decapod crustaceans by G. Morgan appear in this volume.

Water Resources represent an important aspect of the present settlement of Cocos,
and have been studied over the last 6 years by A. Falkland. He describes the climate of
Cocos, and the implications for Water Resources in this volume. Drilling undertaken for
the water resources study has also provided data for a geomorphological study of the
Cocos (Keeling) Islands by C. Woodroffe and R. McLean. Their geological reassessment
of Cocos has involved detailed descriptions of reef islands and subsurface stratigraphy and
chronology, as well as other studies. The results of seismic profiling are described by

D.E. Searle, lagoon hydrodynamics by P. Kench and lagoonal sediments by S.G.
Smithers.

There are some aspects of the ecology and geomorphology of the Cocos (Keeling)
Islands which have not been adequately treated in this volume. There is no account of the
insect fauna, for instance, nor have the marine algae been studied in any great detail. It is
hoped that the studies which are presented here provide a stimulus for continued scientific
study and research on the Cocos (Keeling) Islands.

ACKNOWLEDGEMENTS

Research on the Cocos (Keeling) Islands which is presented in this volume has
been made possible through the support of the Cocos (Keeling) Islands Administration, the
Cocos Island Council, and the Australian National Parks and Wildlife Service. Collecting
by the Western Australian Museum was funded by Australian National Parks and Wildlife
Service, while geomorphological research was funded by the Australian Research Council
and the National Geographic Society. The assistance of the Government Conservators,
Andrew Grant, Paul Stevenson and Jeff Tranter has been very important. Logistical
support from the Cocos Islands Co-operative and Australian Construction Services and
John Clunies-Ross is greatly appreciated.

REFERENCES

Abbott, R. T. 1950. The molluscan fauna of the Cocos-Keeling Islands, Indian Ocean.
Bull. Raffles Mus., 22: 68-98.

Ackrill, M. 1984. The origins and nature of the first permanent settlement on the Cocos-
Keeling Islands. Historical Studies, 21: 229-244.

Alfred, A. E. 1961. Some birds of the Cocos-Keeling Islands. Malay. Nat. J. 15: 68-69.

Anonymous 1830. Some account of the Cocos or Keeling Islands: and of their recent
settlement. Gleanings in Science (Calcutta), 2, 293-301. Reprinted in: J. Malay.
Br. Asiat. Soc. (1952) 25, 174-191.

Armstrong, P. 1991. Under the blue vault of heaven: a study of Charles Darwin’s sojourn
in the Cocos (Keeling) Islands. Indian Ocean Centre for Peace Studies, University
of Western Australia.

Berry, P.F. 1989. Survey of the Marine fauna of Cocos (Keeling) Islands, Indian Ocean.
Unpublished report to the Australian National Parks and Wildlife service, 133pp.

Birch, E. W. 1866. The Keeling Islands. Proc. Roy. Geog. Soc. N.S. 8: 263-265.

Bleeker, P. 1855. Derde bijdrage tot de kennis der ichthyologische fauna van de Kokos-
eilanden. Natuurk. Tijd. voor Ned. Ind. 7: 353-358.

Chancellor, G., DiMauro, A., Ingle, R., and King, G. 1988. Charles Darwin's Beagle
collections in the Oxford University Museum. Arch. Nat. Hist. 1988: 197-231.

Clark, A. H. 1912. Crinoids of the Indian Ocean. Echinoderma of the Indian Museum,
part VII, Crinoidea. Calcutta:

Clark, A. H. 1950. Echinoderms from the Cocos-Keeling Islands. Bull. Raffles Mus: 22:
53-67.

Colin, P. L. 1977. The reefs of Cocos-Keeling atoll, eastern Indian Ocean. Proc. 3rd Int.
Coral Reef Symp. 1: 63-68.

Darwin, C. 1842. The structure and distribution of coral reefs. London, Smith, Elder and
Co.

Darwin, C. 1845. Journal of researches into the natural history and geology of the
countries visited during the voyage of H.M.S. Beagle round the world, under the
command of Capt. Fitzroy R.N. London, John Murray.

Fitzroy, R. 1839. Narrative of the surveying voyages of His Majesty's ships Adventure
and Beagle, between the years 1826 and 1836, describing their examination of the
southern shores of South America, and the Beagle's circumnavigation of the globe.
London, H. Colburn.

Forbes, H. O. 1879. Notes on the Cocos or Keeling Islands. Proc. Roy. Geog. Soc. 1:
777-784.

Forbes, H. O. 1885. A Naturalist's wanderings in the Eastern Archipelago. A narrative
of travel and exploration from 1878 to 1883. London, Sampson Row.

Forest, J. 1956. La faune des Iles Cocos-Keelings, Paguridea. Bull. Nat. Mus.
Singapore, 27: 45-55.

Gibson-Hill, C. A. 1947. Notes on the Cocos-Keeling Islands. J. Malay. Br. Roy.
Asiat. Soc. 20: 140-202.

Gibson-Hill, C. A. 1948. The island of North Keeling. J. Malay. Br. Roy. Asiat. Soc.
21, 68-103.

Gibson-Hill, C. A. 1949. The birds of the Cocos-Keeling Islands (Indian Ocean). Ibis
91: 221-243.

Gibson-Hill, C. A. 1950a. Hemiptera collected on the Cocos-Keeling Islands, January-
October 1941. Bull. Raffles Mus. 23: 206-211.

Gibson-Hill, C. A. 1950b. The Myriapoda found on the Cocos-Keeling Islands January-
October 1941. Bull. Raffles Mus. 22: 103-104.

Gibson-Hill, C. A. 1950c. A note on the Cocos-Keeling Islands. Bull. Raffles Mus. 22:

Gibson-Hill, C. A. 1950d. A note on the reptiles occurring on the Cocos-Keeling Islands.
Bull. Raffles Mus. 22: 206-211.

Gibson-Hill, C. A. 1950e. Notes on the birds of the Cocos-Keeling Islands. Bull.
Raffles Mus. 22: 212-270.

10

Gibson-Hill, C. A. 1950f. Notes on the insects taken on the Cocos-Keeling Islands.
Bull. Raffles Mus. 22: 149-165.

Gibson-Hill, C. A. 1950g. Papers on the fauna of the Cocos-Keeling Islands. Based on
material and data collected in the group by C.A. Gibson-Hill, M.A., between
December 1940 and November 1941. Introduction. Bull. Raffles Mus. 22: 7-10.

Gibson-Hill, C. A. (Editor). 1953. Documents relating to John Clunies Ross, Alexander
Hare and the settlement on the Cocos-Keeling Islands. J. Malay. Br. Roy. Asiat.
Soc. 25: 1-306

Guppy, H. B. 1889. The Cocos-Keeling Islands. Scott. Geog. Mag. 5: 281-297, 457-
474, 569-588.

Guppy, H. B. 1890a. The dispersal of plants as illustrated by the flora of the Keeling or
Cocos Islands. J. Trans. Vict. Inst. London 24: 267-306.

Guppy, H. B. 1890b. Preliminary note on the Keeling Atoll. Proc. Vict. Inst. London
23: 72-78.

Henslow, J. S. 1838. Florula Keelingensis. An account of the native plants of the
Keeling Islands. Mag. Nat. Hist. 1: 337-347.

Holloway, J. D. 1982. On the Lepidoptera of the Cocos-Keeling Islands in the Indian
Ocean, with a review of the Nagia linteola complex (Noctuidae). Entomologia
Gen. 8: 99-110.

Holman, J. 1840. Travels in China, New Zealand. (2nd ed.). London.

Hughes, J. S. 1950. Kings of Cocos: the story of the settlement on the atoll of Keeling-
Cocos in the Indian Ocean. London: Methuen.

Jenyns, L. 1842. The zoology of the voyage of H.M.S. Beagle, under the command of
Captain Fitzroy R.M. during the years 1832 to 1836. Part IV. Fish. London:
Smith, Elder.

Maes, V. 1967. The littoral marine mollusks of Cocos-Keeling Islands (Indian Ocean).
Proc: Acad: Nat? Sct., Phila 11993-2135.

Marrat, F. P. 1879. Notes on shells from the Keeling or Cocos Islands, Indian Ocean.
Proc. Lit. Phil. Soc. Liverpool, 33: ili-iv.

Marshall, N. B. 1950. Fishes from the Cocos-Keeling Islands. Bull. Raffles Mus. 22:
166-205.

Owen, E. W. C. R. 1831. Account of the Cocos, or Keeling Islands. J. Roy. Geog.
Soc. 1: 66-69.

Randall, J. E. 1975. A revision of the Indo-Pacific angelfish genus Genicanthus, with
descriptions of three new species. Bull. Mar. Sci. 25: 393-421.

i} al

Rees, W. J. 1950. The cephalopods of the Cocos-Keeling Islands (Indian Ocean). Bull.
Raffles Mus. 22: 99-100.

Ridley, S. O. 1884. On the classificatory value of growth and budding in the
Madreporidae, and on a new genus illustrating this point. Ann. Mag. Nat. Hist.
(Sth series). 13: 284-291.

Ridley, S. O., and Quelch, J. J. 1885. List of corals collected in the Keeling Islands. In
H. O. Forbes (Eds.), A naturalist's wanderings in the Eastern Archipelago (pp.44-
47.). London, Sampson Row.

Ross, J. C. 1836. On the formation of the oceanic islands in general, and of the coralline
in particular. Singapore Free Press, 2 June 1836. reprinted in J. Malay. Br. Roy.
Asiat. Soc. (1952). 25: 251-260.

Ross, J.C. 1855. Review of the theory of coral formations set forth by Ch. Darwin in his
book entitled: Researches in Geology and Natural History. Natuur. Tijds. voor
Neder. Ind. 8: 1-43.

Simpson, C.J., Cary, J.L., and Masini, L.J. in press. Destruction of corals and other reef
animals by coral spawn slicks on Ningaloo Reef, Western Australia. Coral Reefs.

Slocum, J. 1899. Sailing alone around the World. London, Sampson Row, Marston.

Smith-Vaniz, W. F., & Randall, J. E. 1974. Two new species of angelfishes
(Centropyge) from the Cocos-Keeling Islands. Proc. Acad. Nat. Sci. Phil. 126:
105-113.

Tweedie, M. W. F. 1950. The fauna of the Cocos-Keeling Islands, Brachyura and
Stomatopoda. Bull. Raffles Mus. 22: 105-148.

Van der Jagt, H. 1831. Beschrijving der Kokos - of Keeling-Eilanden. Verh. Batav.
Gen. v. Kunsten en Wetenschappen (Batavia), 13, 293-322. translated in. J.
Malay. Br. Roy. Asiat. Soc. (1952), 25, 148-159.

Vaughan, T. W. 1918. Some shallow-water corals from Murray Island, Cocos-Keeling
Islands, and Fanning Island. Carnegie Inst. Washington, Pub. 213: 49-234.

Wallace, A. R. 1902. Island life, or, the phenomena and causes of insular faunas and
floras: including a revision and attempted solution of the problem of geological
climates (3rd ed.). London, Macmillan.

Wells, J. W. 1950. Reef corals from the Cocos-Keeling atoll. Bull. Raffles Mus. 22: 29-
Se

Williams, D. G. 1990. An annotated bibliography of the natural history of the Cocos
(Keeling) Islands, Indian Ocean. Atoll Res. Bull. 331: 1-17.

Wood-Jones, F. 1909. The fauna of the Cocos-Keeling Atoll, collected by F. Wood-
Jones. Proc. Zool. Soc. 1909: 132-160.

Wood-Jones, F. 1912. Coral and Atolls: a history and description of the Keeling-Cocos
Islands, with an account of their fauna and flora, and a discussion of the method of

12

development and transformation of coral structures in general. London, Lovell
Reeve and Co.

Woodroffe, C. D., McLean, R. F., Polach, H., & Wallensky, E. 1990a. Sea level and
coral atolls: Late Holocene emergence in the Indian Ocean. Geology 18: 62-66.

Woodroffe, C. D., McLean, R. F., and Wallensky, E. 1990b. Darwin's coral atoll:
geomorphology and recent development of the Cocos (Keeling) Islands, Indian
Ocean. Nat. Geog. Res. 6: 262-275.

Date

1836

1854-5
1878

1905-6

1940-1

1963, 1974

1961
1985
1986/7

1989

Expedition/ Group
Collectors Collected

H.M.S. Beagle crustacea
fishes
plants
shells

A.J. Anderson and fishes

G. Clunies-Ross

H.O. Forbes corals
plants

F. Wood-Jones brachyurans
corals
echinoderms
plants

C.A. Gibson-Hill fishes
brachyurans
stomatopods
anomura
cephalopods
echinoderms
molluscs
corals
birds

Academy of Natural

Sciences of Philadelphia molluscs
fishes

A.E. Alfred birds

I.R. Telford plants

D.G. Williams plants
marine algae

Western Australian coral

Museum echinoderms
fishes
molluscs
barnacles

13

Table 1. Summary of collections of flora and fauna from the Cocos (Keeling) Islands

Publication

Darwin 1845,
Chancellor et al. 1988
Jenyns 1842
Henslow 1838
Marrat 1879

Bleeker 1855

Guppy 1889, Ridley 1884,
Ridley and Quelch 1985
Forbes 1885
Wood-Jones 1909
Vaughan 1918

Clark 1912

Wood-Jones 1912
Marshall 1950

Tweedie 1950

Tweedie 1950

Forest 1956

Rees 1950

Clark 1950

Abbott 1950

Wells 1950

Gibson-Hill 1949, 1950e

Maes 1967

Randall 1975, Smith-Vaniz
and Randall 1974

Alfred 1961

Flora of Australia

This volume

Berry 1989,
This volume

decapod crustaceans

14

Table 2. Number of species recorded at Cocos (Keeling) and Christmas Islands.
GROUP Cocos Is. Christmas Is.

Reef-building coral 99 85

Decapod crustaceans 198 204

Molluscs c 610 c 490

Echinoderms 88 90

Fishes C550 568

Native birds 38 88

Plants 130 386

15

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The Indian Ocean, showing the location of the Cocos (Keeling) Islands.

Figure 1.

NORTH KEELING ISLAND
0 kilometres 2

all cocos
(KEELING)

! ISLANDS
OCEAN

LOCALITY
DIAGRAM

INDIAN i “i

°

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Figure 2. The Cocos (Keeling) Islands, showing stations from which collections were

made during the Western Australian Museum expedition in 1989. These
stations cover a series of different marine habitats (see Chapter 8, Fig. 1),
which can be summarised as: Outer Reef Slope (9 sites: stations 4, 7, 13,
15, 19, 22, 25, 32, and 33), Reef Flat (13 sites: stations 1, 3, 6, 8, 10, 11,
12, 14, 20, 21, 24, 27, and 30) and lagoon (14 sites: stations 2, 9, 16, 17,
18, 23, 26, 28, 29, 31, 34, 35, 36 and 37).

ATOLL RESEARCH BULLETIN

NO. 400

CHAPTER 2

CLIMATE, HYDROLOGY AND WATER RESOURCES OF THE COCOS
(KEELING) ISLANDS

BY

A.C. FALKLAND

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 2
CLMATE, HYDROLOGY AND WATER RESOURCES
OF THE COCOS (KEELING) ISLANDS
BY
A.C. FALKLAND *

CLIMATE AND HYDROLOGY

GENERAL FEATURES

The Cocos (Keeling) Islands are situated in the Humid Tropical zone. For most of
the year they are under the influence of South East Trade Winds. Cyclonic conditions are
sometimes experienced, particularly between November and March. Rainfall on the island
is influenced to some extent by El Nifio events.

The main climatic features are:

- annual rainfall varying between about 850 and 3300 mm,

- annual potential evaporation of about 2000 mm,

- relatively uniform temperatures, ranging from about 18°C to 32°C,

- relative humidity varying from about 65% to 84%,

- daily atmospheric pressures ranging from 973 to 1018 hectopascals,
and

- mean daily wind speeds varying from 4.7 and 8.1 metres/second
with a maximum gust during a cyclone recorded at 48.8
metres/second (176 kilometres/hour).

METEOROLOGICAL DATA
CURRENT NETWORK

A meteorological station (No. 200284, Cocos Island A.M.O.) has been operated
continuously on West Island on the eastern side of the airstrip by the Bureau of
Meteorology (Australia) since February 1952. It is located at latitude 12°11’S, longitude
96°50’E and at an altitude of 3 metres. At the station, the following meteorological
parameters, important to water resources assessment, are measured and recorded:

- air temperature (wet and dry bulb, and dew point),
- atmospheric pressure,

- cloud cover,

- wind speed and direction,

- rainfall, and

- pan evaporation.

Temperature, atmospheric pressure, cloud cover and wind are measured every 3
hours. Daily averages can be derived from eight readings. Daily total wind run is also

* Hydrology and Water Resources Branch, Australian Capital Territory Electricity and
Water, P.O. Box 366, Canberra, Australian Capital Territory, 2601.

2

recorded. Rainfall and pan evaporation are measured daily at 9 a.m. Rainfall is also
recorded on a pluviograph (continous recorder). In addition to the above surface level
measurements, upper air data is collected via regular balloon releases from the station.

Daily rainfall is measured and recorded at two other sites on the South Keeling
atoll. The first site is located on a peninsular about 100 metres north of the jetty on Home
Island. Data has been recorded at this site by the Cocos (Keeling) Islands Council
(formerly Home Island Council) since 28 May 1986. This site is now described as station
number 200733 by the Bureau of Meteorology. The second site is located on the eastern
side of the administration building at the Quarantine Station on West Island. Data has been
recorded at the second site by Quarantine Station personnel since 1 January 1989. Some
of the data at both of these sites has not been recorded each day but rather recorded as a
total for two or three days. Therefore, these records cannot be used for accurate daily
rainfall analyses but they are suitable for monthly rainfall analyses. No meteorological data
is recorded on the North Keeling atoll.

PREVIOUS DATA COLLECTION SITES

In 1904 a rainfall station was opened on Direction Island and operated by staff at
the cable station. A climatological station was opened "probably soon after, although no
files survive to prove this" (Bureau of Meteorology 1978). Other notes in the file entry
indicate that this station operated to 1952 when the current station opened on West Island.

There is some anecdotal evidence that the Clunies-Ross family recorded rainfall on
Home Island. However, no records were sighted and it is not known whether any of these
records were incorporated into the Bureau's records. As the rainfall records extend back to
December 1901, it is probable that rainfall was recorded on Home Island from then until
the rainfall station on Direction Island was opened in 1904.

Rainfall records under the heading 'Cocos Island Composite’ are available from the
Bureau of Meteorology for all but 17 months from December 1901 to the present. Months
with missing data are November and December 1914, all months of 1915, January 1916,
April 1946 and February 1952. An early entry in a Bureau of Meteorology file states that
"the records for 1915 were incomplete on account of the instruments being destroyed in
November 1914 by German warship 'Emden'. Records were recommenced in November
1915". The missing data in 1946 and 1952 appears to be due to staff and location
changes. Overall, the length of record and the small number of missing months (and hence
days) of record, have ensured a very good data set for the Cocos (Keeling) Islands.

SELECTED METEOROLOGICAL DATA FROM WEST ISLAND

Graphical and tabular summaries of important meteorological parameters recorded
at the West Island meteorological station are presented in this and the next two sections.
Summaries of temperature, relative humidity (a derived parameter), atmospheric pressure,
cloud cover, wind speed and wind direction are presented in this section. More extensive
summaries of rainfall and evaporation are provided below. The data used for these
summaries, unless otherwise indicated, are for the period February 1952 to December
1991.

TEMPERATURE

Mean, maximum and minimum daily temperatures are shown in Figure 1 and in
Table 1 for each month of the year. The maxima and minima are extreme values derived
from all of the 3 hourly data. The mean values were estimated by averaging mean daily
maxima and minima.

The mean daily temperature is highest in March (27.5°C) and lowest in July and
August (25.8°C). The extreme maximum temperature is 32.4°C recorded in February 1979
and the extreme minimum temperature is 18.3°C recorded in August 1979.

RELATIVE HUMIDITY

Mean, maximum and minimum daily relative humidities are shown in Figure 2 and
in Table 2, for each month of the year. These values are derived from 9 a.m. and 3 p.m.
readings of wet and dry bulb temperature and atmospheric pressure using standard
meteorological methods.

The mean daily relative humidity is highest from April to July (77%) and lowest
from September to December (72%). The mean daily maximum relative humidity is 84%
recorded in the months of June and July 1960, April and August 1973, and April 1974.
The mean daily minimum relative humidity is 65% recorded in November 1956. Extreme
maxima and minima were not computed.

ATMOSPHERIC PRESSURE

Mean, maximum and minimum daily atmospheric pressures are shown in Figure 3
and in Table 3, for each month of the year for the period February 1952 to July 1987. The
shorter period was used as extreme maxima and minima had not been computed for the full
data set. The maxima and minima are extreme values for each month and, as with the mean
values, they are derived from the full 3 hourly data set.

The mean daily atmospheric pressure is highest in September (1012.2
hectopascals) and lowest in February (1008.4 hectopascals). The extreme maximum
atmospheric pressure is 1018.5 hectopascals recorded during the months of October 1952
and July 1984 and the extreme minimum atmospheric pressure is 970 hectopascals
recorded during cyclone 'Doreen' on 21 January 1968.

It is noted that the atmospheric pressures referred to in this section are at the level
of the station. The atmospheric pressure at mean sea level is obtained from these readings
by adding an amount of less than one hectopascal. Due to this small difference and the low
altitude of the islands, the atmospheric pressure at the station can be used as an indicator of
atmospheric pressure throughout the islands.

CLOUD COVER

Cloud cover (or cloudiness) is measured in oktas or the number of eigths of the sky
filled with cloud. Mean, maximum and minimum daily values for each month of the year
are shown in Figure 4 and Table 4. Data are derived from all observations for the period
1952 to 1987.

The mean daily cloud cover varies between 5.0 and 5.3 oktas, from April to July
and 4 oktas for the other 8 months. The mean daily maximum cloud cover is 6.8 oktas
recorded in November 1973 and the mean daily minimum cloud cover is 3 oktas recorded
in December 1987. Extreme maxima and minima were not computed.

WIND SPEED

Mean, maximum and minimum wind speed are shown in Figure 5 and in Table 5,
for each month of the year. The mean values are taken from the 3 hourly data set from
February 1952 to July 1987. The maxima and minima are extreme instantaneous values
for each month for the full period of record (February 1952 to December 1991).

The mean daily wind speed is highest in January (8.1 metres/second) and lowest in
February (4.6 metres/second). The mean daily maximum wind speed is highest in August
(14.2 metres/second) and the mean daily minimum wind speed is lowest in March (just
above zero). The extreme maximum wind speed was recorded at 48.8 metres/second
during cyclone 'Doreen' on 21 January 1968. This wind speed is equivalent to 95 knots
or about 175 kilometres/hour. The extreme minimum wind speed is zero (calm) which has
been recorded on many occasions during all months of the year.

WIND DIRECTION

Figure 6 shows the wind direction resolved as a percentage of time for each month
(January to June in left hand graph and July to December in right hand graph). Eight
points of the compass are used. The graphs are for average wind directions from 9 a.m.
and 3 p.m. readings for the period February 1952 to December 1990. The legends show
the percentage of time that calm periods were recorded for each month .

The predominant wind direction is east to south east for all months, showing the
influence of the South East Trade Winds on the islands. South easterly winds varied from
37% of the time in February to 60% of the time in November and December. Easterly
winds varied from 17% in January to 44% in September. By comparison winds from the
north, north east, south west, west and north west occurred for less than 6% of the time in
all months and were often 2% or less. Southerly winds were experienced from a low of
2% of the time in September and October up to 17% of the time in January.

OCCURRENCE OF CYCLONES

A cyclone database maintained by the Bureau of Meteorology shows that a number
of cyclones have affected the Cocos (Keeling) Islands. Table 6 presents data about
cyclones since 1959 which have passed within approximately 100 kilometres of the island.
One of the most damaging cyclone appears to have been ‘Doreen’ which passed directly
over the South Keeling atoll. An interesting account of this cyclone is provided in Ryan
(undated).

RAINFALL DATA AND ANALYSES

INTRODUCTION

As rainfall is one of the most important determinants of the water resources of the
islands, a more detailed analysis of rainfall is presented. This section describes
characteristics of the annual, monthly and daily rainfall. In addition to analyses of the
temporal distribution of rainfall, comments about the spatial distribution of rainfall on the
South Keeling atoll are made.

It is noted that from a water resource viewpoint, rainfall at time scales of days and
months are of most significance. For recharge analysis, as part of groundwater studies on
atolls such as South Keeling, daily rainfall data has been found to have sufficient time
resolution. Monthly rainfall data can be used instead of daily rainfall data with a small loss
in accuracy. For rainwater catchment studies, long sequences of daily rainfall data are
ideal.

SPATIAL VARIATION OF RAINFALL

At the scale of the Indian Ocean, the variation of rainfall has been reported in
Stoddart (1971) and Unesco (1977). Stoddart (1971) reviewed earlier reports and
produced updated isohyetal maps for annual, seasonal and monthly rainfall based on coral
island stations, primarily those with records longer than 10 years. The mean annual
rainfall distribution is shown in slightly modified form in Figure 7.

The isohyetal map of mean annual rainfall shown in Unesco (1977), not shown
here, is quite different particularly in the centre of the ocean. In the region of the Cocos
(Keeling) Islands, however, the two maps are similar with isohyets approximately
horizontal. The reason for the differences is not clear. On the South Keeling atoll, the
spatial variation rainfall has been analysed by Falkland (1992a).

ANNUAL RAINFALL

The mean annual rainfall recorded at the West Island meteorological station is 1954
mm for the 40 year period of record from 1953 to 1992. Using the available annual record
from 1902 to 1992, the mean annual rainfall is 1982 mm. In the longer data set, the annual
rainfalls in 1914, 1915, 1916, 1946 and 1952 are missing giving a total number of 86
years. For the period 1902-1952, during which time the rainfall was recorded primarily on
Direction Island, the mean annual rainfall is 2006 mm. Figures 8 and 9 show,
respectively, histograms of annual rainfall for the periods 1902 to 1952 and 1953 to 1992.

Using the meteorological station records, the highest annual rainfall on record is
3291 mm which occurred in 1942 (Direction Island) while the lowest is 856 mm in 1991
(West Island). By comparison, the annual rainfall in 1991 on Home Island and at the
Quarantine Station were, respectively, 837 and 820 mm.

The difference in the mean annual rainfalls for the two periods 1902-1952 and
1953-1992 is 2.6% of the latter period mean annual rainfall. This is considered a minor
difference, given that site differences can easily account for long term rainfall depth
differences of 10% or more. This result shows that the total depth of rainfall in the first

6

half of the century (1902-1951), recorded primarily on Direction Island, is similar to that
recorded in the second half of the century (1953-1991 ) on West Island.

The standard deviations of the annual rainfalls for the periods 1902-1992 and
1953-1992 are, respectively, 519 and 594 mm, showing a higher variability in the second
half of the century. The coefficient of variation (Cv) of annual rainfall (obtained by
dividing the standard deviation by the mean) for the two periods are, respectively, 0.26
and 0.3, again indicating the higher variability of recorded rainfall in the second part of this
century on the island. These Cv's of annual rainfall are moderate when compared with
other islands, especially low lying coral atolls. Christmas Island (Australia), a raised
limestone island, about 900 kilometres north east of the Cocos (Keeling) Islands, has a
similar Cv of 0.29. The atolls of Tarawa and Kiritimati (Christmas Island), Republic of
Kiribati in the Pacific Ocean have higher Cv's (0.42 and 0.64, respectively). By
comparison, Kwajalein atoll in the Marshall Islands Pacific Ocean has a much lower Cv of
0.14 (Falkland et al. 1991). The variation in annual rainfall between the three raingauge
sites can be seen in Table 7.

From the data in Table 7, the rainfall for 1987 on Home Island is suspect as it is
very low (only 65% of that at the meteorological station) and is inconsistent with the
relative rainfall pattern between Home and West Island for the following years.
Disregarding the suspect 1987 data for Home Island, there is slightly less rain occurring on
Home Island than on West Island. The total rainfall recorded on Home Island from 1988
to 1992 is 5.3% less than at the meteorological station. The data also shows that the
rainfall recorded on Home Island and at the Quarantine Station is, respectively, 3.4% less
and 5.3% greater than at the meteorological station during the four year period 1989 to
1992.

Overall, the variation of rainfall between the three sites is not greatly significant
when it is considered that the recording accuracy of rainfall at any one site is generally not
better than about 10%. Although the period of concurrent rainfall records is short and
therefore not suitable for making long term predictions, it is reasonable to conclude that the
annual rainfall on the South Keeling atoll can be adequately described by the rainfall record
at the West Island meteorological station.

MONTHLY RAINFALL

Mean, maximum and minimum monthly rainfalls recorded at the West
meteorological station are shown in Figure 10 and in Table 8, for the March 1952 to
December 1991. The mean monthly rainfall is highest in April (234 mm) and lowest in
October (70 mm). The maximum monthly rainfall is 649 mm recorded in June 1988 and
the minimum monthly rainfall is 2.8 mm recorded in September 1986.

A comparison of the monthly rainfalls recorded at the meteorological station and on
Home Island for the period 1987 to 1991 is shown in Figure 11. A comparison of the
meteorological station and the Quarantine Station monthly rainfalls for the period 1989 to
1991 is shown in Figure 12. A comparison of the cumulative monthly rainfall recorded at
the three sites for the period of concurrent records (1989-1991) is shown in Figure 13.

Figures 11 and 13 indicate that the rainfall recorded at the Home Island site is less
than that at the meteorological station. The lower rainfall recorded on Home Island may be
due to a rain shielding effect of nearby tall vegetation at the raingauge site. Similarly,

Te

Figures 12 and 13 show that the rainfall recorded at the Quarantine Station site is slightly
greater than that recorded at the meteorological station.

Double mass curves using cumulative monthly rainfall were plotted to check if any
changes in the relative rainfall at the Home Island and the Quarantine Station sites had
occurred during the periods of concurrent record. Figure 14 is the double mass curve
using the rainfall data from the meteorological station and Home Island for the period
1987-1991. The plotted line shows some variation in slope, particularly from the early
(1987) data to later data. Figure 15 is the double mass curve using the rainfall at West
Island meteorological station and at the Quarantine Station for Home Island for the period
1989-1991. The corresponding Home Island data is also plotted in Figure 15. Very little
variation in slope is shown for the Quarantine Station curve, indicating that there has been
no major changes in this site or the method of recording since data collection commenced.
However, the Home Island data indicates a greater variation. The variations in the Home
Island record could be due to a number of reasons including progressive ‘shading’ of the
raingauge from nearby trees, and errors or changes in the method of reading and recording
rainfall data.

Regression analyses of monthly rainfalls at Home Island and the Quarantine Station
with the meteorological station are summarised in Figures 16 and 17. The analysis using
60 monthly rainfall pairs for Home Island and the meteorological station gave a correlation
coefficient (r) of 0.92 which indicates a reasonably good correlation. The value of r for 36
pairs of data from the Quarantine Station and the meteorological station was 0.97 which
indicates a very good correlation. The regression equations are shown in Figures 16 and
17, respectively. These could be used to estimate monthly rainfalls at the two sites from
the meteorological station monthly rainfall. They should be updated with additional data if
they are considered for future use. The Home Island equation should be treated with
caution as some of the Home Island data is suspected of being in error.

DAILY RAINFALL

While daily rainfall records are available from the Bureau of Meteorology for the
full period of record (1904-1992) from the stations on Direction Island and West Island,
only the data from the latter station were obtained for analysis. Daily rainfall has been
recorded at the West Island meteorological station from 15 February 1953 to the present.

Daily rainfall has also been recorded on Home island (28 May 1986 to present) and
at the Quarantine Station (1 January 1989 to present), as described previously. Daily data
from all 3 stations was reviewed to the end of 1992.

The maximum recorded daily rainfall at the West Island meteorological station is
287 mm on 28 August 1956. There have been 54 days when the rain exceeded 100 mm
and 6 days when it exceeded 200 mm. The maximum daily rainfall on Home Island, 242
mm, was recorded on 11 November 1989. On the same day the rainfalls recorded at the
meteorological station and the Quarantine Station were, respectively, 203 mm and and 220
mm. The maximum daily rainfall at the Quarantine Station was 248 mm, recorded on 4
July 1992. On the same day the rainfalls recorded at the meteorological station was 252
mm. No daily rainfall was recorded at Home island on 4 July 1992 but the three day total
to 6 July was only 141 mm.

On a daily basis, the rainfall records show considerable variation between the three
rainfall recording sites, as some of the above results show. This is confirmed by general

8

observations that individual storms can affect small areas of the atoll while leaving other
areas quite dry. Hence, in the short term the rainfall pattern on Home island or elsewhere
on West Island cannot necessarily be deduced from the West Island meteorological station
records. Daily variability can also be seen from a number of high rainfall days in 1990 and
1992 when all three rain gauges were operational. The list below shows, in order, the date
and the rainfalls at the meteorological station, Home Island and the Quarantine Station:

12 January 1990: 162, 164 and 171 mm,
14 April 1990: 117, 83 and 116 mm,
17 July 1990: 158, 210 and 115 mm,
6 September 1990: 30, 23 and 116 mm,
28 February 1992: 26, 112 and 87 mm,
14 April 1992: 6, 102 and 8 mm, and
4 May 1992: 11, 122 and 29 mm.

The longest period without any rainfall at the meteorological station is a period of
28 days in November 1985. The longest period when the total rainfall was less than 10
mm occurred between November 1985 and January 1986 when only 6.2 mm fell in 69
days. Long dry periods are of particular interest in the study of the island's water
resources, as described below.

PLUVIOGRAPH RECORDS

A pluviograph (continuous rainfall recorder) is operated at the West Island
meteorological station. These records enable rainfall patterns to be analysed (at time
resolution in minutes). Such data are useful to analyse storm events and to construct
rainfall intensity-frequency-duration (IFD) curves, for possible use in the design of
stormwater facilities (e.g. roof gutters and downpipes). The Bureau of Meteorology has
processed IFD information from pluviograph records between 1971 and 1991. This
information is not presented here.

EVAPORATION DATA AND ANALYSES

INTRODUCTION

Estimation of actual or catchment evaporation is essential for any water resources
study. Evaporation from a catchment includes evaporation from soil, water and other open
surfaces such as paved areas and from the leaves of grasses, plants and trees. Evaporation
from the stomates of leaves is called transpiration and the combined effects of this process
and other evaporation is often described as evapotranspiration. The two processes are
basically variations of the one process, namely, the conversion of water from a liquid to a
gaseous state and some authors use the term evaporation instead of evapotranspiration. The
term evaporation will normally be used instead of evapotranspiration for present purposes.

The estimation of actual evapotranspiration (ET4) is generally done as a two stage
process. Firstly, ETp is estimated using a method based on meteorological data, such as
the Penman (or Contbination) formula (Penman 1948, 1956), or from pan evaporation data
multiplied by appropriate pan coefficient(s). The Penman equation has generally been
found to be a good ETp estimation method in the humid tropics (Fleming 1987).
Estimations using both Phe pan and Penman methods were made for the study of

9

groundwater resources on the South Keeling atoll (Falkland 1988). Secondly, ET, is
determined using a water balance procedure taking into account the soil and vegetation
conditions present on the island.

The estimation of ETp, using both pan evaporation records and the Penman
approach, is described below while the estimation of ETg is described in a later section on
water balance.

PAN EVAPORATION DATA

Daily pan evaporation has been recorded at the West Island meteorological station
using a U.S. Class A pan from December 1981 to the present. Mean, maximum and
minimum monthly pan evaporation totals are shown in Figure 18 and Table 9, for the
period January 1982 to December 1991.

The mean monthly pan evaporation is highest in December (241 mm) and lowest in
June (171 mm). The maximum monthly pan evaporation is 273 mm recorded in both
December 1983 and December 1985. The minimum monthly pan evaporation is 146 mm
recorded in May 1987.

EVAPORATION ESTIMATION (Penman equation)

The following meteorological parameters were available for use in the Penman
equation:

- dry bulb temperature,
- wet bulb temperature,
= dew point temperature,
- cloud cover, and

- wind speed.

Using mean monthly values of the parameters above, estimates of monthly ET,
were made using the Penman equation (Penman 1948, 1956) for the period January 198
to March 1986. This period was the longest period of available concurrent data at the time
of investigations (Falkland 1988).

Water balance simulations (Falkland 1988) showed that similar results in terms of
groundwater recharge were obtained from monthly data sets using either actual or mean
values of ETp. This shows the relatively constant nature of potential evaporation for a
given month from year to year in a humid tropical environment such as the Cocos
(Keeling) Islands. In the humid tropics, the net radiation energy term dominates the
aerodynamic term in the Penman equation and it has been found that the simplified
Priestly-Taylor method can also be used (Chang 1989). In the Priestley-Taylor method
ETp is equated to 1.26 times the energy term from the Penman equation (Priestley and
Taylor 1972).

EVAPORATION ESTIMATION (pan method)

Pan evaporation requires multiplication by an appropriate pan coefficient to obtain
estimates of ET). An initial estimate of the pan coefficient of between 0.7 and 0.75 was

10

obtained by a procedure developed by Doorenbos and Pruitt (1977) using meteorological
and specific site parameters.

The pan coefficient was later adjusted to 0.8 after sensitivity analyses were
conducted with trial data using water balance simulations. The water balance results in
terms of recharge to groundwater using five years of rainfall data (1982 to 1986) were
found to be very similar for Penman estimates of ET, and for pan data using a pan
coefficient of 0.8 (Falkland 1988). Results were also similar for simulations using actual
and mean monthly pan data.

Figure 19 shows the comparison of mean monthly ET» estimates using both the
Penman and pan methods for the five year period 1982 to 1986. The pan estimates are
mean values for each month. The Penman estimates are based on mean monthly values of
the relevant meteorological parameters. The mean annual ET, based on the pan method
was 1983 mm compared with the annual ET, of 2048 mm based on the Penman method.
This difference of about 3% is insignificant for practical purposes.

As the results from the two methods are very similar, the pan method using mean
monthly data was adopted as ETp estimates could be more easily computed with this
method. Later studies (Falkland {991, 1992a) used mean monthly pan evaporation data
for the period 1982 to 1987. Recently, additional pan data to December 1991 was obtained
and the mean monthly estimates of ET, for the periods 1982-1987 and 1982-1991 were
compared. The results are very similar. The mean annual values are in fact only 1 mm
different (1986 and 1987 mm for the shorter and longer periods, respectively).

TRANSPIRATION MEASUREMENTS

At the commencement of detailed water resources investigations in 1987, it was
realised that coconut trees (Cocos nucifera), prolific on most atolls including the Cocos
(Keeling) Islands, are a major source of transpiration and, hence, loss from freshwater
lenses. Direct measurements of coconut tree transpiration were, therefore, undertaken
during the study. Due to time limitations, lysimeter or ventilated chamber methods could
not be used. Instead, measurements were undertaken using a heat pulse velocity meter.
The meter and its associated electronic data logger measures and records the velocity of an
injected heat pulse in the sapwood of a tree by timing movement over a known distance.
The technique had been used successfully on other types of trees but never, to the author's
knowledge, on coconut trees. The results obtained from the one-week study suggested that
transpiration rates per tree varied from about 70 to 130 litres/day (Bartle 1987). The range
of values was considered to be the result of diurnal climatic variations.

The values obtained must be considered preliminary owing to a number of
simplifying assumptions and the short period of observations. Further study over a longer
time period is warranted as part of general scientific research. Based on this limited data,
the total transpiration rate due to coconut trees is about 400-750 mm per year per tree in
areas with 100% tree cover, where typical tree spacings of about 8 metres prevail. This
has implications for water resources management and it may be prudent to selectively clear
coconut trees from some freshwater lens areas to maximise the supply of water.

11

INFLUENCE OF EL NINO ON THE CLIMATE

Considerable research has been undertaken into the influence of the El Nifio
phenomenon (also called the El Nifio Southern Oscillation or ENSO) on climatic patterns,
particularly in the Pacific Ocean. Effects of strong El Nifio events in the Pacific Ocean
include significant sea surface temperature changes, ocean current and wind direction
reversals, extreme variations in rainfall patterns, higher tides, storm activity in some
locations and severe droughts in others.

The influence of the El Nifio phenomenon is felt more widely than just the Pacific
Ocean. Some research has been conducted into the connections between El Nifio events
and the weather patterns occurring in the north-eastern Indian Ocean area around
Indonesia. Quinn et al. (1978) studied the connections between El Nifio events and
droughts in Indonesia. Their general conclusion was that droughts in Indonesia, indicated
by low rainfall periods on Java, occurred in years when El Nifio events were evident. A
significant connection between low rainfall years and El Nifio events was found for
Christmas Island in the Indian Ocean (Falkland 1986).

The influence of El Nifio events on the rainfall of the Cocos (Keeling) Islands is
outlined in Falkland (1988, 1992a). A graph showing the relationship between the
Southern Oscillation Index (an index of the strength of ENSO activity) on an annual basis
and annual rainfall (expressed as a percentage of mean annual rainfall) is shown in Figure
20 for the period 1953 to 1991. Negative values of SOI are associated with El Nifio
activity with the more negative values indicating increased strength. Positive values
indicate that El Nifio activity is absent.

Figure 20 shows that there is a reasonable correlation between SOI and annual
rainfall, with negative annual SOI values corresponding in general with less than average
rainfall and vice versa. This trend is not always present, an example being the highly
negative SOI during the 1982/83 El Nifio when the rainfall was near average. Using linear
regression analysis between annual SOI and rainfall data, a correlation coefficient of only
0.58 was obtained, indicating that the correlation is not strong. In certain periods (for
example, 1953 to 1960, 1967 to 1981) the correlation is much better as can be seen in
Figure 20 (r=0.89 and 0.82, respectively). It can be concluded that there is a reasonable
correlation between El Nifio activity in the Pacific Ocean and rainfall in the Cocos
(Keeling) Islands.

WATER RESOURCES
TYPES

The water resources of the Cocos (Keeling) Islands consist essentially of
groundwater and rainwater. Where conditions are favourable, fresh groundwater occurs
on coral islands in the form of shallow freshwater lenses. Such lenses are found in some
of the larger islands within the Cocos (Keeling) Islands. The groundwater from these
lenses has been and is currently used as the major source of freshwater for potable and
other uses on Home and West Islands.

Due to the generally porous nature of the soils and underlying geology, there is no
significant surface runoff. Runoff only occurs in localised areas where the ground is
compacted or paved and only for very short periods after heavy rain. Rainwater collected
directly from roofs of buildings is a valuable supplementary source of water.

12

GROUNDWATER OCCURRENCE

FRESHWATER LENS CHARACTERISTICS

Freshwater lenses occur beneath the surface of some islands. The upper surface of
a freshwater lens is the water table and the lower surface is a boundary between freshwater
and saline water. The lower boundary is not a sharp interface but rather is in the form of a
transition zone. Within the transition zone the water salinity increases from that of
freshwater to that of seawater over a number of meters.

A typical cross section through a small coral island showing the main features of a
freshwater lens is presented in Figure 21. It must be noted that there is considerable
vertical exaggeration in the diagram. In practice, the vertical scale is much smaller
compared with the horizontal scale. The transition zone tends to be as thick as or thicker
than the freshwater zone on many small coral islands. As shown in the diagram, there is
often an asymmetric shape to the lens with the deepest portion displaced towards the
lagoon side of the island.

The salinity of the upper surface of a freshwater lens‘can be obtained by
measurements at exposed water surfaces such as wells and pumping galleries. The lower
surface can be determined accurately by establishing a recognisable salinity limit for
freshwater and drilling through the lens and testing the water at different depths for
salinity. It can also be estimated approximately by surface geophysical (electrical
resistivity and electromagnetic) techniques.

The salinity limit adopted for freshwater for the Cocos (Keeling) Islands is 600
mg/l chloride ion concentration. This limit is approximately equivalent to an electrical
conductivity (specific conductance) reading of 2600 umhos/cm at the standard temperature
of 25°C (Falkland 1988, 1992a).

According to classical 'Ghyben-Herzberg' theory (Badon Ghyben 1889, Herzberg
1901), for every unit height of fresh water occurring above mean sea level there will be
about 40 equal units of underlying fresh water below mean sea level. This theory assumes
that the two fluids, freshwater and seawater, are immiscible (i.e. that they do not mix). In
practice, the two fluids do mix due to mechanical and molecular diffusion and a transition
zone forms with salinity gradually increasing from that of freshwater to that of seawater.
In practical situations, the 1:40 ratio can be used as a guide to determine the mid-point of
the transition zone from the water table elevation above mean sea level. It does not provide
a means of determining the base of the freshwater zone and other methods described above
are required.

INFLUENCING FACTORS ON FRESHWATER LENSES

The size and salinity distribution of freshwater lenses, particularly the thickness of
freshwater and transition zones, are dependent on many factors but the most important are:

- rainfall amount and distribution,
- amount and nature of surface vegetation and the nature and
distribution of soils (these factors influence the evapotranspiration),

13

- size of the island, particularly the width from sea to lagoon,

- permeability and porosity of the coral sediments, and the presence
of solution cavities,

- tidal range, and

- methods of extraction and quantity of water extracted by pumping.

For small coral sand islands, an approximate relationship has been derived
(Oberdorfer and Buddemeier 1988) between freshwater lens thickness, annual rainfall and
island width as follows:

H/P = 6.94 log a - 14.38

where

an
rl

lens thickness (depth from water table to sharp interface or
mid-point of transition zone in metres),
P = annual rainfall (metres), and

= island width (metres).

This equation indicates that no permanent freshwater lens can occur regardless of
rainfall where the island width is less than about 120 metres. Using the mean annual
rainfall (1938 mm measured at the West Island meteorological station) for the Cocos
(Keeling) Islands, the minimum island width for a small freshwater lens (say 5 metres
thick) to occur is about 280 metres (say 300 metres). Thus, as an approximate guide, it is
unlikely that a permanent freshwater lens suitable for groundwater extraction could be
found on the South Keeling atoll where the width of the island is less than about 300
metres. It is noted, however, that other factors which are not accounted for in the above
relationship, particularly the permeability of the coral sediments and the density of
vegetation, have an effect on the occurrence of freshwater lenses. Further comments based
on observed data on West Island are given later. The geological influences are considered
in more detail below.

GEOLOGICAL INFLUENCES ON FRESHWATER LENSES

The geology of the South Keeling atoll consists of coral sediments, several
hundreds of metres thick, overlying a volcanic seamount. From a hydrogeological
viewpoint, the geology of most interest is that of the upper part of the atoll where
freshwater lenses are found to occur. From a number of recent water investigations on the
South Keeling atoll (Falkland 1988, 1991, 1992a, 1992b), freshwater lenses do not
exceed 20 metres in thickness. Within this 20 metre zone, two major geological layers are
found: a younger (Holocene), upper layer consisting of unconsolidated coral sediments
and an older (Pleistocene), deeper layer of coral limestone. While no extensive
investigations of surface geology have been undertaken on North Keeling atoll, it is
expected that similar geological conditions would prevail there.

Similar to findings on other atolls in the Pacific Ocean, an unconformity was found
from drill cores between the relatively low permeability Holocene sediments and
underlying higher permeability Pleistocene limestone at depths of less than 20 metres
(Falkland 1988). Using the early results and data from additional boreholes on West
Island, Home Island, South Island and Horsburgh Island, the unconformity was found at
depths varying between about 8 and 17 metres below ground surface (Woodroffe et al.
1991). These depths correspond, respectively, to depths between 7 and 16 metres below
mean sea level.

14

The presence of this unconformity is due to a period of emergence of the island
with solution and erosion forming a karst surface. Uranium-series dating of the older
limestone indicates that it was formed during the last inter-glacial period about 120,000
years ago (Woodroffe et al. 1991). The upper sediments have been laid down in the
Holocene since about 10,000 years ago. Three phases of deposition have been identified
in the Holocene (Woodroffe et al. 1990a, this volume). From the start of the Holocene to
at least 5000 years ago, sediments accumulated rapidly as sea level rose. A conglomerate
platform radio-carbon dated at 3000 to 4000 years ago was then formed during a period of
relatively stable sea level. Since then unconsolidated sands and larger sediments have been
deposited to form the present reef islands. Dating of in-situ corals has shown that the sea
level was about 0.5 to 1.5 metres higher about 3000 years ago than today (Woodroffe et
al. 1990a, 1990b).

The unconformity described above is very significant to the formation of
freshwater lenses. The limestone sediments below this unconformity have relatively high
permeabilities and mixing of freshwater and seawater is readily facilitated. In the relatively
less permeable upper sediments, mixing is less likely to occur. The unconformity,
therefore, is one of the main controlling features to the depth of freshwater lenses.

WATER BALANCE AND RECHARGE ESTIMATION
RECHARGE

The freshwater lenses in the Cocos (Keeling) Islands are recharged naturally from
rainfall. Not all rainfall incident on the islands, percolates to groundwater, as much of it is
evaporated or transpired. Essentially, natural recharge is the net input from rainfall to
groundwater after all evaporative losses have been deducted and soil moisture requirements
have been met.

It is important that accurate estimates of recharge be obtained as it is one of the
main determinants of the sustainable yield of freshwater lenses. Recharge can be estimated
by a number of techniques. One of the most common and useful techniques is a water
balance (or water budget) approach where water inputs to, and water outputs from, the
surface of the island are quantified. This approach was used in water resources
investigations of Home and West Islands (Falkland 1988, 1992a) and South Island
(Falkland 1991).

WATER BALANCE EQUATION

Recharge can be described by a water balance equation using a specified reference
zone and a specified time interval. The reference zone for a freshwater lens on a coral atoll
is that zone extending from above the surface of the island down to the water table. In this
zone, the flow of water is essentially vertical. The water balance equation for the upper
zone on a coral island, such as those in the Cocos (Keeling) Islands, can be described as:

R = P-ET,+dV
where

R = recharge,

P = rainfall,

AS

ET,
dV

actual evaporation from all surfaces, and
change in storage within the soil moisture zone (it can be a
positive or negative change)

As noted earlier, there is no term for surface runoff as this does not occur due to
the very high infiltration capacity of the coral soils.

The actual evaporation term (ET4q) includes evaporation from interception storage
(for example, the leaves of trees, bushes and grass), from vegetation tapping water from
the soil moisture zone and from trees with roots that penetrate to the water table and thus
transpire water directly from the freshwater lens.

Computations with this equation were conducted using a daily time interval, as
recommended by Chapman (1985). It has been shown that computations using a monthly
time step leads to an under-estimation of recharge for the Cocos (Keeling) Islands
(Falkland 1988) and on other atolls (for example, Kwajalein: Hunt and Peterson 1980).
Daily rainfall data and mean daily evaporation estimates were, therefore, used.

DESCRIPTION OF THE RECHARGE MODEL

A recharge model was developed, and a computer programme (WATBAL) written,
to simulate the water balance in the upper zone and derive a monthly time series of
recharge. The model is shown in Figure 22 and a brief description follows.

The recharge model allows for interception storage by vegetation. A maximum
value for the interception storage (ISMAX) can be defined and it is assumed that this store
must be filled before water is made available to the soil moisture storage. Typical values of
ISMAX are 1 mm for predominantly grassed catchments and 3 mm for catchments
consisting predominantly of trees (particularly coconut trees). The airfield area on West
Island is predominantly grassed while South Island and some of the northern parts of West
Island consist predominantly of trees. Much of Home Island is intermediate between these
two limits. Evaporation is assumed to occur from the interception storage at the potential
rate.

The recharge model incorporates a soil moisture zone from which the roots of
shallow rooted vegetation (grasses, bushes) and the shallow roots of trees can obtain
water. Water requirements of plants tapping water from this zone are assumed to be met
before any excess drains to the water table. Maximum (field capacity) and minimum
(wilting point) limits are set for the soil moisture in this zone. Above the field capacity,
water is assumed to drain to the water table. Below the wilting point, no further
evaporation is assumed to occur.

The thickness of the soil moisture zone (SMZ) for the Cocos (Keeling) Islands was
estimated as 500 mm based on observations of the soil profile and from studies on other
atolls. Field capacity (FC) was assumed to be 0.15 based on observations of local soil
type and typical values for this type of soil. Wilting point (WP) was assumed to be 0.05
based on typical values (for example, Linsley and Franzini 1973) for sand-type soils and
from studies elsewhere. The operating range of soil moisture is thus assumed to be from
25 mm to 75 mm.

In the model, the amount of evaporation from the SMZ is assumed to be related to
the available soil moisture content. At WP, zero losses due to evaporation are assumed to

16

occur from this zone. Maximum or potential evaporation is assumed to occur when the
soil moisture zone is at FC. A linear evaporative loss relationship is assumed to apply
between the two soil moisture limits. Thus, at a soil moisture content midway between FC
and WP, for instance, the evaporation rate is half that of the potential rate.

Water entering the water table is 'gross recharge’ to the freshwater lens. A further
loss, however, is experienced due to transpiration of trees whose roots penetrate to the
water table. 'Net recharge’ is that water remaining after this additional loss is subtracted
from ‘gross recharge’. Observations in dug pits and trenches on Home and West Islands
reveal that a considerable number of roots penetrate to the capillary fringe just above the
water table which typically occurs at depths of one to two metres below ground level. It is
estimated that about 50% of the roots from mature coconut trees penetrate to the water
table. Because the movement of the water table is relatively small, even during drought
periods, these roots allow transpiration to occur even when the soil moisture store has been
depleted. This is the reason that coconut trees are able to survive prolonged drought
periods on coral atolls when other shallow rooted vegetation has reached wilting point and
possibly died.

Vegetation is assigned a 'crop factor' (Doorenbos and Pruitt 1977) according to its
type. Each plant (or crop) type has its evaporative potential compared with that of a
‘reference crop’. The reference crop evaporation is equal to the potential evaporation, as
derived from an appropriate method. The crop factor is a coefficient which is used to
derive an adjusted potential evaporation of other crops from the potential evaporation (or
the reference crop evaporation).

The crop factor for most grasses and other shallow rooted vegetation is assumed to
be 1.0. The crop factor for coconut trees was taken as 0.8 based on values for similar
types of trees listed in Doorenbos and Pruitt (1977). Thus, the potential evaporation rate
for coconut trees is taken to be 80% of that for grasses or other shallow rooted vegetation.

The proportions of freshwater lens areas covered by deep rooted vegetation were
estimated from coloured aerial photographs taken in April 1987 and from ground
inspection. From recent investigations (Falkland 1991, 1992a), the proportions were
estimated to be 0.15 for Home Island, 0 for the West Island Airfield and 0.8 for the
northern part of West Island and South Island.

RESULTS AND DISCUSSION

Water balance analyses were conducted for freshwater lenses on West, Home and
South Islands in a number of studies (Falkland 1988, 1991, 1992a). Series of monthly
recharge estimates were obtained in each case, enabling drought sequences to be further
analysed for estimation of sustainable yields.

Graphical comparisons of annual recharge and annual rainfall (obtained by
summation of monthly values) for the period 1953 to 1991 are provided in Figures 23 and
24 for, respectively, the West Island Airfield Lens and the West Island Northern Lens.

A significant variation in recharge from year to year can be seen from Figures 23
and 24. In some years, recharge is actually negative (i.e. there is a net loss of water from
the freshwater lens). Figure 24 shows that 'negative recharge’ occurred in the Northern
Lens in 1953, 1962, 1977 and 1991 with the most negative value occurring in 1991
(corresponding to the lowest annual rainfall). In general, years of high annual rainfall

17

result in years of high annual recharge and vice versa. However, there is no simple
relationship between the two parameters. This is because annual recharge is a function of
the pattern of daily rainfall and not simply a function of the annual rainfall total.

For the 39 year period of record (1953-1991), the following mean annual recharge
estimates were obtained:

- West Island Airfield Lens: 950 mm/year (49% of rainfall),
- Home Island Lens: 855 mm/year (44% of rainfall),
- West Island Northern Lens: 564 mm/year (29% of rainfall).

The results for South Island are the same as for the Northern Lens as similar
parameters were used in the recharge analysis.

Figure 25 compares the annual recharge estimates from three lenses (West Island
Airfield and Northern Lenses and the Home Island Lens). There are significant recharge
differences between the three lenses, the main cause being differences in the density of the
deep rooted vegetation, predominantly coconut trees, above the freshwater lens areas.
Figure 26 shows the relationship between mean annual recharge (as a percentage of
rainfall) and the percentage tree cover. This graph and the tabulated results above show
that recharge can nearly be doubled by reducing the tree cover from 80% (as for the
Northern Lens) to zero (as for the Airfield Lens). Due to the significant effect that coconut
tree density has on groundwater recharge, one management option for increasing
freshwater supplies is to selectively clear vegetation in areas where freshwater lenses occur
(see also section on transpiration measurements).

Cumulative annual recharge graphs for the West Island and Home Island lenses are
shown in Figure 27. These graphs enable sequences of dry and wet years to be easily
seen. For instance the lowest 5 year recharge period occurred from early 1976 to the end
of 1981. Another low recharge period of 5 years occurred from early 1961 to the end of
1965.

GROUNDWATER INVESTIGATIONS

In the previous section, a number of freshwater lenses were named (e.g. West
Island Airfield Lens, West Island Northern Lens and Home Island Lens). Groundwater
investigations over a number of years were conducted to locate and quantify the depth and
areal extent of these lenses. This section briefly describes these investigations and details
of the freshwater lenses.

PRELIMINARY INVESTIGATIONS

The groundwater resources were first studied by Jacobson (1976a, 1976b). His
investigation was limited to Home Island and involved observations of water table
elevations and salinities of shallow water obtained from wells. Using this limited
information he estimated the thickness of the freshwater lens at 10 to 15 metres and the
sustainable yield to be 200 kilolitres per day. He recommended that more detailed
investigations were warranted to confirm the preliminary results obtained. Later
investigations showed that the actual thickness of the lens was not greater than 6 metres
and that the estimated sustainable yield was approximately half of his estimate.

18

DETAILED INVESTIGATIONS

Detailed investigations of the groundwater resources were undertaken from 1988 to
1992 (Falkland 1988, 1991, 1992a, 1992b). The aims of the groundwater investigations
were to determine the location, lateral extent and depth of freshwater lenses and to
determine hydrogeological properties necessary for an analysis of long-term sustainable
yields from the lenses.

A combined drilling and geophysical programme was used. This combined
approach allowed for an accurate determination of the thickness of lenses at selected
locations using the drilling programme and for reasonable estimates at intermediate sites
using the electrical resistivity method. The drilling programme was relatively slow and
costly but yielded accurate data whereas the resistivity programme was relatively quick and
inexpensive but had a lower level of accuracy. The latter method, however, provided good
estimates of lens thickness after correlation with salinity profiles obtained at borehole sites.

A limited amount of seismic work was conducted at boreholes to gain a better
understanding of the subsurface geological properties. Observations of topographic
features, measurement of salinity levels at exposed water surfaces (wells, ponds, pumping
galleries) and recording of water table movements relative to tidal movements were
conducted to provide additional data.

Details of all the investigations are beyond the scope of this report. Some details
about the drilling programme are provided, however, as they were the most useful in terms
of initial and continuing data about the freshwater lenses.

A total of 29 boreholes were drilled from 1988 to 1992 on West Island (16 holes),
Home Island (12 holes) and South Island (1 hole) and equipped with salinity permanent
monitoring systems. Details of these holes including year of drilling, reduced level (RL)
relative to mean sea level (MSL), depth to water table and depth to the unconformity
between Holocene and Pleistocene sediments are shown in Table 10. The location of the
boreholes are shown in Figure 28. Drilling logs with further details are contained in
Murphy (1988), Falkland (1991), Murphy and Falkland (1992a) and Falkland (1992b).

The permanent salinity monitoring system used in each borehole is shown
diagrammatically in Figure 29. Water samples are pumped to the surface from each of the
separate tubes by a portable electric pump and tested for electrical conductivity. Using the
monitoring data, salinity profiles can be constructed for each borehole at intervals of
typically one to three months. By obtaining a set of such salinity profiles, the salinity
distribution over time can be viewed for each borehole. This data has yielded valuable
information about the response of the freshwater lenses to variations in recharge. Figures
30 and 31 show the variation in the depth to the base of the freshwater zone in a number of
West Island (Airfield Lens) and Home Island boreholes together with monthly recharge for
the period 1988 to 1991. The antecedent recharge in 1987 is also shown.

The permeability of the coral sediments was measured in-situ using falling head
tests in some of the boreholes during drilling. The average permeability in the Holocene
sediments was about 6 metres per day while the average permeability in the upper part of
the Pleistocene sediments was about 30 metres per day. On occasions during drilling
below the unconformity, karst zones such as solution channels were intersected where
circulation (of water and drilling mud) was lost. In some of these zones, the permeability

19

was estimated to reach 1000 metres per day. The specific yield (or effective porosity) was
estimated to be 0.3.

FRESHWATER LENS DETAILS

Using the results of the drilling, geophysical and other investigations, freshwater
lenses were located on West, Home and South islands.

On West Island, two permanent freshwater lenses have been identified underlying,
respectively, the airfield and the northern part of the island. These have been named,
respectively, the Airfield Lens and the Northern Lens. A permanent freshwater lens has
been identified on Home Island underlying the inhabited area. In addition, one large and
two smaller lenses have been identified on South Island (Falkland 1991). The locations of
these lenses are shown in Figure 28.

Approximate areas, maximum freshwater thicknesses, volumes and turnover times
of these lenses are shown in Table 11. The areas and volumes vary with time according to
antecedent recharge conditions. The areas shown in Table 3 are the maximum values and
the volumes are the range of values estimated during the period of record. The turnover
times are a measure of the average residence time of water within the freshwater zone and
are calculated by dividing the average thickness of the freshwater zone by the mean annual
recharge. A cross section through one of the lenses including details of a number of
boreholes is shown in Figure 32.

Some of the other islands in the Cocos (Keeling) Islands also have small
freshwater lenses. Based on limited on-site tests (Jacobson 1976a, Falkland 1988), a
freshwater lens is known to exist on Horsburgh Island but its sustainable yield cannot be
assessed without further investigation. Preliminary investigations on North Keeling
(Falkland 1988, 1992b) indicate the presence of a very thin freshwater lens at least on part
of the island. It is not known whether the lenses on Horsburgh Island and North Keeling
are permanent.

A major influence on the thickness of the thicker lenses, particularly the Airfield
Lens, is the geological unconformity between upper and lower sediments. As stated
earlier, this unconformity is a very significant influence on the formation of freshwater
lenses as the sediments below this unconformity have relatively high permeabilities and
mixing of freshwater and seawater is readily facilitated. The depths to the unconformity
are shown in Table 10. In all but one borehole in the Airfield Lens, the freshwater limit
(2600 umhos/cm) occurs at all times within a zone about 2 to 3 metres below this
unconformity. In general, it is evident that the unconformity is providing a limit to the
formation of a deeper freshwater lens. When recharge is low, as occurred in 1991, the
lens contracted to a position close to or above the unconformity. In dry periods, therefore,
the lens becomes limited by recharge at this location while in wetter periods the lens is
limited by the geology. It can be concluded that the underlying geology has a strong
influence on the freshwater lens at the Airfield. Some of the boreholes in the Northern
Lens exhibit similar behaviour while others within that lens and all of the Home Island
boreholes show that the freshwater lens is contained wholly within the Holocene
sediments.

An interesting observation was made in the most recent investigations (Falkland
1992b).-At borehole W1 22 near the southern end of the Northern Lens a reasonably thick
freshwater zone of 7 metres was found during drilling in August 1992. The thickness of

20

the lens to the mid-point of the transition zone (25,000 umhos/cm) was about 11 metres.
This result was better than expected as the width of the island at this location is only about
270 metres. Based on the approximate relationship outlined earlier, the minimum width
required to support a freshwater lens of this thickness is over 750 metres. This shows that
the approximate relationship should be treated with some cautign as other factors not
accounted for may have a significant bearing on lens thickness. At this borehole the
unconformity occurs at almost precisely the same depth as the limit of the freshwater zone,
indicating that it is a major influencing factor. Based on thickness and salinity of the
freshwater zone at borehole WI 22, it is considered that the lens at this location will not
disappear during drought periods. Future monitoring data will be used to establish the
validity of this assumption.

FRESHWATER LENS DYNAMICS AND MODELS

Flow through freshwater lenses is complex and is influenced by hydrologic
(variable recharge), geologic (variable permeabilities with depth and with distance from
one side of island to the other), oceanic (tidal movements) and anthropogenic (water
extraction) factors.

Early conceptual models and solution techniques for freshwater lens flow assumed
a sharp interface between freshwater and seawater. Observations have shown that this is
not the case on atolls and wide transition zones are the norm. Sharp interface models can
at best only provide an estimate of the depth to the mid-point of the transition zone,
yielding no information about transition zone width. Such models also assumed horizontal
flow within the lens with freshwater outflow occurring around the perimeter of the island
and did not account for tidal movements.

A more realistic conceptual freshwater lens flow model has evolved (Buddemeier
and Holladay 1977, Wheatcraft and Buddemeier 1981, Oberdorfer et al. 1990, Peterson
1991, Underwood et al. 1992) based on detailed observations on atolls. The conceptual
model accounts for vertical and horizontal tidal propagation through a dual aquifer system
consisting of the upper (Holocene) and lower (Pleistocene) sediments. This conceptual
model is supported by observations on a number of atolls in the Pacific (Buddemeier and
Holladay 1977, Hunt and Peterson 1980, Wheatcraft and Buddemeier 1981, Anthony et
al. 1989) and in the Cocos (Keeling) Islands (Falkland 1988) which have shown that tidal
lags and efficiencies at water level monitoring locations within atolls are largely
independent of horizontal distance from the shore. Tidal lag and efficiency (or the time
difference between, and amplitude ratio of, water table movement to tidal movement) are in
fact greatly influenced by the depth of the holes used for water level monitoring. Vertical
propagation of tidal signals tends to be dominant in the middle of the island whereas both
horizontal and vertical propagation are significant near the edges.

Using the above conceptual model, the numerical solution of freshwater lens flow
problems can more realistically be made with models which can account for a two layered
hydrogeologic system, flow of variable density water and the mixing of fresh water and
seawater. One such computer model, SUTRA, developed by the United States Geological
Survey (Voss 1984) has been applied to the study of freshwater lenses and coastal aquifers
on a variety of islands. Case studies of atolls and small carbonate islands include
Enewetak atoll, Marshall Islands (Oberdorfer and Buddemeier 1988, Oberdorfer et al.
1990), Majuro atoll, Marshall Islands (Griggs and Peterson 1989) and Nauru, a raised
atoll, (Ghassemi et al. 1990).

21

SUSTAINABLE YIELDS

The sustainable (or safe) yield of an aquifer is the rate at which water can be
extracted without causing adverse effects. For non-coastal mainland aquifers, the
sustainable yield can be approximately equated to the long-term recharge. For freshwater
lenses on small islands and some coastal mainland aquifers, such an approximation is not
valid as only a small portion of the recharge is available as sustainable yield. Most of the
recharge is required to counteract the effects of dispersion between the freshwater layer and
underlying saline water.

To avoid adverse effects from extraction (i.e. to avoid an increase in the salinity of
extracted water), the overall extraction rate from the lens should not exceed the sustainable
yield. An additional requirement is that pumping be distributed over the surface of the lens
to avoid local upconing of saline water.

Methods for estimating sustainable yield range from simple empirical approaches to
complex numerical models (e.g. SUTRA). Due to time limitations, an empirical approach
suggested by Mink (1976) was adopted for the Cocos (Keeling) Islands. Mink suggested
that an extraction equal to 25% of the 'flux' or flow through the lens was a good first
approximation to the sustainable yield. This is equivalent to 20% of the mean annual
recharge based on the simple water balance equation for the freshwater lens outlined
below.

The water balance equation within the lens can be expressed simply as:
R=Q+X+dVvV
where
R is the recharge into the lens after all evapotranspiration losses have
been taken into account, including transpiration directly from the

lens by deep-rooted vegetation,

Q is the lens ‘flux’ (outflow at the edge of the lens and mixing with
the transition zone at the base of the lens),

Xx is the total amount of water pumped from the lens,
dV is the change to the freshwater volume.

In the long term, dV tends to be negligible and can be removed from the equation.
Hence, the equation can be written as:

R=Q+X

This indicates that the maximum extraction (or sustainable yield) is 20% of mean
annual recharge based on the condition that extraction should be less than 25% of flow
through the lens. Given that mean recharge in the Cocos (Keeling) Islands is in the order
of 25 to 50% of mean rainfall, the allowable extraction (or sustainable yield) is about 5 to
10% of mean rainfall.

In relatively stable lenses, a proportion greater than 20% of the available recharge
can be extracted without adverse effects on the lens. In a study of the 'Central Lens’ on

22

Bermuda, for instance, it has been suggested that about 75% of recharge could be extracted
(Rowe 1984). This, however, is not considered appropriate for thin lenses, such as the
Home Island Lens, at least until further monitoring results provide a more accurate insight
into lens dynamics. In fact, because the Home Island Lens is a very thin and fragile lens,
there is a strong case for lowering the sustainable yield estimate to slightly less than 20%
of recharge. A value of 17% of recharge based on current pumping there (115
kilolitres/day) was adopted as the sustainable yield at least until more extensive salinity
monitoring records are obtained and analysed.

Under present vegetation conditions, the sustainable yields of the major lenses are
estimated to be (Falkland 1991, 1992a, 1992b):

- West Island Airfield Lens: 520 kilolitres/day,
- West Island Northern Lens: 300 kilolitres/day,
- Home Island Lens: 115 kilolitres/day,
- South Island lenses: 220 kilolitres/day,

If vegetation was substantially cleared from above some of these lens areas, the
sustainable yield could be increased. In particular, it is estimated that the yields from the
Northern Lens and from the lenses on South Island could be increased, respectively, to
400 and 330 kilolitres/day.

It is noted that the sustainable yields for the Cocos (Keeling) Islands are based on
an empirical approach. This approach, based on observations of the effects of pumping
and on the results of extensive modelling on other atolls, has been shown to be at least a
good approximation. It is noted that a similar 20% of mean annual recharge was used to
estimate sustainable yield for the island of Laura on Majuro atoll in the Marshall Islands
(Hamlin and Anthony 1987). The effects of pumping at different rates were investigated
by Griggs and Peterson (1989) using the SUTRA model. They concluded that the lens
was capable of extracting at least 20% and up to 30% of mean annual recharge. At
extraction rates of 40% of mean annual recharge, the upconing of seawater below the
gallery systems was found to be excessive.

For the freshwater lenses in the Cocos (Keeling) Islands, it is intended that salinity
monitoring at the network of monitoring boreholes will continue. Long term records
obtained from these boreholes will enable the effects of recharge and extraction on the
lenses to be evaluated. Adjustments to the present sustainable yield estimates may then be
warranted.

GROUNDWATER DEVELOPMENT

On small coral islands, such as the Cocos (Keeling) Islands, small hand dug wells
have been used for extraction of small quantities of water (e.g. at the household level).
For larger centralised water supply systems, more extensive systems are required. There
are three main alternative systems for larger scale pumping of water from freshwater
lenses, as follows:

- borehole systems,
- wells, and
- infiltration galleries.

23

Boreholes and wells, while possibly suitable in large freshwater lenses, are not
considered suitable in the Cocos (Keeling) Islands because they extract from a localised
area and can lead to excessive drawdowns. To avoid excessive drawdowns, many
boreholes or wells would need to be drilled or dug. The cost of drilling or excavating,
pumps and pipework would not be economical for the quantity of water extracted.

Infiltration galleries (or ‘skimming wells’) are considered to be the best solution as
they skim water from the surface of the lens thus minimising drawdown. These types of
systems have recently been installed on Home Island and in the West Island Northern
Lens. In many cases they have replaced earlier dug well systems with short radial pipes
extending from their bases.

Infiltration galleries consist of a horizontal, permeable conduit system laid at or
close to mean sea level, enabling water to be easily drawn towards a central pump pit.
Figure 33 shows the type of infiltration gallery used on Home Island (Falkland 1988).
Salinity data collected before and after the galleries were installed have shown a general
reduction in the salinity of the pumped water.

Current water usage from each of the major lenses as a proportion of the estimated
sustainable yields are as follows:

- West Island Airfield Lens: 27%

- West Island Northern Lens: 50% (present vegetation),
30% (cleared vegetation),

- Home Island Lens: 100%, and

- South Island lenses: 0%

It can be seen there is ample capacity for expansion of current water usage at the
Airfield Lens and no spare capacity on Home Island. The Northern Lens has sufficient
spare capacity for some additional use, particularly if some clearing of the existing thick
vegetation occurred. South Island remains at present an untapped resource.

OTHER WATER RESOURCES

Roof catchments and relatively small tanks (mainly 4.5 kilolitre capacity) provide
supplementary rainwater to Home Island residents. Rainwater is also collected from a
limited number of buildings on West Island.

Desalination of seawater or brackish groundwater is a possibility but would be
expensive. A detailed analysis of water resources (Falkland 1988) showed that
groundwater is the cheapest resource to develop. Using Home Island for a pilot study, it
was found that the unit costs (capital plus operating costs) of a desalination plant using the
reverse osmosis principle would be about 7 times more expensive than the development of
groundwater. Even if groundwater was piped from South Island to Home Island, an
option which in the long term may be preferable if the Home Island lens becomes polluted,
desalination would be more expensive by a factor of 3. By comparison, rainwater
catchment as the sole source of water is the most expensive, being about 10 times more
expensive than groundwater development on Home Island.

The most appropriate option from an economic, quality and security viewpoint was
the development of groundwater as the primary source of water with rainwater being used
as a supplementary source. This option has been implemented.

24

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Jacobson, G. 1976b. The freshwater lens on Home Island in the Cocos (Keeling) Islands.
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26

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Ou

Woodroffe, C.D., Veeh, H.H., Falkland, A.C., McLean, R.F. and Wallensky. 1991.
Last interglacial reef and subsidence of the Cocos (Keeling) Islands, Indian Ocean.

Marine Geol. 96: 137-143.

28

Table 1. Temperature (°C): 1952-1991 data.

Month Daily Mean Extreme Max. Extreme Min.
January 27.0 32.1 20.1
February 27.4 32.4 20.1
March PU fe) 32.1 19.8
April 213 32:2 19.6
May 27.0 31.4 19.4
June 26.3 30.7 20.1
July 25.8 29.9 20.4
August 295.8 29.8 18.3
September 26.0 30.0 19.0
October 26.3 30.6 20.6
November 26.6 Se) 19.3
December 26.8 32.2 21.1
Table 2. Relative humidity (%): 1952-1991 data.

Month Daily Mean Mean Daily Max. Mean Daily Min.
January 74 82 66
February 74 81 66
March 16: 81 69
April al 84 69
May Ti 82 70
June 99) 84 69
July aA 84 va
August 74 84 69
September 2 81 67
October 72 82 66
November 2 84 65

December 7d 82 65

29

Table 3. Atmospheric pressure (hectopascals): 1952-1987 data.

Month Daily Mean Extreme Max. Extreme Min.
January 1008.8 1015.8 970.0
February 1008.4 1018.1 992.1
March 1008.8 1015.7 987.0
April 1008.8 1015.8 998.2
May 1009.5 1017.7 1000.4
June 1010.3 1017.2 1002.5
July 1011.1 1018.5 1001.0
August 1011.6 1018.5 987.5
September 1012.2 1017.7 1004.8
October 1011.6 1018.5 1001.6
November 1010.8 1017.8 989.4
December 1010.0 1017.6 993.8
Table 4. Cloud cover (oktas): 1952-1987 data.

Month Daily Mean Extreme Max. Extreme Min.
January Spl 6.0 Ss)
February 5.1 6.3 3.0
March 5.1 6.4 4.2
April 5.3 6.3 4.1
May 5.3 6.4 4.4
June 2 6.6 4.2
July 5.3 6.2 3.8
August 5.1 6.1 3.9
September D5 6.5 3.8
October Sal 6.4 3.8
November 5.0 6.8 3.8
December 5.1 6.4 3.5

30

Table 5.

August
September
October
November
December

Wind speed (metres/sec).

Daily Mean

(1952-1987)

ANN WWINAAA RY
ONNKH OOD OR WD W

Extreme Max.
(1952-1991)
48.8
34.0
28.3
29.3
27.8
30.9
24.7
36.0
24.2
24.2
40.1
27.3

Extreme Min.
(1952-1991)

SX AIO OOO IovoeeS}

3 1

Table 6. Cyclones passing over or close to the Cocos (Keeling) Islands, since 1960.
Name and Date of Approx Min. central Max. wind Total
number passing distance pressure when speed on rainfall
closest away (km) passingclosest island (mm)
to island toisland/ min. (km/hour)

pressure on

island(hecto-

pascals)
Unnamed (668) 13/2/61 60 991/992 122 71
Hazel (542) 9/3/64 80 988/991 102 121
Carol (548) 27/12/65 100 997/1002 95 48
Nancy (555) 14/3/66 100 997/1000 91 26
Doreen (566) 21/1/68 20 970/970 176 219
Dianne 6/1/70 80 996/1005 98 124
Paula (591) 27/3/73 20 999/1006 83 25
Annie (682) 25/11/73 40 995/1002 145 71
Deidre (684) PAV AV Ae) 30 995/994 85 72
Denise (455) 23/5/75 30 995/1002 100 28
Daphne (711) 15/1/82 60 995/998 81 66
Annette (696) 5/2/84 30 994/999 81 142
Daryl (699) 11/3/84 80 984/1001 92 253
Ophelia (742) 12/1/86 30 986/1002 93 252
Alison (752) 8/4/86 30 988/1002 106 Wp
Frederic (784) 30/1/88 40 988/995 111 90
Herbie (783) 19/5/88 50 990/995 87 Si)
John (767) 25/1/89 10 997/1000 61 106
Leon (769) 17/2/89 90 990/1006 63 27
Pedro (786) 10/11/89 100 982/1001 137 299
Graham (802) 5/12/91 100 925/1004 98 49
Harriet (803) 27/2/92 10 975/982 163 80
Ken 21/12/92 35) 990/1001 ath 162
Notes:

- data are from the Bureau of Meteorology's cyclone database and other information

- listed are cyclones which passed within 100 km of the islands and had a minimum
central pressure less than 1000 hectopascals

- rainfall totals are to the nearest 1 mm over a 2 day period.

32

Table 7. Annual rainfall (mm) at three raingauge sites on the South Keeling atoll.

Year West Island Home West Island % variation

(Met Station) Island (Quarantine) from West Island
1987 1871 1222 -
1988 2220 1976 -
1989 1963 1863 2210
1990 2271 2145 2410
1991 856 837 820
1992 2579 2568 2637
Total (1987-92) 11760 10611 - -10.8
Total (1988-92) 9889 9389 . -5.2
Total (1989-92) 7669 7413 8077 -3.4/+5.3
Table 8. Monthly rainfall (mm): 1952-1991 data.

Month Monthly Mean Mean Monthly Max. __ Mean Monthly Min.
January 199 561 i
February 161 409 /

March 232 630 39
April 234 551 21
May 194 646 17
June 201 649 7
July Diy? 643 25
August 201 468 18
September 2, 211. 3
October 70 S12 4
November 94 574 3
December 114 447 5

33

Table 9. Pan evaporation (mm): 1982-1991 data.

Month Monthly Mean Mean Monthly Max. Mean Monthly Min.
January 220 254 195
February 198 220 170
March 205 226 195
April 189 207 165
May 189 211 146
June 171 186 150
July 186 198 174
August 208 226 171
September 219 249 201
October 229 251 217
November 231 246 222

December 241 273 217

34

Table 10. Monitoring borehole details.

Lens and Year of RL relative Depth of Depth of
Borehole drilling to MSL (m) water table (m) _unconformity (m)
Airfield Lens, West Island

WI 1 1987 2.16 1.8 12.6
WI 2 1987 2.84 2.6 NONE 7/
WI16 1987 283 te7/ 11.8
WI17 1987 Saki 2.5 12.9
WI8 1988 1.33 0.9 10.3
WI19 1988 3{57 333 13.4
WI 11 1990 2.93 1.9 12.9
Northern Lens, West Island

WI13 1987 1.74 i35) 12.0
WI14 1987 1.65 12 14.9
WI5 1987 1.85 1.9 14.8
WI 10 1988 1.70 12 132
WI 12 1990 1.43 1.4 10.5
WI 13 1990 1.18 13 15.2
WI 14 1990 ey 15 14.7
WI 15 1990 Lvl 1.4 14.6
WI 16 1990 n.a. 1.4 123
WI 17 1992 2.56 PED? 1297
WI 18 1992 2.09 1.6 10:5
WI 19 1992 2.19 1.8 15.4
WI 20 1992 1.81 1.6 122
WI 21 1992 AST AG 1.4 122
WI 22 1992 2.21 Zl 93
Home Island

HI 1 1987 2.05 1.6 S55
HI 2 1987 1.26 1.0 10.6
HI 3 1987 1.89 1.6 11.9
HI 4 1987 1.70 1.1 9.6
HI 5 1987 1.65 1.1 >12.2
HI 6 1987 1.59 1:2 2
HI 7 1987 Bey 1.0 >15.6
HI 8 1987 127 10 >12.2
HI 9 1990 1.27 ial >15.8
HI 10 1990 1.26 1.0 >16.0
HI 11 1990 1.08 | Bes >16.1
HI 12 1990 1.14 7. >15.9
South Island

SI 1 1990 n.a. 1.4 13.8

n.a. = not available

35

Note: Maxima and minima are the extreme values for each month

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37

Note: Maxima are the extreme values for each month; minima are all zero

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Figure 7. Isohyetal map of mean annual rainfall for the Indian Ocean (modified from

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Figure 8. Annual rainfall, 1953-1991 (composite record with some missing data).

39

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1990 1991

Month and Year

1989

Monthly rainfall at the meteorological and Quarantine stations, 1989-1991.

Figure 12.

4l

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1991

1990

Month and Year

1989

Cumulative monthly rainfall at the meteorological station, Home Island and the
Quarantine Station, 1987-1991.

Figure 13.

8000 9000 10000

7000
West Is Met Stn Monthly Rainfall (mm)

6000

5000

2000

BaD is seemless cd
im in meee

(=) oO
a Be ee
3 vy oO N -

(uw) jweyurey AjUuJLOW S| WOH

y rainfall for the meteorological station and Home

Double mass curve of monthl

Island, 1987-1991.

Figure 14.

42

Monthly Rainfall at other gauge (mm)

Figure 15.

Home Is Monthly Rainfall (mm)

Figure 16.

0 1000 2000 3000 4000 5000 6000
West Is Met Stn Monthly Rainfall (mm)

—#- Home Is —- Quarantine Stn

Double mass curve of monthly rainfall for the meteorological station and Home

Island and the Quarantine Station, 1989-1991.

Regression Equation:
H=0.865*W+2
where H = Home Is monthly rainfall (mm)
and W = West Is Met Stn monthly rainfall (mm)

0 100 200 300 400 500 600 700

West Is Met Stn Monthly Rainfall (mm)

Regression analysis of monthly rainfall at the meteorological station and Home

Island, 1987-1991.

43

(mm) |

Quarantine Stn monthly rainfall (mm)
West Is Met Stn monthly rainfall

1.044*W+4

j
HS
é

where Q

(wuuu) jeyureY AjYJUOW LIS © S| ISOM

(

and W

200 250 300 350 400 450

150
West Is Met Stn Monthly Rainfall (mm)

100

50

Regression analysis of monthly rainfall at the meteorological station and the

Quarantine Station, 1987-1991.

300

Figure 17.

VAALLILEELEDPSILDILIDL ALOE LAL AAEASLEELPDOEPDDELEPELTTADL ED

A A

PEEDILOSS LS LDA L ODL ALE.

PILLILIAIIL ALIA ELDAEL ASSL LITLE SSS SSIS SS So

LOLLPIL ISLIP ILL ,

PPLE PEPLISLILOPL ESE OSASLSIDOPLSSS SPOS LOIS PPLE EIA

PLL LL OLLIPLESL PEPE DA ,

VOEUDIOADILLILLSSLSSLLD DIP LLDL As

aa SIL IL DLS

VLPILLAEOLIILIDAAESAAANAEEL PSA LLEL ESL ASIELLAL EDA

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month

(oe) (eo) fo) (oe) [e) (eo)
Ww (oe) w) [e) w
N N _- -

(ww) uolesodeng ued AjyjuoW

Minimum

Maximum {jj Mean

Mean, maximum and minimum pan evaporation.

Figure 18.

44

250

(ww)

LLL hhihde
ee | | |

ada sEsssitihidititthitEsidttshhtidittihthis

“assitthiititiissstittttttthti;¢ddddlithtt¢sséisss

AILS ISASSDASSALSS IDS ADDS DDS Uusititittttiiittit

SLITS LLLADISSS DS ASE

bd hedhitithtit¢seeisssithttttishhsssda

COL ALLISIS PIAL APLAL LAL

SIDPLLSPAPSA SDE. S,

MOANA MISA AM ptt tht) tht ltt ltl th

YULIIDIILILILILLILILLILLIDDIDI DLL LLLLLLD SDSS Sb
WLLL dldddldddddddddéiidddés

WIMIMMMMIUMMM LILI LL LL LSA SEL,

|
oO
Oo
=

200
5

c

onesodeng jeiuajog Ajujuopy ueayy

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

jo) oO
Ww

Month

GB Penman method

Pan method

Mean monthly potential evaporation estimates using pan and Penman methods.

Figure 19.

(uw) JJesuleYy jenuulyy UBAaY JO %

1970 1975 1980 1985 1990 1995

1965

1960

1955

15

° w ° rs)
=

-10
15

(IOS) xepuy UOHE)|!OSC WaUNOS

Year

~s<- West Is Rainfall

SOl

Relation between Southern Oscillation Index and annual rainfall.

Figure 20.

45

Evapotranspiration
Rainfall

MAW //

mitre

\ iar See ee eres 2-3m
Mean sea level Lore ee
— an e <i i
Unconsolidated Freshwater Yl
Holocene <4
sediments yy
(low permeability) N Wh 10-20m
] | to Seawater |
Pleistocene
limestone
(high permeability)
300-1000m -——
Figure 21. Typical cross-section through a coral island with a freshwater lens.
P
Eftencgt
ue or, Coconut Tree
LEP ON MODEL E
interception, 1°! ISMAX
STORAGEL__ “| cea.
E SMCMAX
Bush/Shrub § SOIL MOISTURE , _ ‘st (Brees = FC x SMZ
STORAGE: Pim R IEE Toe iy
zy SOIL MOISTURE = WP x SMZ
S$ ZONE GROUNDWATER Tif a
UNSATURATED STORAGE iy =”
ZONE fee CNN Se SS pan
WATER 4th
Fee a iene ar Oe DT Ae Zetia oa
—==—CAPILLARY ZONE {LOSSES (OUTFLOW,

TABLE
NET RECHARGE To DISPERSION)|

FRESHWATER LENS

Figure 22. | Recharge model.

46

Annual Rainfall and Recharge (mm)

Figure 23

Annual Rainfall and Recharge (mm)

Figure 24

500

0 hs SS . N PS Ny le a
1953 1958 1963 1968 1973 1978 1983 1988 1991
Year

MS West Is Rainfall ij Airfield Recharge

P Annual rainfall and recharge, Airfield Lens, 1953-1991.

50048 M8

-500
1953 1958 1973 1978 1983 1988 1991
Year
M8 West Is Rainfall GM North Lens Recharge

, Annual rainfall and recharge, Northern Lens, 1953-1991.

47

Annual Recharge (mm)

WG Airfield Lens (J Home Is Lens KQ Northern Lens

Figure 25. Annual rainfall and recharge, West Island and Home Island Lenses, 1953-1991

Recharge (% of rainfall)

| Northern Lens & South Island Lens

Figure 26. Effects of tree vegetation on mean annual recharge.

% Tree Cover

48

Cumulative Annual Recharge (mm)
(Thousands)

—#- Airfield Lens —+— HomelsLens —* Northern Lens

Figure 27. Cummulative annual recharge for West Island and Home Island Lenses, 1953-
1991.

49

96°50'E 96°55'E

\\ Horsburgh Is.

km.
12°05'S

SOUTH
KEELING
ISLANDS

: Freshwater lens
e Salinity monitoring borehole

Figure 28. Location of Boreholes and freshwater lenses.

150 dia. PVC collar and
screw cap assembly.

Ryco quick- fit
non-return volves.

Concrete.

5mm nylon tubing.

Ceramic cylinder.

\ Bore dia. 89mm
Selected gravel. (N size casing)

See
Bentonite layer. “0003

1-5 or 3-0 metres

No permanent
casing.
Selected gravel. —— — i

Bentonite layer. > LAS

q

?
Z

Selected gravel \
6mm maximum. ork Base of bore.

Figure 29. _ Borehole salinity monitoring system.

51

West Is Recharge —+— Bore WI6 >< Bore WI7 —- Bore WI8

Monthly Recharge (mm)
Freshwater Depth (m)

Month & Year

Figure 30. Depth of freshwater zone and recharge for boreholes WI 16, WI 17 and WI 18
on West Island.

West Is Recharge —+— Bore HI1 >< Bore HI3

Freshwater Depth (m

Monthly Recharge (mm)

ZB

NNN NE
NS

N N N N ‘meh SN No NNN ; 0
AMJJASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJASOND
1987 1988 1989 1990 1991

Month & Year

Figure 31. Depth of freshwater zone and recharge for boreholes HI 1 and HI 3 on West
Island.

(ALLA LALLIL ALA LLL LL ALLL
CL OLTT OLED.

\-ZZZZzAaaee

52

, (Electrical Conductivity for
PS5 is offset 10m PS2 Seawater = 46000 umhas/cm)

Lagoon '
approx. ground surface

——— Sees. Ny Gowan

ar eS Se a7 Mean Sea Level

x | [eugene Kd
—s Z =» =i 5 _— ae - = i"
ages 2 B50: \ Electrical Conductivity
= 2600 umhos/cm

(Base of Freshwater Zone)

7200
/
/
/
aa
ie Electrical Conductwity
eat = 23000 umhos/cem

HIS. (Midpoint of Transition Zone)

a NOTE:
Boreholes show depth in metres on the left and
18 + 37200 on the right Electrical Conductivity of sample
Horizontal Scale: 41. :/5000 obtained during drilling in umhos/em
Vertical Scale: 1 : 200 21
HI6

Figure 32. Cross-section through Home Island lens showing shape of lens at time of
drilling in Oct/Nov 1987.

Cover with good seal
for pump well

‘Gatic’ Cover
*Gatic’ Cover at or 50 dia. PVC pipe at surface Level

just below surtace (for Salinity tests)

1500 dia. (approx.) To supply Back fill
conc. pump well

Mean Sea Level (MSL)

ph ee

Water Table
ens:

150 | Concrete base

1
ir | 100, 150 of 225
3 . slotted PVC pipe impermeable membrane
}—__—_——_—_—_—- Maximum 100 metres ——--—+ (Class 6 water (thick polytfiene sheet)
supply pipe) placed across trench,
about 100-200 above top of pipe

—
RL-0 30 To manhole
(relative to MSL)

NOTES:

1. All joints between pipes and pump wells/manholes to be well sealed

2. Float switch level to be as close above base of pump suction as possibje
(without causing vortex)

3. Optional housing over pump well and pump/meter (not shown)

4. All figures in mm but drawing not to scale

Figure 33. Cross-section through typical Home Island infiltration gallery.

ATOLL RESEARCH BULLETIN

NO. 401

CHAPTER 3

LATE QUATERNARY MORPHOLOGY OF THE COCOS
(KEELING) ISLANDS

BY

D.E. SEARLE

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 3
LATE QUATERNARY MORPHOLOGY OF THE
COCOS (KEELING) ISLANDS
BY
D.E. SEARLE *

ABSTRACT

Seismic profiles have been obtained from Cocos lagoon and correlated with
radiometric-dated core data. They show that the Last Interglacial atoll had a very similar
morphology to the present atoll, and lies 8 to 28 m below sea level. It is overlain by 8 to
18 m of Holocene reefal deposits. Two deeper surfaces, of similar shape to the overlying
reef surfaces, are recorded beneath the lagoon. These are tentatively identified as solution
unconformities formed during glacial lowstands at oxygen isotope stages 6 and 8. Blue
holes in Cocos lagoon are interpreted as solution dolines modified by clastic-controlled
growth during submergence and relief enhancement by facies-controlled solution
weathering during emergence. The data support the antecedent model of reef development
on a subsiding base. However, unlike Purdy's (1974) antecedent karst model, both
constructional relief and differential erosion are emphasised. Preservation of thin reef caps
indicates that the atoll surface may have been lowered by as much as 18 m during each
glacial cycle by subaerial erosion and solution. This allows an improved estimate of 0.02
mm/yr for subsidence of the atoll during the late Quaternary.

INTRODUCTION

Charles Darwin visited the Cocos (Keeling) Islands in 1836 and collected field
evidence in support of his subsidence theory of atoll formation. This theory recognises an
evolutionary sequence by vertical reef growth from volcanic island fringing reefs, through
barrier reefs, to coral atolls driven by gradual subsidence of the volcanic island core.
Drilling through Pacific atolls has encountered thick, shallow-water, reef-associated
limestone overlying basal basalt; these results have substantiated Darwin's theory.
Isostasy and plate tectonics provide explanation for subsidence and co-existence of
evolutionary reef phases along linear island chains.

Darwin's field evidence from Cocos consisted of observation of erosion of the
shoreline and collapse of coconut palms by undercutting at the shoreline. He inferred
subsidence from this geomorphic evidence - an interpretation that has been strongly
questioned, for example by Ross (1855).

A cemented coral conglomerate platform underlies many of the Cocos Islands and
is exposed along the ocean shoreline. Dating of material from this platform, which has
been identified as a former reef flat, indicates that sea level was about 1 m higher than
present some 3000 years ago (Woodroffe et al. 1990).

Drilling on the Cocos Islands has intersected the "Thurber" discontinuity, a
solution unconformity separating Holocene from Pleistocene reef that, at one site, has been
dated at about 120, 000 years B.P. This corresponds to the Last interglacial oxygen

* Department of Minerals and Energy, P.O. Box 194, Brisbane, Queensland, 4001.

2

isotope substage 5e (Woodroffe et al. 1991). The discontinuity lies at 6-16 m below sea
level (revised depths, see Fig. 1 and Woodroffe et al. this volume). Woodroffe et al.
(1991) interpreted the data to imply a subsidence rate of 0.1 mm/yr over the last 120, 000
years.

Thus, the Cocos (Keeling) Islands have been undergoing gradual, long term
subsidence. Superimposed on this are millennia scale, glacially-induced eustatic
movements in relative sea level and consequent hydro-isostatic adjustments. The most
recent relative sea-level change has been a slight fall over the last few thousand years.

This paper is concerned with the structure of the Cocos (Keeling) Atoll during the
Late Quaternary, and the influence of antecedent topography on the morphology of the
modern atoll.

REGIONAL SETTING

The Cocos (Keeling) Islands, in the eastern Indian Ocean, consist of an atollon -
North Keeling Island, and a horseshoe-shaped atoll - South Keeling Islands. The South
Keeling atoll lies 40km south of North Keeling and consists of a shallow circular lagoon
fringed by a series of reef islands. The islands vary in size from West Island, which is
11km long, to small islands less than a kilometre long (Fig. 1).

The lagoon of South Keeling atoll is 10 km across east to west, and 12 km from
north to south. To the south and east, the lagoon connects with the open ocean through
inter-island channels that are about 1 m deep. To the north and north west, deep openings
occur on either side of Horsburgh Island (see Kench, this volume). Cocos lagoon is
shallow to the south, with much of it being exposed at low tide. To the north the lagoon
deepens to over 15 m. Much of the central south-eastern part of the lagoon is occupied by
steep-sided "blue-holes", some over 15 m deep (Fig. 5). The holes average 100 m across
but are generally smaller and more isolated to the south east while towards the centre of the
lagoon the holes commonly coalesce. Submerged patch reefs occur in the central lagoon
(see Williams, this volume).

METHODOLOGY

A high resolution continuous seismic reflection survey was carried out in the
lagoon of the South Keeling Islands. The continuous seismic profiling (CSP) was
conducted using a "Uniboom" sound source, triggered every half-second at an energy level
of 200 Joules. A single-channel, 8-element hydrophone was used to receive the seismic
signal after reflection from the seabed and subsurface. The signal was filtered to remove
noise below 500 Hz and displayed as a seismic cross section on a graphic recorder.
Seismic profiling was carried out at a speed of 4 knots. Position fixes were obtained every
2 minutes (about every 250 m) using a Trimble GPS unit.

In order to limit the presence of seabed multiples the sound source and hydrophone
were deployed from opposite quarters of the vessel. This field technique imposes a
geometrical depth scale on the records, and corrections have been applied to depths
measured from the seismic records.

RESULTS

A total of 70 km of seismic profile was recorded over the northern and central part
of the lagoon, Figure 1. This includes profiles across the blue holes, and profiles
approaching Home and West Islands to allow correlation of seismic with drill data.
Seismic profiling was not feasible in the very shallow southern part of the lagoon.

Seismic data quality was only fair owing to noise from wind waves in the lagoon
generated from the persistent Trade Winds. In the shallow seagrass-covered parts of the
lagoon, particularly off Home Island, no seismic signal was received by the hydrophone
array. This was due to attenuation of the signal by gas bubbles adhering to the seagrass.

The seismic profiles from Cocos lagoon record subsurface data down to 45-50
milliseconds of reflection time, being limited by the system used and the nature of the
sediments encountered. This converts to about 35 m in depth, assuming a conversion
velocity of 1500 m/s. This value is close to the seismic velocity of sea water and reef
limestone of Holocene age. Older sediments, which may be more compacted and
cemented, can have higher velocities. Thickness of older units may be overestimated since
a conversion velocity of 1500 m/s has to be used in the absence of measured values.

INTERPRETATION

The seismic profiles record the seabed and subsurface reflectors. The subsurface
reflectors are derived from changes in physical properties at geological discontinuities.
Experience in reef provinces elsewhere suggests that these discontinuities are commonly
solution unconformities formed when reefs were exposed to subaerial processes during
glacially-induced, sea-level lowstands (Orme et al. 1978, Searle and Harvey, 1982). Thus
reflections from unconformities imply atoll emergence, while the seismic sequences
bounded by these reflections are due to reef and lagoonal deposition during interglacials.

. Lagoonal bathymetry is one of high relief except for the marginal areas where
shallow subtidal flats commonly extend for 2 to 3 km into the lagoon. The deepest water
encountered during the seismic survey was in the blue holes. One hole was 18 m deep
with a rim barely deep enough to allow passage (0.5 m at high tide). Water to 16 m deep
was traversed in the centre of the lagoon and close to the southern tip of Direction Island.

Three subsurface reflectors (referred to as A, B, and C in descending order) are
present on the seismic records (Figs. 2 and 3). These reflectors, together with the seabed
reflection, form the sequence boundaries of 4 depositional units.

The seismic sequence bounded by reflector A and the seabed varies in thickness
from 8 to 18 m. It is thickest towards the southern part of the lagoon where blue holes
appear to be infilled (Fig. 3). Unlike seismic data from the Great Barrier Reef Province
(see Orme et al. 1978; Searle, 1983; Searle and Flood 1988) little internal structure is
apparent in this sequence, and it is not possible to differentiate between reef rock and
bioclastic facies.

Reflector A varies in depth from 11.5 m where it rises towards West Island, to 28
m in the centre of the lagoon. The shape of the subsurface defined by reflector A closely
matches that of the lagoonal seabed. Both have high relief, except where they rise gently
towards the islands; are deepest in the centre of the lagoon; and steepest dips are apparent
over the blue holes and their rims. The data have been tested for velocity distortion using

4

published refraction velocities for reefal limestone of Holocene age (Harvey and Hopley
1981). Less than 20% of the relief on reflector A can be accounted for by this effect.
Similarities in the morphology of the lagoon and its subsurface as seen on the seismic
records are, therefore, real and not attributable to distortion.

A thin sequence separates reflectors A and B. This sequence averages only 1 - 2m
in thickness except off the northern part of West Island where it increases to 5 m (Fig. 2).

Reflector B lies at depths of 16 to 32 m, and generally conforms with the shape of
reflector A. It is deepest beneath the centre of the lagoon and shallowest off the northern
part of West Island. Here it forms a terrace at -17 m overlying a -20 m terrace defined by
reflector C (Figure 2). Beneath the blue holes reflector B lies at a depth of 24 to 26 m,
being deeper below the holes and somewhat shallower below their rims.

Sequence B/C, where recognised, is only 1-2 m thick (Figs. 2 and 3).

Reflector C, although commonly lost below the limit of penetration, lies at depths
of 18 to 32 m. Reflector C is best developed between the northern part of West Island and
the central lagoon where it forms the -20 m terrace that then dips towards the centre of the
lagoon (Figure 2). Reflector C is also present at about -22 m off Direction Island, dipping
towards the centre of the lagoon.

DISCUSSION

Drilling on the Cocos (Keeling) Islands (Woodroffe et al. 1991; Woodroffe et al.
this volume; Falkland, this volume) intersected the "Thurber" discontinuity at depths of 6
to 16 m below mean sea level (Fig. 1). Projection of reflector A from the seismic profiles
that come closest to the drillholes on West Island allow correlation with the top of the older
limestone at the "Thurber" discontinuity (Figs. 2 and 4). On Cocos this older limestone
has been dated as Last Interglacial in age (123 + 7 ka B.P., Woodroffe et al. 1991). Thus
reflector A is interpreted as the weathered surface of the Last Interglacial atoll modified by
subaerial exposure prior to the Postglacial transgression, and upon which Holocene reef
has developed. Reflector A marks the Holocene/Pleistocene boundary.

Reflectors B and C (Figs. 2 and 3) are interpreted as older solution unconformities
formed by subaerial exposure on progressively older atoll surfaces. The sea-level curve of
Chappell (1983) shows glacial lowstands reaching minina at 150, 000 and 260, 000 years
B.P.; reflectors B and C, respectively, may represent the subaerial surfaces formed during
these episodes (oxygen isotope stages 6 and 8) and upon which subsequent reef
development took place.

The sequence below reflector C probably consists of reefal deposits dating from the
highstand of oxygen isotope stage 9. Seismic sequences B/C and A/B represent reefal
limestone deposited during highstand stages 7 and Se, respectively.

Although reflectors B and C are imperfectly recorded by the seismic system, the
shape of the ancestral atoll lagoon (after subaerial weathering) appears to have been
preserved during the Late Quaternary through to the present day. Even at the relatively fine
scale of blue holes, shape has been preserved, and possibly enhanced (Fig. 3). The most
noticeable difference in atoll shape since the formation of surface B has been the
progradation of Last Interglacial age reefal sediments over the -17 m terrace off West
Island (Fig. 2).

The unconformity defined by reflector A is interpreted as the weathered surface of
the Last Interglacial reef. This surface lies 6-16 m below mean sea level beneath the
islands (Woodroffe et al. 1991, and this volume), and dips beneath the lagoon to a depth
of 28m below mean sea level. Off West Island, where the best subsurface data is
available, this Holocene/Pleistocene interface dips at 4 m/km into the lagoon (Fig. 4).
Below the blue holes and the submerged patch reefs in the centre of the lagoon surface A is
substantially mimiced by the modern reefal surface (Fig. 3). Thus the morphology of the
modern atoll is inherited from its antecedent platform, which, in its turn appears to have
been inherited from older atoll landforms. In this respect, the data from Cocos support the
antecedent karst theory of Purdy (1974).

It appears that atoll landforms maintain and even amplify their antecedent relief.
This may be due to either differential accretion during submergence, or to differential
erosion during subaerial exposure, or a combination of both processes. Accretion by
vertical reef growth during marine transgressions would be more rapid in the shallow
photic zone, aided by a process of clastic control whereby coral growth can be retarded by
biodetritus deposited in low areas (Goreau and Land 1974).

Subaerial erosion may also amplify relief by facies control of solution weathering
(Bloom 1974). Under this process the less permeable lagoonal sand and mud facies would
dissolve away faster than the more permeable reef framework and coarse
rubble/conglomerate facies. On a smaller scale, facies control accounts for the
development of blue holes. Once elevation differences were present in the proto-atoll
lagoon the positive features would be exploited by coral colonisation and vertical growth.
Then, as now, the lagoon would tend to silt up by progradation of bioclastic sand and mud
behind the windward margin. The negative areas between reef patches would gradually
infill as an intertidal reef flat developed in the lagoon. Upon emergence the surface would
experience facies-controlled differential weathering through internal drainage and solution.
This would result in the formation of residual prominences at the site of former patch reefs,
and the development of solution dolines in the intervening lagoonal mud and sand facies.
Subsequent glacial cycles would emphasise relief by constructional (highstand phases) and
solution weathering (lowstand phases) processes forming relatively deep blue holes.

While blue holes are relatively numerous in the Caribbean, few have been reported
from the Indo-Pacific region (Purdy 1974). Deep blue holes are not common in the Great
Barrier Reef; they occur singly, and partly for that reason are considered as collapsed
doline features (Backshall et al. 1979). The blue holes on Cocos, by contrast, dominate
the southern central area of the lagoon. They are unlikely to be juxtaposed collapse
features, and are considered to be multi-generational solution dolines.

The Holocene pattern of atoll development may be taken as a model for earlier
cycles. The difference in thickness between the older Pleistocene reef and associated
lagoonal sediments, and Holocene deposits is presumably due to subaerial erosion of the
older sediments. It is interesting to speculate on the relationship between reef growth and
subaerial erosion, and consider implications of sea level and subsidence for the
preservation of the resulting reef cap.

The data from Cocos implies a mean accretion rate of 2 mm/yr, based on an
average thickness of Holocene of 16 m deposited since the sea flooded the atoll some 8000
years ago. Reefal accretion could only occur during submergence for, say 10% of each
Late Quaternary glacial cycle. This would add 20 m to the reef cap during each interglacial
cycle. As sequences A/B and B/C are only 1-2 m thick, 18 m of reef cap must have been

6

eroded during the remaining 90% of time when the atoll was emergent, hence an erosion
rate of 0.2 mm/yr is implied.

Data on erosion rates is sparse and values vary greatly. For instance, Trudgill
(1976) provides an average value of 0.26 mm/yr from Aldabra Atoll from a range of
values that vary with lithology, mineralogy and soil cover. Purdy (1974), quoting Land et
al (1967), provides values of 0.01-0.04 mm/yr that vary with rainfall. Data for reefal
accretion appears less extreme and better established. On Cocos, Holocene accretion
estimated from the seismic and core data falls within the range of estimates for other atolls,
see, for example, Marshall and Jacobsen (1985).

For the reef cap to be repeatedly accommodated, highstand sea levels must rise, or
the atoll must subside. Accepting the latter as the most feasible in the longer term, a
subsidence rate of 0.02 mm/yr is implied from the data. This allows for a 2 m increment to
the reef cap during each glacial cycle. Subsidence rates for Cocos (Woodroffe et al. 1991)
can now be refined to the lower value of 0.02 mm/yr, which is closer to global average
oceanic subsidence rates (Ladd et al. 1970, Menard 1986).

CONCLUSIONS

Continuous high resolution seismic data has been obtained from Cocos lagoon.
Correlation with radiometric-dated core data from the Cocos islands allows reconstruction
of the shape of the Last interglacial atoll.

The Last Interglacial atoll surface, both island and lagoon, has a very similar
morphology to the present atoll, and lies 8 to 28 m below sea level. It is overlain by 8 to
18 m of Holocene reefal deposits.

Two deeper surfaces, of similar shape to the overlying reef surfaces, are recorded
beneath the lagoon. These are tentatively identified as solution unconformities dating from
subaerial exposure of earlier atolls during glacial lowstands at oxygen isotope stages 6 and
8.

A field of partially-infilled blue holes seen in the southern central part of the lagoon
is underlaid by antecedent depressions. These are interpreted as solution dolines modified
by clastic-controlled growth during submergence and relief enhanced by facies-controlled
solution weathering during emergence.

The seismic data, correlated to core data, supports the antecedent model of reef
development on a subsiding base. However, unlike Purdy's (1974) antecedent karst
model, both constructional relief and differential erosion are envisaged as mechanisms for
preserving atoll morphology through late Quaternary time.

The preservation of only thin former reefs indicates that the atoll surface was
significantly lowered by subaerial erosion and solution during each glacial cycle. The data
allow an improved estimate of 0.02 mm/yr for subsidence of Cocos Atoll during the late
Quaternary.

ACKNOWLEDGMENTS

The seismic work in the Cocos (Keeling) lagoon was undertaken at the kind
invitation of Colin Woodroffe, Roger McLean and Eugene Wallensky. The survey was

7

conducted aboard John Clunies-Ross' vessel "Madaeke". Major John Mobbs (Australian
Defence Force Academy, Canberra) provided full survey control for this work. Colin
Woodroffe has provided useful comments on this paper. The research was funded by the
Australian Research Council. This paper is published with the permission of the Chief
Government Geologist, Department of Minerals and Energy, Brisbane.

REFERENCES

Backshall, D.G., Barnett, J., Davies, P.J., Duncan, D.C., Harvey, N., Hopley, D.,
Isdale, P., Jennings, J.N. and Moss, R., 1979. Drowned dolines-the blue holes
of the Pompey Reefs, Great Barrier Reef. BMR J. Aust. Geol. Geophy. 4: 99-
109.

Bloom, A.L., 1974. Geomorphology of reef complexes. In Laporth, L.F. (editor) Reefs
in Time and Space. Soc. Econ. Palaeont. Mineral. Spec. Pub. 18: 1 - 8.

Chappell, J,. 1983. A revised sea level record for the last 300 000 years from Papua New
Guinea. Search 14: 99 - 101.

Goreau, T.F., and Land, L.S. 1974. Fore-reef morphology and depositional processes,
north Jamaica. In Laporth, L.F. (editor) Reefs in Time and Space. Soc. Econ.
Palaeont. Mineral. Spec. Pub. 18: 77 - 89.

Harvey, N. and Hopley, D. 1981. The relationship between modern reef morphology and
a pre-Holocene substrate in the Great Barrier Reef Province. Proc. 4th Int. Coral
Symp. 1: 549-554.

Land, L.S., Mackenzie, F.T, and Gould, S.J. 1967. Pliestocene history of Bermuda.
Geol. Soc. Amer. Bull. 78: 993-1006.

Marshall, J.F. and Jacobsen, G. 1985. Holocene growth of a mid-Pacific atoll: Tarawa,
Kiribati. Coral Reefs. 4: 11-17.

Menard, H.W. 1986. Islands. Scientific American Library, 230pp.

Orme, G.R., Flood, P.G. and Sargent, G.E.G. 1978. Sedimentation trends in the lee of
outer (ribbon) reefs, Northern Region of the Great Barrier Reef Province. Phil.
Trans. R. Soc. Lond. A291: 85 - 99.

Purdy, E.G. 1974. Reef configurations: cause and effect. In Laporth, L.F. (editor) Reefs
in Time and Space. Soc. Econ. Palaeont. Mineral. Spec. Pub. 18:9 - 76.

Ross, J.C. 1855. Review of the theory of coral formations set forth by Ch. Darwin in his
book entitled: Researches in Geology and Natural History. Natuurkd. Tijdschr.
Ned. Indie. 8: 1-43.

Searle, D.E. 1983. Late Quaternary controls on the development of the Great Barrier
Reef: Geophysical Evidence. BMR J. Aust. Geol. Geophy. 8: 3, 267-276.

Searle, D.E., and Harvey, N. 1982. Interpretation of inter-reefal seismic data: A case
study from Michaelmas Reef, Australia. Marine Geol. 46: MR-MR16.

8

Searle, D.E., and Flood, P.G. 1988. Halimeda bioherms of the Swain Reefs - southern
GBR. Proc. 6th Int. Coral Reef Symp. 3: 139-144.

Trudgill, S.T. 1976. The subaerial and subsoil erosion of limestones on Aldabra Atoll,
Indian Ocean. Z. Geomorph., Suppl. Bd. 26: 201 - 210.

Woodroffe, C.D., McLean, R.F. Polloch, H.A. and Wallensky, E. 1990. Sea level and
coral atolls: late Holocene emergence in the Indian Ocean. Geology. 18: 62-66.

Woodroffe, C.D., Veeh, H.H., Falkland, A.C., McLean, R.F. and Wallensky, E. 1991.
Last interglacial reef and subsidence of th Cocos (Keeling) Islands, Indian
Ocean.Marine Geol. 96: 137-143.

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lagoon, based on seismic and drillhole data.

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Figure 5. Oblique aerial photograph, looking east, of southen part of Cocos lagoon
showing field of blue holes and atoll rim (between Home and South
Islands). The holes are infilled to the south, coalesce in the midfield and
pass into submerged patch reefs to the north. The seismic profile shown in
Figure 3 passed close to the foreground in this photograph. Foreground
width = 1500m.

ATOLL RESEARCH BULLETIN

NO. 402

CHAPTER 4

GEOMORPHOLOGY OF THE COCOS (KEELING) ISLANDS

BY

C.D. WOODROFFE, R.F. McLEAN AND E. WALLENSKY

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 4
GEOMORPHOLOGY OF THE COCOS
(KEELING) ISLANDS
BY
C.D. WOODROFFE *, R.F. McLEAN ** AND E. WALLENSKY ***

INTRODUCTION

Charles Darwin's subsidence theory of coral reef development has gained wide
acceptance. The initial idea had occurred to Darwin while he was in South America, and
he refined it during his voyage across the Pacific, writing an early draft of a manuscript
on Coral Islands, probably between Tahiti and New Zealand (see Stoddart 1962), much
of which subsequently appeared in his book on the structure and distribution of coral
reefs (Darwin 1842). The Cocos (Keeling) Islands, which Darwin visited in April 1836
during the voyage of H.M.S. Beagle, were the only coral atoll on which he ever landed.
He sought evidence there in support of the theory of coral reef development, and he left
convinced that he had found such support. He wrote enthusiastically to his sister
Caroline on 29 April 1836, some days after leaving Cocos, saying “I am very glad we
called there, as it has been our only opportunity of seeing one of these wonderful
productions of the Coral polypi.- The subject of Coral formation has for the last half year
been of particular interest to me. I hope to be able to put some of the facts in a more
simple and connected point of view, than that in which they have hitherto been
considered”.

Lyell (1832) had earlier proposed that atolls, with their characteristic annular reef
rims which encircle a central lagoon, consist of a thin veneer of coral growing over the
rims of submerged volcanic craters. Darwin considered it improbable that so many
volcanic rims would lie within the narrow depth range required for reef growth, ard
proposed that there “is but one alternative; namely, the prolonged subsidence of the
foundations on which atolls were primarily based, together with the upward growth of
the reef-constructing corals. On this view every difficulty vanishes; fringing reefs are
thus converted into barrier-reefs; and barrier-reefs, when encircling islands, are thus
converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the
ocean.” (Darwin 1842 p109).

Darwin used his observations during his brief visit to Cocos in support of his
theory of coral reef development, and wrote a manuscript (termed the Cocos Coral
Manuscript by Armstrong 1991) shortly after leaving the islands. Much of the debate
for the next 100 years also centred around the Cocos (Keeling) Islands. Thus, although
John Murray did not himself visit Cocos, during the voyage of H.M.S. Challenger, he
funded the visit of Henry Brougham Guppy in 1888 (though his prime interest seems to
have been to get Guppy to examine phosphate deposits on Christmas Island). Guppy

td Department of Geography, University of Wollongong, Northfields Avenue,
Wollongong, New South Wales, 2522.

i Department of Geography and Oceanography, Australian Defence Force
Academy, Canberra, Australian Capital Territory, 2601

*k* Department of Biogeography and Geomorphology, Australian National
University, P.O. Box 4, Canberra, Australian Capital Territory, 2601

was already critical of Darwin's subsidence theory of reef development, having observed
fossil coral reefs elevated above modern sea level in the Solomon Islands, and was
sympathetic to the alternative theory put forward by Murray (1889). Murray proposed
that atolls were the result of solutional processes concentrated in the lagoon. Guppy
(1889) clearly demonstrated that the Cocos lagoon was infilling with sediment, and he
described the reef islands in detail. He was on Cocos for 10 weeks and he propounded
the view that the reef rim was building out episodically , as Murray had suggested.

Wood-Jones was the doctor on the Cable Station on Direction Island, 1905-1906.
He spent a considerable period examining the atoll, and based on his observations wrote
a volume entitled Coral and Atolls, in which he put forward an alternative view, that the
present morphology of the atoll had developed in response to the pattern of sediment
production and deposition.

Thus the three views, summarised by Wood-Jones as the Subsidence, Solution,
and Sedimentation hypotheses each had a particular connection with Cocos, and had
each been tried and accepted by one of its major proponents in these islands. The only
other hypothesis deserving serious consideration according to Davis (1928), in a review
of the coral reef problem, was the glacial control hypothesis proposed by Daly (1915,
1934).

In this account we present results from a geomorphological reappraisal of the
atoll based on a number of visits, and a series of surface and shallow subsurface
observations. Our concern is primarily with the development of the surface morphology
of the atoll rather than the atoll's structure, a distinction which needs to be made
(Stoddart 1973), but which is not always clear in the preceding references. All of the
surface features have formed in the mid-late Holocene, over a pre-Holocene surface;
there are no surface outcrops of late Pleistocene or older materials anywhere on the atoll.
Nevertheless, our interpretations of the surface morphology and Holocene evolution
have implications for the structure and longer-term development of the atoll.

REGIONAL SETTING

The Cocos (Keeling) Islands comprise the main atoll of the South Keeling
Islands (lat. 12°12'S, long. 96°54'E) and an isolated atollon, North Keeling (lat 11°50'S,
long. 96°49'E), 27 km to the north. These are connected by a submerged ridge at a
maximum depth of 1000 m. They comprise a single feature rising from an ocean floor
depth of about 5000 m (Fig. 1). The age of the ocean floor at this location is not clear,
but lies in the range 60-90 million years (Jongsma 1976). In this region the seafloor gets
younger to the north, and appears to have been formed from a spreading centre that has
been subducted into the Java Trench.

The Cocos (Keeling) Islands lie on the Cocos Rise. To the south, the Umitaka
Mary seamount reaches to within 16m of the sea surface. This chain of seamounts, the
Vening Meinesz seamounts, can be traced northeastwards towards Christmas Island.
They are not, however as regular as linear chains of islands and seamounts seen in the
Pacific, and it is uncertain whether they have developed from a single hotspot in the
same manner as may Pacific seamounts (Scott and Rotondo 1983).

That Cocos represents a carbonate reefal capping on a volcanic seamount seems
extremely likely although the depth to oceanic basalt is unknown. Magnetic surveys
show an anomaly, reading 250nT in vertical intensity (Chamberlain 1960, Finlayson

1970). There is also a pronounced gravity anomaly over the island. In addition a basalt
and tuff pebble has been dredged from the western end of the Cocos Rise (Bezrukov
1973), further supporting the idea that carbonate overlies a volcanic basement.

The southern atoll consists of a reef rim that surrounds the atoll with two major
passages, one to the northwest and one to the northeast. A series of reef islands
(described in detail by Woodroffe and McLean, this volume) occur on the horseshoe-
shaped reef rim which is continuous from Direction Island to the northern end of West
Island. Horsburgh Island is isolated at the north of the lagoon (see Fig. 2). Marine
habitats of the atoll are described in detail by Williams (this volume); the reef front,
which is relatively barren of living hard corals rises to the reef crest which is algal-
veneered with surge channels at intervals of 50-250 m. The reef flat is covered by 1-2 m
of water at high tide and part of it dries at low tide. The northern part of the lagoon
averages around 15 m deep and is covered with dead coral or sand (see Smithers, this
volume). The southern part of the lagoon is shallow, but contains a network of ‘blue
holes' (see Chapter 3, Fig. 5). Individual holes are 12-20 m deep, but their rims are
emergent at low spring tides. Extensive sand flats and sand aprons occur around the
margin of the lagoon (see Smithers, and Williams, this volume).

METHODS

Surface sediment characteristics were examined in exposures of lithified
sediments, and along surveyed transects. Subsurface investigations were carried out by
drilling and by seismic survey. The results of seismic reflection surveys within the
Cocos lagoon are described by Searle (this volume). Seismic refraction on the islands
was undertaken using a 12-channel Geometrics seismograph.

Drilling was undertaken during several visits. In addition to drilling, aimed
specifically at unravelling the geomorphological history of the islands, drillcore logs and
in some cases cores drilled as part of a water resources survey (see Falkland, this
volume) were also examined. An initial reconnaissance visit was made by Woodroffe in
1986. In 1988 Woodroffe, McLean and Wallensky undertook drilling with a portable,
trailer mounted Jacro 105 rotary drill, to depths of up to 9 m on Home Island, West
Island and Pulu Wak Banka. In 1990 deeper drilling was undertaken using a Jacro 500,
operated by P. Murphy; holes were sunk on Horsburgh, South, West and Pulu Blan
Madar Islands. In 1991 seismic reflection surveys were undertaken in the lagoon, and
exploratory drillholes were put down to 2.3 m using a hand-held Mindrill on the reef flat
to the east and south of West Island. Several vibrocores were taken from the southern
and eastern part of the lagoon (Smithers et al., in press), using 75 mm diameter
aluminium pipe, vibrated into the lagoon floor with a concrete vibrator. Three long
cores of up to 4.2 m length were recovered, together with several shorter ones. Sediment
compaction was around 30% in most vibrocores.

Recovery in drillholes varied, but was rarely greater than 70%. Samples of coral
and Tridacna recovered in the cores were submitted for radiocarbon dating. Samples of
coral from the conglomerate platform, or from pits within islands were also submitted
for dating. Radiocarbon dating was undertaken principally at the ANU Radiocarbon
Dating Laboratory.

Marine carbonate samples usually require an environmental correction for ocean
reservoir effect because organisms at their time of death are already somewhat depleted
in radiocarbon, as the oceanic reservoir. has a substantial circulation time. Marine

carbonates therefore have an apparent age at the time of their death. For marine shells
from the Australian coast this environmental correction varies, but is generally minus
450 + 35 years from the conventional radiocarbon age (Gillespie and Polach 1979). On
coral atolls there has been some questioning of the estimate of the correction factor, and
indeed whether any correction needs to be made. In particular, Pirazzoli has argued that
no correction should be necessary for dating of coral samples from within the lagoons of
Tuamotu atolls, where there may be limited exchange of waters with open ocean
(Pirazzoli et al. 1987). We have examined this in Cocos, taking advantage of earlier
coral collections, and by dating samples of corals collected by Wood-Jones in 1906 and
Gibson-Hill in 1941 (pre-1950 samples of known age are necessary for such dating as
post-1950 samples have elevated radiocarbon levels as a result of radiocarbon released
by bomb tests). Results are shown in Table 1, indicating the average correction to be
460 years. The correction is indeed around 450 years, and that is the value that we
have used throughout this paper to conform with similar studies elsewhere.

PLEISTOCENE LIMESTONE

Boreholes undertaken as a part of a Water Resources survey of the Cocos
(Keeling) Islands (see Falkland, this volume), together with our own drillholes, indicate
that a well-lithified, but porous, limestone underlies the poorly consolidated coral
shingle and sand deposits of the Cocos reef islands, at depths of around 11-14 m (see
Chapter 2, Table 10 and Chapter 3, Fig. 1). This older limestone contains corals, with
some travertine deposits in voids, and in at least one drillcore, cemented oolites.
Uranium-series disequilibrium dating of a sample of coral at the top of this facies, from
12.6 m depth (10.5 m below MSL) in drillhole WI1 gave an age of 118,000 + 7000 years
B.P. on a bulk sample, but after preparation removing calcite under binocular
microscope, the age determined was 123,000 + 7000 years B.P. (Woodroffe et al. 1991).
The age of this limestone suggests it formed during the last interglacial, when the sea
was around or slightly higher than present, about 125,000 years ago.

The morphology of the Pleistocene atoll has been revealed in greater detail by
seismic reflection profiling across the lagoon, results of which are discussed by Searle
(this volume). Woodroffe et al. (1991) argued that the atoll had subsided at a rate of
about 0.1 mm/yr based upon subsidence of this surface from above present sea level to
8-11 m below present sea level. The seismic results indicate that the surface actually has
a considerable slope on it, becoming much deeper with distance into the lagoon, towards
the centre of which it is more than 24 m below present sea level. This morphology
seems likely to result from solution during subaerial exposure of the atoll when the sea
was low, and Searle (this volume) suggests that the subsidence rate may be only 0.02
mm/yr.

CONGLOMERATE PLATFORM

An important feature of reef islands on Cocos is a platform of coral conglomerate
which underlies most of the islands on the atoll rim. The platform was termed
‘brecciated coral-rock’ by Darwin (1842), 'reef conglomerate’ by Guppy (1889), and
‘breccia platform’ by Wood-Jones (1912).

This near-horizontal conglomerate platform comprises cemented clasts of coral
shingle or rubble, found especially along the oceanward shore of many of the islands,
but also underlying part of the islands as shown in pits and wells. It occurs up to 0.5 m

above MSL, and is thus inundated by the highest tides. Individual coral boulders of
Porites of up to 2 m in diameter occasionally protrude from the platform, the highest
points of which may reach up to 1 m above MSL.

In some places, notably on North Keeling and Horsburgh, and at the
southwestern end of West Island, the surface of the conglomerate platform is composed
of arcuate, seaward-dipping beds of cemented coral cobbles. These appear to have been
interpreted as former reef crests by Guppy (1889), but there is nothing in their
composition to substantiate this. Instead, they resemble the foot of the modern beach
where there is a rubble component, and we interpret them as beach conglomerate,
marking the former position of rubble-strewn beaches.

Guppy (1889) indicated that compositionally the conglomerate platform
resembles the modern reef flat. The reef flat is characteristically 1.0-1.5 m lower than
the surface of the platform, which is undergoing erosion on its seaward side. The reef
flat often forms a hard, relatively smooth surface with encrustation by calcareous algae.
This veneer may cover formerly truncated conglomerate platform. On the basis of
constituent materials, gross fabric and surface morphology, we have interpreted the
conglomerate platform as a fossil emergent reef flat (Woodroffe et al. 1990a, 1990b).
Radiocarbon dates on corals from within the conglomerate platform indicate a spread of
ages from 4010 + 85 to 3050 + 85 years B.P. (Table 2, Fig. 2).

There are a number of sites at which apparently in situ fossil Porites microatolls,
both massive and branching, have been found within the conglomerate, and which
further serve to indicate that sea level was higher than the modern sea level when the
conglomerate was formed. These provide a discontinuous record of the pattern of sea-
level change over the late Holocene, and are discussed in greater detail below.

Shallow drilling on Home Island and Pulu Wak Banka on the eastern rim of the
atoll indicates that the platform is generally better cemented, and consists of coarser
clasts nearer to the ocean. Shingle sticks of Acropora, often cemented by calcareous
algae, form a major component of oceanward drillholes. Similar drilling on the modern
reef flat has revealed that that it is also underlain by Acropora sticks cemented by
calcareous algae. On lagoonward exposures of the platform drilling often encountered
sand at 1-2 m depth.

HOLOCENE REEF GROWTH

The stratigraphy and chronology of the Holocene reef rim was examined along a
series of transects around the atoll (Fig. 2), with drillholes through islands and the
conglomerate platform which surrounds and underlies them, and through the reef flat.

Figure 3 shows a cross-section (transect I) of the southern part of Home Island
where observations were obtained from a trench and associated drillhole in the trench
floor (CK7). The conglomerate platform was encountered in the floor of the trench at the
same elevation that it outcrops on the oceanward side of the island. A radiocarbon date
of 5760 + 95 years B.P. at 310 cm (-2.4 m below MSL) was obtained from the drillhole
CK7. The island sediments, which are discussed in more detail in the next chapter,
range in age from 1840 + 125 years B.P. to 1440 + 80 years B.P.

The age of the conglomerate platform on Home Island is indicated by a
radiocarbon date of 3680 + 105 years B.P. on a coral cemented into the top of the

platform at the site of CK1, a drillhole in a sequence (transect II) on the platform at the
southern end of this island. The cross-section at this point includes drillhole CK3 which
is on the oceanward edge of this platform and is more then 6 m deep. This core contains
coral shingle, generally well-cemented with calcareous algae, and at its base is dated
6160 + 95 years B.P. (see Table 3). The ages above are reversed, but their errors render
them statistically indistinguishable. There is apparently a decrease in age as the lagoon
is approached with a radiocarbon date of 3490 + 85 years B.P. at 2.4 m below MSL in
the lagoonward core CK2. The platform is less well cemented in this core, and drilling
was aborted in sand.

A similar sequence of drillholes was drilled through the conglomerate platform
on transect III at the southern end of Pulu Wak Banka. The channel south of this island
contains numerous living microatolls. A fossil microatoll was identified within the
conglomerate, and this has been radiocarbon dated at 1960 + 80 years B.P. (Fig. 5),
indicating that some material has been added to the conglomerate platform on the
margin of the channel in the last 2000 years. A coral within the conglomerate has been
dated at 3220 + 85 years B.P. just near the transect (Fig. 2). The conglomerate platform
becomes thinner closer to the lagoon, and drilling in CK6 was aborted in sand. A core
into the sand spit extending from the southern end of Pulu Wak Banka into the lagoon,
contains coral shingle at about 1 m depth, which has been dated 3170 + 85 years. It can
also be inferred from this date that the lagoon has partially filled since the time of
conglomerate platform formation.

Figure 6 indicates the stratigraphy beneath South Island on transect IV, and
Figure 7 indicates the stratigraphy beneath Pulu Blan Madar. Both are similar,
intercepting the Pleistocene limestone at 13.8 m depth (11.6 m below MSL) and 12.6 m
depth (11.2 m below MSL) respectively. The cores recovered shingle or shingle and
sand. Coral fragments at 10 m in CK15 dated 6790 + 80 years B.P. and Tridacna at 6 m
in CK14 dated at 6040 + 80 years B.P.

Figure 8 shows shallow cores into the reef flat on transect VI, south of Pulu
Maria. The reef flat appears about 1000 years older close to the oceanward edge, than
beneath the island 750 m lagoonward. Radiocarbon dates of 5800 +70 years B.P. at 2.15
m depth, and 5630 + 205 years B.P. at 0.6 m depth in CK21 (not statistically
significantly different), compare with a date of 4740 + 85 years B.P. at 2.1 m depth in
CK23 (Fig. 8). The conglomerate platform on Pulu Maria contains only relatively fine
clasts, and recovery in CK23 was poor, but generally also indicated weakly cemented
sand.

Figure 9 shows transect VI across the spits at the eastern end of West Island.
Radiocarbon dates on coral shingle, recovered from a series of pits into the sandy spits,
demonstrate progressive development of the spits from around 1400 years ago to present
(Table 6), with the last spit giving a modern age. CV1 is a vibrocore sunk into the
muddy sediments flanking the recent spit and penetrating sand and shingle, and from
that vibrocore a date at around 0.9 m (about halfway down the core, allowing for
compaction of the core) is 3240 + 85 years B.P.. This date appears to reflect lagoonal
infilling, which must have occurred before the spits began to form. Though hard pan
was encountered beneath some spits, this area is not underlain by typical conglomerate
platform.

Figure 10 at the southern end of West Island is a combination of several different
drillholes undertaken at different times, and amalgamated schematically into a single
transect (Transect VIII). Pleistocene limestone was encountered at 6.5 m below MSL. in

CK13, but was not encountered in CK9 which went slightly deeper. CK13, drilled next
to a telok (lagoonlet), but through a shingle substrate, encountered mud at 2-4 m depth,
similar to that being deposited in the telok, implying that the island sand and shingle
have been deposited over the surface of a formerly larger telok (Fig. 10). The sequence
of 4 radiocarbon dates from drillholes CK13, CK9 and CK10A show the opposite trend
to that generally observed on other transects, in that the older dates (6140 + 85 years
B.P. at 4.4 m in core CK13) are to lagoonward, with younger dates beneath the reef flat
(4770 + 85 years B.P. at 1.5 m in CK10A).

Figure 11 shows transect IX which is at the southern boundary of the Quarantine
Station on West Island and crosses the island where it is both especially low and
particularly narrow. The most interesting feature of this transect is that there are a
number of microatolls, up to 2 m in diameter, which are found along the shore, above
the modern limit to coral growth. This together with elevated beachrock at this site
provides convincing evidence that the sea has been relatively higher than it is at present.
Radiocarbon ages of 2690 + 85 and 2730 + 85 years B.P. have been determined on two
massive Porites microatolls at this site, where they are about 50-60 cm above their
modern, living equivalents. In addition a sample of Porites, almost certainly a
microatoll, was recovered from drillhole CK8 and dated 3190 + 85 years B.P. at a very
similar elevation, indicating that similar, though in this case slightly older microatolls
continue beneath the island sediments. The significance of these emergent, in situ corals
will be examined below.

Figure 12 shows the stratigraphy of two deep holes drilled on transect X on
Horsburgh Island. The Pleistocene substrate was only encountered in the more
oceanward drillhole, where it was found at a depth of 13.1 m (10.6 m below MSL). A
coral sample from a massive coral colony recovered from almost directly above the
Pleistocene/Holocene contact was radiocarbon dated 5540 + 80 years B.P., while a coral
from 4.8 m has been dated 5260 + 80 years B.P.. These samples are more than 8 m apart
and imply a rapid rate of reef accretion in the order of 25-30 mm/yr. CK11 at the
lagoonward end of Horsburgh Island was presumably not drilled deep enough to
encounter the Pleistocene surface, as subsequent seismic profiling in that part of the
lagoon has indicated a reflector, believed to represent the last interglacial surface at
depths of more than 20 m. Nevertheless the date of 4610 + 85 years B.P. on a sample of
Tridacna at the base of that core, indicates that sedimentation here lagged about 1000
years behind that on the more oceanward side of Horsburgh.

MICROATOLLS AND HOLOCENE SEA LEVEL

The radiocarbon dates from Tables 3, comprising dated samples from transects I-
X, have been plotted on an age-depth plot in Figure 13. These ages do not permit the
accurate reconstruction of early to mid-Holocene sea-level history on Cocos, because it
cannot be established that the corals in the cores are in their position of growth, and even
if they were in situ they could have grown in water depths of up to several metres.
Samples from the conglomerate platform (Table 2) on the other hand are manifestly not
in growth position, and do not indicate the level of the sea at time of deposition. Some
corals, however, do record former sea level. Microatolls are flat-topped colonies of
coral which have been constrained in their upward growth by subaerial exposure at low
spring tides, and have therefore continued to grow only laterally (Scoffin and Stoddart
1978). Their upper surface is related to sea level and the upper surface of fossil
microatolls can be used to reconstruct late Holocene sea-level change (Chappell 1982).
On the Cocos (Keeling) Islands there are modern, living microatolls, of massive and

branching Porites, on the reef flat, in interisland passages, and within the lagoon
(Woodroffe and McLean 1990). These corals were described by Wood-Jones (1912),
though he attributed their form to sedimentation on their upper surface. Detailed survey
of modern microatolls around the atoll indicates that they occur in a relatively narrow
elevational range (around 0.3 m below MSL), and supports the idea that they are limited
by water level (Smithers, unpublished results).

Fossil microatolls, though by no means common, have been identified within the
conglomerate platform at several sites on West Island, and on Pulu Pandan and South
Island. At the southern end of West Island fossil microatolls of both massive and
branching species of Porites are found together. Fossil microatolls can also be identified
on the reef flat, and at one location in a telok on South Island, where the oldest
microatolls so far dated on Cocos have been found (3560 + 85 years B.P., see Fig. 2).
The exact elevation of these remains uncertain, but they appear to be lower than younger
specimens on West Island (Table 4). In addition, Porites cored in CK8 (CK8.1B/2)
almost certainly represents a microatoll dated 3190 + 85 years B.P. and at a similar
elevation to those on the present shoreline (see transect IX, Fig. 11), and so too does that
in CK5 (CK5.1B), dated 1960 + 80 years B.P. and found at around MSL (see transect
Ill, Fig. 5).

The upper surface of these microatolls gives an indication of the elevation of sea
level. When compared with the modern elevation of microatolls (around -0.3 m MSL),
these corals indicate a trend of gradually falling sea level (Fig. 13), from about 0.9 m
above present around 3000 years ago, on the basis of branching microatolls on Pulu
Pandan and slightly less if massive microatolls on West Island are considered. A
discontinuous record of relative sea-level fall is preserved at the foot of the beach near
the Quarantine station on West Island, where a series of microatolls is located (see plot
in Fig. 13).

LAGOONAL INFILL

The nature of lagoonal sediments in the South Keeling Islands has been
examined by Smithers (this volume), who demonstrates that sediments in the lagoon
range from strongly fine skewed gravelly muds (as in the teloks and blue holes) to
gravelly sands where sand aprons have encroached upon lagoonal corals.
Compositionally they are entirely biogenic, dominated by three factors, coral sediments,
molluscan sediments and sediments in which calcareous algal fragments and Halimeda
plates are an important constituent (Smithers et al., in press).

The lagoon is particularly shallow around much of the southeastern corner, and
the surface, which is covered by seagrass, dries out at low tide (Williams, this volume).
There is anecdotal evidence that it has filled in rapidly in historical times. Captain John
Clunies Ross established his settlement on the middle portion of South Island, where
access is now extremely difficult for a boat of any draft at almost any stage of the tide.
Rapid infill has been inferred by Forbes (1879, p779). Guppy detected sediment in
suspension being carried into the lagoon through the passages, by the predominantly
unidirectional currents. He made a series of calculations of sediment transport and
sedimentation into the lagoon (Guppy 1889). His estimates were based upon rates of
coral growth and sediment production, distributed across the area of the reefs and lagoon
that contained coral cover. He calculated that 5000 tons of sediment was carried into the
lagoon each year. The majority (5/6) he considered to be deposited in the first 700 m of
the lagoon, on the sand aprons. He estimated that these aprons were prograding at a rate

of around 1 m/yr (1 yard per year). Vertical sedimentation averaged over the southern
part of the lagoon, Guppy estimated to be 1ft/100 years (c. 3mm/yr). Extending these
calculations to the northern lagoon, Guppy considered that the lagoon would require a
further 4000 years to infill, and that the total time from initiation to complete infill for a
lagoon would be about 15-20,000 years.

Wood-Jones, not only realised the importance of this sediment accumulation in
the lagoon, but he interpreted sedimentation as the prime control on the formation of the
atoll. He compared the atoll as a whole with single colonies of Porites microatolls (he
termed them an ‘atoll reef in miniature’, Wood-Jones 1912, p108-109), which he
interpreted to be limited in their upward growth by sediment accumulation on their
upper surface. Wood-Jones proposed his sedimentation theory of atoll development in
Opposition to Darwin's subsidence theory, and the solution theory of Murray.

We have examined lagoonal sedimentation in Cocos, based on a series of
vibrocores taken in the southern and eastern lagoon. The stratigraphy, sediment grain-
size and components, and radiocarbon dating from vibrocores indicate spatial and
temporal variations in the nature and rate of sedimentation, controlled primarily by the
pattern of sea-level change and the response of the atoll environments, particularly the
formation of reef islands on the atoll rim (Smithers et al., in press).

The main contrast is between sand apron sediments, on the one hand, which are
composed of skeletal grains typical of a reef flat assemblage, being coarse, clean sands
and shingle, with fragments of the algal rhodoliths, Spongites sp., and island lee
sediments, on the other hand, which are higher in mud content, with occasional coral
fragments. The base of vibrocores contains more shingle, and coral, algae and Halimeda
are generally more common, perhaps reflecting lagoon reefs which have been covered
by sand apron and island lee sediments. Sand aprons have encroached episodically into
the lagoon and sand appears to have spilled into blue holes as the sedimentation front
advanced. It seems highly probable that the sands of the southeastern section of the
lagoon have already filled over a patchwork of blue holes, and this may explain the
patchy penetration of vibrocores; the shorter ones reaching shingle at much shallower
depths than those which penetrated into former sand-filled blue holes.

The sands radiocarbon dated in vibrocores were all younger than 4000 years B.P.
(Table 5); the base of CV11 dated 3850 + 80, while CV1 and CV12 had dates of 3240 +
85 and 3530 + 80 years B.P. respectively. These older dates are in those cores closest to
islands, and consequently also close to the reef. Cores further into the lagoon had
younger dates: CV15 dated 420 + 65, and CV10 910 + 80 at its base 2.2 m below the
sediment surface, and 130 + 110 years B.P. in the centre, recording the present
progradation of the sand sheets into the area of blue holes.

Radiocarbon dates record the time of death of the coral shingle, and not the time
of its deposition. Sediments flooring the lagoon are also likely to be subject to
considerable bioturbation. Nevertheless, despite minor age reversals in vibrocores such
as in CV2, the dates are generally stratigraphically consistent and indicate the general
trend of sedimentation. Vertical accumulation rates are higher in sand aprons than in
island lee sediments, being 0.5-1.0 mm/yr in the former, and in the latter, over the last
2000 years, ranging from 0.25-0.5 mm/yr (Smithers et al., in press).

10

HOLOCENE EVOLUTION OF THE ATOLL

The Holocene atoll has developed over a Pleistocene limestone surface, which
has been shown by seismic reflection profiling to be basin shaped probably as a result of
solutional weathering during the glacial sea-level low (Searle, this volume). This
surface has been flooded by the sea during the postglacial marine transgression. Seismic
and drilling results indicate that there is a relatively continuous Pleistocene rim at about
9-10 m below MSL, around the western, southern and eastern sides of the atoll, with a
deeper basin to the north, which opened out to the northeast, and perhaps also northwest.
When the sea was 12-15 m below present, the Pleistocene rim was still emergent, and
lagoonal exchange must have been predominantly through the northern passages. Since
that surface has been inundated, as a result of the final stage of the postglacial marine
transgression, there has been a phase of rapid vertical reef growth, following the rising
sea level, recorded by radiocarbon dates from cores, and shown in Figure 13.

During periods of rising sea level reef growth has adopted one of three
strategies, keep-up (where the reef closely tracks the rising sea), catch-up (where reef
growth lags behind sea level) and give-up in which there is negligible net reef growth
(Neumann and Macintyre 1985). As described above, the coral dates do not indicate the
position of the sea, except for during the last 3000 years where there are dated
microatolls which have been constrained by water level. Regional sea-level curves
indicate a sea-level history in which sea level rose rapidly up until around 6000 years
ago when it reached a level close to its present level and has changed by only a metre or
so since (Thom and Chappell 1975, McLean et al. 1978, Geyh et al. 1979, Thom and
Roy 1985). Vertical reef accretion on Cocos appears to have lagged behind sea level, as
also shown on atolls in the Pacific (Marshall and Jacobsen 1985). The three modes of
response can be found at different points around an atoll. Reef growth on Cocos has
varied from place to place; nowhere does it seem to have kept up with sea level (there
are no 6000 year dates at present sea level), but it has lagged behind sea level by
different amounts at differing points on the atoll rim.

We identify this period of catch-up reef growth as the first of three phases in the
Holocene development of the atoll. The second phase was a period of reef flat
consolidation, represented by the conglomerate platform. On the basis of fabric and
morphology we attribute the conglomerate platform to formation as a reef flat under
conditions of sea level slightly higher than present. That the sea was higher than present
is shown most convincingly by the presence of microatolls above the modern limit to
coral growth (Table 4). Other data, such as the elevated beachrock (in Fig. 11), and the
consistent difference between the conglomerate platform and the modern reef flat, also
substantiate that the sea was relatively higher in the mid-Holocene.

Elsewhere similar conglomerate platform has been interpreted as lithified storm-
rubble ridges or ramparts similar to those deposited as a result of Tropical Cyclone Bebe
on Funafuti in Tuvalu in the Pacific, in front of the elongate reef islands, and
subsequently observed to migrate landwards and redistribute over the shoreface (Baines
and McLean 1976). We discount this interpretation of the conglomerate platforms on
Cocos because of the horizontal nature and width of the platform, and the relatively
narrow range of radiocarbon ages from coral clasts. Storm rubble is evidently a
component of the platform, with addition of material under non-storm conditions, bound
by biological and chemical processes, in a similar way that material is supplied to and
incorporated into the interisland reef flat areas on the modern atoll. Reef blocks, as seen
in the Pacific storm belt, are relatively rare, though there are blocks of more than 1 m

11

diameter on the reef flat at the southern end of the atoll, one of which has been dated to
610 +75 years B.P. (Table 6).

The third phase is a phase of reef island development. The modern reef islands
lie primarily on an oceanward outcrop of conglomerate platform, and the appearance of
islands in their modern location and form must therefore postdate the formation of the
platform. Islands have formed during the last 3000 years when the sea level has been
undergoing a relative fall. The age structure of reef islands is still poorly known; some
dates are given in Table 6, indicating substantial deposition in the period 1800-1000
years B.P. The issue is examined in greater detail in the next chapter (Woodroffe and
McLean, this volume). Progradation of the southern end of West Island in the last 1400
years is apparent from Figure 9.

The three phases that are identified (Fig. 13), have not necessarily been discrete,
but some overlap between them is likely. Reefs at the southern end of the atoll appear to
have grown fastest, and although they did not keep up with sea level, they lagged only
slightly (<1000 years) behind sea level, whereas reefs at Horsburgh appear to have
undergone a greater lag before commencing to grow, but to have accreted vertically at a
faster rate. Similarly the early stages of island formation appear to have occurred within
the final stages of conglomerate platform development, as indicated by beachrock and
beach conglomerate outcrops within the platform (i.e. Horsburgh, West Island, and
North Keeling). Progression from one phase to another must have been accompanied by
substantial changes of energy regime, particularly in the lagoon, which must have been a
relatively high energy environment before the reef rim caught up with sea level, and
subsequently underwent a further reduction in energy as reef islands were formed around
the margin.

DISCUSSION

This three phase model of the Holocene evolution of the atoll incorporates
components of each of the earlier theories on the development of atolls. We now
examine some of these issues.

The first issue at Cocos is whether the atoll has subsided, and whether it is
continuing to subside. As discussed above, the depth of the last interglacial surface is
taken by us as an indication of subsidence. The exact elevation of the sea at the peak of
the last interglacial is contentious; in some parts of the world it is considered to have
been around 5-6 m above present, elsewhere up to 10 m above present. Lambeck and
Nakada (1992) indicate that flexural responses of the earth's crust and upper mantle need
to be taken into account, and that it need not have been any higher than present. There
are many parts of the world where the last interglacial reef is found above present sea
level, the nearest being Christmas Island, where coral-bearing reef reaches 12 m above
present sea level, but with associated deposits reaching 30m (Woodroffe 1988). We
believe that the last interglacial reef on Cocos would have caught up with sea level
during the oxygen-isotope Se sea-level high stand, and we attribute the fact that it is
everywhere below present sea level to subsidence. Seismic results indicate that solution
is likely to have occurred and deepened the lagoon, but we attribute the fact that
contemporaneous limestones are around 12 m above sea level on Christmas Island and
12 m below sea level on Cocos to uplift of the former and subsidence of the latter.
Indeed if the atoll were not subsiding, there would be no reason why interglacial
limestones should occur in layer-cake fashion beneath the Holocene, as appears to be
indicated by seismic profiling (Searle, this. volume).

12

Darwin himself realised that confirmation of his subsidence theory would come
from deep drilling of coral atolls. He postulated that such drilling should reveal
extensive thicknesses of shallow water limestones, in excess of the present depth range
over which corals can grow. The final proof came after World War II with drilling of
Enewetak, Mururoa and Midway atolls in the Pacific, in which basalts were encountered
beneath the coral limestones at depths down to 1200 m (Ladd et al. 1953, Emery et al.
1954, Lalou et al. 1966). Deep-drilling has not been undertaken on Cocos, and so the
ies of the volcanic basement, probably around 400-500 m (Jongsma 1976), is still
unknown.

Confirmation of the volcanic basement of open-ocean atolls, and more recently
demonstration of the way in which plate tectonics can provide a mechanism (horizontal
plate motion), by which subsidence can occur (Scott and Redondo 1983, Grigg and Epp
1989), give strong support to Darwin's theory of atoll origins. Relative and absolute
dating of the basement volcanic rocks, and palaeontologic and diagenetic changes within
the limestone, indicate that subsidence rates are “imperceptibly slow except in
geological perspective” (Stoddart 1973).

While we believe that gradual subsidence is continuing at Cocos, we are unable
to accept the local evidence that Darwin invoked to prove his theory. Darwin was
shown erosion of the shoreline on West Island, with undercutting of coconuts, which he
believed was “tolerably conclusive evidence” of subsidence. His interpretation of this
geomorphological evidence has been disputed by several other scientists who have
visited the atoll. Most vehement of those disagreeing with Darwin was John Clunies
Ross, who was resident on Cocos but, much to his subsequent regret, had been absent on
the occasion of Darwin's visit. Evidently concerned at Darwin's suggestion that the
islands of which he was in possession were about to disappear beneath the sea, he
claimed that a “moderable attentive investigation of the Cocos islets affords ample
reasons for believing that they have stood up to the present time above the level of the
ocean during hundreds if not thousands of years” (Ross 1855).

Guppy described each of the reef islands but decided that there was evidence for
neither recent uplift nor recent subsidence of the atoll (Guppy 1889). On the other hand
Forbes, and later Wood-Jones, believed that there was evidence that the sea had been
higher with respect to the atoll. Wood-Jones wrote “the undermining of trees and the
denudation of shore-lines do not necessarily indicate subsidence, for they are inconstant
effects, and an area of land denudation is compensated for by an area of land
construction at another part of the island ring” (Wood-Jones 1909 p674). Forbes had
similarly argued that the erosion of islands was compensated by the debris being
deposited further around the shore, and interpreted elevated fossil shells of clams and
oysters on Workhouse Island (south of Direction Island, no longer existing as a distinct
island), as an indication of former higher sea levels (Forbes 1879, 1885). The views of
Forbes and Wood-Jones for a sea level higher than present revolved around their
interpretations of the coral conglomerate that underlies much of the reef islands.

Our data confirm the interpretation of recent emergence (that is a slight fall of sea
level relative to the atoll) since the mid-Holocene (Woodroffe et al. 1990a, 1990b).
However, although the geomorphological data on the surface morphology of the atoll
were misinterpreted by Darwin, the overall atoll structure we do attribute to gradual
subsidence as Darwin postulated.

13

Radiocarbon dates from western, eastern and southern reef flat or oceanward
conglomerate platform, imply that the reef near the reef crest lagged only about 1000
years behind sea level. The reef caught up first near the reef margin, and there was more
gradual infill to lagoonward; thus on each of these sides we see radiocarbon ages getting
younger with distance into the atoll lagoon.

This is contrary to most of the views of other geologists on the atoll. Thus
Guppy, following the suggestion of Murray that reefs prograded out over their own
talus, considered that there was proof that the reef flat had built out in a series of steps.
His view appears to have been based upon description of the reef buttresses off the atoll
given him by George Clunies-Ross, and his interpretation of the fossil reef rims as he
viewed imbricated, arcuate ridges on North Keeling and Horsburgh Islands. The latter
he called parallel lines of old reef margins that protrude above the reef flat, but we have
interpreted these as beach deposits, marking instead the former foot of rubble-strewn
beaches. Wood-Jones similarly supposed that the breccia (conglomerate platform) was
oldest towards the lagoon and youngest toward the ocean (Wood-Jones 1909); whereas
our results indicate the reverse trend.

In Figure 14 we summarise the late Quaternary development of the Cocos
(Keeling) Islands. Wood-Jones recognised three theories, Subsidence, Solution and
Sedimentation (ie. the theories of Darwin, Murray and himself respectively), to which
we may add Sea-level (the glacial control theory of Daly).

The surface of the last interglacial at depths of 10-20 m below sea level indicates
that the island was not planated as Daly has suggested at the time of sea level low,
although our interpretation does emphasise sea-level fluctuations which have been the
principal control over the late Quaternary of periods of reef establishment and their
demise. We also interpret that it indicates that the atoll is continuing to subside as
Darwin envisaged, although at a rate that is imperceptibly slow, even compared with
rates of sea-level fluctuation. The form of the lagoon does not result from solution as
Murray envisaged, but nevertheless solution does appear to have been important at times
of low sea level in accentuating, through karst erosion, the basin-shape of the lagoon as
inferred by Purdy (1974) in his antecedent karst hypothesis. Holocene reef morphology
mimics this antecedent surface as suggested by Purdy. Finally, the lagoon has been one
of the major areas of sediment accumulation, along with reef islands, over the last 3000
years, as envisaged by Wood-Jones, but we interpret this not as the cause of atoll
morphology, but more as a response to the evolving morphology.

ACKNOWLEDGMENTS

This research has been funded by the Australian Research Council, National
Geographic Society, and the Department of Arts, Sports, Environment and Territories.
We are grateful to the Cocos (Keeling) Islands Administration, Cocos Island Council,
the Cocos Co-operative, and Australian Construction Services for assistance on the
island. We thank Peter Murphy, Scott Smithers and Paul Kench for their help in the
field.

14

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17

Table 1. Radiocarbon dating results on museum specimens of coral, Cocos (Keeling)
Islands.

ANU Lab Coral species Date of Conventional Age Reservoir
No. collection radiocarbon age _(pre-1950) correction
6151 Acropora scherzeriana 1906 [W-J] 370 + 60 40 330 + 60
6152 Montipora foliosa 1906 [W-J] 670 + 60 40 630 + 60
6153 Porites nigrescens 1906 [W-J] 410+ 60 40 370 + 60

(=P. cylindrica)
7638 § Montipora ramosa 1941 [G-H] 510+ 70 10 500 + 70

7639 __ Montipora lobulata 1941 [G-H] 480 + 60 10 470 + 60
Note: W-J = Wood-Jones, G-H = Gibson-Hill.

18

Table 2.

ANU
Lab No.
5411
5412
5414
5416
5417

5418

5419

5420

5421
6220
6221
6222

6224

7134

Pocillopora_merate transect VIII

Radiocarbon dating results on conglomerate platform Cocos (Keeling)
Islands.

No.
C4
C5
C16
C26
C43

C48

C59

C64

C65
CK1/5
C172
C158

C154

C202

Sample Material

Coral

Coral
Coral,
Porites
Coral

Coral

Coral,
Porites

Coral

Coral

Coral
Coral
Coral
Coral,

Porites
Coral

Coral,

Location

from conglom-
erate in base of
well

from conglom-
erate platform
beneath beach
conglomerate
from conglom-
erate platform
from conglom-
erate platform
cemented to
conglomerate
platform

lower unit of
conglomerate
platform

upper unit of
conglomerate
platform

from conglom-
erate platform
from conglom-
erate platform
from conglom-
erate platform
from conglom-
erate platform
from conglom-
erate on tran-
sect IX

In upper conglo-

Island

West Is.

West Is.
North
Keeling
Direction
Is.

Pulu Wak
Banka
North
Keeling

Pulu Labu

Pulu Labu

Home Is.
Home Is.
South Is.
West Is.

West Is.

West Is.

Conventional
radiocarbon age

1770 + 70

3890 + 80
3480 + 80
3740 + 80
3670 + 80

4290 + 80

3950 + 80

3940 + 80

4000 + 80
4130 + 100
3500 + 80
4460 + 80

3550 + 80

3690 + 80

Environmentally
corrected age

1320 + 80

3440 + 85
3030 + 85
3290 + 85
3220 + 85

3840 + 85

3500 + 85

3490 + 85

3550 + 85
3680 + 105
3050 + 85
4010+ 85

3100 + 85

3240 + 85

19

Table 3. Radiocarbon dating results from drillholes; Cocos (Keeling) Islands

ANU Sample Material Location Island Elev- Conventional Environmentally
Lab No. ation radiocarbon corrected
No. (m)? age age
6223 C153 Coral frag from lagoonal Pulu Wak -1.0 3620 + 80 3170+ 85
ments infill Banka
6227 CK3-5B-4 Coral Depth 6.2m in Home Is. -6.1 6610 + 90 6160 + 95
core CK3
6641 CKI10A.1B Coral, 150cm in core West Is. -1.9 $220 + 80 4770+ 85
Porites on reef flat
6642 CK9.3B Coral, 230cm in core West Is. ~1.7 6000 + 80 5550 + 85
Faviid on conglomerate
6643 CK9.4B Tridacna 380cm incore West Is. -3.0 6370 + 90 $920 + 95
on conglomerate
6644 CK8.1B/2 Coral, 140cm in core West Is. +0.2 3640 + 80 3190 + 85
Porites through beachrock
6645 CK7.3B Coral 310cm in core Home ls. -2.4 6210+ 90 5760 + 95
6646 CKS5.1B Coral, Scm in core Pulu Wak 0.0 2410+ 70 1960 + 80
Porites on conglomerate Banka
6647 CK3.3B Coral 300cm in core Home ls. -3.0 5530 + 80 5080 + 85
on conglomerate
6648 CK3.2B Coral 140cm in core Home ls. -1.4 5610 + 80 5160 + 85
on conglomerate
6649 CK2.2B Coral In core Home ls. -2.4 3940 + 80 3490 + 85
on conglmerate
7546 CKI11/10B Tridacna 1305cmincore Horsburgh -11.1 5060 + 80 4610 + 85
Is.
7547 CK12/3B Coral 480cm in core Horsburgh -2.4 5710 + 70 5260 + 80
fragments Is.
7548 CK12/12B Coral 1300cmincore Horsburgh -10.6 5990 + 70 5540 + 80
Flaviid Is.
7549 CK13/5B_ Coral 440cm in core West Is -3.0 6590 + 80 6140+ 85
7550 CKI14/5B Tridacna 600cm incore South Is. = -2.5 6490 + 70 6040 + 80
7551 CKI15/6B Coral 1000cmincore PuluBlan -9.0 7240 + 70 6790 + 80
fragments Madar
8196 CK21215 Coral 215cm in core south of -2.4 6250 + 60 5800 + 70
on reef flat West Is.
8198 CK2160 Coral 60cm in core south of -0.8 6080 + 200 5630 + 205
on reef flat West Is.
8200 WI16/12 Coral 1220cmincore West Is. ? 41,100 + 890
8201 WII16/5 Coral 500cm in core West Is. ? 6170+ 70 5720 + 80
8404 HI12/15 Coral, 1550cmincore Homels. -14.0 7480+ 110 7030 + 115
Acropora
8197 CK17-235 Coral 235cm in core West Is. -2.5 6410+ 70 5960 + 80
8199 CK23-210 Coral 210cm in core Pulu Maria -1.7 $190 +70 4740+ 85
on reef flat
Note: 2 metres relative to Mean Sea Level.

20

Table 4. Radiocarbon dating results on fossil microatolls; Cocos (Keeling) Islands

ANU _ Sample
Lab No.
No.

5415 C18
6218 C156
6226 C174
6228 C155
7135 C 204
7136 C 206
7552 2
75534
75546
8408 4
8409 5

Note:

Material Location

Microatoll,
branching
Porites
Microatoll,
massive
Porites
Coral,
Porites
Microatoll,
massive
Porites
Microatoll,
massive
Porites
Coral,
branching
Porites
Microatoll,
Porites
Microatoll,
Porites
Microatoll,
Porites
Microatoll,
Porites
Microatoll,
Porites

in situ within Pulu
conglomerate Pandan
platform

in situ West Is.
adjacent to

C155

microatoll in South Is.

lagoon sediments
in situ beneath West Is.
beachrock

in situ West Is.
in conglomerate

in situ West Is.
in conglomerate

foot of beach West Is.
foot of beach West Is.
foot of beach West Is.
foot of beach West Is.
foot of beach West Is.

4 metres relative to Mean Sea Level.

(m)?
+0.6

+0.15

-0.15

+0.15

+0.35

+0.35

+0.1

+0.07

3400 + 80
3180 + 80

4010 + 80

3140 + 80
3690 + 80
3710 + 80

1500 + 60
2990 + 70
3470 + 80
3160 + 50

3430 + 60

Island Elev- Conventional Environmentally
ation radiocarbon age _ corrected age

2950 + 85

2730 + 85

3560 + 85

2690 + 85

3240 + 85

3260 + 85

1050 + 70
2540 + 80
3020 + 85
2710 + 60

2980 + 70

Table 5. Radiocarbon dating results from vibrocores; Cocos (Keeling) Islands

ANU Sample Material Location Island Conventional Environmentally
Lab No. No. radiocarbon age corrected age
7531 CV2-240 Coral 240cm in vibrocore Lagoon 2780 + 100 2330 + 105
fragments

1532 CV2-300 Coral 300cm in vibrocore Lagoon 3050 + 90 2600 + 95
fragments

7533 CV2-414 Coral 414cm in vibrocore Lagoon 2660 + 130 2210+ 135
fragments

7534 CV3-80 Coral 80cm in vibrocore Lagoon 1670+ 110 1220+ 115
fragments

7535 CV3-240 Coral 240cm in vibrocore Lagoon 2980 + 70 2530 + 80
fragments

7536 CV10-110 Coral 110cm in vibrocore Lagoon 580 +100 130 + 105
fragments

7537 CV10-222 Coral 222cm in vibrocore Lagoon 1360 + 80 910+ 85
fragments

7538 CV12-50 Coral 50cm in vibrocore Lagoon 2520 + 110 2070 + 115
fragments

7539 CV12-158 Coral 158cm in vibrocore Lagoon 3980 + 80 3530 + 85
fragments

7540 CV1-90 Coral 90cm in vibrocore Lagoon 3690 + 80 3240 + 85
fragments

7541 CV5-66 Coral 66cm in vibrocore Lagoon 2490 + 80 2040 + 85
fragments

7542 CV6-48 = Coral 48cm in vibrocore Lagoon 1850 + 90 1400 + 95
fragments

7543 CV8-76 Coral 76cm in vibrocore Lagoon 2970 + 120 2520 + 125
fragments

7544 CV11-96 Coral 96cm in vibrocore Lagoon 4300 + 80 3850 + 85
fragments

7545 CV15-130 Coral 130cm in vibrocore Lagoon 870 + 60 420+ 70
fragments

8398 CV3 378 Coral 378cm in vibrocore Lagoon 3190 + 50 2740 + 60
fragments

8400 CV3 320 Coral 320cm in vibrocore Lagoon 3140 + 60 2690 + 70
fragments

8402 CV2 360 Coral 360cm in vibrocore Lagoon 3180+ 50 2730 + 60

21

fragments

22

Table 6. Radiocarbon dating results on reef island sediments; Cocos (Keeling) Islands

ANU Sample Material Location Island Conventional Environmentally
Lab No. No. radiocarbon age corrected age
5413 Gi, Coral boulder exposed North 2070 + 70 1620 + 80

in eroded ridge Keeling

6219 C171 Coral, reef block on southern 1060 + 70 610+ 80
Porites reef flat atoll rim

6225 C138 Coral, in bedded sand Home Is. 1890 + 70 1440+ 80
Pocillopora in wall of trench

7127 C72 Coral, In pit West Is. 1570 + 80 1120+ 85
Porites

7128 C 104 Bulk sand, _In pit, eastern West Is. 102.6 + 3.7 %M MODERN
foraminifera ridge

7129 C106 ~=Coral, 80cm in pit West Is. 1550 + 90 1100 + 95
Pocillopora

7130 C118 ~~ Coral, 70cm in pit West Is. 830 + 100 380 + 105
Acropora

qAtsy C133 Coralsand intrench Home Is. 2290 + 120 1840 + 125
and shingle

F132 C135 Coralsand intrench Home Is. 2020 + 170 1570 + 175
and shingle

733 C136 ~—Coral shingle in trench Home Is. 1950+ 70 1500 + 70
Porites

7747 C108 Coral 20-30cm in pit _ West Is. 1890 + 60 1440 + 60

23

MALDIVES ,;

SEYCHELLES

CHRISTMAS Is. _
COCOS (KEELING) IS.”
MADAGASCAR

MAURITIUS ,

CHRISTMAS
ISLAND

~
COCOS (KEELING)
ISLANDS

Figure 1. Location of the Cocos (Keeling) Islands and bathymetry (in metres) of the
northeastern Indian Ocean.

96°50'E 96° 55'E

12°05'S

/z=~Direction Is.
NS

Ate

——sZ 50'S ~ c
NORTH \ 3290
KEELING INDIAN

COCOS

West Is.
(KEELING)

ISLANDS

Coral Boulder s
In Situ Microatoll a
Vibrocore e

96° 50°E 96°55'E

Figure 2. Cocos (Keeling) Islands, showing locations of stratigraphic transects I-X,
vibrocores, and radiocarbon dates on coral from conglomerate platform
(Table 2) and fossil microatolls (Table 4).

Figure 3.

+ MSL
400

Sand

metres

Conglomerate platform
Shingle (core) leat
Large coral (core) 4
Cemented sand egee=25

Shingle cemented by
calcareous algae

Transect I, Home Island (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

D5

26

CK2

3680+105

MSL

200 a

Neal

Floor of channel — —~ — My ky ‘
ky
Hi ly lial
| ! VI In =
1 | a
Vy VI ce Hs
i I! 5160-85
It Vl | =
i md
3490=85 Mi i F
uy :
11 =
Lt =3)),22
‘Ht nS E
W |
pang 4 5080:85
~*“ Conglomerate platform Mi .
x 4
‘4s Shingle (core) De
@® Large coral i
Cemented sand gal -5
ar Shingle cemented by in
calcareous algae ral
1 |
6160:95 mC
Figure 4. Transect II, Home Island (see Fig. 2 for location): stratigraphy and

radiocarbon dates.

27

W E
ue
CK6
Sand spit
2 MSL
ae pl 100 &
ale SSCE a eae Pa ot oe Al )
Sri —e? Floor of channel i i
3170=85 : | y i 4
tl |
1
lel \ ul
mM }
i fe G ee
Li il L o
a PI 3
fH ul E
Cl ig
i y lame
A id
«Sand NM <
q '
~~ Conglomerate platform 4 ul [ey
I
\~ Shingle (core) \ Hl
@ Large coral ti im
Cemented sand No recovery “tl p75
aa Shingle cemented by i
calcareous algae al
lll Reef flat i +-6
=e: Sand/mud/shingle ut

Figure 5. Transect III, Pulu Wak Banka (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

1 2)
(< ©
IA -3 5
E
6040-80—~Lay }-4
MA
ry Kes
I-
Sand x
ky lL
xxx Conglomerate platform is
Dy hee
coro Shingle uf
F L-8
4 Tridacna WJ
14 ee
I|1I11 Reef flat cl
ra
“It Pleistocene limestone D L-10
K
/<! Shingle (core) (A [baer
ia
ZT 2

Figure 6. Transect IV, South Island (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

28

metres
|
fe>)

Figure 7.

A
S< Conglmerate platform
0 eee m1
#5 Sand and shingle it
i
Ill Reet flat Ms
ay ais) | ,
Pleistocene limestone oe 6790+80
Six Sand and shingle (core) is
I
Py
la

Transect V, Pulu Blan Madar (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

Reef crest

metres

800

29

ss Sand
e¢e Shingle
s Coral
lll Reef flat
UV Shingle cemented by
calcareous algae

“~~~-/ Shingle (core)
CK23

No recovery

Figure 8.

MSL

Figure 9.

— 5630-205 y H
uN

nN

it 4740-85

i! iF

|

a 5800-70

Transect VI, Pulu Maria (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

Bulldozed topography

ss Conglomerate platform :

@ Coral shingle

-—= Sand and mud it
-Il<~ Sand and shingle (core)

Transect VIL, eastern end of West Island (see Fig. 2 for location):
stratigraphy and radiocarbon dates.

30

3
S N
CK9
2 ES
g950:105— CiKig
? 23
’
1 ae
| jo
CK20 At 1
MSL 100 200 300 400 Ny 500 SS
CK10B CK10A hy WI 600
K4 m1
ckig OK ! Ter A i
2 nl 1 A 3
] iy iw a F i
¢ ; e ae 15550285 2
( x Hey age
=) ! =
i a ares a Ly |
ga Wl 4 kf
g Sy hi ta
S l-5920-95 EI
e -3 (! i — 6140285
\! Pi
Ss Conglomerate platform Gi a
\
hy 4/> Shingle (core) al
No recovery at | ra
@ Coral ‘| y
i I+
=f “2. Cemented sand 4 b
ax Shingle cemented by in |
calcareous algae eS re
ry Al
ae (II| Reef flat A 4
e.°. Shingle IS
: a
= Sand and shingle rm
Sy U f
=== Mud ni
“1 ~Pleistocene limestone re
i :
aT
f
:
|
i
-10 i

Figure 10. _—- Transect VIII, southern West Island (see Fig. 2 for location): stratigraphy
and radiocarbon dates.

Sit

W ES
3 AorH n i
CK8 ae Sand Microatolls
CK8A <“ Conglomerate platform =~ Sand and mud
\-7= Shingle (core) iil Reef flat
2 Road = Large coral <z~ Beachrock
2690+85 22% Shingle
2730285
w
Sat
o
E
MSL

400

'~ 5960+80

Figure 11. | Transect IX, Quarantine station (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

=
i 1200
4— No recovery

mas
RING REIS TS

‘4
=3 "—~ 5260-80 it
A
8 5) it
oa "y V1
o Hs) Vt
Eee Dy Sand i
1 ie
=6 5 ~~~ Conglomerate platform A
~ ty
nt
a s°¢ Shingle 4
=i mi 1
"A = Coral |
-8 N
" 211 Shingle cemented by j
-9 m calcareous algae
Le IT Plei limest
ra leistocene limestone a
aye 4 Tridacna 1! 4610-85
S il
“i R 5540-80 La> Shingle (core) \ Wa
le

Figure 12. Transect X, Horsburgh Island (see Fig. 2 for location): stratigraphy and
radiocarbon dates.

32

RADIOCARBON YEARS BP
8000 6000 4000 2000 0)

MSL

(W) Hld3ad / NOILVAA14

e Cocos, coral
« Cocos, microatoll > 14

Figure 13. | Age-depth plot of radiocarbon dates from Cocos, showing dates from
drillholes (Table 3), from conglomerate platform (Table 2) and from fossil
microatolls (Table 4). Three phases can be recognised: 1) catch-up reef
growth, 2) reef flat consolidation, and 3) reef island formation. See text for

details.

33)

INTERGLACIAL GLACIAL MODERN
ATOLL FORM ne ees oe ATOLL
Karst

HOLOCENE
REEF GROWTH
AND
LAGOONAL
SEDIMENTATION

PRESENT
SEA LEVEL

DEPTH
(metres)
100

150
160 120 80 40 te)

TIME
(thousands of years before present)

Figure 14. | A model of the late Quaternary development of the Cocos (Keeling) Islands.
The sea-level curve is derived from Chappell and Shackleton (1986). The
atoll is gradually subsiding. The interglacial atoll surface is subject to
solutional weathering particularly when the sea is low. During the
postglacial marine transgression reefs have re-established over the pre-
Holocene surface and the three phases of Holocene atoll development
identified in Figure 13 can be recognised.

ATOLL RESEARCH BULLETIN

NO. 403

CHAPTER 5

REEF ISLANDS OF THE COCOS (KEELING) ISLANDS

BY

C.D. WOODROFFE AND R.F. McLEAN

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 5
REEF ISLANDS OF THE COCOS
(KEELING) ISLANDS
BY
C.D. WOODROFFE *
AND
R.F. McLEAN **

INTRODUCTION

Reef islands have developed during the final phase of the Holocene development
of the Cocos (Keeling) Islands. The islands are low-lying, and are generally composed
of unconsolidated, biogenic sand. In places coral shingle is an important element of the
sediments, and in a few localities, as for instance towards the southern end and on the
oceanward shore of Pulu Wak Banka, coral rubble, composed of boulders of more than
50 cm diameter, covers the islands seaward margin.

Reef islands often overlie a cemented coral breccia, referred to as conglomerate
platform (see previous chapter). Guppy (1889) noted the compositional similarity
between this and the material comprising the modern reef flat and reef crest, and as we
have demonstrated this platform appears to be an emergent, fossil reef flat dating from
the mid-Holocene (Woodroffe et al. 1990a, 1990b). The conglomerate platform
underlies many of the islands, although is not found everywhere (Jacobson 1976); it
appears to act as an anchor, determining island location. A clinker-like conglomerate,
undercut by solution and ringing metallic to the hammer, is found along the lagoonward
shore of many islands, and is particularly conspicuous around the perimeter of the
lagoonlets or teloks.

In addition to the conglomerate platform there are also cemented deposits of
beachrock. Beachrock can be distinguished from conglomerate platform because it is
bedded and exhibits a seaward dip (Russell and McIntire 1965, p35); beds are scarped at
the landward face, and the deposits are undercut along bedding stratification (Stoddart
1971, p9). In places beachrock overlies conglomerate platform, as on the western shore
of Horsburgh Island. In addition there are some isolated cemented deposits which
resemble cay sandstone. These are generally less well lithified, and are horizontally
bedded; an example occurs on the oceanward shore at the southern end of the airstrip on
West Island.

In this section the physical and major vegetation characteristics of individual reef
islands are described and mapped. Mapping was undertaken from 1:10,000 colour
vertical aerial photographs taken in 1987, supplemented by ground truthing. Elevational
information was derived from a series of profiles surveyed across reef islands and related
to mean sea level datum. Additional data come from existing surveys and benchmark
records.

* Department of Geography, University of Wollongong, Northfields Avenue,
Wollongong, New South Wales, 2522.
** Department of Geography and Oceanography, Australian Defence Force Academy,
Canberra, Australian Capital Territory, 2601.

The general form of reef islands was summarised diagrammatically by Darwin,
who recognised a ledge of conglomerate platform which protruded on the oceanward side
of islands, and a ridge, generally sandy, but also of coarser material, which formed the
oceanward beach. In common with reef islands on other atolls, Cocos reef islands often
show a lower lagoonward beach ridge, in addition to the oceanward beach ridge.

Individual reef islands were described by Guppy (1889). Details of perimeter and
island area are given in Table 1; they are examined sequentially below.

REEF ISLANDS
DIRECTION ISLAND

Direction Island (also known as Pulu Tikus, or Rat Island) is a crescent-shaped
island. It appears to have been the first island to be inhabited, for it was on Direction
Island that the crew, together with the rats, of the Mauritius were marooned after their
ship was wrecked in 1825. The island was also inhabited for a short period by Alexander
Hare and his followers in the same year. It is 1.6 km long and 300 m maximum width,
with an area of 0.34 km2. It is dominated by coconut woodland, but with a band of
Scaevola scrub along its eastern margin. This island was the site of the Cable Station,
with undersea links to Australia, Singapore and South Africa, which came into operation
in 1901 and ceased in 1966. In the late 1960s buildings on the island were either
translocated to Home and West Island, or bulldozed into the sea along the oceanward
margin, and considerable building rubble is conspicuous along the oceanward shore (Fig.
19a).

The eastern portion of the oceanward shore comprises a prominent ledge of
conglomerate platform, extending up to 35 m seaward from the beach (Fig. 14). This
conglomerate platform is composed particularly of heads of branching Acropora. The
oceanward beach ridge is composed of coral rubble and shingle along most of the island,
and fragments of Pocillopora are especially frequent. This coarse substrate overlies
sand, and the island can be seen to be composed of sand just over the ridge crest which
reaches a height of around 3.0 m along much of the island, but 3.5 m towards the
northern end (Fig. 11). The lagoonward shore is dominated by a broad sandy beach. At
the northwestern end of Direction Island there are a series of shingle berms marking
periodic accretion, in relation to which Guppy proposed that 'as the reef grows seaward
the island also gains on the reef flat by a succession of ridges, thrown up during heavy
gales, the remains of which are still to be seen in its interior' (Guppy 1889, p463).

Small outcrops of beachrock are found at the northern and southern ends of the
lagoonward beach, indicating minor recession of this shoreline at some stage in the past.
There is a strong current running through the inter-island channel at the southern end of
Direction Island, and called the Rip. Guppy (1889) proposed that such currents served to
give the island its crescentic shape.

WORKHOUSE ISLET

There is presently no permanent land at the site of Workhouse Islet, or Pulu Pasir.
However, there has been an island of variable size there in the past. A sand bank 150 ft

by 100 ft was described by van der Jagt in 1829; Guppy (1889) records that in 1888 it
was 6 ft high and dominated by one seaward leaning coconut.

PRISON ISLAND

The island north of Home Island is known as Prison Island; it has been known as
Pulu Beras (Rice Island) or Pulu Tuan (Master's island), from the time of Alexander
Hare. It is now considerably smaller (88x75 m) than it must have been when Alexander
Hare moved his household there in 1827 from Home Island. van der Jagt (1831)
recorded that it was 20 ft high in 1829, and Guppy (1889) also states that it was 20 ft
high in 1888 and was composed of blown sand. It presently reaches a height of 6.7 m,
and so has changed little in overall height in this time, though it is now eroding on all
sides (Fig. 19b). It contains a mixture of coconut, Scaevola and Tournefortia. Bunce
(1988) implies that much of this erosion has taken place in the 30 years since Pulu
Gangsa has been connected to Home Island.

BUTTON ISLETS

Guppy (1889) records that there were a series of islands, termed the Button Islets,
on the 1829 map of van der Jagt, between Prison Island and Pulu Gangsa. The sandy reef
islands had already disappeared by 1888, with only conglomerate platform remaining
(this platform can be seen in the foreground in Fig. 19b).

HOME ISLAND

Home Island has been a centre of habitation since Alexander Hare chose it for his
first permanent settlement in 1826. The burial island, Pulu Gangsa, termed Clunie Island
by Guppy (1889), was artificially joined to Home Island by placing coconut logs and
concrete-filled drums across the channel in the late 1940s (Bunce 1988). In 1888 the
channel between the two had been less than 2 ft deep at low tides (Guppy 1889, p464).
The island is also known as Water Island, New Selima or Pulu Selma. It is covered by
well-managed coconut woodland, with extensive groves of Calophyllum. Casuarina was
reported as widespread on the island in 1888 by Guppy (1889).

The combined islands have a length of 2.6 km, and reach a maximum width of
800 m (Fig. 2). Their area is 0.95 km?. Some part of this has been reclaimed from the
sea; this is especially true of the landing area north and south of the present jetty, and the
part of the village called kampong baru (new village), reclaimed by teams of women
earlier this century (Bunce 1988). Oceania House was designed and built by George
Clunies-Ross in 1893.

There is considerable survey data available for Home Island. Most of the
kampong is 1.20-1.60 m above mean sea level. The island rises generally to an
oceanward beach crest that is around 3.30 m (Fig. 11). This beach is covered with coral
shingle and coral boulders, but as excavations into the island have shown, these are
underlain by sand which is dipping gradually oceanward at 2-6’.

North of the village there is the remnant of a wind-blown dune (see Fig. 11); sand
from similar dunes appears to have been removed and used to assist fill in reclaimed
areas. The dune presently rises to 5.50 m above mean sea level and contains one of the

few remaining stands of Pandanus. The sandy lagoonal shore has been extensively
modified; sand has been bulldozed, and there is evidence of a series of seawalls along
parts of the shore. The village extended along the southern shore, east of Oceania House
earlier this century (Gibson-Hill 1950).

On the oceanward shore of Home Island there is a narrow outcrop of
conglomerate platform within which branching corals are especially prominent (Fig. 15).
Individual Porites blocks within the conglomerate platform reach up to 1.0 m mean sea
level. The conglomerate platform is overlain by boulder and shingle deposits. It widens
into a broader platform at the southern end of the island. Conglomerate also underlies
much of the island, as can be seen on the profiles in Figure 11, and from descriptions in
Jacobson (1976).

PULU AMPANG KECHIL

Pulu Ampang Kechil is the small island south of Home Island, and forming the
northern outlier of the Ampang Islands (Fig. 3). It was called Scaevola Islet by Guppy
(1889). It is dominated by Scaevola, although with individual coconut and Tournefortia.
The island is composed of coral shingle, with a sand spit extending to seaward and to
lagoonward. It lies on an outcrop of conglomerate platform which contains some
particularly large heads of Porites coral of over 1 m diameter.

PULU AMPANG

The Ampang Islands, termed Steward's group in van der Jagt's map of 1829, are a
group of several small islands on one outcrop of conglomerate platform. The term Pulu
Ampang is generally applied to the northernmost of the group, distinguished as Ampang
Major by Guppy. This island is horseshoe shaped 625 m long and 275 m wide, with
sandy spits extending into the lagoon around the island margins. Pemphis grows on these
spits and also occurs along a minor bar cutting off the interior lagoonlet. This lagoonlet
dries at low tide, and Guppy recounts that J.C. Ross remembers this feature silting up
(Guppy 1899, p466). It appears to have changed little from the account given by Guppy
over 100 years ago (Fig. 3)

The conglomerate platform is extensive along the oceanward shore of each of the
Ampang Islands (see Fig. 19c). It forms a much flatter surface than on Pulu Ampang
Kechil, and rises up to heights on individual coral heads within the platform of 0.76 m
mean sea level. Much of the conglomerate platform is inundated at high tide, particularly
when there is a large swell. The oceanward beach on Pulu Ampang is composed of
shingle overlying sand, with individual boulders at the foot of the beach of diameters up
to 1 m. The crest of this ridge has a cover of Scaevola scrub, which is replaced 10-20 m
inland by coconut woodland (Fig. 3).

PULU WA-IDAS

Pulu Wa-idas, called Ampang Minor by Guppy, is separated from Pulu Ampang
to the north by a deep pool, which resembles other inter-island passages except that it
does not continue through the conglomerate platform as a channel. The conglomerate
platform is fissured, and is evidently eroding at this point, and given time it would appear
that a channel will form between these two islands. The island is 75 m from north to

south, and 320 m from oceanward to lagoonward; it is covered with coconut woodland,
with a margin of Pemphis along its southern side (shown in Fig. 19c).

PULU BLEKOK

The southernmost of the Ampang islands is Pulu Blekok, called Pulu Bruko by
Guppy. In form it is a mirror image of Pulu Wa-idas, with a fringe of Pemphis along its
northern margin. It is 230 m from oceanward to lagoonward (Fig. 3). The conglomerate
platform, although embayed on the oceanward side at this point, does not show the same
indications that a channel will form as to the north of Pulu Wa-idas. Indeed Guppy
suggested that the vegetation of the two islands was encroaching, and that over time the
two islands would unite (Guppy 1889, p466); they have not done so in the 100 years
since he observed them. There is a lagoonlet, largely cut off from the lagoon, on the
lagoonward side.

PULU KEMBANG

Pulu Kembang, spelt Pulu Kumbang by Guppy, but not described in any detail,
Sits on its own outcrop of conglomerate platform. The island is 150 m north to south and
390 m from oceanward to lagoonward; it is predominantly sandy, but it has extensive
shingle along the margins flanking inter-island channels, and shingle is found at the
beach top, where there is a narrow band of Scaevola. Much of the island is covered with
coconut woodland, though Pemphis occurs on the lagoonward most parts of the sandy
spits. The sand on the oceanward beach comprises an abundance of foraminifera; it
appears to be actively accreting, particularly at the southeastern corner, where Pemphis is
colonising this sand.

PULU CHEPELOK/PULU WAK BANKA

The island south of Pulu Kembang is a long island which has several names. It
was called Armstrong Island on the 1829 map of van der Jagt; Guppy called it
Gooseberry Island. On the recent maps its northern part is called Pulu Chepelok (also
spelt Pulu Cepelok), while the southern half is named Pulu Wak Banka. The island is
1.15 km long, and up to 400 m wide. It has prominent spits at the northern and southern
ends. There are also a couple of similar features extending into the lagoon in the middle
of the island, giving the impression that this island may have comprised two or three
islands in the past (Guppy 1899, p466).

The island along its oceanward shore is underlain by an extensive conglomerate
platform. This contains large boulders in places; there is a large boulder 1.5 m long and
1 m higher than the general conglomerate platform level, reaching an elevation of 1.50 m
mean sea level, at the southern end of the island. The nature of the beach sediments on
the oceanward shore changes markedly along the island. There are coarse coral rubble
deposits, with boulders up to 1 m in diameter, along much of the southern half of the
island, reaching up into the Scaevola scrub which is dense along the ridge crest (Fig.
20e). On the other hand, where the island is narrowest, the conglomerate platform is no
longer present along the oceanward shore, and instead there is a broad sand beach. The
ridge crest rises to 3.5 m mean seal level at the southern end of the island, but is only 2.1
m mean seal level where a profile has been surveyed across the island in the centre. On
that profile (Fig. 11), it can be seen that the coral shingle overlies sand, and that the

conglomerate platform also continues under much of the island. Conglomerate forms a
thin crust along the margin of the channel along the southern end of the island.

PULU PANDAN

Pandan Island or Pulu Pandan (also called Misery Island) is the clearest example
of a horseshoe shaped island (Fig. 3), called an atollon by Guppy (1889). Despite its
name, Pandanus is no longer conspicuous element of the island's vegetation. It consists
of two distinct sandy spits with a shingle veneer, both covered by coconut woodland with
Pemphis on the lagoonward extremity (Fig. 16). Maximum width is about 800 m, and
the island measures 1.8 km from the end of one spit to the end of the other spit. These
spits serve to partially enclose a lagoonlet, with a soft muddy floor and cover of seagrass.
The southern spit in particular has recently extended into the lagoon, and there is a
further shoal of intertidal sand, with an outpost of Pemphis on it which represents a
continuation of the island.

On the oceanward shore there is a margin of conglomerate platform extending
along the island. For much of its extent this conglomerate comprises an upper unit of
shingle-sized clasts cemented into a near horizontal layer (Fig. 19d); this overlies some in
situ fossil microatolls of branching Porites at the eastern end of the surveyed transect.
The conglomerate platform surface rises to 1.20 m mean sea level, rather higher than on
other islands on the eastern rim of the atoll, suggesting that this shingle conglomerate
surface may overlie the more conventional conglomerate platform surface. The transect
(Fig. 11) illustrates that the island is composed primarily of sand, rising up to a ridge
crest of 4.50 m mean sea level, and does not have the shingle or rubble veneer
characteristic of the oceanward shore of islands to the north. Shingle does form low
elevation ridges along the lagoonward shore, and there are small outcrops of a clinker-
like conglomerate around the margin of the lagoonlet.

PULU SIPUT

Pulu Siput (also called Goat Island) is dominated by coconut woodland, and is
660 m oceanward to lagoonward, and 240 m from north to south (Fig. 3). It has formed
on an outcrop of conglomerate platform, and the island is predominantly sandy, with
foraminiferal sand accumulating at the northeastern corner of the island. Spits, with a
cover of Pemphis, but also with occasional Suriana, extend into the lagoon.

PULU JAMBATAN

Pulu Jambatan is the name given to the island formed largely of coconut
woodland, 340 m long, at the lagoonward end of a long, narrow outcrop of conglomerate
platform. There is a much smaller island, less than 50 m long, at the seaward end of this
conglomerate platform outcrop, apparently without a name, with a vegetation cover of
Scaevola with some coconut and Tournefortia (Fig. 3). The conglomerate platform
between these two islands is smooth, and cover with a veneer of pink algal mat. Seaward
of the more oceanward island, the platform is highly irregular, and contains much coarser
coral boulders.

PULU LABU

Pulu Labu is the island directly north of South Island, separated from it by a
narrow channel (Fig. 3). Most of the island, which is 430 m long, is composed of
coconut woodland; there is a broad band of Scaevola scrub along the oceanward ridge
crest, and on the southeastern corner where sand has recently accumulated, Pemphis is
established. The form of the island is very similar to that of a series of lagoonward
promontories on neighbouring South Island, and it is not unlikely that similar islands to
Pulu Labu may have existed in the past, but have now been united with South Island.

SOUTH ISLAND

South Island, also called Pulu Atas (meaning top island in reference to it being
upwind), Scott Island and Southeast Island, is the windward island of the atoll. It was
chosen as the site for the first settlement by Captain John Clunies Ross in 1827, who
dredged a boat channel through the southern lagoon to the centre of the island. The long
lagoonal shore is the preferred site for a number of Home Islanders pondoks (weekender
shacks), and was also home to a regiment of Kenyan soldiers, the Fifth African Rifles,
who were stationed at the southwestern end near the highest point termed “Gunong’, as
coastwatchers in World War II.

The island is 9.5 km long, and reaches a maximum width of 1.1 km and is
mapped in Figures 5 and 6. Much of the oceanward shore of South Island is formed of a
dune (see Fig. 19f). Windblown sand reaches up to 6.3 m on profile I and profile J (Fig.
11). A dune reaches up to 11 m at the 'Gunong’ at the southwestern corner of the island.
A coral rubble veneer reaches 4.7 m mean sea level on profile H. The vegetation of the
dunes is primarily Scaevola, though with considerable Tournefortia, particularly as
isolated shrubs within blowouts along the dune crest. Guppy (1889) recorded that
Pandanus was found along this dune crest, but it is not a conspicuous element of the
vegetation now. While dunes, which are rare on coral atolls, characterise much of the
shoreline of South Island, there is also a substantial outcrop of conglomerate. This takes
two forms; conglomerate platform occurs in irregular outcrops along much of the eastern
part of the island, often rising up to 1.20 m mean seal level. There are also outcrops of
conglomerate ramp, a highly worn form of conglomerate platform, which has been
bevelled back to a steep ramp-like profile (Fig. 19e). The latter superficially resembles
beachrock, which can also be found at sites along the oceanward shore of South Island,
but is not imbricated, and on inspection can be seen to have been bevelled to form the
dipping outcrop, rather than deposited in dipping stratification. Similar conglomerate
ramps are described on Diego Garcia, an atoll in the Chagos group (Stoddart 1971, p18).

The interior of the island is now covered by thick, overgrown coconut woodland
which has degenerated from the organised and harvested coconut plantations of the
heyday of the Clunies Ross estate. On the oceanward shore and over the narrow necks of
the island, there is dense, impenetrable Scaevola scrub. Little remains, except isolated
stumps of the Pisonia and Cordia stands which were once widespread on the island.
There is a large stand of Calophyllum at the southwestern corner of the island (Fig. 5).

The lagoonward shore of South Island is highly irregular. The lagoonal flats are
composed of mud or sandy mud, and there are irregular linear shoals, covered by
Pemphis and inundated at high tide, partially enclosing some of the larger lagoonlets,
termed Teloks (Fig. 20c). It is said to have been silting rapidly, which may have lead to

the abandonment of the first settlement there; though there can be little doubt that the
southern flats of the lagoon must have been shallow even at that time, and access cannot
have been easy. The western end of the island has a series of recurved spits; these are not
as distinct as those of West Island; nevertheless they were Lae by Guppy (1889)
to indicate that the island had been extending to the west.

Upon first impression this elongate island appears to have been made up from
several islands which have been joined together. There are two areas, traversed by
profiles H and I respectively, which resemble infilled passages between these former
islands. These are covered mainly by Scaevola scrub, with few coconuts; those coconuts
which do grow there are stunted, and stressed. There is no freshwater lens developed
beneath these narrow areas. Soil is absent or poorly developed, and the lagoonward
portion of the island is composed of clinker coral shingle. Darwin interpreted these as
former channels, and his interpretation was aided by a map that Leisk, the manager in
charge of the islands at the time of his visit, told Darwin he had seen. Guppy was rather
dismissive of the likelihood that the channels had been infilled as recently as Darwin
implied, pointing out that they were closed, and the island one entity even in the map
shown in van Keulen's Atlas of 1753 (Guppy 1889, p467). We examine this issue in
more detail below.

PULU KLAPA SATU

Pulu Klapa Satu, the island directly west of South Island, is about 125 m long and
75 m wide (Fig. 5). It sits on a long linear exposure of conglomerate platform, which in
common with the other islands of the southern passage, is relatively free of large coral
clasts, and contains largely sand-sized grains cemented together. In petrography it
resembles beachrock, but lacks the stratification which distinguishes the latter.

PULU BLAN AND PULU BLAN MADAR

Pulu Blan and Pulu Blan Madar, also known as Burial Island and East Cay, sit on
the same outcrop of fine-grained conglomerate platform. They are composed of sand
with some shingle, and carry a vegetation of coconut and Scaevola. The oceanward
shore of Pulu Blan Madar rises up to a height of 1.20 m mean sea level.

PULU MARIA

Pulu Maraya or Pulu Maria lies on an outcrop of fine-grained conglomerate
platform just west of the eastern end of West Island (Fig 8), and is named after one of
two European children who disappeared without trace from the island shores in the
1860s. The island is predominantly sandy though with a series of shingle berms on the
oceanward shore. It is dominated by coconut woodland, with a fringe of Scaevola,
replaced with Pemphis along the lagoonward flanks.

WEST ISLAND

West Island, also known as Ross Island, or Pulu Panjang (Long Island), is the
island upon which the airstrip was built, initially in 1944, but seeing little action in the
war, and revamped for use by Qantas in 1951. It was first settled in 1826 by some of

Alexander Hare's followers, probably in the vicinity of Rumah Baru, and has been
inhabited discontinuously since. It was home to more than 7000 troops from Britain,
Canada, Australia and India in 1944, and has been associated with the airstrip and
contains an Australian expatriate population at present.

The island is 12.6 km long and reaches up to just less than 1 km wide at its
maximum width. It is mapped in Figures 6, 7 and 8. Most of the 6.2 km2 was covered by
coconut plantation, but much is now covered by buildings, the airstrip, or radio
transmitter and receiver aerials. The coconut woodland has ceased to be cleared
regularly, and has become largely overgrown, and penetrable with difficulty.

The island comprises three broad sections, connected by narrow sections which
may have been former inter-island passages. These lead into the two large lagoonlet
areas, Telok Jembu (Fig. 20a) and Telok Kambing (Fig. 20b). Much of the western shore
is a sandy beach, with a dune, reaching more than 7 m high, at Beacon Heights, which
has been excavated. Groynes have been constructed in front of the settlement to stop
northwards movement of sediment, but accumulation within them indicates little net
movement. There are extensive outcrops of beachrock, particularly at the southern end
of the island, and adjacent to the Quarantine station, at those sites which appear to mark
former passages. There is a large area of conglomerate platform at the southwestern end
of the island, and isolated outcrops at the westernmost point and to the northwest. The
outcrop to the southwest is one of the more elevated outcrops on the atoll rising up to
1.20 m mean sea level, with a further cemented shingle conglomerate up to 1.80 m mean
sea level outcropping on the beach behind the conglomerate platform. There are a
number of dipping arcuate ridges within this platform, especially at the southwestern
corner, resembling the bassett edges recorded on the Great Barrier reef islands (Stoddart
et al. 1978).

The easternmost end of the island is characterised by a number of sand spits and
ridges, suggesting gradual buildout of the island into the southern passage. Radiocarbon
dating of coral shingle from shallow pits in those shown in Figure 9, in the previous
chapter, indicates that these spits have been built progressively. The ages are shown on
an aerial photograph of the spits in Figure 17.

HORSBURGH ISLAND

Named after James Horsburgh, the British hydrographer, who compiled detailed
sailing directions of this part of the Indian Ocean in 1805, Horsburgh Island is also
known as Pulu Luar (Outside island). It is 1.7 km long and 0.9 km wide, covering an
area of over 1 km? (Figs. 9 and 18).

It was almost continuously inhabited from 1826 until after World War II. Initially
Alexander Hare put people on the island to grow vegetables and fruit for other islands.
This tradition was maintained by the Clunies Ross proprietors, and George Clunies Ross
kept deer on the island for hunting. In 1941, gun emplacements were installed on the
southern point of the island and manned by Ceylonese troops.

This island sits partly on an outcrop of conglomerate platform. The conglomerate
differs from that on other islands; on the eastern shore of Horsburgh it is generally
narrow, and often bevelled into a conglomerate ramp. On the western shore there is a
broad platform which consists of a series of strata dipping seaward at up to 5°, which

10

resemble beachrock. The platform appears to combine conglomerate platform and
beachrock, and suggests that islands here may have formed almost contemporaneously
with the development of the emergent reef flat.

Along the southern shore there is a broad sandy beach, in places with outcrops of
beachrock which indicate that in the past the shoreline has had a slightly different
orientation in this part of the island. The northern shore of the island is particularly
exposed and consists of a bevelled conglomerate platform ledge, and boulder deposits
over the top. A particularly noteworthy feature of this island is the small lagoonlet which
occurs within the interior of the island to the northeast. This feature, blocked of from the
sea by a boulder rampart, presently contains brackish water, and a stand of mangrove
Rhizophora apiculata. Associated with the mangroves are Cordia stumps and Sesuvium.
In his account of Horsburgh in 1888, Guppy (1889) describes the inland lakelet, but does
not record mangroves growing there naturally; indeed he makes the point that mangrove
propagules are regularly brought to the shores of Cocos, but have not colonised (Guppy,
1890). Guppy indicates that mangroves were planted there by John George Cluines Ross
(Guppy 1890, p278). In a photograph of the lakelet, taken in 1941, the mangroves can be
still seen (Gibson-Hill, 1950).

Much of the northern part of Horsburgh is composed of shingle or rubble, while
the southern part is predominantly sand. Coconut scrub is especially open over the
southern part of the island with a sward of grass and the sedge Fimbristylis, but forms
denser coconut woodland to the north. Scaevola scrub is widespread over the island; to
the south it is relatively open, but to the north it is dense, and made almost impenetrable
by a tangle of Turnera, Triumfetta, Wedelia, Premna and the parasitic Cassytha.

NORTH KEELING ISLAND

North Keeling Island is named after Captain William Keeling who is believed to
have sighted the island in 1609. It was sketched, showing coconuts, by the Swedish
captain Ekeberg in 1749 and appears on the chart reproduced by Dalrymple the English
hydrographer in 1787. Fitzroy examined and mapped it from H.M.S. Beagle in 1836,
but made no landing. Unlike the South Keeling Islands, North Keeling has been visited
relatively infrequently by naturalists, and therefore does not have the same history of
description. It was first described in detail by Guppy (1889) who was there for 6 days in
1888. Wood-Jones (1912) spent a few hours ashore in June 1906, and the most detailed
account, especially of the fauna is that of Gibson-Hill (1948, 1950) who visited for 1 day
in January and 2 days in early July in 1941.

The island has not been inhabited for any continuous period, and is presently
relatively little changed in comparison with the South Keeling Islands. It was visited
from Cocos by the Clunies-Ross family, and Home Islanders (up to 40-60) stayed there
for up to three months over the November-February period cutting firewood. The Emden
beached on the southern shore of North Keeling after being routed by the Sydney in
1914; and the longest period of settlement was probably during the salvage of the Emden
October 1915 to January 1916.

The island is 2.0 km long and 1.3 km wide, with a reef crest around all of the
island, except the northwestern corner (Fig. 10). Reef island is almost continuous around
the perimeter of a shallow lagoon, reaching a maximum width of 320 m and a minimum
width of 50 m. There is one major opening into the lagoon on the southeastern corner of
the atollon. This is the windward side, and the opening has no channel through the reef,

11

but is a shallow conduit which drains almost totally at lowest tide. The lagoon is
shallow, reported as nowhere deeper than 8 feet by Guppy. It's surface sediments are
muddy sands, except for two sandy spits which trail in through the entrance. These did
not appear on Fitzroy's chart of the island; Guppy added them in his sketch of the island,
but shows them scrolled back on themselves. As can be seen in Figure 10 they are
presently linear features which extend flanking the channel. Much of the lagoon is
covered with sea grass.

The island varies from sand to rubble. On the northern shore there is a broad
sandy beach. This continues along the western shore but with varying amounts of
shingle. On the profile (Fig. 10) the sandy beach rises up about 4 m above mean sea
level. A pit shows some shingle fragments, but indicates that the majority of the
substrate is sand. This becomes coarser to the south, where rubble outcrops on the beach,
and there is an erosional cliff cut into this rubble. The southern shore of the island is
composed of a spectacular steep shingle beach, with a series of berms identifiable. Much
of the eastern shore is composed of a series of shingle berms, these are particularly well-
developed just south of the channel into the lagoon, but continue to the north as well.
Guppy (1889) recorded that pumice from the eruption of Krakatoa had advanced the
shore into the lagoon; no evidence of this can be seen today.

There are also outcrops of coral conglomerate. A broad platform of conglomerate
extends out over the reef flat at the eastern part of the island, almost closing the channel
into the lagoon completely. Along much of the southern and eastern shore the
conglomerate outcrops at the foot of the beach but contains a series of parallel rubble
ridges, dipping and stratified like beachrock. These appear to be the lines described by
Guppy (1889) as old reef margins, and upon which he based his argument that the reef
built out by a series of jumps rather than prograding gradually. Similar boulder
conglomerates have been described from other reef settings; they closely resemble the
adjacent beach in structure and composition and we call them beach conglomerate,
believing that they mark the position of former beach lines rather than reef crests (Fig.
20f). At the site of the southern transect (Fig. 10) there are a number of algal terracettes
veneering these old beach deposits. Beach conglomerate overlies conglomerate platform
in some places (Fig. 10).

The vegetation of the island was conveniently divided into four zones by Gibson-
Hill (1950). Much of the island is dominated by Pisonia forest (see Williams, this
volume, Chapter 6). Coconuts are a conspicuous element of all stands of Pisonia, and
over much of the island we have chosen to map this as Pisonia and coconut woodland.
Tournefortia is a conspicuous element of the vegetation of the eastern shore, dominating
the crest of the shingle or rubble ridges. In some cases Tournefortia is monospecific,
north of the channel into the lagoon it occurs with Scaevola also. Around the margins of
the lagoon, Pemphis forms a thicket. Cordia is also important in this location, and it was
to cut this latter species that the Clunies-Ross sent workers. It may have been less
important when Gibson-Hill visited because of this history of cutting. Where Cordia
forms a lagoonal fringe at present it is often fairly even-aged, and much may have grown
back since cutting ceased. The final area that Gibson-Hill identified are cleared areas;
the grassy and Sesuvium covered area to the northwest of the lagoon is the most extensive
area of this type.

There has been considerable speculation as to how North Keeling has developed.
In particular it seems unusual because the remaining entrance to the lagoon occurs on the
most windward side, rather in the shelter that might develop on the leeward. Indeed the
island is quite the inverse of the horseshoe shape that Guppy considers the typical style of

12

development on the main atoll. This has lead a number of observers, starting with
Fitzroy, to suggest that the island developed from a series of formerly unconnected
islands.

REEF ISLAND MORPHOLOGY

The surveyed traverses (Fig. 11 and 12) show three basic cross-island profiles, the
simplest of which was first described by Darwin (1842) and illustrated by a woodcut in
the chapter on Keeling atoll (this illustration is in fact a section across Whitsunday atoll
and not Cocos (Keeling)). Darwin notes that the highest part of the islets is close to the
outer beach and that “from the outer beach the surface slopes gently to the shores of the
lagoon”. Such simple asymmetric profiles are common on West and South Islands and
across the centre of the small horseshoe shaped islands on the atoll’s eastern side.

The second type of profile is basin shaped, again with a prominent seaward ridge
which slopes inland to a central depression before rising to a lower lagoonward ridge.
Such profiles are illustrated from Direction Island and the southern end of Home Island
(Fig. 11). The third profile type is more complex being composed of a series of subdued
ridges and swales between the ocean and lagoonward ridges. This form suggests a more
complicated accretionary history.

A characteristic feature of the islands on Cocos is their plan shape, which Guppy
(1889) described as semi-crescentric or horseshoe shaped with their convexities to
seaward. “The crescentric form is possessed in various degrees by different islands;
some of the smaller ones are perfect horse-shoe atollons and enclose a shallow lagoonlet,
others again exhibit only a semi-crescentic form, whilst the larger islands have been
produced by the union of several islands of this shape.”” Examples of the first type would
include Pulu Ampang, of the second type Direction Island and of the third type South
Island.

To Guppy the islands fitted into an evolutionary sequence all stages of which are
represented on Cocos “from the islet recently thrown up on the reef to the perfect horse-
shoe atollon”. Critical in Guppy’s interpretation are the lagoonward recurving
extremities of the islands which he believed were formed from material brought in by
uni-directional currents through the interisland passages and “heaped up in such a
manner as to prolong the extremities of each island lagoonward in the form of two
horns”. In the case of the larger islands a crescentric form results, while for the smaller
islands a more perfect horseshoe shape is first attained. After the two horns are stabilised
by vegetation, and providing there is an adequate supply of sand, the horns would tend to
approach each other and ultimately they would be joined by a bar enclosing a lagoonlet
on the island’s lagoon side, Guppy called this occluded island form an atollon, and noted
that Horsburgh Island “represents the last condition of an atollon, the earlier stages being
illustrated by Pandan Island and Pulu Ampang Major”.

This view of island evolution differed from that of Darwin who envisaged a
difference in formative processes between islands on the windward and leeward sides of
the atoll (Darwin 1842). On the windward side, the islands “increase solely by the
addition of fragments on their outer side”. Thus the gently sloping surface on the
western side of the windward island predates the high ridge to seaward, and is lower
because waves had further to go from the reef edge and “had less power to throw up
fragments”. On the leeward islands, Darwin recognised a combination of two processes
operating. First, waves from seaward formed the high ocean ridge, and second “‘little

13

waves of the lagoon, heap up sand and fragments of thinly branched corals on the inner
side of the islets on the leeward side of the atoll”. As a result “these islets are broader
than those to windward, some being even eight hundred yards in width, but the land thus
added is very low”.

Both Darwin and Guppy, as well as subsequent workers; recognised the
association of islands with the conglomerate platform and the fact that the unconsolidated
sands and gravels which go to make up the island commonly rest on a solid foundation of
conglomerate platform. Indeed Guppy went so far as to suggest that where bare level
patches of conglomerate are exposed on the windward side of the atoll these were “the
foundation of the islets that have long since swept away” (Guppy 1889, p462).

In our view, the evidence for such an assertion is generally lacking, except in
those places where linear or arcuate bands of beachrock or beach conglomerate are firmly
cemented onto the conglomerate platform. Examples of such exposures are found along
the northwestern side of Horsburgh Island, adjacent to the Quarantine Station on West
Island, around the southwestern corners of West and South Island and on North Keeling
Island. We believe that these outcrops are residuals from the earliest phase of island
building and represent shorelines developed concurrently with the formation of the
conglomerate platform at the time of higher sea level. A radiocarbon date of 3030 + 85
years B.P. from a coral boulder in beach conglomerate to the southwest of North Keeling
gives some support to this argument. Landward erosion of these shorelines has
subsequently occurred. In some other locations high beachrock or beach conglomerate is
found congruent with the present shoreline. In such cases the position of the initial
shoreline has been maintained.

While the association of islands and conglomerate platform is the norm, Guppy
(1889) also recognised that conglomerate platform is not everywhere present beneath the
islands being “absent in those situations where ancient passages have been filled up with
sand and reef debris, and also in those places where recent additions have been made to
the land surface” (p. 462). Our drilling and field data confirm the validity of this
comment, particularly with respect to the “horns” and “bars” of the horseshoe islands and
atollons, as well as the extensive area of lagoonward recurving spits at the western end of
South Island and eastern end of West Island. Radiocarbon dates recording the
development of the last area are shown in Figure 17.

REEF ISLAND FORMATION

Reef islands post-date the conglomerate platform, and it has been demonstrated
that the conglomerate platform was deposited 4000-3000 years ago, as shown by the
narrow range of radiocarbon ages from within it (Woodroffe et al. 1990a, 1990b, this
volume; see chapter 4, Fig. 2). The platform has been interpreted as a former reef flat,
deposited under a sea level around 1 m above present, and the islands have formed in the
last 3000 years during the time that the sea has fallen to present level.

Some indication of island age has already been given for Home Island
(Woodroffe et al. this volume, see last chapter Fig. 3). Samples of coral shingle from a
trench through island sediments (shown in Fig. 20d), indicate an age range of 1400-1800
years B.P.

Nevertheless there remains a series of different possible models of island
formation, both in terms of oceanward or lagoonward accretion, and in relation to the

14

gradual or episodic nature of deposition of sediment. In order to examine the chronology
of island formation in greater detail, three transects of pits were examined on West Island
(Fig. 13) and samples of coral shingle submitted for radiocarbon dating.

The radiocarbon dates shown in Figure 13 confirm that the islands contain few
sediments greater than 3000 years old. The date of 4280 + 70 on transect O (T2) came
from a depth around mean sea level which would be within conglomerate platform
elsewhere. There is no lithified platform at this site, but the date appears to indicate a
similar chronology of deposition. Although this transect is across a narrow neck of
island flanking a telok (see Fig. 12), termed a barachois in relation to the atoll of Diego
Garcia, a date of 3030 + 70 elsewhere on the transect indicates island formation at an
early stage at this site.

Transect P (T1) has been date in some detail. The oldest date 2710 + 90 years
B.P. comes from pit 7 to lagoonward. There is then a progressive decrease in age
towards the ocean. Thus contrary to Darwin's expectation, the island appears to have
built out towards the ocean even here on the leeward side of the atoll. Dates from pit 3
are stratigraphically consistent and indicate rapid vertical build up. The dominant mode
of accretion is horizontal.

A similar trend of older dates to lagoonward, and younger ages to oceanward is
seen for transect L (T3), which also ranges from 3000 years B.P. to present. This is
particularly significant because this eastern part of West Island has been extending
further eastward over the last 1500 years (see Woodroffe et al., this volume, Fig. 9).
Radiocarbon ages on individual spits are shown in Figure 17. The main part of this
southern section is evidently 3000 years old, like the northern section of West Island.

North Keeling is morphologically distinct from the South Keeling Islands and
may have developed differently. It is not unusual in other Pacific and Indian Ocean atoll
archipelagoes for the smaller reef platforms to be occupied by one island which is low in
the middle, with a lagoon that may or may not be connected to the open ocean. The
history of development of these is not known in detail, although there are some
radiocarbon dates available from table reefs, or reef-top islands, of this type in Tuvalu
(McLean and Hosking 1991).

We have three further radiocarbon dates from North Keeling. A coral from
conglomerate on the northeast of the island dated 3840 + 85 years B.P., similar to but at
the older end of the range of dates for conglomerate platform from the South Keeling
Islands. An age of 3060 + 60 years B.P. was derived for coral shingle in a pit in the
centre of the island, suggesting little time difference between the formation of the beach
at the margin of the reef platform, and the formation of the island. The final date was on
a boulder exposed within an erosional scarp in the rubble beach on the southwest of the
island, which gave an age of 1620 + 80 years B.P. Guppy (1889) suggested that the
boulders on this beach indicated that it was prograded by coral blocks piled up during a
cyclone; this age implies that cyclones may have occurred over the last 1500 years or
more. We note that this equates with a phase of island building on other parts of the
Cocos (Keeling) Islands.

The radiocarbon ages suggest continual addition to islands over the last 3000
years, but we have insufficient dates to indicate whether this accretion was gradual or
whether it occurred in a series of episodes. At this stage we have no dates which allow
us to address the morphological issues raised by Guppy. Nevertheless reef islands are
geologically young and morphologically dynamic; sediment is continuing to be produced

15

and supplied to islands and the islands are continuing to change through the addition of
sediment at some points, but its erosion from elsewhere.

REFERENCES

Bunce, P. 1988. The Cocos (Keeling) Islands: Australian Atolls in the Indian Ocean.
Milton: Jacaranda Press.

Gibson-Hill, C. A. 1948. The island of North Keeling. J. Malay. Br. Roy. Asiat. Soc.
21: 68-103.

Gibson-Hill, C. A. 1950. A note on the Cocos-Keeling Islands. Bull. Raffles Mus. 22:
11-28.

Guppy, H. B. 1889. The Cocos-Keeling Islands. Scott. Geog. Mag. 5: 281-297, 457-
474, 569-588.

Guppy, H. B. 1890. The dispersal of plants as illustrated by the flora of the Keeling or
Cocos Islands. J. Trans. Vic. Inst. London, 24: 267-306.

Jacobson, G. 1976. The freshwater lens on Home Island in the Cocos (Keeling) Islands.
BMR, J. Aust. Geol. Geophys. 1/4: 335-343.

McLean, R. F., and Hosking, P. L. 1991. Geomorphology of reef islands and atoll motu
in Tuvalu. South Pacific J. Nat. Sci. 11: 167-189.

Russell, R. J., and McIntire, W. G. 1965. Southern Hemisphere beach rock. Geog. Rev.
55: 17-45.

Stoddart, D. R. 1971. Geomorphology of Diego Garcia Atoll. Atoll Res. Bull. 149: 7-
26.

Stoddart, D. R., McLean, R. F., and Hopley, D. 1978. Geomorphology of reef islands,
northern Great Barrier Reef. Phil. Trans. Roy. Soc. Lond. B 284: 39-61.

Van der Jagt, H. 1831. Beschrijving der Kokos-of Keeling-Eilanden. Verh. Batav.
Gen. v. Kunsten en Wetenschappen (Batavia), 13: 293-322. translated in J. Malay.
Br. Roy. Asiat. Soc. (1952), 25: 148-159.

Wood-Jones, F. 1912. Coral and Atolls: a history and description of the Keeling-Cocos
Islands, with an account of their fauna and flora, and a discussion of the method of
development and transformation of coral structures in general. London: Lovell
Reeve and Co.

Woodroffe, C. D., McLean, R. F., Polach, H., and Wallensky, E. 1990a. Sea level and
coral atolls: Late Holocene emergence in the Indian Ocean. Geology 18: 62-66.

Woodroffe, C. D., McLean, R. F., and Wallensky, E. 1990b. Darwin's coral atoll:

geomorphology and recent development of the Cocos (Keeling) Islands, Indian
Ocean. Nat. Geog. Res. 6: 262-275.

16

Table 1. Perimeter and area of the Cocos reef islands
Island Perimeter (km) ‘Area (km2)

Horsburgh Island 4.4 1.04

Direction Island 3.4 0.34

Prison Island 0.4 0.02

Home Island 6.7 0.95

Pulu Ampang 1.8 0.06

Pulu Wa-idas 0.7 0.02

Pulu Blekok 1.1 0.03

Pulu Kembang 1.6 0.04

Pulu Wak Banka 2.4 0.22

Pulu Pandan 3:9 0.24

Pulu Siput 2D 0.10

Pulu Labu 1.3 0.04

South Island 28.5 3.63

Pulu Klapa Satu 0.5 0.02

Pulu Blan Madar 0.7 0.03

Pulu Blan 0.8 0.03

Pulu Maria 0.7 0.01

West Island 38.5 6.23
Table 2. Radiocarbon dating results on reef island sediments, West Island and North

Keeling Island.
Beta Sample Island Depth of Material Conventional
No. No. sample radiocarbon age
(cm)

59845 NKI-60 North Keeling 60 Coral shingle 3060 + 60
59846 WI-T1-P295 West Island 95 Coral shingle 570 + 60
59847 WI-TI P3 85 West Island 85 Coral Shingle 1990 + 70
59848 WI-T1 P3120 West Island 120 Coral Shingle 2010 + 60
59849 WI-T1 P3160 West Island 160 Coral Shingle 2110+ 60
59850 WI-T1 P4140 West Island 140 Coral Shingle 2130 + 60
59851 WI-T1 P7 75 West Island WS Coral Shingle 2710 + 90
59852 WI-T1P260 West Island 60 Coral Shingle 3030 + 70
59853 WI-T1 P4140 West Island 140 Coral Shingle 4280 + 70
59854 WI-T1 P1200 West Island 200 Coral Shingle 420 + 50
59855. WI-T3P270 West Island 70 Coral Shingle 1970 + 70
59856 WI-T3P455 West Island 55 Coral Shingle 3100 + 70

Note: Radiocarbon ages determined by Beta Analytic have not been corrected for 0 C}3 or for
environmental reservoir effect. These corrections are of similar magnitude (c 400 years), but

cancel each other out.

Thus these Beta dates are more-or-less comparable to the
environmentally-corrected ages given in the previous chapter.

17

DIRECTION ISLAND

WORKHOUSE

| Conglomerate platform

PRISON
Beachrock

= Coconut woodland

Scaevola scrub

500 metres

Figure 1. Direction Island, mapped from 1987 aerial photography.

18

Open coconut woodland
Coconut woodland
Calophyllum woodland
Pandanus

Sand

Shingle

Rubble

Beachrock

Artificial marine structures

Conglomerate platform

SOUTH
KEELING

ISLANDS

500 metres

Figure 2. Home Island mapped from 1987 aerial photography.

ee al

PULU AMPANG
KECHIL

PULU CHEPELOK -«:

ye
ae

19

SOUTH

KEELING

ISLANDS

Rubble

Sand and shingle

Intertidal sand
Conglomerate platform
Coconut woodland

Scaevola scrub

Scaevola and Tournefortia scrub

Pemphis scrub PULU ‘SIPUT-.

Cordia stumps

Barringtonia

500 metres

Figure 3.
mapped from 1987 aerial photography.

Islands of the eastern rim of the atoll from Pulu Ampang to Pulu Labu,

20

|
;
:

SOUTH ISLAND

|

Sand

Intertidal sand

:*:) Sand and shingle

“SK | Beachrock

++ Conglomerate ramp

Conglomerate platform

Coconut woodland

| Low coconut woodland
hSsd
ee

ne

Scaevola scrub Lagoon

Pemphis scrub

0 500 metres
a aaa refi]

Figure 4. South Island, northern section, mapped from 1987 aerial photography.

21

-Kydes3ojoyd [esse 186

qnios ejOneeos ISS
qnios siydwad LZ

puejpoom wnj|Aydojedg pue jnuod0D nage

pue}poom wnjijAydojeo ae

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pue|poom jnuos0D =

aNv1sI

HLNOS

| wos poddew ‘uonoes wioyjnos “purys] YINoS ¢ oInsIy

(ia sehen Geel Ge ee
wuojjejd 9a}ye1aw0j;bu0D se a cue i

yoouyoeag |Z

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| ce |
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NS SQNVISI ng
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eS
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)
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D Ny 7
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GEN
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é ry

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NvIg ind

22

500 metres

SOUTH
KCELING

ISLANDS

'\ Transmitter ——

aerials

Lagoon

WEST ISLAND

ERS
Clearing),

:) Sand

Intertidal sand

Sand and mud

Beachrock

Conglomerate platform

Coconut woodland

Calophyllum woodland

Barringtonia

Scaevola scrub

Pemphis scrub

Figure 6. West Island, northern section, mapped from 1987 aerial photography.

23

500 metres

]

WEST

|
ISLAND i

7

I.

$7
f\}Quarantine/

| Station f

Sand

Intertidal sand

Sand and mud

Beachrock

me Conglomerate platform |

= Coconut woodland Lagoon
= Low coconut woodland x
S
Scaevola scrub BN
NIN N\
Pemphis scrub \
essa
rary
ae
SS
=
SEE
AUTH SS
KEELING YS EZAN q
ISLANDS. eS
YW

Figure 7. West Island, central section, mapped from 1987 aerial photography.

24

SSeS
sajjaW OOS

VAVUYVIN

nind

yoouyoeag

SONVISI

ONIND3y

HANGS

ajbulys pue pues :

pues yepreyuy a

wes [_]

JUBWAI}}AS

\

\

\

aN
N \N\
‘ VA

ZS

HORSBURGH ISLAND

Sand

“| Sand and shingle

Beachrock

Conglomerate platform
Tidal pool

Open coconut woodland
Coconut woodland

Calophyllum woodland

Cordia woodland

Cordia stumps

Rhizophora

”’| Pemphis scrub
500 metres
' Scaevola scrub

Figure 9, Horsburgh Island, mapped from 1987 aerial photography.

26

‘suonjoes poXoains yim ‘Aydessojoyd [ese / 86] Wor poddew ‘pues] 3ul[soy YON

sesjaw OOSt

a|6buius pue pues

aj6uiys
pnw

pues

ayesawojbu09g S

woyejd ajesawo;bu05
yoouyoeag

ssi] Jeuoisosy

pues jepijayu|

pues

aj6ulus

9igqny

=

sauyjaw oz

GNV1ISI ONINSSyN HLYON

ye]} wniansas |*

qnios elJojauuno] pue ejOAeeOS fas]

qnios elojauinoy
Foa)

Pue|POOM eIPIOD

qnios RB|/OABPDS

qnios siydwad

PUE|POOM eIUOSIq Pue JNUOD0D

PUP|POOM eIUOSIG

pue|poom jnuos0D

‘OT Ounsi.y

wnjep
BHuljaay
YON

Z sayew >

—

vA

\
)
\

sae Tae 4s S
y,
K xs
F . Ss
‘i ‘i A sa}jaoeuel

-\

«— jebiyv

| sea ‘Fe a OF
saujaw 00S

TP

SOUTH

KEELING <i

ISLANDS

99°50E

ES Sand
Sand and shingle

fo Shingle

* e,| Rubble

-_—| Mud

EW Beachrock
Conglomerate platform
[mm ] Reet flat

SS) rl ee ial mas ees

metres

D

Di.

metres

metres

200

metres

200 0

metres

metres

Figure 11.

a si vena n Essen = yee n \ i re n msl
0 200 400 600 800 1000 1200
metres

Surveyed sections across islands on the eastern atoll rim.

28

metres
3
o
o
= KEELING
oO
(=
ISLANDS
msi — =f L
200 400
metres

metres

==>.

metres as Sand

metres
D
cS
ley
S
0)

————
[| Beachrock
metres
Conglomerate platform
4 F [ mm | Reef flat

metres

msl if eee je eee Le = Se = aye 3
Bs 200 400 600 800 1000
metres

metres

=e = =
600 800

metres

Figure 12. | Surveyed sections across West and Horsburgh Islands.

29

Sand
xs Conglomerate platform

30% Shingle

|
; 44 280=70
200 300 400 500 E

P3

metres

ty
"Ny i]
1990-704 ea)
aod Il ty r
2010-608) te i
t ie
HI

2130-60

mad

2110-60 b!
ih

4

+ aaa + +
300 400 500 600 700 800 900 1000

Figure 13. Cross-section and pits from three transects on West Island (see Fig. 12 for
locations), showing radiocarbon dates (see Table 2).

Aerial photograph of Direction Island, 1987 (reproduced by permission of
the General Manager, Australian Surveying and Land Information Group,
Department of Administrative Services, Canberra).

Figure 15.

3)

Aerial photograph of Pulu Ampang and neighbouring islands, 1987
(reproduced by permission of the General Manager, Australian Surveying
— and Land Information Group, Department of Administrative Services,

Canberra).

32

Figure 16.

= jim i 4

Aerial photograph of Pulu Pandan and neighbouring islands, 1987
(reproduced by permission of the General Manager, Australian Surveying

and Land Information Group, Department of Administrative Services,
Canberra).

33

Figure 17. _ Aerial photograph of eastern end of West Island, 1987. Radiocarbon dates
on coral shingle indicate the progressive buildout of the spits (reproduced by
permission of the General Manager, Australian Surveying and Land
Information Group, Department of Administrative Services, Canberra).

34

Pe. 2

Figure 18. Aerial photograph of Horsburgh Island, 1987 (reproduced by permission of
the General Manager, Australian Surveying and Land Information Group,
Department of Administrative Services, Canberra).

oo

Figure 19.

a: Oceanward shore of Direction Island; rubble is from ruins of Cable
Station, b: View looking North from Home Island. Conglomerate platform
in middle distance is where Button Islets were, Prison Island is in the middle
of the photograph and Direction Island in the distance, c: Conglomerate
platform on Ampang Island, d: conglomerate platform on Pulu Pandan; it
appears to consist of a shingle conglomerate layer overlying typical
conglomerate platform, e: Conglomerate ramp, oceanward shore of South
Island, f: Sandy and beach dune on the southern side of South Island.

Figure 20.

a: Telok Jambu, West Island viewed from the north, b: Telok Kambing, West
Island viewed from the west, c: Sheltered telok on South Island with stand
of Pemphis on ridge at the mouth of lagoonlet, d: Ocean-dipping bedding
revealed in trench on Home Island, e: Rubble-strewn shoreline on Pulu Wak
Banka, f: Arcuate ridges, southern North Keeling; these appear to have been
termed former reef margins by Guppy, but are reinterpreted as beach
conglomerate marking foot of former rubble-strewn beaches.

ATOLL RESEARCH BULLETIN

NO. 404

CHAPTER 6

VEGETATION AND FLORA OF THE COCOS (KEELING) ISLANDS

BY

D.G. WILLIAMS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 6

VEGETATION AND FLORA OF THE COCOS
(KEELING) ISLANDS

BY

D.G. WILLIAMS *

ABSTRACT

The vegetation and plant species occurring on the 22 vegetated Cocos (Keeling) islands have been
classified numerically based on sample plots for the large islands as well as from checklists developed for
each island from extensive reconnaissance. The vascular flora of about 130 species comprises
approximately 50% native species, but there are no endemic species described. Most of the 69 introduced
species are to be found on the larger settled islands and only one of these species has spread to the smaller
islands. The relationship between island area and indigenous species richness shows a close fit to a power
relationship. The more remote island of North Keeling has a distinct species composition compared to
similar-sized islands of the main atoll.

The pre-settlement vegetation has been extensively modified for coconut plantations, except for
certain parts of North Keeling, where tall Pisonia grandis - Cocos nucifera forest occurs with small
amounts of Cordia subcordata and other species. These forests are fringed on the lagoon shore by Pemphis
acidula tall shrubland and on the exposed ocean shores by Argusia argentea shrubland. Each of these
communities support breeding colonies of seabirds. On the main atoll, remnant vegetation occurs most
commonly along the strand and in some places appears to be relatively recent. Many species on the Cocos
(Keeling) atolls are restricted in their distribution there. In some cases these represent relict distributions,
whilst a few could be considered to be pioneer populations.

INTRODUCTION

The Australian external Territory of the Cocos (Keeling) Islands is situated in the
north-eastern Indian ocean at 12°S, 96°, is 2400 km north-west of North West Cape on
the Australian mainland and 960 km south-west from Java. The Territory consists of two
coral atolls about 25 km apart with a maximum ground elevation of 9 m above mean sea
level. The smaller, northern atoll, is known locally and historically as Keeling Island and
was inhabited intermittently and on a seasonal basis between ca. 1830 and 1929 (Gibson-
Hill 1948). The main atoll, which continues to be known by various names and is here
referred to as the Cocos atoll, consists of 21 vegetated islands, some of which have been

Applied Ecology Research Group, University of Canberra, P.O. Box 1,
Belconnen, Australian Capital Territory, 2616.

2

inhabited since 1827 and all of which have been extensively cleared for coconut
plantations. Keeling Island (North Keeling), on the other hand, has retained more natural
vegetation and is still a major seabird rookery for at least six species (Stokes et al. 1984).

As the only atolls in the eastern Indian Ocean, and being relatively recently settled,
these islands are of considerable scientific interest, but their isolation has prevented
intensive scientific study. A series of naturalists have visited, the most notable being
Charles Darwin for 11 days in 1836 (Darwin 1845); H.O. Forbes for 22 days in 1879
(Forbes 1879, 1885); H.B. Guppy for 5 months in 1888 (Guppy 1889); F. Wood-Jones
for a year in 1905 (Wood-Jones 1912); and C.A. Gibson-Hill for 11 months in 1941
(Gibson-Hill 1950). Gibson-Hill (1948) presented the only systematic account of the
vegetation in the form of a description of dominants and a sketch map of the plant
communities of Keeling Island. Major plant collections have been made by C. Darwin
(Henslow 1838), H.O. Forbes, F. Wood-Jones (1912), H.B Guppy (1889), I. Telford
(1985) and the author in 1986-7.

The Cocos (Keeling) Islands lie on an isolated spur of the submarine Ninety-East Ridge
and are formed on a volcanic base rising from a depth of 5,000 m, with an unknown
thickness of coral over the base (Jongsma 1976). Large solution and/or collapse dolines
up to 20 m deep cover the south-eastern bed of the Cocos lagoon and possibly indicate a
considerable depth of underlying limestone. Most of the islands are developed from coral
sand, shingle and rubble deposits over a breccia platform that is just above mean sea
level (Woodroffe et al. 1990) and beach rock commonly outcrops on the more exposed
sandy shores.

The highest elevations occur on the south and east ocean shores where sand and shingle
deposits rise briefly to a maximum of 9 m forming a single elongate coastal dune best
developed along the entire length of Pulu Atas as a sand dune and on North Keeling as a
shingle ridge. Apart from these dunes, most of the islands are less than 3 m above sea
level. The most leeward island of the Cocos atoll (Pulu Luar) displays a more complex
geomorphology, being a mature moat island (Stoddart & Steers 1977) with a small
saltwater lagoon. Jacobson (1976) studied the freshwater lens on Pulu Selma (Home
Island) and concluded that the minimum width of island to sustain an exploitable
Ghyben-Herzberg lens was 400 m. However during the present study in April and May
1986, fresh water was observed in wells on islands down to 100 m width (see Falkland
1988). The only naturally occurring surface freshwater is at the seasonal swamp known
as Bechet Besar on the north-east shore of Pulu Panjang (West Island). On Pulu Luar
(Horsburgh Island) there is a seasonal groundwater swamp identified by a ground layer
of Mariscus javanicus.

Meteorological records for various periods and locations on the Cocos atoll are
available as a composite record from 1902, at least for rainfall. The annual average
rainfall for the period 1902-1982 was 1994 mm with a range from 1099 mm to 3288 mm
and a median of 1969 mm. Mean monthly rainfall varies from 81 mm in October to
256mm in April, with the dry season extending from September to December.
Temperatures and humidities vary little throughout the year with an absolute annual
temperature range from 21°C to 31°C. The wind régime is one of predominantly south-
east trades for over 300 days per annum. Wind direction frequency analysis show south-
easterly winds dominating from December to March whilst for the rest of the year there
is a strong easterly component as well. Cyclone frequency within a five degree cell is
about 0.25 in the region. Cyclones have passed near enough to the main atoll to cause
damage in 1862, 1876, 1893, 1902, 1909, 1944, 1968, 1973 and 1988.

3

The purpose of the present survey was to establish the present composition of the
flora on an island basis and to analyze the floristic and vegetation patterns of the entire
Territory. The delineation of communities, relict stands and rare species distributions will
serve as a basis for land use planning, the establishment of conservation priorities and the
development of management aims.

METHODS

Circular sample plots of radius 10m were located on the six largest islands
(Keeling, Luar, Tikus, Selma, Atas, Panjang) along transects selected to maximize the
detection of vegetation and floristic change along environmental gradients (Gillison &
Brewer 1986). The major environmental gradients considered in the layout of the
transects were:-

- ocean strand to lagoon strand;
- potential for a freshwater lens; and
- ocean coastline aspect.

Transects were oriented at right angles to the ocean coastline (Fig. 2) and sample
plots were positioned on both strandlines (ocean/reef and lagoon) and at 60 m intervals
along the transect; unless there was a change in the height or composition of the top
stratum, in which case additional plots were selected. In each plot, plant species present
were recorded, as well as litter depth, soil surface texture and canopy height and
dominants.

All vegetated islands were surveyed (Pulu Pasir supports only occasional sprouting
coconuts and was not included). For consistency, the Cocos-Malay names for the islands
have been used throughout. Several islands have two Malay names apparently related to
their origin from separate islands. In this report, Pulu Selma includes Pulu Gangsa
(joined by human intervention) and Pulu Cepelok includes Pulu Wak-Banka, apparently
joined by storm deposits before settlement in 1825. During the course of systematic
collecting on the islands, the presence of each species on each island was recorded as
well as an overall estimate of the species abundance on the island. A six-point ordinal
abundance scale from very rare (less than 10 plants sighted) through rare, occasional,
frequent, common to abundant was used. A complete set of voucher specimens is
deposited at the Australian National Botanic Gardens (CBG) and nomenclature follows
the Flora of Australia (1993).

The floristic and quantitative data were primarily analyzed using the Pattern
Analysis Package (PATN, Belbin 1992) at the C.S.I.R.O. Division of Water and Land
Resources. The dissimilarity coefficient used for sites was the Bray-Curtis measure or the
Kulczynski coefficient and the two-step procedure (Austin & Belbin 1981) was used for
the between-species dissimilarity. Cluster analysis was hierarchical agglomeration using
UPGMA fusion with B set to -0.1 to minimize space distortion (Belbin 1992).

Vegetation patterns were also derived from panchromatic aerial photographs taken
in 1976 ata scale of 1:44,400 (R.A.A.F. Film No. 8737) and 1987 colour photography at
1:10,000 (A.S.O. Film SOC760). Interpretation was done using a Zeiss Interpretoscope
and transferred to a base map using a Zoom Transfer Scope. Island areas were measured
off the R.A.S.C. Series R811 Cocos Island Sheet Special (1:25,000).

RESULTS

THE FLORA

Exclusive of plants found only in cultivation the total vascular species count for
these islands is 130 (Appendix 1). Given the variation in sampling intensity by past
collectors (Table 1), it is difficult to be certain which species are introduced, except by
examination of their biology, biogeography and present-day distribution as well as the
historical record. Species found only in heavily disturbed areas and often on one or two
large islands only, have usually been regarded as introduced in this analysis, and these
account for about 50% of the flora (Table 2). Most of these species are pantropical herbs
(Table 2) found on Pulu Panjang and many were probably introduced since the airfield
was built on Pulu Panjang in 1944.

The vast majority of the native species are Indo-Pacific strand plants that are
predominantly sea-dispersed. There are no endemic species described at this stage, save
for the variety cocosensis of Pandanus tectorius (Appendix 1). Of the 19 vascular species
collected by Darwin (Henslow 1838) all but one have been recorded by recent collectors.
Most are still common except for Cordia subcordata, Achryanthes aspera, Neisosperma
oppositifolia and Laportea aestuans (Appendix 2).

ISLAND FLORISTICS
INDIGENOUS SPECIES

The relationship between island area and indigenous species richness (Fig. 2)
shows a closer fit to a power relationship (r? = 0.87) than a logarithmic one. When exotic
species are included, the power relation is still a good fit (r? = 0.82), as the larger islands
are also the most disturbed and colonized by exotic species.

Cluster analysis for the 22 islands (i.e. including Keeling) based on the species
abundance scores shows a clear grouping of islands by size, with Keeling being the most
distinct floristically (Table 3, species groups A & E). The strand species form a distinct
group (Table 3, species group D) well represented on all but the two smallest islands,
Beras and Ampang Kecil, which have areas less than 0.5 ha and support only three of the
six common strand species. This strand group comprises Argusia argentea, Pemphis
acidula, Guettarda speciosa, Cocos nucifera, Scaevola taccada and Ipomoea macrantha,
all of which have marine dispersal powers.

Some species were found almost exclusively on islands larger than 20 ha, and most
of this group were more abundant on Keeling (Table 3, group A). These included the
trees Cordia subcordata, Hernandia nymphaeifolia and Pisonia grandis as well as
Achryanthes aspera, Dicliptera ciliata, Portulaca oleracea, Boerhavia repens,
Stenotaphrum micranthum, Lepturus repens and Sesuvium portulacustrum.

Species group B (Table 3) represents those species common on the larger Cocos
islands but absent or less abundant on Keeling. Of those species which do occur on
Keeling, most are rare there, often recorded from one or two locations only. Species
group C consists of three species each found at just a single site on Pulu Panjang. These
are Lepturopetium sp., Ximenia americana and Enicostema axillare (Appendix 2).

EXOTIC SPECIES

Only one exotic species, Turnera ulmifolia, has spread to all the islands of the
Cocos atoll, and it is usually abundant wherever it has established (Table 4). The large
but relatively unsettled Pulu Atas has been colonized by six exotic species and five have
reached Keeling. Most exotic species are confined to the four large islands that have had
or still have intensive settlement. Thirty two of the 63 exotic species occur only on Pulu
Panjang and/or Pulu Selma (Table 4, groups C & D, part of A) and nineteen occur on
Pulu Panjang only (group C). At the other end of the size scale, the four islands without
exotic species (Beras, Blan, Blekok, Jambatan) are all less than 2.5 ha.

VEGETATION PATTERN ON KEELING

Analyses of the transect plot data for Keeling were done with the total set of 26
species recorded in 65 plots along 11 transects. Another 10 species were recorded for
North Keeling in reconnaissance. The floristic classification analysis does not exactly
correspond with the dominance-based units able to be mapped from aerial photography
and ground checking.

Stands of Pemphis acidula tall shrubland (2-4 m) and Cordia subcordata tall
shrubland (3-6 m) occur close to the lagoon shore and are commonly mono-specific
(Table 5, site groups 1, 2 & 3), and, where there are finer sediments accumulated, a
Sesuvium portulacustrum herbland is developed (Table 5, group 1), often lying between
or within the two former types (Fig. 3). Site group 4 (Table 5) is characterised by
exposed shore halophytes, such as Portulaca oleracea, Lepturus repens and Boerhavia
repens, Cocos is absent.

Site groups 5 to 8 highlighted floristic sub-units within the closed forest stands
characteristically dominated by Pisonia grandis and/or Cocos nucifera (Table 5, Fig. 3).
Group 5 contains the beach halophytes (species group A), group 6 has an understorey of
forest mesophytes (species group C), group 7 are stands of pure Cocos and Pisonia,
while group 8 are virtually pure Pisonia.

Group 5 mainly represents relatively richer plots (s = 6.7) found within 20 m of the
shore which have strand forest dominated by Cocos along with halophytic shrubs and
herbs which typically occur only near the shoreline. Pisonia grandis and Stenotaphrum
micranthum are constants and the former may be co-dominant on sheltered shores. Some
plots in this class fall within areas which are mappable as Pisonia shrubland occurring on
exposed shores usually behind a beach-fringing Argusia shrubland.

Site group 6 (Table 5) corresponds with relatively species-poor areas of forest
(mean richness of 3.9) dominated by Cocos nucifera and/or Pisonia grandis. The
associated species include broad-leaved plants such as the climber Canavalia cathartica,
Morinda citrifolia, Rivina humilis and Carica papaya. Sites in groups 9 & 10 contain
species which are uncommon on North Keeling (species groups A & D).

Many species on Keeling have a restricted distribution and most of these are found
on the northern peninsula at the entrance to the lagoon or on the north-west lagoon shore
and adjacent habitats. The same pattern is evident for the species recorded in transect
plots. The richest floristic units, apart from the herblands, are the forest types found near
the lagoon entrance and on the northwest side of the island.

6

VEGETATION CHANGE

A comparison of Fig. 3 with the vegetation map of Keeling Island produced by
Gibson-Hill in 1941 (Gibson-Hill 1948) shows geomorphic and a a changes
evident over the intervening 45 years.

The west-building peninsulas at the lagoon entrances have extended considerably
into the lagoon. On the northern peninsula the Argusia shrubland mapped by Gibson-Hill
is possibly the small area in a similar position mapped in 1986, since it is on a rocky
substrate which may have conferred a degree of site stability. The southern arm has a
similar clump of Argusia that has apparently extended and been flanked by Cocos and
Pemphis. Observations on sand and shingle bars in the lagoon entrance channels show
that Argusia is the first woody plant to colonize such places in exposed locations and
Pemphis does the same on more sheltered shores. Both peninsulas show a definite
sequence of changing dominance along their strands from Argusia, Pemphis and Cocos
on the younger shores to Cordia and Pisonia on the older ones, reinforcing the
interpretation of rapid development of these peninsulas. Being more sheltered, the
southern peninsula has developed an area of Pisonia forest on its southern end, perhaps
largely since 1941.

Another change in the vegetation since 1941 is the loss of the Argusia zone along
the southwest coastline and possibly on the southeast also. Both locations have 4-5 m
high shingle ridges with their seaward faces lying at the repose angle, and show evidence
of episodic deposition of shingle into the Pisonia zone suggesting storms have removed
the Argusia.

Gibson-Hill (1948) mapped an area of open grassland on the south-eastern lagoon
shoreline which he said was a breeding habitat for shearwaters (Puffinus sp.). These birds
have not been seen on the island for some years (Stokes et al. 1984) and this grassland
has now become in parts an open shrubland colonized by Pemphis, Pisonia and Argusia
to 3 m high.

VEGETATION OF THE COCOS ATOLL

Cluster analysis of the 106 sample plots on the larger islands (containing 52
species, native and introduced), produced at the ten-group level five major site groups
and five further groups represented by a few sites each (Table 6). Floristic definitions of
the major site groups emphasise variation in the coconut woodlands and forests in
relation to ground layer composition and location relative to the ocean and lagoon. On
the most exposed southern and eastern strands of Pulu Atas there are areas of Argusia -
Scaevola shrubland and patches of Lepturus - Triumfetta herbland on the sand and
shingle ridge topping the beach.

The minor site groups reflect distinctive relict communities, mainly on Pulu
Panjang and Pulu Luar, where strand trees have survived land clearing or colonized
recent deposits. Species such as Calophyllum inophyllum, Guettarda speciosa, Hibiscus
tiliaceus and Barringtonia asiatica characterize these sites and their distribution over the
Cocos atoll is very restricted (Fig. 1, Appendix 2). These species occur scattered along
the lagoon shores and on the sheltered west shore of Pulu Panjang, mostly as single trees
or small clumps. The largest remaining stands of these species are to be found on Pulu
Panjang along the northwest shore and adjacent to the swamp at Bechet Besar; along the

7

lagoon shore opposite the northern end of the runway; and on the southern lagoon shore
of Pulu Luar (Fig. 1).

Pemphis acidula shrubland forms 2-4 m high shrublands scattered all along the
lagoon shore, particularly in areas where sand deposition is occurring (e.g. at Tanjong
Klikil at the east end of Pulu Panjang) and also at the lagoonward edge of intertidal
sandflats. No other species of plants grow in these offshore strands except for an
occasional coconut seedling and epiphytic mosses and lichens.

DISCUSSION

FLORA

Island floras originate from a variety of sources depending on their geographic
location and suitability of their habitats for immigrant diaspores. The origins of the
Cocos (Keeling) biota have long fascinated biologists, particularly those who have
examined their plants and insects (see Guppy 1890, Holloway 1982).

Renvoize (1979) suggested that island structure in terms of elevation and
geological substrate are key factors in determining the richness of island floras. In this
respect, the Cocos (Keeling) islands bear the greatest similarity to the central Indian
Ocean islands (Laccadive, Maldive, Chagos) and to only some of the western Indian
Ocean group (Cargados Carajos, Tromelin, Agalega, Amirante group, Alphonse,
Gloriosa, Europa and Farquhar group). All these low islands have evolved in isolation
from a continent, through the combined forces of vulcanism, subsidence and coral
growth, and presently rise less than 10 m above sea level.

The low habitat diversity of these islands leads to a flora characterized by very low
endemicity with indigenous taxa of pantropical or Indo-Pacific distribution dominating
(Renvoize 1979). Cocos (Keeling) is no exception to this general pattern; it has no
endemic flora save for the variety cocosensis of Pandanus tectorius, and with 61
indigenous species (Table 2), is comparable with the Laccadives (40 indigenous species),
the Addu atoll in the Maldives (52 species) and the Chagos group (ca. 100 species)
(Renvoize 1979). It is also similar in species richness to western Pacific atolls such as
Nui (44 species) and Kapingamarangi (50 species) (Woodroffe 1986).

The mechanisms of natural dispersal to oceanic islands include wind, ocean
currents, birds and bats. Undoubtedly all of these have contributed to the Cocos flora,
(even bats have been occasionally sighted, Marlow 1970), but the only agent for which
evidence is certain is that of oceanic drift. Most of the strand species are found as seeds
on beaches and there is a further component of the flora that is found only on the drift
line (Guppy 1890). The main currents around Cocos (Keeling) are westward and would
be expected to derive propagules from northern Australia, Torres Strait and Java. These
currents are reinforced for most of the year by the prevailing southeast trade winds.

ISLAND RICHNESS AND COMPOSITION

The power relationship established between indigenous species richness and island
area (Fig. 2) is similar to that reported for Nui atoll in the Pacific (Woodroffe 1986) and

8

for the lagoonal islands of Aldabra (Hnatiuk 1979). None of these three species-area
relationships support the notion of the small-island effect suggested for Kapingamarangi
(Niering 1956, 1963), where very small islands tended to have area-independent species
richness.

The six commonest strand species are not always present on the smaller islands and
show an increase in frequency of occurrence up to an island size of 10 ha, and are always
present above this area (Table 3). If one sets aside these species, i.e. Argusia argentea,
Pemphis acidula, Guettarda speciosa, Cocos nucifera, Scaevola taccada and Ipomoea
macrantha, then the similarities between the smaller islands are very low. Among the 20
other species, there are only 41 occurrences on the 16 islands smaller than 25 ha. The
presence of these species was often correlated with minor and possibly ephemeral
habitats; e.g. Hibiscus tiliaceus on a small sheltered lagoon-facing shore of Pulu
Jambatan where a channel had cut across the prograding western (lagoon) side of the
island; Suriana on recently formed sandy spits extending lagoonwards on Pulu Siput; and
Mariscus javanicus, Fimbristylis cymosa and Lepturus repens where lagoon shorelines
distant from inter-island channels had relatively flat shingle embayments at upper tide
levels. These observations support the idea that habitat diversity needs to be considered
in modelling species richness on islands (Buckley 1982).

Dispersal routes may also contribute to differences between the smaller islands,
especially where islands are more likely to receive a high density of propagules. For
example, Pulu Labu probably intercepts a higher number of propagules because of its
position at the tip of Pulu Atas, where the equatorial current flows northward along Pulu
Atas then some sweeps into the lagoon. An exceptionally high abundance of drift seeds
was found to occur on the sand dunes at the northern tip of Pulu Atas and in a similar
situation on the ocean beach of Pulu Gangsa. This may help to explain the occurrence of
Calophyllum, Barringtonia and Neisosperma on the former island and on no other small
islands, save for a single Calophyllum on Pulu Beras. The latter is also an island which is
well situated to receive propagules concentrated by northward transport along the ocean
shores of Pulu Selma. However these data are insufficient to suggest such islands have
more species for their area, and there are presumably other factors operating, such as
stability and age of an island.

Amongst the six larger islands, Pulu Atas has a relatively low richness for its area,
possibly related to its more uniform geomorphic structure, rugged ocean coastline and
lack of currents flowing along its lagoon shores (although they would have done so in
times past before channels closed off).

North Keeling has seven species not found on the main atoll but is also different in
composition from the other large islands. Some species (Table 3, group A) are relatively
more abundant there, either because of greater areas of suitable habitat on Keeling (e.g.
for Boerhavia repens and Portulaca oleracea in exposed herblands; Sesuvium
portulacustrum in saltmarshes; Stenotaphrum micranthum, Achryanthes aspera,
Dicliptera ciliata in the Pisonia grandis rainforest); or due to clearing over the last 160
years (e.g. Cordia subcordata, Hernandia nymphaeifolia and Pisonia grandis). Species
group E (Table 3) found only on Keeling may represent in large part the extreme effects
of vegetation clearance on the southern atoll. The restricted distribution of Thespesia
populnea (in a clump of six individuals on Pulu Tikus and in a small mixed stand with
Cordia on Pulu Luar), probably also represents a relict distribution resulting from
extensive cutting in the past, as the bark fibres were once used for netting (Gibson-Hill
1947).

ACKNOWLEDGEMENTS

This study was initiated in 1986 whilst the author was on study leave from the
University of Canberra (then Canberra College of Advanced Education). I am grateful to
the Cocos (Keeling) Islands Council for its interest in the project and for allowing access
to all parts of the Territory; to the Administration of the Territory for providing field
logistic support; and to the Bureau of Flora and Fauna and the Australian National
Botanic Gardens who supported the plant collecting. Ian Telford provided a plant species
list and identified voucher collections. Amat Noor bin Anthoney, Peter Goh and Tony
Stokes helped with survey work on the atolls. The C.S.I.R.O. Division of Water and
Land Resources provided facilities for numerical analysis and I am grateful to Mike
Austin, Lee Belbin, Dan Faith and Peter Minchin for advice on these analyses.

REFERENCES

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floristic analysis. Aust. J. Ecol. 7: 75-89.

Belbin L. 1992. PATN Analysis Package: Technical Reference Manual. Division of
Wildlife and Ecology, CSIRO, Canberra.

Birch, E.W. 1866. The Keeling Islands. Proc. Roy. Geog. Soc. N.S. 8: 263-265.

Buckley, R. 1982. The habitat-unit model of island biogeography. J. Biogeog. 9: 339-
344.

Darwin, C. 1845. Journal of researches into the natural history and geology of the
countries visited during the voyage of H.M.S. Beagle round the world, under the
command of Capt. Fitz-Roy, R.N. John Murray, London.

Faith, D.P., Minchin, P.R. & Belbin, L. 1987. Compositional dissimilarity as a robust
measure of ecological distance. Vegetatio 69: 57-68.

Falkland, A.C. 1988. General Report. Vol. 1. Cocos (Keeling) Islands Water Resources
and Management Study. Hydrology and Water Resources Unit, A.C.T. Electricity
and Water, Report No. 88/12.

Flora of Australia 1993. Volume 50, Oceanic Islands 2. Australian Government
Publishing Service, Canberra.

Forbes, H.O. 1879. Notes on the Cocos or Keeling Islands. Proc. R. Geog. Soc. 1: 777-
784.

Forbes, H.O. 1885. A Naturalist's Wanderings in the Eastern Archipelago. A narrative of
travel and exploration from 1878 to 1883. Sampson Row, London.

Fosberg, F.R. & Sachet, M.H. 1982. Micronesica 18: 73.

Gibson-Hill, C.A. 1948. The island of North Keeling. J. Malay. Br. Roy. Asiatic Soc.
211: 68-103.

10

Gibson-Hill, C.A. 1950. A note on the Cocos-Keeling Islands. Bull. Raffles Mus. 22: 11-
28.

Gillison, A.N. & Brewer, K.R.W. 1986. The use of gradient directed transects or
gradsects in natural resource surveys. J. Env. Mgt. 20: 103-127.

Guppy, H.B. 1889. The Cocos-Keeling Islands. Parts I-III. Scot. Geog. Mag. 5, Part I,
281-297, Part I, 457-474, Part II, 569-588.

Guppy, H.B. 1890. The dispersal of plants as illustrated by the flora of the Keeling or
Cocos Islands. J. Trans. Victoria Inst. Lond. 24: 267-303.

Henslow, J.S. 1838. Florula Keelingensis. An account of the native plants of the Keeling
Islands. Nat. Hist. Mag. 1: 337-347.

Hnatiuk, S.H. 1979. Numbers of plant species on the islands of Aldabra Atoll. Phil.
Trans. R. Soc. Lond. B 286: 247-254.

Holloway, J.D. 1982. On the Lepidoptera of the Cocos-Keeling Islands in the Indian
Ocean, with a review of the Nagia linteola complex (Noctuidae). Entomologia
Generalis 81: 99-110.

Jacobson, G 1976. The freshwater lens on Home Island in the Cocos (Keeling) Islands.
Bureau of Mineral Resources Australian Journal of Geology and Geophysics. 1:
335-343.

Jongsma, D. 1976. Review of geology and geophysics of the Cocos Islands and the
Cocos Rise. Bureau of Mineral Resources, Australia, Record 1976/38
(unpublished).

Marlow, B.J. 1970. A record of a Mastiff Bat, Tadarida plicata, from the Cocos
(Keeling) Islands, Extrait de Mammalia, 34.

Niering, W.A. 1956). Bioecology of Kapingamarangi Atoll, Caroline Islands: terrestrial
aspects. Atoll Res. Bull. 49: 1-32.

Niering, W.A. 1963. Terrestrial ecology of Kapingamarangi Atoll, Caroline Islands.
Ecol. Monogr. 33: 131-160.

Renvoize, S.A. 1979. The origins of Indian Ocean floras. in Plants and Islands. (ed. D.
Bramwell). pp107-129. Academic Press, London.

Stoddart, D.R. & Steers, J.A. 1977. The nature and origin of coral reef islands. In Biology
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pp59-105. Academic Press, New York.

Stokes, T., Sheils, W. & Dunn, K. 1984. Birds of the Cocos (Keeling) Islands, Indian
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11

Wood-Jones, F. 1912. Coral and Atolls: a history and description of the Keeling-Cocos
Islands, with an account of their fauna and flora, and a discussion of the method
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12

Table 1. Sampling intensity and the number of native and naturalized (not
horticultural) vascular plant species recorded by major collectors and
naturalists on the Cocos (Keeling) Islands.

Collector Year Period of visit Islands visited ’ Number of species

C.R. Darwin 1836 10 days Cocos atoll 21

H.O. Forbes 1879 22 days Cocos atoll 38

W.E. Birch 1885 8 days Cocos atoll 11

H.B. Guppy 1888 10 weeks Both atolls 53

F. Wood-Jones 1909 15 months Cocos atoll 46

LR. Telford 1985 2 weeks Panjang, Tikus, Atas, 93
Selma, Keeling

D.G. Williams 1986/7 9 months All, including Keeling 130

Table 2. Life forms of the native and naturalized flora.

Origin Climber Forb Graminoid Seagrass Shrub Tree. otal

Native 7 13 11 3 9 18 61

Naturalized 3 29 2 0 10 6 69

Table 3. Two-way classification for native species occurring on all islands.
Classification based on abundance data standardised by species
maximum. The first four letters of the generic name and specific epithet
are read vertically. Numerical values represent the abundance scores
standardised by species maximum.

Island Species groups

BOSS ASSSe> E, BOSSSS2309355 Be — s-=--> <C> <-D--> <-E-->

| ABPHDSASACPL | CDCCCPTZITEHTCMMMF PSCPVTR|ELX|AIPCSG|V|BN|Q|CEPACL|
| COOETECTCOTE | AARAYHHOPEUIRAEAOIRULAIHH | NEI |RPEOCU|I|AE|U|ARALLA |
| AERRCSHEARSP | EDILPYUYORPBISLRRMERENTEI | IPM| GOMCAE|G|RI|E|NYSLEP |
| LRTNLURNLDOT | SONOELASMMHIUSAIIBMIRDESZ | CTE | UMPOET|N|RS|E|ATPOOO |
| | | | HU vo
| LRONCPAMISGR | BVAISAIMPCATPFBJCCSMITTPA | AMA | AMANTS |M|AO|H|CVVCGA|
| AELYIOSINURE | O[ISNTMNAEATIRIIAIYEANEROP | XAM|RACUAP |A|SP|Y|AAAOYE |
| NPEMLRPCDBAP | NSIOOAVTSTOLOLFVTMRRECIPI | IRE|GCICCE|R|IP|A|TRGBNS |
| CERPITERICNE | DCAPLRORCATICILARORIRTFUC|LSR|ERDICC|I|AO|L|HIIBAT|

Keeling 1166666666666|1..... oh ob Die, 0) ook A si Slope overlies so) 450025. - 1666666]
Luar |.43.111..311]6626641646163655563....66]...|452662|. a clo so'o.c.c0 |
Panjang |.1361..1.223111151166666645455634.1...|666|/466664|.|/1.].]......1]
Selma le TR RES ree eR Ee cs, oalletiliis) «er 016 |
Atas [hei AGrewsuoneneens 3|...4.1414..665545.41.....]...1646662|.].1].]......1
Tikus 16.3......3..11162664146...21666..3..1.]...1]122661|.|]..|/6]...... |
Cepelok loScooogoocodabllooadtocoototooke lost ooo olloco IMOSOGGRI lls sifollons oor |
Pandan lSCoo0c000 pL Vet SilioveHeNovolloMerielelloHellellsueyold Mr MioievenereyeronltereNo iO OO O.GlOilrellwoul veil teoiteweronononll
Ampang loobocannnc co llondooonopoU OOOO Ooto OOOO ooo SOOO SIGI So lls ooacas |
Kembang VosbSSb6o0bb00 owooogG 6 be cotex ooo do05 ollobo IOTSGGS Ic lS loons so |
Wak-Idas oogoaoeodocolloococccsonodotloosdoodoosolloeolS50005lcllaclloiliccc oa |
Blekok Voe60 60006004 losogoodooood obo 7456 00006 6 [oloo JEKSSOA I cio ollolleocéoc |
Blan lo ooo ogo0006 codecs coco ada bO8 O0'd “|... 11566151. oollolloog eon |
Kambing 7 erase RP Aaa Ue ac ede nny Meets nal eg © ofSCSG6 [ollos lolioos soo
Kelapa Satu loo ooosoocoDR loodaodad eKelisfoneyellevole Sooo go olblooolloMoOoIDolloollollaooocs |
Blan Madar lo Go5 6 0b0 S60 polloocoooodbodoo oO Kdss g oie SISSON No oo [loilleson5c ||
Maraya looodocoo ods loSoSdosedagccgoshoosoodcollooo LESBO lolloollollodsacs |
Siput loGooSoo cos0ollogoan0b concn odbaon06DocodollsooSoA606| oho ollelloodoss |
Jambatan lWemcttonoweitsHeiteere so llocccoodoooododgbncooooddb ooo IMoBOOS ooo lho lecoccs |
Labu logoooodio6e collosotlotocoddcoagoo oboe loo ICMOER io lGSlle lec u0s |
Beras Hio-o O:0'0-0'0.0 cooollooodboooudodooodocceoooooollooo Io st!Oallatlos lic llocoson'l|

AMPANG PREC al ieoveiey si siehelienes siete evekonclelencdelciedersieker evens coo oo loool Ob oOo'llai}o%s' [ls lo7adi6 35 |

Table 4. Two-way classification for exotic species occurring on all islands.
Classification based on abundance data standardised by species
maximum. The first four letters of the generic name and specific epithet
are read vertically. Numerical values represent the abundance scores
standardised by species maximum.

Island Species groups
groups

BR OSSS0S555 FN Pe 6a Ba ie inn C=----=—=—— > <2)

| BTVEEEMACDEEESDSHCSMRP | LCSPR| BBCCCHDCCEIPDAEBSGS |CS|RTT|IS|VS|CBLSSIAZ|
| OREURUUUEALULPIPEYTAHH | EYCHI | OREHYIEHOMMAEPRRORT |AI|IRU|SE|EO|AREOENEE |
| ETRPAPNSNCEPEOGEDNACOY | PNOYV | TENLPPSRNIPSSLIARAR|RD|CIR|CS|RL| SYUNNDRP |
| RDNHGHTTCTUHURIRYOCRES | IOPLI | HYCOEPMYYLESMUOCGST | IA| IPN|HB|NA|UOCCNIVH |
| | | tol lip ghea al
| DPCHTPCIEAICRISACDJASM | VADNH | BDCBPLTABSCFBMMBBSA | PA| CTU |MG|CA|EPLOOHLR |
| IRITERANCENYUNESOAATPTI | IRUOU | LITAOORCOOYOIUERIPS |AC|ORL|UR| IM|QIELCIAO |
| FONRNOLUHGDADDTSRCMRAN | RCLDM| ASLRLNIINNLEPTYIC1TI | PU|MIM|TA|NE|UNUECRNS |
| FCETESALIYITEIIUYTAOTI | GUCII | DTIBYGFCACITIIEZOOA|AT|MFI|IN|ER| INCRISAE |

Keeling [PSP Men okel oxelotatel shettotcvetetetel of oll POO 1 O00. 6 OOO. 0 OORTEOS OGiP Lea serllReks. [evsiexenon owes |
Atas [retenctie\thiee arse e cloveie ofete re) o sel Ol otel Ol lloveterelenoneteretetete e)/ctens sient besten Loe lisse healleurorcaos 6 |
Luar GOD h eit er eleratareretere HY V7 Bosra SS omc. coop OOOO C [rere [1Gs.:53]'GGilhy clio ete eres crems |
Tikus [rover eG ST ret rover d dds Giotel'|! reverent lietettovetevetetetctete eo ererolencrele: [voted [Ascii lKereM LOO ill otehenelerens i|
Selma 11164666116666666661664|..... [Roterevetohetetetetel ciel eelete elers |..1164|..1..166666666|
Panjang 16666666666666166611111 | 66111 | 6666666666666666666|..1]..6]..]..]....266. |
Kambing [Keervetorstetchelerstate av oreh sVetel of oi of |Holel Olet onl hefetocete tel shictictetelel lel cheloters Gel beuex’j hoo lomlloonoa5 o.0||
AMDPANG RECA) "css stes sues el cl el oi eiene rere eheiereke [Rexel suet [Rokshetetclelotetscoteveleretsl sf clots [Foren lher cdl vere! Ineredl kenehenetenerete |
Ampang |hahedshetelstenetete aictiotavetemetetahetele [foteretete [RokakeheteteNetotateteleletetoletelets eaeel eeteal lecacal Waxed OtC00-0.0.0 |
Cepelok [Fopeteustevere’ clevetetereorereleyerenciors [Reterorete [Berctevertoncieicharstetsyereveterere’s [Pico [Ps oc! | ere l csc caltovenenctonetene |
Pandan Wpasatotersteletayetene ale Mev hctotetoton|Vohetetelod iotetoletetet Reteletetete | cle leletons [icken Foret DilHenen[Neke: IWenoeenenete rel
Siput [Po emeetc! cratelereleteleter everetshetetove [BototteRoteMlichetohelet hetolictetetslstetoiehene [retetl revel) [hetoa led cl we) orenestonetem
Labu [Retetetel eles tote skated eteNeVoksletvolehet Retetotetel lNehetotstotclcleReletetotelohetet eters Pesecul boson heel [es | srenenonedl
Blan Madar [sotonetokeketetolehetsfetevonere oh ofot ater’ lovee Noted Weketotetehoncteletote teks Better [eoten [retsi Di lioted [VoroMioretonaione vel
Maraya |Hercxchetelstelsteloleretetehateteretetelete [Nokekctete [Pokerctchctehetststakehahet alate shotel [sree [beret Stfleron hele [ila itetetamerets |
Wak-Idas 5-5-0. 00-5-3.0-6 cS ESO OO.Oe otol lberetoNetol oMekoreteekeNed sotto! olekehetoters Reset Wee] bitiecte eronl Heron b:5:0.010 |
Kembang |;e¥evatotolatatatatehotetereteretoletetetote |Koweharete [HcFaltetetotelotetersteterotetelclctels Wezel booe tl Focdloallo a o6.06.0 |
Kellapa: Satu « s[hcicctoe.rcyere cn etcret svete avototetetete [Wetemettete [NellebeteWelalaterstete ts ahekevetolote? [ster [fete Ail boron Weheull aterekettete cnet

15

Table 5. Two-way classification for all species recorded in transect plots on North
Keeling Island. First letter of the site code represents the island name,
second and third letters refer to the aspect of the ocean coastline.

Site Species
groups groups

CRCPCCDMT
AIOIOAIOR
NVCSRRCRI
AIOODILIP

CHNGSPCCT
AUURUAIIR
TMCABPLTI
HIINCAIRP

uw
a
my
~
e

a
2g
~
e

eee te eee

Ss)
z
—
wo

eo
a
~
a

16

Table 6. Two-way classification for all species recorded in transect plots on the
Cocos atoll. First letter of the site code represents the island name, second
and third letters refer to the aspect of the ocean coastline. Asterisks
indicate presence of a species.

Species Site groups
groups

| LTLLLLLLSSLLPSSPPPPPP | LAAAATPPPSPPPPPPPPAAAPPP | LAAATAAAAAPAAPAPAAAP PAPPAAAAAPAAAAPAA | TTATTAPPPPPTTT | AAAAAAAAP |A|
| NENNNNNNNNWNSNNWWWNWW | NSSSSNSSSNWWWHWNNREWWHNY | HSSWESSSNSSSSWSWHNSSSESSNNSHEWNNNNWS S | NNSNNSSSSSWNEE | NESNSSSES|S|
|\////////88/ /8BB111W11| /BWWW/BEBB221W1iWWwW/ //Ww| /BW/ /EHEEERBH2W1E8HEE/ HERES / /1HBHB2BW| //B/ /BEBEE2///|B/BEBEB/B|B/|
100462538//792////////\14///S119/////////112///\16/0346316133/ //2222152221434/2111/2/ | 0144221111/312 | 202132222}3)
| 32 /04347656/0/234 ///101132012 748) /0 SISIIILIESOSII11 S1T1/) OFF FF2/11 FI A11713 \/ ///17 SNA
| 1 14 132 16 12240043 01548 32233 32013 | 5S 45467 14 05021 0/1)

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a
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LEPI VIRG | I a | ! | iil

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BNIC AXIL | | ' | | Plat
PAND TECT | | | ' | uel

CALO INOP | ** eS,
CYPB STOL | *** * bd
STAC JAMA |***** u
IPOM PBSC |* oe

DODO vIsc |* be

*
teteeeree er eee © © |
* eervore ‘| *
* ef ee ee]

FPIMB CYMO | * **#tteeeene eee
ZOYS MATR I* . eerereeerrerereee)

ener tee esee * |

TRID PROC | trees wee 1

COCO NUCI |**#teetereerrareerere ieee tee eeree Pee eee ee ereeeeKeHHHESe | HetEseeseHeeEe| *

SCAB TACC |** *### tees & & [eereeres

TURN ULMI | eee leeee eneee
MBLA BIFL | we oe eeeerel|eeres eeeeeee e| ee ter 1 . Il

teeere oo je eereecere « teeeres [ete ee | teeweeres

cere tere fete eeeeerets serete|sereeeete see | *

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CRIN ASIA | i} * ] | * tee]
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we eee . reece)

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5

BARR ASIA | | eal | | UW |
CABS BOND | | Pica | | lint

HIBI TILI | | oh AS | | av
SS SS SES

65

17

64

62

60

59

55

x

5!

50

49

(Pulu Panjang)

Horsburgh Island
(Pulu Luar)
Directi
(ACHES INDIAN OCEAN
Pulu Pasir a om
t Pulu Beras
= ith
Pulu Gangsa
|
Home Island ie
(Pulu Selma)
WESTERN ENTRANCE 9 Pulu ameang Kecil | ;
Pulu Ampan
ee a Pulu Wak Idas
| |—#2_. Pulu Blekok ———t—
PuluKembang &. |
Pulu Cepelok |
= Pulu Wak Banka
|
Pulu Pandan
{ if See}
Pulu Jambatan ) Pulu Sleu
=} — ai Pulu Labu
Pulu
Pulu. Kelapa
Pulu EIN SSN : i
West Island Maraya

—I

South Island
(Pulu Atas)

62

Figure 1.

Location map showing island names, localities mentioned in the text and
remnant vegetation patches on the Cocos atoll. Refer to Appendix 3 for a
description of the remnant vegetation units. Gridlines represent 1000 m grid of
the Australian Map Grid, Universal Transverse Mercator Projection. Map base
derived from R.A.S.C. Series R811 Sheet Special Cocos Island 1979.

18

Figure 2.

Number of native species

100

10

/
Kelapa Satu
/

A
74
Beras ,/

0.01 0.1 1 10 100 1000
Area (ha)

Species-area relationship for indigenous plant species richness for the 21
vegetated islands of the Cocos atoll and the island of North Keeling, showing
approximate 95% confidence limits. Non-linear regression fitted to obtain the
equation s = 6.73a°-28.

Cocos Forest

Pisonia Forest

Cordia Tall Shrubland
Pemphis Tall Shrubland
Argusia Shrubland
Pisonia Shrubland
Sesuvium Herbland
Boerhavia Herbland

Mixed Shrubland
Premna Tall Shrubland

1000 m

Figure 3. Vegetation map of North Keeling Island.

19

20

Figure 4. Pulu Beras, one of the smallest vegetated islands, with a cover of Cocos
nucifera, Argusia argentea and Scaevola taccada.

Figure 5. Boerhavia repens herbland grading into wind-sheared Argusia argentea
shrubland on the south-east coast of North Keeling island. This is the
breeding habitat for the Brown Booby.

21

Figure 6. Sesuvium herbland adjoining Pemphis shrubland with Cocos -Pisonia forest in
the background, on North Keeling island.

Figure 7. Rhizophora apiculata grove on Pulu Luar lagoon. Sesuvium herbland on coral
shingle in the foreground.

22

Appendix 1. Vascular plant species list for the Cocos (Keeling) Islands.
Asterisk indicates introduced species.

Family Generic Specific Authority Var,/ Common __ Local
Name Epithet Subsp. Name Name
ACANTHACEAE Dicliptera ciliata Decne.
AIZOACEAE Sesuvium portulacustrum fee) nL Sea Purslane
AMARANTHACEAE Achryanthes aspera (es var villosior Chaff Flower
(Henslow)
D.Porter
*__Aerva lanata L.) Schult.
APOCYNACEAE Neisosperma oppositifolia (Lam.) Fosb. Kayu Laki
& Sachet

ASTERACEAE * Austroeupatorium inulifolium (Humb.,Bonpl. Stinkweed

et Kunth) King
et H.Robinson

*__Eleutheranthera ruderalis Sw.) Sch. Bip.
* Emilia sonchifolia L.) DC.
Melanthera biflora (L.) Wild. Beach
Sunflower
*___Tridax procumbens -L.
*__ Vernonia cinerea L.) Less. var. cinerea
* Vernonia cinerea (L.) Less. var lanata
J.T. Koster
BORAGINACEAE Argusia argentea (L.f.) Heine Octopus Bush Kayu
Sireh
Cordia subcordata Lam. Sea Trumpet Geron-
ggang
BRASSICACEAE *_Lepidium virginicum L.
CARICACEAE * Carica papaya LE. Pawpaw Katis
CASUARINACEAE Casuarina equisetifolia Le: subsp. Coastal Cemara
equisitifolia Sheoak
CLUSIACEAE Calophyllum inophyllum L. Alexandrian Nyampl-
Laurel ong
COMBRETACEAE Terminalia catappa ke: Sea Almond Ketapang
CONVOLVULACEAE |pomoea macrantha Roem. & Moon Flower
Schult.
CONVOLVULACEAE |pomoea pes-caprae (L.) R.Br. subsp. Goat's-foot Kangkong
brasiliensis Convolvulus Meryap

L.) Ooststr.
Acalypha lanceolata Willd.
* — Breynia disticha J.R.Forst. &
G.Forst.
Euphorbia atoto G. Forst.
* Euphorbia cyathophora Murray Dwarf

Poinsettia
* Euphorbia hirta Le

EUPHORBIACEAE

FABACEAE

FLACOURTIACEAE

GENTIANACEAE

GOODENIACEAE

HERNANDIACEAE

LAURACEAE

LECYTHIDACEAE

LYTHRACEAE

MALVACEAE

‘

MIMOSACEAE
MYRTACEAE

NYCTAGINACEAE

OLACACEAE
PASSIFLORACEAE

PORTULACACEAE
RHIZOPHORACEAE

* Euphorbia
Phyllanthus

* Ricinus

* Sauropus

* _ Alysicarpus
Canavalia

* Crotalaria
* __ Desmodium
Erythrina

* _ Indigofera

*_ Macroptilium

* Sesbania

*___ Sesbania
Vigna

* — Muntingia

Enicostema

Scaevola

Hernandia

Cassytha

Barringtonia

Pemphis

Hibiscus

*___ Sida
Thespesia

*

Leucaena
* Eugenia

* — Psidium

a Boerhavia

Pisonia

Ximenia
* Passiflora

Portulaca
Rhizophora

prostrata
amarus

communis
androgynus
vaginalis
cathartica
retusa
triflorum
variegata
hirsuta
atropurpureum
cannabina
grandiflora
marina

calabura

axillare

taccada

nymphaeifolia

filiformis

asiatica

acidula

tiliaceus

acuta
populnea

guajava

albiflora

grandis

americana
foetida

oleracea
apiculata

Aiton
Schumach &
Thonn.

L.) Merr.

L.) DC.
Thouars. in
A.N. Desvaux

(le
DC.) Urb.
(Retz.) Poir.

L.) Poir.
Burm.) Merr.

(Gaertn.)Roxb.

(C.Presl)
Kubitzki

fe
(L.) Kurz.

J.R.Forst. &
G.Forst.
(

Burm. f.

(L.) Sol. ex
Correa

Fosberg

var. retusa

var.
cannabina

subsp.
litiorale
(Blume)
A.Raynal

subsp.
tiliaceus

var hispida
(DC. ex
Triana &
Planch.)
Killip

Castor Oil
Plant

Sea Bean

Coral Tree

Siratro

Sea Lettuce

Sea Hearse

Devil's Twine
Box Fruit

Cotton Tree

Portia Tree

Leucaena

Pisonia
Yellow Plum
Stinking

Passionflower

Pigweed
Spider
Mangrove

Pokok
Jaru
Jarak

Kayu
Dedap

Kayu
Kankong
Kayu
Jambu
Hutan

Kayu
Besagi
Kayu
Keriting
Pokok
Waru

Ampol

Rukam

24

RUBIACEAE Guettarda speciosa i Kembang

Melati
Morinda citrifolia L. Cheesefruit Mengkud
u
*_Oldenlandia corymbosa LE:
*___ Spermacoce assurgens Ruiz & Pav.
RUTACEAE * — Triphasia trifolia (Burm.f.) ; Buah
P.Wilson Kengkit
SAPINDACEAE Allophylus cobbe L.) Blume
Dodonaea viscosa Jacq. subsp. Hopbush
viscosa
SCROPHULARIACEAE *_ Scoparia dulcis Ee
* Striga angustifolia (D.Don)
Saldanha
SOLANACEAE * ___Physalis minima E Chepelok
* Solanum americanum Mill. Blackberry
Nightshade
SURIANACEAE Suriana maritima L.
TILIACEAE Triumfetta repens (Blume) Merr. Bingil Burr
& Rolfe

URTICACEAE Laportea aestuans L.) Chew.
VERBENACEAE *___ Clerodendrum indicum L.) Kuntze
Clerodendrum inerme (L.) Gaertn. Sorcerer's
Flower
poe ehvia nodiflora L.) Greene
Premna serratifolia EE
* — Stachytarpheta jamaicensis (L.) J.Vahl Blue
Snakeweed

Vitex trifolia

ARECACEAE Cocos nucifera Coconut Kelapa
COMMELINACEAE *__Rhoeo spathacea Sw.) Stearn
CYMODOCEACEAE Syringodium isoetifolium Asch.) Dand sea grass
Thalassodendron ciliatum (Forssk.) sea grass
Hartog

Fimbristylis cymosa R.Br.
Mariscus javanicus (Houtt.) Merr.&
F.P.Metcalfe
* — Pycreus polystachyos (Rottb.)
P.Beauv.
Queenslandiella hyalina (Vahl)
F.Ballard
HYDROCHARITACEAE Thalassia hemprichii (Ehrenb.) sea grass
Asch.
LILIACEAE Crinum asiaticum LE: Crinum Lil
* — Zephyranthes rosea (Spreng.)
Lindl.
PANDANACEAE Pandanus tectorius Park. Var. Screw Palm Pandan
cocosensis
B.C.Stone
| * — Bothriochloa bladhii (Retz.)
S.T.Blake
* Brachiaria brizantha (Hochst.ex
A.Rich.)Stapf

* Cenchrus ciliaris
* Cenchrus echinatus Sand Burr
* Chloris barbata Sw.

D5
*_ Cynodon arcuatus J.Presl. &
C.Presl.
*__ Dactyloctenium aegyptium L.) Willd.

* Eleusine indica (L.) Gaertn. Crowsfoot
Grass

* Eragrostis tenella (L.) P.Beauv.
ex Roem. &
Schult.

* _Eriochloa meyeriana Nees) Pilg.

* __Imperata cylindrica L.) P.Beauv. var. major Bladey Grass

: Ischaemum muticum i

Lepturopetium sp. aff.

marshallense

Lepturus repens (G.Forst.) Stalky Grass
R.Br.

* Panicum repens (ky
Paspalum vaginatum Sw.

* Sporobolus fertilis (Steud.) Sand Couch

Clayton

Stenotaphrum micranthum (Desv.) Beach Buffalo
C.E.Hubb, Grass

Thuarea involuta (G.Forst.) Bird's-beak
R.Br.ex Roem. Grass
& Schult.

Zoysia matrella (L.) Merr. subsp.

matrella

*_ Unidentified sp. ‘

26

Appendix 2. Notes on plant species of restricted distribution on the Cocos
(Keeling) Islands, along with collection numbers held at CBG.

Achryanthes aspera: Common on Keeling and found elsewhere only near some
senescent Pisonia trees around the small lagoon on Pulu Luar. [D.G. Williams
45,52,211]

Barringtonia asiatica: A solitary tree of great stature occurs on Pulu Panjang with
numerous supressed-advance seedlings underneath the canopy. The only other
Barringtonia seen were a few saplings in the recent strand forest along the lagoon shore
150 m south of the northeast point of Pulu Panjang. [D.G. Williams 110]

Casuarina equisetifolia: Planted indiviuals are found in and near the settlements on
Pulu Panjang and Pulu Selma and one large tree is on the lagoon shore north of the
kampong. Guppy (1890) reported that the plant was introduced and spreading from
island to island but no evidence was found for the latter. No seedlings were seen. [D.G.
Williams 155]

Cordia subcordata: Now occurs on the Cocos atoll only as large senescent
individuals along the lagoon shore. No young plants were seen, although germination
was common on North Keeling lagoon shore in April. [D.G. Williams 20,54]

Enicostema axillare: Known only from two adjacent locations on southern Pulu
Panjang, where it occurs amongst Zoysia matrella and Ipomoea pes-caprae in open
coconut woodlands. It occurs from the ocean beach up to 100m inland. Although
flowering freely, these populations appear to be extending largely by rhizome extension,
to judge by their compact, circular distribution. [D.G. Williams 79]

Erythrina variegata: A small but healthy grove of trees found at the north end of
Keeling in Pisonia forest [D.G. Williams 53]. Likewise Allophylus cobbe [D.G. Williams
44,48] and Cleome gynandra [D.G. Williams 36] were found only in this area, the latter
at the upper limit of the saltmarsh.

Laportea aestuans: Previously collected here only by Darwin on the Cocos atoll in
1836. Since collected only on the beach top along the western shore of North Keeling
island. [D.G. Williams 154]

Lepturopetium sp.: A western Pacific genus of putative hybrid origin (Fosberg and
Sachet 1982), found here only at the southern end of the runway on Pulu Panjang,
growing on low-lying land occasionally inundated by rain or heavy seas. [D.G. Williams
267]

Neisosperma oppositifolia: Found occuring as a stand only on Pulu Labu, where
there are twenty or so mature trees forming abundant fruits. A solitary specimen without
fruit was found on Pulu Atas and two apparently planted trees occur in the Pulu Panjang
settlement. [D.G. Williams 25,145,175]

Pandanus tectorius var. cocosensis: The only stands are on Pulu Selma where some
of the clumps on high dunes have died out recently, possibly due to firing. A single
clump on Pulu Panjang at the entrance to Telok Jambu appears to be all male, and
therefore probably a single genet representing a solitary establishment event. [D.G.
Williams 103]

27

Pisonia grandis: A few small clumps remain on the Cocos atoll of what must have
been the dominant tree on the larger, higher islands before settlement. [D.G. Williams
21,43]

Rhizophora apiculata: Occurs around the saline swamp on Pulu Luar and produces
numerous seedlings there. One established seedling was found on the southern point of
Pulu Selma but had disappeared a year later. Guppy (1890) stated that the populations
were derived from beach drift planted on Pulu Luar by J. G. Clunies-Ross about 1850-60.
[D.G. Williams 171]

Suriana maritima: Occurs, in any abundance, only on recent sand deposits. Said by
Guppy (1890) to have first colonized the atoll in about 1850, when it appeared on the
ocean side of Pulu Cepelok, although it was not found there in this survey. [D.G.
Williams 176]

Ximenia americana: Found only as a few plants on the lagoon shore of Pulu
Panjang. [D.G. Williams 183]

28

Appendix 3. Remnant native vegetation of the Cocos atoll referred to map units

indicated by letters on Fig. 1. The map does not show the following
types of native vegetation:-

— Pemphis acidula and Suriana maritima shrublands on sheltered shores;

— Scaevola taccada and Argusia argentea shrublands along exposed
coastlines;

— solitary individuals or small clumps of native species.

Pulu Panjang (West Island)

Major area of strand forest with single large Barringtonia asiatica, several
Cordia subcordata, Calophyllum inophyllum, Hibiscus tiliaceus, Hernandia
nymphaeifolia, and Morinda citrifolia.

Strand vegetation of Pemphis acidula with the only stand of Pandanus tectorius
on West Island (burnt in October 1987) and some Hibiscus tiliaceus and
Hernandia nymphaeifolia.

A small clump of mature Pisonia grandis.

Scattered individuals of Hernandia nymphaeifolia occur in this area, most of
which is cleared for the aerial field.

Strand lined with patches of large Calophyllum inophyllum and freshwater
swamp lined with Hibiscus tiliaceus. Suriana maritima, Guettarda speciosa and
Pemphis acidula occur locally.

Guettarda speciosa and Scaevola taccada scrub along the strand opposite the
aerial field and merging northward with tall Guettarda speciosa and
Calophyllum inophyllum strand forest which extends inland, indicating a former
shoreline.

Pulu Luar (Horsburgh Island)

Well developed strand forest of Calophyllum inophyllum, Terminalia catappa,
Dodonaea viscosa, Hibiscus tiliaceus, Premna serratifolia, Guettarda speciosa.

Stand of Thespesia populnea and Cordia subcordata trees growing along a
saltwater seep.

Disturbed forest of Morinda citrifolia, Premna serratifolia, Guettarda speciosa,
Terminalia catappa. Associated with a seasonally water-logged swamp
dominated by Mariscus javanicus.

Saltwater swamp with fringing Cordia subcordata, Rhizophora apiculata and a
few Pisonia grandis. Achryanthes aspera and Sesuvium portulacustrum also
occur.

Pulu Tikus (Direction Island)

A small clump of Thespesia populnea occurs here amongst Scaevola taccada at
the top of a rubble beach.

29

Pulu Selma (Home Island)

L Scattered clumps of Pandanus tectorius occur on the coastal dune; some burnt in
1987. Guettarda speciosa and Premna Serratifolia are also present.

Pulu Labu

M The interior of this island has several large Barringtonia asiatica and a number
of small and large Neisosperma opposSitifolia.

Pulu Atas (South Island)
N Strand forest ranging from exposed to sheltered with Calophyllum inophyllum

mainly, but also Hibiscus tiliaceus, Guettarda speciosa, and Premna
serratifolia.

ATOLL RESEARCH BULLETIN

NO. 405

CHAPTER 7

AN UPDATE ON BIRDS OF THE COCOS (KEELING) ISLANDS

BY

T. STOKES

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 7
AN UPDATE ON BIRDS OF THE
COCOS (KEELING) ISLANDS
BY
T. STOKES *

INTRODUCTION

The birds of the Cocos (Keeling) Islands were reviewed by Stokes et.al. (1984)
and this paper summarises that paper and provides additional species records. It also
provides an update of conservation comments provided in that paper.

Forty-four species of bird (6 introduced) have been recorded from the Cocos
(Keeling) Islands (Appendix). The following species notes are additional to those
recorded by Stokes et. al. (1984).

SPECIES

Herald Petrel Pterodroma arminjoniana. A few were recorded on two occasions at
North Keeling Island in April and June 1986 on the ground and in the air, suggesting
nesting (Stokes and Goh 1987).

Christmas Frigatebird Fregata andrewsi. An adult female was recorded on 21
March 1986 at North Keeling Island (Stokes and Goh 1987).

Glossy Ibis Plegadis falcinellus. Four were recorded by a party of touring bird-
watchers at the airstrip on 8-9 May 1990 (Richard Jordan and Peter Goh pers. comm.).

Greater Flamingo Phoenicopterus ruber. A vagrant was recorded on North
Keeling Island from April-June 1988 (Marchant and Higgins 1990).

Australian Kestrel Falco cenchroides . A pair were recorded over several weeks at
the West Island airport in May-June 1990 (P. Stevenson, pers. comm.). They are common
on Christmas Island and may have originated from there.

Buff-banded Rail Rallus philippensis andrewsi. An endemic endangered
subspecies, formerly widespread on the main atoll and now virtually restricted to North
Keeling Island where it is common (Stokes et. al. 1984). However occasional birds are
still seen on the main atoll and the latest was a carcass, probably cat killed, found in 1991
at the West Island settlement (P. Stevenson, pers. comm.).

Bridled Tern Sterna anaethetus. A specimen was collected on North Keeling Island

by Gibson-Hill (1948) and there was a local report that it nested there. It has not been
recorded since.

* Great Barrier Reef Marine Park Authority, P.O. Box 1379, Townsville, QLD 4810

CONSERVATION

When Charles Darwin visited the Cocos (Keeling) Islands in April 1836, the
"immense number" of marine birds recorded in 1828-29 on the main atoll (cited Gibson-
Hill 1949) were probably still present though somewhat diminished. He refers to trees on
the island where he first landed on the main atoll, as being occupied by many nests of
gannets (sic), frigatebirds and terns, and to a smell in the air which led him to call it a "sea
rookery" (Darwin 1979). From his diary it would appear that the forest of the main atoll
was by then well on the way to be being transformed into the monoculture coconut
plantation that it was by 1885 when most main atoll birds had been eliminated (Forbes
1885). The reason for the decline in main atoll birds was almost certainly due to habitat
change, intense hunting by people and predation by cats and rats . Today there are still
very few birds on the main atoll.

However birds remain in large numbers on North Keeling Island due to its
isolation, the difficulty of landing, and access restrictions placed by the former Clunies-
Ross clan rulers up to the mid 1970s. In the late 1970s and early 1980s, the lifting of
access restrictions and the acquisition of more efficient boats and weapons by the Cocos-
Malay people greatly increased the frequency and efficiency of bird-hunting on North
Keeling Island. In the early 1980s the Australian Government became aware of concern on
the islands and elsewhere that the number of seabirds being taken was not sustainable. I
was despatched in January 1982 by the Australian National Parks and Wildlife Service
(ANPWS) to investigate the situation and urgent control of hunting was recommended
(Stokes et. al. 1984).

In March 1986, the ANPWS Conservator on Christmas Island, about 900 km east
of Cocos, was required also to provide conservation advice to the Cocos (Keeling) Islands
Administrator. As incumbent at the time, I or my assistant (Peter Goh) flew to the Islands
every 4-6 weeks to discuss conservation matters on the Islands and to survey North
Keeling Island seabirds. By July 1986 agreement had been reached with the Cocos-Malay

people :

- to introduce a moratorium on seabird hunting on North Keeling Island
pending seabird survey results,

- to restrict any future seabird hunting to red-footed boobies,

- to permit while the North Keeling moratorium was in place, certain
numbers of red-footed boobies to be taken on Horsburgh Island on the
main atoll (where small numbers come to roost in certain weather
conditions at certain times of the year),

- that hunters would try to avoid killing adult birds, and on

- a series of administrative arrangements to regulate seabird hunting.

The conclusion of the 1986 seabird hunting agreement brought considerable praise
to the Cocos-Malay community from the Australian and international community.
ANPWS created a permanent Conservator position on the Cocos (Keeling) Islands in
December 1986. The moratorium on hunting at North Keeling Island eventually extended
to December 1988 by which time surveys had revealed that about 34 000 pairs of red-
footed boobies nested annually on the Island. Although hunting was prohibited on North
Keeling between 1986-88 many illegal hunting trips probably occurred and one person
was prosecuted. Hundreds and possibly thousands of red-footed boobies are believed to
have been taken in the period. A cyclone in January 1989 caused considerable damage to
the North Keeling Island vegetation and post-cyclone surveys suggested that more than
40% of red-footed booby chicks raised in the previous breeding season , and 1300 (or

3

1.9%) of breeding adults were killed (ANPWS 1989). In the subsequent breeding season
there was a 60% reduction in the number of red-footed booby nests on North Keeling
Island compared to the number at the peak of the best previous season in 1987 (ANPWS
1990). Although seabird poaching was reported to have declined in the 1989/90 with the
purchase of a new patrol vessel, no seabird population surveys occurred in 1990 or 1991
due to lack of suitable transport (ANPWS 1990, J. Tranter pers. comm. ). Monthly
surveys recommenced in the second half of 1992. A clear picture of the red-footed
population status will not emerge until late 1993. However it appears that a cyclone in
February 1992 caused sufficient damage to significantly reduce breeding success in the
year (J. Tranter pers. comm.). The level of seabird poaching is reported to have been very
high in 1990 and 1991 (J Tranter pers. comm. ). This was exarcerbated by a lack of
adequate patrol vessels. However a new vessel was acquired in late 1992.

An action plan to assist the recovery of the endangered rail population has been
proposed by Garnett (1992). It includes enhanced access by management staff to North
Keeling Island, a research program on the Island, declaration of the Island as a reserve, rat
and cat control on main atoll islands and, if necessary, the re-introduction of rails to
predator-free islands as conditions become suitable. Education to assist conservation is
also proposed. Restrictions to ensure that North Keeling Island remains cat and rat free
should also be considered.

Since the mid-1980s ANPWS has developed a limited conservation education
program in the Islands. This is being enhanced (J. Tranter pers. comm.) and should be
accompanied by the declaration of North Keeling Island as a Nature Reserve, as
recommended by Stokes et. al. in 1984. Seabird populations have low natural recruitment,
and usually only inhabit and survive on islands free of predators. Although there may be a
case for arguing that seabird hunting on the Cocos (Keeling) Islands is a legitimate part of
the traditional Cocos-Malay culture, it should only continue if the take is sustainable and
hunting is restricted to red-footed boobies on the main atoll under tight and enforcable
controls. There will remain justifiable cause for conservation concern about seabird status
in the Islands until this occurs. For this reason the International Council for Bird
Preservation (ICBP) and other conservation agencies should continue to monitor the
situation and seek rectification where necessary.

ACKNOWLEDGEMENTS
I thank Richard Jordan (New South Wales), Peter Goh (Christmas Island), Paul
Stevenson (former Conservator, Cocos (Keeling) Islands), and Jeff Tranter (current
Conservator, Cocos (Keeling) Islands) for assistance with this paper.
REFERENCES
Australian National Parks and Wildlife Service Annual Report 1988/89
Australian National Parks and Wildlife Service Annual Report 1989/90

Darwin, C. 1979. The journal of a voyage in HMS Beagle. Guildford (England). Genesis
Publications.

Forbes, H.O. 1885. A naturalists's wandering in the eastern archipelago. London:
Sampson, Low, Marston, Searle and Rivington.

Garnett, S. 1992. The Action Plan for Australian Birds. Canberra : Australian National
Parks and Wildlife Service.

Gibson-Hill, C.A. 1948. The Island of North Keeling. J. Malay Br. Royal Asiatic Soc.
21: 68-103.

Gibson-Hill. C.A. 1949. The birds of the Cocos-Keeling Islands. Ibis 91 : 221-243.

Marchant, S. and P. Higgins (Co-ordinators). 1990. Handbook of Australian, New
Zealand and Antarctic Birds. Vol. 1. Melbourne: Oxford University Press.

Stokes, T. and P. Goh. 1987. Records of Herald Petrels and the Christmas Frigatebird
from North Keeling Island, Indian Ocean. Aust. Bird Watcher 132-133.

Stokes, T., W. Shiels and K. Dunn. 1984. Birds of the Cocos (Keeling) Islands.
The Emu 23-28.

LIST OF BIRDS RECORDED FROM THE COCOS
(KEELING) ISLANDS

KEY TO SYMBOLS
* = introduced,
fenu= | resident.
m = migratory,
v = vagrant,
e = nolonger occurs on the Islands ,
b = breeding,
? = unknown status.

Herald Petrel Pterodroma arminjoniana (?)

Wedge-tailed Shearwater Puffinus pacificus (mb)

Red-footed Booby Sula sula (rb)

Masked Booby Sula dactylatra (rb)

Brown Booby Sula leucogaster (rb)

Christmas Frigatebird Fregata andrewsi (v)

Great Frigatebird Fregata minor (rb)

Least Frigatebird Fregata ariel (rb)

Red-tailed Tropicbird Phaethon rubricauda (rb)

White-tailed Tropicbird Phaethon lepturus (rb)

White-faced Heron Ardea novaehollandiae (r - possibly breeding)

Cattle Egret Ardeola ibis (v)

Eastern Reef Egret Egretta sacra (rb)

Rufous Night Heron Nycticorax caledonicus (rb)

Glossy Ibis Plegadis falcinellus (v)

Greater Flamingo Phoenicopterus ruber (v)

Unidentified hawk (v)

Marsh Harrier Circus aeruginosus (v)

Australian Kestrel Falco cenchroides (v)

Feral Chicken Gallus gallus (rb)

Guinea Fowl Numida meleagris (*rb)

Buff-banded Rail Rallus philippensis andrewsi (rb-endemic
subspecies)

Lesser Golden Plover Pluvialis dominica (m)

Ruddy Turnstone Arenaria interpres (m)

Little Curlew Numenius minutus (m)

Common Sanfdpiper Tringa hypoleucos (m)

Greenshank Tringa nebularia (m)

Pin-tailed Snipe Gallinago stenura (m)

Sanderling Calidris alba (m)

Oriental Pratincole Glareola maldivarum (m)

White-winged Tern Chliudonias leucoptera (m)

Sooty Tern Sterna fuscata (rb)

Bridled Tern Sterna anaethetus (v b - specimen record

of Gibson-Hill 1948,

overlooked by Stokes

et. al. 1984)
Common Noddy Anous stolidus (rb)

6

White Tern Gygis alba

Christmas Island Imperial-Pigeon Ducula whartoni
Unidentified dove

Unidentified nightjar

Unidentified swift

Barn Swallow Hirundo rustica

Unidentified wagtail

Christmas Island Thrush Turdus poliocephalus erythropleurus
Christmas Island Whiteye Zosterops natalis

Java Sparrow Padda oryzivora

(*e)
(*rb-restricted to
Horsburgh and
possibly West
Islands)

(*e)

ATOLL RESEARCH BULLETIN

NO. 406

CHAPTER 8

MARINE HABITATS OF THE COCOS (KEELING) ISLANDS

BY

D.G. WILLIAMS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 8

MARINE HABITATS OF THE COCOS
(KEELING) ISLANDS

BY

D.G. WILLIAMS *

ABSTRACT

The marine environments of the main atoll of the Cocos (Keeling) Islands have been mapped at a
field compilation scale of 1:25,000 scale using 1976 and 1987 aerial photography and field survey. Twenty
two habitat units were recognized and mapped, with greater differentiation possible in the lagoon because
of easier access and shallower depth. Qualitative descriptions of the habitats were made based on surface
and SCUBA observations in the field.

INTRODUCTION

The Cocos (Keeling) Islands, located in the north-east Indian Ocean, comprise a
main atoll (96° E; 12° S) called here the Cocos atoll and consisting of 25 vegetated coral
cays, and a northern atoll 27 km away, called North Keeling Island, which is now a
single island atoll. The nearest other land mass is Christmas Island, 900 km to the
northeast and Java, 1200 km to the north. The islands were discovered (apparently not
previously inhabited) in the early 17th century but were not settled until 1826 (Bunce
1988).

Various naturalists have visited the islands, including Charles Darwin on H.M.S.
Beagle in 1836 (see Armstrong 1991), just 10 years after settlement. Of the hundreds of
atolls seen by Darwin during the voyage, this was the only atoll which he explored on
foot. The experience was significant in the development of his coral reef theory
(Woodroffe et al. 1990). Faunal studies of the corals, echinoderms, molluscs, crustacea
and fishes were made by Gibson-Hill in the 1940's but, save for one survey by Maes
(1967) on molluscs and Colin (1977) on fishes, there were no modern studies of the
marine environments and organisms prior to those contained in the present volume
(Williams 1990).

Applied Ecology Research Group, University of Canberra, P.O. Box 1,
Belconnen, ACT 2616

Despite the various studies mentioned, no consistent overview of the marine
habitats was able to be achieved until aerial photographic coverage was available. In this
context, and that of an increasing need to better manage the atoll's marine living
resources, the objective of this study was to describe and delineate the distribution of the
major marine habitat types for both the lagoon, reef flat and outer reef slopes of the
Cocos atoll. Difficulty of access prevented sub-tidal survey on North Keeling.

METHODS

A preliminary photo-interpretation was done on panchromatic 1976 Royal Australian Air
Force 1:44,400 complete coverage photography and this was used as a basis for field
sampling. Location of sample sites attempted to include several examples of each of the
photo-pattern units defined on the basis of tone, texture, bathymetry and location. The
exact placement of field sites was able to be done with an accuracy of 100 m in most
cases by reference to the photographs in the field. Over 50 sites were observed using
SCUBA for depths over about 8 m and on snorkel or walking for shallower areas and
observations recorded on a data sheet.

Initially, fifteen different lagoon photo-patterns were described using the
panchromatic photography. Further detail of the reef flats and of the outer reef was
obtained from colour photographic coverage of the land areas only (1987 Australian
Survey Office 1:10,000). These included the location of the "drop-off", (i.e. the top of a
Pleistocene cliff at 18 m depth), the presence of sand chutes and deposits on the outer
reef slope, spurs and grooves, reef crest surge channels, aligned coral flats, seagrass beds,
conglomerate platform (Woodroffe et al. 1990) and beach rock deposits (Russell &
McIntire 1965).

Some further refinement of the map units was done from a classified SPOT image
taken in May 1987. This imagery enabled more consistent delineation of some of the
shallow water habitats but did not provide as much detail in the deeper lagoon and outer
reef slope zones. Seagrass beds of two species in the deeper lagoon were not detected on
the classified image, although no specific training was attempted.

A description of each of the final mapping units is given below with cross
referencing to map units (Table 1) and grid references on Fig. 1. The descriptions
include habitat structure and dominant organisms as observed in the field, with other
comments on structure or function within and between habitats. Reef classification and
terminology varies considerably between authors and, where possible, the terms used
here follow those of Hopley (1982). The marine areas of atolls and other reefs are
commonly divided into three major zones. These are the seaward reef front which lies
outside the line of breaking waves, the reef flat, which extends from the breakers to the
shore or into the lagoon, and the lagoon itself. Each of these major units are further
subdivided and described in the following scheme.

RESULTS
REEF FRONT

The reef front (unit A) on Cocos is marked by a major slope change, usually at 15-
18 m depth, and below this the slope is greater than 45 degrees to depths over 50 m.
Above the abyssal slope there is a gentle terrace of about 50 m to 2 km width, rising
gradually to the reef crest at approximately the mean low water mark. On aspects more
exposed to the south-east trades, the terrace has a well-developed spur and groove
(buttress) morphology, which in several locations on the west side appears almost to
form a secondary reef front due to very large buttresses located beyond the reef crest.
The buttress systems are most pronounced on the southern reef.

The reef terrace is the habitat of most abundant and diverse coral growth. In places
the terrace has up to 60% cover, mainly of soft corals, whereas elsewhere there are sand
deposits or very sparsely covered rock or sand slopes. Much of the wide terrace opposite
the West Island settlement (grid reference 6251), for example, has a sparse coral cover
on a hard basement, whereas the terrace further north (6256) is well covered in coral
from the reef crest to the outer terrace.

Because of the water depth over the terrace there were few mappable features.
These were:- the break of slope at ca. 18 m, the presence and orientation of buttresses
(spurs and grooves) and the presence of large sand deposits on the terrace. Terrace sand
deposits are most abundant on the leeward side of the atoll. Opposite the northern half of
West Island they form shore-parallel dunes at around 10 m depth (6257), usually lying
between a buttress system and the coral-covered lower end of the terrace. Around
Horsburgh Island sand is abundant and often covers much of the terrace and flows into
deeper water via sand chutes (6561).

THE REEF FLATS

This component of the reef is also very varied and grades into the lagoon habitat in
the channels between islands. The following units or features of the reef flat have been
mapped:-

— position of the coralgal crest and its surge channels;
— sand and coral flats;

- seagrass beds (Thalassia hemprichii);

— aligned coral flats.

Components of the flats which were not able to be mapped were boulder zones and
algal flats. The former are especially well developed on parts of the southern inter-island
reef flat where the combination of southeast wind and southwest swell produce the
highest wave energy conditions. This is also reflected in the greater development of
buttress systems and surge channels along the southern reef front.

The structure of the coralgal crest also varies in relation to aspect. On the eastern
and northern sides of the atoll it is poorly developed and very close (< 50 m) to the shore.
Along the southern crest, calcareous red algae dominate and often form a honeycomb-
like matrix that is exposed only during calm weather low tides. Along the western reef
opposite West Island, the crest is dominated by seasonally varying stands of brown algae
(mainly Turbinaria sp.), or a turf of red algae growing on smooth rock or algal-encrusted

4

pavements. The crest exposed at the lowest tides is usually less than 10 m wide and rises
30-50 cm above the adjacent reef flat.

The reef crest has well-developed surge channels every 50-250 m, particularly
along high-energy shores opposite islands. Associated with these channels are pockets of
deeper water on the reef flat, these being possibly important in the movement of larger
animals onto the reef flat, e.g. turtles, parrotfish and crayfish.

The reef flats opposite islands (unit B) are generally zoned landward from the crest
with a sparse coral zone, then an algal zone (usually brown algae), then a sand or rock
zone and in places an inshore seagrass bed on trapped sediment. However, much
variation exists and these zones are not always present nor clearly defined.

Beds dominated by the seagrass Thalassia hemprichii (unit E) are developed on the
inshore reef flat where sand has accumulated to about 5 cm or more depth and this
usually occurs within 20 m of sandy beaches. In a few places sand has been trapped by
exposed beach rock formations and this has enabled seagrass beds to develop.

The coral zone of the reef flats (unit C) is well developed in only two localities —
at the northern end of West Island (6257) and the south-western side of Horsburgh Island
(6563). In both locations there are reef flats dominated by hard branching corals and this
may be attributable to both sites being of moderately low wave energy as well as
experiencing a constant flow of fresh oceanic water that is relatively less turbid.

The aligned coral zone (unit D) is developed only on inter-island reef flats and
usually extends from the crest into the lagoon to a point opposite the lagoon shores of the
adjacent islands. The aligned corals are mostly hard massive species orientated parallel
with the current. This is a faunally rich area dominated by clams, echinoderms and
holothurians. At the lagoon end of the aligned coral zone and where the water is deeper
than a metre, there is sometimes a well-developed area of outcrops composed of massive
hard corals, surrounded by sand sheets.

Beach rock deposits are common around the seaward beaches of Cocos (Keeling)
and when exposed they provide a protective rampart to the coastline, which they often
parallel. In some places they diverge from the shore and so indicate recent changes in
shoreline position.

THE LAGOON

Moderately large by Pacific standards, the Cocos lagoon is distinctive for the high
proportion of its area covered by what appear to be fields of collapse and/or solution
dolines, commonly known as "blue holes" (units K, L & M). These depressions vary in
their size, shape and depth of their surrounding patch reefs. Other major habitats mapped
are the prograding sand sheets (unit F), opposite to and fed by the aligned coral zone;
seagrass beds dominated mainly by Thalassia hemprichii (unit H) and with smaller areas
of Syringodium isoetifolium (unit U) and Thalassodendron ciliatum (anit T); intertidal
sand and mud flats (unit G); sand flats and shoals; coral flats and patch reefs.

The continuous supply of sand from the outer and inner reef flat produces
extensive sediment fans (unit F, Fig. 2), which are size proportional to the area of reef
flat supplying them and the energy level of the coastline. The largest prograding sand
sheets are the ones opposite the southern pass (between West and South Islands) and
another fed by passes either side of Pulu Siput in the east. These deposits slope gently

down into the lagoon and slowly engulf lagoon patch reefs and blue holes. Their margin
with the aligned coral zone is not always distinct and it may be that the coral zone is
extending slowly lagoonward across the sand sheet in places.

In their most active places the sand sheets appear almost devoid of surface life
other than algal crusts, but in more stable locations there is a sparse covering of
Thalassia hemprichii, Halimeda (a sand-producing alga), Padina and Hydroclathrus
(both brown algae). Areas of high bioturbation due to sea cucumbers and worms are also
common. The spider shell, Lambis lambis, is locally abundant.

Thalassia hemprichii dominates the seagrass beds (unit H, Fig. 3) developed from
the Low Water Mark to depths of about one metre, close inshore to all the islands except
Direction and Horsburgh. There is some variation in the structure of the beds with water
depth and distance from the shore. Closer inshore, Thalassia is dominant but forms a
discontinuous cover due to wave effects. Shallow intertidal areas are dominated by the
seagrass and algae such as Gracilaria and Acanthophora, whilst subtidal areas have more
coral and algal cover. In several places these seagrass beds (unit I, Fig. 3) show obvious
lineation, and this represents overgrowth among the remnants of a prior aligned coral
zone in places where a channel between islands has been closed off by storm activity.
These sites are off South Island (7351, 7353) and West Island.

The most conspicuous fauna of the inshore seagrass bed is the Portunid crab,
Thalamita crenata, which makes shallow burrows, as does the much less common mud
crab, Scylla serrata. The crabs appear to feed on burrowing bivalves and winkles, and
numerous small fish shelter in the extensive crab burrow systems.

Syringodium isoetifolium (units U, V) is a more restricted seagrass growing at
depths from 1-6 m on sand in relatively clear water, mainly at the northern end of Home
and West Island and in the bay of Direction Island (6962). It grows with Thalassia and
various green algae including Caulerpa spp. in the former shallow sites, but is almost
mono-specific dominant at Direction Island in 2-6 m of water.

Thalassodendron ciliatum, a large, robust seagrass, grows attached to rubble and
rock. There is one large bed (unit T) of this species in the central northern lagoon in 8 m
of water on sandy rubble, and smaller patches of this species possibly occur on the outer
reef south-east of Horsburgh Island. The species grows in the lagoon in large circular
clumps, some of which appear to be showing central die-off and hence taking on an
annular shape. Small hard coral outcrops occur within some of these beds.

All three seagrasses appear to be grazed by green turtles, which are regularly seen
along the northeast shore of West Island and in Direction Island bay. None were seen
near the Thalassodendron bed but it did show signs of grazing by large animals —
possibly turtles.

Shoreward of the Thalassia beds along the southern and eastern sides of the lagoon
there are extensive intertidal sand and mud flats (unit G, Fig. 3). These are often
demarcated from the seagrass by a sandbank which is usually colonized by a line of the
shrub Pemphis acidula, which thereby stabilizes the bank and forms a mangrove-like
vegetation. It is rather surprising that no mangroves have colonized these flats since such
habitats are generally occupied by them on other reefs around the world. The finer
sediments tend to accumulate in the more sheltered inlets of the lagoon side of the islands
and generally where current and wave action is minimal. These form the major habitat

6

for the fiddler crab Uca chlorophthalmus and Macrophthalmus verreauxi, which occur
here in high numbers.

Major subtidal sand flats (unit Q) which are not directly associated with passes
between islands occur northeast of West Island and south of Horsburgh Island. These
locations are where sand is accumulated on the leeward lagoon margin and where it may
eventually be carried to the outer reef. At West Island the sand flat has a highly mobile
offshore sand bank (unit R) and there is major sand accretion onshore. The sand flat
south of Horsburgh Island lies in a westerly current flow and is connected to the outer
reef slope by a major sand chute which continues across the reef terrace.

Much of the central lagoon is a mosaic of "blue holes" of varying sizes and shapes
and depth of surrounding patch reefs. Smaller, more discrete holes (unit K) occur
towards the shallows and these ones are, in some cases, being filled by prograding sand
sheets. Around the fringe of each depression there is a band of staghorn coral rubble
which extends down the sides of the hole for about 2-5 m before passing into a sand
slope going to as deep as 20 m. The water in the smaller holes is usually fairly turbid
and the bottom is composed of sand and finer sediments.

In a few places large clumps of the foliose hard coral, Echinopora, were dominant
on the edges of holes. These seemed to be more common in the small patch reefs
developed in the middle of large holes (units L, M, Fig. 2) where turbidity was low.
Away from the fringes of holes the coral cover is usually sparse and consists of the
branching Acropora and outcrops of massive corals such as Porites. Bivalve molluscs
and holothurians are often abundant and there is, in places, a high degree of bioturbation,
perhaps associated with areas of finer sediments. At least two species of mushroom
corals also occur around these patch reefs.

Although several different blue hole morphologies have been mapped, sampling
has not been sufficiently intense to determine whether there are significant biological
differences. The main difference evident on photography is between small, iso-diametric
holes which cover 10-30% of the area, through to the holes in deeper water which are
large, irregular and occupy more than 80% of the area. These sub-units tend to be
separated by east-west lines of shallow water (of unit J), these perhaps representing
former beachlines.

The deeper central lagoon opposite Home Island appears to show a broad pattern of
reticulate reefs (unit N) but without deep blue holes. Much of the bottom cover is very
thick staghorn rubble, tightly interlaced and bonded by overgrowth of algae, particularly
a Padina sp. There are occasional sandy patches, as well as large mostly dead outcrops
of Porites spp.

North of the previously described habitat is an extensive area (unit O) composed of
mainly dead outcrops of massive corals with intervening sand patches. There are large
areas of included sand flat on the eastern side and generally very small amounts of hard
coral regrowth.

Well-developed coral flats lie between West Island and Horsburgh Island and,
since there is no reef crest here, these lagoon flats at a depth of around 8 m merge into
the outer reef terrace.

Between the seagrass beds on the east and west sides of the lagoon and the deeper
habitats of the central lagoon, there is a large and variable shallow-water habitat (unit J)

7

with various mixtures of sand, algal and coral cover. The sandy substrate, which appears
to be rather thin, is often strewn with fine coral and shell fragments and there may be a
sparse cover of Thalassia and/or Caulerpa spp. Patches of very dense Halimeda cover
occur and these are often overgrowing small coral boulders. A small black sea cucumber
is very abundant here. Large skeins of the net-like alga Hydroclathrus drift along and
accumulate on obstructions. Colonies of Porites occur, some forming microatolls of
considerable size.

Acknowledgements

This project was completed in 1987 whilst the author was appointed as
Environmental Resource Adviser to the Territory of Cocos (Keeling) Islands. I am
grateful to the Cocos (Keeling) Islands Council for its interest in the project and for
allowing access to all parts of the Territory; to the Administration of the Territory for
providing field logistic support and to the members of the Cocos Dive Club and Amat
Noor bin Anthoney for assistance in the field surveys. The Australian National Parks
and Wildlife Service provided access to the classified SPOT satellite image.

REFERENCES

Armstrong, P. 1991. Under the Blue Vault of Heaven: A study of Charles Darwin's
sojourn in the Cocos (Keeling) Islands. Indian Ocean Centre for Peace Studies,
Nedlands, Western Australia.

Bunce, P. 1988. The Cocos (Keeling) Islands. Australian Atolls in the Indian Ocean.
Jacaranda, Milton, Queensland.

Colin, P.L. 1977. The reefs of Cocos-Keeling atoll, eastern Indian Ocean. Proceedings,
Third International Coral Reef Symposium. University of Miami, Florida.

Hopley, D. 1982. The Geomorphology of the Great Barrier Reef: Quaternary
Development of Coral Reefs. J. Wiley & Sons, New York.

Maes, V. 1967. The littoral marine molluscs of Cocos-Keeling Islands (Indian Ocean).
Proceedings of the Academy of Natural Science of Philadelphia 119: 93-217.

Russell, R.J. and McIntire, W.G. 1965. Southern hemisphere beach rock. Geographical
Review 55: 17-45.

Williams, D.G. 1990. An annotated bibliography of the natural history of the Cocos
(Keeling) Islands, Indian Ocean. Atoll Research Bulletin 331: 1-17.

Woodroffe, C., McLean, R. & Wallensky, E. 1990. Darwin's coral atoll: geomorphology
and recent development of the Cocos (Keeling) Islands, Indian Ocean. National
Geographic Research 6: 262-275.

Table 1. Marine Habitats of the Cocos (Keeling) Islands Main Atoll
and their corresponding map units.

A
stipple areas indicate sand deposits
hatching indicates the approximate length, width and
direction of major buttresses
outer solid line indicates lower depth limit of the outer
terrace
REEF FLAT | Coral and Algal Flat
|e includes areas of platform rock, beach rock and beaches
e reef crest (coralgal rim) shown as a dashed line
e surge channels shown as an arrowhead
Aligned Coral Flat - small massive corals dominant
Seagrass Flat (Thalassia hemprichii)
LAGOON | Prograding Sand Sheet
Intertidal Sand and Silt Flat
e lines of Pemphis acidula on offshore sandbanks shown
stiooled
Seagrass Sand and Silt Flat (Thalassia hemprichii)
Seagrass Flat - on prior aligned coral flat (Thalassia hemprichil
Coral and Algal Flat with sparse Thalassia hemprichii
Blue Hole Mosaic 1 - small scattered isodiametric depressions
Blue Hole Mosaic 2 - large, irregular depressions, prominent
shallow coral rims
Blue Hole Mosaic 3 - large, irregular depressions, deep rims
Algal-covered Staghorn Rubble with occasional sandy
patches
Massive Coral Outcrops with sandy patches
Emergent Reef (Turk's Reef)
Sandy Lagoon Floor with occasional Coral Outcrops
Sand Shoal
Sandy Lagoon Floor with scattered Coral Outcrop and
Seagrass Beds (Thalassodendron ciliatum)
Seagrass Bed (dense Thalassodenaron ciliatum) and
occasional coral outcrops
Seagrass Bed (Syringodium isoetifolium) and occasional coral
outcrops
Mixed Seagrass & Algal Bed (Syringodium isoetifolium,
Thalassia hemprichii, Halimeda spp., Caulerpa spp.)

ali Sail
a)
-
ale |
crit
sv
Ber
ers
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Mice |
tai

T aT
65
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ex |__HORSBURGH\ \A INDIAN |OCEAN
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63 S B Mi a i = |
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i of \\\,. ) (PULU TIKUS)
62 mils 2 (aa
2 5 :
Bi:
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ay \
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60 Bs came T - 7
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59 i
s : 2 Md p/P ‘
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DAR *
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SS
56 = :
a0 A D fe,
ai ‘ DY L -
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4 J H \e
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53 fs sN 2 Gi K | | it \
B G re
Z S
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NS | Ue
51 » H SG is
WEST ISLAND \°k \ D is
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= ha ISLAND
“9 LS (PULU ATAS)
| |
62 63 64 65 66 67 68 69 70 7\ 72 73 74 75

Fig. 1. Marine Habitats of the Cocos (Keeling) Main Atoll.

Numbered grid lines are 1000 m intervals of the Universal Transverse
Mercator Grid, Zone 47. Habitats mapped from field survey by D.G.
Williams in 1986/7, using R.A.A.F. 1976 panchromatic (1:44,400) and
A.S.O. 1987 colour (1:10,000) aerial photography. Map field compiled at
1:25,000 on base derived from R.A.S.C. Series R811 Sheet Special Cocos
Island 1979.

10

Figure 2. Aerial oblique view over the southern lagoon, looking east towards the

Figure 3. Aerial oblique view of the southern lagoon, looking east across Pulu Atas,
showing seagrass beds (Unit H) and lines of Pemphis acidula at the edge of

sand and silt flats.

ATOLL RESEARCH BULLETIN

NO. 407

CHAPTER 9

SEDIMENT FACIES OF THE COCOS (KEELING) ISLANDS LAGOON

BY

S.G. SMITHERS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 9
SEDIMENT FACIES OF THE COCOS
(KEELING) ISLANDS LAGOON
BY
S.G. SMITHERS *

ABSTRACT

Surficial sediments from the Cocos (Keeling) Islands lagoon were classified
according to texture and composition using factor analysis. Six main textural facies: 1)
slightly gravelly coarse sands, 11) slightly gravelly medium sands, iii) gravelly sands, iv)
sandy gravels, v) gravelly muds, vi) slightly gravelly fine sands; and three main
compositional facies (i) coral-type sediments, ii) molluscan mud sediments, i11) coralline
algae/Halimeda type sediments were identified, accounting for over 90% of sediment
variation in the lagoon. These facies can be related to the provenance of constituent
components and lagoonal hydrodynamics.

INTRODUCTION

The main atoll of the Cocos (Keeling) Islands (96948'-56'E; 12°04'S) consists of a
horse-shoe shaped reef rim, on which 26 reef islands lie, surrounding a central lagoon of
approximately 190 km2. The lagoon can be divided into two broad provinces, the deeper
(8-15 m) northern basin and the shallower southern flats (0-3 m) (Fig.1). Blue holes
exceeding 20m depth occur in several parts of the lagoon, but are most obvious across the
shallower southern flats. A more detailed description of lagoonal marine habitats is
provided by Williams (this volume), and they are mapped in Figure. 2. At the north of the
atoll, deep and wide passages either side of Horsburgh Island connect the lagoon to the
open ocean. Other exchange between the lagoon and ocean is restricted to 11 shallow reef
flat passages situated on the eastern and southern atoll rim. Currents through these reef
passages are predominantly unidirectional into the lagoon, probably driven by the
persistent southeast trade winds which prevail for most of the year, and wave set-up
generated by the swells which continually break over the windward reef crest. The
hydrodynamics of this atoll have been examined recently by Kench (this volume).

Lagoonal infilling by sediments produced on the reef rim is generally accepted as
the dominant constructional process on atolls after the reef rim has reached a stable sea
level (Marshall and Davies 1982, Frith 1983, Tudhope 1989). Upward growth of the reef
rim has been limited by sea level for more than 2000 years on the Cocos (Keeling) Islands
(Woodroffe et al. 1990a, 1990b, this volume), and historical accounts (Darwin 1842,
Guppy 1889) indicate that much of the southern part of the lagoon has been rapidly
infilled. During his visit in 1836 Darwin sailed to the south of the lagoon through channels
dredged through living coral. Sand sheets or seagrass meadows which are often exposed
at low tides now cover these areas. Vibrocore data were used to establish the nature and
chronology of longer term (mid-late Holocene) accretion in several parts of the lagoon
(Smithers et al. in press).

id Department of Geography, University of Wollongong, Northfields Avenue,
Wollongong, New South Wales, 25272.

Sediments infilling atoll lagoons consist almost entirely of skeletal carbonate
secreted by reef organisms, and facies development within atoll lagoons is governed by
interaction between the supply and physical properties of the source material and the
various processes which degrade, redistribute and stabilize sediments (Maxwell et al.
1964, Milliman 1974). Biogenic carbonates may consist of either rigid reef framework or
unconsolidated detrital material, and may be produced and deposited in situ
(autochthonous) or produced outside the lagoon and transported in before deposition
(allochthonous). The relative contributions of allochthonous and autochthonous sediments
usually varies around a lagoon, and can be determined from the texture and provenance of
contributory components (Swinchatt 1965, Orme 1973). Reconciling the habitat zone of
the source organism with the location of the depositional zone, and the determination of
textural gradients between sediment sources and sinks, allows hydrodynamic, sediment
transport, and facies development processes to be inferred.

There have been few studies of the lagoonal sediments of Indian Ocean atolls and
the lagoon of the Cocos (Keeling) Islands differs in several ways from other atolls where
sedimentation has been examined. Firstly, the sediment producing biota of the Cocos
(Keeling) Islands appear to differ from other atolls, possibly due to its extreme isolation.
Secondly, the size, bathymetry and hydrodynamics of this lagoon differ from other atolls
where carbonate sedimentation has been investigated. Early studies chiefly examined
sediments from the relatively large and deep Pacific atolls with lagoons which deepen
towards the centre (e.g. Kapingamarangi - McKee et al. 1959, Bikini, Rongelap,
Enewetok - Emery et al. 1954). Smaller atoll lagoons with complex bathymetry have more
recently received some attention (Mataiva, Takapoto - Adjas et al. 1990, Henderson Reef -
Chevillon and Clavier 1990, Mataiva - Desalle et al. 1985), but once again are concentrated
in the Pacific. This paper reports on an examination of the surficial lagoonal sediments of
the Cocos (Keeling) Islands, a moderately sized Indian Ocean atoll with a complex
lagoonal bathymetry. The primary aims were to: (1) determine the textural and
compositional characteristics of lagoon surface sediments; (2) identify and map textural and
compositional facies; and (3) relate facies distribution to specific biotic/physiographic
environments.

METHODS AND MATERIALS

The lagoon floor was examined on a series of boat and snorkel transverses. A total
of 167 sediment samples were collected from the lagoon bed (Fig. 3), using a sampling
strategy based on environments determined from aerial photographs and SPOT satellite
imagery. Not surprisingly, the lagoonal environments delineated in this way are very
similar to the marine habitat units established by Williams (this volume). Samples were
collected by scooping unconsolidated sediments into plastic bags except in depths that
exceeded 8m when a weighted steel dredge was used.

Seventy-six sediment samples were analysed granulometrically using the
techniques of Folk (1974), making sure that several samples from each lagoonal
environment were examined. Where necessary the mud fraction was first separated by wet
sieving; these samples were washed with 200 ml of distilled water and approximately 1ml
of 10% Calgon for each gram of estimated mud content. The mixture was left to stand
overnight then mechanically stirred for 3 minutes and washed through a 4¢ sieve.
Sediments larger than 49 were dried, weighed and between 50-70grams transferred to a
nest of sieves ranging from -2¢ to 4g, with a 0.5¢g interval. The sieves were mechanically
shaken for 15 minutes and the fraction retained on each sieve (and the pan) weighed.

Mean grain size, sorting and skewness were determined using the graphic methods of Folk
and Ward (1957).

The skeletal compositions of 50 sediment samples were examined. Representative
subsamples were taken from sieve fractions greater that 3.5¢ and grains were identified
and point-counted using a binocular microscope. Approximately 100 grains were
identified for each sieve fraction. Fifteen component categories were recognized: (i) coral
shingle and grit; ii) Halimeda fragments; 111) coralline algae (principally Spongites rhodolith
fragments); iv) Homotrema; v) gastropod fragments; vi) pelecypod fragments; vii)
unknown molluscan fragments; viii) Marginopora; ix) Amphistegina; x) other
foraminiferans; xi) echinoids; xii) annelids; xiii) alcyonarian spicules; xiv) crustacean
fragments; and xv) indeterminate or unrecognisable grains. Component representation in
the total sample was expressed as a weight percentage of the total sample. Granulometric
and compositional data were analysed using Q-mode factor analysis (Klovan 1966, 1975,
Gabrie and Montaggioni 1982, Montaggioni et al. 1986) in order to classify sediments
according to their compositional and textural characteristics (Smithers 1990).

RESULTS
SEDIMENT TEXTURE

The textural characteristics of seventy-six sediment samples from the Cocos
(Keeling) Islands lagoon are presented in Table 1 and descriptive statistics for each of the
lagoonal environments provided in Table 2. These results indicate that the Cocos
(Keeling) Islands lagoon is dominated by poorly sorted, slightly gravelly (<10%) fine to
coarse sands. Several general trends in sediment texture can be identified. Mean grain size
is greatest in the interisland channels and is lowest in the seagrass meadows and intertidal
sand and mud flat areas. Gravel abundance appears closely related to coral outcrop
proximity, the highest mean values occuring in the interisland channels where
autochthonous gravels are deposited with allochthonous gravels transported from the reef
flats, and in the blue hole mosaic where gravels derived from patch reefs are common.
Occasional high gravel values in samples collected elsewhere in the lagoon can largely be
attributed to the deposition of autochthonous carbonates. Mud content peaks at around
45% in the seagrass meadows but generally comprises 0-2% of most sediment samples.
Sorting is typically poor, but improves in the exposed sandy areas in the north of the
lagoon. Skewness values range from strongly fine skewed to strongly coarse skewed, and
in different areas may reflect either in situ sediment production or else the selective removal
of certain grain sizes by incident currents. The significance of variation in the textural traits
of lagoon sediments will be addressed in the discussion.

Six factors were extracted from the data matrix of 14 variables (weight % of
sediment in each sieve fraction) and 76 observations (sediment samples) using a Q-mode
factor analysis which can account for 91.7% of the data variance. Communality values are
high for all samples indicating that a good description of all samples is given by these
factors. Sediment samples were classified according to the factor axis each was most
heavily loaded upon; samples belonging to each class are listed in Table 3. The grain size
distributions of samples with the highest loading on each factor axis are presented in
Figure 4 and the average textural statistics of sediments assigned to each factor are given in
Table 4.

Descriptions of the textural sediment types classified on each factor axis are
provided below and their distribution is shown in Figure 5:

Factor One - Slightly Gravelly Coarse Sands. These sediments account for over one third
of the samples and are chiefly composed of coarse sands with a minor gravel component
(Fig. 4a and Tables 1 and 2). The grain size distribution is characterised by a primary
mode in the 0¢-0.5¢ range and the mean grain size is around 0.5g. Muds usually form
less than 1% of these sediments. Sorting and skewness are variable; ranging from
moderately well to poorly sorted and from strongly fine to strongly coarse skewed.
Slightly gravelly coarse sands occur throughout the lagoon, but appear to be most
concentrated in the exposed areas of the deeper northern part of the lagoon and around the
interisland channels.

Factor Two - Slightly Gravelly Medium Sands. These sediments are very similar to those
defined by factor one, however the sand fraction is finer with the principle mode being
between 1.59g-29 (Fig. 4b). Sediments represented by this factor range from moderately
well to poorly sorted and show a tendency to be coarse skewed. These sediments cover
much of the lagoon floor, being patchily interspersed with the slightly gravelly coarse
sands in the north of the lagoon and covering large areas north of the southern passage.

Factor Three - Sandy Gravels. High gravel content is the definitive trait of these
sediments, with the grain size distributions peaking in the >-2¢ interval (Fig. 4c). They
are typically finely or very finely skewed and range from poorly to moderately sorted. A
second, smaller modal peak may occur in the sand sized range. Sandy gravel patches are
sporadically distributed within the lagoon, with three distinct patches located in the centre
of the lagoon and another occuring south of Horsburgh Island. Smaller pockets of sandy
gravel are located just north of both Pulu Maria and the seagrass meadows behind South
Island.

Factor Four - Gravelly Sands. These sediments are composed principally of sands, but
also have a moderate gravel content (Fig. 4d). Grain size distributions are often bimodal,
reflecting the poor sorting and variable skewness of most of these sediments. Gravelly
sands are also patchily distributed over the lagoon, with a distinct band located lagoonward
of the islands on the eastern rim. Several smaller patches occur towards the lagoon centre.

Factor Five - Gravelly Muds. Abundant fine sands and muds characterize these sediments,
although gravels are also moderately well represented (Fig. 4e). Sorting, therefore, is
typically poor and most grain size distributions coarsely skewed. Gravelly muds occur in
the lee of the windward islands and in the shallow embayments locally known as Teloks.

Factor Six - Slightly Gravelly Fine Sands. Fine sands in the 2.5¢-3.0¢ range dominate
these sediments. The fine sands may grade into muds in some samples and they are
usually coarse skewed and poorly to moderately sorted (Fig. 4f). Patches of slightly
gravelly fine sands are found throughout the lagoon, however they are more common in
the north central areas.

SEDIMENT COMPOSITION

The skeletal compositions of 50 samples collected from the Cocos (Keeling)
Islands lagoon are listed in Table 5 and the average composition of sediments deposited in
each lagoonal environment presented in Table 6. It is evident from this table that the
abundance of skeletal constituents may vary markedly between different lagoonal
environments. Furthermore, relatively large standard deviation values suggest that
sediment composition may also vary markedly within lagoonal environments.

Nevertheless, several general statements can be made about the composition of sediments
deposited within this lagoon. Coral debris clearly dominates most samples (range: 81.46%
in sample 12 to 11.05% in sample 58), comprising the major identifiable component in all
lagoon environments (see Table 6). Halimeda and coralline algae also contribute
significantly to many samples (Halimeda >15% of samples 24, 29, 45, 48, 49, 58, 124,
171; coralline algae >15% of samples 6, 34, 58, 66, 125, 164, 165, and vibrocore cv15),
particularly those collected where hard coral substrates exist, such as the blue hole mosaic
and the interisland channels. Coralline algae may either encrust other constituents or
consist of rhodolith debris, the later being spherical coralline algae colonies which are
particularly abundant in the high energy interisland channels. The Acropora shingle which
is widespread over the central lagoon floor is also heavily encrusted with coralline algae
and represents a potential source of this material. Homotrema is a minor contributor to
lagoonal sediments (range: 2.48% in sample 24 to 0% in many samples) but appears most
abundant close to high energy, hard substrate environments. Gastropod detritus comprises
around 5% of the sediment in most lagoonal environments, rising to an average of over
10% in the intertidal sand and mud flat areas, and accounting for more than 10% of some
samples from the seagrass meadows (117, 122). Pelecypods comprise less than 5% of
most samples, but contribute 9.8% and 9.35% of samples 108 and 38 respectively.
Marginopora tests make up 0-4% of most samples with no clear pattern to their distribution
being immediately apparent. Amphistegina is a widespread but locally significant
component, being most prolific on the reefs south of Horsburgh Island and in the sandy
lagoon floor region in the north of the lagoon. Annelida, alcyonarian spicules, crustacean
debris and echiniod spines are generally present in small quantities. Crustacean detritus
can, however, occasionally be quite high in areas where living crustaceans are plentiful
(i.e. sample 39 from Telok Jambu - 7.85%). Alcyonarian spicules represent only a small
proportion of most sediments (range: 6% in sample 50 to 0% in many) but appear most
abundant in samples just lagoonward of the reef rim. Indeterminate sediments include
sediments <3.5¢ and those not readily recognisable because of corrosion. As outlined in
the textural results, the abundance of fine sediments is greatest in the seagrass meadows
and intertidal sand and mud flat areas. The -0.5¢ fraction of a sheltered seagrass meadow,
interisland channel, interisland channel/ sand apron and central lagoon sample is presented
in Figure 10a-d.

Three factors were extracted from the data matrix covering 15 component variables
and 50 sediment samples. All samples except 153 have high communality values,
suggesting that a good description of most samples is given by these factors. The lower
value for sample 153 probably reflects the exceptionally high representation of
Amphistegina in this sample, this being more than five times greater than in the sample
with the next highest representation. Samples were classified according to the axis upon
which they were most heavily loaded except where samples had similar loadings on more
than one axis. Loadings were considered similar if the absolute difference between
loadings on different axes was less than a third of the larger loading value, and where this
occurred samples were deemed to be hybrids. Samples belonging to each class defined by
the factor analysis are listed in Table 7 and pie charts showing the composition of the
sample most heavily loaded on each factor axis are presented in Figure 6. These and the
average compositional facies statistics are presented in Table 8.

Descriptions of the compositional sediment types discriminated by the factor
analysis are provided below and their distribution is presented in Figure 7.

Factor One: Coral-Type Sediments. Coral-type sediments are chiefly characterised by the
compositional dominance of the sample by coral debris. More than 60% of samples
collected from the Cocos (Keeling) Islands lagoon are classified as coral-type sediments,

conforming with the preponderance of coral evident in the raw compositional data.
Skeletal material derived from organisms commonly associated with hard coral substrates
(i.e. Homotrema, Amphistegina, annelids and alcyonarian spicules) also reach their highest
representation in this facies. Most of the lagoon bed is covered by sediments most
adequately described as coral-type, the main exceptions being the areas in the lee of the
windward islands.

Factor Two: Molluscan Mud Sediments. A large indeterminate component is characteristic
of these sediments and they contain a noticeably smaller quantity of recognisable coral
debris than the coral-type sediments depicted by factor one. Gastropod debris is also
found in these sediments in moderate amounts, reaching its highest representation in this
facies. Crustacean debris is also significantly more abundant in these sediments than in
any of the other facies, and Marginopora is most prolific in these sediments. Molluscan
mud sediments are predominately restricted to the shallow protected parts of the lagoon,
however there are outlying patches in the north and central lagoon.

Factor Three Coralline Algae/Halimeda Type Sediments. These sediments are essentially
differentiated because they contain a relatively high proportion of coralline algae and
Halimeda and a relatively low proportion of coral debris. Abundant rhodolith debris
determines that sediments deposited in the lee of Pulu Maria and Pulu Siput are most
heavily weighted on this factor, whilst Halimeda debris is responsible for sediments on
the edge of the seagrass meadows in the lee of South Island being loaded on the third
factor axis.

DISCUSSION

The nature and distribution of sedimentary facies in the Cocos (Keeling) Islands
lagoon essentially reflects the interaction of wave and current energy on skeletal sediments
derived from a range of organisms growing in different lagoon environments. The reef
islands and a discontinous reef rim control the distribution of wave and current energy
within the lagoon; directly controlling the entry and distribution of allochthonous sediment,
indirectly controlling the distribution of autochthonous sediments by influencing biotic
zonation, and controlling the redistribution of sediments within the lagoon. Three main
features characterise the sedimentary facies of the Cocos (Keeling) Islands lagoon, these
being: 1) the domination of the lagoon by coral derived sediments; 2) sediment sorting in
areas of relatively high hydrodynamic energy and the deposition of predominantly poorly
sorted sands and gravels in the centre of the lagoon; and 3) the concentration of mud
deposits in the lee of the windward islands, almost exclusively in the seagrass and
intertidal sand and mud flat environments.

The predominance of coral derived sediments and subsequent coverage of most of
the lagoon by the coral-type compositional facies is a striking feature of the Cocos
(Keeling) Islands lagoon (Fig. 7), which is even more remarkable considering the dearth
of living coral presently on this atoll. Compared to other carbonate lagoons coral
components comprise an inordinate proportion of the sediments deposited in this lagoon
(Fig. 8). Several possible reasons exist for the high representation of coral sediments in
this lagoon, including its relatively small size and shallow nature. Milliman (1974)
suggested that because the ratio of lagoonal area to reef rim becomes smaller as atoll size
declines smaller lagoons are more likely to receive a higher proportion of reef flat
sediments, including a substantial proportion of coral material. Alternatively, because
much of the Cocos (Keeling) Islands lagoon is less than 10 m deep, a depth range
dominated by corals in many reef environments (Emery et al. 1954 Stoddart 1969,

Milliman 1974), it is perhaps not surprising that coral sediments are abundant here.
Indeed, coral outcrops are common throughout most of the Cocos (Keeling) Islands
lagoon, imparting a reefal character on most lagoonal sediments. Moreover, lack of net
bathymetric relief has restricted the habitat potential of this lagoon and many components
and facies derived from organisms normally found in deeper water are poorly represented
here (e.g. the deep water Halimeda facies reported from deeper lagoons like Suwarrow
(Tudhope et al. 1985), Kapingamarangi (McKee et al. 1959) and Enewetok (Emery et al.
1954)).

The geomorphic history of the atoll may provide another explanation for the
abundance of coral derived sediments in this lagoon. Woodroffe et al (1990a, 1990b, this
volume) have established that approximately 3000 years ago sea level on this atoll was
close to 1m higher than present, and that at this time a sea-level limited reef flat encircled
much of the lagoon. Sea-level has subsequently fallen to its present level and most of this
higher reef flat has been substantially eroded, remnants existing as the contemporary
conglomerate platform. Clearly the erosion of this fossil reef flat comprises a potentially
significant source of coral sediments which may have been transported around the atoll
under different physiographic conditions as the atoll has developed. Prior to the
consolidation of the larger islands (particularly South Island), for example, coral sediments
were presumably transported into the lagoon through more numerous interisland SHAME S
and could potentially achieve a more widespread coverage of the lagoon.

Although coral-type sediments veneer most of the lagoon (Fig. 7), specific areas
are covered by sediments which are more or less coral-type than others (i.e. are more or
less heavily loaded on the first factor axis due to variations in the abundance of coral and
other components), and textural parameters delineate two distinct source zones, the reef
rim and the lagoon. Deposits formed by allochthonous material transported from the reef
rim are typically most strongly defined as coral-type sediments and those composed of
autochthonous material produced within the lagoon less so, reflecting a change from a
strongly reefal component assemblage (i.e. coral, coralline algae, Homotrema, alcyonarian
spicules, Amphistegina) to a moderately lagoonal one (reefal components less well
represented, fine indeterminate sediments more abundant) (Table 6).

The sandy lagoon floor region is exposed to high levels of wave and current action
due to the discontinuous nature of the reef rim at the north of the atoll and the textural traits
of sediments deposited there reflect this position. Extensively rippled coarse sands which
are near symmetrically skewed and well sorted dominate this area, interupted sporadically
by localised seagrass patches and small coral bommies. Sediments deposited here are
texturally mature; reflecting the relatively high levels of wave and current energy affecting
this area and the rarity of locally generated gravels. Speculation of a peripheral reef source
for these sediments is supported by high Homotrema, Amphistegina and alcyonarian
spicule content; these components normally originating from high energy reef zones and
confering a strong coral-type classification on these sediments. Ripple orientation suggests
that most of this material is transported from the northeast reef rim. Unlike in much of the
southern part of the lagoon these sediments remain submerged at all tidal stages and are
continually affected by waves and currents, enhancing their sorting potential. Similarly
well sorted and rippled sands are described from the Alacran Reef Complex, Mexico
(Kornicker and Boyd 1962) and the lagoon of Enewetok atoll (Wardlaw et al. 1991) and
are thought to have developed under similar environmental conditions.

Interisland channels link the high energy and highly productive outer reef flats to
the lagoon along the eastern and southern atoll margin and act as a conduit for
hydrodynamic energy and sediments entering the lagoon. Waves and currents forced over

the windward reefs are concentrated through these channels developing relatively high
levels of hydrodynamic energy which dissipates into the lagoon. The composition and
texture of sediments deposited through these channels is distinctly reefal, consisting of
sands and gravels derived from organisms typically located on high energy reefs such as
coral, coralline algae, alcyonarian spicules, Homotrema and Amphistegina. Not
suprisingly these sediments are unequivocally coral-type in composition. The relatively
high levels of hydrodynamic energy which affect these channels is reflected by the mean
grain size (0.02¢: the largest in the lagoon), and by the deficiency of fine sediments which
are continually winnowed and transported into the lagoon. Despite the winnowing of fine
sediments interisland channel deposits are generally poorly sorted and texturally immature,
reflecting the heterogeneity of contributing organisms and the continual addition of variably
degraded 'in-train' clasts. Three samples from the Southern Passage illustrate the coarse
nature, in-train addition and textural immaturity of sediments deposited in the interisland
channels, these samples (23, 24, 58) located in close proximity to each other and classified
respectively as a slightly gravelly coarse sand, a sandy gravel and a gravelly sand.

Coral-type sediments dominate the slightly gravelly medium sands which extend
from the interisland channels over the sand aprons and through much of the lagoon centre
(Figs. 4 and 6). Despite the continuity of these facies beyond the sand apron fringe (Fig.
2), however, textural gradients in samples collected from the sand aprons and changes in
minor component abundance suggest that sediments deposited over sand aprons are
allochthonous whilst those deposited beyond these features are autochthonous. The
evolution of analogous textural attributes in skeletal carbonate deposits due to either
hydrodynamic sorting or skeletal architecture is a principal shortcoming of carbonate
texture as an environmental discriminator (Stoddart 1969, Montaggioni et al. 1986) and is
well demonstrated here. The redeeming usefulness of textural gradients for environmental
interpretation is, however, also confirmed.

Extending into the lagoon over the sand aprons a marked decline in gravel content
(24.89% to 7.94%) and an increase in the proportion of sands (74.92% to 90.97%) and
muds (0.18% to 1.08%) occurs, conforming elegantly with models of lagoonal
sedimentation which predict a systematic decline in mean grain size with distance from the
reef rim (Frith 1983, Chevillon and Clavier 1988). Size-sorting is characteristic of
backreef sand aprons on other reefs where hydrodynamic energy levels abate into the
lagoon and are paralleled by a decline in mean grain size (Macintyre et al. 1987). Size-
sorting generally becomes evident from around the mid-range of sand aprons extending
into the Cocos (Keeling) Islands lagoon; sediments deposited at this distance from the
interisland channels sufficiently removed from locally generated sediment sources to attain
some degree of textural maturity. Textural gradients and composition indicate that the sand
aprons predominantly comprise allochthonous sediments shed from the reef rim. Similar
backreef sand deposits are described in the Pacific (Marshall and Jacobson 1985, Scoffin
and Tudhope 1985, Tudhope 1989), where medium grade coral sands also dominate the
lagoonward fringe. The penetration of allochthonous sand aprons in the Cocos (Keeling)
Islands lagoon is similar to that reported from other reefs (Scoffin and Tudhope 1985),
however at this atoll they are spatially restricted to where interisland channels link the outer
reef flat to the lagoon and concentric backreef facies belts do not develop.

The systematic decline of mean grain size ceases at the lagoonward margin of the
sand aprons essentially marking the limit of allochthonous slightly gravelly medium sand
penetration into the lagoon. Grain component data (Table 6) support the assertion that
allochthonous sediments (greater than mud-sized) penetrate the lagoon only as far as the
sand apron margins, sediments deposited over the lagoonward parts of the sand aprons
being generally rounded whilst those deposited beyond sand apron fringes are

predominantly angular and autochthonous. The range of the coralline algae/Halimeda
facies which extend from the interisland channels immediately east of West Island and
north of South Island further supports this speculation, and demonstrates the utility of
skeletal carbonates derived from habitat specific organisms as biogenic tracers of sediment
transport. These facies are chiefly comprised of rhodolith debris originating from these
channels which can be traced, and is size-sorted, towards the lagoonward sand apron
fringe. Kench (pers. comm) has suggested that the flood tidal wave entering the lagoon
from the north opposes currents flowing through the Southern Passage around the
lagoonward sand apron fringe, possibly impeding the transport of allochthonous sediments
beyond this point. Immediately beyond the lagoonward sand apron margins the textural
trends imposed by hydrodynamic sorting are corrupted by the addition of autochthonous
gravels and sands and the skeletal architecture of contributing organisms becomes the
principal determinant of facies texture. The lagoonal limit of allochthonous sediments may
be obscured, however, when they prograde over gravel bearing reefs such as those
fringing the blue holes behind the eastern reef islands. Here a band of gravelly sands has
developed when transported and sorted allochthonous sands mix with and are texturally
overwhelmed by gravels derived from the lagoonal patch reefs.

The irregular mosaic of textural facies covering the central part of the lagoon
suggests that sedimentation is chiefly governed by the locally abrupt bathymetric (and
environmental) change imposed by the blue holes and the sporadic occurrence of patch
reefs and lag gravel deposits. Formed as autochthonous material is deposited in situ, the
textural characteristics of these facies are dependant on the grain sizes yielded as
contributing organisms degrade, and the extent to which hydrodynamic conditions modify
these deposits. Sediments through the centre of the lagoon are characteristically poorly
sorted and coherent textural gradients are lacking, indicating the absence of significant
hydrodynamic modification. Low mud values suggest, however, that fines may be
winnowed from exposed deposits. The prevalence of coral debris through the centre of the
lagoon is convincingly demonstrated by the distribution of the coral-type compositional
facies, and the mosaic of textural facies which occurs through the same region can largely
be ascribed to the variable representation of epilithic gravels derived from lagoonal patch
reefs. The irregular bathymetry around the blue holes further ensures an erratic
distribution for textural facies in this part of the lagoon via its control of patch reef
distribution. Essentially these sediments are composed of medium to coarse coral sands
supplemented with varying amounts of epilithic coral gravels to form various grades of
gravelly sand and sandy gravel facies. The distribution of compositional facies other than
coral-type is related to the occurrence of the definitive organisms, the presence of which
may also impart distinctive textural properties. Isolated molluscan mud and coralline
algae/Halimeda facies in the central part of the lagoon, for example, occur where the
representation of their definitive components is high, and where largely intact and gravel
sized mollusc shells and Halimeda segments respectively induce local coarsening of facies
texture. Though coral detritus undoubtedly dominates most sediments through this area of
the lagoon, the extent to which it does so and the representation of minor components
varies considerably both within and between lagoonal environments (Tables 5 and 6),
largely reflecting the diffuse and weakly zoned distribution of contributing organisms and
the in situ deposition of derived sediments. Despite local variations in the representation
of minor components, however, the overwhelming dominance of coral debris and the
relative constancy of the component assemblage through the lagoon centre, which can be
attributed to the lack of strong environmental and hydrodynamic gradients, has determined
that except for at the extreme environments in this lagoon distinctive correlations between
lagoonal environment and compositional/textural facies are difficult to define. Widespread
facies-environment coincidence has been demonstrated in many carbonate emvironments
(Ginsburg 1956, Swinchatt 1965, Boscence et al. 1985), however similarly poor

10

correlations between facies distribution and lagoonal environment are reported from other
lagoons where environmental/hydrodynamic condtions remain constant over most of their
area (Colby and Boardman 1989).

The distribution of fine sediments within the Cocos (Keeling) Islands lagoon
exhibits the strongest and most consistent textural/compositional facies and lagoonal
environment correlation. In contrast to other lagoons where muds winnowed from the
high energy peripheral zones accumulate in the lagoon centre (McKee et al. 1959, Roy and
Smith 1971), significant mud deposits in the Cocos (Keeling) Islands lagoon are confined
to the sheltered depositional environments in the lee of the windward islands. The
concentration of mud facies behind windward reef islands is also described from the
Tarawa atoll and Chesterfield Islands lagoons where reef islands effectively isolate the
lagoon in their lee from erosional waves and currents. In the Cocos (Keeling) Islands
lagoon muds are almost exclusively deposited in the seagrass meadow and intertidal sand
and mud flat environments in the lee of South Island and in the West Island teloks (Figs. 2
and 4), with a marked concurrence of environment and facies boundaries. In addition to
the sheltered position, the current reducing affects of benthic flora may enhance fine
sediment deposition over the seagrass meadows (Ginsburg and Lowenstam 1958,
Swinchatt 1965, Scoffin 1970), and intertidal periods of subaerial exposure may aid the
accumulation of fine sediments in the intertidal sand and mud flat areas. Adjas et al.
(1990) have demonstrated that most carbonate muds deposited in atoll lagoons are biogenic
rather than chemogenic, and it is likely that the muds deposited in the Cocos (Keeling)
Islands lagoon are produced by the attrition of larger skeletal carbonates (due to biological
and physical action). Although some of these fine sediments are no doubt produced in situ
it is likely that fines winnowed from elsewhere in the lagoon and transported to these sites
comprise a significant proportion of these muds. In these low energy settings ‘currents of
delivery’ rather than ‘currents of removal’ (Orme 1973) principally govern facies texture.
The muds are deposited with autochthonous gravels and sands derived from indigenous
molluscan, and to a lesser extent crustacean and coral gravels to form the gravelly
mud/molluscan mud facies depicted in Figures. 3, 4, 5 and 6. Abundant molluscan and
crustacean faunas presently inhabit the areas of the lagoon where muds are deposited and
generate significant quantities of gravel sized sediment, however coral gravels in these
deposits usually consist of lag material deposited under different physiographic conditions
(i.e. prior to being isolated from the reef rim by the reef islands) or else brought to the
surface by bioturbation. The skeletal remains of organisms indigenous to the seagrass
meadows and intertidal sand and mud flats are particularly well represented in the
recognisable fraction of these sediments (e.g. crustaceans, gastropods, Halimeda,
Marginipora), and are normally deposited reasonably intact. The fragile tests of the
epibiontic foraminiferan Marginopora, for example, remain relatively undamaged in these
deposits but are usually fragmented in sediments deposited elsewhere. Furthermore,
minor components derived from high energy reef areas (e.g. Homotrema, Amphistegina,
alcyonarian spicules) are poorly represented.

Muds are only nominally present outside of these areas, isolated deposits of finer
sediment elsewhere in the lagoon essentially developing due to local modification of the
hydrodynamic regime by seagrass beds, patch reefs and bathymetric change. Isolated
patches of slightly gravelly fine sand amongst the generally coarse sediments of the high
energy sandy lagoon environment can be directly attributed to patches of the seagrass
Thalassodendron, the blades of which reduce current velocity and induce the deposition of
finer sediment which is then stabilised by the root system (Scoffin 1970). The association
of molluscs (and molluscan debris) and seagrass evident in the Thalassia seagrass
meadows behind South Island is also apparent in the isolated Thalassodendron patches,
and sediments over these patches are compositionally classified as molluscan mud

11

sediments. Muds also settle from suspension and accumulate at the base of many of the
blue holes where low energy levels predominate, and pockets of muddier sediment are
often deposited around patch reefs which impede current flow. These sediments are also
often compositionally classified as molluscan muds, however it is the domination of fine
indeterminate/mud sediments in these areas which confers this classification. The
deposition of muds adjacent to patch reefs due to their modification of lagoonal currents
has similarly been reported by Frith (1983) and Delasalle et al. (1985) and muds are
reported to accumulate at the bottom of lagoonal 'pools' in Fanning Lagoon (Roy and
Smith 1971). The concentration of fine sediments in sheltered areas behind the windward
islands and their general absence elsewhere suggests that ambient lagoonal currents are
sufficient to entrain and transport most fines out of the lagoon. The burrowing shrimps
which inhabit areas of the lagoon bedded by sand may aid this process by resuspending
sediments ejected from their burrows into the water column (Tudhope and Scoffin 1984,
Scoffin and Tudhope 1985, Tudhope 1989). A sizable sediment shute extending seawards
between Turk's reef and Horsburgh Island physically records the transport of sediment out
of this lagoon, although the character of these sediments is not known. The purging of
sands and muds outside of reef systems has, however, been well documented (Neumann
and Land 1975, Roberts and Suhayda 1983, Frith 1983).

It is interesting to note that the sediments deposited in this lagoon do not appear to
conform with the Sorby principle (Folk and Robles 1964) which predicts the generation of
size specific grain size populations controlled by the skeletal architecture of the contributing
organisms (Fig. 9). Non-conformance with the Sorby principle is not uncommon
however, with several authors reporting no apparent size specificity in sediments derived
from different constituent organisms (Clack and Mountjoy 1977, Flood and Scoffin 1978,
Gabrie and Montaggioni 1982). The ubiquity of coral sediments at all grain sizes is
apparent in Figure 9, and may possibly distort the recognition of distinctive component-
specific grain size populations simply by dominating grain counts.

CONCLUSION

The lagoonal sediments of the Cocos (Keeling) Islands are principally composed of
gravels and sands derived from corals with minor components such as mollusc, Halimeda
and rhodolith debris becoming locally important. Coral-type sediments overwhelmingly
dominate the lagoon, reflecting the lack of significant populations of carbonate producing
organisms other than coral on this atoll. Textural and compositional trends indicate that
allochthonous sediments are deposited in this lagoon only as far as the sand aprons and
sandy lagoon floor environments, beyond which sediments are almost entirely
autochthonous. Allochthonous coral-type sediments can be identified by the inclusion of
significant quantities minor components which are of distinctly high energy reef origin and
by size-sorting along established hydrodynamic gradients. The irregular distribution
patttern of textural facies in the centre of the lagoon reflects the deposition of epilithic
gravels and sands produced as sporadically distributed patch reefs and lag material
degrades in situ .

The concurrent distribution of the gravelly mud textural facies, the molluscan mud
compositional facies and the seagrass meadow and intertidal sand and mud flat
environments is remarkable, and largely reflects the extent to which depositional conditions
in these facies/environments are differentiated from the rest of the lagoon. Depositional
conditions in these areas are characterised by low hydrodynamic energy levels, either as a
function of position relative to the high energy interisland channels and/or as a function of
the current reducing action of benthic flora. Fine sands and muds, which may be both

12

allochthonous and autochthonous are deposited in these zones with a coarse gravel
component derived from the remains of indigenous organisms such as gastropods and
crustaceans

ACKNOWLEDGEMENTS

This paper is largely based on an Honours thesis submitted to the Geography Department
of the University of Wollongong. I am most grateful to the supervisor of this thesis, Dr.
Colin Woodroffe, for the opportunity to undertake such a study and for encouragement,
advice and constructive criticism at all stages. Thanks also go to Prof. Roger McLean and
Eugene Wallensky for helpful advice and guidance in the field, and to Assoc. Prof. Ted
Bryant for assistance with problems statistical. The logistical support of the Cocos
(Keeling) Islands Administration and Cocos Islands Council whilst in the field was also
much appreciated, with special thanks to Paul Stevenson, the Government Conservator
whose field and administrative assistance proved invaluable.

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18

Table 2. Summary of textural statistics for each lagoonal environment: (n) denotes number of

samples per environment.

Lagoonal Environment

I II Hl IV Vv VI VII Vill IX
(n) (10) (9) (12) (8) (8) (3) (6) (8) (12)
0.02 0.87 1.34 0.56 0.72 1.46 0.83 0.74 1.05
Mean (@) (0.68) (0.15) (1.02) (0.70) (1.22) (0.02) (1.20) (0.24) (0.89)
Coarse Coarse Medium Coarse Coarse Medium Coarse Coarse Medium
Sand Sand Sand Sand Sand Sand Sand Sand Sand
1.28 les, 1.54 E52 1.41 PPh 9 1.23 1.39 1.00
Sorting (0.45) (0.27) (0.53) (0.24) (0.30) (0.04) (0.26) (0.30) (0.34)
(PD) PS PS eS PS PS VPS PS PS MS
0.08 -0.15 -0.21 -0.04 0.05 -0.09 0.23 0.03 -0.10
Skewness (0.28) (0.20) (0.35) (0.17) (0.39) (0.05) (0.67) (0.35) (0.15)
NS GS GS NS NS NS FS NS NS
Gravel % 24.89 7.94 12.82 18.55 24.45 12.81 2.03 10.98 6.90
(20.71) (6.19) (10.46) (13.86) (25.59) (0.68) (2.68) (6.14) (7.93)
Sand % 74.92 90.97 13°35 80.29 73.36 65 96.63 88.13 92.58
(20.83) (6.78) (23.10) (13.38) (24.47) (6.40) (3.26) (5.94) (7.79)
Mud % 0.18 1.08 13.70 1.15 2.18 22.19 1:33 0.88 0.61]
(0.45) (1.24) (19.16) (1.07) (2.84) (7.03) (0.94) (1.16) (1.35)
Key
Sorting Skewness
PS Poorly Sorted NS Near Symmetrical
VPS Very Poorly Sorted Cs Coarse Skewed
MS Moderately Sorted SCS Strongly Coarse Skewed
Ws Well Sorted FS Fine Skewed
MWS Moderately Well Sorted SFS Strongly Fine Skewed
Environment
I Interisland Reef Flats VI Intertidal Sand and Mud Flats
I Sand Aprons Vil Algal Covered Acropora Rubble
II Seagrass Meadows Vill Massive Corals Interspersed with
Sandy Patches
IV Variable Coral and Algal Flat IX Sandy Lagoon Floor

Vv Blue Hole Mosaic

19

Table 3. Sediment sample textural classification based on factor analysis. Bold numbers represent
samples with the highest loading on each factor axis.

Sediment Classification Samples

1, 6, 12, 13, 14, 15, 16, 21, 24, 34, 50, 70, 134, 136, 141, 144, 148, 149, 150,
Factor One LS TISSS IS4e SON 67e

. 2, 3, 9, 32, 35, 38, 45, 46, 48, 49, 84, 89, 114, 128, 130, 143, 155, 163.
Factor Two

Factor Three

Factor Four

Factor Five

Factor Six

5; 10; 585665125, 12:

8, 23, 29, 30, 164, 165, 169, 170, 171.

SOUT 20%1225 16:

57, 60, 104, 142, 147.

Variable Mixtures 11, 65, 79, 124, 126, 132, 145, 146, 157.

Table 4. Textural characteristics of sediment types discriminated by factor analysis. Abbreviations as
per Table 2. Standard deviations in parentheses.

Factor 1 2) 3 4 5 6
(n) 25 19 6 9 5 5
Var. % 3m 23.4 12.3 6.8 5.8 5.3
Cum. Var.% B75 61.1 73.4 80.2 86 91.3
“ 0.55 1.31 -0.74 0.63 1.82 2.49
Mean (9) (0.44) (0.55) (0.60) (0.35) (0.42) (0.41)
1.11 1.26 1.56 1.61 NOY] Dui?
Sorting (9) (0.24) (0.45) (0.42) (0.15) (0.14) (0.32)
Skewness 0.03 -0.14 0.53 0.07 -0.34 -0.33
(0.23) (0.23) (0.35) (0.15) (0.26) (0.54)
ae > 8.02 8.32 55.48 15.45 15.16 1.55
Gravel % (7.89) (9.51) (17.20) (5.10) (3.74) (2.27)
91.51 90.29 43.84 82.83 49.32 91.60
Sand % 5
(7.82) (10.12) (16.62) (4.21) (14.97) (6.86)
0.46 1.25 0.67 1.82 35.52 6.83
Mud %

(0.84) (1.46) (0.72) (1.19) (12.66) (7.05)

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23

Table 7. Component classification based on factor analysis. Bold numbers represent samples with

the highest loadings on the three factor axes.

Sediment Classification Samples

Factor One: 3, 9, 10, 12, 24, 29, 32, 34, 38, 48, 50, 56, 65, 66, 77, 79, 84, 89, 104,
412012425 130M 12S OS 8S 434453. 156. IS7. 1632
Milevls:

Factor Two: 39, 45, 49, 60, 147, 161, 117, 122.

Factor Three: 58, 164.

Hybrid: Factors One and Two 305i.

Hybrid: Factors One and Three 6, 165.

Hybrid: Factors Two and Three _108.

24

Table 8. Component facies statistics. Bold values denote representative component types.

Factor

Var. %
Cum. Var. %
Sediment-type

(samples)

Coral

Halimeda

Coralline Algae

Homotrema

Gastropods

Pelecypods

Unknown

Molluscs

Marginopora

Amphistegina

Unknown

Foraminiferans.

Annelida

Alcyonarians

Crustaceans

Echinoids

Indeterminate

I 2, 8 Hybrid Hybrid Hybrid
69.9 20.6 9.5
69.9 90.5 100
Coral -type Molluscan Coralline Coral- Coral-Coralline | Molluscan
Muds Algae/ Molluscan Mud Algae/ Mud-Coralline
Halimeda Type Hybrid. Halimeda Algae/
Hybrid Halimeda
Hybrid
59.9 Dil Dn 29.84 42.59 45.72 31.01
(11.5) (11.97) (11.97) (2.38) (1.68) |
9.38 9.54 10.38 13.76 8.14 14.76
(6.86) (6.08) (6.16) (0.15) (5.71) .
6.47 2°33 32.84 2.92 25.94 12.71 |
(6.02) (4.02) (10.96) (0.87) (5.65)
0.52 0.16 0.21 0) 0.04 0
(0.71) (0.32) (0.28) (0.06)
4.97 Uap 0.67 6.94 S25 5.93
(3.70) (4.77) (0.57) ((0.20) (2.73)
DAS 1.55 1.48 1.88 1.22 9.80
(2557) (1.65) (0.77) (2.41) (1.57)
2.97 3.04 6.30 4.60 5:23 3.70
(1.62) (2.0) (0.38) (0.40) (1.93)
2.19 2.36 1.43 2.0 0.76 1.19
(2.60) (1.28) (1.49) (0.91) (0.78)
1.71 0.05 0.33 0 0.19 0.08
(4.70) (0.07) (0.31) (0.27)
1.19 3.24 1.84 1.07 1.48 DDS
(1.28) (2.29) (1.60) (0.16) (1.97)
0.33 0.04 0.1 0 0.04 0.07
(0.74) (0.1) (0.17) (0.06)
0.92 0.3 0.72 0.54 0.5 0.25
(1.26) (0.35) (0.22) (0.06) (0.5)
0.88 3.05 0.37 125 1.16 1.84
(1.14) (2.37) (0.52) (0.42) (1.64)
0.55 0.02 0.28 0.06 0.67 0.09
(0.78) (0.03) (0.29) (0.08) (0.13)
5.88 39.62 7.20 22.41 3.66 16.36
(6.02) (12.83) (6.84) (3.74) (5.18)

Figure 1.

Turks feelin

25

XL ERS RSOOR
Poa rarerereretece
SA, RK ORR 6

Se atte SRK

eretetet INDIAN OCEAN ()
eranones Cocos

Horsburgh eee (KEELING)

is. x oe ISLANDS ay

COCOS
(KEELING)
ISLANDS

peg
Deeper Northern a ee)

~< Basin yi

& —_— acy
Se ee oe eon

Shallow Southern
Flats

ae rey ‘
South Passage

) km. 5 96°55’

Location map of the Cocos (Keeling) Islands, showing bathymetric precincts.

26

12°05’

SOSOPOOAOOOOASAAAAAS
SOSA AAAAAG
SOSA AGASLSAS V

96° 50’

1) Interisland channels

il) Sand apron

lll) Seagrass meadows

IV) Variable coral and algal flat

V) Blue hole mosaic

Figure 2.

A
NON
SSNS
NN
XEN
NEN
NEN
EN
Sy
NEN
NEN
NN
NN
NEN
NN
NUN

96°55’

Vi) Inter-tidal sand and mud flats

Vil) Algal covered Acropora rubble

Vill) Massive corals interspersed
with sandy patches

IX) Sandy lagoon floor

Reef edge

NNAN
ANNS

Lagoonal environments of the Cocos (Keeling) Islands.

;
|

ee Ys

Dal

96°50' 96°55’

12°05’.

1494 1384

147, ‘1484 1374
1364

4 Surface samples ‘ud’ denotes unsuccessful dredge.
seat !

Figure 3. Sediment sample locations.

28

Percentage Weight

Figure 4.

TEXTURAL TYPES

a) Sample 15

Coarse Sands

40

20

‘|c) Sample 152

40

20

5 CHM Aa

e) Sample 117

Gravelly Muds

40

20

Sandy Gravels qd) Sample 8

Slightly Gravelly b) Sample 143 Slightly Gravelly
Medium Sands

Gravelly Sands

f) Sample 147 Slightly Gravelly
Fine Sands

2 AG ft 23 te
Particle Size (phi)

Grain size histograms of samples with the highest loadings on a) factor 1; b)

factor 2; c) factor 3; d) factor 4; e) factor 5; f) factor 6.

96° 55'E

29

12°05'S

TS, Slightly Gravelly Coarse Sands Gravelly Sands
jj Slightly Gravelly Medium Sands Sandy Gravels
| YH Slightly Gravelly Fine Sands WariabiolMixture
WN Gravelly Muds Unsuccessful Dredge

Figure 5. Textural facies distribution, Cocos (Keeling) Islands lagoon.

IM TTT

+

30

a) Factor 1 b) Factor 2 c) Factor 3
Sample 12 Sample 58 Sample 122
Coral Type Sediments Coralline Algae / Molluscan Muds

Halimeda Sediments

Figure 6.

ED Coralline Algae / Halimeda

icy Molluscs
Y

Miscellaneous
Indeterminate

Pie charts showing sediment composition of samples with the highest loadings
on a) factor 1; b) factor 2; c) factor 3.

31

96°50'E laste

Ya a :
pay Factor 1 - Coral Type Sediments
SS Factor 2 —- Molluscan Muds

HHI Factor 3 - Coralline Algae/Halimeda
a006 Unsuccessful Dredge

Figure 7. Compositional facies distribution, Cocos (Keeling) Islands lagoon.

32

LAGOON SEDIMENT COMPOSITION

PACIFIC OCEAN : INDIAN
ie : CARIBBEAN SEA ocean
70 4

fe :
a 60 N
a N
S 50 ———__ N
=
m 40 —=
= N
= N : ;
=. 30 — DL wa\Co ala | jo
: \
2 20 —__—_| — se Ne=|=s5== EEE —
SS cat
Gai _is ENS 1 —
10 i met | [od NN Cot wT
oon Tes. rT : oO Tks: : ro
0 ALE hE Hoe RES Ts A ||
BIKINI. ENIWETOK JOHNSON FLORIDA ALACRAN COCOS
ATOLL REEF (KEELING)
ISLANDS
@ Coral ki] Foraminiferans 1) Halimeda
} Molluscs SJ Coralline Algae fl Miscellaneous
Figure 8. Histogram comparing of skeletal composition of the Cocos (Keeling) Islands

lagoon to other carbonate lagoons. Data for other lagoons from: Bikini - Emery
et al. 1954, Enewetok - Emery et al. 1954, Johnson Atoll - Emery 1962,
Florida - Ginsburg 1956, Alacran Reef - Hoskin 1966.

33

30
1 Other Foraminiferans
HM Indeterminable
Bryzoans
5 fi Amphistegina
3 20 Unknown Molluscs
E | os M Pelycepods
5 fl == ved bree Gastropods
ep oe bss, O Red Coralline Algae
5 “ ANd Hi Halimeda
= 10 ee ay | Be E] Coral
A. CIR ETE Baan <7
SS ES si
0 nh 4 a Ch ie aaes
Dae Nee OM SemOe OFS le MAS, 25 25.435) Sana 4
Grain Size (@)
Figure 9. Histogram showing grain size distribution of sample 104 and the size

distribution of skeletal components.

34

Figure 10. -0.5¢ fraction of sediments from various parts of the Cocos (Keeling)
Islands lagoon. (a) Sample 24 from the interisland channel. Note the dominance
of coral components. Mixed rounded and angular sediments indicative of texturally
immature deposit. (b) Sample 58, collected from the lagoonward margin of the
interisland channel. Samples predominantly rounded, reflecting the high levels of
hydrodynamic energy through this zone. Note rhodolith debris. (c) Sample 120,
collected from the seagrass meadow behind South Island. Note the abundance of
molluscan material and Halimeda flakes. Angular fragments common. (d)
Sample 70 collected from the centre of the lagoon. Note the dominance of coral
which is variably rounded and encrusted with coralline algae. Halimeda flakes,
mollusc debris, echinoid spines also apparent. Key: C - coral; E - echinoid; H -
Halimeda, M - Marginopora; Mg - gastropod; Mp - pelecypod; R - rhodolith.

ATOLL RESEARCH BULLETIN

NO. 408

CHAPTER 10

HYDRODYNAMIC OBSERVATIONS OF THE COCOS (KEELING)
ISLANDS LAGOON

BY

P. KENCH

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 10
HYDRODYNAMIC OBSERVATIONS OF THE
COCOS (KEELING) ISLANDS LAGOON
BY
P. KENCH *

INTRODUCTION

Atoll lagoon hydrodynamic studies to date have primarily focused on the mass flux
of water and nutrients through lagoon systems and identified the principle driving
mechanisms of lagoon circulation and flushing (von Arx 1948, 1954, Gallagher et al.
1971, Stroup and Meyers 1974, Smith and Jokiel 1978, Atkinson et al. 1981, Gilmour
and Colman 1990).

In general, lagoon circulation has been found to respond to three driving
mechanisms: wind-driven set-up on the windward ocean reef; wind stress on the lagoon
surface, and tides (Atkinson et al. 1981, Andrews and Pickard 1990). Wind has been
identified as the the primary driving mechanism of lagoon circulation in deeper lagoon
systems (e.g. Bikini Atoll - 60m deep, von Arx 1954, Enewetak Atoll- 50 m deep,
Atkinson 1981). Wind is not, however, thought to play a large role in the exchange of
water between lagoon and ocean. In shallow lagoons such as that of Fanning Atoll (5 m)
tidal forces are found to dominate both lagoon circulation and lagoon-ocean water
exchange (Stroup and Meyers 1974).

The degree to which a lagoon is dominated by wind or tidal forces is found to
depend on the lagoon depth and the degree of connection between the lagoon and open
ocean (Wiens 1962, Stroup and Meyers 1974). The speed of lagoon-ocean exchange is
also reliant upon the ‘openness’ of the lagoon with the ocean.

The majority of atoll hydrodynamic studies have been performed in the Pacific
Ocean within deeper lagoons (50-60 m, Enewetak, Bikini lagoons) with the exception of
the shallow Fanning Atoll lagoon (5m). There has been little research on the
hydrodynamic processes within Indian Ocean atolls, except for research on the tidal
characteristics of several atolls in the Western Indian Ocean (Farrow and Brander 1971,
Pugh 1979, Pugh and Rayner 1981).

This paper describes results from the examination of the hydrodynamic processes
of the lagoon of the Cocos (Keeling) Islands, in the eastern Indian Ocean (Fig. 1). It has
three aims: first, to describe the tidal regime of the Cocos atoll lagoon; second, to examine
the water currents and circulation within the lagoon and connections between the lagoon
and ocean; and third, to establish the flushing characteristics of the atoll.

* Department of Geography and Oceanography, Australian Defence Force Academy,
Canberra, Australian Capital Territory, 2601.

FIELD LOCATION

The main lagoon of the Cocos (Keeling) Islands is enclosed by 26 islands and has
a surface area of 190 km2. The lagoon can be divided into two distinct morphological
zones: a deep (8-12 m) northern portion and a large shallow (0-3 m) southern region (Fig.
1). A network of deep blue holes exists in this shallow region with depths in excess of
20m. The lagoon opens to the northwest and northeast either side of Horsburgh Island
where passes are deep (12-14 m) and wide (2-5 km). Eleven shallow passages (<2 m)
connect the ocean and reef to the lagoon on the eastern and southern sides of the atoll.

The atoll is dominated by the southeast trade winds which prevail for most of the
year. The islands also lie within the equatorial (westward flowing) ocean current
(Neumann 1968), which reaches a maximum velocity of more than 1 knot (Tchernia
1980). In the northern hemisphere winter, movement of the Inter Tropical Convergence
Zone (ITCZ) south of the equator produces variable winds and the Equatorial Counter
Current (eastward flowing) may develop. The degree to which the Cocos (Keeling)
Islands are affected by this counter current is dependent upon the extent of southward
migration of the ITCZ (Neumann 1968).

The closest amphidromic point to the Cocos (Keeling) Islands is situated off the
southwest coast of Australia (Platzman 1984, for the M2 tide). The anti-clockwise rotation
of the tidal wave around this point and the location of the Cocos (Keeling) Islands, suggest
the tidal wave sets from the east-northeast.

METHODS

A field measurement program was undertaken from November 1991 to January
1992. Tidal observations have been taken on Cocos, by the Australian CSIRO
Oceanography Division since 1963, from a permanent tide gauge on Home Island jetty
(Fig. 1). For the duration of the field measurement period a temporary pressure tide gauge
was deployed in the south of the atoll (Fig. 1) to identify any changes in tidal
characteristics between the northern (deep) and southern (shallow) regions of the lagoon.
This gauge operated successfully for 20 days before being fouled by marine algae. The
permanent tide gauge was inoperative during the period of measurement by the temporary
gauge. This limits direct comparison of observed elevation and time data. A harmonic
analysis (Foreman 1979a) of water level observations from November 17 to December 6
(temporary gauge), and from March to April 1988 (permanent tide gauge) has been made
to resolve the major tidal constituents at each location (ease of access to permanent tide
gauge data being the primary factor deciding the period analysed).

Current speeds and directions were obtained using five bidirectional
electromagnetic current metres. These metres were deployed for 16 day periods in 7
shallow passages and 5 sites within the lagoon (Fig. 1). Current metres were mounted 0.4
m above the bed in the passages and 0.5 m above the bed in the lagoon. Additional, shorter
records (1-2 day) were obtained from the deeper passages to the northwest and
northeastern sections of the lagoon, and from one station in the middle of the lagoon (Fig.
1). For these experiments 3 current metres were deployed vertically, at depths of 2 m
below the surface, mid-depth and 1m above the bed. Current records, in all sampling
periods, were 1 minute averages of current velocity taken at 10 minute intervals.

Current time series have been harmonically analysed to resolve the major tidal
current constituents (Foreman 1979b). Constituents resolved for each time series were

3

used to predict the tidal currents for the period analysed. Predicted currents were then
subtracted from the observed current data to identify those components of the current
record not attributed to tidal forces. These currents are termed ‘residual currents’.

Velocity profiling using an impellor current metre was undertaken during neap and
spring tidal conditions in all shallow passages. Velocity measurements at stations across
each channel were corrected to 20 minute intervals and the cross-sectional area of each
channel identified for each time increment. Cross-sectional area discharge relationships
were then derived for each shallow passage.

Tidal prism - the volume of water entering and leaving the lagoon during a tidal
cycle -was calculated for a 1m and 0.4m spring and neap tide respectively. Bathymetric
charts (1983) provided lagoon depths relative to 0.7m below Mean Sea Level,
corresponding to zero on the Home Island tide gauge. The surface area of the lagoon at
low and high tide was estimated through planimetric analysis. The change in depth (1m-
spring; 0.4m-neap) was then applied to the respective low and high tide surface areas to
calculate the volume of the lagoon. Differences between high and low tide lagoon volumes
provide estimates of tidal prisms for the neap and spring tides. With an estimation of total
lagoon tidal prism, the contribution of shallow passage water flux to lagoon flushing is
identified, and the ocean lagoon exchange time calculated.

RESULTS

Tides

Harmonic analysis of the tidal records identify the semi-diurnal constituents of
greatest importance (Table 1) with the M2 and S> constituents having amplitudes of 29 and
14 cm in the north of the lagoon and 25 and 5.6 cm in the south of the lagoon. These
amplitudes also display a marked attenuation from north to south within the lagoon. The
Kj, constituent has an amplitude of 12.19 cm and 10.28 cm for the north and southern
parts of the atoll respectively (Table 1).

The southern lagoon tides lag those of the northern lagoon (Table 1). This lag is
evident in the tidal records with observed high tides lagging those in the north by 15-55
minutes dependent on the tidal range and regime (spring or neap tides). Shallow water
tides (M4) are much larger in the shallow southern region of the atoll than the deeper
northern lagoon.

The form of the tides as identified by the amplitude ratio [F = (K; + O1)/(S2 + M2)]
is 0.44. This describes the tides as mixed mainly semi-diurnal. These tides
characteristically have large inequalities in range and time between the highs and lows each
day (Pond and Pickard, 1983). Mean spring tidal ranges using the equation S = 2(M2 +
S2) are 87 cm and 61.2 cm for the north and south of the atoll. These amplitudes display a
marked attenuation of the tide from north to south. The analysis also identifies a 6.02 cm
(north) and 7.21 cm (south) increase in Mean Sea Level between neap and spring tide
conditions (Msf constituent, Table 1).

Current Circulation
Progressive vector plots of current information are shown in Figures 2-5 for forty-
eight hour periods during neap and spring tides. Distance between the 6.5 hour increments

4

allow comparison of the relative velocity and/or duration of tidal flow to be made between
stations.

Lagoon
In all areas of the lagoon, except for the western shoreline, currents appear to be
tidally modulated during both neap and spring tides (Figs. 2 and 3). The western shoreline
of the lagoon exhibits a unidirectional northwestward flow throughout the rising and
falling of the tide.

In the eastern part of the lagoon the net flow westward, during neap tides (Fig. 2),
is indicative of the longer duration or faster velocity of the westward flowing ebb currents.
This pattern changes during spring tidal conditions to a net movement to the northwest
(Fig. 3). The southeastward rising tide current is however more prominent during spring
tides and penetrates the lagoon to within 1 km of the lagoon shoreline of the eastern
islands.

In the southeast of the lagoon net current movement is toward the southwest (neap
tides) and west (spring tides). Westward drift is reduced during spring tidal conditions due
to the greater oscillation of rising and falling tide currents in the southeast and
northwestward directions (Fig. 3).

Current patterns in the southwest lagoon are similar for both the neap and spring
tidal conditions. There is a net movement northwestward throughout the 48 hour period
displayed. It is evident that rising tide currents penetrate south to within 1 km of the
southern passage.

Tidal elevation plays an important role in the magnitude and time period of current
reversal in the east and southeast sections of the lagoon. Comparisons of the neap and
spring tidal currents identify a greater net movement of water during neap tidal conditions
as shown by the distance between starting and finishing points of each 48 hour period. Net
flow direction in the east and southeastern sectors of the lagoon rotate 45° toward north
during spring tide conditions. This highlights the increased importance of the south/north
tidal flow on current direction during spring tides.

Current measurements taken at the deep northeastern passage (Fig. 2) convey a
tidally modulated reversal in direction between the ocean and lagoon. This is accompanied
by a net movement to the west. Measurements taken in the northwest passage, however,
display a unidirectional flow to the southwest. This movement is hard to interpret. There
appears to be no marked reversal of current direction with the oscillation of the tide and the
direction seems to suggest water is leaving the lagoon. These currents are weak (5-10
cm/s)when compared to those of the northeastern passage. Measurements taken at mid-
depth and 1m above the sea bed display similar current patterns to those shown by the
surface current record in the deeper passages. Currents in the mid-lagoon are weak (0-7
cm/s) and appear to oscillate with the rising and falling tide (Fig. 2).

Shallow Passages

The shallow passages display a unidirectional flow from ocean-side reef to lagoon
during neap tide conditions (Fig. 4). During spring tides the southern passages maintain
the unidirectional flow (Fig. 5), while the eastern passages display a reversal in flow
direction around low tide (Fig. 5). Due to the intertidal nature of the eastern passages at
spring low tide the current record is broken causing distortion to the observed pattern. It is

5

however clear that currents do travel from lagoon to ocean for part of the spring tidal cycle
in the eastern passages.

Tidally Driven Currents

As tidal currents vary in speed their direction rotates, usually with a semi-diurnal
period dominating (Pond and Pickard 1983). The figure traced out by the tip of a vector
representing the tidal current will be an ellipse. Tidal current constituents are presented in
Table 2 as properties of tidal current ellipses for the M2 and Kj constituents. Figure 6
presents the physical appearance of the M2 tidal ellipses within the lagoon and shallow
passages.

Lagoon currents are dominated by the M2 tidal constituent (Table 2, Fig. 6) which
is strongest in the southwest section of the lagoon at 16.95 cm/s. This constituent is also
strong in the eastern side of the atoll at 11.36 cm/s. While the K1 currents are the second
strongest, they are much weaker than the M2 currents ranging between 0.77cm/s and
4.84cm/s. M3 and Mg constituents (not listed) are the next strongest but are generally less
than 1 cm/s. The narrow Mp) current ellipses in the east and southwestern sections of the
lagoon (Fig. 6) reveal the strong oscillatory nature of tidal currents in these zones which
are enhanced by the shallow passage flow. The small and wide ellipse of the southeastern
lagoon portrays the weaker currents experienced in this zone. The shallow nature of this
area and the curvature of South Island may contribute to the observed weak currents and
direction of net flow to the west.

The Mp currents in the southeast section of the lagoon have a phase lead over the
eastern and southwestern areas of the lagoon. The K1 constituent, however, shows a
phase lead of 5° in the east of the lagoon followed by the southwestern section of the
lagoon, with the southeastern portion lagging the east by 13°. This lag may reflect the
location of the current metre in the wide shallow western section of the lagoon causing
shoaling of the tide. This is supported by the shallow water constituent (M4) having its
largest magnitude in this zone (2.2 cm/s).

As with the lagoon currents, the shallow passage tidal currents are dominated by
the M2 tide which is strongest in the southern passages at 7.6 cm/s. The K] constituent is
of secondary strength within the passages (Table 2).

Residual currents are those components of the observed currents that cannot be
explained through gravitational tidal forces. They are produced by wind stress, wind
waves and or internal waves (i.e. temperature or pressure gradients). Analysis of lagoon
currents identifies a mean of 15.6% of observed currents that are produced by these
‘other’ forces (Table 2 and Figs. 7a and 7b). Within the lagoon residual currents have their
greatest magnitude in the southeast lagoon where 17.2% of the northing component and
27% of the easting component not driven by tidal forces (Table 2). Residual currents
account for up to 52% of the observed shallow passage currents. This explains the small
semi-major axes lengths of the M2 ellipses within the passages (Fig. 6), with residual
currents being twice as strong as the M2 tidal current. The orthogonal with the greatest
residual strength coincides with the orientation of the passage, i.e. in the southern passages
the residual current is greatest for the north-south component of velocity (Table 2 and Fig.
eye

Figures 7a, b and c show the observed and residual current data for locations
within the southeast and southwest regions of the lagoon and the southern passage. Apart
from the first four days of observations within the southeast section of the lagoon the

6

residual easting component currents flow to the west (Fig. 7a). It is suggested that residual
currents in this section of the lagoon are driven by the southeast trade winds. The strength
of the residual current would, therefore, depend on wind strength. Residual currents in the
southwest section of the lagoon (Fig. 7b) appear to fluctuate with tidal elevation. The
magnitude of these currents is small. The large node in the southern passage residual
current (Fig. 7c), coincides with tropical cyclone activity that influenced the island from
December 5-8, 1991. The marked velocity increase, may have been the result of increased
wave action and tidal elevation at the reef crest together with increased wind speeds.
Correlation of wind strength and direction, and current direction, is required to identify the
driving mechanisms of the residual currents.

Shaliow Passage Water Flux, Tidal Prisms and Lagoon Exchange

Lagoon tidal prisms calculated for a 1m (spring) and 0.4m (neap) tide are presented
in Table 3. The spring tidal prisms for each shallow passage are shown in Figure 8 and
cumulative spring and neap prisms for the shallow passages are presented in Table 3. A
relationship is found between the cross-sectional area of each passage and the tidal prism,
with larger passages transmitting greater volumes of water from ocean to lagoon (Fig. 8).

On the rising spring tide the shallow passages contribute 10% to the tidal prism.
The deeper passages to the north and northeast therefore must transmit 90% of the rising
spring tide prism. During the falling tide shallow passages still transmit water from the
ocean to the lagoon (approximately 50% of the flood tide contribution). Over a full tidal
cycle, therefore, the shallow passages contribute 14% of the total spring tidal prism.
Invoking a neap tidal range of 0.4 m the rising tide prism is much smaller than the spring
tide prism (Table 3). The shallow passages contribute 16.9% to the neap rising tide prism.
Over an entire tidal cycle the contribution of the shallow passages to the prism is
proportionately much greater than it is for spring tides (22%).

In calculating the flushing time of the lagoon several assumptions have been made.
First, the volume of water that enters the lagoon during the rising tide equals that leaving
the lagoon during the falling tide. Water entering the lagoon through the shallow passages
during the falling tide, will however, be retained within the lagoon. The semi-diurnal
nature of the tidal regime would also result in more water being retained in the lagoon if the
low tide did not equal the original tide level. Second, the falling tide prism expels water
that resided in the lagoon at low tide. With these assumptions it requires a minimum of
2.36 days (spring tide) and 5.54 days (neap tide) for the lagoon to exchange its volume
with the ocean.

DISCUSSION

It is evident that the Cocos (Keeling) Islands lagoon experiences mixed semi-
diurnal tides with a marked diurnal inequality (Table 1). The spring tidal range in the north
of the lagoon of 0.82 m, although higher than most central Pacific atolls, falls within the
lower range of Indian Ocean tidal ranges (Farrow and Brander 1971) and is considerably
less than the 2.74m experienced at Aldabra atoll. A phase lag is identified within the
lagoon; with the tide in the south of the atoll lagging the north. This phase lag is also
manifested in the tidal current properties for the K; currents (Table 2). Southern passage
M2 currents lag those of the eastern passages by 111°. This evidence supports the tidal lag
relationship, suggesting that the tide sets from the east-northeast and travels south through
the lagoon.

7

Attenuation of tide heights was observed from north to south within the lagoon but
due to the short length of data in the south of the atoll (20 days) it is not appropriate to
place great significance on these differences. The broad, shallow nature of the southeastern
section of the lagoon is responsible for the significant shallow water effects (M4
constituent) in this region. Shallow water effects were identified by Pugh and Rayner
(1981) in Salomon atoll, which they attributed to the more enclosed nature of the lagoon.

Pugh and Rayner (1981) highlighted the importance of an atoll's tidal
characteristics in contributing to the ecological behaviour of reef systems. Farrow and
Brander (1971) established that the timing of extreme low water at Aldabra Atoll was
synchronous with maximum solar radiation. This was thought to maximise stress on many
organisms on the reef. Within the Cocos lagoon the maximum exposure of reef flats
occurred at midnight with the second, higher low-tide of the day occurring around midday.
Reef organisms were, therefore, not stressed by solar radiation during the most extreme
low tide levels.

Lagoon currents and circulation are driven by the tidal regime (Table 2, Figs 2 and
3), with rising tide currents penetrating south into the lagoon within 1km of the eastern and
southern passages. The component of observed currents not attributable to tidal forces,
may be driven by the influence of wind and lagoon generated waves, or internal salinity
differences within the lagoon. These currents are small within the lagoon (mean 15%),
during the observation period, and have not been further investigated. It is suggested
however, that the southeast trade winds would play a major role in driving these currents.

The unidirectional ocean to lagoon flow that occurs in the shallow passages, for all
but spring low tides in the east of the atoll, can be explained through the interaction of tidal
height and wave action, with the height of the reef crest. As the tide rises above the reef
crest, waves incident at the reef break, reform (Gourlay 1990), travel over the reef and
through the passage. These translatory currents comprise the bulk of the current accounted
for by the residuals (Table 2). As the waves travel across the reef-flat, friction (induced by
the reef flat morphology) slows the wave induced currents. This produces a build up of
water at the reef crest which forms a hydraulic gradient from the reef crest to lagoon (Tait
1972). The movement of waves across the reef is still possible on the falling tide until the
water height falls below that of the reef crest. The reversal in current direction in the
eastern passages, around spring low tide, results from the interaction between tidal height
at the reef crest and the height of the lagoonward sand bodies. As shown in Figure 9 the
maximum height of the lagoonward sand body is greater than the reef crest. As the spring
low tide falls below the level of the reef crest, water is ponded inside the sand apron with
no connection to the deeper lagoon. A surface water gradient forms from lagoon to ocean
producing a slow reefward flow. The magnitude of this reversing flow is small.

That tidal currents were observed within 1km of shallow passages, indicate that
shallow passage currents have negligible effect in driving circulation beyond 1km of the
passage exit. They may, however, be important in retarding and deflecting lagoon
currents.

During the rising tide there is an opposition of currents entering the lagoon through
shallow passages and the tidal currents penetrating the lagoon from the north-northwest
toward the lee of the islands. The angle of opposition of these currents on the eastern side
of the lagoon would indicate there is a deflection of rising tide water to the southeast. Net
flow westward is the result of longer duration ebb flow which is reinforced by the
continued flux of water through the shallow passages. Water behind South Island flows
southward on the rising tide and west-southwest on the falling tide, as if of a semi-circular

8

nature, driven by the shallow bathymetry and closed lagoon shoreline in this region (Figs.
2 and 3). Flow in the southwest is predominantly in the north-south direction with net
movement northward. This net flow direction is thought result from the increased volume
of water entering via the south passage and that volume of the lagoon prism that flows
from the eastern side of the lagoon. The build up of water in the west of the lagoon is
evacuated by the unidirectional northward flow along the western shoreline. Water may
also be built up along this shoreline due to the southeast trade winds forcing surface water
northwest. As the trade winds drop there may be a small flow of water toward the east to
equalise this pressure gradient.

The northeastern passage experiences strong current reversals with tidal stage,
whilst the northwestern passage exhibits a unidirectional and slow movement exiting the
lagoon. The increased influx of water entering through the shallow passages for the
duration of the tidal cycle must increase the length and or velocity of currents exiting the
lagoon on the falling tide through these large passages. It is proposed that as the tidal wave
sets from the east-northeast, the northeast passage is the major conduit for tidal inflow,
while the northwest passage is dominated by net flow out of the lagoon (Fig. 2).

A general circulation model of the lagoon, therefore, has water entering and
flowing down the eastern and central sections of the lagoon, on the rising tide; being
deflected west inside South Island and flowing north up the central and western sides of
the lagoon, and exiting the northwest pass during the falling tide (Fig. 10). The northeast
pass also evacuates water from the lagoon on the falling tide. Results from vector plots
(Figs. 2-5) identify a net flow within the lagoon which mirrors that of the falling (Fig.
10b) except for the northeast passage experiencing a westward flow. Tidal oscillation is
superimposed on this net flow. There are two possible mechanisms of this net
northwestward flow. First, the prevailing southeast wind may produce a small surface
current, as seen in the southeast lagoon residual current (Fig. 7a). If this mechanism is
important, ocean-lagoon exchange time will decrease during stronger wind conditions.
Second, due to the ebb prism being greater than the flood prism, because of the continuous
shallow passage input, the falling tide is of longer duration, producing a net movement in
the vector plots toward the deep northwest passage. The unidirectional ocean to lagoon
flux of water through the passages also retards the rising currents penetrating the lagoon
from the north. Continued influx of water at slack tide and the falling tide may create a
pressure head from the south and east toward the northwest and may also accelerate flow
toward the northwest deep passage.

That circulation in the Cocos (Keeling) Islands lagoon is driven by tidal forces is
consistent with other shallow lagoon studies in Pacific atolls (e.g. Stroup and Meyers
1974). While tidal forces dominate ocean-lagoon water exchange, the wave induced water
flux through the shallow passages plays an important role in this exchange, especially
during neap tides where shallow passage flux can represent 22% of the entire prism.
Shallow passage water flux is also identified as a primary mechanism of lagoon-ocean
water exchange by Atkinson et al. (1981) in Enewetak Atoll.

The flushing time of the lagoon is estimated at a minimum of 2.36 days and a
maximum of 5.4 days for spring and neap tides. This time period is comparable with
lagoons of similar size and depth including Aldabra atoll (Pugh and Rayner 1981) and
Britomart lagoon, Great Barrier Reef (Wolanski and Pickard 1983). Fanning and Canton
Atoll lagoons which have similar dimensions to the Cocos lagoon (15 km wide, 6 m deep)
have far greater flushing time scales (50-95 days, Canton and <300 days Fanning) due
primarily to the enclosed nature of the lagoon with few connections to the ocean.

CONCLUSION

The Cocos (Keeling) Islands are influenced by mixed mainly semi-diurnal tides.
Tides in the shallow south of the lagoon and currents in south passage, lag those of the
deeper northern lagoon and eastern passages.

The Cocos (Keeling) Islands lagoon circulation is tidally driven with strong tidal
currents penetrating the lagoon from the northeastern passage to within 1km of the shallow
passages. The tidal range has a significant impact on net flow direction in the east and
southeastern sections of the lagoon. Shallow tidal constituents are important in the shallow
southeastern section of the lagoon that is bordered by South island.

A general circulation model has been derived in which water entering the
northeastern passage travels down the eastern shoreline of the lagoon, is deflected
westward, and flows northwestward exiting through the northwest deep passage.

The role of wind was found to be small in driving lagoon circulation. Wind stress
may contribute to the residual currents which produce a northwestward flow. However,
these currents were weak within the lagoon.

Shallow passages experience unidirectional ocean to lagoon flow throughout neap
tides and during spring tides in the south of the atoll. This unidirectional flow contributes
to the net movement of lagoon water toward the northwest throughout the tidal cycle.
Eastern passages display a reversal in current direction around spring low tides due to the
interaction of tidal height at the reef crest and height of the sand apron lagoonward of the
passage. Exposure of the sand apron crest produces a temporary reversed hydraulic
gradient and current flow.

Shallow passage currents are dominated by translatory wave motion across the reef
flat. Tidal currents contribute less than 50% to observed passage currents. The influence
of shallow passage hydrodynamics on lagoon circulation is negligible. Shallow passage
currents penetrate up to 1km lagoonward of the passage exit. These currents deflect water
entering the deep lagoon to the southeast in the eastern side of the lagoon. Unidirectional
passage flow increases the ebb prism and ebb tide current velocities.

Shallow passages were found to be important mechanisms for the exchange of
water between ocean and lagoon with up to 15% (springtides) and 22% (neap tides) of
total water entering the lagoon over a tidal cycle being transmitted through the shallow
passages.

Flushing times of the Cocos lagoon were found to vary between 5.4 and 2.3 days
for neap and spring tidal conditions respectively. These results were consistent with atoll
lagoons of similar dimension and high degree of connection with the ocean.

10

REFERENCES

Andrews, J.C., and Pickard, G.L. 1990. The Physical Oceanography of Coral-Reef
Systems. Chapter 2 In Dubinsky, Z. ed. Coral Reefs. p 11-48.

Atkinson, M., Smith, S.V. and Stroup, E.D. 1981. Circulation in Enewetak Atoll
Lagoon. Limnology and Oceanography, 26:1074-1083.

Farrow, G.E. and Brander, K.M. 1971. Tidal Studies on Aldabra. Phil. Trans. Roy.
Soc. Lond. B. 260: 93-121.

Foreman, M.G.G. 1979a. Manual for Tidal Heights Analysis and Prediction. Institute of
Ocean Sciences, Patricia Bay Canada. Pacific Marine Science Report pp77-10.

Foreman, M.G.G. 1979b. Manual for Tidal Currents Analysis and Prediction. Institute
of Ocean Sciences, Patricia Bay Canada. Pacific Marine Science Report pp78-6.

Gallagher, B.S., Shimada, K.M., Gonzales, F.I., Jr. and Stroup, E.D. 1971. Tides and
Currents in Fanning Atoll Lagoon. Pacific Sci. 25: 191-205.

Gilmour, A.J. and Colman, R. 1990. A Pilot Study of the Outer Island Development
Program Republic of Kiribati. Report to AIDAB on environmental studies,
Kiribati.

Gourlay, M. 1990. Wave Set-up and Currents on Reefs. Cay Formation and Stability.
Conference on Engineering in Coral Reef Regions, Magnetic Island Townsville
Nov. 5-7.

Neumann, G. 1968. Ocean Currents. Elsevier Oceanography Series Volume 4. Elsevier
publishing company, 351pp.

Platzman, G.W. 1984. Normal Modes of the World Ocean. Part IV: Synthesis of Diurnal
and Semidiurnal Tides. J. Phys. Ocean. 14: 1532-1550.

Pond, S. and Pickard, G.L. 1983. Introduction to Dynamical Oceanography, Second
Edition. Pergamon Press, 329pp.

Pugh, D.T. 1979. Sea Levels at Aldabra Atoll, Mombasa and Mahe, Western Equatorial
Indian Ocean, Related to Tides, Meteorology and Ocean Circulation. Deep-Sea
Res. 26: 237-258.

Pugh, D.T. and Rayner, R.F. 1981. The tidal regimes of three Indian Ocean atolls and
some ecological implications. Estu. Cstl. Shelf Sci. 13: 389-407.

Smith, S.V. and Jokiel, P.L. 1978. Water Composition and Biogeochemical Gradients in
the Canton Atoll Lagoon. Atoll Res. Bull. 221:15-54.

Stroup, E.D. and Meyers, G.A. 1974. The flood-tide jet in Fanning Island Lagoon.
Pacific Sci. 28: 211-223.

11

Tait, R.J. 1972. Wave Set-up on Coral Reefs. J. Geophys. Res. 77: 2207-2211.
Tchernia, P. 1980. Descriptive Regional Oceanography. Pergamon Press.

von Arx, W.S. 1948. The Circulation Systems of Bikini and Rongelap Lagoons. Trans.
Am. Geophys. Uni. 29: 861-870.

von Arx, W.S 1954. Circulation systems of Bikini and Rongelap Lagoons, Bikini and
nearby atolls, Marshall Islands. U.S. Geol. Surv. Prof. Pap. 260-B: 265-273.

Wiens, H.J. 1962. Atoll Environment and Ecology. Yale University Press, New Haven,
532 pp.

Wolanski, E., and Pickard, G.L. 1983. Currents and Flushing of Britomart Reef
Lagoon. Coral Reefs 2: 1-8.

12

Table 1: Harmonic analysis of lagoon tides, centimetres and degrees in relation to Green-
which. Major tidal constituents at the permanent Home Island tide gauge and temporary
location in South Passage. Symbols indicate tidal properties of amplitude (a) and phase
(g). Due to the short length of record from the temporary tide gauge (co days) the No con-
stituent was unable to be resolved.

‘Constituents Frequency Home Island + South Passage
(hours) a (cm) g(deg) a(cm) g(deg)
MSF 354.37 6.02 60.16 Wael 237.33
O; 25.82 7.82 236.50 8.23 256.37
Ky 23.93 12.19 259.44 10.29 282.27
No 12.65 10.92 118.03 — —
M2 12.42 29.39 140.84 25.02 149.35
So 12.00 14.26 186.36 5.58 186.48
M4 6.21 0.21 205.31 3.92 244.04

Table 2: Tidal current constituents at M2 (12.42 hrs) and K1 (23.93 hrs) frequencies. The
symbols indicate current ellipse properties of semi—major axis length (a), semi—minor axis
length (b), phase (g) and orientation (6) measured anticlockwise from east. Residual, per-
centages of the orthogonal components of velocity (northing — n and easting — e) indicate
the percentage of observed currents not able to be accounted for by tidal forces.

Mo Ky Residuals
Mooring a b g (3) a b g 8 n e

(cm/s) (cm/s) (deg) (deg) (cm/s) (cms) (deg) (deg) (%) (%)
E Lagoon 11.36 0.56 219.36 146.98 2.61 0.17 325.44 142.01 13.8 5.0
SE Lagoon 7.03 3.68 216.32 117.84 2.49 0.99 338.25 140.17 17.2 27.0
SWLagoon 16.95 1.03 219.09 105.81 556 0.03 330.13 111.03 12.1 19.1
South Pass 7.60 2.11 337.79 263.88 4.13 0.80 235.32 82.21 46.4 29.9
East Pass 5.15 1.13 22633 2947 219 0.18 181.89 210.49 38.96 528

Table 3: Lagoon volumes and tidal prism calculations for the Cocos (Keeling) Islands
Lagoon. Low-High = low to high tide shallow passage flux.

Lagoon Volume Tidal Prism Shallow Passage Total
(M3 x 108) (M3 x 10®) Flux (M2? x 10) (M®x 108)
High Tide Low Tide Low-High High-Low
SprinTides 6125 905:5 107 10.5 Bal 15:6

Neap Tides 571.9 524.5 47 8.0 3.6 116

Maldive Is. ,
INDIAN OCEAN

5 COCOS (KEELING)
~ Mauritius ISLANDS

60°E 90°E

Deep Lagoon
(10-12m)

SOUTH KEELING
ISLANDS

Shallow Lagoon
(<3m)

West Is.

South Is

i. mea
B

Reef Crest

Current metre deployment — 17 days .
Current metre deployment — 1 day
Tide gauge stations

Sand aprons t SD

96°50'E 96°55'E

Figure 1. Field and Instrument location

13

14

0001
10 Jan 92
“A 631

30 Dec 91

400 .

F \
‘ — Ss ».
: [ 130 .
!
\ 28 Dec 91 / 30 Dec 91 ‘ H
Ki \ x H
\ XQ we Yi ow
x 1450 18 Jan 92
ee S
130 30 Dec 91
SS)
3.5 km
Distance travelled
/
/
t 400
SS 28 Dec 91 400
\ 28 Dec 91
30 Dec 91

130

Figure 2. Lagoon progressive vector plots, neap tide. The four shallow
lagoon locations show a 48 hour period starting 28/12/91 at 4am (low tide).
The northwest passage is a 12 hour record and the northeast and mid lagoon
locations are 24 hour records of current speed and direction.

Tian \

Uy

/

/

yell EB \\ AN
7X s I

— 19 Dec 91

21 Dec 91_

3.5 km
Distance travelled

830

1 1 1
600 9 Dec 9

21 Dec 91

Figure 3. Lagoon progressive vector plots, spring tide. Each location displays
a 48 hour period beginning 19/12/91 at 830am (low tide).

hd

16

510

- We Nov 91
\
2.

“15 Nov 91
N
.
‘

\

1700
3 Dec 91

14.5 km
Distance travelled

1930
2 Dec 91

Figure 4. Shallow passage progressive vector plots, neap tide. 48 hour
periods starting at low tide on the 15/11/91 at 510am in the eastern passages
and 1/12/91 at 730pm in the southern passages.

Rad

24 Nov 91

Distance (Km)

Distance Cea

i;

a ey
14.5 km
920 Distance travelled

11 Dec 91

Figure 5. Shallow passage progressive vector plots, spring tide. 48 hour
periods starting at low tide on the 22/11/91 at 1030am in the eastern
passages and 9/12/91 at 1150am in the southern passages.

WW

18

Figure 6. M2 tidal current ellipses for the shallow lagoon and passages. All
display anti-clockwise rotation.

Observed Currents Southeast Lagoon - Easting Velocity

ntototaigditttoecoct.
-20

mn oF T
21 23

DEC

Residual Currents Southeast Lagoon - Easting Velocity

10]

-10

23

‘DEC
Residual Currents Southwest Lagoon - Northing Velocity

104

\ ATA
NA aaron
-20]

30 u
NOV 91

Residual Currents South Passage - Northing Velocity

Cyclone Graham

Figure 7. Observed and residual current information for selected sites.
Residuals are derived by subtracting tidal current components from the
observed current record. (a) Southeastern lagoon Showing the easting
component of velocity. Negative values indicate flow to the west. (b) South
west lagoon, showing the northing component of velocity. Negative values
indicate flow to the south. (c) Southern passage, northing component of
velocity.

as

20

Tidal Prism (M3)

10 100 1000
Cross-sectional Area (M2)

Tidal Prism - Eastern Passages @
Tidal Prism - Southern Passages a

Figure 8. Spring tidal prism vs cross-sectional area (at MSL) relationship for
the shallow passages.

Zero velocity
Opposing flow |

from lagoon | Lagoonward flow

<---> eee

Deposition

Sand apron

Passage,\

Figure 9. Relative height of sand apron and reef crest, eastern side of the
atoll. The opposition of currents entering the lagoon via the deep passes and
shallow passages is also shown.

(A) Rising tide

(B) Falling tide

Figure 10. General circulation of the Cocos (Keeling) Islands lagoon on the
rising (A) and falling (B) tide.

2 1

ATOLL RESEARCH BULLETIN

NO. 409

CHAPTER 11

HERMATYPIC CORALS OF THE COCOS (KEELING) ISLANDS:
A SUMMARY

BY

J.E.N. VERON

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER I1
HERMATYPIC CORALS OF COCOS (KEELING)
ISLAND: A SUMMARY
BY
J.E.N. VERON *

ABSTRACT
Ninety nine species of reef corals are recorded from Cocos (Keeling) Atoll. Of these, all
but twelve are known from Western Australia. Nine species are not recorded elsewhere in

the eastern Indian Ocean and two (one being taxonomically doubtful) are possibly
endemic.

This account is a summary only of Re-examination of the reef corals of Cocos (Keeling)
Atoll (Veron 1990a)

SYSTEMATIC ACCOUNT

FAMILY Astrocoeniidae Koby

Genus Stylocoeniella Yabe and Sugiyama

Stylocoeniella guentheri (Bassett-Smith)

Records: Wells (1950), Veron (1990a)

Notes: Found on most reef slopes. Inconspicuous. Usually dark green, encrusting to
submassive. Septa strongly alternate. Primary septa do not reach the boss-like
columella.

Stylocoeniella armata (Ehrenberg)

Records: Veron (1990a)

Notes: Rare, inconspicuous. Septa clearly alternate. Primary septa reach the columella
which is thin, style-like.

Australian Institute of Marine Science, P.M.B. No. 3, Townsville M.C.
Queensland, 4810.

2

Stylocoeniella cocosensis Veron 1990

Record: Veron (1990b)

Notes: Corallites are irregularly exsert. Septa are in two sub-equal cycles, fine.
Columellae are very small. Coenosteum spinules very fine. Each corallite has a
prominent style.

FAMILY Pocilloporidae Gray

Pocillopora is abundant in almost all coral communities, Seriatopora is usually uncommon.
The other genera, notably Stylopora, have not been recorded.

Genus Pocillopora Lamarck
Pocillopora damicornis (Linnaeus)

Records: Ridley and Quelch (1885) (as P. brevicornis), Vaughan (1918), Wells (1950),
Veron (1990a)

Notes: | Uncommon but found in a wide range of environments. Usually pink in colour.
Indistinguishable from mainland Australian colonies.

Pocillopora verrucosa (Ellis and Solander)

Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes: Common on most upper reef slopes. Yellow or pinkish in colour.
Indistinguishable from mainland Australian colonies.

Pocillopora meandrina Dana

Records: Vaughan (1918), Wells (1950), (both as P. elegans Dana), Veron (1990a)

Notes: | Common on most upper reef slopes. Distinguished from P. verrucosa by
having smaller verrucae and as described by Veron and Pichon (1982).

Pocillopora woodjonesi Vaughan

Records: Vaughan (1918) with the Cocos (Keeling) Islands as type locality, Wells (1950),
Veron (1990a)

Notes: | Uncommon. Difficult to distinguish from P. eydouxi. Colonies identified as P.
woodjonesi in situ did not have the species specific skeletal characters described
by Vaughan (1918) and Wells (1950) and used by the present author. The
“taxonomic status of this species requires further study.

Pocillopora eydouxi Edwards and Haime

Records: Vaughan (1918), Veron (1990a)

Notes: Common in most coral communities. Indistinguishable from mainland
Australian colonies.

Genus Seriatopora Lamarck

Seriatopora hystrix Dana

Records: Vaughan (1918), Wells (1950) (both as S. angulata Klunzinger), Veron (1990a)

Notes: The few colonies observed during the present study were small and isolated.
Indistinguishable from mainland Australian colonies.

Family Acroporidae Verrill

Genus Montipora de Blainville

Montipora monasteriata (Forskal)

Records: Veron (1990a)

Notes: Common ina wide range of environments. Indistinguishable from mainland
Australian colonies.

Montipola tuberculosa (Lamarck)

Records: Veron (1990a)

Notes: | Common. Indistinguishable from mainland Australian colonies.

Montipora lobulata Bernard
Records: Wells (1950), Veron (1990a)

Notes: | Has not been recorded elsewhere in Australia.

Montipora mollis Bernard
Records: Veron (1990a)

Notes: Probably uncommon. Indistinguishable from mainland Australian colonies.

4

Montipora peltiformis Bernard
Records: Veron (1990a)

Notes: Common on some reef slopes.

Montipora capricornis Veron

Records: Veron (1990a)

Notes: | Uncommon except in the atoll lagoon where this species is an early coloniser of
denuded areas.

Montipora spumosa (Lamarck)

Records: Vaughan (1918) and Wells (1950)

Notes: Possibly now extinct at Cocos (Keeling).

Montipora danae (Edwards and Haime)
Records: Veron (1990a)

Notes: | Uncommon. Indistinguishable from mainland Australian colonies.

Montipora angulata (Lamarck)

Records: Vaughan (1918) (as M. cocosensis Vaughan, with Cocos (Keeling) Island as
type locality), Veron (1990a)

Notes: Uncommon. Found only on reef flat or sub-tidal sand flats with M. digitata.
Thick branches becoming columnar, with conspicuous open corallites.
Montipora digitata (Dana)

Records: Ridley and Quelch (1886) (as M. laevis Quelch), Wells (1950) (as M. laevis
Quelch M. ramosa Bemard and M. rubra Quoy and Gaimard), Veron (1990a)

Notes: Forms extensive monospecific stands on intertidal sand flats. Intermixed with
Montipora sp. Indistinguishable from mainland Australian colonies.

Montipora sp.

Records: Veron (1990a)

Notes: A sub-arborescent species similar to M. digitata, primarily distinguished by high
reticulum ridges between corallites and flattened branch tips with few corallites.

The present specimens do not belong to any previously recorded or described
species known to the author.

Montipora efflorescens Bernard
Records: Veron (1990a)

Notes: _Indistinguishable from mainland Australian colonies.

Montipora grisea Bernard
Records: Veron (1990a)

Notes: —Indistinguishable from mainland Australian colonies.

Montipora informis Bernard
Records: Vaughan (1918), Veron (1990a)

Notes: Rare. Indistinguishable from mainland Australian colonies.

Montipora foliosa (Pallas)
Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes: | Uncommon.Indistinguishable from mainland Australian colonies.

Montipora aequituberculata Bernard

Records: Veron (1990a)

Notes: _ Common on some outer slopes. Usually dark grey or brown. Indistinguishable
from mainland Australian colonies.

Genus Anacropora Ridley

Anacropora forbesi Ridley, 1884

Records: Ridley (1884), with Cocos (Keeling) Atoll as type locality

Notes: Many now be extinct at Cocos (Keeling).

Genus Acropora Oken

One of the most distinctive characters of Cocos (Keeling) Island corals is the low diversity
and, usually, the low abundance of Acropora. The only extensive stands of living

6

Acropora are on reef flats. Very extensive stands of dead arborescent species, mainly
pulchra and formosa, occur in the lagoon and extensive dead tabular colonies, no longer
identifiable, occur at North Keeling Island.

Acropora palifera (Lamarck)
Records: Vaughan (1918), Veron (1990a)
Notes: Seldom common. Both reef slope and lagoon colonies are similar in growth

form and corallite structures and represent only a small part of the variation
described by Veron and Wallace (1984).

Acropom ocellata (Klunzinger)
Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes: | Uncommon. This species belongs with the A. humilis group, with a growth
form similar to A. humilis (Dana). Axial corallites are similar in size and shape
to those of A.monticulosa (Bruggemann). Radial corallites are large, round,
irregular, some immersed, others large and elongated, becoming incipient axials.
Living colonies are pale brown with white branch tips.

Acropora robusta (Dana)

Records: Wells (1950) (as A. pinguis, described as a new species from Cocos (Keeling)
Atoll), Veron (1990a)

Notes: Very rare.

Acropora danai (Edwards and Haime)

Records: Wells (1950) (as A. irregularis, described as a new species from Cocos
(Keeling) Atoll), Veron (1990a)

Notes: Rare. Growth form is the same as mainland Australian colonies. Corallites near
branch tips may become relatively elongate.

Acropora sp. 1

Records: Vaughan (1918), Wells (1950) (as A. pharaonis Edwards and Haime), Veron
(1990a)

Notes: | Sometimes common in shallow water. Colonies are arborescent, forming
thickets in shallow water where some branches may be fused. Branches are
mostly straight and tapered. Radial corallites are of two sizes, the larger
arranged in rows. They are similar in structure to those of A. valenciennesi.

Acropora formosa (Dana)

Records: Wells (1950), Veron (1990a)

Notes: Uncommon except on some reef flats. Reef flat colonies have short branches
with proliferous sub-branches. No colonies with long undivided branches were
seen. Mostly yellowish in colour.

Acropora microphthalma (Verrill)

Records: Veron (1990a)

Notes: Common on reef flats and some reef slopes. Indistinguishable from mainland
Australian colonies.

Acropora exquisita Nemenzo

Records: Possibly Wells (1950) (as A. irregularis (Brook), Veron (1990a)

Notes: | Uncommon. Indistinguishable from more robust colonies from mainland
Australian North-west shelf reefs. Pale colours.

Acropora aspera (Dana)

Records: Vaughan (1918) (possibly as A. spicifera), Wells ( 1950) (as A. hebes), Veron
(1990a)

Notes: Mostly uncommon and only found on reef flats. Reddish-brown in colour.
Indistinguishable from mainland Australian colonies.

Acropora pulchra (Brook)

Records: Vaughan (1918), Veron (1990a)

Notes: Formerly very abundant throughout much of the southern lagoon, forming very
extensive stands often over 20 m across. Now common on some reef flats and

also found on some reef slopes. Indistinguishable from mainland Australian
colonies.

Acropora cytherea (Dana)
Records: Veron (1990a)

Notes: Uncommon. The largest colonies observed were < 1 m diameter.
Indistinguishable from mainland Australian colonies.

Acropora paniculata Vernill

Records: Veron (1990a)

Notes: Rare. It appears that this is a distinct geographic sub-species of A. paniculata,
but as the latter is know in the Indian Ocean from only a single specimen (from
Ashmore Reef, Veron and Marsh, 1988), no definite conclusion is possible.

Acropora hyacinthus (Dana)

Records: Veron (1990a)

Notes: Rare. Only stunted reef flat colonies were found.

Acropora latistella (Brook)
Records: Veron (1990a)

Notes: Rare, found only on reef flats. This species was not found as large tabular
colonies. Branchlets are thinner than usual for shallow-water mainland
Australian colonies.

Acropora nana (Studer)

Records: Wells (1950), Veron (1990a)

Notes: Found only on outer reef flats and upper slopes. Colonies are relatively small,
otherwise indistinguishable from mainland Australian colonies.

Acropora subulata (Dana)
Records: Veron (1990a)

Notes: Rare. Nothing is known of environment-related growth form variation.

Acropora valida (Dana)

Records: Vaughan (1918) and Wells (1950) (as A. variabilis (Klunzinger)), Veron
(1990a)

Notes: Rare, Gibson-Hill records this species from several reef flat localities (Wells
1950). Corallites are smaller and have thinner walls than usual for the species,
but nothing is known of environment-related variation. Coralla from Cocos
(Keeling) illustrated by Vaughan (1918, pl. 80) have the characters of the
species more clearly developed. Gibson-Hill (and this author) records the colour
as "dirty-white, with faint lavender-blue tips" (Wells 1950).

Acropora sp. 2

Records: Veron (1990a)

Notes: Rare. Colonies are irregularly arborescent. Corallites are very irregular, some
being valida-like and strongly oppressed. The species was not sufficiently
abundant for detailed study and nothing is known of environment-related skeletal
variation.

Acropora schmitti Wells

Records: Wells (1950), described as a new species from Cocos (Keeling) Atoll, Veron
(1990a)

Notes: Not found during the present study. Gibson-Hill notes, "This coral, which is
rather similar to [A. valida] in both colour and form, occurs in shallow pools on
the middle section of the barrier, and on part of its seaward edge. It is not very
plentiful, but it seems to be most numerous at the back of Pulo Tikus, where
[five] specimens were taken" (Wells 1950). Wells (1950) notes that "the
distinctive character of this species is the extraordinary thickness of the outer lip
of the radial corallites, which gives them the appearance of hemispherical bowls
attached to the branch by one side or by a very short thick handle”.

Genus Astreopora de Blainville

Astreopora myriophthalma (Lamarck)

Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes: | Common in a wide range of environments. Indistinguishable from mainland
Australian colonies. Colours vary from dark purple to cream and pale pink.

Astreopora gracilis (Bernard)

Records: Veron (1990a)

Notes: | Usually uncommon. Indistinguishable from mainland Australian colonies.
Colours are cream and pale pinkish-purple.

Family Poritidae Gray
Goniopora and Alveopora have not been recorded from Cocos (Keeling) Atoll.
Genus Porites Link

Porites solida (Forskal)

10

Records: Vaughan (1918) and Wells (1950), Veron (1990a)

Notes: Uncommon. Two specimens studied were indistinguishable from mainland
Australian coralla.

Porites lobata Dana
Records: Veron (1990a)

Notes: _Indistinguishable from mainland Australian colonies.

Porites australiensis Vaughan
Records: Veron (1990a)

Notes: Corallites have a very distinct wall formed by lateral fusion of denticles.

Porites somaliensis Gravier

Records: ?Guppy (1889) (as P. clavaria), Vaughan (1918), Veron (1990a)

Notes: |The most abundant massive Porites on some reet flats. Colonies from shallow

water usually have a knobbly growth form. Corallites are closest to P.

stephensoni but the present species appears to be distinct from any mainland
Australian species. The triplet is sometimes fused and columellae are laterally
compressed in the line of the directive septa forming a conspicuous line.

Porites cf. evermanni Vaughan

Records: Veron (1990a)

Notes: Rare, but very distinctive. Indistinguishable from specimens of this species
recorded from Australia, the Philippines (Veron and Hodgson 1989) and
elsewhere.

Porites cylindrica Dana

Records: Guppy (1889) (as P. palmata), Ridley and Quelch (1885) (as P. levis Dana),

Vanghan (1918) (as P. nigrescens), Wells (1950) (as P. nigrescens and P.
gibsonhilli). Cocos (Keeling) atoll is the type locality of P. gibsonhilli Wells.

Porites cocosensis Wells, described from two specimens from Cocos (Keeling)

Atoll, may also be a synonym of P. cylindrica

Notes: |The most common species of intertidal reef flats and forms extensive stands on
some upper reef slopes. Indistinguishable from mainland Australian coralla.

11

Porites lichen Dana
Records: Vaughan (1918)

Notes: _Indistinguishable from mainland Australian coralla.

Porites rus (Forskal)

Records: Veron (1990a)

Notes: Common. Forms extensive flat plates with short, irregular columns and
branches. Usually fawn or brown.

Porites sp.

Records: Veron (1990a)

Notes: Forms plates and irregular branches and columns. Corallites are essentially
similar to those of P. rus and P. latistellata Quelch, but are smaller than both.
The species appears to be undescribed. Usually brightly coloured: green, blue
or yellow.

Family Siderastreidae Vaughan and Wells
Pseudosiderastrea and Coscinaraea have not heen recorded from Cocos (Keeling).
Genus Psammocora Dana

Psammocora digitata Edwards and Haime

Records: Wells (1950) (as P. togianensis Umbgrove)

Psammocora superficialis Gardiner

Records: Vaughan (1918) (as Psammocora sp.), Veron (1990a)

Notes: Uncommon. Indistinguishable from mainland Australian colonoies. Colonies
are encrusting and may be over 1 m diameter. These large colonies have
relatively coarse skeletal characters. Colour is very uniform within colonies,
mostly battleship grey, rarely bright green.

Psammocora profundacella Gardiner

Records: Vaughan (1918) and Wells (1950) (as P. haimeana), Veron (1990a)

Notes: | Very common in a wide range of environments. Indistinguishable from

mainland Australian colonies. It may form coralliths. Usually pale pink or
green, but may be dark green. Sometimes with blue centres. Gibson-Hill,

le

referring to reef-flat colonies, notes that “it is a pearl-grey colour” (Wells 1950)

Family Agriciidae Gray

Genus Pavona Lamarck

Pavona cactus (Forskal)

Records: Wells (1950), Veron (1990a)

Notes: | Common only in small isolated patches. Indistinguishable from mainland
Australian colonies

Pavona frondifera Lamarck

Records: Veron (1990a)

Notes: | Common only in small isolated patches intermixed with P. cactus. Colonies are
partly encrusting and have small, irregular, upright fronds. Dark greenish-
brown with pale fronds.

Pavona decussata (Dana)

Records: Vaughan (as P. danai (Edwards and Haime), Wells (1950), Veron (1990a)

Notes: | Known from two reef flat colonies only. Coralla are colllposed of highly
anastomosed plates, a growth form common on reef flats. Skeletal detail is
indistinguishable from mainland Australian coralla.

Pavona explanulata (Lamarck)

Records: Veron (1990a)

Notes: | Usually uncommon but conspciuous. Colonies are massive or columnar. Pale
or dark brown in colour. Plate-like colonies common in Australia, were seldom
seen.

Pavona minuta Wells

Records: Veron (1990a)

Notes: | Common on some exposed reef sites. Colonies are massive or columnar, rarely
encrusting. All colonies observed were < 0.5 m. Grey in colour.

13

Pavona varians Verrill

Records: Vaughan (1918 ), Veron (1990a)

Notes: Very common in a wide range of reef slope environments. Forms large
encrusting plates under overhangs. Very dark colours except in niches exposed
to strong sunlight.

Pavona venosa (Ehrenberg)

Records: Veron (1990a)

Notes: Septa are very coarse making the single specimen found very distinctive.

Pavona maldivensis (Gardiner)
Records: Vaughan (1918), Veron (1990a)

Notes: Rare. Indistinguishable from mainland Australian colonies.

Pavona sp.

Records: Veron (1990a)

Notes: Rare. Colonies are flat unifacial plates. Corallites are very small similar to those
of P. bipartita Nemenzo, but with smaller calice centres and tendency to become
subplocoid.

Genus Leptoseris Edwards and Haime

Leptoseris papyracea (Dana)

Records: Veron (1990a)

Notes: Forms an extensive carpet of some hundreds of square metres at one lagoonal
site. Indistinguishable from fine, highly compact mainland Australian colonies.
Pale pinkish-brown in colour.

Leptoseris explanata Yabe and Sugiyama

Records: Veron (1990a)

Notes: Rare. The single specimen studied is indistinguishable from mainland Australian
colonies.

14

Leptoseris mycetoseroides Wells

Records: Veron (1990a)

Notes: Rare. Indistinguishable from mainland Australian colonies.

Genus Gardineroseris Scheer and Pillai

Gardineroseris planulata (Dana)

Records: Veron (1990a)

Notes: | Uncommon although found in a wide variety of habitats. Colonies flat or dome-
shaped, up to 1 m high, pale brown in colour. Indistinguishable from mainland
Australian colonies.

Genus Pachyseris Edwards and Haime

Pachyseris speciosa (Dana)

Records: Veron (1990a)

Notes: Forms very extensive monospecific stands south of ‘Boat Passsage’.
Indistinguishable from mainland Australian colonies.

FAMILY Fungiidae Dana

Genus Fungia Larnarck

Fungia fungites (Linnaeus)

Records: Wells (1950), Veron (1990a)

Notes: | Uncommon. Indistinguishable from mainland Australian coralla.

Fungia concinna Verrill
Records: Veron (1990a)

Notes: This is the only record of the species. The single specimen collected is
indistinguishable from mainland Australian coralla.

Fungia granulosa Klunzinger
Records: Veron (1990a)

Notes: This is the only record of the species. Indistinguishable from mainland
Australian coralla.

15

Fungia scutaria Verrill

Records: Vaughan (1918), Wells ( 1950), Veron (1990a)

Notes: _ Common on reef slopes. Indistinguishable from mainland Australian coralla
except for colour. Usually cream with blue or white tentacular lobes,
occasionally pink.

Genus Herpolitha Eschscholtz

Herpolitha limax Houttuyn

Records: Vaughan (1918) (as H. crassa Dana), Wells (1950), Veron (1990a)

Notes: Seen, but not examined by the author.

Genus Sandalolitha Quelch

Sandalolitha robusta (Quelch)

Records: Veron (1990a)

Notes: | Usually rare. Colonies are up to 0.5 m diameter, flattened. Small colonies are
oval, larger ones are contorted according to irregularities in the substrate. The
flattened irregular appearance combined with wide corallum margins free of
centres, suggests a different species from that found in Australia is involved.
There are, however, no skeletal details which reliably distinguish Cocos
(Keeling) coralla from those of Australia. Sandalolitha dentata Quelch may be a
distinct species with the growth form of the present species, but this has yet to
be established.

FAMILY Pectiniidae Vaughan and Wells

This family is represented only by Oxpora lacera

Genus Oxypora Saville-Kent

Oxypora lacera (Verrill)

Records: Veron (1990a)

Notes: Rare. Indistinguishable from mainland Australian colonies.

FAMILY Mussidae Ortmann

This family is represented only by Lobophyllia hemprichii

16

Genus Lobophyllia de Blainville

Lobophyllia hemprichii (Ehrenberg)

Records: Veron (1990a)

Notes: | Usually uncommon but very conspicuous. Indistinguishable from mainland
Australian colonies and shows the full range of the species except that very large
colonies were not found. Often brick red in colour.

FAMILY Merulinidae Verrill

This family is represented only by Hydnophora microconos.

Genus Hyndophora Fischer de Waldheim

Wells (1950) lists H. exesa (Pallas) as recorded from Cocos (Keeling) by Vaughan
(1918). This appears to be a mistake.

Hydnophora microconos (Lamarck)
Records: Vaughan (1918), Veron (1990a)

Notes: | Uncommon but occurs in a wide range of habitats. Indistinguishable from
mainland Australian colonies.

FAMILY Faviidae Gregory
Genus Favia Oken
Favia Stelligera (Dana)
Records: Vaughan (1918), Wells (1950), Veron (1990a)
Notes: | Common in most communities with moderate diversity. Indistinguishable from
mainland Australian colonies.
Favia pallida (Dana)
Records: Vaughan (1918) (as F. speciosa), Veron (1990a)

Notes: Colonies are small submassive to encrusting. They are mostly mottled dark
colours.

Favia matthaii Vaughan

Records: Veron (1990a)

Wi

Notes: Uncommon. Corallites are smaller than those of eastern mainland Australian
colonies but similar in size to those from equatorial localities. Skeletal detail is
similar throughout this range.

Genus Barabattoia Yabe and Sugiyama

Barabattoia amicorum (Edwards and Haime)

Records: Veron (1990a)

Notes: Rare. Indistinguishable from mainland Australian colonies. All specimens
observed were dark brown in colour.

Genus Favites Link

Favites abdita (Ellis and Solander)

Records: Vaughan (1918), Veron (1990a)

Notes: Usually uncommon. Colonies are small, usually encrusting. Corallites of
colonies in high energy environments may have greatly thickened walls.

Favites pentagona (Esper)

Records: Vaughan (1918) (as F. melicerum Ehrenberg), Veron (1990a)

Notes: Common. Coralla have most of the range of corallite characters described by
Veron et al. (1977) except that all have exsert irregular septa and no ecomorphs
associated with very strong wave action were found. The size of corallites
overlaps with those of eastern mainland Australian colonies, but most are
slightly smaller.

Genus Leptoria Edwards and Haime

Leptoria phrygia (Ellis and Solander)

Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes: Usually uncommon. Always a uniform dark grey. Indistinguishable from
mainland Australian colonies.

Genus Montastrea de Blainville
Montastrea curta (Dana)

Records: Veron (1990a)

18

Notes:

Usually uncommon. Colonies are small, encrusting, pale coloured. Corallites
are small (most <6mm diameter with calices <3mm) and are uniform in size.
This identification is tentative only because the species is very variable and lacks
conservative character and also because no colonies were found on reef flats
where it would be expected to be most abundant.

Genus Plesiastrea Edwards and Haime

Plesiastrea versipora Edwards and Haime

Records: Vaughan (1918), Veron (1990a)

Notes:

Genus Leptastrea Edwards and Haime
Leptastrea transversa Klunzinger

Records: Veron (1990a)

Notes:

Rare. Colonies are pale cream, submassive to encrusting. Skeletal structure is
indistinguishable from mainland Australian colonies.

Uncommon. The characters of the species are better defined than in most
mainland Australian coralla. Corallites are of relatively uniform size, with well-
defined walls.

Leptastrea pruinosa Crossland

Records: Veron (1990a)

Notes:

Uncommon. Indistinguishable from mainland Australian colonies. Usually
brightly coloured.

Leptastrea bottae (Edwards and Haime)

Records: Vaughan (1918), Wells (1950), Veron (1990a)

Notes:

Common over a wide range of environments. Colonies are submassive or
encrusting. Corallites are relatively uniform in size, circular, with well defined
walls. Septa are thin, with little ornamentation. Colonies from exposed
environments are mostly creamy coloured with very dark calices.

Genus Cyphastrea Edwards and Haime

Cyphastrea serailia (Forskal )

Records: Wells’ (1950) record of C. chalcidicum (Forskal) appears to be this species.

Veron (1990a)

Ls

Notes: Common ina wide range of environments. Indistinguishable from mainland
Australian colonies.

Cyphastrea microphthalma (Lamarck)

Records: Vaughan (1918), Veron (1990a)

Notes: Common. Indistinguishable from mainland Australian colonies.

Cyphastrea agassizi (Vaughan)

Records: Veron (1990a)

Notes: Uncommon. Colonies are encrusting with widely spaced, exsert, corallites.
Colonies are nearly uniform white in colour. May form coralliths.

Genus Echinopora Lamarck

Echinopora lamellosa (Esper)

Records: Ridley and Quelch (1885), Vaughan (1918), Wells (1950), Veron (1990a)

Notes: Only three small colonies were observed in situ. Indistinguishable from
mainland Australian colonies.

FAMILY Dendrophylliidae Gray

Genus Turbinaria Oken

Turbinaria reniformis Bernard

Records: Veron (1990a)

Notes: Usually rare but forms very extensive monospecific stands at 2-20 m depth north
of “Boat Passage’. Indistinguishable from mainland Australian colonies and has

the same yellow polyps as Great Barrier Reef colonies. Polyps were extended
during the day.

BIOGEOGRAPHIC AFFINITIES

Many common and widespread Indo-Pacific taxa have not been recorded from
Cocos (Keeling) and are almost certainly absent. There are no Oculinidae or
Caryophylliidae. The Pectiniidae, Mussidae and hermatypic Dendrophylliidae are
represented by only one species each. There are no recorded Stylophora, Goniopora,
Alveopora, Coscinaraea, Cycloseris, Polyphyllia, Lithophyllon, Podabacia, Goniastrea,
Platygyra and many minor east Indian Ocean genera.

20

Of the genera that are present, only Sandalolitha does not have a distribution range
crossing the Indian Ocean (Veron 1986).

At species level, the isolation of the atoll from Australia is reflected in:

(a) the number of species which are known from western Australia but
are absent from the atoll: (223 species or 70 % of the western mainland
Australian total of 318 species).

(b) the number of species which are present but have not been
recorded from anywhere in Australia (12 species: Stylocoeniella
cocosensis, Montipora lobulata, Montipora sp., Acropora ocellata,
Acropora sp. 1, Acropora sp. 2, Acropora schmitti, Porites
somaliensis, Porites sp., Pavona Frondifera, Pavona sp., Cyphastrea
agassizi), and

(c) the substantial proportion of species (perhaps 30 %) which are
present but show points of difference from their western mainland
Australian counterparts (e.g. differences in colour, habitat preferences
as well as skeletal and growth form differences).

It may be noted that of the 12 species not recorded from Australia (“b’ above), 3
have been recorded from the Philippines (Veron and Hodgson 1989). The remaining 9
have not been previously recorded from any eastern Indian Ocean locality, but only
Stylocoeniella sp. (a doubtful species), Porites sp. and Pavona sp. have not been
previously recorded anywhere. Although it is possible that the latter are endemic, the
corals of Indonesia are poorly known and they, along with most or all Cocos (Keeling)
species, may well occur in Indonesia.

The principal difference between the corals of Cocos (Keeling) and Christmas
Islands, is in the much greater number of species of Montipora at Cocos (Keeling) and the
greater genetic richness of Christmas Island. The latter however, is a high island with a
very restricted range of habitats, especially sheltered ones. The presence or absence of
corals is therefore likely to be as much a function of habitat diversity as geographic
isolation or relative dispersal ability. The only general observation of this data made here
is that there is no clear evidence that Christmas Island has acted as a ‘stepping stone’ for
the dispersal of corals to Cocos (Keeling).

REFERENCES

Bernard, H.M. 1897. The genus Montipora. The Genus Anacropora. Cat.
Madreporarian Corals Br. Mus. (Nat. Hist.) 3: 1-192.

Guppy, H.B. 1889. The Cocos-Keeling Islands. Scot. Geog. Mag. 5: 281-297, 457-
474, 569-588.

Ridley, S.O. 1884. On the classificatory value of growth and budding in the
Madreporidae, and on a new genus illustrating this point. Ann. Mag. Nat. Hist.
(Sth series). 13: 284-291.

Ridley, S.O. and Quelch. J.J. 1885. List of corals collected in the Keeling Islands. In:
H.O. Forbes A Naturalist’s wanderings in the eastern Archipelago. pp. 44-47.

21

Vaughan, T. W. 1918. Some shoal-water coarls from Murray Islands, Cocos-Keeling
Islands and Fanning Island. Pap. Dep. Mar. Biol. Carnegie Inst. Wash. 9: 51-234.

Veron, J.E.N. 1986. Corals of Australia and the Indo-Pacific. Sydney, Angus and
Robertson 644pp.

Veron, J.E.N. 1990a. Re-examination of the reef corals of Cocos (Keeling) Atoll. Rec.
West. Aust. Mus. 14: 553-581.

Veron, J.E.N. 1990b. New Scleractinia from Japan and other Indo-West Pacific
countries. Galaxea 9: 95-173.

Veron, J.E.N. and Hodgson, G. 1989. Annotated checklist of the hermatypic corals of
the Philippines. Pacific Sci. 43: 234-287.

Veron, J.E.N. and Marsh, L.M. 1988. Hermatypic corals of Western Australia. Rec.
Western Aust. Mus. Supplement 29: 1-136.

Veron, J.E.N. and Pichon, M. 1982. Scleractinia of Eastern Australia. 1V. Family
Poritidae. Aust. Inst. Mar. Sci. Monogr. Ser. 5: 1-159.

Veron, J,E.N., Pichon, M. and Wijsman-Best, M. 1977. Scleractinia of Eastern
Australia. II. Families Faviidae, Trachyphylliidae. Aust. Inst. Mar. Sci. Monogr.
Ser. 3: 1-233.

Veron, J.E.N, and Wallace, C. 1984. Scleractinia of Eastern Australia. V. Family
Acroporidae. Aust. Inst. Mar. Sci. Monogr. Ser. 6: 1-485.

Wells, J,W. 1950. Reef corals from the Cocos-Keeling Atoll. Bull. Raffles Mus. 22: 29-
52, pl. 9-14.

ATOLL RESEARCH BULLETIN

NO. 410

CHAPTER 12

MARINE MOLLUSCS OF THE COCOS (KEELING) ISLANDS

BY

F.E. WELLS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 12
MARINE MOLLUSCS OF THE COCOS
(KEELING) ISLANDS
BY
F.E. WELLS*

INTRODUCTION

Compared to other localities in the eastern Indian Ocean, the molluscs of the Cocos
(Keeling) Islands were relatively well known prior to the Western Australian Museum
survey in February 1989. Two short papers on the molluscs of the atolls were presented
by Marratt (1879) and Rees (1950). A much more extensive list was prepared by Abbott
(1950). Mrs. R.E.M. Ostheimer and Mrs. V.O. Maes spent the first two months of 1963
on Cocos collecting for the Academy of Natural Sciences of Philadelphia, as part of the
International Indian Ocean Expedition. Maes (1967) presented a complete list of the
species collected, and included records of species recorded by Marratt (1879) or Abbott
(1950) that she did not collect on the islands. A total of 504 species were recorded, 379 of
which were identified to species.

With their longer time on the atoll Maes and Ostheimer naturally collected more
species than the Western Australian Musuem expedition, but their collections were
primarily restricted to relatively shallow water as they did not scuba-dive. They did
however do some dredging in the lagoon. The Museum team collected in many of the
same localities as Maes and Ostheimer, but also dived in a number of areas. Because of
this many of the species which live in deeper water that were recorded by only a few
specimens by Maes (1967) were shown to in fact be common.

_ The following list shows all of the mollusc species known from Cocos (Keeling).
Station numbers are those of the Western Australian Museum expedition (see Chapter 2).
Indications of abundance are given in four categories: abundant, common, uncommon and
rare. These are subjective and not quantitative. The abundance categories are based partly
on the number of stations at which a species was collected, but also on the number of
specimens collected and whether or not the specimens were collected alive or as a broken
dead shell. Thus it is possible for a bivalve species collected at two stations as single dead
valves to be rare while another species collected at one station may be listed as common
because several live animals were collected. Despite these limitations use of the four
categories can provide an idea of the relative abundances of the different species. In a
number of cases species recorded by previous papers were not collected by the Western
Australian Museum team; these are included in the species list and are annotated. In some
cases Maes (1967) recorded a species whose name has subsequently been changed or
provided a photograph that we consider represents a different species. To avoid confusion
by people not familiar with molluscs in comparing the two species lists I have annotated
our identification of the species with the name used by Maes. Several pelagic molluscs
recorded by Maes have been deleted as they occur in the water column and not on the
bottom. Maes recorded species in a number of families that were identified only to generic
level. To avoid the possibility of duplication, these have been excluded from the list where
the Western Australian Museum team found species recorded in the family that were not

Western Australian Museum, Francis Street, Perth, Western Australia, 6000.

2

found by Maes. In a survey such as this where molluscs of all groups have been collected
species identifications should be regarded with caution. The list however does provide a
good basic knowledge of the molluscs which live on the Cocos (Keeling) Islands.

The following list shows that 610 species of molluscs are known from the Cocos
(Keeling) Islands. There are 496 gastropods, 109 bivalves, 1 chiton, and 4 cephalopods.
No monoplacophorans, aplacophorans or scaphopods are known from the islands. The
fauna is diverse, and compares favourably with the total number of species known from
nearby areas that have been studied: 543 from the Maldives (Robertson, unpublished list
cited by Maes), 490 from Christmas Island (Wells and Slack-Smith, 1987), and 581 from
atolls off the coast of northwestern Australia (Wells, 1987).

Maes (1967) was intrigued by the zoogeographical relationships of the 379 mollusc
species she was able to identify to species: 82% were widespread Indo-Pacific forms, 15%
were Pacific species and only 3% had Indian Ocean affinities. She thus concluded that
while Cocos (Keeling) is in the Indian Ocean, the islands have a greater faunal affinity with
the western Pacific than with the remainder of the Indian Ocean. However since her paper
was published the Western Australian Museum has had a number of expeditions to the
coral atolls off the northwest coast of Western Australia and also to Christmas Island,
some 900 km northeast of Cocos (Keeling), the molluscs of which are reported in a series
of papers and reports (Wells 1986; 1987; Wells and Slack-Smith 1987). Comparison of
these recent data with Cocos (Keeling) will provide a better idea of the zoogeographic
relationships of the atoll.

Many of the species at Cocos and in the other areas are either not identified to
species or are identified only provisionally. For these reasons Wells (1986) selected 20
families of prosobranch gastropods for a detailed examination of the zoogeographic
relationships of the molluscs of the atolls off northwestern Australia. The families were
selected because the individual species are generally large and well known taxonomically,
and they are well represented in museum collections. The same 20 families are examined
here. For the Cocos material 248 species of the total of 584, or 42%, of all species
collected belong to the 20 families. Thus they can be considered as representative of
molluscs as a whole. An index of overlap (Krebs 1978) was calculated for all
combinations of Cocos (Keeling), Christmas Islands and atolls off the northwestern
Australian coast. The index varies from 0 where there is no overlap to 1 where the overlap
is total. Values obtained were:

Cocos-Christmas 0.52
Cocos-Northwestern Australian atolls OS7
Christmas-Northwestern Australia 0.52

All three overlaps are relatively low, probably due to our rather limited knowledge
of the fauna of the three areas. However the overlaps are similar among the three areas.
Most of the species recorded were found at two or three of the areas. Maes (1967)
commented upon several species as not occurring in Western Australia; all were found on
the surveys of offshore coral reefs. Based on the increased data now available it appears
that the molluscs of Cocos (Keeling) have very close faunal affinities with those of
Christmas Island and the offshore areas of Western Australia. Many of the species that
Maes considered to be western Pacific are in fact found throughout the three areas of the
eastern Indian Ocean and should be considered to be Indo-Pacific species. Perhaps if there
is a specific Indian Ocean mollusc fauna it occurs primarily in the western Indian Ocean

3

and only a few species reach as far east as Cocos (Keeling), or in the case of species such
as Drupa lobata even as far as the west coast of Western Australia.

Neither Maes (1967) nor the Western Australian Museum survey recorded the
largest of the giant clam species, Tridacna gigas, as living on Cocos (Keeling). However
large numbers of long dead shells line the shoreline of Home Island. This suggests that T.
gigas occurred on the atoll when it was first inhabited but became locally extinct as it was
collected by Cocos Malays for food.

The spider shell Lambis lambis occurs in large numbers in shallow water in the
southern part of the lagoon at Cocos. It is easily collected and is regarded as a delicacy by
the Cocos Malays. The same species is also collected for food in many other areas of the
Indo-Pacific but a thorough literature search failed to find a single study of the fishery
biology of any species of Lambis. Being a relatively large species that occurs in shallow
water L. lambis could be easily fished out, and become locally extinct as did T. gigas. If
there is to be effective management of the marine environment of the Cocos (Keeling)
Islands a study of the population biology of Lambis lambis is urgently needed.

ACKNOWLEDGEMENTS

I would like to personally thank the people and organisations acknowledged at the
beginning of this report for their help to the Museum team, and would also like to thank the
other team members for help in the field and provision of specimens. In addition to his
technical work for the entire group, C.W. Bryce collected numerous mollusc species and
photographed most of the opisthobranchs alive. G.M. Hansen and G.W. Buick identified
most of the specimens during my absence on other museum projects, and C.W. Bryce
identified many of the opisthobranchs; their contribution is significant and very much
appreciated.

REFERENCES

Abbott, R.T. 1950. Molluscan fauna of the Cocos-Keeling Islands. Bull. Raffles Mus.
22: 68-98.

Krebs, C.J. 1978. Ecology. The explanation of distribution and abundance. Second
edition. Harper and Row, New York.

Marratt, F.P. 1879. Note on some shells from the Keeling or Cocos Islands, Indian
Ocean. Proc. Lit. Philos, Soc. Liverpool, 33: 53-54.

Maes, V.O. 1967. The littoral marine mollusks of Cocos-Keeling Islands (Indian Ocean).
Proc. Acad. Nat. Sci., Phila. 119: 93-217.

Rees, W.J. 1950. The cephalopods of the Cocos-Keeling Islands collected by C.A.
Gibson-Hill. Bull. Raffles Mus. 22: 99-100.

Wells, F.E. 1986. Zoogeography of prosobranch gastropods on offshore coral reefs in
northwestern Australia. Veliger 29: 191-198.

4

Wells, F.E. 1987. Molluscs. In: Berry, P F. (Ed.) Faunal surveys of Ashmore reef and
Cartier Island. Unpubl report to Australian National Parks and Wildlife Service.

Wells, F.E. and Slack-Smith, S.M. 1987. Molluscs. In: Berry, P F. (Ed). Faunal

survey of Christmas Island (Indian Ocean.). Unpubl rept to Australian National
Parks and Wildlife Service.

LIST OF MOLLUSCS

CLASS POLYPLACOPHORA

ACANTHOCHITONIDAE
Acanthochitona sp.

CLASS GASTROPODA

SCISSURELLIDAE
Sp.

FISSURELLIDAE
Emarginula sp.

TROCHIDAE

Ethalia striolata (A. Adams, 1853)
Euchelus foveolatus (A. Adams, 1851)
Euchelus cf. instrictus (Gould, 1851)
Monilea cf. nucleus (Philippi, 1849)
Trochus maculatus Linnaeus,1758

STOMATIIDAE

Broderipia rosea (Broderip, 1834)
Stomatella impertussa (Burrow, 1815)
Stomatia phymotis Helbling, 1779
Stomatia cf. rubra (Lamarck, 1822)
Synaptocochlea sp.

TURBINIDAE

Astralium calcar (Linnaeus, 1758)
Astraea helicina (Gmelin, 1791)
Leptothyra solida Preston, 1908
Parviturbo parvissima (Hedley, 1899)
Turbo lajonkairii Deshayes, 1839

Turbo petholatus Linnaeus, 1758

PHASIANELLIDAE
Hiloa variabilis (Pease, 1860)

NERITIDAE
Nerita albicilla Linnaeus. 1758

Nerita costata Gmelin, 1791
Nerita maxima Gmelin, 1791
Nerita plicata Linnaeus, 1758

Maes

Maes

Maes

Maes

Maes

Maes

9, 13, 23, Rare

1, 2, 6, 9, 10, 12, 14, 15,
1617 ,.23, 25; 268 27.4295
36, Abundant.

Maes
Maes
Maes
Maes
Maes

32, Uncommon

6, 9, 10, 12, 15, Uncommon
Maes

Maes

Sr LO ellen el 5)
23, 27, 30, 32, Abundant

2, 16, 17, 23, Uncommon

Maes

2, 6, 10, 12, 27, 30,
Common

Maes

Maes

12610312) 21230,
Abundant

6

Nerita polita Linnaeus, 1758

Nerita undata Linnaeus, 1758

Nerita sp.

Smaragdia rangiana (Recluz, 1841)
Smaragdia souverbiana (Montrouier, 1865)

PHENACOLEPIDAE
Phenacolepas cf. senta Hedley, 1899
Phenacolepas sp.

NERITOPSIDAE
Neritopsis radula (Linnaeus, 1758)

LITTORINIDAE

Littoraria coccinea (Gmelin, 1791)
Littoraria glabrata (Philippi, 1846)
Littoraria scabra (Linnaeus, 1758)
Littoraria undulata (Gray, 1839)

Nodilittorina pyramidalis (Quoy and Gaimard, 1833)

Tectarius granularis (Gray, 1839)

VITRINELLIDAE
Teinostoma sp.
Vitrinella sp.

TRUNCATELLIDAE
Truncatella guerinii A. and J. Villa, 1841

RISSOIDAE

Haurakia isolata Laseron, 1956
Pyramidelloides cf. miranda (A. Adams, 1861)
Rissoina ambigua Gould, 1851
Rissoina balteata Pease, 1870
Rissoina ephamilla Watson, 1886
Rissoina exasperata Souverbie, 1866
Rissoina polytropa Hedley, 1899
Rissoina cf.tenuistriata Pease, 1867
Rissoina triticea Pease, 1862
Rissoina turricula Pease, 1860
Rissoina sp.

Zebina semiplicata (Pease, 1862)
Zebina tridentata Michaud, 1860

ASSIMINEIDAE
Assiminea sp.

OMALOGYRIDAE
Omalogyra sp.

RISSOELLIDAE
3 undetermined species

27, Common
2, Common
2, Uncommon
Maes

Maes.

Maes
Maes

13, 23, Rare

Abbott

Maes

2, Uncommon

2, 12, 21, Common
Maes

Maes

Maes
Maes

Maes

Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes
Maes

Maes

Maes

Maes

ARCHITECTONICIDAE
Heliacus sp.
Philippia radiata (Roding, 1798)

VERMETIDAE
Dendropoma maxima (Sowerby, 1825)

CAECIDAE
Caecum sp.

PLANAXIDAE
Planaxis lineatus (DaCosta, 1776)

MODULIDAE
Modulus tectum (Gmelin, 1791)

CERITHIIDAE

Bittum sp.

Cerithium atromarginatum Dautzenberg and Bouge, 1933
Cerithium columna Sowerby, 1831

Cerithium echinatum Lamarck, 1822

Cerithium egenum Gould, 1849

Cerithium cf . ianthinum Gould, 1851
Cerithium nesioticum Pilsbry and Vanetta, 1905
Cerithium nodulosum (Bruguiére, 1792)

Cerithium piperitum Sowerby, 1855
Cerithium purpurascens Sowerby, 1855
Cerithium rarimaculatum Sowerby, 1855
Cerithium rostratum Sowerby, 1855
Cerithium trailli (Sowerby, 1855)

Diala albugo (Watson, 1886)

Gourmya gourmyii (Crosse, 1861)
Obtortio diplax (Watson, 1886)
Rhinoclavis asper (Linnaeus, 1758)
Rhinoclavis diadema Houbrick, 1978

Rhinoclavis fasciatus (Bruguiére, 1792)
(referred to R. procera (Kiener, 1841) by Maes)
Rhinoclavis sinensis (Gmelin, 1791)
Rhinoclavis vertagus (Linnaeus, 1767)
Clypeomorus bifasciata (Sowerby, 1855)

CERITHIOPSIDAE
Cerithiopsis four unidentified species

13, 23, Rare
22, Rare

5, 6, 7, 10, 12, 19, 36
Abundant

Maes

Maes

Maes

9, 16, 23, 29, Common
10, 12, 13, 27, Uncommon
POM 1B) 23427382)
Abundant

STAB 519022. 23:
25, 32, Abundant

13, 27, Rare

13, Rare

13, 19, 22, 32, Common
12) SHOW 2s lg 9:
35, Common

Maes

Maes

7, 13, 22, 25, 32, Common
9, 13, 23, Uncommon

16, 26, 29, Uncommon
Maes

19, Rare

Maes

12, 22, Uncommon
On OZ IS 15019)
22, 23, Adundant

SNA US 7922, 132:
Abundant

1, 5, 6, 9, 10, 27, Common
2 OMIT 27929536
Common

ZONA DT) SOs SO;
Adundant

Maes

8

TRIPHORIDAE

Triphora alveolata Adams and Reeve, 1850
Triphora concors Hinds, 1843

Triphora rubra Hinds, 1843

Triphora ustulata Hervier, 1897

Triphora verrucosa Adams and Reeve, 1850
Triphora violacea Quoy and Gaimard, 1834
Triphora sp.

Viriola cancellata (Hinds, 1843)

Viriola intergranosa (Hervier, 1897)
Viriola interfilata (Gould, 1861)

EPITONIIDAE

Epitonium alata (Sowerby, 1844)

Epitonium martinii (Wood, 1828)

Epitonium "muricatum” Risso (of Kiener, 1838-39)
Epitonium cf. symmetrica (Pease, 1867)
Nodiscala? attenuata (Pease, 1860)

Epitonium 3 unidentified species

EULIMIDAE

Balcis cumingi (A. Adams, 1854)
Balcis 4 additional species

Sp. 1

STILIFERIDAE
?Sulifer dubia Sowerby, 1878

FOSSARIDAE
Couthouyia stoliczkanus Nevill, 1871

VANIKORIDAE
Vanikoro cancellata (Lamarck, 1822)
Vanikoro distans (Recluz, 1843)

HIPPONICIDAE
Sabia concia (Schumacher, 1817)

CALYPTRAEIDAE
Cheilea equestris (Linnaeus, 1758)
Cheilea hipponiciformis (Reeve, 1858)

STROMBIDAE

Lambis chiragra (Linnaeus, 1758)
Lambis lambis (Linnaeus, 1758)
Lambis truncata (Humphrey, 1786)
Strombus aurisdianae Linnaeus, 1758
Strombus gibberulus Linnaeus, 1758

Strombus lentiginosus Linnaeus, 1758
Strombus luhuanus Linnaeus, 1758
Strombus microurceus (Kira, 1959)

Maes
Maes
Maes
Maes.
Maes
Maes
Maes
Maes
Maes
Maes

Maes
Maes
Maes
Maes
Maes
Maes

Maes, 13 Rare
Maes
10, Rare

Abbott

Maes

25, Rare
25, Rare

12, 23, 27, Common

12, 23, Uncommon
Maes

1, 7, 12, Uncommon

9, 12, 35, 36, Adundant
23, Rare

Maes

oF O12 > 15.27, 29:
Common

5, 23, Rare

9A, 23, Uncommon
9A, Uncommon]

Strombus mutabilis Swainson, 1821

NATICIDAE

Eunaticina papilla (Gmelin, 1791)
Natica fasciata (Roding, 1798)
Natica gualtieriana (Recluz, 1844)
Natica lemniscata Philippi, 1852
Natica lineozona Jousseaume, 1874
Natica marochiensis Gmelin, 1791
Natica orientalis Gmelin, 1791
Natica robillardi Sowerby, 1893
Polinices mammilla (Linnaeus, 1758)
Polinices melanostomus (Gmelin, 1791)
Polinices simiae (Deshayes, 1838)
Polinices tumidus (Swainson, 1840)

LAMELLARIIDAE
Lamellaria sp.

ERATOIDAE

Proterato sulcifera (Gray, 1832)
Trivia insecta (Mighels, 1845)
Trivia oryza (Lamarck, 1810)
Trivia pellucidula (Reeve, 1846)
Trivia producta (Gaskoin, 1836)

OVULIDAE

Calpurneus lacteus (Lamarck, 1810)
Calpurneus verrucosus (Linnaeus, 1758)
Ovula ovum (Linnaeus, 1753)
Pseudocypraea adamsoni (Gray, 1832)

CYPRAEIDAE

Cypraea annulus Linnaeus, 1758
Cypraea arabica Linnaeus, 1758
Cypraea boivinii Kiener, 1843
Cypraea caputserpentis Linnaeus, 1758
Cypraea carneola Linnaeus, 1758
Cypraea caurica Linnaeus, 1758
Cypraea chinensis Gmelin, 1791
Cypraea coloba Melvill, 1888
Cypraea depressa Gray, 1824
Cypraea erosa Linnaeus, 1758
Cypraea fimbriata Gmelin, 1791
Cypraea globulus Linnaeus, 1758
Cypraea helvola Linnaeus, 1758
Cypraea hirundo Linnaeus, 1758
Cypraea histrio Gmelin, 1791
Cypraea isabella Linnaeus, 1758

1, 5, 9, 12, 27, Common

19, Rare

17, Rare

2, 27, 35, Common
Maes

Maes

Maes

Maes

9, 29, Rare

Maes

7, Rare

Maes

5, 6, 95°10; 12; 13,15, 23,
Adundant

Maes

Maes
Maes
Maes
Maes
Maes

13, Rare
Maes
Maes
Maes

1, 6, 10, 27, Common

12, 27, Uncommon

Maes

1, 11, 12, 27, Common

13, Uncommon

Maes

Maes

9A, Rare

1, 10, 12, 27, Common

5, 12, 27, Uncommon

13, 19, Rare

3, 13, Rare

1, 12, 13, 23, Uncommon
1, 19, Uncommon

1, 6, 7, 12, 21, 23, Common
9, 12, 13, 25, 32, Common

10

Cypraea labrolineata Gaskoin, 1849

Cypraea lynx Linnaeus, 1758
Cypraea mauritiana Linnaeus, 1758
Cypraea microdon Gray, 1828
Cypraea moneta Linnaeus, 1758

Cypraea nucleus Linnaeus, 1758
Cypraea poraria Linnaeus, 1758
Cypraea punctata Linnaeus, 1771
Cypraea stolida Linnaeus, 1758
Cypraea talpa (Linnaeus, 1758)
Cypraea teres Gmelin, 1791
Cypraea testudinaria Linnaeus, 1758
Cypraea tigris Linnaeus, 1758
Cypraea vitellus Linnaeus, 1758

TONNIDAE

Malea pomum (Linnaeus, 1758)
Tonna canaliculata (Linnaeus, 1758)
Tonna perdix (Linnaeus, 1758)

CASSIDAE
Casmaria erinaceus (Linnaeus, 1758)
Cypraecassis rufa (Linnaeus, 1758)

CYMATIIDAE

Charonia tritonis (Linnaeus, 1758)
Cymatium aquatile (Reeve, 1844)
Cymatium lotorium (Linnaeus, 1758)
Cymatium nicobaricum (Réding, 1798)

Cymatium pileare (Linnaeus, 1758)
Cymatium pyrum (Linnaeus, 1758)
Cymatium rubeculum (Linnaeus, 1758)
Cymatium vespaceum (Lamarck, 1822)
Distorsio anus Linnaeus, 1758
Gutturnium muricinum (Gmelin, 1791)
Septa gemmata (Reeve, 1844)

Gelagna succincta (Linnaeus, 1771)
Linatella clandestina (Lamarck, 1816)

BURSIDAE

Bursa bufonia (Gmelin, 1791)
Bursa cruentata (Sowerby, 1841)
Bursa granularis (R6ding, 1798)

Bursa lamarcki (Deshayes, 1853)
Bursa rhodostoma (Sowerby, 1835)
Bursa tuberosissima (Reeve, 1844)
Tutufa rubeta (Linnaeus, 1758)

Merl 3syl5,. 19922..23;
Common

3, 7, Uncommon

27, Rare

Maes.

12. 5556.09, 102s Lome
26, 27, 29, 35, 36, Adundant
Maes

27, 32, Uncommon

13, Uncommon

32, Uncommon

13, 15, Rare

1133255,;32- Rare

Maes

12, 18, 22, 36, Rare

36, Uncommon

12, Rare
36, Rare
12, 27, 30, Rare

Maes
Maes

12, 21, Rare

16, Rare

Maes

2, 6, 9, 10, 15, 16, 17, 27,
29, 35, 36

Maes

13, 23, Uncommon

9, 32, Uncommon

Maes

6, Rare

1, 9, 29, 36, Uncommon
L105 172 1827829:
Common

13, Rare

Abbott

1, 10, 12, 27, Common
13, 23, 32, Common
19:6) 9S 100120 27
Common

19, Rare

9, 23, Uncommon

25, Rare

23, Rare

COLUBRARIIDAE
Colubraria nitidula (Sowerby, 1833)
Colubraria muricata (Lightfoot, 1786)

MURICIDAE
Aspella anceps (Lamarck, 1822)
Chicoreus saulii (Sowerby, 1841)

(listed as Murex torrefactus Sowerby, 1841 by Maes)

Murex ramosus Linnaeus, 1758
Naquetia triquetra (Born, 1778)

THAIDIDAE

Cronia crassulnata (Hedley, 1915)
Drupa clathrata (Lamarck, 1816)
Drupa grossularia Roding, 1798
Drupa lobata (Blainville, 1832)
Drupa morum (Roding, 1798)

Drupa pophyrostoma (Reeve, 1846)
Drupa ricinus (Linnaeus, 1758)

Drupa rubusidaeus Roding, 1798
Drupella chaidea (Duclos, 1832)
Drupella cornus (Roding, 1798)

Drupella ochrostoma (Blainville, 1832)
Maculotriton digitalis (Reeve, 1844)
Maculotriton sculptilis (Reeve, 1846)
Maculotriton serriale (Deshayes, 1834)
Morula anaxeres (Kiener, 1845)
Morula biconica (Blainville, 1832)
Morula fiscella (Gmelin, 1791)
Morula fusconigra (Dunker, 1871)
Morula granulata (Duclos, 1832)
Morula margariticola (Broderip, 1832)

Morula marginaira (Blainville, 1832)
Morula nodicostata (Pease, 1868)

Morula spinosa (H. and A. Adams. 1835)

Morula uva (Roding, 1798)

Nassa serta (Bruguiére, 1789)
Purpura persica (Linnaeus, 1758)
Thais aculeata (Deshayes, 1844)

Thais armigera (Link, 1807)

Thais hippocastanum (Linnaeus, 1758)

CORALLIOPHILIDAE
Coralliophila deformis (Lamarck, 1822)

11

15, Rare
7, 9, Uncommon

Maes
1.6, 9, 134954195 21) 22°
23,32, Abundant

Abbott
23, Rare

27, Rare

Maes

Maes

23, Uncommon

195316, 11 Ola 12427,
Common

6, Rare

te6snl25 15527430;
Common

13, 15, 23, 32, Common
Maes

10, 13, 16, 29, 30, 36,
Common

Maes

13, 27, Uncommon

Maes

6, 10, 13, 27, 30, Common
6, Rare

Maes

27, Rare

Maes

6, 10, 12, 27, 30, Common
eG! 22-7) 29 3243.6,
Common

Maes

13, 30, Common

be M3995 25.32),
Common

155619) 1Of12; 13.19,
22, 23, 27, 30, 32, Abundant
Maes

Maes

5, 6, 10, 19, 27, Uncommon
1, 10, 12, 27, Uncommon
Maes

Maes

12

Coralliophila erosa (R6ding, 1798)
Coralliophila robillardi (Lienard, 1870)
Coralliophila violacea (Kiener, 1836)

Quoyula madreporarum (Sowerby, 1832)
Rapa rapa (Gmelin, 1791)

COLUMBELLIDAE

Aesopus cumingi (Reeve, 1859)
Mitrella marquesa (Gaskoin, 1851)
Pyrene obtusa (Sowerby, 1832)
Pyrene turturina (Lamarck, 1822)

Pyrene varians (Sowerby, 1832)
Zafra sinensis (Sowerby, 1894)

BUCCINIDAE

Cantharus cf. fragaria (Reeve, 1846)
Cantharus fumosus (Dilwyn, 1817)
Cantharus iostomus (Gray, 1834)
Cantharus pulcher (Reeve, 1846)
Cantharus undosus (Linnaeus, 1758)

Engina incarnata (Deshayes in Laborde and Linant, 1834)

Engina lauta (Reeve, 1846)

Engina lineata (Reeve, 1846)
Engina melanozona Tomlin, 1928
Engina mendicaria (Linnaeus, 1758)
Engina parva Pease, 1867

Engina zonalis (Lamarck, 1812)
Nassaria pusilla (R6ding, 1798)
Pisania fasciculata (Reeve, 1846)
Pisania marmorata (Reeve, 1846)
Pisania truncata (Hinds, 1844)

NASSARIIDAE
Nassarius gaudiosus (Hinds, 1844)
Nassarius graniferus (Kiener, 1834)

Nassarius margaritiferus (Dunker, 1847)
Nassarius oneratus (Deshayes, 1863)
Nassarius papillosus (Linnaeus, 17 58)

FASCIOLARIIDAE
Latirus nodatus (Gmelin, 1791)
Latirus polygonus (Gmelin, 1791)

Latirus turritus (Gmelin, 1790)
Latirus sp.

Peristernia fragaria (Wood, 1828)
Peristernia nassatula (Lamarck, 1822)

Peristernia ustulata (Reeve, 1847)

13, 36, Uncommon

13,30, Uncommon

ST OMI2 AIS lS lO R22
23, 26, 32, Abundant

7, 10, 13, 23, 32, Common
7, 13, 25, 32, Common

Maes

Maes

5, 7, 13, 23, 32, Common
55°79) 10124133 19a
23, 29, Common

9, 13, 32, Uncommon
Maes

7, 13, 19, 23, Common
9, 17, Uncommon

19, 22, 29, Uncommon
7, 19, 32, Uncommon
1, 5, 6, 10, 27, Common
7, Rare

Maes

13, 27, Uncommon
Maes

27, Uncommon

13, Rare

6, 27, Uncommon

32, Rare

Maes

Maes

Maes

1, 7, Rare

5579 9,:135 lo AS wae?
Abundant

6, 12, 27, Uncommon

23, Common

5, 13, Uncommon

10, Rare

5: 110,216;) 17 S19 26827
30, 32, Common

32, Rare

13, 29, 32, Common
Maes

6: 7) 135 1519237275
Common

27, Rare

OLIVIDAE
Oliva annulata (Gmelin, 1791)

Oliva caerulea (R6ding, 1798)
Oliva episcopalis Lamarck, 1811
Oliva panniculata Duclos, 1835

MARGI NELLIDAE
Marginella neville Jousseaume, 1875

MITRIDAE

Cancilla carnicolor (Reeve, 1844)

Cancilla filaris (Linnaeus, 1771)

Imbricaria conovula (Quoy and Gaimard, 1833)

Imbricaria olivaeformis (Swainson, 1821)
Imbricaria punctata (Swainson, 1821)
Imbricaria vanikorensis (Quoy and Gaimard, 1833)
Imbricaria virgo (Broderip, 1836)
Mitra acuminata Swainson, 1824
Mitra ambigua Swainson, 1832
Mitra columbelliformis Kiener, 1838
Mitra contracta Swainson, 1820
Mitra decurtata Reeve, 1844

Mitra eremitarum RGding, 1798
Mitra fraga Quoy and Gaimard, 1833
Mitra imperialis Réding, 1798

Mitra litterata Lamarck, 1811

Mitra mitra (Linnaeus, 1758)

Mitra paupercula (Linnaeus, 1758)
Mitra.oleacea (Reeve, 1844)

Mitra rosacea Reeve, 1845

Mitra scutulata (Gmelin, 1791)

Mitra Stictica (Link, 1807)

Mitra ticaonica Reeve, 1844

Mitra turgida Reeve, 1845
Neocancilla papilio (Link, 1807)
Pusia areolata (Reeve, 1844)

Pusia cancellarioides (Anton, 1839)
Scabricola fusca (Swainson, 1824)
Scabricola fissurata (Lamarck, 1811)

Scabricola granatina Lamarck, 1811
Scabricola scabricula (Linnaeus, 1758)
Subcancilla annulata (Reeve, 1844)

COSTELLARIIDAE

Vexillum armigera (Reeve, 1845)
Vexillum cadaverosum (Reeve, 1844)
Vexillum cancellarioides (Anton, 1838)
Vexillum cf. corallina (Reeve, 1845)

13

HRS e122 523.9325
Common

6, 13, 19, 25, Common
Maes

13, Rare

TO 2s A328
Common

15, 19, 22, Common
22, Rare

Maes

Maes

5, Rare

Maes

12, Rare

13, Rare

6, 10, 27, Uncommon
9, Rare

13, 29, Rare

Maes

6, 27, Common
Maes

6, 10, 27, Uncommon
1, Rare

19, Rare

27, Rare

1, Rare

13, Rare

Maes

19, Rare

Maes

Maes

23, Rare

5, 9, 15, 19, 22, 23,
Common

Maes

Maes

19, Rare

Maes

5, 9, 19, 22, Uncommon
32, Rare

7, Rare

14

Vexillum crocatum (Lamarck, 1811)
Vexillum mutabile (Reeve, 1845)
Vexillum pardalis (Kuster, 1841)
Vexillum speciosum (Reeve, 1844)
Vexillum tuberosa (Reeve, 1845)
Vexillum turrigerum (Reeve, 1845)
Vexillum unifascialis (Lamarck, 1811)
Vexillum zelotypum (Reeve, 1845)

VASIDAE
Vasum turbinellum (Linnaeus, 1758)

HARPIDAE
Harpa amouretta Réding, 1798

TURRIDAE

Carinapex sp.

Clavus laeta (R6ding, 1798)

Clavus lamberti (Montrouzier, 1860 )
Clavus sp.

Crassispira sp.

Daphnella atractoides Hervier, 1897
Daphnella cf. boholensis (Reeve, 1843)
Daphnella delicata (Reeve, 1846)
Daphnella sp.

Etrema scalarina (Deshayes, 1863)
Eucithara souverbii (Tryon, 1884)
Eucithara stromboides (Reeve, 1846)
Hemidaphne reeveana (Deshayes, 1863)
Hemidaphne rissoides (Reeve, 1843)
Tredalea pygmaea (Dunker, 1860)
Tredalea sp.

Lienardia sp.

Macteola cf. thiasotes (Melvill and Standen, 1897)
Mitromorpha atramentosa (Reeve, 1849)
Mitromorpha lachryma (Reeve, 1845)
Mitromorpha stepheni (Melvill and Standen, 1897)
Philbertia barnardi (Brazier, 1876)
Philbertia pustulosa (DeFolin, 1867)
Philbertia granicostata (Reeve, 1846)
Philbertia tincta (Reeve, 1846)
Philbertia sp.

Turridrupa cincta (Lamarck, 1822)
Turridrupa sp.

Turris spectabilis (Reeve, 1843)
Xenoturris cingulifera (Lamarck, 1822)
Xenoturris kingae Powell, 1964

CONIDAE
Conus arenatus Hwass in Bruguiére, 1792
Conus aulicus Linnaeus, 1758

7, Rare

Maes

13, Rare

15, 25, 32, Uncommon
13, 22, 23, Uncommon
9, 19, Uncommon

9, Rare

7, 22, 23, Uncommon

15°5, 75, 10) 115 PAS eho:
22, 23, 25, 27, Abundant

Maes

Maes

7, 13, 15, 22, 23, Common
7, 23, 32, Uncommon
13, Rare

13, Rare

Maes

Maes

Maes

13, Rare

Maes

Maes

Maes

Maes

Maes

Maes

15, Rare

Maes

Maes

5, Rare

Maes

Maes

Maes

Maes

Maes

Maes

27, Rare

Maes

32, Rare

Maes

13, 19, 22, Uncommon
15, 22, 23, Uncommon

1, 9, 19, 22, 23, Common
Maes

Conus betulinus Linnaeus, 1758

Conus capitaneus Linnaeus, 1758

Conus catus Hwass in Bruguiére, 1792
Conus chaldeus (RG6ding, 1798)

Conus coronatus Gmelin, 1791

Conus distans Hwass in Bruguiére, 1792
Conus eburneus Hwass in Bruguiére, 1792
Conus ebraeus Linnaeus, 1758

Conus flavidus Lamarck, 1810

Conus frigidus Reeve, 1848

Conus hevassi A. Adam, 1853

Conus imperialis Linnaeus, 1758

Conus leopardus Roding, 1798

Conus litoglyphus Hwass in Bruguiére, 1792
Conus litteratus Linnaeus, 1758

Conus lividus Hwass in Bruguiére, 1792

Conus marmoreus Linnaeus, 1758
Conus miles Linnaeus, 1758

Conus miliaris Hwass in Bruguiére, 1792

Conus moreleti Crosse, 1858
Conus musicus Hwass in Bruguiére, 1792

Conus obscurus Sowerby, 1833
Conus pertusus Hwass in Bruguiére, 1792
Conus pulicarius Hwass in Bruguiére, 1792

Conus quercinus Solander, 1786
Conus rattus Hwass in Bruguiére, 1792
Conus sponsalis Hwass in Bruguiére, 1792

Conus Straitellus Link, 1807

Conus striatus Linnaeus, 1758

Conus tenuistriatus Sowerby, 1857

Conus tessulatus Born, 1780

Conus textile Linnaeus, 1758

Conus tulipa Linnaeus, 1758

Conus vexillum Gmelin, 1791

Conus virgo Linnaeus, 1758

Conus vitulinus Hwass in Bruguiére, 1792
Conus zonatus Hwass in Bruguiére, 1792

TEREBRIDAE
Hastula penicillata (Hinds, 1844)
Terebra affinis Gray, 1834

Terebra areolata Link, 1807
Terebra argus Hinds, 1844
Terebra babylonia Lamarck, 1822
Terebra casta Hinds, 1844

WS)

Maes

9, 22, 32, Common

1, 12, 27, Uncommon

1, 6, 10, Common

1, 6, 10, 27, Common

7, 10, 23, 27, Common

9, 15, Uncommon

1, 6, 10, 12, 27 Abundant
1, 7, 10, 23, Common
Maes

Maes

1, 7, 10,13,14, 19, Common
9, Uncommon

7, 22, Uncommon

7, 9, 23, 30, Uncommon
PSs ON lO 2 1S O27:
Adundant

23, Uncommon

SOR SHG 722023: 25.027,
32, Abundant

Le Om 12S BIS 23427532:
Abundant

7, 13, Uncommon

Sy He US le), I We os Ds).
Uncommon

5, 22, 23, 32, Common

13, Rare

9 DARI2NES OS wi L9)
23, 27, Abundant

9, 12, Uncommon

5, 6, 7, 13, 27, Common
LE6P 910 MI 2S IS; 19.322"
23, 30, Abundant

13, 22, Uncommon

7, Rare

13, Rare

19, 22, Uncommon

Maes

Maes

9, 32, Uncommon

9, Rare

Maes

Maes

9, 13, Uncommon

Sh 5,9. SS g22 5:23);
Common

Maes

9, 13, Uncommon

13, 15, 32, Uncommon
Maes

16

Terebra cerithina Lamarck, 1822
Terebra chlorata Lamarck, 1822
Terebra columellarisaris Hinds, 1844
Terebra cerithina Lamarck, 1822
Terebra crenulata (Linnaeus, 1758)
Terebra dimidiata (Linnaeus, 1758)
Terebra felina (Dillwyn, 1817)
Terebra funiculata Hinds, 1844
Terebra guttata Burch, 1965
Terebra hectica (Linnaeus, 1758)
Terebra laevigata Gray, 1834
Terebra lanceata (Linnaeus, 1767)
Terebra maculata (Linnaeus, 1758)

Terebra nebulosa (Sowerby, 1825)
Terebra pertussa (Born, 1778)
Terebra subulata (Linnaeus, 1767)

Terebra solida (Gmelin, 1791)
Terebra undulata Gray, 1834
Terenolla pygmaea (Hinds, 1844)

SUBCLASS OPISTHOBRANCHIA

PYRAMIDELLIDAE

Odostomia peasei Dautzenberg and Bouge, 1933
Odostomia 6 species

Otopleura mitralis (A. Adams, 1854)
Pyramidella acus (Gmelin, 1791)

Pyramidella dolabrata (Linnaeus, 1758)

(Listed as P. terebellum (Miiller, 1774) by Maes
Pyramidella sulcata (A. Adams, 1854)
Turbonilla 2 species

ACTEONIDAE

Pupa sulcata (Gmelin, 1791)

(Listed as Pupa glabra (Reeve, 1842) by Maes)
Pupa nitidula (Lamarck, 1816)

BULLINIDAE
Bullina sp.

HYDATINIDAE

Hydatina amplustre (Linnaeus, 1758)

Hydatina physis (Linnaeus, 1758)

Micromelo guamensis (Quoy and Gaimard, 1825)

BULLIDAE
Bulla vernicosa Gould, 1859

Maes

5, 15, Uncommon

15, 19, Uncommon

5, Rare

5, 12, 13, 23, 32, Common
5, 6, 12, 13, 19, Common
7, 9, 12, 22, 29, Common
9, 15, 32, Uncommon

19, Rare

Abbott

Maes

9, 13, 15, 19, Uncommon
5; 9, A215, LON22s De
Common

7, 15, 19, 22, Uncommon
15, Rare

Oo 12 15> 19.23:
Uncommon

19, Rare

15, 19, Uncommon

7, 13323, Rare

Maes

Maes

Maes

12, 13, 17, 23, Common
9, Rare

9, Uncommon
Maes

9, 17, 23, 29, 35 Uncommon

Maes

Maes

Maes
Maes
Maes

9. 12517;59; 27.30;
Uncommon

ATYIDAE

Atys cylindricus (Helbling, 1779)

Haminoea cymbalum (Quoy and Gaimard, 1835)
Phanerophthalmus cylindricus (Pease, 1861)

GASTROPTERIDAE
Gastropteron sp.

SCAPHANDRIDAE
Cylichna sp.

AGLAJIDAE
Philinopsis gardineri (Eliot, 1903)

APLYSIIDAE

Aplysia dactylomela Rang, 1828
Dolabella auricularia (Solander, 1786)
Dolabrifera dolabrifera (Rang, 1828)

PLEUROBRANCHIDAE
Bertheliina citrina (Riippell and Leuchkart, 1828)
Pleurobranchus cf. forskali Riippell and Leuckart, 1828

UMBRACULIDAE
Umbraculum sinicum (Gmelin, 1791)

ELYSIDAE
Elysia sp.

PLAKOBRANCHIDAE
Placobranchus ocellatus van Hasselt, 1824

CYLINDROBULLIDAE
Ascobulla sp.

OXY NOEIDAE
Lobiger sp.
Oxynoe delicatula (G. and H. Nevill, 1869)

VOLVATELLIDAE
Volvatella cincta (G. and H. Nevill, 1869)
Volvatella sp.

JULIIDAE
Julia borbonica (Deshayes, 1863)

HEXABRANCHIDAE
Hexabranchus sanguineus (Riippell and Leuckart, 1828)

AEGIRIDAE
Notodoris minor Eliot, 1904

9, 17, Uncommon
7, 10, Uncommon
12, Rare

13, Rare

Maes

5, 23,Rare

Maes
1, 12, Rare
1, 3, 12, 24, Rare

12, 27, Rare

Maes

1, 18, Common

1, 5, 12, 27, 35, Common

18, Common

Maes
Maes

Maes
Maes

Maes

5, 12, Rare

1, 29, Uncommon

17

18

Notodoris citrina Bergh, 1875

DORIDIDAE

Halgerda tessellata (Bergh, 1880)

Jorunna funebris (Kelaart, 1858)

Platydoris cruenta (Quoy and Gaimard, 1832)
Platydoris scabra (Cuvier, 1804)

Dorid sp.

DENDRODORIDIDAE
Dendrodoris nigra (Stimpson, 1855)

CHROMODORIDIDAE
Chromodoris elisabethina Bergh, 1877

PHYLLIDIIDAE

Phyllidia coelistis Bergh, 1905
Phyllidia elegans Bergh, 1869
Phyllidia cf. pustulosa Cuvier, 1804
Phyllidia sp. 1

Phyllidia sp. 2

Phyllidia sp. 3

TETHYDIDAE
cf. Melibe sp.

SUBCLASS PULMONATA
SIPHONARIIDAE

Siphonaria atra (Quoy and Gaimard, 1833)
Siphonaria cf. normalis Gould, 1848

ELLOBIIDAE

Auricula sp.

Melampus castaneus (Muhlfeld, 1818)
Melampus flavus (Gmelin, 1791)
Melampus fasciatus (Deshayes, 1830)
Pythia sp.

CLASS BIVALVIA

LIMOPSIDAE
Cosa sp.

ARCIDAE

Arca plicata (Dillwyn, 1817)

Arca ventricosa Lamarck, 1819
Barbatia decussata (Sowerby, 1833)
Barbatia tenella Reeve, 1844
Barbatia velata (Sowerby, 1843)

1, Rare

13, Rare

12, Rare

1, Uncommon
13, Uncommon
24, Rare

1, 10, Uncommon

4, 15, Rare

23, Uncommon
13, Uncommon
12, Common

12, 15, 26, Common

4, 25, Uncommon
13, 15, Uncommon

1, Rare

Maes
28, Common

2, Uncommon

1, 7, Common

2, 7, 21, Common
Maes

Maes

Maes

7, 13, Rare

12, Uncommon
Maes

22, Rare

7, 12, 22, 23, Uncommon

MYTILIDAE

Lithophaga nasuta (Philippi, 1846)
Lithophaga teres (Philippi, 1846)
Modiolus phillipinarum Hanley, 1843
(listed as Modiolus modulaides by Maes)
Modiolus sp.

PINNIDAE

Atrina vexillum (Born, 1778)

Pinna muricata Linnaeus, 1758
Streptopinna saccata ( Linnaeus, 1758)

PTERIIDAE

Electroma alacorvi (Dillwyn, 1817)
Pinctada margaritifera (Linnaeus, 1758)
Pteria penguin (Roding, 1798)

Pteria sp.

ISOGNOMONIDAE

Isognomon ephippium (Linnaeus, 1758)
Isognomon isognomum (Linnaeus, 1758)
TIsognomon legumen (Gmelin, 1791)
Isognomon perna (Linnaeus, 1767)

PECTINIDAE

Chlamys coruscans (Hinds, 1844)
Chlamys irregularis (Sowerby, 1842)
Chlamys lentiginosus (Reeve, 1853)
Chlamys squamosus (Gmelin, 1791)
Chlamys sp.

Decatopecten radula (Linnaeus, 1758)
Pecten pyxidatus Born, 1778
Semipallium tigris (Lamarck, 1819)

PLICATULIDAE
Plicatula chinensis Morch, 1853

SPONDYLIDAE

Spondylus lamarckii Chenu, 1845
Spondylus nicobaricus Schreibers, 1793
Spondylus sanguineus Dunker, 1852

LIMIDAE
Lima cf. annulata Lamarck, 1819
Lima fragilis (Gmelin, 1791)

Limaria orientalis (Adams and Reeve, 1850)

OSTREIDAE
Ostrea sp.

ike

Maes
16, Common
1, 2, 22, 27, Uncommon

12, 25, 35, Uncommon

Maes
12, 36, Uncommon
13, 19, 22, Uncommon

Maes
23, Rare
Maes
27, Rare

Maes

9, Rare

Maes

6, 7, 10, 13, Uncommon

Maes

7, 15, 22, 23, 32, Common
23, 25, Common

Maes

13, Rare

9, 29, 36, Uncommon
Maes

26, Rare

Maes

6, 9, 29, Uncommon
13, 16, 17, 19, Uncommon
13, Common

6, 13, 15, 26 29 Uncommon
9, 12, 36, Uncommon

7, 16, 19, 26, 30, 32,
Common

16, 27, 28, 30, Common

20

GR YPHAEIDAE

Hyotissa hyotis (Linnaeus, 1758) 9, Uncommon

CHAMIDAE

Chama aspersa Reeve, 1846 Maes

Chama imbricata Broderip, 1834 Maes

Chama cf. iostoma Conrad, 1837 6, 12, 15, 29, Uncommon

Chama lazarus Linnaeus, 1758 6, 26, 28, 29, Uncommon

Chama sp. 1, 9, 10, 16, Common

LUCINIDAE

Anodontia edentula (Linnaeus, 1758) 15, 31, Uncommon

Anodontia pila (Reeve, 1850) 21, 23, 30, Uncommon

Cavatidens sp. Maes

Ctena sp. 36, Rare

Codakia divergens (Philippi, 1850) Maes

Codakia punctata (Linnaeus, 1758) 5, 9, 10; 12; 19, 32535586;
Common

Glycodonta sp. 15, 19, Rare

Wallucina gordoni E. A. Smith 17, 30, Rare

ERYCINIDAE

Barrimysia incerta (Deshayes, 1863) Maes

Erycinacea sp. Maes

Fronsella cf. fugitaniana (Yokoyama, 1927) Maes

Hitia ovalis Dall, Bartsch and Rehder, 1938 Maes

Besobornia pacifica (Hedley, 1899) Maes

GALEOMMATIDAE

Scintillona sp. 5, Rare

CARDITIDAE

Cardita variegata (Bruguiére, 1792) 5, 7, 13, 15, 16, Common

DIPLODONTIDAE

Diplodonta sp. Maes

SPORTELLIDAE

cf. Anisodonta sp. Maes

CARDIIDAE

Acrosterigma alternatum (Sowerby, 1841) 29, 36, Uncommon

Acrosterlgma orbita (Broderip and Sowerby, 1833) 6,°7; 13, 15, 22, 2359258
Common

Corculum cardissa (Linnaeus, 1758) Maes

Fragum fragum (Linnaeus, 1758) 2. Se 9512235436

Fragum unedo (Linnaeus, 1758) 17, Rare

TRIDACNIDAE

Tridacna derasa (R6ding, 1798) Maes

Tridacna gigas (Linnaeus, 1758) 6 dead valves

Tridacna maxima (R6ding, 1798)

TELLINIDAE

Arcopagia palatum Iredale, 1929
Cadella semitorta (Sowerby, 1867)
Arcopagia scobinata (Linnaeus, 1758)

Macoma obliquilineata (Conrad, 1837)
Quadrans gargadia (Linnaeus, 1758)
Tellina chariessa Salisbury, 1934
Tellina clathrata (Deshayes, 1835)
Tellina crassiplicata (Sowerby, 1869)
Tellina crucigera Lamarck, 1818
Tellina dispar (Conrad, 1837)

Tellina linguafelis Linnaeus, 1758
Tellina obliquaria (Deshayes, 1854)
Tellina palatum (Iredale, 1929)

Tellina perna Splenger, 1798

Tellina pinguis (Hanley, 1845)

Tellina pulcherrima (Sowerby, 1867)
Tellina robusta (Hanley, 1844)

Tellina tenuilirata (Sowerby, 1867)
Tellina tongana (Quoy and Gaimard, 1835)
Tellina sp.

PSAMMOBIIDAE
Asaphis violaceans (Forskal, 1775)
Gari sp.

SEMELIDAE
Semele crenulata (Sowerby, 1853)
Thyella cf. lamellosa H. Adams, 1873

TRAPEZIIDAE
Trapezium oblongum (Linnaeus, 1758)

VENERIDAE

Katelysia cf. striata (Gmelin, 1791)
Lioconcha castrensis (Linnaeus, 1758)
Lioconcha hebraea (Lamarck, 1818)

Periglypta chemnitzii (Hanley, 1844)
Periglypta clathrata (Deshayes, 1853)
Periglypta crispata (Deshayes, 1859)
Periglypta puerpera (Linnaeus, 1771)
Pitar cf. affinis (Gmelin, 1791)

Pitar prora (Conrad, 1837)
Protothaca marica (Linnaeus, 1758)
Tapes cf. literatus (Linnaeus, 1758)
Ventricolaria toreuma (Gould, 1846)

21

1, 5, 6, 7, 10, 12, 19, 36,
Common

Maes

Maes

OL 2S SON 22423)
29, 35, Common

29, Rare

15, Rare

Maes

9, 30, 36, Common
Maes

23, Rare

2, 9, 17, 36, Uncommon
26, Rare

Maes

2, Common

12, 35, Rare

Maes

Maes

9, 13, 36, Uncommon
Maes

30, 32, Rare

17, Rare

35, Rare
17, Rare

17, 29, Rare
Maes

35, Rare

Maes

29, Rare

6, 9, 17, 22, 23, 26, 36,
Common

9, Rare

Maes

29, Rare

9, Rare

22, Uncommon

9, 17, 29, 35, Uncommon
Maes

9, 26, 29, Rare

25, Rare

22

CORBULIDAE

Corbula ustulata Reeve, 1844 Maes

Corbula sp. Maes

GASTROCHAENIDAE

Gastrochaena cuneiformis (Splengler, 1783) Maes
CLASS CEPHALOPODA

NAUTILIDAE

Nautilus pompilius Linnaeus, 1758 5, Rare

LOLIGINIDAE

Sepioteuthis lessoniana Lesson, 1830 Rees

OCTOPODIDAE

Octopus cyanea Gray, 1849 1, 12, Common

SEPIDAE

Sepia latimanus Quoy and Gaimard, 1832 9, Rare

ATOLL RESEARCH BULLETIN

NO. 411

CHAPTER 13

ECHINODERMS OF THE COCOS (KEELING) ISLANDS

BY

L.M. MARSH

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 13
ECHINODERMS OF THE COCOS
(KEELING) ISLANDS
BY
L.M. MARSH *

INTRODUCTION

The first extensive collection of echinoderms of the Cocos (Keeling) Islands was
made by C.A. Gibson-Hill who was Resident Medical Officer at the Cable Station on
Direction Island (Pulu Tikus) between December 1940 and November 1941. Prior to this
Gibson-Hill was Resident Medical Officer at Christmas Island from September 1938 to
December 1940, where he also made extensive natural history collections. His specimens
and field notes were deposited in the Raffles Museum, Singapore in 1941. One of
Gibson-Hill's aims was to be able to compare the fauna of the Cocos (Keeling) Islands
with that of Christmas Island. His other aim was to document the terrestrial and reef fauna
of the Cocos (Keeling) Islands as it stood at that time.

Unfortunately some of his notes and collections were lost during the wartime
occupation of Singapore. Among the marine invertebrates the specimens and field notes of
soft corals and anemones and most holothurians were lost but a copy of the field catalogue
of the holothurians remained (Gibson-Hill 1950a, b).

A.H. Clark (1950) described Gibson-Hill's echinoderm collection and included his
very useful field notes. Clark notes that specimens of the family Linckiidae
(Ophidiasteridae) were sent to Dr H. Engel of Amsterdam who was preparing a
monograph on this family for the Siboga expedition reports. Unfortunately neither the
“Linckiidae’ of the Siboga Expedition nor those of Cocos (Keeling) were published.

' The present collection numbers 82 species collected from 13 reef flat sites, nine
outer slope sites and 13 lagoon sites (Chapter 1, Fig. 2). It consists of 2 species of
Crinoidea, 15 Asteroidea, 17 Ophiuroidea, 14 Echinoidea and 34 Holothurioidea listed at
the end of this report. Most are widespread Indo- West Pacific species but there are several
westward extensions of range from Indonesia or Christmas Island and one south-eastward
extension from Sri Lanka. When added to the species recorded by Clark (1950) the total
known echinoderm fauna is now 89 species (4 crinoids, 17 asteroids, 17 ophiuroids, 17
echinoids and 34 holothurians).

Crinoidea

Clark (1950) noted that crinoids were rare on the accessible portions (reef
platforms) of the Cocos (Keeling) Islands. From the present survey I can confirm this and
note that they are also rare on the outer slopes. Crinoids were only collected at four sites,
three on the outer slopes and one in the northern part of the lagoon. Only two species were
represented, one of which was also recorded by A.H. Clark (1950). Colin (1977) notes
that in five weeks of collecting (fishes) in 1974 only a single small crinoid was found.

Western Australian Museum, Francis Street, Perth, Western Australia, 6000.

The crinoid fauna is even more depauperate than that of Christmas Island where
eight species were recorded (Marsh 1988). This compares with 38 species found at
Ashmore Reef (Marsh et al. in press) and 17 at the Rowley Shoals and Scott Reef (Marsh
1986) off north-western Australia and five from the isolated Western Indian Ocean atoll of
Aldabra (Sloan et al. 1979). Clark and Taylor (1971) did not record any crinoids from
Diego Garcia in the central Indian Ocean.

Coral reef crinoids have a short larval life (Mortensen 1938) and few species are
widely distributed in the Pacific and Indian Oceans. The species found at the Cocos
(Keeling) Islands are among those whose distribution extends from the Red Sea or
Western Indian Ocean to the western Pacific Ocean, apart from Stephanometra spinipinna
(recorded by A.H. Clark), which is known only from Indonesia and northern Australia.

Asteroidea

Clark (1950) recorded only four species of starfishes from Gibson-Hill's collection
but these did not include any members of the family Ophidiasteridae (Linckiidae), the
family generally best represented on coral reefs. Gibson-Hill collected 141 specimens of
this family, which were sent to Engel in Amsterdam who was currently working on a
collection of the same family from Indonesia. Unfortunately Engel did not complete either
project. I had been told that the Cocos specimens were still at the Natural History Museum
in Amsterdam but on a recent visit there the collection could not be found. Neither is it in
the University Museum collection in Singapore (formerly the Raffles Museum Collection).
There is therefore no historical record of Ophidiasterids from the Cocos (Keeling) Islands.

The present collection contains 15 species of Asteroidea and a further two were
recorded by Clark (1950). This is the same number as that recorded from the Rowley
Shoals (Marsh 1986), however only 11 species are in common. If the Rowley Shoals,
Scott Reef and Ashmore Reef are taken together, 15 species are in common with Cocos,
the same number as are in common between Cocos and Indonesia; however, Ashmore
Reef has a much richer fauna (28 species) including four Oreasterids, generally regarded as
‘continental’ species. Cocos has more asteroid species (17) than Christmas Island (13)
with only eight species in common, probably due in part to the more extensive reef flats at
Cocos. When compared with the isolated atoll of Aldabra, in the Western Indian Ocean
only seven of Aldabra's 19 species are in common with the Cocos Islands. A single
species, Culcita schmideliana, is recorded from Diego Garcia, in the central Indian Ocean
(Clark and Taylor 1971).

As at Christmas Island and Aldabra the small Linckia multifora, which reproduces
asexually by autotomy, is the most common asteroid and is found in all habitats at Cocos
(Keeling), from the outer slopes (6 sites) and reef flats (6 sites), where it is usually small,
to the lagoon where exceptionally large individuals (for the species) were found at site 35.

Most other species were found at only two or three sites but Ophidiaster granifer
was unexpectedly found on the outer slope, on reef flats and in the lagoon. This species is
usually confined to reef flats.

Nardoa tuberculata, usually found in the open on reef flats, was only found in
lagoon holes on coral rubble.

Several species were only found at one site and it is possible that other uncommon
species may be found in areas not sampled in this survey.

Acanthaster planci (crown-of-thorns starfish) was found on the outer slope, on a reef
flat and in the lagoon but was only seen at three sites. In a lagoon hole, south of Direction
Island about 20 individuals were observed but the greatest number (> 50) were seen on the
outer slope of Turk Reef (stn 15) at 10-45 m, where there was very little coral. The
following records indicate that large populations of A. planci have been present more than
once in the past. Clark (1950) quoted from Gibson-Hill's field notes stating that "A. planci
is very Conspicuous on the atoll but not very common. It occurs among coral rocks near the
low tide level over the centre and outer portions of the barrier. It is most plentiful on the
north and east coasts of the atoll". In 1971 a former resident of Cocos (Keeling) reported to
the Western Australian Museum that the reef off Ujong Tanjong, at the north end of West
Island, which had been a flourishing coral reef in 1963 was, by the end of 1969,
considerably damaged by A. planci predation and there was a very large population of
young specimens from about 100 to 320 mm in diameter. She did not find any near Pulu
Beras where Gibson-Hill had collected them in 1941. There is no record of any
observations on the outer slopes during this period. Ms Anne Waldron, who collected
echinoderms on the reef flats at a number of localities around West Island in January 1972,
did not find any A. planci, but noted that residents of West Island said they were present but
not in large numbers. During the course of an ichthyological survey of the Cocos reefs in
1974 Colin (1977) found extensive areas of dead coral on the outer slopes to a depth of 45
m which he attributed to Acanthaster predation. Large A. planci were abundant at depths of
15-30 m on the outer slopes, at a density of about 1 per 200-400 m2 but few small
individuals were seen. He also noted ‘islands’ of living coral on some of the buttresses of
the outer slope while adjacent areas were dead. It seems likely therefore that recurring high
levels of Acanthaster predation are responsible for the low level of coral cover on the outer
reef slopes.

Of great interest was the finding of several specimens of Tegulaster ceylanicus, on
the outer slope of the Home Island reef. This species was previously known only from Sn
Lanka and the Lakshadweep Islands, although a congener has been collected on the Great
Barrier Reef, Queensland. The two species differ slightly but, as both are described from
single specimens it is not possible to determine whether they are variations of the one
species.

The collections made on the Cocos (Keeling) reefs have extended the known
distribution of several species: Celerina heffernani for which the only previous Indian
Ocean locality was Christmas Island (Western Australian Museum coll.); it is also known
from Indonesia (Guille and Jangoux 1978) and the Western Pacific. Similarly, the range
of Neoferdina cumingi, is extended westward from Christmas Island; published records
are from the Central Pacific to Christmas Island (Jangoux 1973). Ophidiaster granifer has
not previously been recorded from the Indian Ocean although there is a specimen in the
Western Australian Museum collection from Madagascar; previous records are from the
western Pacific to Indonesia. Nardoa tuberculata is a common species on reef flats in
Indonesia and northern Australia but the only previous record from the Indian Ocean is
Andrews (1900) record from Christmas Island. However, this species was not found
there by the Western Australian Museum in 1987 and its occurrence may be sporadic.

Ophiuroidea

Clark (1950) recorded only eight species of Ophiuroids, most of these being large
species common on the reef flats. The present collection numbers 17 species (including all
the species recorded by Clark) a low number compared with Christmas Island (33) (Marsh
1988), the Rowley Shoals (28), Scott Reef (38) (Marsh 1986), Ashmore Reef (42) (Marsh
et al. in press), Aldabra (39) (Sloan et al. 1979) and Diego Garcia (10) (Clark and Taylor
1971).

The low number of species may to some extent reflect less collecting effort on the
outer slopes than at Christmas Island. However, extensive sampling of lagoon and reef
flat habitats including sand sifting, examination of weed mats and breaking up rocky
substrate yielded very few small species. Large ophiocomids were common and in some
cases abundant under boulders on the reef flats. Ophiocoma scolopendrina and
Ophiomastix annulosa were the most abundant, often with 4-5 of the latter under almost
every boulder. O. scolopendrina was found under boulders but also occupied crevices in
the reef from which it extended 3-4 arms which turn upside down to sweep the surface
scum on the incoming tide. Ophiocoma brevipes was moderately common among
seagrasses on sandy areas of the reef flats while O. erinaceus was found under boulders on
the mid and outer reef flats. O. anaglyptica was found on the mid and outer reef flats,
exposed to surf.

The only new record for the Indian Ocean is Ophiarachnella similis whose range is
extended westward from Indonesia. Fifteen of the 17 species are in common with
Christmas Island and all occur off north-western Australia and Indonesia. Eleven are in
common with Aldabra and six with Diego Garcia.

Echinoidea

A.H. Clark (1950) recorded 15 species of echinoid of which we failed to find
three, but added another two making a total of 17 species now known from the Cocos
(Keeling) Islands. The species are all widespread throughout the Indo-West Pacific
including north-western Australia. Twelve species are in common with Christmas Island
which apparently lacks all but one of the sand-dwelling Brissids and the Clypeasterid but
has several species on surf-swept rocky shores, not found at Cocos, giving it a total of 18
species. In comparison with north-western Australian reefs there are more species than at
the Rowley Shoals, where 14 are recorded although 22 have been found on the Rowley
Shoals and Scott Reef combined and 23 on Ashmore Reef. Fourteen of the species are in
common with Aldabra which has a total of 31 species (Sloan et al. 1979) and eight of
Diego Garcia's nine species are in common with Cocos (Keeling).

The brissids and clypeasterid were found only in the South Passage area and no
live specimens were taken apart from one freshly predated specimen of Metalia spatagus.
Extensive observation of the sand flats at the south end of the lagoon failed to find any
others. Clark (1950) reports that Gibson-Hill found brissids near passages on the eastern
side of the atoll but we were unable to examine this area.

Despite the extensive die-off of lagoon fauna in 1983 (see Woodroffe and Berry,
this volume) we found Parasalenia gratiosa to be abundant under dead coral slabs in lagoon

)

holes in the same habitat as that described by Gibson-Hill (1950). This was the only
habitat in which this species was found.

Holothurioidea

As noted in the introduction, Gibson-Hill's collection of holothurians from the
Cocos (Keeling) Islands was destroyed during World War II in Singapore.

The present collection is thus the only record of holothurians from the islands. The
Cocos (Keeling) Islands have a fairly rich fauna of holothurians, including most of the
species used for trepang (Béche-de-mer). Thirty four species were collected compared
with 16 at Christmas Island, 28 at Scott Reef/Rowley Shoals (Marsh 1986), 47 at
Ashmore Reef (Marsh et al. in press) and 35 species at Aldabra (Sloan et al. 1979).

Although the extensive sand flats in the lagoon might be regarded as suitable habitat
for holothurians, the majority (30 species) were found either on reef flats or in sandy areas
adjacent to reef flats, as at South Passage. Only four species were found on the outer
slopes. Ten species were found at lagoon sites but only one of these (Synaptula recta) was
not found in other habitats.

All but three of the holothurians are species widespread in the Indo-West Pacific,
the exceptions are Holothuria (Acanthotrapeza) coluber, H. (Metriatyla) aculeata and
Chiridota rigida the range of which is extended westward from Indonesia and north-
western Australia to the Cocos (Keeling) Islands.

The zonation of common reef flat species near the settlement on West Island is
shown in Figure 1.

Trepang (Béche-de-mer species)

Species of a large size with a thick body wall are the only ones suitable for
processing for food. At the Cocos (Keeling) Islands seven species of commercial value
have been found. No estimates of population size could be made in the time available but
indications are given of the sites where the commercial species were most common.

The most valuable species are the teat fish, Holothuria (Microthele) nobilis, and
other species of the subgenus. H. (Microthele) spp. are nowhere common but individuals
were seen or collected at five reef flat and two lagoon sites (List of echinoderms).
Thelenota ananas (prickly red fish) is another large, valuable species but this was only
found at one outer slope site. Other commercial species, their value depending to some
extent on size, are two species of Actinopyga (A. echinites and A. mauritiana), both
common to abundant on reef flats particularly at West Island; another commercial species
A. miliaris may occur at Cocos but was not found during the survey. Several less valuable
commercial species were also found: Bohadschia marmorata (chalky fish), Holothuria
(Metriatyla) scabra (sand fish) and H. (Halodeima) atra. B. marmorata and H. scabra were
found on the lagoon side of South Passage near Pulu Maria where the former was
moderately common. B. marmorata was also seen in the lagoon south of Direction Island.
H. atra is the most widespread of any species at Cocos and was common in all habitats but
it is of very little commercial value unless individuals are of a very large size; it is a highly
toxic species. Bohadschia argus (leopard or tiger fish), although of fairly large size, and
common on some of the sandy reef flats has a very low commercial value partly because of

6

the toxic cuvierian tubules ejected when the animal is touched. None of the other species
listed is believed to have any commercial value. Little is known of growth rates of
commercial species and any attempt at exploitation of the populations should be carefully
monitored and certain areas reserved from exploitation. Quantitative population studies
need to be made of the potentially commercial species before any fishing takes place and
on-going studies of recruitment and growth should be initiated.

It should be noted that all the commercial species have water soluble toxins in the
body wall and can only be eaten after correct preparation.

ACKNOWLEDGEMENTS

I am very grateful to Ms Anne Waldron who collected echinoderms for the Western
Australian Museum from various localities during a visit to West Island in 1972 and to Ms
Diana Applehof for her observations of Acanthaster at the Cocos (Keeling) Islands.

REFERENCES
Andrews, C.W. 1900. I Introductory note. In: Andrews, C.W., Smith, E.A., Bernard,
H.M., Kirkpatrick, R. and F.C. Chapman, On the Marine fauna of Chirstmas
Island (Indian Ocean). Proc. Zool. Soc. (Lond.) 1900: 115-117.

Clark, A.H. 1950. Echinoderms from the Cocos-Keeling Islands. Bull. Raffles Mus. 22:
53-67.

Clark, A.M. and Taylor, J.D. 1971. Echinoderms from Diego Garcia. Atoll Res. Bull.
149: 89-92.

Colin, P.L. 1977. The Reefs of Cocos-Keeling Atoll, eastern Indian Ocean. Proc. 3rd
Coral Reef Symp.,1: 63-68.

Gibson-Hill, C.A. 1950a. Introduction to papers on the fauna of the Cocos-Keeling
Islands. Bull. Raffles Mus. 22: 7-10.

Gibson-Hill, C.A. 1950b. A note on the Cocos-Keeling Islands. Bull. Raffles Mus. 22:
11-28.

Guille, A. and Jangoux, M. 1978. Astérides et Ophiurides littorales de la region
d'Amboine (Indonesie). Ann. Inst. Oceanogr., Paris 54: 47-74.

Jangoux, M. 1973. Le genre Neoferdina Livingstone. Revue zool. afr., 87: 775-794.
Marsh, L.M. 1986. Echinoderms, Part VI Faunal Surveys of the Rowley Shoals, Scott

Reef and Seringapatam Reef, north-western Australia, ed. P.F. Berry. Rec. West.
Aust. Mus. Suppl. No. 25: 63-74.

ii

Marsh, L.M. 1988. Echinoderms, Part VII of Survey of the Marine Fauna of Christmas
Island, Indian Ocean, ed. P.F. Berry. Unpubl. Report to Aust. National Parks and
Wildlife Service: 59-67.

Marsh, L.M. Vail, L.L., Hoggett, A.K. and Rowe, F.W.E. in press. Echinoderms, In
Survey of the Marine Fauna of Ashmore Reef, Australia, ed. P.F. Berry, Rec.
West. Aust. Mus.

Mortensen, T. 1938. Contributions to the study of the development of larval forms of
echinoderms IV. D. Kgl. Danske Vidensk. Selsk. Skrifter, Naturv. og Math.
Afd., 9, 7(3): 1-59.

Sloan, N.A., Clark, A.M. and Taylor, J.D. 1979. The echinoderms of Aldabra and their
habitats. Bull. Br. Mus. Nat. Hist. (Zool.) 37: 81-128.

LIST OF ECHINODERMS

KEY TO SYMBOLS:

A.H. Clark, 1950 (C) species by another name

Cc =
+ = Spec. from various sources in Western Australian Museum
eg6 = Western Australian Museum 1989 station numbers
V = Visual records
x - New records
# = Extension of distribution
Echinodermata Previous Collection
Records Station
Crinoidea
COMASTERIDAE
* Comaster multifidus (Miiller, 1841) - - 15,19
MARIAMETRIDAE
Stephanometra indica (Smith, 1876) C - -
S. spicata (Carpenter, 1881) C - 13°23
S. spinipinna (Hartlaub, 1890) C - -
Asteroidea
OREASTERIDAE
Culcita schmideliana (Retzius, 1805) (C) - TAI
OPHIDIASTERIDAE
#* Celerina heffernani (Livingstone, 1931) - . W235
* Cistina columbiae Gray, 1840 - - 25
* Dactylosaster cylindricus (Lamarck, 1816) - - P1224
“3 Fromia milleporella (Lamarck, 1816) - - 13,32
Linckia guildingi Gray, 1840 - - 4,19
3 L. laevigata (Linnaeus, 1758) - - 12,30V
* L. multifora (Lamarck, 1816) - . 33,4.6.7, 1012.13.14.
15319,30;32,35
#* Nardoa tuberculata Gray, 1840 - - 29,36
* N. galatheae (Liitken, 1864) - - 7,9,19,23
#* Neoferdina cumingi (Gray, 1840) - - 13922
#* Ophidiaster granifer (Liitken, 1872) - -

O. cribrarius Liitken, 1872

4,6,26,27,29,30
8

MITHRODIIDAE
Mithrodia clavigera (Lamarck, 1816) C - -
ASTERINIDAE
#* Tegulaster ceylanicus (Déderlein, 1889) - - 33
ACANTHASTERIDAE
Acanthaster planci (Linnaeus, 1758) C - 8,9V,15V
ECHINASTERIDAE
Echinaster luzonicus (Gray, 1840) C - -
Ophiuroidea
AMPHIURIDAE
3 Amphipholis squamata (Delle Chiaje, 1829) - - 24,35,37
OPHIACTIDAE
x Ophiactis savignyi (Miiller and Troschel, - - 9,12,20,28,32,35
1842)
OPHIOTRICHIDAE
Macrophiothrix longipeda (Lamarck, 1816) C - 1,12,13,14,24,32
OPHIOCOMIDAE
Ophiarthrum elegans Peters, 1851 C - 13
* Ophiocoma anaglyptica Ely, 1944 = + 1,12,14,24,27,30
a O. brevipes Peters, 1851 - + 1,5,10,14,24,27,30
O. dentata Miiller and Troschel, 1842 C + 1,10,12,13,14,20,
24,27
O. erinaceus Miiller and Troschel, 1842 C - 1,6,8,9,12,13V,20,
24,27,30,32
O. pica Miiller and Troschel, 1842 Cc - PSA 2732
z O. pusilla (Brock, 1888) - - 32
O. scolopendrina (Lamarck, 1816) C + 1,6,10,12,20,24,27
id O. schoenleini Miiller and Troschel, 1842 _ - - 9
5 Ophiocomella sexradia (Duncan, 1887) - + 3,20,24,35
Ophiomastix annulosa (Lamarck, 1816) C - 1,3V,12,20,24,27,30
OPHIONEREIDIDAE
co Ophionereis porrecta Lyman, 1860 - - 9
OPHIODERMATIDAE
#* Ophiarachnella similis (Koehler, 1905) - - 32
Ophiopeza spinosa (Ljungman, 1867) C - 14
Echinoidea
CIDARIDAE

Eucidaris metularia (Lamarck, 1816) C + UND S32

10

DIADEMATIDAE
Diadema savignyi Michelin, 1845
Echinothrix calamaris (Pallas, 1774)
E. diadema (Linnaeus, 1758)

TEMNOPLEURIDAE
Mespilia globulus (Linnaeus, 1758)

TOXOPNEUSTIDAE
Toxopneustes pileolus (Lamarck, 1816)
Tripneustes gratilla (Linnaeus, 1758)

PARASALENIIDAE
Parasalenia gratiosa A. Agassiz, 1863

ECHINOMETRIDAE
Echinometra mathaei (de Blainville, 1825)

* Echinostrephus molaris (de Blainville, 1825)

Heterocentrotus mammillatus (Linnaeus,

1758)
ECHINONEIDAE

Echinoneus cyclostomus Leske, 1778
CLYPEASTERIDAE

Clypeaster reticulatus (Linnaeus, 1758)
BRISSIDAE
* Brissus latecarinatus (Leske, 1778)

Metalia dicrana H.L. Clark, 1917
M. spatagus (Linnaeus, 1758)
M. sternalis (Lamarck, 1816)

Holothurioidea

HOLOTHURIIDAE
2 Actinopyga echinites (Jaeger, 1833)

* A. mauritiana (Quoy and Gaimard, 1833)

od Bohadschia argus Jaeger, 1833

ES B. graeffei (Semper, 1868)

= B. marmorata Jaeger, 1833

i Labidodemas semperianum Selenka, 1867

#* Holothuria (Acanthotrapeza) coluber
Semper 1868

- H. (Cystipus) rigida (Selenka, 1867)

* H. (Halodeima) atra Jaeger, 1833

* H. (H.) edulis Lesson, 1830
* H. (Lessonothuria) lineata Ludwig, 1875

QOe@

ee)

Q@ee

1,12,30V
30

1,12,24V,27V,30V

16,29

13V,9512V-50
16,17V,36

1,12,24
PH
4, 12, 19

153°V5 12:24 VE27NG
30V
1,3V,5V,10V,12V,
20V,24,27V,30V
5V,8V,12,30V

OV; 12
1

1,2,3V,5V,6V, 9V,
12V, 16, 18V, 19,

20V, 24V, 27V, 30V,

34V,36V,37V
9,16,19,30
3312

eS H. (L.) pardalis Selenka, 1867

* H. (Mertensiothuria) leucospilota (Brandt,
1835)

* H. (Metriatyla) scabra Jaeger, 1833

#* H. (M.) aculeata Semper, 1868

* H. (Microthele) nobilis (Selenka, 1867)

H. (M.) sp.
- H. (Platyperona) difficilis Semper, 1868
* H. (Semperothuria) cinerascens (Brandt,
1835)
cS H. (Stauropora) pervicax Selenka, 1867

a H. (Thymiosycia) hilla Lesson, 1830
* H. (T.) impatiens (Forskal, 1775)

STICHOPODIDAE
* Stichopus chloronotus Brandt, 1835

- S. horrens Selenka, 1867

* S. variegatus Semper, 1868
8 Thelenota ananas (Jaeger, 1833)
PHYLLOPHORIDAE

= Afrocucumis africana (Semper, 1868)

SYNAPTIDAE

i Euapta godeffroyi (Semper, 1868)

S Opheodesoma grisea (Semper, 1868)

“2 Synapta maculata (Chamisso and Eysenhardt
1821)

* Synaptula recta (Semper, 1868)

CHIRIDOTIDAE
#* Chiridota rigida Semper, 1868
2 Polycheira rufescens (Brandt, 1835)

11

1,30

10,12

12

12
1,12,24,27,36V
12,14,23
1,24,27

1, 20, 24, 27

3
8,12,23,30V
8,9,12

1,3V,5V,6V,9, 12,
27V, 30V,34V,36V
12V,16

5

19

1,3,6,14,24,27

12

H. (Halodeima) atra

(abundant)

Actinopyga mauritiana

Actinopyga echinites

Stichopus chloronotus (few)

H. (Microthele) nobilis (few)

H. cinerascens

H. cinerascens (abundant)

Zonation of holothurians on reef flat near settlement, West Island.

Figure 1.

ATOLL RESEARCH BULLETIN

NO. 412

CHAPTER 14

FISHES OF THE COCOS (KEELING) ISLANDS

BY

G.R. ALLEN AND W.F. SMITH-VANIZ

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 14
FISHES OF THE COCOS
(KEELING) ISLANDS
BY
G.R. ALLEN *
AND
W.F. SMITH-VANIZ **

ABSTRACT

Extensive fish collections were obtained at the Cocos (Keeling) Islands by the
Academy of Natural Sciences of Philadelphia in 1973 and the Western Australian Museum
in 1989. The combined collections document the occurrence of 533 species. For many
Indo-west Pacific fishes (about 85 species), Cocos represents their westernmost limit of
distribution. The faunal composition is typical of Indo-West Pacific coral reefs. Only 5
percent of the ichthyofauna consists of exclusively Indian Ocean species. The largest
families are as follows (number of species in parentheses): Labridae (54), Gobiidae (51),
Pomacentridae (38), Apogonidae (30), Serranidae (30), Acanthuridae (25), Muraenidae
(24), Chaetodontidae (23), Blenniidae (21), Scaridae (20), and Holocentridae (20).
Collectively these 11 families comprise 63 percent of the fauna. Little or no endemism is
present.

INTRODUCTION

The first fishes collected at the Cocos (Keeling) Islands were taken by the crew of
the, Beagle and subsequently reported by Jenyns (1842), who listed 10 species. Numerous
fish records were recorded in a series of papers by Pieter Bleeker (1854-1859) that were
published in Natuurkundig Tijdschrift voor Nederlandsch Indie. Fish specimens were sent
to Bleeker from the Cocos Islands by A. J. Anderson and G. Clunies-Ross. The Cocos
fauna was summarised by Bleeker (1859) as consisting of approximately 104 species.
Most of the fishes reported by Bleeker were eventually deposited in the Rijksmuseum in
Leiden.

The only other major ichthyological collection from Cocos was made by C. A.
Gibson-Hill, who visited the islands from January to November 1941. The fishes from
this expedition were reported by Marshall (1950) and included 119 new records, thus
raising the total species known from the island group to approximately 220. The Gibson-
Hill collections are presently housed at the British Museum (Natural History).

In 1973 an expedition from the Academy of Natural Sciences of Philadelphia
(ANSP) collected marine organisms at Cocos (Keeling) during February and March.
Team members, including ichthyologists Patrick L. Colin and William Smith-Vaniz,
collected fishes at 68 stations. A variety of collection methods were employed: rotenone

oe U.S. Fish and Wildlife Service, National Fisheries Research Center, 7920 N.W.
71st Street, Gainesville, Florida 32606, U.S.A.

2

(35 stations), explosives (17), quinaldine (14), angling (1), and spearing (31), usually as a
supplemental means of collection. This effort resulted in a large fish collection containing
6,780 specimens in 1,443 lots. Approximately 425 species were obtained.

A team of biologists from the Western Australian Museum and Australian Institute
of Marine Sciences conducted a faunal survey at Cocos (Keeling) during February 1989.
Fishes were collected mainly with rotenone (24 stations), supplemented by spear and
dipnets (1 station each). These efforts yielded a total of 1,814 specimens, including 465
lots and approximately 245 species. In addition, underwater observations were conducted
in which the name of each species seen was written on a waterproof sheet. These "spot"
identifications were based on the senior author's extensive experience in the Indo-Pacific
region. Only fishes whose identity was absolutely certain were recorded. This method
provided an additional 203 records, thus a total of 448 species was noted. The combined
ANSP-Western Australian Museum collections (and observations) include a total of 533
species.

Many of the species reported by Bleeker (1859) and Marshall (1950) are junior
synonyms or were based on misidentifications. It is beyond the scope of the present study
to determine the current status of most of the species they listed. However, we estimate
that only about 20 of their species represent additions not seen during the 1973 and 1989
visits. Therefore, the total known fish fauna of Cocos (Keeling) is approximately 550
species. The following species listed by Marshall (1950) almost certainly represent
additions to the Cocos ichthyofauna: Albulidae - Albula vulpes (Linnaeus); Exocoetidae -
Cheilopogon atrisignis (Jenkins) and C. cyanopterus (Valenciennes); Syngnathidae -
Hippocampus trimaculatus Leach; Ostraciidae - Lactoria cornuta (Linnaeus).

Some authors have questioned the providence of material Bleeker reported as
originating from Cocos (Keeling), including several new species he described from there.
Dawson (1982) cited the type locality of Micrognathus andersonii (Bleeker) as
"Novaselma, Kokos [Cocos] Is. [Indonesia]," and stated (p. 677) that Marshall's (1950)
listing of the species (as M. brevirostris) from Cocos-Keeling is based on a
"misidentification of the type-locality...". We do not agree with Dawson's assertion that
Bleeker's material did not originate from Cocos-Keeling. In the introduction of his first
paper Bleeker (1854a) gave the correct coordinates for "Kokos-eilanden" and referred to J.
C. Ross. (These islands were originally settled in 1827 by a Scottish sea captain named
John Clunies-Ross.) In a later paper Bleeker (1858) thanked both Dr A. J. Anderson
"geneesheer" [= physician] and J.G.C. Ross "tegeneewoordigen beheerder" [= present-
day administrator] of Cocos Island.

Through the kindness of Dr. Tyson Roberts we received a copy of a letter signed
by A. J. Anderson (original deposited in the RMNH archives), with the heading "Cocos -
July -1860," and addressed to Dr. Bleeker, concerning specimens of "trepang fish" [=
Carapidae] that had been sent to Batavia. In the same letter Anderson asked to have
Bleeker's European address (Bleeker returned to the Netherlands in September 1860) "in
the event of my attaining other interesting specimens." No additional correspondence in
the RMNH Bleeker files apparently exists concerning Cocos Is. (T. Roberts, in lit.).
Presumably much of Bleeker's correspondence while he was in Batavia did not survive.
In the absence of any evidence to the contrary, we conclude that all Bleeker's material
stated to have come from "Kokos-eilanden" refers to Cocos-Keeling. Although we did not
duplicate Bleeker's Cocos record of Micrognathus andersonii, it is a broadly distributed
Indo-Pacific species and we have no reason to doubt its occurrence there.

SPECIES COMPOSITION AND ZOOGEOGRAPHY

The ichthyofauna of Cocos (Keeling) consists primarily of species that are
associated with coral reefs. The largest families are summarised in Table 1. The eleven
most speciose groups (Labridae, Gobiidae, Pomacentridae, Apogonidae, Serranidae,
Acanthuridae, Muraenidae, Chaetodontidae, Blenniidae, Scaridae and Holocentridae)
account for 63 percent of the total fauna. These families are typically abundant throughout
the tropical Indo-Pacific region. Most of these 11 families contain fishes that are diurnally
active which either dwell on or near the reef surface, or forage on plankton a short distance
above it. Exceptions are the nocturnal apogonids and holocentrids, and the crevice-
dwelling morays (muraenidae).

The fish fauna is similar to that of Christmas Island, the nearest land mass, lying
about 850 km to the northeast. Allen and Steene (1987) recorded 575 species from
Christmas, of which about 350 species also occur at the Cocos group. The approximately
175 species that are present at Cocos, but lacking at Christmas are primarily inhabitants of
the lagoon, a habitat that does not occur at Christmas Island. It is more difficult to explain
the occurrence of approximately 210 species of Christmas fishes that are apparently absent
from Cocos (Keeling). Two of the most notable disparities are shown by the Serranidae
and Blenniidae in which 25 and 14 species, respectively, and 7 genera in each family were
found only at Christmas. Perhaps this anomaly can be at least partly be explained by the
greater isolation of Cocos (Christmas Island is only about 290 km from Java).

Compared to other oceanic atolls the Cocos Group appears to have a relatively
impoverished fish fauna. For example Randall and Randall (1988) and Winterbottom et al.
(1989) recorded approximately 800 and 700 species, respectively, for the Marshall Islands
in the central Pacific and Chagos Archipelago (incorporating several atolls) in the western
Indian Ocean. There are probably several reasons for the diminished Cocos fauna
including (1) its small physical size; (2) relative isolation and lack of surrounding "island
stepping-stones;" and (3) lesser collecting activity. In addition, the extensive coral die-
back at Cocos (Colin, 1977) may be responsible for the exclusion of some species.

Although we believe the ichthyofauna of Cocos has been reasonably well sampled
(except for epipelagic fishes), we certainly did not collect all of the species of shorefishes
that occur there. That the fauna may not be as well sampled as we would like to believe is
suggested by the fact that a number of shallow-water, cryptic species were taken at only
one of our combined 59 rotenone stations. Scorpaenids are cryptic bottom dwellers
(except Pterois spp.) yet, inexplicably, only 2 of 16 species we report from Cocos were
collected or observed by both museum expeditions.

A zoogeographic analysis of the Cocos fauna is presented in Table 2. The majority
of fishes have distributions that cover relatively wide areas in the Indo-Pacific region.
There is a much greater affinity to the Western Pacific than to the Indian Ocean region.
Indeed, only about 5.1 percent of the species are Indian Ocean forms. There is no
endemism in the Cocos fish fauna, although one anglefish, Centropyge joculator, is
known only from Cocos and Christmas Island and an undescribed goby of the genus
Trimma may have the same distribution. The Indian Ocean coasts of Java and Sumatra are
poorly sampled, however, and it is likely that one or both species will be found there
eventually. Scorpaenoides keelingensis Marshall which, as the name suggests, Marshall
(1950) believed to be endemic to the Cocos group is almost certainly a junior synonym of
Scorpaenoides kelloggi (Jenkins) (W. N. Eschmeyer, pers. comm.). Nearly all of the reef

4

fishes found at Cocos are characterised by a pelagic larval stage of up to several weeks
duration. Hence, the widespread nature of the individual species distributions.

ACKNOWLEDGMENTS

We thank the following individuals for asisting us in obtaining the correct scientific
names for species in this checklist: Eugenia B. Béhlke, Bruce B. Collette, William N.
Eschmeyer, Ross W. Feltes, Thomas H. Fraser, Douglass F. Hoese, W. Holleman,
Theodore W. Pietsch, John E. Randall, Jeffrey T. Williams, Richard W. Winterbottom,
Thosaporn Wongratana, and David J. Woodland. Curatorial assistance at the Academy of
Natural Sciences was provided by Eugenia B. Bohlke and William G. Saul, and at the
Western Australian Museum by Kevin Smith.

REFERENCES

Allen, G.R. and Steen, R.C. 1987. Fishes of Christmas Island, Indian Ocean. Christmas
Island Natural History Association, 197 pp.

Baldwin, C. and G.D. Johnson. 1993. Phylogeny of the Epinephelinae (Teleostei:
Serranidae). Bull. Mar. Sci. 52 (1): 240-283.

Bleeker, P. 1854a. Bijdrage tot de kennis der ichthyologischefauna van de Kokos-
eilanden. Nat. Tijdsch. Ned. Ind. 7: 37-48.

Bleeker, P. 1854b. Over eenige nieuwe van de Kokos-eilanden. Nat. Tijdsch. Ned. Ind.
7: 353-358.

Bleeker, P. 1855a. Derde Bijdrage tot de kennis der ichyologische fauna van de Kokos-
eilanden. Nat. Tijdsch. Ned. Ind. 8: 169-180.

Bleeker, P. 1855b. Vierde Bijdrage tot de kennis der ichthyologische fauna van de Kokos-
eilanden. Nat. Tijdsch. Ned. Ind. 8: 445-460.

Bleeker, P. 1858. Vijfde bijdrage tot de kennis der ichthyologische fauna van de Kokos-
eilanden. Nat. Tijdschr. Ned. Ind. 15: 457-468.

Bleeker, P. 1859. Tiental vischsoorten van de Kokos-eilanden verzameled door Dr
Anderson. Nat. Tijdschr. Ned. Ind. 20: 142-143.

Burgess, W.E. 1973. Salts from the seven seas. Tropical Fish Hobbyist 21 [May]: 37-38,
40-41.

Colin, P.L. 1977. The reefs of Cocos-Keeling Atoll, eastern Indian Ocean. Proc. 3rd
International Coral Reef Symposium, Univ. of Miami, Miami, Florida: 63-68.

Dawson, C.E. 1982. Review of the genus Micrognathus Duncker (Pisces: Syngnathidae),
with description of M. natans, n. sp. Proc. Biol. Soc. Wash. 95 (4):657-687.

Jenyns, L. 1842. Fish Jn The Zoology of the voyage of H.M.S. Beagle, under the
command of Capt. Fitzroy R.M. during the years 1832 to 1836. Part IV. London.
172 pp.

Marshall, N.B. 1950. Fishes from the Cocos-Keeling Islands. Bull. Raffles Mus. 22:
166-205.

Randall, J.E. 1991. Revision of Indo-Pacific groupers (Perciforms: Serranidae:
Epinephelinae), with descriptions of five new species. Indo-Pacific Fishes 20: 1-
332}

Randall, J.E. and Hoese, D.F. 1985. Revision of the Indo-Pacific dartfishes, genus
Ptereleotris (Perciformes: Gobioidei). Indo-Pacific Fishes, No. 7: 1-36.

Randall, J.E. and Randall, H.A. 1987. Annotated checklist of the fishes of Enewetak Atoll
and other Marshall Islands. Jn The Natural History of Enewetak Atoll. Vol. 2
(Devaney, D.M., Reese, E.S., Burch, B.L. and Helfrich, P., editors) U.S.
Dept.of Eneregy Office of Scientific and Technical Information.

Schultz, E.T. 1986. Pterois volitans and Pterois miles: Two valid species. Copeia 1986
(3): 686-690.

Winterbottom, R.W., Emery, A.R. and Holm, E. 1989. An annotated checklist of the
fishes of the Chagos Archipelago Central Indian Ocean. Life Sciences Contrib. 145
Royal Ontario Mus.: 1-226.

CHECKLIST OF COCOS (KEELING) FISHES

The following list includes fishes that were either collected or observed during the
1973 and 1989 surveys. Asterisk or numbers preceding species names indicate the
following distributional data: * = also known from Christmas Island; 1 = widespread Indo-
Pacific or Indo-west Pacific; 2 = West Pacific species that reach their western distributional
limit at Cocos (Keeling); 3 = Indian Ocean species (may include western extremity of west
Pacific); 4 = Circumtropical or cosmopolitan; 5 = uncertain extralimital distribution; Square
brackets appearing after each species citation indicate that specimens are deposited at the
Academy of Natural Sciences, Philadelphia [P], the Western Australian Museum [W], or
were observed only [O].

Sphyrnidae - Hammerhead sharks

4 *Sphyrna lewini (Grffith and Smith, 1834) [O]
Carcharhinidae - Requiem sharks

1 *Carcharhinus amblyrhynchos (Bleeker, 1856) [P]

1 *C. melanopterus (Quoy and Gaimard, 1824) [O]

4 *Galeocerdo cuvier (Peron and LeSueur, 1822) [O]

1 *Triaenodon obesus (Riippell, 1837) [O]
Mobulidae - Manta rays

4 *Manta birostris (Donndorff, 1798) [O]
Moringuidae - Worm eels

1 Moringua ferruginea Bliss, 1883 [W]

1 *M. javanica (Kaup, 1856) [W]

1 *M. microchir Bleeker, 1853 [P,W]
Chlopsidae - False morays

3 *Kaupichthys n. sp. [K. Tighe, pers. comm., 1993] [P,W]
Muraenidae - Moray eels

2 Anarchias cantonensis (Schultz, 1943) [P]

1 *A. seychellensis Smith, 1962 [P,W]

1 *Echidna nebulosa (Ahl, 1789) [P]

1 *E. polyzona (Richardson, 1844) [P]

2 *Enchelycore bayeri (Schultz, 1953) [W]

1 *E. pardalis (Temminck and Schlegel, 1842) [P,W]

2 *Enchelynassa canina (Quoy and Gaimard, 1824) [P]

1 *Gymnothorax enigmaticus McCosker and Randall, 1982

1 *G. buroensis (Bleeker, 1857) [P]

1 G. fimbriatus (Bennett, 1831) [P,W]

1 *G. flavimarginatus (Riippell, 1830) [P,W]

1 *G. javanicus (Bleeker, 1859) [O]

1 *G. margaritophorus Bleeker, 1865 [P,W]

1 *G. melatremus Schultz, 1953 [P]

1 G. monochrous Bleeker, 1864 [P]

1 *G. monoStigma (Regan, 1909) [P]

1 *G. rueppelliae (McClelland, 1845) [P,W]

1 G. undulatus (Lacepéde, 1803) [P,W]

1 *G. zonipectus Seale, 1906 [P,W]

1 *Siderea picta (Ahl, 1789)

1 *S. thrysoidea (Richardson, 1845)

1 *Uropterygius concolor (Riippell, 1838)
1 *U. marmoratus (Lacepéde, 1803)

1 *U. xanthopterus Bleeker, 1859

Ophichthidae - Snake eels

2 Callechelys catostomus (Bloch and Schneider, 1801)

1 *Leiuranus semicinctus (Lay and Bennett, 1839)
2 Muraenichthys brevis Ginther, 1876

1 *M. laticaudata (Ogilby, 1897)

1 M. macropterus Bleeker, 1857

2 Schultzidia johnstonensis (Schultz and Woods, 1949)

Congidae - Conger eels
1 *Conger cinereus Riippell, 1830

3 Gorgasia maculata Klausewitz and Eibl-Eibesfeldt, 1959
1 *Heteroconger hassi (Klausewitz and Eibl-Eibesfeldt, 1959)

Clupeidae - Herrings
1 Sardinella melanura (Cuvier, 1829)
1 Spratelloides delicatulus (Bennett, 1831)

Synodontidae - Lizardfishes
1 *Saurida gracilis (Quoy and Gaimard, 1824)
1 *Synodus englemani Schultz, 1953

Chanidae - Milkfishes
1 Chanos chanos (Forsskal, 1775)

Ophidiidae - Cusk-eels
1 *Brotula multibarbata Temminck and Schlegel, 1846

Bythitidae - Viviparous brotulas
1 *Brosmophyciops pautzkei Schultz, 1960
5 *Ogilbia sp.

Antennariidae - Anglerfishes
1 *Antennarius coccineus (Lesson, 1831)
1 A. dorehensis Bleeker, 1859

Notocheiridae [=Isonidae] - Surf spites
3 Iso natalensis Regan, 1919

Hemirhamphidae - Halfbeaks
1 Hyporhamphus affinis (Giinther, 1866)
1 H. dussumieri (Valenciennes, 1847)
2 Zenarchopterus dispar (Valenciennes, 1847)

Belonidae - Needlefishes
1 Platybelone argalus platyura (Bennett, 1831)
1 *Tylosurus crocodilus (Peron and LeSueur, 1821)

8

Holocentridae - Squirrelfishes

1 Myripristis adusta Bleeker, 1853 [P,W]

1 *M. berndti Jordan and Evermann, 1903 [W]

1 M. chryseres Jordan and Evermann, 1903 [P]

1 *M. kuntee Cuvier, 1831 [W]

1 *M. murdjan (ForsskAl, 1775) [P]

1 *M. parvidens Cuvier, 1829 [P]

1 M. pralinia Cuvier, 1829 [W]

1 *M. vittata Valenciennes, 1831 [Ww]

1 M. violaceus Bleeker, 1851 [O]

1 Neoniphon argenteus (Valenciennes, 1831) [P,W]

1 N. opercularis (Valenciennes, 1831) [O]

1 N.sammara (Forsskal, 1775) [P,W]

1 *Plectrypops lima (Valenciennes, 1831) [P,W]

1 *Sargocentron diadema (Lacepéde, 1801) [P,W]

3 *S. lepros (Allen and Cross, 1983) [W]

1 *S. microstoma (Giinther, 1859) [W]

1 *S. caudimaculatum (Riippell, 1838) [W]

1 *S. punctatissimum (Cuvier, 1829) [P]

1 *S. tiere (Cuvier, 1829) [P]

1_ S. spiniferum (Forsskal, 1775) [P]
Aulostomidae - Trumpetfishes

1 *Aulostromus chinensis (Linnaeus, 1766) [P]
Fistulariidae - Cornetfishes

1 *Fistularia commersonii Riippell, 1838 [O]
Syngnathidae - Pipefishes

1 *Choeroichthys sculptus (Giinther, 1870) [P,W]

1 Corythoichthys flavofasciatus (Riippell, 1838) [P,W]

1 *Cosmocampus banneri (Herald and Randall, 1972) [W]

1 *Doryrhamphus excisus excisus Kaup, 1856 [P,W]

2 *Micrognathus brevirostris pygmaeus Fritzsche, 1981 [W]

1 Phoxocampus belcheri (Kaup, 1856) [W]
Scorpaenidae - Scorpionfishes

1 Parascorpaena mossambica (Peters, 1855) [P]

1 *Pterois antennata (Bloch, 1787) [W]

1 *P. radiata Cuvier, 1829 [P,W]

2 *P. volitans (Linnaeus, 1758)
[We follow Schultz (1986) in recognizing Pierois miles Bennett as an Indian
Ocean species distinct from the Pacific P. volitans.]

1 *Scorpaenodes albaiensis (Evermann and Seale, 1907) [P]
1 *S. guamensis (Quoy and Gaimard, 1824) [P]
1 *S. hirsutus (Smith, 1957) [P,W]
1 S. kelloggi (Jenkins, 1903) [P]
1_ S. littoralis (Tanaka, 1917) [P]
1 S. minor (Smith, 1958) [P]
1 *§. parvipinnis (Garrett, 1863) [P]
1 *Scorpaenopsis diabolus (Cuvier, 1829) [O]
1 *Sebastapistes cyanostigma (Bleeker, 1856) [P]

1 *S. strongia (Cuvier, 1829) [P,W]

5 Sebastapistes sp. [P]
1 *Synanceia verrucosa Bloch and Schneider, 1801 [P]

Platycephalidae - Flatheads

1 *Thysanophrys otaitensis (Cuvier, 1829) [P]
Caracanthidae - Orbicular velvetfishes

2 *Caracanthus maculatus (Gray, 1831) [P]

1 *C. unipinna (Gray, 1831) [P]

Serranidae - Sea basses
[We follow Baldwin and Johnson (1993) in including the Grammistidae
and Pseudogrammidae in this family.]

1 *Anyperodon leucogrammicus (Valenciennes, 1828) [P]}
1 *Cephalopholis argus Bloch and Schneider, 1801 [P,W]
1 *C. leopardus (Lacepéde, 1801) [P,W]
1 *C. polleni (Bleeker, 1868) [P]
1 *C. spiloparaea (Valenciennes, 1828) [P,W]
1 *C. urodeta (Valenciennes, 1828) [P,W]

[Randall (1991 p.70) noted that this species consists of two allopatric color
forms, the western Indian Ocean C. nigripinnis (Valenciennes) and the nominal
Pacific form; he regarded them as conspecific because Christmas Is. specimens
have somewhat intermediate color patterns. The color pattern of Cocos specimens
agrees well with the Pacific form.]

3 Epinephelus faveatus (valenciennes, 1828) [W]
1 E. fuscoguttatus (Forsskal, 1775) [O]
1 *E. hexagonatus (Bloch and Schneider, 1801) [W]
2 E. maculatus Bloch, 1790 [O}
1 *E. merra Bloch, 1793 [P,W]
1 E. macrospilus (Bleeker, 1855) [P]

[Randall (1991 p.187) noted that this species consists of two allopatric color
forms, the western Indian Ocean E. cylindricus Giinther said to differ from

the Pacific and eastern Indian Ocean E. macrospilos by larger and more closely
spaced spots. Because only spot size appeared to distinguish the two forms
they were considered to be conspecific. ]

1 E.microdon (Bleeker, 1856) [P]
1 *E. spilotoceps Schultz, 1953 [P,W]
1 *E. tauvina (Forsskal, 1775) [P,W]
1 *Gracila albomarginata (Fowler and Bean, 1930) [P]
1 *Grammistes sexlineatus (Thunberg, 1792) [P,W]
5 *Luzonichthys sp. [O]
2 *Plectranthias nanus Randall, 1980 [P,W]
1 Plectropomus areolatus Riippell, 1828 [P]
2 P. leopardus (Lacepéde, 1802) [P]
2 P. maculatus (Bloch, 1790) [P]
1 Pseudanthias cooperi (Regan, 1902) [P,W]
3 *P. evansi Smith, 1954 [P,W]
2 *P. smithvanizi (Randall and Lubbock, 1981) [P,W]
5 Pseudanthias sp. [P]

[Winterbottom et al. (1989) give color photographs (plates IVE,F) of this species,
which they report as Anthias sp. from the Chagos Archipelago. ]

2 Pseudogramma bilinearis (Schultz, 1943) [P]

1 *P. polyacantha (Bleeker, 1856) [P,W]

10

2 *Suttonia lineata Gosline, 1960
1 *Variola louti (Forsskal, 1775)

Pseudochromidae - Dottybacks
1 Pseudoplesiops n. sp.
2 P.multisquamatus Allen, 1987

Plesiopidae - Longfins
1 *Plesiops coeruleolineatus Riippell, 1835
2 *P. corallicola Bleeker, 1853

Kuhliidae - Flagtails
1 *Kuhlia mugil (Bloch and Schneider, 1801)

Priacanthidae - Bigeyes
1 *Heteropriacanthus cruentatus (Lacepéde, 1801)

Apogonidae - Cardinalfishes
1 *Apogon angustatus (Smith and Radcliffe, 1911)
2 A. bandanensis Bleeker, 1854
. crassiceps Garman, 1903
. cyanosoma Bleeker, 1853
dispar Fraser and Randall, 1976
. evermanni Jordan and Snyder, 1904
. exostigma (Jordan and Starks, 1906)
guamensis Valenciennes, 1832
. kallopterus Bleeker, 1856
. leptacanthus Bleeker, 1856
melas Bleeker, 1848
. novemfasciatus Cuvier, 1828
. taeniophorus Regan, 1908
. taeniopterus (Bennett, 1835)
*Apogonichthys ocellatus (Weber, 1913)
1 A. perdix Bleeker, 1854
1 *Cercamia eremia (Allen, 1987)
1 Cheilodipterus lineatus Cuvier, 1828
2 *C. macrodon (Lacepéde, 1802)
1 *C. quinquelineatus Cuvier, 1828
1 *Fowleria aurita (Valenciennes, 1831)
1 F. isostigma (Jordan and Seale, 1906)
1 F. variegata (Valenciennes, 1832)
2 Gymnapogon urospilotus Lachner, 1953
1 Neamia octospina Smith and Radcliffe, 1912
1 Pseudamia gelatinosa Smith, 1955
2 *Pseudamiops gracilicauda (Lachner, 1953)
1 Rhabdamia gracilis (Bleeker, 1856)
2 Siphamia majimae Matsubara and Iwai, 1959
2 Sphaeramia nematoptera (Bleeker, 1856)

*

*

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1
1
2
1
1
1
1
1
2
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1
1

Malacanthidae - Tilefishes
1 *Malacanthus brevirostris Guichenot, 1848
1 *M. latovittatus (Lacepéde, 1801)

Carangidae - Trevallies
1 *Carangoides ferdau (Forssk§l, 1775)
1 *C. orthogrammus (Jordan and Gilbert, 1882)
1 *Caranx ignobilis (Forsskal, 1775)
4 *C. lugubris Poey, 1860
1 *C. melampygus Cuvier, 1833
1 *C. sexfasciatus Quoy and Gaimard, 1825
4 *Decapterus macarellus (Cuvier, 1833)
4 *Elagatis bipinnulatus (Quoy and Gaimard, 1825)
1 *Scomberoides lysan (Forsskal, 1775)
1 *Trachinotus bailloni (Lacepéde, 1801)
1 T. blochii (Lacepéde, 1801)

Lutjanidae - Snappers
1 *Aphareus furca (Lacepéde, 1802)
1 *Aprion virescens Valenciennes, 1830
1 *Lutjanus bohar (Forsskal, 1775)
1 *L. fulvus (Bloch and Schneider, 1801)
1 *L. gibbus (Forsskal, 1775)
1 *L. kasmira (Forsskal, 1775)
1 L. monostigma (Cuvier, 1828)
1 *Macolor niger (Forsskal, 1775)

Caesionidae - Fusiliers
1 *Caesio teres Seale, 1906
1 C. xanthonota Bleeker, 1853
1 *Pterocaesio lativattata Carpenter, 1987
1 *P. tile (Cuvier, 1830)

Haemulidae - Sweetlips
2 Plectorhinchus chaetodontoides Lacepéde, 1800

Lethrinidae - Emperors
1 *Gnathodentex aurolineatus (Lacepéde, 1802)
Gymnocranius grandoculis (Valenciennes, 1830)
Lethrinus atkinsoni Seale, 1909
L. harak (Forsskal, 1775)
L. hypselopterus Bleeker, 1873
L. lentjan (Lacepéde, 1802)
L. microdon Valenciennes, 1830
L. obsoletus (Forsskal, 1775)
L. xanthochilus Klunzinger, 1870
*Monotaxis grandoculis (Forsskal, 1775)

pee ee LD

Nemipteridae - Threadfin breams
2 Scolopsis lineatus (Quoy and Gaimard, 1824)

Gerreidae - Mojarras
1 Gerres acinaces Bleeker, 1854

Mullidae - Goatfishes
1 *Mulloides flavolineatus (Lacepéde, 1801)
1 *M. vanicolensis (Valenciennes, 1831)

ql

12

1 Parupeneus barberinus (Lacepéde, 1801)

1 *P. bifasciatus (Lacepéde, 1801)

1 *P. cyclostomus (Lacepéde, 1801)

1 *P. macronemus (Lacepéde, 1801)

2 *P. multifasciatus (Quoy and Gaimard, 1824)
1 *P. pleurostigma (Bennett, 1831)

Kyphosidae - Rudderfishes
1 *Kyphosus cinerascens (Forssk§l, 1775)
1 K. vaigiensis (Quoy and Gaimard, 1825)

Pempheridae - Sweepers
1 *Pempheris oualensis Cuvier, 1831

Ephippidae - Batfishes
1 *Platax orbicularis (Forsskal, 1775)
1 *P. teira (Forsskal, 1775)

Chaetodontidae - Butterflyfishes
1 *Chaetodon auriga (Forsskal, 1775)
1 C. bennetti Cuvier, 1831
1 *C. citrinellus Cuvier, 1831
1 C. ephippium Cuvier, 1831
3 *C. guttatissimus Bennett, 1831
1 *C. kleinii Bloch, 1790
1 *C. lineolatus Cuvier, 1830
1 *C. lunula (Lacepéde, 1803)
3 *C. madagaskariensis Ahl, 1923
1 *C. melannotus Bloch and Schneider, 1801
1 *C. meyeri Bloch and Schneider, 1801
3 *C. mitratus Giinther, 1860
1 *C. ornatissimus Cuvier, 1831
1 *C. semeion Bleeker, 1855
1 *C. trifascialis Quoy and Gaimard, 1824
1 *C. trifasciatus Park, 1797
2 C. ulietensis Cuvier, 1831
1 *C. unimaculatus Bloch, 1787
1 *C. vagabundus Linnaeus, 1758
1 *Forcipiger flavissimus Jordan and McGregor, 1898
2 *Hemitaurichthys polylepis (Bleeker, 1857)
1 Heniochus chrysostomus Cuvier, 1831
1 *H. monoceros Cuvier, 1831

Pomacanthidae - Angelfishes
1 *Apolemichthys trimaculatus (Lacepéde, 1831)
2 Centropyge colini Smith-Vaniz and Randall, 1974
1 *C. flavissimus (Cuvier, 1831)
3 *C. joculator Smith-Vaniz and Randall, 1974
2 C. multifasciatus (Smith and Radcliffe, 1911)
2 Genicanthus bellus Randall, 1975
1 *Pomacanthus imperator (Bloch, 1787)

Pomacentridae - Damselfishes

1 *Abudefduf notatus (Day, 1869)

1 *A. septemfasciatus (Cuvier, 1830)

1 *A. sordidus (Forsskal, 1775)

1 *A. vaigiensis (Quoy and Gaimard, 1825)
2 *Amblyglyphidodon aureus (Cuvier, 1830)
2 A. curacao (Bloch, 1787)

1 *Amphiprion clarkii (Bennett, 1830)

2 *A. perideraion Bleeker, 1855

2 *Chromis alpha Randall, 1988

2 *C. amboinensis (Bleeker, 1873)

2 *C. atripes Fowler and Bean, 1928

2 *C. caudalis Randall, 1988

2 *C. delta Randall, 1988

3 *C. dimidiata (Klunzinger, 1871)

1 *C. elerae Fowler and Bean, 1928

1 *C. lepidolepis Bleeker, 1877

2 *C. margaritifer Fowler, 1946

3 *C. nigrura Smith, 1960

3 *C. opercularis (Giinther, 1867)

1 *C. ternatensis (Bleeker, 1856)

1 C. viridis (Cuvier, 1830)

2 *C. xanthura (Bleeker, 1854)

1 Chrysiptera biocellata (Quoy and Gaimard, 1824)
1 *C. glauca (Cuvier, 1830)

1 Dascyllus aruanus (Linnaeus, 1758)

2 *D. reticulatus (Richardson, 1846)

1 *D. trimaculatus (Riippell, 1828)

1 *Plectroglyphidodon dickii (Liénard, 1839)
1 *P. imparipennis (Vallant and Sauvage, 1875)
1 *P. johnstonianus Fowler and Ball, 1924

1 *P. lacrymatus (Quoy and Gaimard, 1825)
1 *P. leucozonus (Bleeker, 1859)

1 *P. phoenixensis (Schultz, 1943)

1 Pomacentrus pavo (Bloch, 1787)

1 *Stegastes albifasciatus (Schlegel and Miiller, 1839)
1 *S. fasciolatus (Ogilby, 1889)

1_ S. lividus (Bloch and Schneider, 1801)

1 S. nigricans (Lacepéde, 1802)

Cirrhitidae - Hawkfishes
1 *Amblycirrhitus bimacula (Jenkins, 1903)
2 Cirrhitichthys aprinus (Cuvier, 1829)
1 *C. oxycephalus (Bleeker, 1855)
1 *Cirrhitus pinnulatus (Schneider, 1801)
1 *Oxycirrhites typus Bleeker, 1857
1 *Paracirrhites arcatus (Cuvier, 1829)
1 *P. forsteri (Schneider, 1801)
2 *P. hemistictus (Giinther, 1874)

Musgilidae - Mullets
1 *Crenimugil crenilabis (Forsskal, 1775)
1 Liza vaigiensis (Quoy and Gaimard, 1824)

13

14

Sphyraenidae - Barracudas
4 *Sphyraena barracuda (Walbaum, 1792)
1 *S. flavicauda Riippell, 1838

Polynemidae - Threadfins
1 Polydactylus sexfilis (Valenciennes, 1831)

Labridae - Wrasses
1 *Anampses caeruleopunctatus Riippell, 1829
1 *A. meleagrides Valenciennes, 1840
1 *A. twistii Bleeker, 1856
1 *Bodianus anthioides (Bennett, 1830)
1 *B. axillaris (Bennett, 1831)
1 *B. diana (Lacepéde, 1801)
1 Cheilinus bimaculatus Valenciennes, 1840
1 C. chlorurus (Bloch, 1791)
1_ C. fasciatus (Bloch, 1791)
1 *C. trilobatus Lacepéde, 1801
1 *C. undulatus Riippell, 1835
2 *C. unifasciatus Streets, 1877
1 *Cheilio inermis (Forsskal, 1775)
1 *Cirrhilabrus exquisitus Smith, 1957
2 Cirrhilabrus rubrimarginatus Randall, 1992
1 *Coris aygula Lacepéde,1801
2 *C. dorsomacula Fowler, 1908
1 *C. gaimard (Quoy and Gaimard, 1824)
1 Cymolutes praetextatus (Quoy and Gaimard, 1834)
1 *Epibulus insidiator (Pallas, 1770)
2 *Gomphosus varius Lacepéde, 1801
2 Halichoeres chloropterus (Bloch, 1791)
1 H. hortulanus (Lacepéde, 1801)
1 *H. marginatus Riippell, 1835
2 *H. melasmapomus Randall, 1980
2 *H. ornatissimus (Garrett, 1863)
1 *H. scapularis (Bennett, 1831)
2 *H. trimaculatus (Quoy and Gaimard, 1834)
1 *Hemigymnus fasciatus (Bloch, 1792)
1 *H. melapterus (Bloch, 1791)
1 *Hologymnosus doliatus (Lacepéde, 1801)
1 *Labroides bicolor Fowler and Bean, 1928
1 *L. dimidiatus (Valenciennes, 1839)
2 *L. pectoralis Randall and Springer, 1975
1 *Labropsis xanthonota Randall, 1981
2 Macropharyngodon meleagris (Valenciennes, 1839)
1 Novaculichthys macrolepidotus (Bloch, 1791)
1 *N. taeniourus (Lacepéde, 1801)
1 *Pseudocheilinus hexataenia (Bleeker, 1857)
1 *P. octotaenia Jenkins, 1900
2 Pseudocoris aurantifasciatus Fourmanoir, 1971
1 *Pseudodax moluccanus (Valenciennes, 1839)
2 *Stethojulis bandanensis (Bleeker, 1851)
1 *S. strigiventer (Bennett, 1832)
1 *Thalassoma amblycephalum (Bleeker, 1856)

1 *T. hardwickei (Bennett, 1828)

1 *T. jansenii (Bleeker, 1856)

1 *T. lunare (Linnaeus, 1758)

1 *T. lutescens (Lay and Bennett, 1839)

1 *T. purpureum (Forsskal, 1775)

1 *T. quinquevittatum (Lay and Bennett, 1839)
1 *T. trilobatum (Lacepéde, 1801)

2 Xyrichtys aneitensis (Ginther, 1862)

1 *X. pavo Valenciennes, 1840

Scaridae - Parrotfishes
1 *Bolbometopon muricatum (Valenciennes, 1840)
Calotomus carolinus (valenciennes, 1840)
C. spinidens (Quoy and Gaimard, 1824)
Hipposcarus longiceps (Valenciennes, 1840)
Leptoscarus vaigiensis (Quoy and Gaimard, 1824)
Scarus atropectoralis Schultz, 1958
S. enneacanthus Lacepéde, 1802
*§. forsteni (Bleeker, 1861)
1 *S. frenatus Lacepéde, 1802
1 *S. ghobban Forsskal, 1775
1 S. globiceps Valenciennes, 1840
1 *S. niger Forsskal, 1775
2 *S. oviceps Valenciennes, 1840
1 *S. prasiognathos Valenciennes, 1840
1 *S. psittacus Forsskal, 1775
1 *S. rubroviolaceus Bleeker, 1847
2 *S. schlegeli (Bleeker, 1861)
1 *S. sordidus Forsskal, 1775
3. S. strongylocephalus Bleeker, 1854

NWNRNR

[This species, restricted to the Indian Ocean and Indonesia, has frequently been

misidentified as S. gibbus Riippell, a closely related Red Sea endemic. ]

3 S. viridifuratus (Smith, 1956)

Pinguipedidae - Sandperches
1 *Parapercis clathrata Ogilby, 1911
1 P. hexophthalma (Cuvier, 1829)
1 *P. schauinslandi (Steindachner, 1900)

Creediidae - Sandburrowers
2 *Chalixodytes tauensis Schultz, 1943
3. Limnichthys nitidus Smith, 1958

Tripterygiidae - Triplefins
3 *Enneapterygius elegans (Peters, 1876)
5 *Enneapterygius tutuilae Jordan & Seale, 1906
5 *Enneapterygius sp. 1
2 Helcogramma capidata Rosenblatt, 1960

Blenniidae - Blennies
1 Aspidontus dussumieri (Valenciennes, 1836)
1 *A. taeniatus Quoy and Gaimard, 1834
1 *Cirripectes castaneus (Valenciennes, 1836)

[P]

16

3 C. gilberti Williams, 1988

1 *C. polyzona (Bleeker, 1868)

1 C. quagga (Fowler and Ball, 1924)

1 *Escenius bicolor (Day, 1888)

1 *E. midas Starck, 1969

2 *Entomacrodus caudofasciatus (Regan, 1909)
1 *E. epalzeocheilus (Bleeker, 1859)

1 E. striatus (Quoy and Gaimard, 1836)

1 *Exallias brevis (Kner, 1868)

1 Glyptoparus delicatulus Smith, 1959

2 *Istiblennius chrysospilos (Bleeker, 1857)

1 *7. edentulus (Schneider, 1801)

1 */. lineatus (Valenciennes, 1836)

1 *J. periophthalmus (Valenciennes, 1836)

1 Petroscirtes xestus Jordan and Seale, 1906

1 *Plagiotremus rhinorhynchos (Bleeker, 1852)
1 *P. tapeinosoma (Bleeker, 1857)

1 Stanulus seychellensis Smith, 1959

Callionymidae - Dragonets
1 Diplogrammus goramensis (Bleeker, 1858)

Gobiidae - Gobies
2 Amblygobius decussatus (Bleeker, 1855)
2 A. phalaena (Valenciennes, 1837)
3 A. semicinctus (Bennett, 1833)
3. A. tekomaji (Smith, 1959)
1 Asterropteryx semipunctatus Riippell, 1830
1 *Bathygobius cocosensis (Bleeker, 1854)
1 *B. cyclopterus (Valenciennes, 1837)
1 Bryaninops ridens Smith, 1959
1 Cabillus tongarevae (Fowler, 1927)
1 Callogobius maculipinnis (Fowler, 1918)
1 *C. sclateri (Steindachneri, 1880)
5 Callogobius sp.
1 Discordipinna griessingeri Hoese and Fourmanoir, 1978
2 Eviota lachdeberei ? Giltay, 1933
2 E. latifasciata ? Jewett and Lachner, 1983
1 E. melasma Lachner and Karanella, 1980
1 E. prasina (Klunzinger, 1871)
5 *Eviota sp. 1
5 *Eviota sp. 2
5 *Eviota sp. 3
5 Eviota sp. 4
1 Exyrias belissimus (Smith, 1959)
1 Fusigobius duospilus Hoese and Reader, 1985
1 F. neophytus (Giinther, 1877)
5 *Fusigobius sp.
1 Gnatholepis anjerensis (Bleeker, 1850)
3. G. caurensis (Bleeker, 1853)
5 Gnatholepis sp.
2 *Gobiodon okinawe Sawada, Arai, and Abe, 1973
1 *G. rivulatus (Riippell, 1830)

5 Oplopomops sp.

1 Oplopomus oplopomus (Valenciennes, 1837)
1 Palutrus pruinosus (Jordan and Seale, 1906)

1 Paragobiodon echinocephalus (Riippell, 1830)
1 *Priolepis cincta (Regan, 1908)

1 P.inhaca (Smith, 1949)

1 *P. semidoliatus (Valenciennes, 1837)

2 Psilogobius prolatus Watson and Lachner, 1985
1 Sueviota lachneri Winterbottom and Hoese, 1988
1 *Trimma emeryi Winterbottom, 1985

1 T. hoesei Winterbottom, 1984

1 T.macrophthalma (Tomiyama, 1936)

1 *T. taylori Lobel, 1979

1 T. undisquamis (Gosline, 1959)

3 T. winchi Winterbottom, 1984

3 *Trimma sp.

2 *Trimmaton sagma Winterbottom, 1989

1 *Valenciennea helsdingenii (Bleeker, 1858)

1 *V. sexguttata (Valenciennes, 1837)

1 *V. strigata (Broussonet, 1872)

1 Vanderhorstia ornatissima Smith, 1959

Xenisthmidae - Sandfishes
3 Xenisthmus africanus Smith, 1958
2 X. clara (Jordan and Seale, 1906)

Microdesmidae - Hovergobies

[We follow Randall and Hoese (1985) in including Nemateleotris and Ptereleotris

in this family.]
1 *Gunnelichthys monostigma Smith, 1958
1 *Nemateleotris decora Randall and Allen, 1973
1 *N. magnifica Fowler, 1938
1 *Ptereleotris evides (Jordan and Hubbs, 1925)
1 *P. heteroptera (Bleeker, 1855)
1 *P. microlepis (Bleeker, 1856)
1 *P. zebra (Fowler, 1938)

Kraemeridae - Sand darts
1 Kraemeria samoensis Steindachner, 1906

Acanthuridae - Surgeonfishes
1 *Acanthurus blochii Valenciennes, 1835
2 *A. guttatus Bloch and Schneider, 1801
2 *A. leucosternon Bennett, 1832
1 *A. lineatus (Linnaeus, 1758)
2 *A. maculiceps (Ahl, 1923)
1 *A. mata (Cuvier, 1829)
2 *A. nigricans (Linnaeus, 1758)
1 *A. nigricauda Duncker and Mohr, 1929
1 *A. nigrofuscus (Forsskal, 1775)
1 A. nigroris Valenciennes, 1835
2 *A. olivaceus Bloch and Schneider, 1801
1 *A. pyroferus Kittlitz, 1834

18

1 *A. thompsoni (Fowler, 1923) [P]
1 *A. triostegus (Linnaeus, 1758) [P]
1 *A. xanthopterus Valenciennes, 1835 [O]
1 *Ctenochaetus striatus (Quoy and Gaimard, 1825) [P,W]
1 *C. strigosus (Bennett, 1828) [P,W]
1 *Naso brevirostris (Valenciennes, 1835) [P]
1 *N. hexacanthus (Bleeker, 1855) [P]
1 *N. lituratus (Bloch and Schneider, 1801) [P,W]
1 *N. unicornis (Forsskal, 1775) [P,W]
1 *N. vlaminghi (Valenciennes, 1835) [P]
1 *Paracanthurus hepatus (Linnaeus, 1766) [P]
3 Zebrasoma desjardinii (Bennett, 1835) [P]

[Most recent authors have recognized this Indian Ocean surgeonfish as a subspecies
of the Pacific Z. veliferum. We follow Burgess (1973) in recognizing them

both as distinct species, and note that in contrast to Cocos, Christmas Is. fish

have the typical veliferum coloration. ]

1 *Z. scopas (Cuvier, 1829) [P,W]
Zanclidae - Moorish Idols

1 *Zanclus cornutus (Linnaeus, 1758) [P]
Siganidae - Rabbitfishes

1 Siganus argenteus (Quoy and Gaimard, 1825) [P]

2 S.puellus Schlegel, 1852 [P]

2 S. punctatus (Bloch and Schneider, 1801) [P]

3. S. stellatus Forsskal, 1775 [O]
Scombridae - Tunas

4 *Acanthocybium solandri (Cuvier, 1831) [O]

1 *Gymnosarda unicolor (Riippell, 1836) [O]

4 *Thunnus albacares (Bonnaterre, 1788) [O]

Bothidae - Flounders
1 *Bothus mancus (Bonnaterre, 1782) [P,W]
1 *B. pantherinus (Riippell, 1830) [W]

Soleidae - Soles

5 *Aseraggodes sp. 1 [P]
5 Aseraggodes sp. 2 [P]
Balistidae - Triggerfishes
1 *Balistapus undulatus (Park, 1797) [P]
1 *Balistoides viridescens (Bloch and Schneider, 1801) [O]
1 *Melichthys indicus Randall and Klausewitz, 1973 [P]
4 *M. niger (Bloch, 1786) [P]
1 *M. vidua (Solander, 1844) [P]
1 *Odonus niger (Riippell, 1837) [P]
1 Pseudobalistes flavimarginatus (Riippell, 1829) [P,W]
1 Rhinecanthus aculeatus (Linnaeus, 1758) [P,W]
1 *R. rectangulus (Bloch and Schneider, 1801) [P]
1 *Sufflamen bursa (Bloch and Schneider, 1801) [P]
1 *S. chrysopterus (Bloch and Schneider, 1801) [P]

1 S. fraenatus (Latreille, 1804) [P]

1 *Xanthichthys auromarginatus (Bennett, 1831)
1 *X. caeruleolineatus Randall, Matsuura and Zama, 1978

Monacanthidae - Leatherjackets
4 *Aluterus scriptus (Osbeck, 1765)
1 *Cantherines dumerilii (Hollard, 1854)
1 *C. pardalis (Riippell, 1837)
1 *Pervagor aspricaudus (Hollard, 1854)

Ostraciontidae - Boxfishes
1 *Ostracion cubicus Linnaeus, 1758

Tetraodontidae - Puffers
1 *Arothron hispidus (Linnaeus, 1758)
1 *A. nigropunctatus (Bloch and Schneider, 1801)
1 *Canthigaster amboinensis (Bleeker, 1865)
1 *C. bennettii (Bleeker, 1854)
1 *C. janthinoptera (Bleeker, 1855)
1 *C. valentini (Bleeker, 1853)

Diodontidae - Porcupinefishes
4 *Diodon hystrix Linnaeus, 1758

LS)

20

Table 1. Comparison of total ichthyofauna' and selected families of fishes
occuring at Cocos-Keeling (CK) or Christmas Island (CI); numbers in
parentheses are percent of total fauna; data for Christmas Island based on
Slightly updated version of checklist given in Allen and Steene (1987).

number of species shared CK cI
Family CK (%) CI (%) spp. only only
Labridae 54 (10.2) 61 (10.8) 43 as 16
Gobiidae 51 (9.6) 36 (6.4) 18 33 18
Pomacentridae 38 (7.2) 44 (7.8) 3 7 11
Apogonidae 30 (5.7) 22 (3.9) 12 20 10
Serranidae 30 (5.7) 44 (7.8) 19 11 25
Acanthuridae 25 (4.7) 26 (4.6) 24 al 2
Muraenidae 24 (4.5) 34 (6.0) 20 4 14
Chaetodontidae 23 (4.3) 27 (4.8) 19 4 8
Blenniidae 21°'(450) ° 28° (5.0) 14 7 14
Scaridae 20 (3.8) US 12/07.) 11 9 6
Holocentridae 20 (3.8) 1S) 627571) 12 8 3
Scorpaenidae 16 (3.0) 19 (3.4) 11 5 8
Balistidae 14 (2.6) 12 (2.1) 11 3 1
Carangidae V1 (2). 1) aSI(272:3)) 10 1 2
Lethrinidae 10 (1.9) 2 (0.0) 2 8 0
Lutjanidae $902.5) 15) (2:7) 7 a 8
Cirrihitidae 8 (1.5) 7 (1.2) 7 a 0
Mullidae 8. (PSS). 27 12) 7 1 0
Pomacanthidae > Keb) 121 (2;s1) 4 3 8
Microdesmidae qe) CL e3') Te \(lser2}) 7 ) 0
Tetradontidae Gren(dist)). ¢i9res( 136) 6 0 3
Ophichthidae 6 (1.1) mm (lie:2)) 2 4 5
Syngnathidae 6 (1.1) 7 (1.2) 4 2 3
Total fauna! 530 563 351 176 212

'The following families of epipelagic fishes were unsampled or under-
sampled at Cocos (Keeling) Island, and to make the above faunal comparisons
more meaningful, species of these families are not included in the total
fauna counts (percentages were also calculated using the adjusted totals):
Rhincodontidae, Exocoetidae, Coryphaenidae, Gempylidae, Scombridae and
Istiophoridae.

Table 2. Zoogeographic analysis of the Cocos (Keeling) fish fauna.

Distribution

Widespread Indo-Pacific
or Indo-west Pacific

West Pacific & Cocos Is.
Indian Ocean
Circumtropical

Uncertain

No. species

388
85
31

12

percent of
total fauna

ZA

Also known from Christmas Is.

ATOLL RESEARCH BULLETIN

NO. 413

CHAPTER 15

BARNACLES (CIRRIPEDIA, THORACICA) OF THE COCOS
(KEELING) ISLANDS

BY

D.S. JONES

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 15
BARNACLES
(CIRRIPEDIA, THORACICA)

OF THE COCOS (KEELING) ISLANDS
BY
D.S. JONES *

INTRODUCTION

The barnacle fauna of the Cocos (Keeling) Islands has not been documented prior
to the present report. Previous reports on the crustaceans of these islands have listed
Brachyura, Anomura, Caridea, Stomatopoda and Paguridae (Calman 1909, Wood-Jones
1909, Gibson-Hill 1947, 1948, Tweedie 1950, Forest 1956).

The present collection of barnacles was made by sampling a wide variety of
habitats throughout the atoll. Sampling stations included all reef flat zones and a range of
lagoonal habitats and outer reef slopes (see Chapter 1, Fig. 2, List of barnacles).
Specimens were collected by walking on shores and reef flats during low tide, snorkelling
and SCUBA diving.

A total of 13 species of barnacles in 11 genera are now recorded from the Cocos
(Keeling) Islands. Nine of these species were collected at one locality only. Although the
number of barnacles is small, this collection is of considerable interest since nothing is
known of the barnacles of these islands, and knowledge of the barnacle fauna of coral
atolls in the Indian Ocean in general is scanty. Eleven species were collected during the
Western Australian Musum Cocos (Keeling) Island expedition of February, 1989. Two
additional species from these islands (Capitulum mitella, Megabalanus ajax) are housed in
the crustacean collection of the Western Australian Museum and are included in the species
list. The species list given below must be considered provisional and further detailed
collecting may well reveal additional species, particularly from sub-tidal areas.

DISCUSSION

The barnacle fauna of the Cocos (Keeling) Islands is composed of widespread
Indo-West Pacific species (8) and species exhibiting cosmopolitan distributions (5).

Of the cosmopolitan barnacles, L. anatifera and L. anserifera are pelagic in habitat
and attach to floating objects. Freshly beached specimens were collected on reef platforms
and beaches, attached to bamboo, wood, etc. However, large numbers of the abundant
terrestrial hermit crab Coenobita perlatus Milne Edwards were observed actively predating
these barnacles. Consequently strandings of pelagic barnacles may be more numerous,
and more pelagic species may be represented than are presently recorded, but ensuing rapid
predation (by terrestrial hermit crabs in particular) makes the collection of all but recently
stranded specimens unlikely.

Western Australian Museum, Francis Street, Perth, Western Australia, 6000.

The cosmopolitan pedunculate barnacle O. lowei occurs on the gills of decapod
crustaceans and was obtained from the gills of the rock lobster Panulirus penicillatus Oliver
at the Cocos Islands. The cosmopolitan fouling species, M. tintinnabulum, occurred on
mooring buoys in the main lagoon. This species may have been introduced via shipping
since it was not found elsewhere in island waters and the species is a well-known fouler of
ship hulls. T. divisa has a circumtropical insular and occasional mainland distribution.
This species was first described from material collected on the west coast of Sumatra and
the Java Sea. At Cocos (Keeling) the species was rare, only a few specimens being
collected from deep, narrow crevices in beachrock.

The Indo-West Pacific species T. wireni was the only sessile species collected at
more than one locality. It was collected subtidally from a variety of hard substrata
(mooring buoys, carapace of P. penicillatus, shell of Trochus maculatus Linnaeus) as well
as from a sponge collected in beach drift. L. nicobarica bores into limestone substrates in
the Indo-West Pacific region. The species was rare at the Cocos (Keeling) Islands, boring
into the upper areas of coral and limestone boulders on intertidal and seaward reef flats.
The Indo-West Pacific species C. mitella occurs in crevices in mid-tidal areas under
conditions of semi to full wave exposure. T. fissum occurs on the mouthparts of decapod
crustaceans in the Indo-West Pacific region, and was collected from the third maxillipeds
of P. pencillatus. Two balanomorphs, E. hembeli and M. ajax, both very large, robust
species, are known from the Indo-West Pacific region although both are extremely rare.
E. hembeli occurs on high intertidal rocks and shores and at the Cocos (Keeling) Islands a
solitary individual was collected from high up on the limestone boulder on an ocean reef
flat. M. ajax occurs mainly in the subtidal on corals. The low live coral cover at Cocos is
reflected in the very low number of coral barnacles collected. Although numerous samples
of live and dead coral were examined, only one sample harboured coral barnacles - viz. S.
dentatum on the coral Favia stelligera (Dana). The genus Acasta occurs in sponges and has
many Indo-West Pacific representatives. Parietal plates of Acasta sp. were obtained from a
sponge found in beach drift at the Cocos (Keeling) Islands.

Barnacles are relatively rare and inconspicuous intertidal organisms at Cocos
(Keeling) and their paucity in the overall marine invertebrate community is notable. The
total of 13 species is small and may reflect inadequate sampling procedures. It may,
however, be a true representation, since coral reefs are known to be unfavourable habitats
for cirripedes (Darwin 1854, Borradaile 1903). The lack of development of barnacle
populations on coral reefs has been documented in the tropical West Pacific (Newman
1960), the Tokara Islands, Japan (Utinomi 1954) and Heron Island, Australia (Endean et
al. 1956). The scouring action of waves by rolling light coral limestone fragments and
boulders is restrictive or adverse to barnacle settlement, especially in intertidal areas, where
settlement would be restricted to crevices and underhangs. Newly settled and juvenile
barnacles are indirectly predated on by herbivorous fish, which rasp limestone and coral
reefs for micro-algae. Consequently barnacles may be restricted to higher intertidal areas
or to boring into limestone substrata. Other known predators in the marine environment
are molluscs (e.g. whelks) and sublittoral echinoderms (e.g. Diadema). These factors may
all contribute to the general lack of intertidal barnacles at the Cocos (Keeling) Islands. In
intertidal areas barnacles occur rarely and very sparsely, in interstices in or between and
under rocks (e.g. C. mitella, T. divisa) or high on rocks which are only covered during
high tides (E. hembeli). Burrowing forms occur in limestone and coral boulders (L.
nicobarica) or live coral (S. dentatum). Some T. divisa individuals collected at Cocos
(Keeling) exhibited gastropod bore holes in parietal plates.

On fouling buoys in the main lagoon a small fouling community (e.g. sponges,
ascidians, barnacles) is developing and many large specimens of the fouler M. tintinnabulum

3

were collected here as well as individuals of T. wireni. The presence and abundance of M.
tintinnabulum and T. wireni at this site compared to the paucity of barnacle species
elsewhere may be associated with a lack of coral. This, combined with a lack of shelter
from piscivorous fish, may result in an absence of reef fish (e.g. Scaridae) and hence the
predation pressure on newly settled barnacles and juveniles may be correspondingly
reduced. The origin of the Cocos specimens of M. tintinnabulum is unknown. However,
the presence of this species may be of some concern since it is a noted fouling species
overseas.

The thoracic cirripede fauna of the Indian Ocean is relatively well-known, with
upwards of 280 species estimated to occur there (Stubbings 1936, Nilsson-Cantell 1938,
Daniel 1972). The nearest localities to the Cocos (Keeling) Islands are Christmas Island,
900 km to the east and Java Head, 1000 km to the north-east. Only two cirripede species
are recorded from Christmas Island (Nilsson-Cantell 1934 Daniel 1972), but the Western
Australian Museum crustacean collection holds an additional five species making a total of
seven. Java is part of Indo-Malay faunistic province, an area rich in both number of species
and in the geographical distribution of cirripedes. At least 246 species are recorded from
this area (Hoek 1907, 1913, Broch 1931, Nilsson-Cantell 1934). Compared to the nearest
mainland shores (Sumatra, Java) which exhibit rich barnacle faunas in both the intertidal and
the sub littoral (Nilsson-Cantell 1921), the fauna of the Cocos (Keeling) Islands must be
considered depauperate.

The number of cirripedes recorded from the Cocos (Keeling) Islands is larger than
that at present recorded from other isolated Indian Ocean atolls (e.g. Diego Garcia, Chagos)
but less than that presently known from larger atoll groups (e.g. Maldives and Laccadives).
Table 1 compares the numbers of barnacle species recorded from islands and atolls in the
Indian Ocean, and the species in common with the Cocos (Keeling) Islands. However,
meaningful comparisons with other atolls and islands are difficult to make since the
collecting effort at these localities is not known.

ACKNOWLEDGEMENTS
For identifications I thank Mrs. L.M. Marsh (coral) and Mr. P. Unsworth (gastropod).

REFERENCES

Annandale, N. 1906. Report on the Cirripedia collected by Professor Herdman, at
Ceylon, in 1902. Rep. Pearl Fish. Manaar, 5: 137-150.

Borradaile, L.A. 1903. Marine crustaceans. Part 7. The barnacles (Cirripedia) - In
Gardiner, J.S. The fauna and geography of the Maldive and Laccadive
Archipelagoes Part 1, 2: 440-443.

Broch, H. 1931. Papers from Dr. Th. Mortensen’s Pacific Expedition 1914-1916. LVI.
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Calman, W.T. 1909. Crustacea of Cocos (Keeling). Proc. Zool. Soc. Lond. 1909: 159-
160.

Daniel, A. 1972. Marine intertidal barnacles in the Indian Ocean. Proc. Indian Acad. Sci.,
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Darwin, C. 1854. A monograph on the subclass Cirripedia with figures of all species.
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Endean, R., Stephenson, W. and Kenny, R. (1956). The ecology and distribution of
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Forest, J. 1956. La Faune des iles Cocos (Keeling): Paguridae. Bull. Raffles Mus.
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Gibson-Hill, C.A. 1948. The Island of North Keeling. J. Malay. Br. Asiat. Soc. 21: 68-
103.

Gruvel, J.A. 1909. Etudes des cirrhipédes de l’ocean Indien. Trans. Linn. Soc. Lond.
(Zool.), ser. 2, 13: 23-27.

Hoek, P.P.C. 1907. The Cirripedia of the Siboga Expedition. A. Cirripedia Pedunculata.
Siboga Exped. Monogr. 31a: V-XXV, 1-127.

Hoek, P.P.C. 1913. The Cirripedia of the Siboga Expedition. B. Cirripedia Sessilia.
Siboga Exped. Monogr. 31b: I-XXV, 129-275.

Newman, W.A. 1960. The paucity of intertidal barnacles in the tropical Western Pacific.
Veliger 2: 89-94.

Nilsson-Cantell, C.A. 1921. Cirripeden-studien. Zur Kenntnis der Biologie, Anatomi
und Systematik Diesser Gruppe. Zool. Bidrag. Uppsala 7: 75-395.

Nilsson-Cantell, C.A. 1934. Indo-Malayan cirripedes in the Raffles Museum,
Singapore. Bull. Raffles Mus. 9: 42-73.

Nilsson-Cantell, C.A. 1938. Cuirripedes from the Indian Ocean in the collection of the
Indian Museum, Calcutta. Mem. Indian Mus. 13: 1-81.

Smith, W.A. 1971. Crustacea: cirripedes from Diego Garcia. Atoll Res. Bull. 149:
103.

Stubbings, H.G. 1936. Cirripedia. John Murray Expeditions, 1933-1934. Sci. Rep.
Murray Exped. 4: 1-70.

Taylor, J.D. 1968. Coral reef and associated invertebrate communities (mainly
molluscan) around Mahe, Seychelles. Phil. Trans. Roy. Soc. Lond. (Biol.),
B254: 129-206.

Tweedie, M.W.F. 1950. The fauna of the Cocos-Keeling Islands; Brachyura and
Stomatopoda. Bull. Raffles Mus. 22: 105-148.

Utinomi, H. 1954. Invertebrate fauna of the intertidal zone of the Tokara Islands IX.
Cirripedia. Publ. Seto Mar. Biol. Lab. 4: 17-26.

5

Wood-Jones, F. 1909. The fauna of the Cocos-Keeling Islands. Proc. Zool. Soc. Lond.
1909: 132-160.

LIST OF BARNACLES
x = specimens without precise locality data
ORDER THORACICA
Suborder Lepadomorpha

Family Scalpellidae Pilsbry, 1916
Subfamily Lithotryinae Gruvel, 1905
Lithotrya nicobarica Reinhardt, 1850

Subfamily Pollicipinae Gruvel, 1905
Captitulum mitella (Linnaeus, 1767)

Family Lepadidae Burmeister, 1834 (Fam. Lepadea")
Lepas anatifera Linnaeus, 1767
Lepas anserifera Linnaeus, 1767

Family Poecilasmatidae Annandale, 1910
Temnaspsis fissum Darwin, 1851
Octolasmis lowei (Darwin, 1851)

Suborder Balanomorpha

Family Chthamalidae Darwin, 1854
Subfamily Euraphiinae Newman & Ross, 1976
Euraphia hembeli Conrad, 1837

Family Tetraclitidae Gruvel, 1903
Subfamily Tetraclitinae Gruvel, 1903
Tetraclita divisa Nilsson-Cantell, 1921
Tesseropora wireni Nilsson-Cantell, 1921

Family Archaeobalanidae Newman & Ross, 1976
Acasta sp.

Family Pyrgomatidae Gray, 1825
Savignium dentatum (Darwin, 1854)

Family Balanidae Leach, 1817
Megabalanus ajax (Darwin, 1854)

Collection Station

132

24, 27, 30
Zils SOE

10
20

10
1, 2; 6, 20528

31

xX
Megabalanus tintinnabulum (Linnaeus, 1758) 28

Table 1 : A comparison of the numbers of thoracic cirripede species recorded from
Indian Ocean atolls (A) and islands, and the species in common with the
Cocos (Keeling) Islands.

Locality Total Spp. in common References
Species with Cocos (Keeling)

Christmas I. ih 4 Nilsson-Cantell 1934;
Daniel 1972; WA Museum
Collection

Diego Garcia (A) 3 8 Smith 1971

Chagos (A) 6 3 Gruvel 1909

Andamans &

Nicobars 17 D Gruvel 1909; Daniel 1972

Sri Lanka 31 3 Annandale 1906;
Daniel 1972

Maldives &

Laccadives (A) 25 Z Borradaile, 1903; Annandale
1906; Daniel 1972

Seychelles 9 2 Gruvel 1909; Taylor 1968

Providence I. My, 0 Gruvel 1909

ATOLL RESEARCH BULLETIN

NO. 414

CHAPTER 16

DECAPOD CRUSTACEANS OF THE COCOS (KEELING) ISLANDS

BY

G.J. MORGAN

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
FEBRUARY 1994

CHAPTER 16
DECAPOD CRUSTACEANS OF THE COCOS
(KEELING) ISLANDS
BY
G.J. MORGAN *

INTRODUCTION

Prior to the present study, the crustacean fauna of the Cocos (Keeling) Islands had
been collected intensively only once, by C.A. Gibson-Hill in the years 1940-41. The
Brachyura and Stomatopoda of his material were taxonomically reviewed by Tweedie
(1950) and the hermit crabs by Forest (1956). Gibson- Hill's collection represents almost
exclusively intertidal and terrestrial faunas. In the present survey, SCUBA was employed
extensively to augment the poorly known subtidal faunas. Xanthoid crabs (families
Xanthidae, Trapeziidae, Pilumnidae, Menippidae) and marine hermit crabs (families
Diogenidae and Paguridae) are dominant decapod components of tropical rocky and coral
reef ecosystems and were collected preferentially. Conversely, some taxa (e.g. caridean
shrimps) are poorly represented in the present collection.

Specimens were sampled by reef walking in the intertidal and by SCUBA or
snorkelling in the subtidal habitats. A total of 198 species of Decapoda is recorded of which 78
are new records for the Cocos (Keeling) Islands (see list of species). Station localities are
listed by number (see Chapter 1, Fig.2) and some additional sites sampled are recorded by
name. Station 9 (Direction Island) has been divided for this list into 9(a): blue hole south of
Direction I. and 9(b): sand shallows between island and blue hole. In order to compile as
complete a record of decapod crustaceans as possible, the list includes species recorded by the
previous workers noted above. The species names are those currently used in the scientific
literature and not necessarily the names cited by historical workers. The historical collections
have not been examined and hence the accuracy of early identifications cannot be ascertained.

DISCUSSION

The most diverse decapod taxa of the Cocos (Keeling) Islands are the xanthoid and
paguroid crabs with 77 and 48 species recorded respectively. Both taxa are particularly
evident in subtidal and intertidal reef habitats, although the abundance of xanthoids was
found to be somewhat lower than expected on the 1989 sampling expedition.

The islands can be divided broadly into several major habitat types with a
convenient dichotomy between lagoon and outer oceanic environments.

In the lagoon, only a few species of hermit crab notably Clibanarius longitarsus
and Calcinus laevimanus are present in the sheltered shallow intertidal areas of fine mud
sediment. Hermits appear to be absent from the very extensive soft grey sediment flats in
North and South Lagoons of West Island, but these flats support high numbers of

2 Western Australian Museum, Francis Street, Perth, Western Australia, 6000.

Z

Macrophthalmus verreauxi and Uca chlorophthalmus. The latter produces a distinct pattern
of hexagonal territories in some upshore areas. The portunid Thalamita crenata is common
in the shallows of the lagoon. Tweedie (1950) identified T. spinimana as the species
plentiful in the shallow sandy, slightly weedy water of the lagoon’ (Gibson-Hill, in
Tweedie 1950) but in 1989 the common portunid in this habitat was T. crenata. It is
possible that Tweedie's identification was spurious but he has recorded T. crenata from the
‘outer edge of the atoll’. The large edible mud or mangrove crab Scylla serrata
occasionally is caught by locals in the very sheltered areas of the lagoon but is rarely seen
and presumably occurs in very low numbers. Ghost crabs, Ocypode ceratophthalma and
O. cordimana, forage across the lagoon flats from their upshore burrows and are also
numerous on the oceanic beaches. O. ceratophthalma occurs in its two colour morphs,
with the olive green form far outnumbering the cream and brown morph. The terrestrial
crab Cardisoma carnifex also feeds on exposed flats of the lagoon at low tide.

The continual natural process of sedimentary infilling of the lagoon, together with
the occurrence of the above crabs in very high numbers, indicate that the populations of
soft sediment crustaceans are relatively secure for the foreseeable future. In deeper areas
of the lagoon and near the major channels allowing entry of oceanic water, hard and soft
corals are present to a variable extent.

The 1983 El Nino effect resulted in very extensive coral death and over much of the
lagoon only small colonies of live hard corals have re-established. As many species of
crustaceans are either symbiotic with live corals or prefer the live coral habitat, loss of
corals is reflected in crustacean occurrences. Where live coral, especially Pocillopora spp.,
is present, the crustacean assemblage resembles that discussed for outside reef coral
habitats. The dead coral rubble supports a lower diversity of hermit crabs with the
diogenid Calcinus latens and several small species of pagurids dominant in numbers.
Portunids and xanthoids are also present but often difficult to collect in the deep layer of
coral fragments. Sandy areas and beds of the seagrass Thalassia and the alga Caulerpa
support Calcinus latens and C. laevimanus in relatively low populations and several
pagurids in high numbers, especially Micropagurus vexatus. Sandy areas are also habitat
for several portunid species and Calappa hepatica.

If further live coral dieback were to occur in the lagoon, the symbiotic faunal
communities would be placed at considerable risk. Presumably there has been, and would
continue to be, replacement of coral crustacean communities by rubble and sand-living
species.

The oceanic reefs of the Cocos (Keeling) Islands have also experienced major
reduction of the live coral habitat. Percentage cover of live hard corals is low and many of
the outside reefs are dominated by bare, wave scoured dead coral or coral rubble. The
shallow subtidal and intertidal reef habitats are home to a variety of hermit crabs with
Calcinus minutus, C. latens, C. sp. 1 (an undescribed species), Dardanus crassimanus and
D. lagopodes common. The large Dardanus species, D. megistos, D. guttatus, D.
gemmatus and D. deformis occur on shallow reef flats and adjacent sandy environments.
A variety of xanthoids especially Pilodius areolatus, are fairly numerous under the coral
and coral rubble. Where live branching coral is present, especially Pocillopora, symbiotic
species of xanthoids (e.g. Trapezia and Cymo), and alpheids (e.g. Alpheus lottini), occur.
Under coral slabs, particularly in the subtidal, several species of pagurid are common with
the bright lilac Pylopaguropsis magnimanus especially obvious. As was recorded for
Christmas Island (Morgan, unpublished), pagurids can be quite diverse and common in
tropical reef habitats and their taxonomy requires considerable attention. Interestingly, the
populations and diversity of porcellanids (porcelain crabs) were low at Cocos (Keeling).

3

There seemed no obvious explanation for this apart from the possible effects of a paucity
of live coral.

Intertidal rock and rock-sand platforms support quite high populations of hermit
crabs with Calcinus laevimanus most widespread and C. latens and Clibanarius humilis
common in areas. High on the platforms, in very warm pools flushed only by spring
tides, the only hermit crab is Calcinus seurati. Xanthoids are also characteristic of rocky
platforms, especially species of Leptodius. Grapsids are usually the most conspicuous
crabs on intertidal hard substrata, with Grapsus tenuicrustatus and G. intermedius the
largest species on Cocos (Keeling). Three species of Pachygrapsus occur in a range of
intertidal habitats, usually on or under rock or coral slabs.

Prior to this study, two species of rock lobster, Panulirus penicillatus and P.
versicolor were recorded from the Cocos (Keeling) Islands (George 1968). The presence
of a third species, P. ornatus, commonly referred to on the islands as the “leopard cray',
was confirmed during the 1989 study. All three species are very widespread in the Indo-
West Pacific area. Panulirus species have extended larval stages of several months with
the planktonic phyllosoma capable of drifting great distances on ocean currents before
settlement as the puerulus. It is probable that rock lobster stocks at Cocos (Keeling) are
dependent upon larvae originating considerable distances from the islands and hence
fishing overexploitation of the local breeding population is unlikely to severely effect
settlement. It is certainly possible, however, that heavy fishing might deplete the
population of table-size lobsters. Some form of monitoring of fishing effort would
provide information on distribution of the species and their present abundance.

The Cocos (Keeling) Islands do not support the numbers or diversity of true
terrestrial crabs so obvious on Christmas Island (Indian Ocean). The gecarcinid
Cardisoma carnifex is very common on West Island, with apparently lower populations
elsewhere. No specimens of C. rotundum recorded by Tweedie (1950) (as C. frontalis),
were collected on the 1989 expedition. The grapsids Geograpsus crinipes and G. grayi co-
occur on the islands, in lower numbers than Cardisoma. The presence of the Christmas
Island ‘red crab', Gecarcoidea natalis, was confirmed on North Keeling Island, but the
species occurs in only small numbers. Tweedie (1950) stated that its occurrence was due
to introduction with soil from Christmas Island to Direction Island and thence by larvae to
other islands in the Cocos. This argument is convincing, given the small population of G.
natalis on Cocos (Keeling) and the great distance (900 km) to Christmas Island, the only
other habitat of the species.

Only one species of the terrestrial hermit crab family Coenobitidae had been
recorded previously from Cocos (Keeling), namely Coenobita perlatus (Forest 1956). It is
odd that the two additional species collected in this study, C. rugosus and C. brevimanus,
were not represented in Gibson-Hill's collection as the former in particular is not
uncommon. The coconut or robber crab, Birgus latro, was not found during the 1989
expedition, despite searches for it, but is reported by local people to occur on at least West
and North Keeling Islands, the latter occurrence being confirmed by the ANPWS ranger,
Mr Paul Stephenson (pers. comm.). In addition, a specimen of B. latro is on display in the
local museum on Home Island, reportedly collected on Cocos (Keeling). Charles Darwin
(1845) noted that B. latro was common at the time of his visit in 1836 and it might be
suggested that the presently very low population of the species is due to overexploitation
by the islands’ local inhabitants. Protection of the existing specimens will be necessary to
ensure their continued survival on Cocos (Keeling).

There are no naturally occurring bodies of freshwater on the islands, although a
brackish lake (Bechet Besar) is present towards the north end of West Island. Freshwater
must be accessed by sinking wells into subterranean reserves. It is scarcely surprising
therefore that no freshwater crustacea were collected, unlike Christmas Island. Cardisoma
carnifex was observed to concentrate at temporary rainwater pools and several specimens
were seen in a shallow well, totally immersed in freshwater.

REFERENCES

Darwin, C. 1845. Journal of researches into the natural history and geology of the
countries visisted during the voyage of H.M.S. Beagle round the world, under the
command of Capt. Fitroy R.N. London. John Murray

Forest, J. 1956. La Faune des iles Cocos-Keelings Paguridea. Bull. Raffles Mus. 27: 45-
59!

George, R.W. 1968. Tropical spiny lobsters Panulirus spp., of Western Australia (and
the Indo-West Pacific). J. Roy. Soc. W.A. 51(2): 33-38.

Tweedie, M.W.F. 1950. The fauna of the Cocos-Keeling Islands, Brachyura and
Stomatopoda. Bull. Raffles Mus. 22: 105-148.

LIST OF DECAPOD CRUSTACEA

KEY TO SYMBOLS
+ New record for Cocos (Keeling) Islands
= Not collected during this survey
$ Not collected but occurrence confirmed

Numbers = sampling station (see Chapter 1, Fig.2)

STENOPODIDEA
STENOPODIDAE
+ Stenopus hispidus (Olivier, 1811) 1
CARIDEA
ALPHEIDAE
+ Alpheus lottini Guérin, 1829 WW
+ Alpheus macrodactylus Ortmann, 1890 1
+) Alpheus strenuus strenuus Dana, 1852 PD
+ Alpheus sp. 1
+ Synalpheus stimpsoni (De Man, 1888) 19
PALINURA
PALINURIDAE
Panulirus penicillatus (Olivier, 1791) 1,10,20
$ Panulirus versicolor (Latreille, 1804)

+$ Panulirus ornatus (Fabricius, 1798)

ANOMURA
DIOGENIDAE
+ Aniculus retipes Lewinsohn, 1982 4,19,32
Aniculus ursus (Olivier, 1811) 1,11
+ Aniculus sp. 1
+ Calcinus argus Wooster, 1984 4
Calcinus elegans (H. Milne Edwards, 1836) 1,6,11,12,18,30
Calcinus gaimardii (H. Milne Edwards, 1848) 1,6,9(a),11,25
+ Calcinus guamensis Wooster, 1984 1
Calcinus laevimanus (Randall, 1839) 2,6,10,12,30,34

+++

++4+4+

+ *¥¥+ ++ *

+++

Calcinus latens (Randall, 1839)

Calcinus minutus Buitendijk, 1937
Calcinus pulcher Forest, 1958
Calcinus seurati Forest, 1951
Calcinus sp. 1

Calcinus sp. 3

Calcinus sp. 4

Calcinus sp. 5

Calcinus sp. 6

Clibanarius corallinus (H. Milne Edwards, 1848)
Clibanarius eurysternus Hilgendorf, 1878
Clibanarius humilis Dana, 1852

Clibanarius laevimanus Buitendijk, 1937
Clibanarius longitarsus (De Haan, 1849)
?Clibanarius merguiensis De Man, 1888
Clibanarius striolatus Dana, 1852

Dardanus crassimanus (H. Milne Edwards, 1848)
Dardanus deformis (H. Milne Edwards, 1836)
Dardanus gemmatus (H. Milne Edwards, 1848)
Dardanus guttatus (Olivier, 1811)

Dardanus lagopodes (ForskAl, 1775)

Dardanus megistos (Herbst, 1804)

Dardanus scutellatus (H. Milne Edwards, 1848)
Diogenes sp.

Paguristes sp.

Trizopagurus strigatus (Herbst, 1804)

PAGURIDAE

+

++ttet+ +4

+FAQ

+

Micropagurus vexatus Haig and Ball, 1988
4,7,9(a),13515,19522,
23325326332
Nematopagurus cf. muricatus (Henderson, 1896)
Pagurixus anceps (Forest, 1954)
Pagurixus tweediei (Forest, 1956)
Pagurixus sp.
Pylopaguropsis magnimanus (Henderson, 1896)
Pagurid sp. 1
Pagurid sp. 2
Pagurid sp. 3
Pagurid sp. 6

OENOBITIDAE

Birgus latro (Linnaeus, 1767)

Coenobita brevimanus Dana, 1852
Coenobita perlatus H. Milne Edwards, 1837
Coenobita rugosus H. Milne Edwards, 1837

PORCELLANIDAE

+

Petrolisthes asiaticus (Leach, 1820)

1,6,8,9(a),9(b),12,
17, 18,22,23,30,34,
36
4°6,7,13,15319325332

4,9(a),15,32

10,30
4A TASS 19225255
32

4
A6, 15925
5

25
6,10,12,30
2,30

2

2

1,4,8,15,19,23,32
12

1,24

1,6,8,11,30
7,8,12,13,15,19,32
6,9(b),11,12,17,18,
19,34
6,9(b),12,17,34
9(b),19,22
4,6,25,32

722

22
1,6;12-30

1

4

1,6
9(a),15,16,26,36
1,16,17,18226
2:

North Keeling
21
1,2,6,10,21
256;10313,21

+ Petrolisthes carinipes (Heller, 1861) 1

GALATHEIDAE
+ Galathea sp. 1,19,23

BRACHYURA
Dromiacea
DYNOMENIDAE
* Dynomene hispida Desmarest, 1825
Dynomene cf. pilumnoides Alcock, 1899 4,32
Dynomene praedator A. Milne Edwards, 1879
Dynomene sp. 4,25,32

+ *+4+

Oxystomata
CALAPPIDAE
Calappa hepatica (Linnaeus, 1758) 9(b),19

Oxyrhyncha
MAJIDAE
EPIALTINAE
+ Huenia grandidierii A. Milne Edwards, 1865 20
Menaethius monoceros (Latreille, 1825 1,20,24
Perinia tumida Dana, 1852 1,24
+ Simocarcinus obtusirostris (Miers, 1879) 18

MAJINAE
Cyclax suborbicularis (Stimpson, 1907) 1
+ Schizophrys aspera (H. Milne Edwards, 1834) 1,32

MITHRACINAE
+ Micippa thalia (Herbst, 1803) 11

PARTHENOPIDAE
AETHRINAE
Actaeomorpha erosa Miers, 1878 20

EUMEDONINAE
= Eumedonus pentagonus (A. Milne Edwards, 1879)

PARTHENOPINAE
Daldorfia horrida (Linnaeus, 1758)

Cancridea

ATELECYCLIDAE

* Kraussia integra (De Haan, 1835)

+ Kraussia cf. nitida Stimpson, 1858 23
= Kraussia rugulosa (Krauss, 1843)

Brachyrhyncha
PORTUNIDAE
CATOPTRINAE
af Carupa tenuipes Dana, 1851

PORTUNINAE
+ Charybdis erythrodactyla (Lamarck, 1818)
i Charybdis obtusifrons Leene, 1936
Portunus granulatus (H. Milne Edwards, 1834)
+$ Scylla serrata (Forskal, 1775)
Thalamita admete (Herbst, 1803)
+ Thalamita chaptali (Audouin and Savigny, 1825)
Thalamita crenata H. Milne Edwards, 1834
Thalamita dakini Montgomery, 1931
Thalamita demani Nobili, 1905
Thalamita integra Dana, 1852
Thalamita picta Stimpson, 1858
Thalamita spinimana Dana, 1852
Thalamitoides quadridens A. Milne Edwards, 1869
Thalamitoides tridens A. Milne Edwards, 1869

+ *¥ eX +4

XANTHIDAE
POLYDECTINAE
Lybia tessellata (Latreille, 1812)
i Polydectus cupulifer (Latreille, 1812)

CYMOINAE
Cymo andreossyi (Audouin, 1826)
* Cymo quadrilobatus Miers, 1884

LIOMERINAE
Liomera bella (Dana, 1852)
Liomera caelata (Odhner, 1925)
Liomera laevis (A. Milne Edwards, 1873)
Liomera monticulosa (A. Milne Edwards, 1873)
Liomera pallida (Borradaile, 1900)
Liomera rugata (H. Milne Edwards, 1834)
Liomera stimpsoni (A. Milne Edwards, 1865)
Liomera tristis (Dana, 1852)

+ Liomera venosa (H. Milne Edwards, 1834)

+ Liomera sp.

+ *¥+ % & *

EUXANTHINAE
x Euxanthus exsculptus (Herbst, 1790)
+ Paramedaeus simplex (A. Milne Edwards, 1873)

ACTAEINAE
Actaeodes consobrinus (A. Milne Edwards, 1873)
Actaeodes tomentosus (H. Milne Edwards, 1834)
Gaillardiellus orientalis (Odhner, 1925)
Gaillardiellus superciliaris (Odhner, 1925)
Paractaea rufopunctata (H. Milne Edwards, 1834)
Psaumis cavipes (Dana, 1852)
Pseudoliomera granosimana (A. Milne Edwards, 1865)
Pseudoliomera speciosa (Dana, 1852)

Se 36 tee

*%

12

el

1,6,9(a),12,17,18,36
36

2
18,24
4

20,25,32
9(a), 16,36

PM |

APA]

13819

6,27
12,20,27

6,12,18
23

ZOSIMINAE
= Atergatopsis signatus (Adams and White, 1848)
Lophozozymus dodone (Herbst, 1801)
Lophozozymus pulchellus A. Milne Edwards, 1867
Platypodia cristata (A. Milne Edwards, 1865)
Platypodia granulosa (Ruppell, 1830)
Platypodia cf. pseudogranulosa Serene, 1984
Zozymodes pumilus (Jacquinot and Lucas, 1852)
Zosimus aeneus (Linnaeus, 1758)

+ * *

XANTHINAE
Lachnopodus gibsonhilli (Tweedie, 1950)
Lachnopodus subacutus (Stimpson, 1858)
Lachnopodus tahitensis De Man, 1889
Leptodius exaratus (H. Milne Edwards, 1834)
Leptodius gracilis (Dana, 1852)
Leptodius nudipes (Dana, 1852)
Leptodius sanguineus (H. Milne Edwards, 1834)
Lioxanthodes alcocki Calman, 1909
Macromedaeus nudipes (A. Milne Edwards, 1867)
Neoxanthias impressus (Lamarck, 1818)

+ % & *X

ETISINAE
+ Etisus bifrontalis (Edmondson, 1935)
+ Etisus demani Odhner, 1925
Etisus dentatus (Herbst, 1785)
+ Etisus frontalis Dana, 1852
x Etisus laevimanus Randall, 1840
Paraetisus sp.

CHLORODIINAE
Chlorodiella barbata (Borradaile, 1900)
Chlorodiella cytherea (Dana, 1852)
Chlorodiella laevissima (Dana, 1852)
Phymodius granulosus (De Man, 1888)
Phymodius monticulosus (Dana, 1852)
Phymodius ungulatus (H. Milne Edwards, 1834)
Pilodius areolatus (H. Milne Edwards, 1834)

* Pilodius pubescens Dana, 1852

Pilodius scabriculus Dana, 1852
+ Tweedieia odhneri (Gordon, 1934)

+ ¥+

TRAPEZIIDAE
TRAPEZIINAE
Tetralia glaberrima (Herbst, 1790)
Be Trapezia areolata Dana, 1852
Trapezia cymodoce (Herbst, 1799)

= Trapezia digitalis Latreille, 1825
Trapezia ferruginea Latreille, 1825
Trapezia guttata Ruppell, 1830
Trapezia rufopunctata (Herbst, 1799)

6,30

30
6,10,12,27
24

18

fel

18

1

1

17,18,20
13
9(a),17,36
1527

1

17,36

6

156, 125118220) 23.27

1,6,12
On 225 32

16,27

1,4;7,13524;25,
DD) ey

M32
25,36
TDD

10

+ Trapezia septata Dana, 1852

DOMECIINAE
Domecia hispida Eydoux and Souleyet, 1842

CARPILIIDAE
* Carpilius convexus (Forskal, 1775)
s Carpilius maculatus (Linnaeus, 1758)

MENIPPIDAE
OZIINAE
Lydia annulipes (H. Milne Edwards, 1834)
* Ozius tuberculosus H. Milne Edwards, 1834

ERIPHITINAE
* Eriphia scabricula Dana, 1852
Eriphia sebana (Shaw and Nodder, 1803)

DACRYOPILUMNINAE
Dacryopilumnus rathbunae Balss, 1932

PILUMNIDAE
+ Pilumnus minutus (De Haan, 1835)

INCERTAE SEDIS
Daira perlata (Herbst, 1790)
Pseudozius caystrus (Adams and White, 1848)

PALICIDAE
+ Crossotonotus brevimanus (Ward, 1933)

OCYPODIDAE
OCYPODINAE
Ocypode ceratophthalma (Pallas, 1772)
Ocypode cordimana Desmarest, 1825
Uca chlorophthalmus (H. Milne Edwards, 1837)

MACROPHTHALMINAE
Macrophthalmus verreauxi H. Milne Edwards, 1848

GRAPSIDAE
GRAPSINAE

Geograpsus crinipes (Dana, 1851)
Geograpsus grayi (H. Milne Edwards, 1853)
Grapsus intermedius De Man, 1887
Grapsus tenuicrustatus (Herbst, 1783)
Metopograpsus thukuhar (Owen, 1839)

+ Pachygrapsus minutus A. Milne Edwards, 1873
Pachygrapsus cf. planifrons De Man, 1888
Pachygrapsus plicatus (H. Milne Edwards, 1837)

SESARMINAE
+ Cyclograpsus integer H. Milne Edwards, 1837

1 AD,22027

9(a),27

Loc. unrecorded
27

ISS 242732
6,30

19

1,2,6,10, West Island
1, West Island
2;

»

Nnww

)

,buoys(lagoon)

RAPENNNNS
—
Sa

LY
ON

Sesarma (Parasesarma) sigillata Tweedie, 1950
Sesarma (Parasesarma) lenzii De Man, 1895

NNW

+ Sesarma (Chiromantes) sp.
PLAGUSIINAE
Percnon abbreviatum (Dana, 1851) 12
a Percnon affine (H. Milne Edwards, 1853)
+ Percnon guinotae Crosnier, 1965 eg)
Percnon planissimum (Herbst, 1804) WHI)
Plagusia depressa tuberculata Lamarck, 1818 Buoys (lagoon)
VARUNINAE
+ Pseudograpsus albus Stimpson, 1858 6
Thalassograpsus harpax (Hilgendorf, 1892) 10
GECARCINIDAE
Cardisoma carnifex (Herbst, 1794) 2, West Island
ce Cardisoma rotundum (Quoy and Gaimard, 1824)
Gecarcoidea natalis (Pocock, 1888) Di
CRYPTOCHIRIDAE

+ Hapalocarcinus marsupialis Stimpson, 1859 4

>

i

ATOLL RESEARCH BULLETIN

NOS. 399-414

NO. 399. SCIENTIFIC STUDIES IN THE COCOS (KEELING) ISLANDS: AN INTRODUCTION
BY C.D. WOODROFFE AND P.F. BERRY

NO. 400. CLIMATE, HYDROLOGY AND WATER RESOURCES OF THE COCOS (KEELING)
ISLANDS
BY A.C. FALKLAND

NO. 401. LATE QUATERNARY MORPHOLOGY OF THE COCOS (KEELING) ISLANDS
BY D.E. SEARLE

NO. 402. _GEOMORPHOLOGY OF THE COCOS (KEELING) ISLANDS
BY C.D. WOODROFFE, R.F. MCLEAN AND E. WALLENSKY

NO. 403. . REEF ISLANDS OF THE COCOS (KEELING) ISLANDS
BY C.D. WOODROFFE AND R.F. MCLEAN

NO. 404. . VEGETATION AND FLORA OF THE COCOS (KEELING) ISLANDS
BY D.G. WILLIAMS

NO. 405. AN UPDATE OF BIRDS OF THE COCOS (KEELING) ISLANDS
BY T. STOKES

NO. 406. MARINE HABITATS OF THE COCOS (KEELING) ISLANDS
BY D.G. WILLIAMS

NO. 407. SEDIMENT FACIES OF THE COCOS (KEELING) ISLANDS LAGOON
BY S.G. SMITHERS

NO. 408. HYDRODYNAMIC OBSERVATIONS OF THE COCOS (KEELING) ISLANDS LAGOON
BY P. KENCH

NO. 409. _HERMATYPIC CORALS OF THE COCOS (KEELING) ISLANDS: A SUMMARY
BY J.E.N. VERON

NO. 410. _MARINE MOLLUSCS OF THE COCOS (KEELING) ISLANDS
BY F.E. WELLS

NO. 411. . ECHINODERMS OF THE COCOS (KEELING) ISLANDS
BY L.M. MARSH

NO. 412. FISHES OF THE COCOS (KEELING) ISLANDS
BY G.R. ALLEN AND W.F. SMITH-VANIZ

NO. 413. .BARNACLES OF THE COCOS (KEELING) ISLANDS
BY D.S. JONES

NO. 414. _DECAPOD CRUSTACEANS OF THE COCOS (KEELING) ISLANDS
BY G.J. MORGAN

ATOLL RESEARCH BULLETIN NOS. 415-425

RESEARCH
BULLETIN

Issued by

NATIONAL MUSEUM OF NATURAL HISTORY

SMITHSONIAN INSTITUTION
WASHINGTON, D.C. U.S.A.
AUGUST 1994

ATOLL RESEARCH BULLETIN

NOS. 415-425

NO. 415.

NO. 416.

NO. 417.

NO. 418.

NO. 419.

NO. 420.

TIKEHAU

AN ATOLL OF THE TUAMOTU ARCHIPELAGO (FRENCH
POLYNESIA)

PARTI. ENVIRONMENT AND BIOTA OF THE TIKEHAU ATOLL

(TUAMOTU ARCHIPELAGO, FRENCH POLYNESIA)
BY A. INTES AND B. CAILLART

PART Il. NUTRIENTS, PARTICULATE ORGANIC MATTER, AND
PLANKTONIC AND BENTHIC PRODUCTION OF THE
TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO, FRENCH
POLYNESIA)

BY C.J. CHARPY-ROUBAUD AND L. CHARPY

PART Ill. REEF FISH COMMUNITIES AND FISHERY YIELDS OF
TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)
BY B. CAILLART, M.L. HARMELIN-VIVIEN,
R. GALZIN, AND E. MORIZE

COLONIZATION OF FISH LARVAE IN LAGOONS OF RANGIROA
(TUAMOTU ARCHIPELAGO) AND MOOREA (SOCIETY
ARCHIPELAGO)

BY V. DUFOUR

CAVES AND SPELEOGENESIS OF MANGAIA, COOK ISLANDS
BY JOANNA C. ELLISON

SHALLOW-WATER SCLERACTINIAN CORALS FROM
KERMADEC ISLANDS
BY VLADIMIR N. KOSMYNIN

DESCRIPTION OF REEFS AND CORALS FOR THE 1988

PROTECTED AREA SURVEY OF THE NORTHERN MARSHALL
ISLANDS

BY JAMES E. MARAGOS

QUATERNARY OOLITES IN THE INDIAN OCEAN
BY C.J.R. BRAITHWAITE

NO.

NO.

NO.

NO.

NO.

421.

422.

423.

424.

425.

LARGE-SCALE, LONG-TERM MONITORING OF CARIBBEAN
CORAL REEFS: SIMPLE, QUICK, INEXPENSIVE TECHNIQUES
BY RICHARD B. ARONSON, PETER J. EDMUNDS, WILLIAM F.
PRECHT, DIONE W. SWANSON, AND DON R. LEVITAN

CHANGES IN THE COASTAL FISH COMMUNITIES FOLLOWING
HURRICANE HUGO IN GUADELOPE ISLAND (FRENCH WEST
INDIES)

BY CLAUDE BOUCHON, YOLANDE BOUCHON-NAVARO, AND
MAX LOUIS

THE SIAN KA'AN BIOSPHERE RESERVE CORAL REEF SYSTEM,
YUCATAN PENINSULA, MEXICO

BY ERIC JORDAN-DAHLGREN, EDUARDO MARTIN-CHAVEZ,
MARTIN SANCHEZ-SEGURA, AND ALEJANDRO GONZALEZ

DE LA PARRA

A PRELIMINARY EVALUATION OF THE COMMERCIAL
SPONGE RESOURCES OF BELIZE WITH REFERENCE TO THE
LOCATION OF THE TURNEFFE ISLANDS SPONGE FARM

BY J.M. STEVELY AND D.E. SWEAT

SPATIAL AND TEMPORAL VARIATIONS IN GRAZING
PRESSURE BY HERBIVOROUS FISHES: TOBACCO REEF,
BELIZE

BY PETER N. REINTHAL AND IAN G. MACINTYRE

NEWS AND COMMENTS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

ACKNOWLEDGMENT

The Atoll Research Bulletin is issued by the Smithsonian Institution to
provide an outlet for information on the biota of tropical islands and reefs and
on the environment that supports the biota. The Bulletin is supported by the
National Museum of Natural History and is produced by the Smithsonian Press. This
issue is partly financed and distributed with funds from readers.

The Bulletin was founded in 1951 and the first 117 numbers were issued by
the Pacific Science Board, National Academy of Sciences, with financial support
from the Office of Naval Research. Its pages were devoted largely to reports
resulting from the Pacific Science Board's Coral Atoll Program.

All statements made in papers published in the Atoll Research Bulletin are
the sole responsibility of the authors and do not necessarily represent the views
of the Smithsonian nor of the editors of the Bulletin.

Articles submitted for publication in the Atoll Research Bulletin should be
original papers in a format similar to that found in recent issues of the
Bulletin. First drafts of manuscripts should be typewritten double spaced and can
be sent to any of the editors. After the manuscript has been reviewed and
accepted, the author will be provided with a page format with which to prepare
a single-spaced camera-ready copy of the manuscript.

COORDINATING EDITOR

Ian G. Macintyre National Museum of Natural History
MRC-125
Smithsonian Institution
Washington, D.C. 20560

EDITORIAL BOARD

Stephen D. Cairns (MRC-163) National Museum of Natural History
Brian F. Kensley (MRC-163) (Insert appropriate MRC code)

Mark M. Littler (MRC-166) Smithsonian Institution

Wayne N. Mathis (MRC-169) Washington, D.C 20560

Victor G. Springer (MRC-159)

Joshua I. Tracey, Jr. (MRC-137)

Warren L. Wagner (MRC-166)

Roger B. Clapp (MRC-111) National Biological Survey

National Museum of Natural History
Smithsonian Institution
Washington, D.C. 20560

David R. Stoddart Department of Geography
501 Earth Sciences Building
University of California
Berkeley, CA 94720

Bernard M. Salvat Ecole Pratique des Hautes Etudes
Labo. Biologie Marine et Malacologie
Université de Perpignan
66025 Perpignan Cedex, France

PUBLICATIONS MANAGER

A. Alan Burchell Smithsonian Institution Press

ey eae ae Bevan Cul oper:

Noveuber 1996.

ANDRE GUILCHER 1913-1993

For over 40 years, André Guilcher was an eminent coastal
geomorphologist and marine geographer. He was born in Brest, France, received
his PhD from the Sorbonne in 1948, taught in several French universities and
retired from the Universitiy of Brest, with which he was affililiated, in 1981. He
served on many national and international editorial boards and scientific
committees, received numerous awards and honors and had been proposed for
the last Darwin Award.

He started work on coral reefs in the early 1950s, taking part in the first
Calypso expedition in the Red Sea. The discovery of reefs was one of immense
excitement for Guilcher, and permanently marked his future research work.
Subsequent field expeditions took him to Madagascar, Mayotte, New
Caledonia, French Polynesia, the Solomon Islands, Kiribati, Vanuatu, Lord
Howe Island, Florida, Sinai, the West Indies, Brazil, Kenya and elseware. The
results of his work were published in over fifty books and articles. One of his
later works was Coral Reef Geomorphology (Wiley, 1988), the first global
synthesis of the morphology and typology of reefs, and a thorough review of the
evolution of modern regional variations in reef structure and development. This
book was also significant in introducing into the international literature important
examples of reef geomorphology found in areas that are seldom visited by
English-speaking workers.

Guilcher assisted and influenced many people in the course of his long
academic career and was a model for many of his students. His scientific and
leadership skills and his integrity earned the respect of all his colleagues. These
and his many friends will greatly miss him.

Paolo A. Pirazzoli

ATOLL RESEARCH BULLETIN

NO. 415

TIKEHAU

AN ATOLL OF THE TUAMOTU ARCHIPELAGO (FRENCH POLYNESIA)

PART I.

ENVIRONMENT AND BIOTA OF THE TIKEHAU (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)

BY A. INTES AND B. CAILLART
PART If. NUTRIENTS, PARTICULATE ORGANIC MATTER, AND PLANKTONIC AND

BENTHIC PRODUCTION OF THE TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)

BY C.J. CHARPY ROUBAUD AND L. CHARPY

PART Il. REEF FISH COMMUNITIES AND FISHERY YIELDS OF TIKEHAU ATOLL
(TUAMOTU ARCHIPELAGO, FRENCH POLYNESIA)

BY B. CAILLART, M.L. HARMELIN-VIVIEN, R. GALZIN, AND E. MORIZE

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

FOREWORD

In 1982, ORSTOM, a french institution for the development of cooperation in scientific research
(Institut Francais de Recherche Scientifique pour le Développement en Coopération) launched
the program "ATOLL" in French Polynesia under the dynamic leadership of André INTES,
who built up the program while going on with his own research on pearl oyster.

The launch of this program took place in a historical context of scientific research and of
institutional specialisms. Research on coral ecosystem in French Polynesia had started to
develop at the end of the nineteen-sixties and the beginning of the seventies (Research on the
atolls of the south-east of Tuamotu was carried out in liaison with the Direction des Centres
d'Expérimentations Nucléaires and the implementation on Moorea in the Society Islands, of
the antenne Museum EPHE Research Center). In 1974, research started under the auspices of the
MAB program (Man and Biosphere) of UNESCO, an interdisciplinary program for ecology and
the rational use of insular ecosystems. The objectives of that program were, even at that time
(20 years ago), to specify the exact, natural and social sciences, which were the necessary basis
for the rational use and conservation of island ecosystems. The two islands of Moorea and
Takapoto were selected. A large number of natural, social and medical research organisations
from both mainland France and the French Territories participated in the work. A great many
reports (1, 2, 3, 4) were produced on these two ecosystems whose coral reefs are among the most
studied and documented in the world.

With the program "ATOLL", ORSTOM started in 1982 its study of the Polynesian coral reef
ecosystem. The choice of Takapoto Atoll was made by the legislature of the Territory in 1973
when the pearl industry was developing, and at the request of scientists. For scientific reasons
the latter had asked for the selection of a closed atoll which had no pass : there is less
complexity in studying such a lagoon thus giving the best approach to the scientific work. The
choice of Tikehau by ORSTOM for the siting of a field station and the development of
programs was due to the fact that it was necessary to select an open atoll with a pass to go
further in the study of (1) a small scale fishery and (2) the assessment of the exchanges
between the lagoon and the ocean. It is in this context that research was developed on Tikehau
between 1982 and 1987, research by scientists from ORSTOM and by other organisations
working in collaboration with them, and research which has proved to be very beneficial.
This station is still in existence with an on-going program, "CYEL" (Energy and Matter Cycles
in Atoll Lagoons) having followed on from "ATOLL".

In a document edited by ORSTOM, André INTES and his collaborators (5) have already
described in minute detail their activities on Tikehau during this five years period. It has now
become necessary to condense this information into synopses which are to be published in
English. Such is the objective of the three aticles which follow. The first (by A. INTES and B.
CAILLART) describes the nature and human environment of the atoll, detailing its
characteristics. This contribution is well suitable for publication in Atoll Research Bulletin,
now the most important reference for useful descriptions of atolls all over the world. The
second article by C.J. CHARPY-ROUBAUD and L. CHARPY deals with matter and energy
budgets for Tikehau's coral reefs. This subject is very topical: what about nutrient enrichment
for coral reef lagoons and atolls? what about autotrophy and eutrophication due to human
activity? The third one by B. CAILLART, M.L. HARMELIN-VIVIEN, R. GALZIN and E.
MORIZE presents all the available information on the fish fauna of the atoll lagoon and outer
slope, including the communities and yields. Such an account is necessary when looking at the
managment of fishing, recruitment, and the movement, or not, of populations between islands.

Bernard SALVAT

Moorea and Perpignan, march 1993.

References

(1) SALVAT B. and J. FAGES, 1977 - Takapoto, Tuamotu, Polynésie Francaise. Programme MAB-
UNESCO - Compte rendu de recherches 1974-1976. Document roneo, Papeete, march 1977, 150 pp.

(2) SALVAT B., 1988 - Bibliographie de l'atoll de Takapoto, archipel des Tuamotu. Bull. Soc. Et.
Océaniennes, Papeete, Tahiti, 243 : 55,60

(3) OFAI, 1989 - Bulletin de liaison Centre de l'Environnement Antenne Muséum EPHE de
Moorea: 1, 188

(4) INTES A. (ed.), 1991 - Ecosystémes de lagons de la Polynésie Francaise. Rapports et Etudes du
PNUE sur les mers régionales n°137, PNUE, 1991 et SPREP Rapports et Etudes n°51,
Programme régional océanien de l'environnement, 1991, 298 pp.

(5) INTES A., CHARPY-ROUBAUD C,J., CHARPY L., LEMASSON L. and MORIZE E., 1990 - Les lagons

d'atolls en Polynésie Francaise : Bilan des travaux du programme "ATOLL". ORSTOM-Tahiti, Notes
et Doc. Océanogr., 43 : 1,136

Manuscript received 8 April 1992; revised 30 April 1993

ACKNOWLEDGMENTS

All the work done on the field would not have been possible without the kind hospitality and
active cooperation of the population of TIKEHAU. It is a great pleasure for the editors to
dedicate this volume to the people of this atoll.

Many scientists from different institutions contributed to the program "ATOLL" in a friendly
collaboration. They came mainly from Centre National de la Recherche Scientifique (CNRS),
Ecole Pratique des Hautes Etudes (EPHE), Museum National d'Histoire Naturelle de Paris
(MNHN), Institut Francais de Recherche pour I'Exploitation de la Mer (IFREMER), Service
Mixte de Contréle Biologique (SMCB), but also from the ORSTOM center of Nouméa (New
Caledonia). Most of them became our friends.

The preparation of the report involved few people who gave unrestricted thought and time to
bring this collective work into publication.

We wish to extend our thanks to all of them, listed below, regardless of the nature of their
contribution. Some of them may have been overlooked, and we apologize for these unfortunate
oversights.

Arnaudin H. Blanchet G. Blanchot J. Bonnet S.
Bourrouilh-Le jan F. Cremoux J.L. Faure G. Florence J.
Galzin R. Harmelin-Vivien M. Jamet R. Laboute P.
Le Borgne R. Lenhardt X. Moll P. Monnet C.
Monniot C. Monniot F. Orempuller J. Paoaafaite J.
Peyrot-Clausade M. Poulsen M. Poupet P. Saliot A.
Sandstr6m M. Sarazin G. Sodter F. Teuri J.
Trichet J. Vigneron E. Villiers L.

edited by

André INTES'~ - Senior Editor

Benoit CAILLART

Loic CHARPY

Claude J. CHARPY-ROUBAUD
Lionel LEMASSON
Eric MORIZE

PART I. ENVIRONMENT AND BIOTA OF THE TIKEHAU ATOLL
(TUAMOTU ARCHIPELAGO, FRENCH POLYNESIA)

BY

A. INTES AND B. CAILLART

THE REGIONAL BACKGROUND

The islands of French Polynesia are scattered throughout a considerable oceanic area located on
the eastern boundary of the Indo-Pacific Province. This area stretches from 134°28' W (Temoe
Island) to 154°40' W longitude (Scilly Island), and from 7°50' S (Motu one Island) to 27°36' S
latitude (Rapa Island). Out of the 118 islands constituting French Polynesia, 35 are high
volcanic islands and 83 are low-relief islands or atolls. Altogether, the territory of French
Polynesia represents an area of 4000 km2 of dry land, 12,000 km? of lagoonal water and a huge
Exclusive Economic Zone (EEZ) covering 5,500,000 km2 of oceanic water (Gabrie and
Salvat, 1985).

French Polynesia is divided into five archipelagos all oriented parallel to a northwest-
southeast axis (Fig. 1). These are the Society archipelago, the Tuamotu archipelago, the
Austral archipelago, the Marquesas archipelago and the Gambier archipelago.

The Tuamotu archipelago stretches over a distance of 1800 km. Its 76 atolls cover a total area of
13,500 km2 of which 600 km2 are dry land.

GEOLOGY OF THE TUAMOTU ARCHIPELAGO

As figured by Montaggioni (1985), the Tuamotu atolls cap the top of cone-like volcanoes which
rise steeply from the floor of a huge ridge forming wide shelves ranging in depth from 1,500 to
3,000 m. Geomorphological and geochronological evidences support the fact that the formation
of the Tuamotu chain is much older than that of other neighboring islands of French Polynesia.
The foundations of extinct volcanoes appear to have been simultaneously, and not sequentially,
active for at least the Northwestern Tuamotu chain. The existence of a massive submerged
' ridge and the lack of high volcanic islands are in accordance with average ages found out by
the Deep Sea Drilling Project (summarized by Clague, 1981 and Schlanger, 1981) : reef debris of
the early to late Eocene (50-51 mybp) have been sampled in two holes drilled on the
northeastern flank of the Tuamotu archipelago and on the ridge itself. The occurrence of these
fossils leads to the conclusion that vulcanism would have stopped between late Cretaceous and
early Eocene for at least the northwestern part of the Tuamotu chain. The large number and the
close-spacing pattern of the Tuamotu atolls are indicative of their origin in shallow waters
close to the East Pacific ridge.

Centre ORSTOM de Brest, B.P. 70, 29280 Plouzané, France

ue: “Motu One

Ratu hi
Noku Hive oe =a Hoke
Fatu Huku
° .
Md ew hive Os
Tehuals # + Mohotani
4 “Motu Nao

”)
S

TIKEHAU ii Tele epuha
ARCHIPE; vane Wr oo d

LES SOUS d Beene

Joa, Kavehi Takume, OFangaiau
EQ sphaata —Taengs PRaroia € oo Fokahne
any Siw Ma vf
ORES AS TepaTOISR Rebate

Anas Motutungs Sete ol _Tevere alatakoto

‘16°

Nau
Fake

Anuanurunga~ - Nukutepipi Vanavana, Turew

Tenararo Tenor
Vahanga sein Marutea(S)
> Mowuroa tureivavad

“Mana
ILES GAMBIER

lematang:

eFangateuta

© JCJ ORSTOM TAHITI. 025/03-85

Fig. 1 : Map of French Polynesia and location of the Tikehau atoll, Tuamotu -

3

In the northwestern Tuamotu, several atolls (including Tikehau), located in the vicinity of
recently active volcanoes (Tahiti, Moorea, Mehetia), have been lifted up. Lambeck (1981)
pointed out that the tectonic uplift of these atolls was a result of the loading effects of the
nearby Tahiti volcanic complex. The magnitude of uplift was a few ten meters with respect to
present sea level, without considering the unusual case of Makatea which, located near the
center of the load, has its highest point 133 m above present sea-level. Since age dating of the
oldest volcano (Moorea) is around 1.5 mybp, the tectonic uplift of atolls is thought to have been
initiated in early Pleistocene.

At Tikehau, the magnitude of uplift can be related to the present day elevation of the numerous
old reef remnants (locally termed Feo) that stand on the atoll rim (Plate 1). Feo are highly
recrystallized and dolomitized old reef remnants, that witness a long period of subaerial
weathering. Although there is insufficient evidence to accurately date the Feo, a comparison
with analogous structures on Makatea confirms their emergence in the early Pleistocene
(Pirazzoli and Montaggioni, 1985). On the southern shores of Tikehau, Feo can be as high as 12m
above present sea-level. Many other lower Feo are located on the eastern and western reef flats.

Studies from Holocene fluctuations in sea level can be useful in interpreting individual reef
histories. In Tikehau as well as in most of the islands of French Polynesia, cemented coral reef
conglomerates, often found around islands and alongshore shallow channels, and notches,
undercutting Feo near their bases are evidences to support a higher-than-present relative sea
level between 5200 and 1200 ybp. This higher sea level may have been 0.9 m greater than the
present sea level. In this region, the lowering of the sea level near to its present datum is
thought to be a very recent phenomenon which has occurred not earlier than around 1200 ybp.

GENERAL OCEANOGRAPHY OF THE TUAMOTU ARCHIPELAGO

Current and oceanic water characteristics

Tikehau, as all the northwestern parts of the Tuamotu archipelago, resides in the South
Equatorial Current. The current has a general westward drift between 40 to 50 cm s-! down to
200 m depth, steady throughout the year. The southern boundary of the current moves
northward during the southern hemisphere summer and shifts back toward the south in winter.
Currents near the atolls may vary in both speed and direction due to the dynamic topography
and rather permanent eddies probably exist, though their occurrence has never been
demonstrated in French Polynesia.

In the south of the northwestern part of the Tuamotu archipelago, variations in the current
directions are considerable and may influence to some extent oceanographic patterns around
Tikehau. Rougerie and Chabanne (1983) pointed out that during the summer, the current in the
vicinity of Tahiti may be an extension of the South Equatorial Countercurrent which originates
in the Solomon Sea and has a general eastward-southeastward drift. The salinity is low
(34.8 %o) reflecting the annual net rainfall in the South Pacific Convergence Zone (SPCZ)
which occurs along a Solomon-Samoa-Tahiti line at this time of year. During winter, the SPCZ
shifts northward and the trade winds strengthen somewhat over the Tahiti region. The current
flows westward carrying high salinity water (36.4 %o) drawn from the Central Pacific barren
zone where evaporation exceeds precipitation by 50 cm per year (Rougerie, 1981).

Surface water temperature varies seasonally in a spread of 25.5°C to 29°C and reaches an
average value of 28°C. The main thermocline is weak and is located between 400 and 600 m in
depth with a temperature of 10°C at 400 m. By 1000 m, the temperature drops to 3°C.

4

Chemical data for ocean water (summarized in Table 1) show that the ocean surrounding the
Tuamotu archipelago is nutrient-poor and is actually one of the poorest oceans in the world. For
example, the average copepod surface population living in that oligotrophic environment is of
20 individuals m-3 near the surface while it is between 50 and 80 between New-Caledonia and
Tonga, greater than 100 in the south of the Coral Sea, reaches 300 at the equator and exceeds
1000 to the south of Galapagos Islands.

Table 1 : Average chemical data for ocean water (0 to 100 m in depth) in the Tahiti zone. (DOM :
Dissolved Organic Matter, chl a : Chlorophylle a, PProd : Primary Production, * : data measured
during winter of southern hemisphere, ** : data measured in summer). Adapted from Rougerie
and Wauthy (1985).

Temp Sal PO4P NO3N _ SiO3 DOM chl a PProd
(°C) (%o) (mmoles m-3) mg m-3 gCm2g-1
25.5% 36.4*
Ocean 0.25 0.10 1.0 0.5 0.1 30

29.0% 34.8**

Waves and Tides

Waves in the Tuamotu archipelago are mostly from the east, a consequence of persistent trade
winds. Waves are generally between 1 and 3 m high, breaking at a 6 to 9 s period. Swells from
distant storms can reach the Tuamotu and create a different situation in which shores exposed
to the swell (which can be either windward or leeward) are heavily pummeled, whereas the
waves produced by the wind in the immediate area may be small. Northern hemisphere storms
that occur in the Alaskan gulf during summer of the southern hemisphere generate waves from
north-northwest which are generally about 4 m high and break at a period between 10 and 18 s
on Polynesian shores. In winter, southern hemisphere storms generated in the lower southern
latitudes may send associated waves to the Tuamotu zone. These 7 to 10 s period waves can
exceed 3 m high and reach the southeast shores of the islands. Several cyclones and near-
cyclones have passed by or over the Northwestern Tuamotu in 1982 and 1983. These storms have
produced waves greater than 10 m high from various directions related to the storm track.

The tides at Tikehau are usually in good agreement with the French Navy (SHOM) tide table
established for Tahiti. However, ocean tide records at Tikehau show differences in timing. The
time-lag between the tide at Tikehau and the tide at Tahiti is approximately 72 hours. The
amplitude of spring tides is only 15 cm in the vicinity of Tikehau whilst neap tide amplitude is
almost zero. Spring tides occur three days before the new moon and the full moon.

WEATHER AND CLIMATE

The Tuamotu archipelago lies in the tropical oceanic climate area. It has a distinct wet-dry
annual cycle. The wet and hot season occurs from November through April and the dry and cold
season from May to October. Since all of the islands are low and of a small area, they do not
alter weather conditions by their presence. Data presented hereafter were provided by the
National Meteorological Station of Rangiroa, except when otherwise mentioned as no weather
records are available at Tikehau. Weather conditions have been recorded continuously from
1972 onward by this station.

Air Temperature

Average air temperature on a monthly basis for the 1972-1985 period ranges from 25.5 °C in
August to 27.5 °C in March. There is little variation in these quantities through the year.
Extreme temperatures have been recorded but provide little additional information since they
rarely occur. The absolute minimum value recorded was 18 °C and the maximum 32 °C.

Wind

A summary of surface wind data is shown in Fig. 2. Tikehau is within the trade wind belt with
a nearly consistent easterly wind. During much of the year, the wind blows from northeast to
southeast 70 % or more of the time (i.e. 250 days/year). From June to September average wind
speed increases slightly but rarely exceeds 6 of the Beaufort scale.

The occurrence of wind from west around to north is very low. The maximum frequency is in
November, December and January when the South Pacific Convergence Zone is closest on the
average and subsequently, disturbances most common.

Tropical storms and cyclones strike Tikehau infrequently, mostly during the wet season. An
average of four cyclones per century is likely to occur in this area.

Precipitation, evaporation

The rainfall distribution throughout the year is shown in Fig. 3. The annual average rainfall of
1780 mm is not distributed uniformly throughout the year as about 65 % comes during the wet
. season. The maximum monthly average value is 229 mm in January and the minimum 75 mm in
August. The variability of rainfall is high from year to year and data presented should be
considered only as a general trend.

Evaporation reaches an average of 1800 mm a year and balances precipitation, as measured by
the National Meteorological Station of Mururoa. Maximum evaporation takes place in
December, January and February (179 mm, 193 mm and 188 mm), minimum values in June, July
and August (109 mm, 109 mm and 124 mm).

Frequency of calms : 37%

wee Wind speed greater than 5 m s-1|
Wind speed below 5 m s-1

Frequency scale
ty

) SO */ee

Fig. 2 : The yearly mean of surface wind data recorded at Rangiroa (Rangiroa is located 30 km to the
east of Tikehau). Data provided by Meteorologie Nationale, Tahiti-Faaa.

Rainfall (mm)
250

200

150

100

10

J F M A M J J A S O N D
Vea

Fig. 3 : Average rainfall amounts for each month recorded at Rangiroa (Rangiroa is
located 30 km to the east of Tikehau). Data provided by National Meteorological
station of Tahiti-Faaa.

LOCATION AND SIZE OF TIKEHAU ATOLL

Atolls can be described as more or less continuous coral reefs (corals or other calcium carbonate
producing organisms) which surround a deeper lagoon and drop steeply to oceanic depth on the
seaward margin. All islands are typically low with soil derived primarily from reef rubble
and sand.

Although almost identical in their general shape, atolls of the Tuamotu archipelago are
different by the characteristics of their lagoon and the number of passes on which depends the
amount of water circulation. As shown in Table 2, a few atolls have one or two passes and are
termed open atolls, most have no pass and are termed closed atolls, four atolls have a dry
lagoon, filled up by reef detritic and are termed filled atolls, one island, Makatea, has been
uplifted by tectonic movements probably linked with the formation of Tahiti and is termed a
raised atoll. Lastly, Portland is a submerged atoll .

Table 2 : Classification of the atolls of the Tuamotu archipelago
based on the geomorphological characteristics of their lagoon.

Atoll group Example
Open atolls with more than one pass Rangiroa
Fakarava
Toau
Open atolls with one pass Tikehau
Mataiva
Arutua
Closed atolls Takapoto
Hikueru
Reao
Filled atolls Akiaki
Nukutavake
Tikei
Raised atoll Makatea
Submerged atoll Portland

Tikehau has a large somewhat elliptically shaped lagoon, numerous shallow channels cutting
the reef flat especially on the windward side, one pass between the lagoon and ocean, and
narrow shelves dropping steeply into deep sea on all sides. A succession of small islands,
locally termed Motu, constitute the dry land.

8

Tikehau is located in the northwestern Tuamotu archipelago with its center at 15°00'S and
148°10'W (Fig. 1). It is approximately 300 km from Tahiti to the south, 30 km from Rangiroa to
the east and 20 km from Mataiva to the west. By French Polynesia standards, Tikehau is a
relatively large elliptical atoll, about 20 km by 28 km in size, covering a total area of about
420 km2 . Among the 76 islands of the Tuamotu archipelago, Tikehau is the 11th largest. It is
exceeded, among others, by Rangiroa (1640 km2 ), Fakarava (1220 km2 ) or Makemo (910 km2 ),
the three largest islands. Small atolls are generally a pattern of the Tuamotu since 45 out of the
77 islands cover less than 100 km2 (Mataiva :50 km2, Taiaro : 14 km2, Tikei : 4 km2 ).

THE TERRESTRIAL ENVIRONMENT

Since few scientists conducted research in the terrestrial environment with respect to the
marine environment of the Tikehau atoll, little is known about this part of the ecosystem. This
section contains a review of what is known about atoll soils and associated vegetation, reports
on the terrestrial fauna (birds and other vertebrates), and finally provides an overview of
Tikehau human population evolution over the last century. Information is drawn from Jamet
(1985) for soils, Florence (1985) for vegetation, Poulsen et al. (1985) for avifauna, and Sodter
(1985) for human demography.

SOILS AND VEGETATION

Tikehau soils exclusively originate from the alteration of a mother rock made up of reef
forming or reef living organisms. The micro-splitting of particles mostly through chemical
processes leads to the formation of clay or carbonated silt in which the percentage can reach
40 % in sandy soils. Carbonates accumulate above the upper zone of the groundwater lens
forming a calcareous crust. Organic matter is usually mixed with fine materials in a topsoil
horizon fairly thick but it can also accumulate superficially in marshy depressions. Following
these alteration processes, Tikehau atoll soils fall into four types :

- Rough mineral soils formed of accumulations of unaltered recent sediment.

- Weakly developed soils made up of coarse materials with low content of organic matter, found
mostly on the oceanic shoreline of the island.

- Magnesium-calcite soils with a dark, developed A horizon more or less thick and with
variable organic matter content. This kind of soils covers the majority of the islands at
Tikehau.

- Marsh soils very rich in organic matter, located in island floor depressions (Plate 2).

Unlike high island soils, atoll soils almost lack silica, aluminium and iron. The mineralogy is
almost exclusively calcium carbonate ( 80 to 95% of calcite and aragonite) which fine soluble
particles represent 3 to 5 % in rough soils, more than 20 % in humus horizon, and exceed 30 % in
marshes. Magnesium carbonate represents less than 1 %. Potassium and phosphorus content are
generally less than 0.05 % in subsoils but fecal matter of birds and vegetation remains locally
contribute to a ten fold increase in K and P concentrations of topsoils. Sodium concentration is
lower (0.5 %) than expected in this kind of ecosystem.

The fertility of atoll soils is almost entirely dependant on the content of organic matter.
Accounting for less than 2 or 3 % in rough soils, organic matter can reach 15 % in humus horizons
and much more in marshy areas. Organic matter not only carries out the normal role of soil
organic matter in storing and recycling nutrients, but it is also the major moisture storage
component in the soils, since coral sands and rocks have an extremely limited moisture storage
capacity. This is all important in atolls where evaporation exceeds precipitation eight months

9
of the year. Organic matter lowers pH which ranges between 8 and 9 in subsoils. The pH is
almost neutral in topsoils, leading to a better nutrient assimilation.

Atoll soils have considerable influence on the composition of vegetation. There is a marked
gradient from the beach toward the center of the island.

- Unaltered rough sediment soils are constantly rearranged and do not enable settlement of
durable vegetation.

- Weakly developed soils constituted by coarse materials oceanward and fine sands lagoonward
have a low organic matter content in the first 10 or 20 cm, forming patches or stretches. Two
types of vegetation settled there :

Vegetation of the oceanic side of the island is a low and open assemblage of Guettarda speciosa,
Scaevola sericea and Tournefortia argentea. Behind the beach, the assemblage gets richer with
Euphorbia atoto, Timonius polygamus and Pandanus tectorius. On cemented coral substrata,
Pemphis acidula forms bushes and on sand patches, Suriana maritima and Lepturus repens
develop.

Vegetation of the lagoon side of the island is still well represented eastward the atoll whereas
it was cleared by coconut plantations in other places. Bush assemblage is dominated by Suriana
maritima and Scaevola sericea, but Guettarda speciosa and Tournefortia argentea occur
sporadically. The herbaceous stratum is varied with Triumfetta procumbens and Lepturus
repens dominating.

Magnesium calcite soils (found in the center of the island) cover the area of the forest.
Although coconut plantation cleared much of the original vegetation, two facies can be
distinguished :

- On weakly developed soils, Pandanus tectorius dominates the tree stratum along with
Tournefortia and Guettarda. Among the bush, Scaevola sericea, Pipturus argenteus and
Timonius polygamus were recorded. Herbaceous vegetation is rare : Psilotum nudum, Cassytha
filiformis and Nesogenes euphrasioides were recorded nonetheless.

- On sandy soils, the original forest of Pisonia grandis has almost disappeared whereas
Guettardia speciosa still occurs. Bushes are made up of Pipturus argenteus, Morindia citrifolia
or Euphorbia atoto. The herbaceous stratum is varied with Achyranthes velutina, Laportea
ruderalis, Digitaria stenotaphrodes, Boerhavia tetrandra.

Coconut plantations

Sand and gravel soils which are the most favourable for coconut agriculture have been planted
mostly during the last century. The western coast has coarse substratum only allowing coconut
trees to be planted on the lagoon side of the islands. From place to place, components of the
original vegetation are encountered such as Guettarda speciosa, Pisonia grandis or Pandanus
tectorius for trees, Euphorbia atoto or Morinda citrifolia for the bush, Lepturus repens,
Boerhavia tetrandra and Triumfetta procumbens on the ground.

Feo vegetation

Feo are located north of the island supporting the main village and surrounded by coconut
plantations. Being as high as 7 meters, they present a compact substratum with a low moisture
storage capacity, and tiny soils in small caves. Tree stratum is composed of Pandanus tectorius
and Thespesia populnea. Bush is made up of Pipturus argenteus, Euphorbia atoto and rarely
Capparis cordifolia. On the ground, Lepturus repens and Triumfetta procumbens were recorded
but also ferns such as Asplenium nidus, Nephrolepis biserrata or Phymatosorus grossus.

In a hydromorphic depression, vegetation is a Cyperaceous assemblage. Cladium jamaicense is

so overwhelmingly dominating that the assemblage is almost monospecific, reaching 3 m high.
On the edges of the marsh, Mariscus pennatus and Eleocharis geniculata are found.

10

THE TERRESTRIAL FAUNA

Avifauna

Sedentary terrestrial species widespread in all atolls are Tuamotu warbler (Acrocephalus
atypha) of which 150 pairs were counted at Tikehau, at least 10 pairs of green pigeon
(Ptilinotus coralensis), between 150 and 200 individuals of pacific reef heron (Egretta sacra).
Tuamotu loriket (Vini peruviana) resides in a few atolls of western Tuamotu and breeds on
Tikehau on western islands. About 20 pairs were counted. Sooty crake (Porzana tabuensis) was
observed in the marshy area of the island supporting the village. New Zealand cuckoo
(Eudynamis taitensis) is the only migrant species exclusively terrestrial sighted in autumn
(May).

Shorebirds : especially present in winter of southern hemisphere, the most readily observable
species are lesser golden-plover (Pluvialis dominica), bristle-thighed curlew (Numenius
tahitiensis), wandering tattler (Heteroscelus incanus). Less abundant though regular visitors of
Tikehau, ruddy turnstone (Arenaria interpres), sanderling (Calidris alba) and pectoral
sandpiper Calidris melanotos account.

Seabirds : Red-footed booby (Sula sula) forms some small nesting colonies in trees (Pisonia
grandis). Brown booby (Sula leucogaster) and frigatebirds (Fregata ariel and great frigatebird
Fregata minor) regularly occur but no breeding evidences were recorded. Terns are well
represented with gray-backed tern (Sterna lunata) of which a 20 pairs nesting colony was
sighted, sooty tern (Sterna fuscata) which seems only vagrant, great crested tern (Sterna bergii)
of which about 50 pairs nest on the atoll, blue tern (Procelsterna coerulea) of which a few pairs
are supposed to nest at Tikehau, the very common brown noddy (Anous stolidus) of which 1500
nests were censused in small trees (Pemphis, Tournefortia), 800 nests of black noddy (Anous
tenuirostris ) in trees (Pisonia, Guettarda), and lastly a nesting population of 3000 individuals
of white tern (Gygis alba).

Other seabirds as petrel (Pterodroma rostrata) and skua (Stercorarius pomarinus) sometimes
approach Tikehau.

Other vertebrates

Except marine green turtle (Chelonia mydas), reptiles reported to occur at Tikehau are lizards
azure-tailed skink (Lygosoma cyanurum) which occurs in sunny forest floor, and house gecko
(Hemidactylus frenatus). Among mammals, rodents are best represented with polynesian rat
(Rattus exulans) and Norway rat (Rattus norvegicus). Some domestic cats returned to the wild
were seen wandering in coconut plantations and marshes.

11

PEOPLE OF TIKEHAU, PAST AND PRESENT

Tikehau could have been one of the atolls discovered by Turnbull in February 1803 when he was
sailing from Tahiti to Hawaii, but neither positions nor name were given. In 1816, Otto von
Kotzebue, Russian master of the "Rurick" first identified the atoll of Tikehau and gave it the
name of one of his shipmates : "Krusenstern". In May 1848, the atoll was once again described by
a trader, Lucett. Given the poor knowledge of the danger of the island, none of those first
discoverers attempted to land and as a result, nothing is known about the population during this
period. However, archeological remains of the past (marae) attest that Tikehau was
inhabited at the time of the Christ. In all probability, age dating of the sites would push the
date for settlement of Tikehau further back in time.

The first information on the total number of inhabitants was given in 1862. Ten persons were
counted but this total is probably unrealistic because the census method did not take into account
the frequent seasonal movements of the population around the island.

In 1902, an official census made by French Authorities gives a total of 156 inhabitants for both
Tikehau and Mataiva. The following census in 1911 gives a total of 95 inhabitants on Tikehau
and 58 on Mataiva. Until the end of World War II, no information on Tikehau and Mataiva
population is available. In 1946, 376 persons had been registered on both Mataiva and Tikehau.

From 1950 to 1983

From 1950 on, census at regular intervals allow to follow population variations. Census
reliability depends however on how the important mobility of the population is taken into
account. Census methods sometime tend to overestimate the population by counting a single
person twice (in 1956 for instance).

As illustrated by information displayed in Table 3, the level of the population of Tikehau in
1983 is slightly the same as in 1951 though the total population of French Polynesia doubled
meanwhile. Trends in population variation are difficult to analyse without precise individual
information on place of birth and location of main home.

Table 3 : Variations of Tikehau, Mataiva, both Tikehau and Mataiva, and French Polynesia
populations between 1946 and 1983. All census were made by French Authorities. Results of 1956
census are to be interpreted very cautiously since census method tends to over-estimate the
actual population by counting some single person twice.

1946 1951 1956 1962 1967 1971 1977 1983

Tikehau -- 259 349 275 287 246 266 279

Mataiva -- 126 241 162 138 147 178 183

Both 376 385 590 437 425 393 444 462
French

Polynesia 55,424 62678 76,327 84551 98,378 119,168 137,382 166,753

12
The Population in 1983

A typical feature of the population of Tikehau , like of the population of French Polynesia, is
the high proportion of young people : 28.7 % of the population is less than 10 years old and
52.7 % less than 20. The worker age class is very low, especially between 30 and 39 which
represents only 5 % of the population.

The high migratory rate of the population, the main source of difficulties to accurately
measure the population, is confirmed by the proportion of Tikehau inhabitants (21 %) having
spent more than six months in a row in another district of French Polynesia. For 91 % of the
people having moved, the island of Tahiti is the main destination, and 70 % of the 91 % go to
Papeete.

The working population is composed by 90 persons, 76 men and 14 women. Among the 76 men, 50
put up with copra production, 14 are fishermen, 9 are artisans, 2 are employed by the
government and 1 is administrative officer. Among women, 8 are administrative officers, 3 are
shopkeepers and 3 are artisans ; 3 men and 33 women have declared to be looking for a job.

Conclusion

The main characteristics of Tikehau population are:

- High proportions of young people under 20 years old and, as a consequence, low proportions of
people in the worker age class.

- High migratory rate.

- Men professional activities primarily oriented toward agriculture, especially copra
production. Women professional activity is low but high employment request exists.

13

THE MARINE ENVIRONMENT

PHYSIOGRAPHY OF THE MARINE AREA

Definition of reef units

In order to classify reef units of the atoll, Faure and Laboute (1984) described three main types
of reef units as follows :

- Compartments defined on a physiographic basis
- Zones assessed on a morphological basis
- Zones divided into biota according to bionomic field data

The three compartments are the outer slope, the reef flat, and the lagoon formations. A fourth
virtual compartment termed morphological discontinuities grouping pass and shallow channels
is also studied. Fig. 4 lists the different units classically found around an atoll.

BIOTA ZONES COMPARTMENTS

Lower part >60-70 m | )
Middle part 35-60 m_ | Deep slope 25-75 m |
Upper part 25-35 m i) |

Lower part 15-25 m_ ) outer terrace 10-25m | OUTER SLOPE
Upper part 0-15 m )

Fore reef platform 4-10m_) Fore reef area 0-10 m
Spur and groove zone 0-4 m
Algal ridge

Submerged reef flat

Inner flat

Inner slope

outer reef flat

inner reef flat
inner slope

Coral patches

Upper zone 0-2 m
Middle zone 2-6m
Lower zone 6-15 m
Pass

Gutter (or Hoa)

Low depth coral patches
Pinnacles

Pass and Hoa MORPHOLOGICAL

DISCONTINUITIES

We eS i Se FS ess SS SS

)
)
)
)
Down slope reef patches )
|
|
)
)
)

Fig. 4 : Inventory and repartition of the different atoll units (from Faure and Laboute, 1984),

14
The outer slope

The outer slope is the seaward part of an atoll which drops more or less steeply to oceanic
depth. In Tikehau, the outer slope is divided into three zones :

- The fore reef area located between 0 and 10 m depth. This zone itself is subdivided
into the spur and groove zone (0-4 m) and the fore reef platform (4-10 m). The spur and groove
system is a succession of reef fingers projecting seaward where the waves break, oriented
perpendicular to the reef front. Spurs are relatively flat on top. Their width ranges from 8 to
12 m with a low slope gradient of 2 to 4°. Grooves are shallow (1 to 3 m) and relatively narrow
(2 to 3 m). The walls of the grooves are sub-vertical and their bases are floored with cobbles and
dead coral boulders, precluding the development of any significant sessile benthic life
(Plate 4). Just seaward of the spur and groove, the bottom flattens somewhat with the fore reef
platform.

- The outer terrace begins at a depth of 10 m with a distinct change from a gentle slope
of a few degrees to an angle of approximatively 45 °. It presents an irregular surface with small
periodic shallow grooves oriented parallel to the slope direction, well distinguished from the
spur and groove formations described above. This structure could be considered as an old spur and
groove system (Chevalier, 1973).

- The deep slope (or drop off) begins below 25 m at an angle often greater than 45°.
According to coral community distribution, the slope can be separated into three biota : the
upper part (25-35 m), the middle (35-65 m) and the lower part from 70 m downwards.

The reef flat

The outer reef flat begins seaward by the algal ridge and ends lagoonward by the emerged
conglomerate or the island. On leeward reef, the algal ridge is low (20 cm above low tide level)
and has a width of 10 m while on windward shelves, the algal ridge is larger (30-40 m) and
higher (40 cm above low tide level). Numerous deep grooves (1-3 m) extend across the
windward algal ridge. Just inshore of this formation, a slight depression of the reef flat can
occur, especially on the windward sides of the atoll. To this follows an emerged hardened
conglomerate which can be considered as the remains of a past algal ridge. As shown in Fig. 5,
the outer reef flat morphology varies considerably in different area, particularly between the
windward and the leeward sides. Its width ranges from 150 to 180 m as measured on West-
Southwest transects to 20 to 40 m on eastern shores. It consists of an area of rock pavement
derived from an old conglomerate submerged under 10 to 50 cm of water with a rough bottom,
pitted by small erosional pools. The floor is covered by a thin sedimental detritic layer that
get thicker toward the beach.

The inner reef flat begins just lagoonward of the motu or the emerged conglomerate, and ends
where the bottom starts to slope into the lagoon. The width of the inner reef flat varies
considerably around the atoll rim. On windward shores, the inner lagoon margin flat is
protected from trade winds by the outer reef flat, the motu and its associated vegetation. The
inner reef flat is therefore somewhat dead and resembles a slight sandy slope. A different
situation exists on the lagoon border in the lee of the atoll. Because of exposure to trade wind
across the fetch of the lagoon, these areas are well-formed reef flats composed of an old
conglomerate covered by a thin sedimental layer that gets thicker lagoonward.

Fig. 5 : Cross atoll rim sections at various locations of the Tikehau atoll (OS : outer slope; AR : algal ridge;
OF : outer reef flat; MO : island; CO : conglomerate IF : inner reef flat; IS : inner slope; LA : lagoon; PR :
pinnacle reef) - from Harmelin-Vivien (1985).

Lagoon structures

Immediately after the inner reef flat, the lagoon inner slope is a relatively steep sediment and
rubble slope which extends to depth of 2-6 m. When the slope begins to flatten out, numerous
coral patches protrude from the sediment bottom. Where the water flow across the reef is
‘ unimpeded by islands, these coral colonies can be numerous and healthy. The lagoon floor is
essentially flat with a low slope gradient. The bottom is primarily a fine sandy bottom. This is
studied in more detail in a subsequent chapter of this volume.

Many coral pinnacles are scattered all over the lagoon. Up to 300 pinnacles visible from the
surface (locally called Karena) have been counted. They are quite unevenly spaced throughout
the lagoon since half of them can be found in the southwest part. Pinnacle reefs vary greatly in
size, ranging from a few tens of meters to over 200 m in diameter for the largest.

The shape of the pinnacles can be roughly related to their size : the smaller the pinnacle reef's
diameter, the steeper its slope. On small pinnacles, much of the slope is nearly vertical. The
largest pinnacles are somewhat flat on top and an emergent one can support bushes or small
trees. However, they still slope to the lagoon floor at an angle of at least 20°. Pinnacle reef
shapes also vary considerably between the windward and the leeward sides. The windward
side usually presents a steep subvertical slope whereas the leeward side of the pinnacle gently
slopes to a detrital zone. Coral community zonation is rather regular among pinnacle reefs, and
three biota may be recognized : the upper (0-2 m), middle (2-6 m) and lower zones
(6 m downward).

16
Morphological discontinuities

Passes can be defined as major deep channels between the ocean and the lagoon. In Tikehau, the
only pass, called Tuheiava, is located at the western part of the atoll. Localisation of the pass
on the leeward side of atolls appears to be a general trend of the Tuamotu archipelago.
Minimal depth of the pass is about 4 m and is sufficient for a small boat to traverse. The bottom,
of bare eroded flagstone, slopes steeply seaward and gradually deepens lagoonward until it
merges with the lagoon floor. Current direction in its vicinity reverses, depending on the tide
and on the height of water in the lagoon. When tidal currents run against the trade winds,
steep standing waves can occur in the pass, hampering sailing and fishing activities. When sea-
level is high in the lagoon, the current is mostly unidirectionnal out of the lagoon. This occurs
frequently when storm associated waves break on windward reef and drive large quantities of
water into the lagoon. On an annual basis, the net flow through the pass is an outflow. Main
features of water circulation at Tikehau are studied out in details in a subsequent chapter of
this volume.

Hoa, also termed rips or gutters, are shallow channels which cut the reef flat superficially.
They draw their flow from the shallow reef flat and channelize the flow of water into the
lagoon between the motu (Plate 5). In Tikehau, their width ranges from a few tens of meters to
500 m. When currents can freely flow through hoa across the atoll rim, hoa are termed open or
functional hoa. On the contrary, when currents do not flow or flow only when a storm occurs
because the channel is obstructed by boulders on the outer flat and/or is closed by littoral sand
shoals or rubble accumulations lagoonward, hoa are termed closed or non functional hoa. The
shape of these channels is subject to major changes owing to sedimentation and high erosion.
Hoa are shallow on the outer reef flat (10 to 20 cm) but deepen towards the lagoon (1-3 m). On
their lagoonward end where current flow slows down, hoa usually have shallow sand shoals.
Hoa have sandy bottoms sculptured by current fluxes with more or less patch reefs. The amount
of patch reefs are directly related to the intensity of water circulation through them.

Up to 150 hoa have been counted around the atoll rim. More than 100 are concentrated on the
southeast coast and are mostly open channels. The current flow through them is almost
unidirectional, from ocean into the lagoon, depending on water level in the lagoon. The 50 other
hoa are principally located on the northwest coast. A few of them are functional.

Hoa, as well as the pass, are the major source of water movements between the ocean and
lagoon.

BATHYMETRY OF THE LAGOON

Knowledge of the bathymetry of the lagoon is basic data for all marine research carried out on
the lagoon. There is no detailed marine chart of the lagoon available and an attempt to map
the Tikehau lagoon bottom from the satellite LANDSAT proved to be unsuccessful. The main
cause was the high and uneven turbidity of the water in the lagoon which prevented
LANDSAT from mapping the bottom efficiently. The bathymetry of the lagoon of Tikehau was
mapped using field measurements (Lenhardt, 1987). A SIMRAD EY-M echo-sounder (frequency
70 khz, range 0-60m) was used on board a motor boat and depth continually recorded on eight
transects across the lagoon. The boat was steaming at a regular speed of 3.2 knots on the
magnetic North-South axis (declination : 13 °). Results obtained have been cross-checked with
results from five other transects. To discretize the continuous series of data, one depth measure
was taken every 80 mand raw data smoothed to eliminate numerous local minor unevenness of
the bottom.

Pass morphology was studied by recording depth on three transects, one through and two across
the pass.

17

Bathymetric map

Smoothed depths recorded on transects were contoured to map the bathymetry of Tikehau
(Fig. 6). The greatest depth recorded was 38 m in the central northeastern part of the lagoon.
The main lagoon basin appears to be a relatively flat area with gentle slopes.

Depth histogram

The histogram presented on Fig. 7 shows that the general shape of the lagoon is that of a basin
with steep walls. Depths between 0 and 15 m represent only 7 % of the total surface of the
lagoon S (S = 420 106 square meters).

Other geometric data

The mean depth P as well as the total volume V of the lagoon is of great interest for other
studies. Mean depth is calculated by computing the mean depth of each transect with mean
length and width of each transect. The result is an average depth of P = 25 m. The total volume
of the lagoon is calculated by multiplying the total surface of the lagoon by its mean depth.
The result is V = 1019 cubic meters. The confidence interval of those data is about 5% which
meets the requirement for precision of other research.

“Mott Deoe

«
35

15°05’ S

\ 148°05'W
\. Tuherahera
(village) afi

Fig. 6 : Contoured depths (in m) in the lagoon of Tikehau.

18

%
30

20

10

Fig. 7 : Average Tikehau lagoon surface per 5 m depth intervals
expressed as a percentage of total lagoon surface .

Characteristic of the pass

Fig. 8 shows the bathymetric map of the pass, transects to record the depth and the smoothed
shape of the bottom. The minimal depth recorded in the pass is 4 m. For further modelisation of

the flow through this channel and water circulation in the lagoon, the mean section of the pass
is estimated at 1000 square meters and average length at 600 m.

on

ESWC ay es Lary I
SLRS GEREN
Re A AAAI

Kt
wt

PLSS TUMHELIAVA

LAGOON

Fig. 8 : Bottom profile of Tikehau atoll pass.

19

NATURE AND DISTRIBUTION OF LAGOON SEDIMENTS

The bottom sediments of the Tikehau lagoon were characterized by Intes and Amaudin (1987).
Fifty four samples of bottom sediment were taken in various location of the lagoon and
subsequently sorted and analyzed in the laboratory.

Findings were that the sediments are all calcareous organic sands. They consist of the following
chief components : Halimeda segment sand, Foraminifera (family Miliolidae) test sand,
mollusc shell sand and miscellaneous debris.

Halimeda segment sand is the first common material. It is present in almost all samples and
predominates in most of them, especially in samples taken in the western part of the lagoon. As
shown on Fig. 9, Halimeda segment distribution follows an horizontal west-east gradient and a
vertical gradient since its abundance decreases steadily below a 20 m depth. Foraminifera test
is the second most common material. Large stretches of foram sand occur on shallow bottoms less
than 10 m deep along the southern and southeastern lagoon margin. Moreover, a large foram
sand patch extends in the northern central part of the lagoon between a depth of 20 and 35 m.
Mollusc shell sand and gravel are never abundant and never dominate the sediment
composition.

NS

SS

//

Y
S

Mi

SS.

SS

yi
,

[LT LE S = Ta

M
~~
i)
EMM
Ci?
Spy

i)
dy)

Fig. 9 : Contoured bottom sediment data of Tikehau lagoon characterized by their chief
components (H : Halimeda sands, F : Foraminifera sands).

20

The mean size of the sand taken in every sample was estimated by sieving in order to classify
the sediment into three size classes : very fine sand (STF - less than 0.25 mm), fine sand (SF -
between 0.25 and 0.50 mm) and medium sand (SM - greater than 0.50 mm). Sediment smaller
than 0.04 mm was not studied. Contoured data (Fig 10) show that lagoon sediments are mostly
fine sand, found in a wide range of depths. However, a large stretch of very fine sand was found
in the central northern part of the lagoon between 15 and 30 m, and on an irregular discontinuous
strip located 20 to 30 m leeward the eastern and southern reef at depth between 9 and 30 m.
Some small medium sand patches are scattered along the lagoon margin down to a 10-15 m
depth and a large stretch occurs across the deep central basin of the lagoon.

Most of the materials of the sand sample taken proved to be quite heterogeneous with a large
size range and a symmetric distribution, except for foram medium sands that are homogeneous.
Sands easily driven by currents are logically found in area of important water transport
(i.e. lagoonward hoa, in the vicinity of the pass) and unexpectedly at a 34 m depth in the
center of the lagoon which is an area thought to be calm.

14,
wie

Fig. 10 : Contoured bottom sediment data of Tikehau lagoon characterized by mean sand size
(STF : very fine sand, SF ; fine sand; SM medium sand; see text for definition of size-classes).

———————o

21

BIOLOGICAL COMMUNITIES OF THE OUTER SLOPE

This chapter, as well as the following ones, does not attempt to provide a comprehensive
description of the fauna in Tikehau but descriptive information about marine habitat.
Determination of many coral and sponge species is still underway and furthermore, fauna
description is limited to the first 90 m in depth. Depths below are unpractical for sustained
SCUBA diving operations and should be sampled remotly. The information presented hereafter
has been drawn from publications of Faure and Laboute (1984) for coral species census and
distribution, Peyrot-Clausade (1984) for cryptofauna distribution and unpublished data of Intes
for zoobenthos of sediments. Fish fauna distribution will be studied in a subsequent chapter of
this volume.

The fore reef area

In the spur and groove zone (0-4 m), corals are largely dominated by calcareous algae which
become increasingly dominant as exposure to trade wind increases. Total coral coverage rate
ranges from 5 to 25 %. Spur and groove have on them coral adapted to withstand this high
energy environment. The top of the spur and the parts of the wall of the grooves are colonized
by small branching Pocillopora (P. verrucosa, P. meandrina, P. damicornis) ; small massive
Favia rotumana, F. stelligera, Montastrea curta, Pavona clavus ; encrusting forms of Montipora
caliculata, Acropora robusta, Millepora platyphylla and Acropora abrotanoides.

Algae are the major component of this substrate. The main species are green algae Halimeda
opuntia, H. discoidea, Caulerpa pickerengii, C. seuratii, Neomeris van bosse, Microdyction and
the red algae Dasya to some extent.

Sessile cryptofauna is abundant, sheltering among coral branches or small grooves in the rock.
The highest richness is reached on overhangs and in small caves as noticed on the south
southeast coast (Sponges, Hydroids Solanderia, Bryozoans, Stylasterids, Dendrophiliids,
Didemnid and Polyclinid Ascidians). An important motile cryptofauna occurs in this zone.
Polychaetes and Crustaceans dominate and borers (mainly Sipunculids) are rare.

On the fore reef platform (4-10 m), the amount of coral coverage increases (60-80%) as well as
its diversity. The most conspicuous coral species are short bunches of Acropora humilis,
‘A. digitifera, A. variabilis, Astreopora myriophtalma, the first noticed Fungid (Fungia
fungites and F. scutaria), and all the coral species cited above. On the northwest shelves where
the platform is wide, the fore reef platform is also highly colonized by algae of the genus
Microdyction, Halimeda and Caulerpa.

Cryptic community biomass decreases slightly, still dominated by Polychaetes and
Crustaceans.

The outer terrace

Between 10 and 15 m depth, grooves floored with rubbles alternate with coral ridges.
Communities are made up of Favia stelligera, Pocillipora eydouxi, Astreopora myriophtalma,
Acropora abrotanoides, Platygyra daedalea, Porites lobata, Favia rotumana, Millepora
platyphylla. Coral coverage rate is about 60 %. From 15 m to 25 m, Porites lobata progressively
dominate followed in, order of abundance, by Pocillipora eydouxi, Favia stelligera,
F. rotumana, Astreopora myriophtalma, Acanthastrea echinata, Pavona varians, Herpolitha
limax and Acropora sp..

Calcareous algae Porolithon and Peyssonnelia along with soft algae colonize the outer terrace
bottom to depth of 25 m. On the windward coast, algae coverage can be important to some
extent.

22

Sessile fauna, except for some sponges as Astroclera sp., shelter among coral patches and is
rather scarce. Echinoderms, Molluscs and Crustaceans are abundant but remain hidden during
daytime. The only occurrence of the invertebrate coral predator, the crown-of-thorn starfish
Acanthaster planci, was recorded in this zone. Its population level seems to be very low and no
evidence of an extensive coral predation was found.

Motile cryptofauna is dominated by Polychaetes and Crustaceans. Its biomass is low and is
reduced by half between 10 and 20 m in depth.

The deep slope

The living coral coverage rate of the deep slope is high ranging from 50 to 100 %. At these
depths, the amount of light energy reaching the bottom decreases steadily, inducing a
colonization of the bottom by coral species fitted to dim recess conditions. The plate-like
Pachyseris speciosa is thus the major component of the coral fauna, so much that this zone is
termed the "Pachyseris speciosa area". In the upper zone (25-35 m), most of the dominant
species of the previous zone (Porites lobata, Pocillipora eydouxi, Favia stelligera and Acropora
sp.) are progressively replaced by species more shade-tolerant as Gardinoseris planulata,
Lobophyllia sp., Coscinarea sp. and small colonies of Pachyseris speciosa are located in the
shade of large vasiform coral species. The live coral coverage rate is above 50 %. In the middle
zone (35 to 60-70 m), Pachyseris speciosa sharply predominates colonies of Porites lobata,
Pavona varians, Leptoseris incrustans, Gardineroseris planulata and Echinophyllia aspera. In
the lower zone (from 60-70 m downwards), numerous colonies of Leptoseris (Leptoseris
hawaiensis, L. scabra, Leptoseris sp.) and Echinophyllia (E. aspera, E. echinata) appear
among well-developed colonies of Pachyseris speciosa with a nearly flat upper surface well
adapted for best capturing sunlight. Stylaster and especially the red coral Stylaster sanguineus
are common species below 60 m but they are already found from 40 m downward in places well
protected from light (i.e. : on overhangs, in small caves or in the shade of larger species). No
SCUBA diving investigations were made below 85 m but given the transparency of the water, it
has been observed that the Pachyseris-Leptoseris population is still developing with the same
energy below a depth of 90 m.

Algae zonation is not restricted to the upper strata of the slope. When a dead coral leaves a
living site, the vacated space can be reoccupied by Caulerpa urvilliana (to depths of 65 m),
Caulerpa seuratii (15-70 m), Caulerpa bikinensis (to depths of 75 m and probably below),
Microdyction sp., (1-65 m) or an unidentified species of Halimeda.

The black sponge Astroclera sp. remains the most conspicuous species among the 25 observed
sponge species. It reaches its maximum density at a depth of 40 m but is still abundant in small
colonies at 70 m. The paucity of other sessile invertebrates like Gorgonians, Anthipatharians or
large Hydroids is noteworthy. Unlike many Indo-Pacific coral reefs, this is a common feature of
outer slope of atoll in the Tuamotu archipelago.

BIOLOGICAL COMMUNITIES OF THE REEF FLAT

In all aspects, the reef flat is quite variable. Various authors have described this zone at
Tikehau, usually in combination with a description of cross-reef flat transects on several parts
of the atoll rim.

The algal ridge

The algal ridge is mostly built by calcareous algae of genus Porolithon and Chevaliericrusta
along with Pocockiella variegata and algal turf made of Caulerpa, Halimeda, Microdyction
and Liagora.

23

Coral coverage rate is low, less than 2 % on windward reef and less than 10 % on leeward shelf.
Coral colonies generally flourish on the wall of the grooves which are emergent only when low
spring tide occurs. Coral species are short, small and blunt ecomorphs fit to withstand the high-
energy environment generated by wave action. The main components of this community are :
Pocillipora damicornis, Porites lobata, Pocillipora verrucosa, Montipora caliculata, Acropora
humilis, A. digitifera and Millepora platyphylla.

Three echinoderms, Heterocentus mammillatus, Colobocentrotus pedifer, Actinopyga
mauritania and lesser number of juvenile sea-urchins sheltered in holes with Echinometra sp.,
are often abundant. Among molluscs, the most seaward species is Platella flexuosa followed
lagoonward by Drupa ricinus, D. morum, Turbo setosus, Morula uva and two species of Vermetid.

The algal ridge structure provides numerous small cavities which afford protection from the
wave surge (and predation) to motile cryptofauna. Its biomass is high and mostly consists of
Polychaetes and Crustaceans. Sessile cryptofauna has a high species richness index but since its
living space is restricted by the availability of cavities always submerged, the total biomass is
low.

The outer reef flat

The coral community of the outer reef flat is extremely poor with only two species censused,
Pocillipora damicornis and Porites lobata, covering less than 1 % of the area. Algae are scarce.

Among the most conspicuous molluscs, Drupa grossularia, Conus sponsalis, C. ebraeus, Erosaria
moneta, Cerithium alveolus, young Tridacna maxima and Chama imbricata are frequently
encountered.

The conglomerate has evidence of extensive rock boring by numerous Lithophagids (up to
50 individuals m-2). Various sessile invertebrates shelter under blocks and in cavities but their
abundance is quite low. Motile cryptofauna is scarce and of low biomass, dominated by
Polychaetes and Molluscs.

The inner reef flat

Algae are the main components of the innermost part of the reef flat. The primarily fine sandy
bottom is colonized by Halimeda opuntia, Caulerpa serrulata and C. urvillana. Many sand
mounds of the mud shrimp Callichirus armatus are scattered all over this area, attesting an
important burrowing activity.

Lagoonward the inner reef flat and down to a 2 m depth, the coral community consists of
Pocillipora damicornis, Acropora digitifera, A. abrotanoides, A. corymbosa, A. humilis, Favia
stelligera, Montastrea curta, Platygyra daedalea. Live coral fauna covers about 25 % of the
substrate.

Algae coverage is high over blocks and sites left by dead coral colonies. Species identified are
Dictyotales, Halimeda sp., Mycrodyction sp., Pocockiella sp. and a thick algal turf. A great
abundance of Cerithium alveolus and Erosaria moneta is remarkable.

Shapes and extensions of dead coral colonies provide a lot of space for a motile cryptofauna
settlement. As a consequence, its biomass is high, dominated by motile and boring Molluscs and
Sipunculids which account for more than 30 % of the total cryptofauna biomass. Main species of
Ascidians are from the families of Didemnidae and Polycitoridae.

24

BIOLOGICAL COMMUNITIES OF THE LAGOON

The lagoon slope

The important sedimental layer of the inner slope hampers somewhat the development of coral
communities. Live coral coverage rate is less than 10 % and consists of Pocillipora sp. mostly
settled in the shallowest part of the slope, followed downward by massive and encrusting forms
of Porites lobata, Leptastrea purpurea, Pavona varians, Platygyra daedalea, Montipora
verilli and Fungia sp..

Algae are generally scarce. Microdyction have colonized hard substrate on the windward side
of the atoll. On the west coast, not far from the pass, an algal flat community dominated by
Caulerpa sp. extends on the slope with some Halimeda sp. found where the slope flattens out
and merges with the lagoon bottom.

Invertebrates occur sporadically in this barren area.

Between 6 and 12 m depth, the lagoon margin has areas of abundant patch reefs. Particularly in
places exposed to an abundant water circulation but protected from sediment overwash, lagoon
margin patch reefs have well developed coral communities which can be either multispecific
coral heads of Pseudocolumastrea pollicata, Platygyra daedalea, Leptastrea purpurea, Pavona
varians, P. minuta, Stylocoeniella sp., Astreopora sp., Fungia ssp., Porites lutea, Stylophora
pistillata, Montipora verrucosa, M. verrilli or paucispecific bunches of Acropora formosa and
Acropora vaughani.

A few sessile bivalves grow on the sides of the patch reefs. The most frequently encountered
species are Arca ventricosa, Pinctada maculata and rarely the pearl oyster Pinctada
margaritifera. In addition to some echinoids hidden in shelters provided by coral patches,
beche-de-mer Halodeima atra, Thelenota ananas and several species of synaptid commonly
feed in this area.

The lagoon bottom

The nature of lagoon bottom substrate has not been studied in detail but obviously, soft sediment
substrata overwhelmingly dominate hard coral substratum. The lagoon floor can be
characterized as large stretches of sand with occasional patch reefs. Wide areas of soft bottom
are covered with a thin algal mat of brown Cyanophycae. Other Cyanophycae are visible on
the sediment as large red balls. Species of Halimeda (principally H. opuntia) and Caulerpa
(C. serrulata, C. urvilliana) can build up large algal flat areas. Caulerpa sp. grows via
rhyzomes, spreading out over the bottom in easily distinguishable patterns. Sea grass beds of
the marine phanerogame Halophila ovalis reach high density in some places.

Little is known on the fauna buried in, or on, sediments. Epifauna is composed mostly of sponges
(Echinodictyon, Axinella) scattered over sediment surface. From place to place, some bivalves
of the genus Pinna raise from the sediment. Holothurian Halodeima atra concentrates in great
numbers, up to 10 individuals per square meter in the shallowest sandy areas. Polychaetes and
Molluscs alternatively dominate the endofauna. Sedentary Polychaetes are well represented
mostly by the families of Spionidae (Prionospio sp., Aonides oxycephala), Maldanidae
(Axiothella sp.), Capitellidae (Dasybranchus and Notomastus) and Terebellidae. A few errant
species live in the sediments ; they belong to the families of Glyceridae, Eunicidae and
Nephtyidae. Molluscs are essentially little bivalves like Tellinidae but some carnivorous
gastropods exist (Naticidae, Strombidae). Among Echinoderms, only a few ophiuroids may be
encountered. Very motile crustaceans as Portunid crabs may bury in sediments. Lancelets are
locally abundant, especially in coarse sands. Small conical mounds disrupting the sediment
surface are evidences of the presence of mud-shrimps. Their density is quite high,
approximately 15 mounds per ten square meters. Mounds can be as large as 50 cm diameter on
bottom of deep zones.

25

Stretches of hard bottom are found down to a 20 m depth. They are often restricted to areas of
a few square meters but around the largest pinnacle reefs, they can cover areas of hundreds of
square meters. Coral communities are made up of either multispecific patches of Porites
lobata, Psammocora sp., Montipora sp. Astreopora sp., or paucispecific bunches of Acropora
spp.. Macroalgae, particularly species of Halimeda, are often found among the corals.

Pinnacle reefs

The pinnacle reefs of Tikehau cover only a few percent of the lagoon bottom area but
concentrate a great biological diversity, harbouring a wealth of various organisms. The upper
zone (0-2 m) can be emergent at low tide. The center of the largest pinnacle reefs is rugged
with sediment and rubble, colonized by algae Halimeda, Pocockiella, Caulerpa, Padina and
Lobophora. On the windward side, very large colonies (6 to 8 meters) of Porites lutea and
Millepora platyphylla grow along with a few Pocillipora meandrina and Acropora
abrotanoides. The leeward side supports branched colonies dominated by Acropora
variabilis, A. hyacinthus, A. hemprichi and Montipora spp..

The motile cryptofauna of the upper zone is rich and dominated by Molluscs. Borers are rare.

The bottom of the middle zone (2-6 m) is largely a rocky substrate with shelves on which
considerable quantities of sediment and rubble are retained, promoting the development of
Halimeda and Caulerpa algal flat. Some coral heads of Montipora verrucosa, Astreopora sp.,
Psammocora sp., Porites lobata, Platygyra daedalea and Pavona varians intersperse among
sediment stretches.

Cryptofauna abundance decreases somewhat, being still dominated by Molluscs. Boring
invertebrates, mostly Moliuscs and Sipunculids, represent almost 40 % of the total biomass.
The important sediment deposition in this zone precludes the development of any significant
sessile fauna.

The lower zone (6-15 m) of the pinnacle reef is covered by coral patches of Montipora
verrucosa, Stylocoenilla sp., Platygyra daedalea and branched forms of Acropora formosa,
Stylophora pistillata and Favia favus. Below 15 m, coral colonies vanish under the
sediment.

. BIOLOGICAL COMMUNITIES OF MORPHOLOGICAL DISCONTINUITIES

The pass

Numerous live coral ridges oriented parallel to the pass axis are scattered over the bottom of
the pass. These colonies are characterized by an outstanding development of Pocillipora
(P. meandrina, P. verrucosa, P. eydouxi, P. damicornis) measuring up to 3 m. Live coral
coverage rate is about 80 % and reaches 100 % alongshore. Small colonies of Leptastrea
purpurea, Montipora sp. Fungia fungites, F. scutaria and Millepora platyphylla are found
protected from current on the flagstone between ridges.

Algae and invertebrates are rare in the pass owing to extremely rough current conditions.
Some sponges (Aurora sp.), beche-de-mer (Thelenota ananas) or Asterids settled there
nonetheless.

Hoa

The seaward bare bottom of hoa is colonized by a great number of Cerithium alveolus and
often bored by numerous lithophagid. The top of many dead coral blocks is covered with the
black Cyanophyceae Hassalia byssoides. Pink sands rich in Cyanophyceae and bacteria
have accumulated alongside the edge of the channel. Coral patches of Porites lobata,
Leptastrea purpurea, Porites cf andrewsi and Platygyra daedalea appear lagoonward,
downcurrent of the reef where sediment overwash is weaker. Echinoid species (Echinometra,

26
Echinothrix, Diadema) are concentrated in some numbers around these coral heads. Some
bivalves Tridacna grow on top of them.

The motile cryptofauna dominated by Crustacean and Polychaetes is poor due to the paucity
of suitable substrates.

OCEANOGRAPHY OF THE TIKEHAU LAGOON

The understanding of lagoonal water circulation is of primary interest for all biological and
chemical studies carried out in the lagoon. Current data were recorded by four current meters
set in the hoa of the windward reef, of the southwestern reef, of the northwestern reef, and in
the pass. A tide gauge continually recorded water height in the lagoon. Modeling of the
lagoon circulation was furthermore attempted.

Pass currents

The pass current is reversing. Its speed and timing are in phase with the tide. Data from
Lenhardt (1991) show that the current speed usually ranges from 0 to 120 cm s-1, increasing
from 0 to maximum speed in about 3 hours and then decreasing to slack water in another
3 hours. The period of slack water in the pass is only a few minutes. When water level is high
in the lagoon, the pass has a nearly continuous outflow. The current speed may exceed 3 ms!
under these frequent conditions and can last from 3 to 10 days.

The volume of transport of the pass current varies between neap and spring tide and more
importantly with water height figures in the lagoon. Data available did not enable us to
estimate the outflow through the pass but the average inflowing water transport was
estimated to be 400 m3 s-! over a tidal cycle. It was furthermore estimated that the net
transport volume of the pass is approximatively zero over a tidal cycle under normal lagoon
water level conditions.

Hoa currents

Hoa currents or cross-reef currents involve a shallow flow over the reef margins. Hoa draw
their flow from the outer reef flat and channelize the water off the reef into the lagoon
between islands. Hoa currents are a result of breaking waves over the algal ridge on the
windward reef. They vary in response to surf height and therefore to regional oceanographic
patterns. Lenhardt (1991) pointed out that Hoa currents do not reverse direction at Tikehau,
they always flow from ocean to lagoon even when water level is high in the lagoon.

Cross-reef currents do not flow in any well developed pattern as summarized in Table 4. The
average current speed is low, generally less than 30 cm sl. It ranges from 0 to 120 cm s-! when
high surf occurs. Current speed also varies seasonally, it is highest in hoa of the northwestern
coast in summer of southern hemisphere while it is maximum in hoa of southeastern and
southwestern reefs in winter. Table 4 shows that volume transport across the windward reef
(southeast shore) accounts for more than 60 % of cross-reef water input whereas southwestern
water transport accounts for 31 % and northwestern reef for 9 %. Average inflow per unit
length of open coast (hereafter expressed lineic flow rate in m3 s-1/m or m2 s-!) is an useful
data. Its variations over the year are summarized in Fig. 11. Bases for calculation are :
length of South-East coast 23 km; length of South-West coast 11 km; length of North-West
coast 11 km.

27,

Table 4 : Estimates of monthly inflowing current speed and associated water transport in hoa and pass
of the Tikehau atoll. Sse : current speed in southeastern channels, Ssw : current speed in southwestern
channels, Snw : current speed in northwestern channels, Tse, Tsw and Tnw : relevant water volume
transport. Rt : residence time. Bases for calculation : equivalent section of southeastern reef front :
5000 m2 ,southwestern reef : 2600 m2 , northwestern reef : 80 m2 . Total inflow is the sum of inflow
through pass and hoa.

Month Cross-reef current and transport Pass Total Rt
inflow inflow

Sse Tse Ssw Tsw Snw Tnw
cm s-1 m3 s-1 cm s-1 m3 s-1 cm s-1 m3 s-1 m3 s-1 m3 s-l days

January 55 270 25 65 18 15 260 600

February 3.0 140 3 75 21 18 180 400 230
March 4 100 17 14 150

April 75 200 28 18 250

May 15 800 105 280 9 i 100 1200

June 20 1000 6 160 13 11 70 1200 105
July 11 550 7.5 190 3 2 100 900

Fig 11 : Variations of lineic flow rate through hoa of Tikehau over the year.

28
Lagoon currents

Suspended acoustic drifter releases at a 4 m depth, in various points of the lagoon, show that
the surface current in the lagoon is primarily wind-driven. The general surface drift is
downwind (or roughly westerly) at a speed of approximately 1 % of the wind speed. Lagoon
currents in the vicinity of pass and hoa is strongly altered by local current conditions. Current
patterns were found to vary with depth. Current in the deep layers of the lagoon is upwind
and flows at about one half of the surface current speed.

Water budget and residence times

Because the cross-reef currents never reverse, the volume transport over the reef through hoa
represent a net input of water into the lagoon. Water furthermore flows into the lagoon from
the pass. The water can flow out of the lagoon only from the pass. As the quantity of water
entering the lagoon and the quantity of water exiting out of the lagoon must be balanced, the
net inflow must exit as outflow out of the pass. Thus, water transport in the pass is indicative
of water budget figures in the lagoon. The volume transport Q (m3 s-1) flushing in the pass
was found to be a simple function of the difference in m between height of lagoon (h) and
ocean (Zz) according to:

Q=e3000 \ |h-z|

€ being -1 if water flows out of the lagoon, +1 if water flows in.

The average residence time of water in the lagoon can be estimated by dividing the lagoon
volume (i.e. 10. 10? m3) by the net rate of water input presented in Table 4. Under these very
simple assumptions, the calculation yields a residence time of 230 days in summer and 105
days in winter, the yearly average value being 170 days. Because the water entering the
southeastern lagoon must transit the entire lagoon before exiting through the pass and because
it probably undergoes mixing by the wind-driven circulation, during that transit, the
residence time of this part of the inflow will be longer. Conversely, water inflowing through
northwestern channels will be expected to have a residence time shorter than the average.
The residence times estimated at Tikehau can be compared to those estimated in the lagoon of
a high island (Moorea, 6.5 hours) and in the lagoon of a closed atoll (Takapoto, between 4 and
5 years).

Circulation model

Lagoon circulation can be explained as a response to three sources of energy : the tide, the surf
on the ocean reef and the wind. Lenhardt (unpublished data) proposed a bi-dimensional
finite difference model using vertically integred Navier-Stockes equations to model the
response of lagoon circulation to these three sources of energy taken separately then
altogether.

Fig. 12a shows the residual tide-induced circulation in the lagoon. Tidal currents influence
the flow of water only in the immediate area of the pass. Current speed is greater than
1 cm s-! only within 4 km of the pass. Elsewhere in the lagoon, tidal current speed is very low
(a few mm s-1) and can hardly be measured. The tide generates a conspicuous clockwise local
eddy south to the pass and a weak counter clockwise eddy north of the pass.

Fig. 12b shows the circulation induced by the surf on the windward reef. The oceanic water
spreads into the lagoon, moving downwind toward the pass. Currents are significant only in
the southern part of the lagoon with speed of about 1 cm s-!. The northern part of the lagoon
appears to be poorly affected by this circulation with modeled current speed less than
0.5 cms-1.

29

0.001 m/s

tere erm n eee

Fig 12a : Lagoon residual circulation generated Fig 12b : Lagoon circulation generated by
by the tide at Tikehau surf on the windward reef of Tikehau
(amplitude 10 cm ; arrows : current vectors). (lineic flowing current : 0,3 m3 s-l/m).

Fig. 12c shows the circulation generated by a constant, unidirectionnal easterly windstress of
10 ms-1 (about 20 knots). Closed and impermeable boundaries were set to the atoll rim in order
to avoid effects of water inflow for modelisation purposes. As measured by drogue releases,
current speeds are strongly related to wind speeds (e.g. current speed is 1 to 2 % of the wind
speed). In shallow part of the lagoon, the wind creates a downwind drift and an upwind drift
in the deepest area. The wind-driven circulation induces two large conspicuous counter-
rotating bodies of water, a counter clockwise northern eddy and another clockwise southern
eddy.

Fig.12d shows the connection the effects of the three sources of energy, the tide, the surf and
the wind. Given the low current speed of the tide-induced circulation, the connection of the
three sources is actually the sum of the wind and surf-driven circulation. Fig. 12d shows a
general downwind drift toward the pass in the southern lagoon and a weak water circulation
in the northern lagoon.

The relevance of the model is somehow limited by the fact that it is bi-dimensionnal. The
model gives only an average of the current speed and direction over the whole water layer
and cannot take into account changes in current with depth. In all probability, and as
confirmed by acoustic drogue releases and current speed records at various depths, the pattern
of circulation in the lagoon must be a general downwind surface drift oriented toward the
pass, balanced by an upwind low-depth drift. Moreover, the lagoon rim is closed neither to
the pass nor windward. Large quantities of water are introduced along the windward edge
and flushed out of the pass, and considerably modify wind-driven current patterns in the
lagoon. Further circulation models should therefore be developed in three dimensions though
information supplied by the bi-dimensional model meets biological research requirements.

Fig 12c : Lagoon circulation generated by Fig. 12d : Lagoon circulation generated

a constant 10 ms"! easterly wind at Tikehau. by the connection of the three sources of
energy (tide : 10 cm, surf : 0,3 m3 s-1/m
and wind :4ms-1) at Tikehau.

AN EXAMPLE OF MAJOR DISTURBANCE : CYCLONES

About four cyclones per century are likely to occur in the Tuamotu archipelago but during the
hot season 1982-1983, no less than four cyclones (Orama, Reva, Veena and William) and a
tropical storm (Lisa) ravaged French Polynesia, causing severe damages to human
installations, vegetation and coral reef ecosystems. This meteorological phenomenon of an
outstanding frequency and intensity induced waves measuring more than 10 meters, a sea-
level rising of 3 meters above predicted tidal levels, and a wind blowing in excess of 160 km
per hour with gusting to over 200 km per hour. In particular, the cyclone Veena occurred in the
vicinity of Tikehau between the 6th and 13th of April 1983. SCUBA Dive surveys carried out
on the same transects before and after that disaster allow to assess the magnitude of damage
caused to coral communities, and to explain destruction mechanisms. Two years later, SCUBA
Dive surveys carried out on the same transects showed that time of recovery is very long. It
will take at least five decades to have the coral communities in the state observed prior 1983.

Damage assessment

Damaged area (SD) is assessed by multiplying the length of destroyed reef (L) by 200 m (this
value is the average length / of the outer slope between the depth of 0 and 90 m where
hermatypic corals live). L is an estimation based on field observations made during 22
SCUBA Dive surveys around the atoll rim. In Tikehau, an area of 13 million square meters is
estimated to have been damaged. This represents 80 % of the outer slope (Laboute, 1985). The
area located windward of the atoll (from the north around to the south-west through the
east) has been destroyed to a magnitude exceeding 90 %. Areas located north-north-west and
west have been damaged to a magnitude varying between 30 and 80 %. The western side of the
atoll remained intact.

31

Destruction mechanisms

Based on the outer slope morphology, three types of destruction mechanism were figured by
Laboute (1985) and Harmelin-Vivien and Laboute (1986) following field observations. These
theoretical processes are subject to variations with local details of the slope.

The reef flat is narrow, the fore reef area above a depth of 15 m and the slope very steep
(> 45°) as on the western coast of the atoll. Between 0 and 15 m, plate-like and branching
madreporic species are abundant. They are of the genus of Pocillipora, Acropora, Montipora,
Astreopora, Favia and Pavona. All those species are fragile and have been uprooted then
reduced to rubble by the strength of the swell. The remains have contributed to destroy more
resistant species by recurrent impacts and abrasion. Most of the remains have been thrown up
on the reef flat.

At 12-15 m on the fore reef area, massive and heavy madreporic species like Porites lobata
and Montipora prevail. As above, those species have been uprooted by the swell but since
they were growing near or on high-angle substrates, remains rolled down the steep slopes
weeping deeper colonies often more fragile, such as the plate-like Pachyseris speciosa, the
dominant species below 40 m. Destructive effects of this underwater avalanche increased
with depth as shown in Fig. 13. It is likely that coral blocks accumulated at some level
between 300 and 500 m where the slope begins to flatten out, contributing to the formation of a
detrital cone surrounding the atoll (Harmelin-Vivien and Laboute, 1986).

So far, this avalanche phenomenon has never been described elsewhere. All previous
hurricane effect descriptions were done for islands without this typical steep outer slope and
as a result, cyclone damages were thought to be limited to the upper level of the ecosystem.

OUTER REEF
LAGOON PSB boulder rampart

sea level
direct destruction
by storm induced

SS 2RP Tey PSS eee

coral

destruction Soooces
50% to 80% : destruction

by
avalanche

MOVEMENT OF BROKEN CORALS
SURVIVING COLONIES 100% coral
SAND AND RUBBLE destruction

Fig. 13 : Cross section of the west coast of Tikehau with explanatory hypothesis of deep coral
destruction : direct coral destruction by storm-induced waves occured between the surface and 20 to 22
m depth. Most remains of broken coral rolled down the slope breaking fragile deeper colonies (after
Harmelin-Vivien and Laboute, 1986),

32

The reef flat is large with a low slope gradient, the fore reef area deeper (25 m) and the outer
slope less steep (< 45 °) as on the northern coast of the atoll. Coral colonies have been broken
down to 15 m. Part of their remains were thrown up on the reef flat, the other part remaining
on the same area. Many coral skeleton were covered by algae (genus Microdyction and
calcareous algae). Massive species between 15 and 25 m have been uprooted too but given the
distance to the steep slope, no avalanche occurred and therefore deeper colonies remained
undamaged.

The reef flat is equally large or narrow but there is a depression or a very low-angled zone just
before the fore reef area. Madreporic species located above a depth of 15 m have been
destroyed following the previous process, but part of their remains have been trapped in that
depression, preventing an avalanche. Thus, Porites lobata and Pachyseris speciosa colonies of
deeper zones have been preserved.

Whatever the shape of the deep slope is a shallow fore reef coral community (composed of
small colonies well adapted to withstand high energy level environment) suffered less than
deeper reef communities. Coral destruction, estimated at 50 %, resulted primarily from
abrasions by dislodged material, rolling remains and scouring sand.

Destruction mechanism in the pass and in the vicinity is of a particular nature. The Tikehau
pass, located at the west of the atoll, was colonized by numerous species of the genus
Pocillopora (P. meandrina, P. verrucosa, P. eydouxi and P. damicornis). The live coral
covering rate was high, reaching 80 % to 100 % alongside the edge of the pass, between 2 and
8 meters. Those colonies remained intact as observed during SCUBA Dive surveys carried out
six months after the cyclone Veena. More than one year later, all species were dead and
skeleton still in place. This can be explained by the following observations : after the cyclone,
the sea-level in the lagoon was high and currents constantly flowed out of the lagoon. Water
was loaded with a considerable amount of suspended particulate matter and was, as a result,
very turbid. Sedimentation was very important in the vicinity of the pass and therefore the
amount of light energy reaching the bottom decreased dramatically and subsequently, corals
died.

In all cases, most of the coral associated fauna (sessile fauna and fish) disappeared owing to
a high mortality rate and to a lack of food and shelter.

Recovery processes

Coral resettlement became visible only one year after the cyclone in an area restricted to the
upper 15 m as pointed out by Laboute (1985). In May 1984 Pocillipora (measuring between
2 and 4 cm) were dominating followed by encrusting forms of Favia stelligera, Acropora (size
range : 2-7 cm), Millepora platyphylla and to some extent, small colonies of Pavona minuta
and Favia rotumana. In the ravaged areas, no new madreporic colonies were seen below
15-20 m.

In February-March of 1985, an important madreporic and algae resettlement could be seen on
the West coast of the atoll between 3 and 15 m. Species inventoried were : Pocillipora -
obviously the most numerous - (size range : 1-20 cm), Montipora caliculata, Montipora verrili,
Astreopora myriophtalma (size range : 10-30 cm), Favia stelligera (size range : 2-12 cm),
algae Halimeda taenicola, Mycrodyction and Caulerpa urvilliana.

In June of 1985, algae and madreporic species were still resettling on the outer slope especially
between 3 and 15 m. Species were : Pocillipora (size range : 4-23 cm), two or three species of
Acropora (4-20 cm), Favia rotumana (4-15 cm), Porites lobata (2-11 cm), Pavona minuta
(5-9 cm), Millepora platyphylla (15-50 cm). Algae Halimeda taenicola, Microdyction and
Caulerpa urvilliana were as abundant as before the cyclone. In the area partly damaged and
below a depth of 15 m, madreporic resettlement seemed to be faster owing to the presence of
some sparse colonies which survived the cyclone. For instance :

At 20m Acropora robusta was 60 cm large but still very encrusting except on its edge, Favia
stelligera numerous in some place (size range : 10-40 cm), sparse Porites lobata (6-17 cm).

33
At 30 m, numerous Fungia fungites (size range : 8-10 cm), Millepora platyphylla as large as
1 m but still thin and encrusting.
At 40 m, Astreopora myriophtalma measuring between 8 and 35 cm, sparse 17 cm Porites
lobata very thin which had settled on previous base of same species.
At 50 m, rare Fungia sp. of 3 cm and Pachyseris speciosa (size range : 4-7 cm).

The impact of cyclones on fish fauna has been studied in detail and the results are presented
in a later number of this issue.

Literature cited

CHEVALIER (J.P.) - 1973 - Geomorphology and geology of coral reefs in French Polynesia. In : Geology
and Biology of Coral Reefs, I. Academic Press, New York : 113-141

CLAGUE (D.A.) - 1981 - Linear island and seamount chains, aseismic ridges and intraplate volcanism :
results from DSDP. Soc. Econ. Paleontolog. Mineralog., Spec. Publ., 32 : 7-22

FAURE (G.), LABOUTE (P.) - 1984 - Formations récifales : I - Définition des unités récifales et
distribution des principaux peuplements de Scleractiniaires. In : L’atoll de Tikehau (Archipel
des Tuamotu, Polynésie Francaise), premiers résultats. ORSTOM Tahiti, Notes et Doc.
Océanogr., 22 : 108-136

FLORENCE JJ.) - 1985 - Introduction 4 la flore et a la végétation. In : Contribution a I’étude de J’atoll de
Tikehau. ORSTOM Tahiti, Notes et Doc. Océanogr., 24 : 98-113

GABRIE (C.), SALVAT (B.) - Généralités sur les iles de la Polynésie Frangaise et leur récifs coralliens.
Proceeding of the Fifth International Coral Reef Congress, Tahiti, 1985, 1 : 1-16

HARMELIN-VIVIEN (M.L.) - 1985 - Présentation générale de l'atoll. In : Contribution a l’étude de
I’atoll de Tikehau. ORSTOM Tahiti, Notes et Doc. Océanogr., 24 : 2-27

HARMELIN-VIVIEN (M.L.), LABOUTE (P.) - 1986 - Catastrophic impact of hurricanes on atoll outer
reef slopes in the Tuamotu (French Polynesia). Coral Reefs, 5 : 55-62

INTES (A.) - 1984 - Présentation générale de l'atoll. In : L’atoll de Tikehau (Archipel des Tuamotu,
Polynésie Francaise), premiers résultats. ORSTOM Tahiti, Notes et Doc. Océanogr.,
22: 4-12

INTES (A.), ARNAUDIN (H.) - 1987 - Esquisse sédimentologique du lagon. In : Contribution a l'étude
de l'atoll de Tikehau : IV. ORSTOM Tahiti, Notes et Doc. Océanogr., 35 : 71-100

JAMET (R.) - 1985 - Les sols de I'atoll. in : Contribution a l’étude de I’atoll de Tikehau. ORSTOM Tahiti,
Notes et Doc. Océanogr., 24 : 74-97

LABOUTE (P.) - 1985 - Evaluation des dégats causés par les passages des cyclones de 1982-83 en
Polynésie Francaise sur les pentes externes des atolls de Tikehau et de Takapoto (Archipel
des Tuamotu, Polynésie Francaise). Proceeding of the Fifth International Coral Reef
Congress, Tahiti, 1985, 3 : 323-329

LAMBECK (K.) - 1981 - Flexure of the ocean lithosphere from island uplift, bathymetry and geoid
height observations : the Society islands. Geophys. J. R. Astr. Soc., 67 : 91-114

LENHARDT (X.) - 1987 - Etude bathymétrique du lagon de Tikehau. In : Contribution 4 l'étude de l'atoll
de Tikehau : IV. ORSTOM Tahiti, Notes et Doc. Océanogr., 35 : 53-70

LENHARDT (X.) - 1991 - Hydrodynamique des lagons d’atoll et d’ile haute en Polynésie Frangaise.
ORSTOM Paris ed., Etudes et Theses : 132 p

34
MONTAGGIONI (L.F.) - 1985 - Makatea island, Tuamotu archipelago. Proceeding of the Fifth
International Coral Reef Congress, Tahiti, 1985, 1 : 103-158

PEYROT-CLASADE (M.) - 1984 - Cryptofaune mobile des formations récifales. In : L’atoll de Tikehau
(Archipel des Tuamotu, Polynésie Francaise), premiers résultats. ORSTOM Tahiti, Notes
et Doc. Océanogr., 22 : 137-144

PIRAZZOLI (P.A.), MONTAGGIONI (L.F.) - 1985 - Lithospheric deformation in French Polynesia
(Pacific Ocean) as deduced from quaternery shorelines. Proceeding of the Fifth
International Coral Reef Congress, Tahiti, 1985, 3 : 195-200

POULSEN (M.K.), INTES (A.), MONNET (C.) - 1985 - Observations sur l'avifaune en octobre 1984. In:
Contribution a l’étude de I’atoll de Tikehau. ORSTOM Tahiti, Notes et Doc. Océanogr.,
24: 114-124

ROUGERIE (F.) - 1981 - Evaporation and salinity survey in French Polynesia. Tropical Ocean-
Atmosphere Newsletter, 7 : 8

ROUGERIE (F.), CHABANNE JJ.) - 1983 - Relationship between Tuna and Salinity in Tahitian coastal
waters. Tropical Ocean-Atmosphere Newsletter, 17 : 12-13

ROUGERIE (F.), WAUTHY (B.) - 1986 - Le concept d'endo-upwelling dans le fonctionnement des
atolls-oasis. Oceanol. Acta, 9 : 133-148

SCHLANGER (S.O.) - 1981 - Shallow-water limestones in oceanic basins as tectonic and
paleoceanographic indicators. Soc. Econ. Paleontol. Mineralog., Spec. Publ., 32 : 209-226

SODTER (F.) - 1985 - Eléments d’une histoire démographique. In : Contribution a l’étude de I’atoll de
Tikehau. ORSTOM Tahiti, Notes et Doc. Océanogr., 24 : 125-134

Plate 1 : Uplifted reefs, locally known as "FEO", are distributed along the northern coast of the atoll.
Some of them, basaly notched, may be seen on the outer reef flat. (Photo Intes)

Plate 2 : The marshy depression is covered with the cyperaceous assemblage dominated
by Cladium jamaicense. (Photo Intes)

Plate 4 : The spur and groove zone (eastern coast, 4 m). (Photo Laboute)

Plate 5 : The ocean water flows into the lagoon through shallow channels called "Hoa". (Photo Intes)

Plate 6 : A large Acropora colony overturned by the wave action induced by the hurricane "Veena"
in April 1983 (eastern outer slope, 8 m). (Photo Laboute)

Plate 7 : The avalanche effect may destroy 100% of the corals of the outer slope
(eastern outer slope, 22 m). (Photo Laboute)

Plate 8 : Recolonisation of the fore reef platform two years after hurricane "Veena"
(eastern coast, 8 m ). (Photo Laboute)

PART II. NUTRIENTS, PARTICULATE ORGANIC MATTER, AND
PLANKTONIC AND BENTHIC PRODUCTION OF THE
TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)

BY

C.J. CHARPY-ROUBAUD AND L. CHARPY

NUTRIENTS IN OCEANIC AND LAGOONAL WATERS

Matter and energy budgets for coral reefs, their components, and the world around them can, do,
and must balance in a theorical context (Smith and Kinsey, 1988). In this paper, we will try to
establish nitrogen, phosphorus and silica budgets between ocean and lagoon waters of Tikehau atoll
in the purpose to learn more about the functioning of coral reef lagoons. Nutrient concentrations
(dissolved components and particulate organic matter) were measured in the lagoon and in the
surrounding oceanic surface waters between 1983 and 1987.

DISSOLVED COMPONENTS

Ocean waters

Five oceanic stations shown on Fig. 1 have been sampled to a 500 m depth. At the most remote ocean
station, OS7 (considered as representative of oceanic conditions), the upper 50 m surface layer
displayed the characteristic temperature (29.5 °C) and the salinity (35.5 %o) of oceanic waters. Below
this superficial layer (120 to 150 m) a temperature of 25 °C and a maximum salinity of 36.2 %o were
recorded. Nutrient profiles were typical of offshore oceanic waters, with a very low nutrient
. concentration down to 200 m depth. As summarized in Fig. 1, nutrient concentrations increased to 15
mmol NO3 m-3 and 2.5 mmol PO4 m-3 at 500 m.

The nitrite concentration displayed a maximum at 175 m (0.1 mmol m-3). Nutrient concentrations in
the upper 200 m proved to be higher at the stations located in the immediate vicinity of the atoll.

The atoll therefore seems to disturb the standard vertical profiles of nutrient observed at station OS7,
which in turn, results in an enrichment of nitrogen and phosphorus in the euphotic layer. The
enrichment is probably due to a turbulent vertical mixing caused by the atoll mass effect, i.e. by
internal waves (so, Andrews and Gentien , 1982, consider upwelling to be a source of nutrients for
the Great Reef ecosystem ) and also, perhaps, by an up surge of deep waters from the atoll coral base
as hypothesized by Rougerie and Wauthy (1986).

ORSTOM-Tahiti, BP 529, Papeete, French Polynesia

mmol m7?
O01 nt 10 100

0.01 0.1 1 10 100

TIKEHAU

100
0.01 01 1 10 100

1
<x
=
a
ea
oO

Fig. 1 : Inorganic nutrient concentration profile (mmol m3) at oceanic stations near the Tikehau Atoll (from
Charpy-Roubaud et al., 1990),

Table 1 : Summary of concentrations (mmol m-3 ) of nutrients, dissolved organic phosphorus (DOP), and
dissolved organic nitrogen (DON) in the lagoon of Tikehau (s : standard deviation, (n) : number of samples)
(from Charpy-Roubaud eft al., 1990).

Variable Range Mean S (n)

NH4 0.14 - 9.11 2.10 1:95 (96)
NO? 0.01 - 0.18 0.02 0.03 (180)
NO3 0.01 - 0.83 0.08 0.12 (184)
DON 0.40 - 8.20 1.80 2°39) (93)
PO4 0.01 - 0.89 0.16 0.13 (232)
DOP 0.01 - 1.47 0.39 0.24 (142)

SiO? 0.07 - 1.72 0.83 0.42 (130)

Lagoonal waters

The average nutrient concentrations listed in Table 1 were not unusual, being of the same order of
magnitude as the standing stock nutrient concentrations in coral-reef waters as reviewed by
Crossland (1983).

Nutrient concentrations vary considerably with time. NH4, PO4 and SiO? concentrations were twice
as high in 1985 as in other years. The average monthly NO3 count lays close to the detection limit
(between 0.01 and 0.1 mmol m°3), except in February (0.24 + 0.06 mmol m-3) and August (0.14 + 0.05
mmol m-3). The monthly average value of POg4 varies in a spread of 0.1 to 0.2 mmol, except in
January (0.4 + 0.1 mmol). Concentrations of nutrients were found to be homogeneous throughout the
lagoon.

PARTICULATE ORGANIC MATTER (POM)

Charpy (1985) emphasized that the particulate organic matter (POM) content of the water column
appears to be a good indicator of lagoon productivity. Measurements of deposition rates of organic
material are very important. Nutrient requirements for lagoonal production may be met partially
through recycling autochthonous material in sediments. One of the principal factors which governs
the rate of nutrient regeneration from sediments is the amount of organic matter incorporated into
these sediments from the overlying waters (Koop and Larkum, 1987).

POM in oceanic waters

Table 2: Cruises between 1983 and 1985 in oceanic waters near Tikehau Atoll.

July 1983 November 1983 March 1984 November 1985
(stiecs e
082, 085 052, 083, 054,055 _| 082, 053, 054, 055

Depths(m) | 0,25, 50, 100, 150, 200 0, 25, 50, 75, 100, 125, | 9, 50, 100, 125, 150, 0, 25, 50, 75, 100, 125,
150, 175, 200, 250 175, 200 150, 200
Parameters Chl a, Phaeo a Chl a, Phaeo a, Chl a, Phaeo a, Chl a, Phaeo a,
ATP ATP, POP ATP, POP, POC, PON

ATP concentrations are greatest in the upper 100 m of ocean waters ranging from 0.05 to
0.12 mg m-3. No significant differences among sampling stations were detected.

Chlorophyll profiles displayed in Fig. 2 show a deep maxima between 100 and 200 m depth.
Concentrations recorded in March 1984 reached 0.24 mg m-3 at these depths whereas surface
concentrations were five time smaller (0.05 mg m°3).

Particulate organic phosphorus, carbon and nitrogen (respectively POP, POC and PON) profiles are
shown on Fig. 3. Concentrations generally decrease with depth. The high concentration values that
were observed in surface waters in March 1984 were probably due to abundant detritus export from
the reef flat and thus overestimated.

dapthim)

TIKEHAU

StationOS3
Chips

=
Ee
~
£
=
a
@
a7

Station OSS

7 Station OS4
/ Station OS2

poe POP

Station OS2
Poc

Fig.3 : Particulate organic phosphorus, carbon and nitrogen (POP, POC and PON) concentration profiles
(mg m-3) at oceanic stations near Tikehau (from Charpy and Charpy-Roubaud, 1991).

POM in the lagoon and oceanward the pass.

Average POC, PON, POP, ATP and pigments concentrations in samples taken between 1983 and
1987 in the lagoon (all stations and depths included) are presented in Fig. 4. The level of POM
concentration observed at OS1 is correlated with the level of POM concentration observed in
lagoonal waters. This is more evident for POC (r = 0.94, p = 0.0005) and PON (r = 0.86, p = 0.006) but
is also true for chl a (r = 0.59) and POP (r = 0.50). Therefore, the POM water content of OS1 was
influenced by the lagoonal discharge. Quasim and Sankaranaryanan (1970) observed a similar
feature : POC concentration in surface oceanic waters at 2 km from the Karawatti atoll (Laccadives)
was 3 times higher than POC concentration 12 km seawards. We can estimate the average POC and
PON concentrations in oceanic waters when the lagoonal discharge is zero by the intercepts of the
regression lines : POC concentration at OS1 versus POC concentration in the lagoon (58 + 26 mg
C m® ), and PON concentrations at OS1 versus PON concentration in the lagoon (6 + 3 mg N m-3).
The POP concentration in oceanic waters can be calculated from the POP average concentration
measured in the upper 100m (0.7+0.3mg Pm-3)

Table 3 : Average concentrations of POM in the lagoon of Tikehau and oceanward the pass.

Chla Phaeoa ATP POC PON POP C/N
mgm? mgm3 mgm3 mmolm3 mmolm-?3 mmolm-3 at:at

Ocean
Mean 0.06 0.03 0.02 52 6 0.7 8.7
SE 0.004 0.003 0.004 3 0.5 0.1 0.4
(n) 58 58 13 31 31 41 31
Lagoon
Mean 0.18 0.07 0.11 192 21 Delf 9.1
SE 0.003 0.002 0.005 5 i 0.1 0.2
(n) 409 409 162 290 289 224 289
aoe 5 0.35
i POC As DOR Chia
200 i ij 3 I | 0.25
2 I | a 8s
fo) 1 0.15
83 84 85 86 87 83 84 85 86 83 84 85 86 87
40 0.16 OA
PON ATP
AG q ] T } Gos | Phaeoa
0.08 {
56 | } { ] 0.06
0.04
10 O :
years years years

Fig 4 : Mean (+ SE) POC, PON, POP, ATP and pigment concentrations in the lagoon of the Tikehau atoll as
function of year (expressed in mg m-3).

Concentrations are found to vary with depth in response to a resuspension of detritus that
accumulates in deep waters. On the average, POC concentrations recorded near the lagoon floor
were 37% higher than those measured in surface water, whereas PON were 27% greater, 31% for
POP, 32% for Chla, 43% for phaeo a and 1% for ATP. The average POM concentrations in the lagoon
may be strongly influenced by climatological events such as storms or hurricanes. The average POC
concentration in the lagoon was unusually high in July 1983 (466 mg m3) after cyclones that occured
at Tikehau in early 1983.

POM size and composition

Size repartition of the POM is summarized in Table 4. On the average, 50% of the POM is made up
of suspended particles smaller than 5 jm but this percentage can vary considerably : i.e. : 72 to 90%
of the POM was in the 0.7-3 ym size class in April 1986. This discrepancy is probably due to the use
of Nucleopore filters instead of Millipore filters. New results at different times have shown that 80 %
of the POM pass through a Nucleopore 3 pm. Therefore, the average POM passing through 5 ym is
probably much higher than 50 %.

Table 4 : Means (+ SE) of POM passing through a 5 pm (1984 and 1985) or 3m (1986) pore filter as a percentage
of total POM at the Faufaa station, south of the Tikehau lagoon. Standard error of samples taken at same dates
are given (from Charpy and Charpy-Roubaud, 1991).

Date Chla(%) Phaeoa (%) ATP (%) POC (%) PON (%) POP (%)
23 Nov 1984 - 47+2 35 +0 24+1 75 £19

24 Nov 1984 66+5 - 48 + 26 61+7 57S 88

2 Apr 1985 5725 - - 43 +14 55 + 23 74/2 7f

9 Apr 1985 3246 40 +35 68+11 33 £11 46 + 16 47 + 20
12 Jul 1985 57 29+17 30 35 32 29

13 Aug 1985 25+4 34 20+5 - - 24+ 12
7 Apr 1986 92+5 7443 75 +24 81+1 TUES 99+2

Average + SE 50 +6 45 +8 4646 50+6 54+£5 49 +6

Phytoplankton account for 35% of the living carbon with a strong dominance of cyanobacteria while
heteroflagellates and ciliates account for 6% of the living carbon (fig.5) (Blanchot et al., 1989).

&

=

g

i

$s

2 & N
3 § S
2 = i)

s 2 = oT 2.5 4.4
a = s al
8 5

cyanobacteria
om Microp
mesoplankton-

SO heterofia

ou

| | | | |
ise « EN Seo el eo sopm |7— 35 10 200pm — |= 200 to 2000 pm—,

| | | | |

Fig. 5 : Size distribution of organic seston weight (mg C m3) for different size-classes of seston (<3 um, 3 to 35
Lim, 35 to 200 um, 200 to 2000 pm) in the Tikehau lagoon. Data for living C of 35 to 200 um and 200 to 2000 um
size class were calculated using ATPx125 (from Blanchot et al., 1989).

Sedimentation of Particles

Sedimentation rates as well as settling velocities of POM were studied by setting a sediment trap far
enough from the bottom (5 m) to collect only materials sinking from surface layer. Results listed in
Table 5 show that the sedimentation rate of POC and PON (i.e. : 350 and 36 mg m-2 d-1) are close to
the values given by Taguchi (1982) in Hawaii. Sedimentation rates at Tikehau are however four
times lower than the values for organic deposition in the lagoon of One Tree Island (Australia) given
by Koop and Larkum (1987) and are also 2.4 times lower than the POC deposition rate found by
Chardy and Clavier (1989) in New Caledonia.

The mean sedimentation rate of total pigments (i.e. : 0.23 mg m-2 d-1) is four times lower than
sedimentation rate given by Taguchi (1982) in Hawaii and four times lower than Chl a deposition
rate calculated from Chardy and Clavier (1989) in New Caledonia.

The average POC:PON:POP ratio on a mass basis in trapped material was 117:12:1 while the ratio in
suspended material estimated during trapping experiment was 68:7:1. The loss of phosphorus in
trapped particles indicates that organic matter was dead and that a non-negligible part of POM is
mineralized in the water column. This was latter confirmed by ATP measurements in trapped
materials which were all zero.

Table 5 : Mean (16 data) trapping rate (TR ; mg m-2 d-1), settling velocities (SV ; m d-1 ) and C:N:P ratio (w/w)
of trapped material measured at Faufaa station, south of the Tikehau lagoon.
In brackets, coefficient of variation (%)
Phaeo a POC C:N:P
TR Vs TR VS TR VS TR Vs TR Vs

0.11 0.6 0.12 14 3.2 1.7 350 2.6 36 2.2 117:12:1
(66) (72) _ (67) (74) (78) (25) (94) (116) (97) (104) |

Origin of lagoonal POM

Findings of Charpy and Charpy-Roubaud (1990b) indicate that the detritus pool (84% of POC)
originates in lagoonal primary production whereas detritus reef flat export toward the lagoon is
insignificant. The phytoplankton production ingested and then excreted as fecal pellets by
zooplankton cannot alone explain the levels of POC sedimentation rate. Export of POM from lagoon
pinnacle reefs may thus be the other major POC source.

NUTRIENT BUDGET

Fluxes between lagoon and ocean can be estimated by :

Flux (mmol m-2 d-1) = F \f(Cl-Co,Ls)

Where F is the annual average flow through the pass and the reef-flat spillways (6 108 m-3 d-1 in
Lenhardt, 1991), Ls is lagoon surface (4.2 108 m2) and Cl and Co are concentration of total nitrogen
(XN), total phosporus (XP) or silicate in the lagoon - Cl -and ocean - Co - (XN =
NO2+NO3+NH4+DON+PON and XP = PO4+DOP+POP where DON and DOP are dissolved
organic nitrogen and phosphorus concentrations). Average concentrations in the lagoon and ocean
are recapitulated in Table 6.

If we compare this data with the water composition at Christmas Island given by Smith et al. (1984),
we observe that Tikehau surrounding waters present similar YP concentration but lower XN and
silicon concentrations. Inside the lagoon, nutrient concentrations are quite similar exept for the
silicon which was 3.5 times higher in Christmas Island.

Table 6 : Average concentrations + 95% confidence intervals (mmol m-3) of total nitrogen (XN), total
phosphorus (P) and silicate in oceanic (Co) and lagoonal waters (Cl) (from Charpy-Roubaud et al., 1990).

Nutrient Ocean waters Lagoon waters
NH, 0.80 1.90
NO 0.04 0.02
NO3 0.30 0.09
DON 2.30 4.60
PON 0.40 1.40

x=N 3.80 + 1.30 8.01 + 0.90
PO, 0.38 0.16
DOP 0.26 0.39
POP 0.02 0.10
xP 0.66 + 0.12 0.65 + 0.06
SIO2 1.00+ 0.20 0.80+ 0.40
Nitrogen budget

During their crossing over the reef-flat and their residence in the lagoon, oceanic waters become
impoverished in NO2 and NO3 and enriched in NHg4 and organic nitrogen. The total nitrogen
concentration in the lagoon is roughly twice as great than in the ocean (i.e. : 8.0 mmol N m°3 vs
3.8 mmol N m-3 in ocean). Therefore, according to the flux equation, the nitrogen concentration of
oceanic water increases at a rate of 0.6 mmol N m-2 d-1 during its residence time in the lagoon.

Increase in the nitrogen content of water flowing above the reef-flat is attributed to gaseous nitrogen
fixation mostly by cyanobacteria of which a great variety occur on limestone substrata of coral reefs.
At Tikehau, large quantities of cyanobacteria (i.e. : 150,000 cells ml-1) were recorded in the lagoon
water column by Blanchot et al. (1989). Charpy-Roubaud et al. (1989) have estimated that their
productivity, added to that of benthic cyanophycean communities, is 0.69 g C m2 d-1. This carbon
production would require nitrogen assimilation of approximately 3.6 mmol N m2 d-1, part of which
could originate from dissolved molecular nitrogen.

Phosphorus budget

Mineral phosphorus (PO4) water content decreases and organic phosphorus (DOP+POP) content
increases during crossing of oceanic waters over the reef edge and during the residence time in the
lagoon. Depletions of reactive phosphorus below oceanic levels were also observed by Smith (1984)
and Smith and Jokiel (1975) in Christmas Island and Canton Atoll lagoons, both located in the
Pacific. The total phosphorus concentration in the lagoon (XP = 0.65 mmol P m~°3) is of the same
order of magnitude than phosphorus in the surrounding oceanic waters (XP = 0.66 mmol P m-3). The
phosphorus budget therefore appears to be well balanced.

The pattern of production emerging from all the foregoing discussion is that the high primary
production over the reef and in the lagoon results from an input of nitrate and phosphate from
enriched oceanic waters, from a great gaseous nitrogen fixation by cyanobacteria and from the
mineralization of organic compounds in the lagoon.

NUTRIENTS IN SEDIMENTS OF THE LAGOON : FIRST RESULTS

Nutrient mineralization may occur in the water column (excretion and bacterial metabolism), at the
sediment-water interface (hereafter expressed SWI) or within the sediments. The importance of
recycling of autochtonous material at SWI and within sediments was estimated by measuring
nutrient fluxes at the sediment-water interface. Two different approaches were used in order to
assess these fluxes. These were : 1) direct measurement which uses a benthic chambers technique
described by Hall (1984), carrying out the experiments in oxic (supply with oxygen) and anoxic
(asphyxiation) dark conditions and 2) calculations through measurements of chemical gradients
close to SWI, in peeper, following method previously described by Hesslein (1976). The results
presented here have to be considered as preliminar.

Nutrients in sediment were studied at four sampling stations shown in Fig. 6.

148° 16'W
14°55'S

LEEWARDS
ZONE

See ae

Out_flow
Of lagoon
water

St. Faufaa (19m)

. @ Gi(24m) 9
SBE
pe Per : 148° 05°W

AT In_ a of
oceanic water

SEAWARDS
ZONE

Fig. 6 : Location of sediment flux sampling stations (e.g. : Ds, G1, Q, P1 and Station Faufaa).

Dark benthic chambers were used at stations Q and P1 because of the shallowness of these sites. In
order to compare fluxes measured in oxic and anoxic conditions, the only analytical results taken
into account are those obtained after oxygen depletion was achieved in the non-O2 supplied
chamber (hereafter termed asphyxiated chamber). Fluxes (F in mol m-2 d-1) can be estimated from
the slope dC/dt of a plot of concentrations versus time multiplied by the ratio of supernatant-water
volume V to chamber area S (V = 0.025 m3; S$ = 0.11m2). The formula is:

F = \f(dC,dt) x \f(V,S)
The in situ peeper sampling method was used at three stations (DS, G2 and P1 see Fig. 6)

10

Benthic chambers

Variations of the chemical composition of water enclosed in the benthic chambers vs time is shown
on Fig. 7. NO3 and NO? concentrations do not appear because they were below the detection limit
(<1 mmol m-3).

Station Q Station p1

NH,

time (in hours) time (in hours)

Fig. 7 : Evolution of inorganic nutrients (mmol m3), dissolved O7 (mmol m-3) and pH of overlying water
inside asphyxiated and oxygenated dark benthic chambers at station Q and P1. Nutrient fluxes are calculated in
the shaded area.

11

Station Q : In the asphyxiated chamber, O2 concentration decreases with time and was less than 30
mmol m-3 after 90 hours of incubation while nutrient concentrations sharply increased. In the
oxygenated chamber, a slight increase in concentration was observed for NH4 and SiO? , but the PO4
concentration remained nearly constant at a very low level. The concentration plateau that was
observed after 125 hours was most likely due to a steady state occuring between enclosed and
interstitial waters. Therefore fluxes are calculated between 90 and 120.25 hours, figured by the
shaded area on Fig. 7.

Station P1 : Oxygen depletion in asphyxiated chambers occured after 69 hours. The same trends
were observed for PO4 and NHjg like at station Q in both chambers. Silica concentrations exhibit a
plateau after 65 hours of incubation. NH4 and PO, fluxes were therefore calculated between 68.75
and 95.25 hours while the SiO? flux was calculated between 24 and 64.5 hours.

The foregoing drives to notice that an increase in NH4 and PO, occurs in asphyxiated chambers at
both sites. When oxygen concentration is preserved, a slight increase occurs in NH4 while PO4
remains constant at a very low level. Dissolved silica exhibit similar patterns at both sites and do not

seem to be related to oxic/anoxic conditions. Calculations of nutrient fluxes are summarized in
Table 7.

Table 7 : Dissolved nutrient concentration increases (dC in pmol m3) during dt = 30.25 hours at station Q and
dt = 26.5 hours at station P1 and fluxes (F in pmol m2 d-1) from the sediments of the Tikehau lagoon. asph. =
asphyxiated chamber; oxy. = oxygenated chamber.

NH4 PO4 N/P SiO2
Station param. _asph. Oxy. asph. oxy. asph. Oxy. asph. Oxy.
Q dC 92.7 6.6 2) 0.21 18 5)
dt 30.25 30.25 30.25 30.25 30.25 30.25
F 16.71 1.18 521 38 32 31 329 274
P1 dC 12.2 9.2 YP 0.0 4.7 3:1
dt 26.5 26.5 26.5 26.5 40.5 40.5
F 2.25 1.89 356 0 7 630 411

As a general trend, fluxes of nutrients are higher in anoxic than in oxic conditions. This is more
obvious for PO4, of which fluxes were close to 0 when oxygen was present but when the oxygen
level was less than 0.30 mmol m°3, they reach between 356 and 521 pmol m-2 d-! . These differences
can be interpreted as the result of biological and/or chemical processes. The biological process can
be summarized as follows : the onset of anoxia allows some micro-organisms to metabolize organic
material in the upper part of the sediment column (i.e. : increase in NHg flux may be due to
amnonifier metabolism). Anoxia can possibly kill aerobic micro-organisms at SWI which in natural
conditions have a dark uptake of N and P without any silica requirement. The chemical process can
be that in oxic conditions, scavenging of P onto FeEOOH?2 is commonly observed in marine
sediments. Therefore, fluxes measured in asphyxiated chambers probably overestimate actual fluxes
while those obtained when oxygen is present can estimate a nutrient availability for lagoonal
primary producers.

Pore water

Pore-water profiles of nutrients display significant concentration gradient with depth as shown in
Fig. 8. These gradients are maximum within the first top centimeters and correlated with the
decrease in pH. Pore-water nutrient concentrations increase with depth, being greater at deep
sampling stations. H2S appears to be below the SWI, at about 1 cm depth at station DS and 5 cm at
P1 and G2.

12

oe
e

STATION G1

STATION

a
a

STATION Ds

Fig. 8 : Variations of pH, inorganic nutrients (mol m-3), hydrogen sulphide (mol m-3), chloride (mmol m-3)
and sulphate (\1mol m-3) in sediment pore-waters at various stations (G1, P1 and Ds) in Tikehau lagoon ,

13

The acidification of pore water downward in the sediment core, reflects the increase in total
dissolved CO? related to mineralization processes. At the top of the sedimentary column, dissolved
O2 is the main electron acceptor. Oxygen is replaced downward by sulfate and H2S appears in
profiles owing to sulfate reduction. Deeper, there is a decrease in H2S concentrations which is
probably linked to a chemical control by FeS precipitation.

Positive gradient of concentrations close to SWI allow diffusion of nutrients from medium pore
water to overlying sea water. PO4 concentrations are lower than NHq concentrations
(i.e. :7 mmol m-3 PO4 against 137 mmol m-3 NH4). However, phosphate has been shown to strongly
adsorb on calcium carbonate. This has been used to explain why calcium carbonate-rich sediments
contain low concentrations of dissolved phosphate in their pore waters (Krom and Berner, 1980).

The calculation of fluxes (F in pmol m-2 d-!) using pore water data can be calculated after Fick 1st
law. The equation can be written :

F=@ x Ds x \f(dC,dz)

where @ is the interconnected porosity estimated at 0.70 + 0.01, Ds is the in situ diffusion coefficient
in m2 d-! where tortuosity is taken into account, dC/dz is concentration gradient in pmol m-4 when
z tends toward zero. Results are presented in Table 8. They show that for each nutrient, flux
increases with lagoon depth.

Table 8 : Average + SE of dissolved nutrient fluxes calculated with pore-water gradient concentrations
(umol m-2 d-1).

Station NH4 PO4 SiO2
Ds 493 + 192 135 466 + 164
Gl IiveeG) 0.5+0.3 164 + 68
Pl 0 0 68 + 27

Comparisons between calculated fluxes with pore water data and observed fluxes in benthic
chamber

_ Observed fluxes for ammonium in oxygenated and asphyxiated chambers are much greater than
fluxes calculated using pore water data (which are close to 0). Observed fluxes for PO4 are higher in
asphyxiated chambers. Observed fluxes for Si are 6 to 9 times higher than calculated fluxes.
Therefore, diffusion processes through SWI are unable to explain NHq, PO4 and Si fluxes observed
in an asphyxiated chamber, but can explain the light POq flux and 17% of Si flux measured in
oxygenated chamber. The enhancement of transport across the interface may be due to bioturbation
of sediment located in the upper part of sedimental layer. Nutrients coming into benthic chambers
are then uptaken following different rates depending on oxygen conditions and on the elements
considered ; P is probably uptaken more quickly than N and Si. So in this kind of environment, it
seems more realistic to define a dispersion coefficient rather than a diffusion one. For dissolved
silica, the dispersion coefficient is 5.7 10-5 cm2 s-1, about 10 times greater than difusion coefficient Ds
(i.e. : Ds = 6.5 10-6 cm2 s-1). Therefore, nutrient fluxes measured in oxygenated chamber are assumed
representative of real fluxes.

14

LAGOON PRIMARY PRODUCTION

PHYTOPLANKTON PRODUCTION

Phytoplankton of coral-reef ecosystems have often been considered as a low primary producer since
the overwhelming majority of coral-reef studies were carried out in shallow ecosystems. In atoll
lagoons, the reef area vs the total area (reef and lagoon) ratio is low. Lagoonal plankton may thus be
a major contributor to total primary productivity of the ecosystem as a whole.

Carbon production

Table 9 gives an account of the average of mean carbon assimilation rates (hereafter expressed AC)
by depth intervals measured through an estimation of 14C and 32P assimilation rates. The average
AC is clearly related to depth, being higher in the surface layer than at other depths. No
photoinhibition at high light intensity occur.

Table 9 : Average carbon assimilation rate (AC ; mg C m°3 hv!) and assimilation number (AN ; mg C mg-1
Chl-a hv) in relation with depth (n = number of samples) (from Charpy-Roubaud et al., 1989).

Depth (m) n AC AN
0-2 52 3.92 + 1.02 Dilelt7-5
2-5 22 2.27 + 0.67 13.0 + 5.1
5-10 42 2.68 + 1.33 13.5449

10-15 21 2.00 + 0.72 11.2+5.6
15 - 20 7. 1171.15 4.7+3.5
20 - 24 2 0.54 4.2

Phytoplankton production integrated up to 15 m depth drops during May, June and August. This
decrease is correlated with light energy reduction that occurs in winter of the southern hemisphere.
Phytoplankton biomass is low (e.g. : 0.18 + 0.01 mg Chl-a m°3) but this is typical of coral reef
ecosystems. Biomass is greater in May, June and July while conversely, production rates are lowest.
Concentrations in the lagoon are approximately three times greater than those found in surface
oceanic waters.

Daily phytoplankton production estimated for each bathymetric intervals reaches an average of
0.44 g C m2 d-! for the entire lagoon, equivalent to 0.012 g P m-2 d-1. This value is high compared to
the low phytoplankton biomass measured. The representative assimilation number estimated from
the average hourly production (i.e. : 44 mg C m2 h-!) and the average chlorophyll integrated over 25
m (4.86 mg m-2) is 9.8 mg C mg Chl a! h-l, a value characteristic of small-sized plankton. The
assimilation number is conspicuously high in the surface layer (i.e. : 21 mg C Chl-a h-!).
Approximately 1.4% of daily production is lost by sedimentation of organisms while the exit of
particles out of the lagoon represents a loss of 0.2%.

15

Phytoplankton biomass and composition

Charpy (1985) and Blanchot et al. (1989) had previously shown that a great part of lagoon
phytoplankton is made up of cells smaller than 5 pm with cyanobacteria dominating. Cyanobacteria
can contribute to up to 75% of the carbon production of plankton primary producers. Table 10 allows
comparison between phytoplankton production of waters pre-filtered on Nucleopore 54m and of
waters unfiltered. The percentage of total production due to phytoplankton of a size smaller than
5m varies in a spread of 13 to 90% with average at 38 + 10%, whereas the percentage of 0-5 um
chlorophyllian organisms is 61 + 12% on the average in unfiltered waters. It appears that the smallest
cells are being differentially ruptured to a greater extent than large cells, leading to an
underestimation of carbon uptake (but not chlorophyll content) by the smallest cells.

Table 10 : Phytoplankton Carbon assimilation (mg m-2 h-!) in samples filtered on 54m (AC<5y) and without

filtrations (ACt); AN = assimilation number (mg Chl a-1 h-1); SAC = AC<5yx100/ACt; %Chl = percent of
chlorophyll passing through 5 pm filter (from Charpy-Roubaud et al., 1989).

Date St. Depth ACt AC<5u %AC ANt AN<Su %Chli

24 Jul 83 2 0 4.9 2.3 47 13.3 Ups) 86
5 2.8 23 82 74 6.4 95

10 Sid 1.8 56 9.0 4.9 99

26 Jul 83 9 0 4.0 2.6 65 14.7 14.0 68
5 3.1 2.8 90 10.0 12.4 73

10 317, 2.0 53 11.8 8.6 74

23 Nov 83 6 0 5.6 2.5 44 18.7 12.4 67
24 Nov 84 6 0 2.6 es) 58 11.7 8.3 81
25 eS 51 12.4 Ue 90

10 3.6 1.5 42 172 8.3 86

5 On Jel 44 13% 6.1 95

27 Jan 85 0 lagi 0.4 18 10.0 3.9 47
12 Jul 85 0 4.5 0.6 14 15.4 3.8 54
13 Aug 85 0 Aek 0.3 14 10.2 4.9 30
2 14 0.2 14 Sh 4.5 17

4 I 0.3 20 Ue) 5°, 28

6 1.4 0.2 15 8.2 4.5 26

8 1.1 0.2 18 7.0 4.1 31

10 0.9 0.2 28 a7, Bel 18

15 0.7 0.1 18 3:3 2.6 18

14 Aug 85 6 0 72 0.3 25 Seo) 3.1 44

16

Relationship between phytoplankton production and light energy

Phytoplankton production is significantly correlated with light energy. Phytoplankton production
(PP in mg C m°3 hr!) can be estimated from the equation :

PP = 1.29 Eh0.39

where Eh is incidental light energy in E m2 h-1.

MICROPHYTOBENTHIC PRODUCTION

Carbon production

Primary production was estimated by O2 budget, measured within clear and dark plexiglass domes.
In order to assess the influence of light energy on net oxygen production, measurements of O2
budgets were carried out continuously at various depths. Net O2 production and light energy were
positively correlated (r=0.7, n=91) and thus, daily production (DBP) was estimated by equation :

DBP (mg O2 m-2 d-1) = Pt-to x \f(Ej ,Et-to)

where P}-to = net production in mg O2 m2 during incubation period t-to
Ej = Daily incidental light energy in E m2 d-1
Et-to = Incidental light energy in E m2 d-! during incubation period t-to

The mean hourly respiration rate measured in dark domes was 31 + 7 mg O2 m~ with a respiratory
and photosynthetic coefficient chosen as being equal to 1 for latter conversion in carbon production.
By averaging production by depth intervals, the overall lagoon microphytobenthos production was
found to be equal to 0.25 gC m-2 d-1- This value is of the same order of magnitude as production
values for tropical marine sediments reviewed by Charpy-Roubaud (1988).

Benthic carbon production (BP) can thus be related to incidental light energy (Eh in E m-2 h-1) by the
equation :

BP (mg C m2 hr!) = 28.78 Eh0-45

Biomass

Microphytobenthic biomass was measured in 185 samples taken at different stations and at different
time of the year. There are considerable variations among sampling stations. The average total
chlorophyll biomass is 19.7 + 1.4 mg m-2 whereas the average active chlorophyll is 9.6 + 1.4 mg m2.
The mean hourly assimilation number estimated from the latter biomass is of 2.6 mg C mg
chlorophyll"! h-1. Biomass is significantly higher in the 0-3 m depth interval than in deeper intervals.

COMPARISON BETWEEN PHYTOPLANKTON AND MICROPHYTOBENTHIC PRIMARY
PRODUCTION

Fig. 9 shows phytoplankton, microphytobenthic and total primary production by a 5 m depth
interval. Total primary production is slightly the same whatever the depth interval is. Phytobenthic
production is greater than phytoplankton production within the first 10 meters, being 25 times
higher in the 0-5 m depth interval. From 20 m downward, phytoplankton is the major contributor to
total primary productivity of the whole ecosytem. On the average, phytoplankton primary
production is 1.8 times greater than phytobenthic production.

17

| Phytoplanktonic production
BB Phytobenthic production
| Total primary production

~~
i
1e)
N
!
E
O
Lo)
iS
—
Cc
(o}
a)
oO
=)
12)
(oe)
(=
Qa
>
(=
WO
iS
(=
jou

as

5-10 10-15 15-20 20-25 25-30 30-35 35-40
Depth (m)

Fig. 9 : Benthic, planktonic and total primary productions in the Tikehau lagoon by a 5 m depth interval (from
Charpy-Roubaud, 1988).

RELATIONSHIP BETWEEN LIGHT AND PRIMARY PRODUCTION IN THE LAGOON.

Light energy

Percentages of light energy measured at surface decreases with depth d (m) according to the
equation :

% of incident energy = e(4.45 - 0.06d)
It was measured that 17% of surface light energy reached 25 m ( average depth of the lagoon).
Phytobenthos and phytoplankton production

According to the foregoing sections, phytoplankton production (PP) can be related to incidental light
energy (Eh) with a standard error of 0.6 mg C m-3 hr! by the equation :

PP = 1.29 Eh0.39 (1)

18

Phytoplankton production per unit volume can then be converted into production per unit area
according to the equation :

d
PPd = | PPz dz (2)
0

where PPd (mg C m-2 h-1) = production at depth d per unit area, PPz (mg C m-3 h-!) = production at
depth z per unit volume.

Using equation (1) and (2), phytoplankton production is related to light by the equation :

d
PPd = | @ 0.254 [e(4.45-0.062)E},, /100 ]0.39
0

where Ehs (E m2 h-1) is light energy at the surface.

Similary, the relationship between phytobenthos production at depth d (BPd in mg C m2 hr1) and
light energy Ehs at surface level can be written :

BPd = 28.78 (e(4.45-0.06d)\ F(Ehs,100)) 9-454 (3)

Predicted plankton and benthic production were calculated at depths between 0 and 36m (ie. :
maximum depth of the lagoon) for different Ehs values observed in natural conditions
(1-8Em-72h-}). Results presented in Fig. 10 indicate that phytobenthos production exceeds
phytoplankton production in the upper 18 m. The total primary production (PT) is relatively
constant with depth and depend primarily on light energy reaching the surface. Therefore, an
average PT can be obtained for each Ehs value and subsequently, a linear relation linking PT and
Ehs, i.e. :

PT = 6.5 Ehs + 31.5

Therefore, daily total production PTd can be calculated assuming a sun time of 10 hours a day by the
equation :

PTd (mg C m2 d-1) = 6.5 Eds (E m2 d-1) +315 (4)

The PTd value for Eds = 0 is 315 mg C m-2 d-1; may be interpreted as the respiration in the water
column and sediments. Daily light energy data obtained in 1986 can be converted into daily primary
production using equation (4). Monthly averages of PTd are plotted in Fig. 11. Over the entire year,
the surface lagoon received a total of 15,550 E m-2 of which water column and sediments produced a
total of 216,709 mg C m-2, equivalent to a daily average of 0.59 mg C m-2 d-1, not very different of
the value of 0.69 mg C m-2 d-! estimated through field experiments.

19

mg C m-2 hv!

0 18 36 0 18 36

depth (m)

Fig. 10 : Predicted phytoplankton production (dashed line), phytobenthic production (dotted line) and total

production for different surface light energy levels (Ehs : E m2 hv!) in Tikehau lagoon from Charpy and
Charpy-Roubaud (1990a).

The photosynthetic efficiency of lagoonal communities can be summarized as follows :
- One mg of Chi a allows an hourly growth production of 4.2 mg carbon

- One Einstein reaching lagoon surface allows the growth production of 14 mg of organic carbon in
_ the water column and sediments.

mg C m2 g-1

month

Fig. 11 : Monthly averages and confidence intervals (p=95%) of predicted total primary production (plankton
and benthos) in 1986 in Tikehau lagoon (from Charpy and Charpy-Roubaud, 1990a).

20

mg dry wt m7?

mean: 33.5 mg m-3

1»)
A
1965 1966

[J bioom [ Xp

Fig. 12 : Variations in mesozooplankton dry weight from April 1985 to April 1986 in the Tikehau lagoon. Blooms
of Thalia democratica (Salps), appendicularians (Appendic.), the pteropod Creseis chierchiae and the copepod
Undinula vulgaris are shown. D: large amount of detritus (from Le Borgne et al., 1989).

Table 11 : Relative contributions (%) of the main taxa to total zooplankton biomass in Tikehau lagoon. Percent
contributions of non-living organisms (detritus) to total dry weight is also shown (from Blanchot and Moll, 1986
and Blanchot et al., 1989).

a: Three samples of mesozooplankton were measured in April 1986 (from Le Borgne et al., 1989).

Date Size class Taxon % total biomass % detritus
April 1985 = Microzooplankton nauplii 39.2
35-200 pm copepods 30.6 70
bivalve larvae 19.8
polychaete larvae 10.4
Mesozooplankton copepods 68.4
500-2000 um chaetognaths 19.3 14
salpids 8.8
Macrozooplankton salpids 63.2
>2000 zm copepods 22.8
chaetognaths 1.8
April 1986 | Mesozooplankton copepods 73.8
200-2000 um larvaceans 5.0 3,10,494
brachyuran larvae 8.7

chaetognaths 5.6

21
ZOOPLANKTON BIOMASS AND METABOLISM

The fate of the abundant particulate organic matter in the Tikehau lagoon and the level of efficiency
of utilization by consumers are two aspects which are of primary importance to an understanding of
the functioning of the lagoon pelagic food-web. Once sunk to the bottom, is seston consumed mostly
by pelagic animals in the water column or by benthic ones ? Do they give rise to a significant
predator biomass or is the efficiency of energy transfer between food and consumers low ? In order
to provide answers to these questions, zooplankton have been studied at Tikehau during two 10 d
periods in April 1985 and April 1986, and additionally by weekly samples taken in between.

ZOOPLANKTON BIOMASS

Fraction 3 to 35 zm (nanozooplankton)

An average number of 71 + 14 heteroflagellates ml-! and 7 ciliates ml-! were found in samples taken
in April 1986 in the lagoon. The mean individual volumes were of 542 + 96 tm? for heteroflagellates
and of 14 246 + 7 427 um for cilates. In order to assess the relative biomass of these taxa, mean
individual volumes were converted into carbon using a conversion factor chosen equal to
0.08 pg C m3 according to Sherr et al. (1984). The average biomass of heteroflagellates is
approximately 3.1 + 0.7 mg C m-3 while ciliate biomass is 7.6 + mg C m-3. These values are of the
same order of magnitude as those found by Hirota and Szyper (1976) in Hawaii though the method
used does not make any difference between dead and live plankters.

Fraction 35 - 200 j1m (microzooplankton)

Microzooplankton consists of 43% of organisms smaller than 100 um of which 73% are protozoans
(tintinnids:Rhabdonella sp., Codonellopsis sp. and Epiplocyclis sp. accounting for 64% ; naked ciliates for
5%). Foraminifers and radiolarians are poorly represented (less than 1%). Metazoans account for
only 27%. The second most abundant taxon smaller than 100 um consists of naupliar copepods (18%)
and the third of meroplankton bivalve larvae (8%). Out of organisms larger than 100 um, protozoans
account for 33% of total numbers of which 23% are tintinnids. Metazoans are noticeably dominant,
accounting for 67% of the total. Copepod nauplii are the most abundant organisms (41%). Bivalve
' larvae do not exceed 7% of total numbers.

By using a C/ATP ratio of 125, live microzooplankton biomass can be estimated at 1.52 mgC m-3-
Together with nanozooplankton, biomass of heteroprophs smaller than 200 jum reaches a value of
3.3 mg C m:3-

Fraction 200 - 2000 jzm (mesozooplankton)

Variations in mesozooplankton dry weight were monitored as regularly as possible in the lagoon
and displayed a measurement of two maxima in October 1985 (65 and 93 mg dry wt m3).
Zooplankton at Tikehau are characterized by periodic blooms of copepods, larvae, pteropods and
salpe. As shown in Fig. 12, the annual mean value is 33.5 mg m-3, which is six times greater than the
oceanic plankton concentrations measured in the vicinity of the pass (i.e. : 5.4 mg m-3). Relative
contributions of various size classes and taxa to zooplancton biomass are displayed in table 11.

22

Table 12 : Live biomass and detritus in terms of C, N, P estimated from the percentage of detritus in seston and
from particulate organic carbon values in the Tikehau lagoon. - a: ATP x 125 b: POC - (ATP x 125)

Sizeclass year Live Dead
(um) Cc N P Cc N P
35-200 1985 0.36 0.07 0.03 0.84 0.16 0.06
1986 1.02 0.19 0.08 2.37 0.45 0.18
1986 1.5a 2.30b

200-2000 1985 5.22 0.98 0.39 0.85 0.16 0.06
1986 2.80 0.53 0.21 0.74 0.14 0.06

1986 2.5a 4.4b
> 2000 1985 3.23 0.61 0.24 0 0 0
1986 0 0

Table 13 : Metabolic atomic ratios and contribution of inorganic excretion to total excretion (%) in the Tikehau
lagoon. O:O2 respired; NH4, Nt, PO4 Pt : ammonia, total nitrogen, phosphate and total phosphorus excreted.

nd : no data (from Le Borgne et al., 1989).

Date Size class/species O:NHqg O:Nt O:POq O:Pt NH4;POq Nt:Pt NHg4:Nt POg:Pt

April 1985 Microzooplankton thee 6.9 144 104 12.1 11.1 85.4 74.4
Mesozooplankton 10.8 10.8 119 92 11.4 8.6 100.0 76.5
Undinula vulgaris 18.4 13.2 132 100 7.9 79 48.2 43.1
Thalia democratica 15.5 8.1 103 56 74 6.9 58.3 54.3
April 1986 Microzooplankton nd ed, 124 96 nd 12.5 nd 77.5

Mesozooplankton nd 7.1 144 110 nd 8.4 nd 76.3

Table 14 : Zooplankton. Net growth efficiencies (K2) in terms of nitrogen and phosphorus for total populations
and sorted species or taxa, calculated from N: P ratios of particles (a1), zooplankton excretion (a2), and body
constituents (a3). Number of replicates in (brackets) (from Le Borgne et al., 1989).

Date Size class/species a a a K K

1 2 3 2,N 2,P

1985 Mesozooplankton (9-10 April) 13.9 (25) 8.6 (4) 15.0 (2) 0.894 0.828
Undinula vulgaris 13.9 (25) 7.9 (2) 25.7 (2) 0.623 0.337

Thalia democratica 13.9 (25) 6.9 (12) 20.4 (2) 0.761 0.519

1986 § Mesozooplankton (7-9 Apr.) 18.2 (4) 10.8 (2) 26.0 (1) 0.695 0.487
(10-12 Apr.) 16.3 (4) 10.8 (2) 26.0 (1) 0.695 0.487

(13-16 Apr.) 13.9 (4) 9.2 (2) 20.5 (1) 0613 0.416

mean 16.1 8.4 23.3 0.748 0.517

Mixed copepods 16.1 (12) 8.4 37.6 (1) 0.616 0.264

Microzooplankton 16.1 (12) 12.5 (6) 16.7 (5) 0.889 0.857

23

Zooplankton biomass in terms of C, N, P

By removing detritus of samples and by calculating their relative contribution to seston dry weight,
live zooplankton biomass can be estimated. Detritus dry weight represents 70% of 5-200 um
particles, between 1% and 21% of 200-2000 jm particles, and 0% of particles larger than 2000 pm.
Contributions of carbon, nitrogen and phosphorus to dry weight of detritus and zooplankton taken
separately were estimated by Le Borgne et al. (1989) enabling them to calculate biomass as shown in
Table 12.

METABOLISM

Zooplankton respiration and excretion were measured in three organism size-classes and in species,
Undinula vulgaris and Thalia democratica, which are abundant in the lagoon. Results of metabolic
atomic ratios and contribution of inorganic excretion to total excretion are summarized in Table 13.
Growth efficiency for the total population and sorted taxa are displayed in Table 14 and assimilation
efficiencies of copepods are listed in Table 15. As a general pattern, efficiencies estimated for
microzooplankton are greater than for mesozooplankton. Excreted nitrogen and phosphorus are
mostly inorganic. They meet 32% and 18% of phytoplankton nitrogen and phosphorus requirements.

Production was then estimated. All P/B ratios presented in Table 16 are greater than 34% which is
equivalent to a three day turnover time of the biomass. The turnover rate is shorter for mixed
zooplankton, close to one day and even shorter for the salp Thalia democratica due to, in all
probability, asexual reproduction, high water temperature (29.5 °C) and abundances of food as
emphasized by Le Borgne and Moll (1986). On the average, P/B ratios for zooplankton are 5.7 times
lower than P/B ratios estimated for phytoplankton.

The nitrogen and phosphorus assimilation rates in Table 17 are the sum of production and total
excretion rates. Ingestion is calculated from assimilation and its relevant effficiency.

Table 15 : Assimilation efficiencies (D) of C, N, P and their ratios (a4=DN:Dp a'4=Dc:DN). Calculations made
by the method of Conover (1966) using organic carbon, nitrogen and phosphorus percentages of dry weight in
feces and food. nd : no data (from Le Borgne et al., 1989).

Date Species Faeces Food D (%) a a’

C N P C N P CoN P
1985 Undinula vulgaris 0.40 0.10 0.048 2.36 0.25 0.081 83.6 60.1 38.3 1.57 1.39

1986 Small copepods 0.59 0.17 0.025 15.4 1.86 0.258 96.8 91.0 90.2 1.01 1.06
0.62 0.09 325/79 0:85m OSIS9 890695 ae ndiaend 0:99

24

Table 16 : Production rates in terms of C, N, P (ug mg7! dry wt d-1) and daily P:B ratios at Station 6. Body C,
N and P, as percentages of dry weight, allows the conversion of rates into P:B (from Le Borgne et al., 1989).

Date Sizeclass /species Production rates Body constituents P:B
C N P C N etre? (%)

April 1985 Mesozooplankton 164 44.65 3.565 20.7. 4.12 0.37 102.0
Undinula vulgaris 108 29.97 2.604 314 873 0.76 343
Thalia democratica 190 4288 5.859 1.91 0.43 0.0725 816.0

April 1986 Mesozooplankton 331 73.64 7.061 384 850 0.81 864
Mixed copepods __ 147 39.80 2.346 = 27.17.31 ~—0.43 54.4

Table 17 : Zooplankton. Assimilation and ingestion rates (ug C, N or P mg“! dry wt d-) in the Tikehau lagoon
(from Le Borgne et al., 1989).

Date Size class/ species Assimilation Ingestion
Cc N P Cc N P

April 1985 Mesozooplankton 656 TACT 10.57 785 102 15.1
Undinula vulgaris 515 48.3 Ups) 616 80 20.2
Thalia democratica 56.4 11.28 617 81 16.1
April 1986 Mesozooplankton 724 98.4 13.54 804 109 15.0

mixed copepods 473 64.6 4.67 526 7? 2

TROPHIC STRUCTURE AND PRODUCTIVITY OF THE ECOSYSTEM

With all data estimated in the foregoing sections of this chapter, biomass and fluxes of matter in
plankton and in benthos can be assessed. In order to enable comparisons between benthic and
planktonic ecosystems, standing stocks are in mg C m2 and fluxes in mg C m2 d-!. The trophic web
is illustrated in Fig. 13.

We did not measure directly the biomass of bacteria, but we think that we can obtain an order of
magnitude by the difference between liv C estimated from ATP and the other biomasses measured
or estimated. Therefore, free bacteria biomass (BB) may be calculated with the equation:

BB = liv C(<5 ym) - phy C(< 5 pm)
with: liv C(< 5 um) = percentage of ATP(< 5 ym) x ATP x 250
phy Cc< 5 ym) = percentage of chl ac< 5 ym) x chl a x (C/chl-a ratio).

The average value C/chl a = 50 (Charpy and Charpy-Roubaud, 1990 b) lies within the range
reported by Takahashi et al. (1985) for picoplankton and is very close to the ratio of 46 found by
Laws et al. (1987) for oligotrophic Pacific waters. Therefore :

BB = (0.46 x O.11 x 250) - (0.5 x 0.18 x 50) = 8.2 mg C m3

25

The liv CS - 35 ym) is made up of heterotrophs and phytoplankton (4.5 mg C m-3). It can be
calculated using ATP(5 - 35 ym) data : 0.54 x 0.11 x 250 = 14.9 mg C m°3. The carbon content of
heterotrophs in the size range from 5 to 35 lm was therefore equal to : 14.9 - 4.5 = 10.4 mg C m3. The
biomass of ciliates and heteroflagellates was equal to 1.8 mg C m-3 (Table 3), and the difference (= 8.6
mg C m°3) was certainly due to bacteria adsorbed onto the detritus (Charpy, 1985).

The total biomass of bacteria was therefore equal to : free bacteria + adsorbed bacteria =
16.8 mg C m-3. Such a biomass is commonly observed in waters over reefs ; Sorokin (1974)
summarizes data for biomasses of bacteria which range from 11 to 170 mg C m°3. More recently,
Moriarty et al. (1985) reviewed the productivity and trophic role of bacteria on coral reefs. They give
biomass values ranging from 19 to 150 mg C m3. Linley and Koop (1986) observed in the coral reef
lagoon of One Tree Island (Great Barrier Reef) a biomass of heterotrophic bacteria ranging from 1.2
to 16.2 mg C m-3, and Hopkinson et al. (1987) observed a bacterial biomass of 2 mg C m°3 in the
water column of Davies Reef (Australia). In Tikehau, in April 1986, the biomass of bacteria was
estimated at 17.1 mg C m-3 by Blanchot et al. (1989). The observed ratio free bacteria / adsorbed
bacteria = 2 is consistent with the ratios given by Moriarty (1979) and Moriarty et al. (1985) in coral
reef areas.

The estimated bacterial biomass was 2 times higher than the phytoplanktonic C in the Tikehau
lagoon. Dominance of bacterial biomass was also observed in the oligotrophic waters of the Sargasso
Sea by Fuhrman ef al. (1989); the interpretation of these authors was that bacteria consume sigificant
amounts of carbon probably released from phytoplankton directly or via herbivores.

DIC
A = 440

ZOOPLANKTON |_P
>35 ym

PHYTOPLANKTON
101

36-200 pm : 38
> 200 pm : 63
P=?
E=3

225

<5 pm : 113
>5 pm : 112

DETRITUS

4268

5 pm : 2050
5-35 pm : 2050
35-200 pm: 58
> 200 pm: 110

| 420 <35 pm

46
ates : 33

cll
fi

BOO OOOO OO Dae OOOO OOOO

Fig. 13 : Trophic structure and productivity of the Tikehau lagoon communities. Standing stocks (mg C m2) are
in boxes , and fluxes (mg C m2 d-1) are represented by arrows. A = assimilation, E = excretion, Ex = export,
I = ingestion, P = production, S = sedimentation, DIC = dissolved inorganic carbon

(from Charpy and Charpy-Roubaud, 1990b).

Detritus, smaller than 35 ym, represent the most important particulate organic carbon pool in the
lagoon. They originate from lagoonal primary production (Charpy and Charpy-Roubaud, 1990b)
and their sedimentation onto the bottom exceeds benthic primary production. Plankton bacteria
biomass is of same order of magnitude as microphytobenthos biomass and is equal to twice the
phytoplankton biomass. Pelagic bacteria dominance can be interpreted by a microbial loop returning
energy released as dissolved organic matter by phytoplankton and zooplankton, but also energy
released as mucus from lagoon coral communities.

26
ZOOBENTHOS BIOMASS IN SEDIMENTS : FIRST RESULTS

A survey of 20 random stations was realised in the lagoon by A. Intes to provide a first assessment of
the macro-zoobenthos of the soft bottoms. These unpublished data have to be considered as
preliminary results.

Taxonomic structure - results (Fig. 14)

In terms of abundance, the Molluscs and the Polychaetes dominate the endofauna with a mean
density of 11.3 and 10.4 ind m- respectively. The crustaceans count for less than 2 ind m-2 and the
Echinoderms as well as the lancelets less than 1 ind m-2. The abundance of the Crustaceans is
probably under estimated as only large apparent Invertebrates were counted and no digging
operations were carried out. Large Invertebrates burrowing in the sediment are not taken into
account and their biomass remains unknown. However, the average density of the big burrowing
species can be estimated to stand around 0.3 ind m~ as revealed by hole density.

Regarding the epifauna, the Sponges clearly dominate with around 0.5 colony m-2. The other
organisms are generally scarce except in some very localised areas harbouring high densities of
holothuroid (Halodeima atra).

TAXONOMIC STRUCTURE

Epifauna
ME Endofauna

Fig. 14 : Taxonomic structure of zoobenthos biomass in sediment (SW : Sea weeds ; ML: Molluscs ;
SP : Sponges ; SC : Sipunculids ; PL: Polychaetes ; CR : Crustaceans ; ED : Echinoderms) expressed in
Ash Free Dry Weight (AFDW).

In terms of biomass, the global structure is not very different : the Molluscs remain at first rank with
36% of the animal organic matter (AOM), followed by the Sponges with 27% of AOM. The third
class includes the Sipunculids, but also all the fauna living in the dead shells and in all probability
some micromolluscs. This represents about 25% of AOM. The other groups stand far behind in
importance : the Polychaetes are mainly small animals and contribute for only 9% to AOM. The
crustaceans are essentially little species such as Tanaidacae or Mysidacae. Some crabs (mostly
Portunids) are rarely collected in the endofauna and the contribution of the group to the biomass is
poor : 2% of AOM. Once again, this is under estimated by the lack of information on the big
burrowing forms. The Echinoderms are very few represented on the soft bottoms (Ophiuroids) with
only 1% of AOM.

27

Considering the total living biomass, the primary producers largely dominate with about 60% of the
total organic matter.

They are sea weeds such as Halimeda or Caulerpa belonging to several species, but they may also be
Phanerogams Halophila ovalis. (the sole species encountered in this lagoon).

Trophic structure - results (Fig. 15)

The deposit feeders are considered as a unique group. No distinction between the surface deposit
feeders and the burrowing deposit feeders is made. They are slightly the best represented with 46%
of AOM, but it must be emphasized that they belong to the endofauna (except the Holothuroid
Halodeima atra).

TROPHIC STRUCTURE

Epifauna

MB Endofauna

Fig. 15 : Trophic structure of zoobenthos in sediments (SW : Sea weeds ; DF : Deposit-feeders ;
SF : Suspension -feeders ; CR : Carnivorous),

The suspension feeders stand in the same order of magnitude with 42% of AOM. Most of them
belong to the same epifauna as Sponges do, but also some molluscs such as the bivalves Pinna are
found.

The carnivores are the least represented with only 12% of AOM. They are collected in the epifauna
(Molluscs as Strombus spp. or Nassarius spp.) as well as in the endofauna (some Crustaceans and
Polychaeta).

The deposit feeders are under estimated because the mud shrimps, or the Cardiidae for example, are
not taken in account by the sampling method.

Discussion:

A first biocenotic survey carried out by Faure and Laboute (1984) concluded from the study of the
coral species distribution that the whole lagoon belongs to a sole community inside which the
species distribution depends on geomorphological or physical factors. The study of the fish
community by Morize et al. (1990) leads to the same finding : there is only one fish community in the
lagoon, but its observed structures (which varies in space and biomass) are greatly heterogenous
without any evident explicative factor. The spatial heterogeneity of the benthic biomasses cannot be
explained by the classic factors such as sediment characteristics, bathymetry, and distance to the rim.

28

Two hypothesis can be advanced nevertheless :

1 -The mapping of the biomasses matches the mapping of the bidimensional modelisation of the
water circulation under the influence of the trade winds (see fig.12 of the first chapter). If the model
can be considered as relevant, the vortex generated by the wind will be a facilitating factor for the
organic matter sedimentation and consequently, would allow the development of the greatest
amount of benthic biomass of bottom invertebrates.

2 - The sample distance from a lagoon reef construction may be the best explicative factor. These
reefs, considered as a source of organic matter via the detritus released, may govern the bottom
invertebrates distribution. This hypothesis will be tested in the forthcoming research program
"Cyel”.

As only the soft bottoms were investigated in this quantitative survey, no cnidarians were collected :
the free living scleractinia as Heteropsammia, Cycloseris, or Trachyphyllia do not exist in French
Polynesia. Apart from this, the general structure is close to the structure observed in the New
Caledonia lagoon by Chardy and Clavier (1989). The three main groups in terms of biomass are the
same, respectively the macrophytes, the sponges and the molluscs. The crustaceans and especially
the echinoderms are relatively less represented in the Tikehau lagoon than in New Caledonia. Few
species of crabs and quite no pagurids, no urchins, no asterids were collected in or on the sediment.

The biomass of the macrophytes is higher than the total animal biomass, but its trophic role in the
bottom network cannot be appraised as few invertebrates seem to feed on them. Among the animals,
the suspension feeders stand to the same order of magnitude of biomass than the deposit feeders in
the Tikehau lagoon. Chardy and Clavier (1989), in New Caledonia, observed a suspensivores
biomass about twice the one of the deposit feeders. The lack of soft bottom free living scleractinians
may partly explain this fact.

The general trends of the trophic network described on the soft bottoms of the Tikehau lagoon may
be summarised as :

A highly simplified fauna in which most of the zoological groups are represented, but with a little
number of species ( about 80 taxa).

The trophic network is basically highly dominated by the macrophytes production, but their
consumers do not belong to the invertebrates fauna.

Among the animals, the suspension feeding guild is mainly represented on the sediment surface by
the sponges, but also by some molluscs or polychaetes living in the sediment.

The deposit feeding guild is better represented among the zoological groups, where the molluscs
and shell living organisms dominate in weight.

The two main guilds are quite equally represented at least on the soft bottoms. A first attempt to
explain this may be the weakness of the currents in the lagoon, allowing a near vertical
sedimentation on which only filter feeding organisms (i.e. actively pumping the sea water) may feed
in sufficient quantity before bottom accumulation. This hypothesis mark a basic difference with the
bottom network of New Caledonia, where the water circulation allows a higher contribution of the
suspension guild to the benthic network.

29

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SOROKIN (Y.I.) -1974 - Bacteria as a component of the coral reef community. Proceeding of the Second
International Coral Reef Symposium, Manilla, 1 : 3-10

TAGUCHI (S.) - 1982 - Sedimentation of newly produced particulate organic matter in a subtropical inlet,
Kaneohe Bay, Hawaii. Estuar. coast. Shelf Sci., 14 : 533-544

TAKAHASHI (M.), KIKUSHI (K.), HARA (Y.) - 1985 - Importance of picocyanobacteria biomass (unicellular,
blue-green algae) in the phytoplankton population of the coastal waters off Japan. Mar. Biol.,
89 : 63-69

PART II. REEF FISH COMMUNITIES AND FISHERY YIELDS OF
TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)

BY

B. CAILLART!, M.L. HARMELIN-VIVIEN’, R. GALZIN*®, AND E. MORIZE’

INTRODUCTION

Fish communities in the lagoon of the Tikehau atoll were studied by only a few researchers.
Harmelin-Vivien (1984) studied the distribution of the main herbivorous families (Scaridae
and Acanthuridae) in the lagoon and on the outer slope to 30 m in depth. The total fish
community of the outer slope was studied by Galzin (1985, 1987) at 12 m in depth. These studies
were carried out in the southwestern part of the atoll. Spatial organization of coral associated
fish community was studied throughout the lagoon by Morize et al. (1990). Most of the other
studies undertaken at Tikehau involved the artisanal fishery (Morize, 1984, 1985 ; Caillart
and Morize, 1986, 1988) and the biology of some target species to the exploited stock (Caillart
et al., 1986; Caillart, 1988; Morize et Caillart, 1987). It seems worthwhile to present in this
special issue of ARB, all the available information on the fish fauna of Tikehau. Furthermore,
this overview allows us to compare our results with others in the Indopacific region.

FISH COMMUNITIES OF TIKEHAU ATOLL

METHODS

To study the fish communities of Tikehau, two complementary methods were used : visual
census and rotenone poisoning.

Many synthesis (GBRMPA, 1978; Barans and Bortone, 1983; Harmelin-Vivien et al., 1985)
describe the method for estimating in situ fish communities and populations using visual
censuses. These methods, widely used on coral reefs, enable scientists to study fish communities
without perturbation. In the Tikehau atoll, visual censuses were carried out by SCUBA diving
on 50 m length and 5 m width transects. The transects on the outer slope and the inner reef flat
were parallel to the reef. Around the pinnacles, the sampling line was curved around them. In
each transect, abundance inside three caregories of size (small - medium - large) were
recordered for all species encountered (St. John et al., 1990).

1: Centre ORSTOM de Brest, BP 70, 29280 Plouzané, France
2: Centre d'Océanologie de Marseille, CNRS-UA 41, Station Marine d'Endoume, 13007 Marseille, France

3: Ecole Pratique des Hautes Etudes, CNRS-URA 1453, Laboratoire d'Ichtyoecologie Tropicale et
Mediterraneenne, 66860 Perpignan Cedex and Centre de l'Environnement, BP 1013 Moorea, French
Polynesia.

2

Fish hidden in reef shelters and in sediment were caught with ichtyotoxic rotenone. Individual
fish were measured to the nearest millimeter (standard and total length), weighted to the
nearest gram and preserved in a 10% neutral formalin. Length-weight relationships were
subsequently computed for all species caught, providing that the sample size was large enough.

The two methods were used to study fish communities in the lagoon, put only visual censuses
were used on the outer slope.

FISH COMMUNITIES OF THE OUTER SLOPE

Fish communities of the outer slope are strongly influenced by environmental factors : primary
substratum types, slope gradient, level of wind exposure, and magnitude of the 1983 cyclonic
damages on coral assemblages. Several surveys of the outer slope fish fauna were carried out on
the southwestern outer slope of the atoll (Fig. 1). For the damages induced by the cyclones and
the description of the outer slope, see the previous chapter on the environment by Intes and
Caillart.

148°15'

14°55°

~ Motu Oeote

Motu Puarua
a

vi y

,Paaie

Mamaa ‘Motu Mamaa RS
Tohuaao ae”
‘a in x
ov a yy
\ « Mauu eos 29 > YZ 15°05’ S

XN %, so

. are ue “Sy os 148°05°W
uherahera
( . fulage) oe

Fig. 1 : Location (Mamaa-arrow) of fish community sampling station on the outer
slope of the Tikehau atoll .

The fore reef area (0-10 m)

The spur and groove zone is an area of very high fish abundance. In particular surgeonfish
Acanthurus achilles, A. nigroris, A. guttatus, A. lineatus and parrotfish Scarus sordidus ,
Scarus sp. are typical features of this zone. Small coral dependant fish found are Cirrhitidae,
small Serranidae (Cephalopholis urodelus), Chaetodontidae (Chaetodon quadrimaculatus)
Pomacanthidae (Centropyge sp.), Labridae (Thalassoma fuscum), numerous Balistidae
(B. viridescens, B. undulatus and Melichthys niger and M. vidua in mid-water). The shark
Carcharhinus melanopterus and a great variety of Carangidae are also frequentely encountered
in this productive and well oxygenated area.

3

On the fore reef platform (4-10 m), benthic fish fauna (e.g. : Gobiidae, Chaetodontidae,
Acanthuridae, Serranidae, Labridae) can be distinguished from zooplankton-feeding mid-
water fish fauna (e.g. : Anthias spp., Pomacentridae, nocturnal Holocentridae and Naso spp.),
and upper-water fish fauna (Balistidae, sharks, tunas and Sphyraenidae).

The outer terrace (10-25 m)

The fish fauna of this zone present a great diversity (more than 100 species), and an abundance
of fishes. The most conspicuous families are Holocentridae (genus Holocentrus, Sargocentron,
Myripristis) numerous around coral patches, Lutjanidae (Lutjanus bohar, L. gibbus, L. kasmira)
forming schools of several hundred individuals, Acanthuridae (Ctenochaetus striatus, C.
strigosus, Zebrasoma scopas, Acanthurus glaucopareius, A. nubilus and schools of Naso spp.),
Serranidae (genus Variola, Gracila and the common grouper Epinephelus microdon),
Chaetodontidae and some Scaridae (Scarus gibbus, S. niger, Cetoscarus bicolor).

The deep outer slope (from 25 m)

Abundance and diversity of fish fauna decrease somewhat but a new, more characterized,
species assemblage occurs with depth. Holocentridae and Scaridae are less important while
the abundance of large Serranidae, some Labridae (genus Bodianus, Cirrhilabrus), Zanclidae
and Heniochus noticeably increase. Among Chaetodontidae still present, species of the genus
Hemithaurichtys appear. Among the Acanthurid censused are, Acanthurus bleekeri, A.
pyroferus, A. xanthopterus and large schools of Naso hexacanthus and Naso vlamingii.
Lutjanidae, with large Lutjanus bohar, are numerous as well. The abundance of parrotfish
decreases rapidly below 30 m.

Fish assemblage was not studied below 40 m on the outer slope of the Tikehau atoll.
Temporal variations of fish communities

Numerous authors working on coral reef ecosytems, and Bell and Galzin (1984) and Galzin et al.
(1990) in French Polynesia, emphasized that a strong relationship exists between the live coral
coverage rate and fish repartition. As shown in Table 1, dramatic changes occured in live coral
coverage rate on transect under investigations in five years, inducing a renewal of fish
assemblages. Most of these dramatic changes were induced by six cyclones which ravaged
french Polynesia during the hot season 1982-83 (Harmelin-Vivien and Laboute, 1986).

Table 1 : Live coral coverage rate of the southwestern outer slope of the Tikehau atoll before,
immediatly after and five years after cyclones.

1982 1983 1987
Depth Before the cyclones After the cyclones (Galzin et Harmelin-
(Faure et Laboute, 1984) (Harmelin-Vivien et Vivien, unp data)
Laboute, 1986)
3m 5 to 25 % <5% -
5m 40 to 60 % 20 to 25 % 56 to 62 %
10 m 40 to 60 % 20 to 25 % 42%
20 m 40 to 60 % 15% 22 to 24 %

30 m 40 to 60 % 15% 16 to 24 %

4

Data displayed in Table 2 permit the assessment of fish fauna temporal variations. Between
1983 and 1987, total number of species on the fore reef area increased from 46 to 56 due to a
conspicuous resettlement of Serranidae, Pomacentridae and Labridae. On all other biota of the
outer slope, the total number of species decreased between 1983 and 1987. Most of the Scaridae,
Acanthuridae and Balistidae left the 10 m depth area whereas most of Holocentridae,
Lutjanidae and Mullidae usually encountered around 20 m in depth, moved away. Fish densities
at 20 m depth decreased dramatically between 1983 and 1987 (i.e. : from 3.4 ind m-2 in 1983 to
2.6 ind m-2 in 1987 on the average).

Table 2 : Main characteristics of the ichtyological fauna on the outer slope of Tikehau at different
depths before, just after, and five years after cyclones of late 1982 - early 1983. Nhs : Number of
herbivorous species, Dih : Number of individuals of herbivorous species . 100 m-2,,Nst : Total
number of species, Dsi : Number of all individuals . 100 m-2. (— : no data).

Depth 1982 1983 1987
(m) Before cyclones After cyclones

Nhs Dih Nst_ Dsi Nhs Dih Nst_ Dsi Nhs Dih Nst_ Dsi

5 155% G59 -- - We 213 46 - 197) 143 56 --
10 20 «188 -- - 21 78 40 337 12 55 69 260
20 21 199 -- - 19 9174 78 - 25 152. 67. -
30 19 =140 - - 7 epel Ot 58 - 220152 - -

Herbivorous species were studied in more detail. Data listed in Table 2 and 3 show that for
herbivorous fishes the mean number of individuals is relatively constant at 5, 20 and 30 m
depths between 1982 and 1987. As previously noticed, the only anomality is found at a 10 m
depth where the number of herbivorous species on the outer slope undergo a veritable decrease :
1.7 ind. m-2 in 1982, 1.4 ind. m-2 in 1983 and 1.2 ind m2 in 1987.

After the cyclones, fish fauna decreased considerably. A great number of cryptic species died
with associated corals, another part remained unsheltered and suffered subsequently from
higher predation by piscivorous species like Epinephelus microdon that became more abundant
after the cyclones. Another part of fish fauna escaped toward undamaged reef areas. A re-
arrangement of fish fauna was noticed on the outer slope ; a greater number of species were
counted in shallow areas.

COMPARISON WITH FISH COMMUNITIES OF OTHER OUTER SLOPES

Galzin (1985) has compared fish communities in the outer slopes of 2 high islands (Moorea,
Mehetia) and 3 atolls (Tikehau, Takapoto and Mataiva) of French Polynesia. Qualitative and
quantitative studies show that fish communities found at a 12 m depth on atoll outer slopes are
different than those found on high island outer slopes (Moorea, Fig. 2).

Out of the 189 species censused in ten sampling stations, 8 (4%) are found exclusively at
Tikehau. These are : Elagatis bipinnulata, Lethrinus elongatus, Lethrinus xanthochilus,
Chromis margaritifer, Bodianus loxozonus, Cetoscarus bicolor and Scarus niger. Pomacentrid
Chromis xanthura is unexpectedly absent from Mataiva and Tikehau outer slopes whereas it is
present at the 8 other sampling stations.

Differences in coral coverage can also be a major factor since outer slope sampled at Tikehau
and Mataiva have been damaged by cyclones to a greater extent than the southwestern outer
slope of Takapoto (Galzin, 1987 ; Harmelin-Vivien and Laboute, 1986). The current state of
knowledge does not enable to isolate the major factors influencing fish repartition on atoll
outer slopes in French Polynesia.

ep ee ee ee © © © © © © © © © co He © © © © © eo ew © oo

16 17 18 19 2015 13 14 11 12

Tikehau are a
A = N

é
19
as?
ar
Aa
Zia 5hm

Mataiva

Jaccard’s similarity indices

Stations

Fig. 2 : Location of sampling stations on each of the five islands and dendrogram
derived from similarity matrices. Numbers refer to the 10 sampling sites distributed
among the five islands (from Galzin, 1987).

Table 3 : Temporal variability for two families of herbivorous fish (Scaridae and Acanthuridae) on
the outer slope of the Tikehau atoll. (number of individuals . 1000 m-2)),

1982 1983 1987
=5 7-10-20)" -30...-5 =10 5-20) =30) -5) =10 .=20)-30
SCARIDAE
Cetoscarus bicolor 7 3 4 2 6 2 2
Hipposcarus longiceps 1 4 2 11 2
Scarus altipinnis 5 12 6 7 3 5 4 1 4 1
Scarus forsteri
Scarus frenatus 5 9 11 14 2 5 4 1 5 2
Scarus frontalis 8 2 5 1 4
Scarus ghobban 5 10 2 1 4 2 3 4 3
Scarus gibbus So eg 304 16 1 10 pe a2 3 1 4
Scarus globiceps 1 4 1
Scarus niger 1 8 3 16 3 2
Scarus oviceps 1
Scarus psittacus 2 6 1
Scarus rubroviolaceus 1 2 1
Scarus schlegeli 1 9 72 6
Scarus sordidus 27 SNS ge 21 Vea 77. 7 SOM Se 14; 9 132 748
Scarus juv. iis) Poee74s) 6 10
Number of species 6 1GW | pa) 5 8 10 8 7 8 4 10 7
Number of individuals 657 103°) ¥88i5 (524 | 107.) 41 78s 100) 7) 4250) 1539) eos
ACANTHURIDAE
Acanthurus achilles 24 «8 51 10
Acanthurus bleekeri
Acanthurus glaucopareius 219 26, yl 5), 35 2 360 4 6 Wis 3)
Acanthurus guttatus 13 13 4
Acanthurus nigricauda 1 2 2: 4 24 «13
Acanthurus nigroris 108 85 145 = 74 170 75
Acanthurus nubilus 9 4 14 4 2
Acanthurus olivaceus 11 9 7 8
Acanthurus pyroferus 2 24 46 40 1937,
Acanthurus thompsoni BA 227 377730
Acanthurus triostegus 2 6 3 86
Acanthurus xanthopterus 14 ~—-60
Ctenochaetus striatus 90149 ena 16) 9-153 o15.S 72a 2 5 14 50 48
Ctenochaetus strigosus 60 6 164 = 104 2 148 74 74 2 75\ 150
Naso brevirostris 10 7 7 NE: 12 5
Naso hexacanthus 8
Naso lituratus 7 13) 52), 15s 12 34. 24 6 20 8 23 «= 46
Naso vlamingtii 1 6 3 6
Zebrasoma rostratum 8 4 1 6 8 7 1 10 3 13 2
Zebrasoma scopas 17 6 21 3 15) 18 1 7 Vey
Zebrasoma veliferum 2 2 1 3 1 8 1
Acanthurus juv. 2 5
Number of species 9 9 abt 14 9 11 11 10 11 8 15) 5

Number of individuals 333. 367 410 299 425 154 358 192 315 123 341 318

FISH COMMUNITIES ASSOCIATED WITH CORAL FORMATIONS

In the lagoon of Tikehau, three main types of biotopes can be distinguished : coral reef
formations, sediments and mid-water. Coral reef formations are composed by the inner reef flat,
pinnacles and coral patches. They are scattered all over the lagoon but are more numerous in the
front of channels (Harmelin-Vivien, 1985). In the southern and western part of the lagoon, the
inner reef flat that edges the atoll rim lagoonward does not extend deeper than 5-6 m. Live
corals extend down to 15 m depth on pinnacle slopes. Pinnacles are more abundant in the western
part of the lagoon, especially between the village and the pass.

Fish abundance on Takapoto’s outer slope (4 to 5 ind . m-2) appears to be greater than that on
the outer slopes of Tikehau and Mataiva (3 to 4 ind . m2) (Table 4). However, the difference
is not statistically significant. This difference can be explained either by geomorphological
considerations (presence/absence of a pass) or by variations in longitudinal position.

Table 4: Comparative quantitative data for the coral reef fish community at 12 m depth
of the outer-slope of 5 islands in French Polynesia. NI : Number of individuals . 100 m-2,
NS : Number of species . 100 m-2,

NI NS
stations NI Mean NI Mean
(s.d.) (s.d.)
11 575 44
12 428 32
MOOREA 13 220 400 27 35
14 378 (146) 37 (7)
16 487 46
TAKAPOTO 17 435 442 41 45
18 404 (42) 47 (3)
MEHETIA 15 516 46
TIKEHAU 19 337 418 43 45
MATAIVA 20 400 (91) 47 (2)

Only the fish community associated with coral formations was studied in detail (Harmelin-
Vivien, 1984; Morize et al., 1990). The total fish fauna of the lagoon is obviously richer because
soft-bottom and mid-water fish communities were under-sampled (St. John ef al., 1990). Lagoon
fish communities are divided as follows : 1) fish species remaining in the lagoon during their
entire life span after recruitment to the reef, 2) fish species that, at least at one time of their
life, live on the outer slope or in ocean water, 3) and species living on the outer slope but that
migrate toward the lagoon for reproduction. Species with different life cycles gather
especially near the pass.

Structure of the coral associated fish fauna in Tikehau lagoon.

A total of 164 fish species, belonging to 34 families were censused around the coral formations in
the Tikehau lagoon : 99 species were observed by visual census and 108 species were caught by
rotenone poisoning (Appendix 1). The most diversified families are Labridae (21 spp.),
Acanthuridae (20 spp.), Scaridae (14 spp.), Serranidae and Chaetodontidae (7 spp.). All
species recorded only by visual census live in mid-water. These species belong to families of
Carcharinidae, Fistularidae, Echeneidae, Carangidae, Lutjanidae, Lethrinidae and
Zanclidae.

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ples,
as ot

oa

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D
aA

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fe)

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hee

- abe y
{- TIKEHAU
°

c\)

oc
ry we
oO p :
TUHERAHERA Lh a need
gy 1489 10° ovest Km

VILLAGE

Fig. 3 : Mean fish densities at different sampling stations in the Tikehau lagoon (2 fish : 100 ind . 100 m-2)
(Morize et al., 1990).

15° suo

VILLAGE
TUHERAHERA

1485 10° ovest

Fig. 4 : Mean fish biomass at different sampling stations (numbers) in the Tikehau Lagoon
(modified from Morize et al., 1990).

9

On the other hand, species recorded only by rotenone poisoning, are cryptic species or live
buried in sediments (Congridae, Ophichthidae, Ophidiidae, Scorpaenidae, Blenniidae and
Bothidae). Only a part of the fish fauna of coral formations can be recorded by each method
(60% by visual census and 67% by rotenone poisoning). Only 30 % of all species are recorded by
both methods.

The composition of fish species is relatively homogeneous throughout the whole lagoon. Down
to a depth of 15 m, the distribution of species does not show any gradient over the whole lagoon
(Morize et al., 1990). The same fish community is found around coral reef patches of the lagoon
of Tikehau. On a biomass basis, this community is made up of about 70% of carnivorous species,
14% of omnivorous species and 17% of herbivorous species (Table 5). However the trophic
structure of the community observed is different according to the method of sampling. Samples
obtained by rotenone poisoning allow to have a better estimation of the abundance of nocturnal
plankton feeders, nocturnal carnivores and omnivores. On the other hand, diurnal plankton
feeders, sessile invertebrates feeders and herbivorous species are better sampled with visual
censuses.

Table 5 : Comparison of trophic structure of fish community in the Tikehau lagoon related
to the two assessment methods (expressed as percentage of total number of species ).

Total Visual rotenone

community counts poisoning
Total number of species 161 97 108
% piscivorous 9.4 8.3 10.2
% other carnivorous nocturnal 18.7 115 20.4
diurnal 20,6 20,8 22,2
% planktivorous nocturnal 8.8 4.2 12.0
diurnal Sul S72 19
% sessile invertebrate browsers 9.4 146 9.3
% omnivorous 13.7 8.3 18.5
% herbivorous 16.3 27.1 55

Spatial distribution of fishes in the Tikehau lagoon

Geographical distribution

The small-scale spatial heterogeneity of fish community in the lagoon is considerable.
However the distribution of this community follows a steady pattern all around the pinnacles.
On the windward area of the pinnacles, species richness, density, and biomass of fish are
always higher (between 1.5 to 4 times) than on leeward ones (Morize et al., 1990).

In spite of a relatively homogeneous distribution of fish in the whole lagoon, densities, biomass
and length frequencies of fish of this community present a heterogeneous spatial distribution.

Densities : Depending on the sites, average fish density around pinnacles of the Tikehau lagoon
vary from 102 to 1274 fishes per 100 m2: The highest mean densities are located windward of
the atoll (in the northeastern part of the lagoon, Fig. 3).

Biomass : The biomass of the 31 most abundant species varies from 0.8 to 34.4 kg . 100 m-2 and
display a considerable spatial heterogeneity. The spatial variations of biomass seem to
depend in part upon the localisation of studied sites from the reef flat, the village and the pass
(Morize et al., 1990). The most important average biomass is recorded near the center of the
lagoon and at the pass of the atoll (Fig. 4).

10

Table 6 : Mean demographic structure of fish populations around coral pinnacles in the
Tikehau lagoon (D : mean density of individuals 100 m2;% : percentage of each total

population size class).

Station location
1 SW
SW

2
4
7
3 E
5
6
8

NNW

pass Tuheiava

Size of juveniles
© 80-120 mm
() 170 mm

Fig. 5: Size-class repartition of Naso brevirostris in the Tikehau Lagoon. (number

Juveniles
D %
12.4 8.0
6.0 12.9
20.7 18.4
7.9 Sy)
26.1 10.7
31.6 6.7
20.5 13.0
19.8 14.0

148°15'

juveniles recorded per transect),

Adults Olds
% D
53.6 59.3
58.5 13.3
43.6 42.8
68.9 39.0
65.3 58.3
62.3 146.5
59)2. 43.8
54.6 41.4

as

148°05'W

24.0
31.0
27.8
29.4

Density of adults (nb. indiv./transect)

A 10-90
A 100 - 300

: number of

11

Age structure : Generally, middle sized fish are the most numerous and represent from 44 up to
70% of the total number of fish (Table 6). The number of the largest fish varies between one
fourth and one third of the total population, while juveniles are less numerous (5 to 8%). The
low abundance of juveniles may be due to the fact that they are not easily seen by divers or that
they recruit somewhere else to other biotopes. Furthermore, the length frequency distribution
throughout the lagoon is not homogeneous. Juveniles are more numerous in northern and eastern
parts of the lagoon. These areas receive oceanic water passing over the reef flat through hoa
which are particularly numerous. The distribution of length frequencies of Naso brevirostris is
a good example that shows differences in juvenile and in adult fish distribution (Fig. 5). All
small juveniles (80-120 mm) were observed in the eastern part of the lagoon while larger
juveniles (170 mm) were seen mostly in the western part (Caillart, 1988). Conversely, the
density of adult fishes in the western part, and particularly near the pass, is four time higher
than in the eastern part.

Distribution with depth

Specific_composition : The species richness of the fish community in the lagoon is greater
between 3 and 5 meters depth : 87 species were recorded at these depths by visual censuses. From
10 to 15 m, the community is poorer (only 65 species censused) but is not qualitatively different.
Only one species, Gobiidae Amblygobius phalaena, appears to be a characteristic species of
this deeper zone. Inversely, some Mullidae (Mulloides spp., Parupaeneus porphyreus),
Pomacanthidae, some Labridae (Gomphosus varius, Thalassoma amblycephalum), Scaridae
(Scarus globiceps) and Acanthuridae (Acanthurus nigroris, Zebrasoma veliferum) were not
inventoried deeper than 5 m.

Density and biomass : For the whole community, there is no significant difference in mean fish
density and biomass between 5 m and 15 m in the Tikehau lagoon (Table 7). However, most
species or families are not uniformly distributed with depth : Scaridae and Acanthuridae
densities are greater on the inner reef flat and on the top of pinnacles, and decrease with depth
(Harmelin-Vivien, 1984). Similarly, Labridae are more numerous near the surface than at 15 m.
Conversely, the density of Lutjanidae, Gobiidae and some Pomacentridae, like Pomacentrus
pavo, are higher at 15 m (Morize et al., 1990).

Table 7 : Mean density and mean biomass of reef fishes estimated from visual
census according to depth (number of replicates n=8).

Density Biomass

Nd indiv. 100 m-2 g 100 m-2
-5m -15m -5m -15m

mean 413.5 318.0 11465.6 10236.0
SD 365.5 195.0 10236.0 10109.6

Age structures : The average density of larger fishes on the whole fish community is more
important between a depth of 3 to 5 m (Fig. 6). It decreases with depth and on reef flats
(Harmelin-vivien, 1984 ; Morize et al., 1990). The average density of juvenile fish is in turn
more important at 15 m deep than at 5 m.

Meanwhile, distribution of length classes with depth differs among families. The highest
densities of juveniles of Scaridae and Acanthuridae were observed in shallow waters (0-2 m)
(Table 8). Conversely, juveniles of Lutjanidae, Labridae and Pomacentridae are more numerous
between 10 and 15 m depth.

Nb individuals . 100 m-2

[Tar] , m

100 YY I5m
80 Y y
L
é U7
7
7;
= YY
i YY

SS

LL

Juveniles Adults old Adults

size class

Fig. 6 : Mean demographic structure of fish community at two depths (5 and 15 m)
around pinnacle reefs of Tikehau lagoon.

Table 8 : Mean density of juvenile parrotfishes (Scaridae) and juvenile surgeonfishes
(Acanthuridae) with depth in Tikehau lagoon (number of individuals . 100 m-).

0-2 m 3-5m 10-15 m
Scaridae mean 12.3 96 7.2
SD 5.4 8.3 5.6
Acanthuridae mean 2.9 0.4 0.2

SD 15 0.9 0.2

13
Comparison with other Tuamotu atolls

The fish communities of atoll lagoons were studied by different authors with a different
sampling design in five other Tuamotu atolls, Takapoto, Scilly, Mataiva, Fangataufa and
Mururoa (Table 9). Each of these lagoonal communities differs somehow from the other, either
by its specific composition or by its average density and biomass, whereas the outer reef slopes
look much alike (Galzin, 1987).

Table 9 : Comparison of lagoon fish communities associated with coral formations of six
Tuamotu atolls : total number of species and mean density of individuals.

Atoll Number of Depth Density reference
fish species (m) (nb indiv 100 m-2)
mean range
Takapoto 170 0-20 - - 1
Scilly 180 0-30 - - 2
Tikehau 161 3-5 414 102-1274 3
10-15 318 104-612 3
Mataiva 157 0-3 50 3-125 4
Fangataufa 128 0.3 164 54-275 5
Mururoa 230 12 188 56-531 6
References :
1. Bagnis, Galzin and Bennett, 1979 (28 sites in lagoon, 16 in hoa)
2. Galzin, Bagnis and Bennett, 1983 (2 transects in lagoon, 2 transects in hoa, 4 transects on outer reef flat).
3. Morize, Galzin, Harmelin-Vivien and Arnaudin, 1990 (8 sites in lagoon, 4 transects on inner reef flat).
4. Galzin, Bell and Lefévre, 1990 (8 sites in lagoon surveyed 4 times in 8 years).
5 . Galzin, unpublished data (7 sites in lagoon).
6. Galzin, unpublished data (10 sites in lagoon, 6 sites on inner reef slope)

The observed species richness is low in the Fangataufa lagoon (128 spp.), an atoll without a
natural pass. It is in turn very high in the Mururoa lagoon (230 spp.), an atoll widely opened to
Oceanic waters. The number of species recorded in the four other atolls are closely related in
spite of differences in morphological structures : Tikehau and Mataiva have a pass whereas
Takapoto and Scilly do not.

The mean fish density is very low in the lagoon of Mataiva (Table 9) ; this phenomenon can be
explained by a distrophic crisis that seems to affect this atoll (Galzin et al., 1990). On the
other hand the mean density of fish is higher in the Tikehau lagoon, in spite of a considerable
exploitation of fish stock. At a 12 m depth, the density of fish is lower at Mururoa than at
Tikehau. However, the average length of fish is much larger at Mururoa where there is no
fishery. The average biomass of fish is probably the same in these two lagoons.

Conclusion

Only one fish community is observed around coral formations (pinnacles) in the lagoon of
Tikehau. The mean fish density and biomass do not vary with depth, although the species
richness is lower at 15 m deep than between 3 and 5 m. The highest fish densities,
characterized by a great proportion of juveniles, are generally found in the northern and eastern
parts of the lagoon. Mean biomass per unit area is generally the highest in the southern and
particularly the western part of the lagoon, near the pass, characterized by a great proportion
of large-sized fishes. The depth vs age structure of population relationship varies according to
families or species. Juvenile densities are higher in shallow water for some families (Scaridae,
Acanthuridae) or in deeper water for other families (Lutjanidae, Labridae, Pomacentridae).

14
Lagoon - outer slope comparison

Fish community of the outer slope of the Tikehau atoll is more diversified than the lagoonal
fish community (Appendix 1). Indeed, twice as many species of fish were recorded on the outer
slope as in the lagoon by visual censuses. Around Moorea island, Galzin (1987) recorded also a
greater fish species richness on the outer slope than in the lagoon and on reef flats.

Among families, some fish species are more numerous on the outer slope than in the lagoon of
Tikehau and vice versa. Serranidae, Cirrhitidae, Carangidae, Lutjanidae, Chaetodontidae
and Balistidae species are more numerous on the outer slope (31 spp.) than in the lagoon
(24 spp.) (Harmelin-Vivien, 1984). However, the mean Acanthuridae density is higher on the
outer slope, whereas Scaridae density is higher in the lagoon (Table 3). Other families, like
Lethrinidae and Mullidae are more diversified and their populations are much more abundant
in the lagoon as compared to the outer slope.

The distribution of length class, and sex ratio may be also different into or out of the lagoon for
a same species or a same family. The most juvenile Scaridae were observed in the lagoon.
Immature males and females are more abundant in the lagoon, whereas ripe males are much
more numerous on the outer slope (Harmelin-Vivien, 1984).

Fish communities of the outer slope and of the lagoon of the Tikehau atoll are different not only
by their species richness and population density, but differ also by their age and trophic
structures.

THE EXPLOITED LAGOON RESOURCE : THE FISHERY OF TIKEHAU

The fishery of Tikehau is of artisanal nature, in which fish are sought for commercial and
subsistence purpose. It is based principally upon the use of a relatively simple gear : bottom-
fixed fish traps. Additionally, an important proportion of fish is occasionally taken with hook
and line or spear gun. The fishery of Tikehau was thoroughly studied for four years. Numerous
data on the fishery yields and on the biology and behavior of the target species have been
gathered in order to assess the reef fish stock for management purposes.

THE FISHERY OF TIKEHAU

The fishing gear

Traditionally, fish traps were built in shallow waters using rocks or coral boulders. Blanchet
et al. (1985) pointed out that yields were low but satisfactory sufficient to meet the needs of the
low-level human population. In the middle of the century, intensive phosphate mining on the
neighboring island of Makatea created and kept a high sustained demand of fish to feed the
population of workers (about 3,000 in 1962). As a result, the subsistence fishery of Tikehau
developed into a commercial fishery by setting traps in more productive areas (in the vicinity
of the pass), using modern building materials (wire net, iron stakes) as well as traditionnal
wooden stakes. After the close-down of the mining site in 1966, fish trading logically reoriented
toward the Tahiti fish market.

CATCHING ROOM

RETAINING Ve

Sketch-view of a trap with two

ROOM retaining room

COEFECTHING
EXTENSIONS

Fig 7 : Diagram of a typical Tikehau fish trap (actually fish-trap n°2, see text for more details). As shown in
the framed sketch-view, there can be two retaining rooms. Dotted line : wire-net, underlined number :
depth at which the part of the trap is set.

The general shape of a Tikehau fish trap is presented on Fig. 7. A fish - or a school of fish -
coming across the large collecting extensions of wire net (locally termed Rauroa) are naturally
driven toward the catching room (locally called Aua) in which they enter through a narrow
opening. At least every day, trapped fish are herded off the trap by fishermen banging on the
water surface and driven into a first retaining room (Tipua) where they can be held alive for a
couple of weeks until they are sold. The fish are landed when the small trading vessel, able to
load between 12 and 15 metric tons of catches, arrives at Tikehau (usually once a week), and
subsequently shipped to Tahiti.

16

TRAP N°4

TRAP N*1

LAGOON

Fig. 8 : Location of fish traps in the pass of Tikehau. Trap n°1 and n°2 located
close to the middle of the pass are far more efficient than the two others located
lagoonward on the reef flat. Although the origin of a great part of the catches has
not been accurately determined, data available indicate that trap n°1 and n°2
yield at least 78 % of the total catches.

The main fishery of Tikehau uses four fish traps, all located in or around the vicinity of the
pass. Two traps (trap #1 and #2) are set quite in the middle of the pass by up to a 5 m depth
(Fig. 8), and the two others traps (#3 and #4) are located lagoonward on the northern shore of
the pass in shallower water (1 to 2 m). When fish is thought to be abundant in the pass and if
current speed allows underwater work, a net is set across the pass between trap #1 and trap #2
and a "scare line" driving technique is used to increase catches.

Handlines and spear-guns are used mostly for a subsistence purpose. The use of these kind of
gears can however significantly contribute to commercial catches when there are huge
concentrations of groupers or emperors in the pass making these species readily available in
large quantities. Fishermen retain a portion of their catch for their own use and sell the
remainder to the trader.

17
Fishery yield

In Tikehau, statistical sampling of the catches was done by a local agent who noted down ona
log sheet the species composition of the catch, weights sold on a species basis and the number of
fish traps that provided the catch. Various information relevant to fishing such as current
strength in the pass and weather were also recorded (Morize, 1984). Data were recorded from
1983 to 1987. As fishing activities are maximal by the end of the year and lower by July -
August, a fishing year was defined to run from Ist of July to 30th June. Thus, the study of the
fishery of Tikehau was carried out upon four fishing years : 83-84, 84-85, 85-86 and 86-87.

Morize (1984) pointed out that fishing effort is somewhat difficult to appraise but since the
shape, the number and the location of the traps have not been modified during the study, the
fishing effort can be assessed as the number of days with a fully efficient presence of the traps
on the fishing grounds. As the level of fishing effort can be estimated to have been constant,
variations of catch per unit effort (c.p.u.e.) correspond with variations of catch.

Table 10 gives an inventory list of species caught in Tikehau fish traps (comprehensive studies
available in Morize, 1985 ; Caillart and Morize, 1986). Almost fifty species are likely to be
trapped, covering a complete trophic spectrum of species ranging from piscivorous to
herbivorous species. Although the selectivity of the gear appears to be poor, no more than
fourteen species significantly contribute to the catch by accounting for about 85 % of the total
landing. These fish include lutjanid Lutjanus gibbus and Lutjanus fulvus, lethrinid Lethrinus
miniatus, carangid Caranx melampygus, Decapterus macarellus and Selar crumenophthalmus,
serranid Epinephelus microdon, acanthurid Naso brevirostris and Acanthurus xanthopterus,
mullid Upeneus vittatus and Mulloides spp., albulid Albula vulpes, sphyraenid Sphyraena
forsteri, and lastly holocentrid Myripristis spp.

Table 11 shows that total harvests obtained through trap fishing range from 144 metric tons to
207 metric tons a year with an average value of 165 metric tons. Lethrinus miniatus is the
principal component of the catches with an average landing of 32 metric tons per year. It is
followed by Lutjanus gibbus, Caranx melampygus and Selar crumenophthalmus representing a
yearly average catch of respectively 17, 16 and 14 metric tons. These species can be dubbed
target species though fishing activity is not specifically oriented toward them. Landings of the
other species are less abundant ranging from 2 to 10 tons a year on the average.

Local consumption of fish is difficult to appraise since every inhabitant of the atoll meets his
needs himself. Morize (1984) had estimated that about 150 kg of fish per year and per person
are likely to be consumed. Given the total population of Tikehau, an additional 40 metric tons
of fish would be landed every year for subsistence. Species readily available to various simple
gear (handline, spear) such as groupers, surgeonfish or parrotfish are probably the principal
components of this secondary fishery.

Temporal variations of the catch

Although total landings are somewhat homogeneous from year to year (average value of 165
metric tons), with a slight upward trend (Table 11), the relative species abundance in the
catches varies considerably. In 1985-86, about 14 tons of Lethrinus miniatus have been fished
whereas more than 50 tons were caught the next year with the same fishing effort applied to
the stock. At the same time, Epinephelus microdon yield changed from 5 to about 50 tons and
that of Naso brevirostris dropped from 19 to 2 tons. These variations are extremes but in
general, only a handful of minor species are equally harvested from year to year. For most of
the target species, yield can double or conversely, be reduced by half from year to year without
any predictive signs. However, the great number of species available to the traps tend to buffer
large fluctuations in total catches by changes in recruited population levels of individual
species.

18

Table 10: Check-list of species (italic) caught in Tikehau fish traps with indicative
figures of their diet (P : piscivorous, I : invertebrate feeders, H : herbivorous) and
indications on their relative abundance in the catches (* : low, erratic catches
generally less than 1 % of the total catches; ** : medium abundance, species often
fished but representing less than 5 % of the annual total catches ; *** : high
abundance, species regularly catched accounting for more than 5 % of the total).

Family Species Diet Harvest

Holocentrid
Sphyraenid
Siganid
Serranid

Priacanthid
Carangid

Lutjanid

Mullid

Mugillid
Chanid
Lethrinid

Chaetodontid
Albulid
Kyphosid
Scarid

Acanthurid

Balistid

Sargocentron spiniferum
Myripristis sp.
Sphyraena forsteri
Siganus argenteus
Epinephelus merra
Epinephelus microdon
Priacanthus cruentatus
Alectis indicus

Carangoides orthogrammus

Caranx ignobilis
Caranx lugubris
Caranx melampygus
Caranx sp.

Decapterus macarellus
Elagatis bipinnulata
Scomberoides lysan
Selar crumenophthalmus
Lutjanus fulvus
Lutjanus gibbus
Mulloides flavolineatus
Mulloides vanicolensis
Parupeneus barberinus
Upeneus vittatus
Mugil cephalus

Liza vaigiensis

Chanos chanos
Lethrinus mahsena
Lethrinus miniatus
Monotaxis grandoculis
Chaetodon auriga
Albula vulpes
Kyphosus cinerascens
Scarus gibbus

Scarus sp.

Acanthurus xanthopterus
Ctenochaetus striatus
Naso _ brevirostris

Naso lituratus

Naso unicornis

Naso vlamingit
Balistoides viridescens

I

~

~
— —

~

PO REO ee te commas ne oe OW a NOLES PEC ed ae
—

—
~

jooeces ecco ae

LH

19

Table 11: Yearly total weight landed (kg) of the fourteen main species caught by Tikehau fish
traps and yearly total (kg) including all species. Mean year calculated by averaging data of the
four year.

83-84 84-85 85-86 86-87 Mean
Lethrinus miniatus 34,812 29,923 13,961 50,983 32,419
Lutjanus gibbus 8,152 11,371 24,374 24,354 17,062
Caranx melampygus 24,357 21,332 10,213 11,214 16779
Selar 8,337 14,201 17,133 16,063 13,933

crumenophthalmus
Epinephelus microdon 180 810 5,183 48,902 13,786
Lutjanus fulvus 11,226 15,962 13,050 7,694 11,983
Naso brevirostris 3,036 15,299 19,374 2,293 10,000
Mulloides sp. 9,593 8,506 11,066 5,359 8,631
Albula vulpes 12,292 7,889 6,391 5,099 7,918
Upeneus vittatus 9,454 882 6,206 1,085 4,406
Sphyraena forsteri 2,835 2,835 5,085 2,954 3,427
Acanthurus 2,085 6,229 307 1,661 2,270

xanthopterus

Myripristis sp. 2,475 1,559 2,931 1,851 2,204
Decapterus pinnulatus m.d. 1,424 3,580 1,582 2,195
Other species 15,484 15,974 16,152 26,348 18,489
total 144,318 154,236 155,006 207,442 165,250

1000

900

800

700

600

C.P.U.E. 500

(Kg day-1) 400

300

200

100

(0)

Jul. Aug. Sep. Oct.Nov.Dec. Jan. Feb.Mar.Apr.May Jun.
YEAR

Fig.9 : Temporal variations of Catch per Unit Effort (C.P.U.E.) over an average year in the fishery of
Tikehau.

20

Fig. 9 shows fairly wide fluctuations in the overall monthly catch per unit effort through an
average year. Yield ranges from 68 kg per day in July to 898 kg per day in November. The
highest productivity of the fishery occurs from October through January and the lowest from
April through August. Individual yields of the overwhelming majority of the target species
follow these variations but maximal c.p.u.e. of a few species are reached at a different time of
the year. Noteworthy is the example of Epinephelus microdon in which the presence on the
fishing ground peaks in April. Behind these strong seasonal fluctuations, c.p.u.e.s have a clear
relationship depending on the time of the lunar month. Yields of the target species noticeably
increase the week prior to the new moon and drop around the full moon.

Obviously, yields of the target species are strongly related to seasonal spawning aggregations
in the vicinity of the pass. Biological sampling of landed fish carried out every month of the
study confirmed that all fish trapped are adult fish, most of them having ripe gonads. Such
spawning movements in other tropical areas are also well documented in numerous published
observations reviewed by Johannes (1978). Thus temporal variations of c.p.u.e.s of the fishery
of Tikehau would have a strong relationship with the time of the breeding period of the major
components of the catches as emphasized by Caillart and Morize (1988).

BIOLOGY AND ECOLOGY OF TARGET SPECIES

The biology of the main species caught by fish traps in Tikehau has been studied. The
overwhelming majority of the fish sampled was collected in the fishery landing.
Additionally, some fish were collected by experimental fishing in the lagoon or on the outer
slope using a handline or spear gun. The biological study presented hereafter is restricted to the
seven major species : lethrinid Lethrinus miniatus, carangid Caranx melampygus, serranid
Epinephelus microdon, lutjanids Lutjanus gibbus and Lutjanus fulvus and acanthurids Acanthurus
xanthopterus and Naso brevirostris.

Reproduction

Reproductive patterns of the target species were followed throughout the year on a monthly
basis. For all samples taken, gonosomatic indices (GSI) were calculated for individual males
and/or females as GSI = 100xgonad wt/fish wt.

Fig. 10 summarizes the observations gathered on the time of spawning of the target species. At
Tikehau, fish typically have extended breeding seasons with more or less conspicuous seasonal
peaks in breeding activity. For Lethrinus miniatus, spawning is virtually confined from
September to December with most spawning through September. The snappers Lutjanus fulvus
and Lutjanus gibbus appear to spawn between October and June with two seasonal peaks that
occur in November and in March. The average GSI remain however at significant levels all
year round suggesting that some individual spawning may occur at an odd time. The data for
Caranx melampygus indicates that spawning occurs throughout the year with slight peaks in
July, October and February. Lastly, spawning of Epinephelus microdon and Naso brevirostris is
virtually confined to a short period of three months. The records for Epinephelus microdon
show a maximum in the period between March and May with the greatest proportion of ripe
fish found in April. The surgeonfish Naso brevirostris spawns between December and February
with most spawning in December. For this last species, the time of spawning was confirmed by
two additional methods : maturity stages assigned to female fish using a five stage scale and a
study of frequency distributions of egg size within ovaries over the year (Caillart, 1988).
Patterns in fecundity of Naso brevirostris were drawn from this last meaningful method. A
female would spawn about 160,000 eggs, on the average, within a breeding season. Batch
fecundity averaged over the complete breeding season, about 221 eggs g-! body weight,
indicated that each female N. brevirostris must release its eggs in about three times, providing
that discrete spawning occurs (Caillart, 1988).

L. gibbus

C. melampygus

A. xanthopterus

Fig. 10 : Summary of information on time of spawning of the target species of the fishery of Tikehau
drawn from GSI variation study, and relationship with time of maximum catch per unit effort (cpue)
over an average year (dark bars : breeding season, dotted bars : cpue). No data available to determine
the breeding season of A. xanthopterus .

For most species, occasional individual spawning is likely to happen in all months, but
maximum activity takes place in the earlier months of the year. However, the sole study of
GSI variations only gives general trends and is probably insufficient to accurately provide
estimates of the occurrence of breeding seasons in the tropics.

Table 12 : Fork-length at first reproduction (mm) of the target species of the
fishery of Tikehau obtained from length-frequency data of the catches in fish traps.
(* : length-frequency data inadequate to calculate length for both sexes ;
*“ : relevant data available only for females).

Species Male Female
Lethrinus miniatus 410 370
Lutjanus gibbus 220 210
Caranx melampygus 270 250
Epinephelus microdon m.d. 310 **
Lutjanus fulvus 200 200
Acanthurus xanthopterus 320 * 320 *
Naso _ brevirostris 260 220

Length at first reproduction was determined under the assumption that the relationship
between fishery yields and spawning activity does exist. The first group in the length-
frequency distributions of the catch is assumed to actually represent the earlier migrating
spawner group (i.e. : fish newly recruited to the fishery). Therefore length at first reproduction
was calculated as the length in which summed length-frequency reaches 50 % of the total
number of fish in the first cohort (Table 12).

22
Growth

Information on the age and growth of fishes is a central element in fishery management
analysis. Common biological characteristics of fishes of Tikehau such as a missing seasonal
growth and an extended breeding season throughout the year, have made growth rate
determination difficult. Basically, three approaches to the determination of age and growth of
the target species were attempted. These were 1) modal progression analysis in a time series of
length-frequency histograms ; 2) tag-recapture study and 3) the aging of individuals on the
basis of regular periodic (daily) markers in otoliths.

The growth rate of fishes has been described by the Von Bertalanffy Growth formula

(hereafter expressed VBGF) because it fits most of the data obtained on fish growth and it can
be readily incorporated into models of stock assessment. The VBGF expression is :

L(t) = Leo (1 - exp( -k(t-to))

where L(t) is the length at time t, Leo is the asymptotic length, k the rate at which the fish
approaches the asymptotic length and to the origin of the growth curve. All length
measurements presented herein are fork lengths in mm unless stated otherwise.

Table 13 : VBGF growth parameter estimations for the main species caught in the fishery of
Tikehau. Leo is given in mm, k and tg on a year basis. (6 : standard deviation of relevant

parameter when available, Meth : method used ; 1 : modal progression analysis of length-
frequency histograms, 2 : tag-recapture study and 3 : otolith microstructure examination),

Leo 2) k OL, to Si Meth

Lethrinus miniatus 560 110 0.42 032 049 1.09 1
Lutjanus gibbus 360 70 0.60 0.26 059 0.83 1
Lutjanus fulvus 280 _ 0.89 -- -0.05 — 3
Caranx melampygus 610 367 0.20 030 -180 150 1
Epinephelus microdon 610 _ 0.35 _ — — 2
Epinephelus microdon 690 301 0.31 0.03 022 0.08 1
Acanthurus xanthopterus 490 _— 0.30 _- -0.00 -— 1
Naso brevirostris (male) 380 _ 0.33 _ 0.39 — ut
Naso brevirostris (female) 350 _— 0.26 _ -0.80 — 1

Length-frequency histograms were examined. A random length sample of the main target
species was taken serially, whenever possible. For species in which spawning season is confined
to a short period (Lethrinus miniatus, Lutjanus gibbus, Epinephelus microdon and Naso
brevirostris), analysis was carried out under the assumption that cohorts are separated by a
time interval of one year. The VBGF parameter estimations presented in Table 13 probably lack
robustness but figures generated correspond to some extent to growth parameters reviewed by
Munro and Williams (1985) and can be considered as reliable. Several limitations arise on the
results presented on Caranx melampygus and Acanthurus xanthopterus because breeding seasons
tend to be prolonged over several months and as a result, age classes are not readily separable
from one another. In that case, mode discrimination involves a large part of subjectivity.

23

A tag-recapture study was undertaken on grouper Epinephelus microdon (Morize and Caillart,
1987). Between 1984 and 1987, over one thousand tags were released all over the lagoon. Most
recoveries occurred within one month of tagging and very close to the point of release but there
is a tendency for at least a part of the population to seasonally migrate toward the pass since a
few fish tagged in various locations of the lagoon were recaptured in the vicinity of the pass
during the breeding season (i.e. : April). For growth rate estimation purposes, all tagged fish
were measured upon release and fishermen were asked to provide information on the length of
fish recaptured. Out of the thousand tags released, only 47 tags recovered met this basic
requirement. Data were fitted to the VBGF using the method of Fabens. The VBGF parameter
estimations are presented in Table 13.

Otoliths are structures that are commonly used to age tropical fishes (Panella, 1971). The
relatively new finding that many fish deposit otolith growth increments with a daily
periodicity appeared to offer a method of assessing age and growth with greater accuracy than
was previously possible through other classical methods. Otolith microstructures of the target
species of the fishery of Tikehau were examined (Caillart et al., 1986 ; Caillart, 1988) for
Lethrinus miniatus, Lutjanus gibbus, Caranx melampygus and Naso brevirostris. Ages
determinated through increment counts appeared to be obviously underestimated although the
actual age-increment discrepancy has not been measured. Tetracycline injected into adult
Epinephelus microdon reared for more than one year was used to verify the periodicity of
increment deposition (Caillart and Morize, 1989). For this species held in captivity, one ring
was laid down every two days on an average. If this result applies to Epinephelus microdon in
their natural environment, aging fishes under the assumption that otolith increments are daily,
would have lead to underestimate the actual age by a factor of two.

In spite of all the limitations raised by the foregoing discussion, growth parameters of Lutjanus
fulous were calculated by fitting the VBGF to the results of otolith increment counts because
either the length-frequency histograms method or the tag-recapture operation failed to give
results (Table 13).

Table 14: Length (in mm) at age (in year) of the target species of the fishery of Tikehau during the
exploited phase (data backcalculated with VBGF growth parameters presented in table 13). (*) :
Data backcalculated with the tag-recapture VBGF, (**) : Data backcalculated with the modal
progression analysis VBGF.

Age L. Ib LE: € E. A. N.

miniatus gibbus fulvus melampygus microdon xanthopterus brevirostris
CDi Ge) male female

1 221 262

1d) 257 210 295 249

2 363 284 235 325 30799293

ZiE9) 400 304 251 352 S50r OU), 234

3 431 376 397 399 256 220

3.5 455 431 440 275 236

4 475 460 476 342 291 250

4.5 491 484 363 304 262

5 504 504 381 316 273

55 515 396 326 282

6 409

6.5 420

7 430

24

Lengths at age back calculated from the VBGF growth parameters are presented in Table 14.
Only the portion of the growth curve covering the range of data used to establish the predictive
equation was taken into account. Since this range of data corresponds with the exploited phase
of the fishes, Table 14 gives insight into the duration of the phase. Certain patterns emerge
pertaining to the main species and can be summarized as follows : the duration of the exploited
phase is generally short ranging from three years (Naso brevirostris, Caranx melampygus) to
four years (Lethrinus miniatus, Epinephelus microdon and Acanthurus xanthopterus). In the
case of lutjanids, the vulnerability to fishing gear appears to last two years. Data furthermore
suggest that fishes are fully recruited to the fishery at an average age of three years for
acanthurids, and two years for the others. It is most likely that fishes disappear from the
fishing ground due to a dramatic mortality rate since experimental fishing carried out in
various locations of the lagoon and off the reef yielded a very few fish beyond the maximal
size recorded in the catches. Caranx melampygus is however an exception. The adult
population of this species shifts later in its life-cycle toward the pelagic environment of the
outer slope, out of the reach of fishing gears.

Length-weight relationships

The relation of weight (W in g) to the fork length (Lf in mm) was calculated for the seven
target species. The parameters a and b of the formula :

W =aLb

are listed in Table 15 (Morize, unpublished data). For all species under investigation, samples
of a few hundred fish taken in the catches were used to derive the regression equations.
Correlation coefficients r obtained ranged from 0.95 to 0.99.

ASSESSMENT OF THE FISHERY OF TIKEHAU

The problem of stock assessment in the fishery of Tikehau mostly relates to the fact that it is
based upon at least fourteen species in which none of them is overwhelmingly dominant. Given
the set of data obtained on the fishery (catch statistics, common biological parameters of
individual species), two techniques are available for appraising potential harvests. Firstly,
assessment can be based upon a comparison with known harvests per unit area taken by fisheries
of a similar environment. Secondly, analytical models requiring reliable estimates of either
biological or fishery parameters can be used in order to model the response of the stock to
exploitation.

Table 15 : Length-weight relationship for the main species caught in Tikehau fish-
traps (a and b, parameters of the equation W=aL> where W = weight in g, L = fork
length in mm).

a (.10-) b
Lethrinus miniatus 3.4 2.8
Lutjanus gibbus 21 3.0
Lutjanus fulvus 11.0 2.8
Caranx melampygus 6.4 2.8
Epinephelus microdon 0.5 3.2
Acanthurus xanthopterus 9.3 2.8

Naso brevirostris 3.8 2.8

25

Yield per unit area

On the average, 200 metric tons of finfishes per year are caught in the main fishery of Tikehau.
Additionally, 40 metric tons are taken for subsistence and another 40 tons are fished by
occasional fishermen for commercial purposes (Morize, 1984 ; Morize, 1985). That is, the fishery
of Tikehau produces an average of 280 tons per year (table 16). The area covered by the lagoon
of the Tikehau atoll is about 420 km2 and the annual harvest per unit area of 0.7 tons . km-2.
Marshall (1980) pointed out that a finfish harvest of 3 to 5 tons . km-2 may be upheld as a
generalization for the potential fishery yields of coral reefs and adjacent shallow water
environments. Although records presented in Table 16 fall far below the suggested potential,
data are somewhat homogeneous, ranging from 0.6 tons . km-2 in the fishery of Ontong Java to
1.3 tons . km-2 in the fishery of Mataiva with the noticeable exception of Rangiroa where
fishery harvests reach only 0.2 tons . km-2. However a limitation arises to permit the
comparison of the different harvests per unit area recorded.

Table 16: Harvests per unit area for a selection of exploited coral atolls (for the Tuamotu coral
atolls, groups included in catch statistics are only finfishes. For Kapingamarangi and Ontong Java,
composition of the catches is unknown),

Total catch Lagoon area Harvest per
(metric tons) (square kilometers) unit area Ref.
(Tons/km2)
Kapingamarangi 280 400 0.7 i

(Caroline islands)
Ontong Java 122 79 0.6 2
(Solomon islands)

Rangiroa (Tuamotu) 350 1600 0.2 3
Kaukura (Tuamotu) 500 500 1.0 3
Mataiva (Tuamotu) 63 50 1.3 3
Tikehau (Tuamotu) 280 420 0.7 4

Reference
1- Stevenson and Marshall (1974) ; 2 - Munro and Williams (1985)
3 - Galzin et al. (1989) ; 4 - Caillart (1988)

As a reef fishery is generally a patchwork of coral reef patches (which are highly productive)
and sandy bottoms (which is not that productive) ; the yield per unit area can very much
depend upon the area and the percentage of area that is actually covered by hard coral
substrate. Some fishery records like these of Rangiroa cover a large area, only part of which is
actually covered by coral, whereas other records of fish yield apply to very small areas like
Mataiva or Ontong Java where a hard substrate coverage is much greater. Moreover the
potential fish yield from a given area cannot be inferred from sole catch records without even a
rough reference to the fishing effort. In Rangiroa and Mataiva, the level of exploitation
applied to the stock is low with regard to fishing effort in Tikehau or Kaukura.

Information on yield assessment and management in the fishery of Tikehau can be drawn from
the comparison with the neighboring atoll of Kaukura. These two atolls have a comparable
surface and morphology. In Tikehau, the fishery is based on bottom fixed fish traps all located
in the vicinity of the pass. Yield relies on the behavior of species most prone to migrate for
spawning. These fish are primarily carnivorous species as indicated by the specific composition
of the catches. In Kaukura, bottom fixed fish traps are set not only in the vicinity of the pass
but also all around the atoll rim, on the shallow inner reef flat.

26

Species caught are for a great percentage non territorial herbivorous species which wander to
seek for food (Stein, in Galzin et al., 1989). So, higher yields in Tikehau could probably be
achieved by setting traps in various locations of the lagoon which in turn would probably
exploit the food chain more efficiently. The total harvest of the Tikehau fishery could also be
increased by diversifying the fishing gears, and setting classical bottom free fish traps around
the numerous coral knolls scattered in the lagoon. Although we believe that it would be quite
impossible to reach the potential yield suggested by Marshall (1980) (i.e. : 3 to 5 tons . km-2), it
would be at least possible to attain a harvest of 1 ton . km-2 recorded at Kaukura. This would
result in a substantial increase of the catch of about 140 tons.

If this simple but nevertheless useful approach can be used to set a likely estimate of the
potential fish yield of Tikehau, it is obvious that more thorough evaluations must be
undertaken in order to focus management issues not only on optimum yield but also on preferred
species.

Analytical assessment models

Analytical assessment models have been widely used in temperate water fisheries but they
have been applied to coral reef fisheries in a limited number of cases. If these models cannot
take into account the numerous and intricate relationships between all the components of the
multi-species fishery, they are nevertheless of great value in giving an insight into the state of
the fishery. There were two means used to provide estimates of the status of the fishery of
Tikehau. One mean was a length converted catch-curve analysis (in Ricker, 1980). The other
mean was to use yield per recruit estimates in a length structured model in which fishing
mortality vector (F) is obtained from a length cohort analysis (Jones, 1974).

No adequate data sets on Tikehau fish stocks exist for an accurate determination of natural
mortality (M). This parameter was estimated by two empirical formulas (Hoenig, 1984 and
Pauly, 1980) that provided rough estimates of the value of M (Table 17). The real value of M is
expected to lie in between these two estimates.

The specific exploitation rate E is given by :

: F
~ F+M

E

where F is the fishing mortality. E estimated through length-converted catch curve analysis is
found greater than 0.5 for Lutjanus gibbus, L. fuluus, Caranx melampygus and Epinephelus
microdon, and less than 0.5 for Lethrinus miniatus, Acanthurus xanthopterus and Naso
brevirostris. Gulland (1973) pointed out that a value of 0.5 of the exploitation rate can be
roughly set as a limit below which a fish stock is lightly exploited and over which over-
fishing may occur.

Table 17 : A range of values of natural mortality M (yr!) chosen for Tikehau
target species. Mmin is given by Hoenig (1984) empirical formula, Mmax by

Pauly (1980) equation.

Species M min M max
Lethrinus miniatus 0.43 0.66
Lutjanus gibbus 0.57 0.96
Lutjanus fulvus 0.46 0.88
Caranx melampygus 0.43 0.72
Epinephelus microdon 0.61 0.88
Acanthurus xanthopterus 0.43 0.72

Naso _ brevirostris 0.60 0.80

27

Yield per recruit model results listed in Table 18 are strongly related to the estimate of M
chosen and have considerable different responses to F variations with respect to the species
under investigation. For Lethrinus miniatus, Acanthurus xanthopterus and Naso brevirostris, a
substantial increase of yield per recruit (more than 10% on the average) can be achieved if the
fishing mortality vector is 50% or 100% higher. The snapper Lutjanus gibbus and L. fulvus yield
per recruit estimates appears to be poorly increased (5% on the average) when fishing
mortality vector increases. Lastly, yield per recruit estimates of Epinephelus microdon and
Caranx melampygus do not significantly increase and can even decrease if an attempt to
increase F is made.

Table 18 : Range of yield per recruit variations of the target species of Tikehau fishery (in % of present
yield per recruit) in response to variations of fishing effort (uF : Fishing mortality coefficient, lowest
value of yield per recruit correspond to the highest natural mortality figure).

Species p= 0:5 el WEES uF = 2
Lethrinus miniatus -30 / -20 0 +20 / +8 +27 / +10
Lutjanus gibbus -30 / -15 0 +12 / +3 +20 / +3
Lutjanus fulvus -25 / -12 0) +10 / +2 +15 / +2
Caranx melampygus -25 / -8 0 +10 /0 +20 / -1
Epinephelus microdon -15 / 6 0 +6 /-1 +8 / -2
Acanthurus xanthopterus -40 / -30 0 +20 / +10 +40 / +20
Naso brevirostris 0 +19 / +26 +32 / +20

According to the foregoing results, the Tikehau fishery appears to be well fitted to carnivorous
fish stock exploitation. The evidence from these analytical models suggests that Tikehau fish
stocks are being fished at or near the Maximum Sustainable Yield (MSY). No major change in
the direction of the present trap fishing strategy (increases or decreases in effort) is justifiable,
although yield per recruit of certain species (emperors, surgeonfishes and snappers to a lesser
extent) could be improved by a moderate increase of fishing effort. And it is unlikely that the
grouper and jack fisheries could tolerate a heavy effort increase.

Higher harvests of carnivorous species could probably be achieved by using more selective
fishing gears. For instance, the abundant stock of Lethrinus miniatus could provide substantial
additional catches if handlines were more heavily used when the fish are abundant in the pass
and hence, readily available. It has been mentioned that the herbivorous fish stock at Tikehau
is very lightly exploited. The principal management issue would probably be to orient fishing
pressure toward this part of the resource by setting traps on shallow areas all around the atoll
rim where availability of herbivorous species is greater.

CONCLUSION

A total of 276 species belonging to 47 families have been recorded on the Tikehau atoll
(Appendix 1). The real number of species is obviously under-estimated since rotenone poisonning
was not used in all sites, and only one transect was regularly studied on the outer slope. The
number of species censused in the lagoon was 167, 39 in the pass and 180 on the outer slope.

28

Only 17 species (6.2% of the total richness species) were encountered in the three environments :
Sargocentron spiniferum, Epinephelus merra, Epinephelus microdon, Caranx melampygus,
Lutjanus gibbus, Lutjanus fulvus, Lethrinus miniatus, Monotaxis grandoculis, Mulloides
vanicolensis, Chaetodon auriga, Scarus gibbus, Acanthurus xanthopterus, Ctenochaetus striatus,
Naso lituratus, Naso unicornis, Naso vlamingti and Balistoides viridescens. An unusual paucity
of Carcharhinidae, Synodontidae, Apogonidae, Mugilidae, Sphyraenidae, Caesionidae and
Tetraodontidae was noted while fish of the families of Holocentridae, Serranidae,
Carangidae, Lutjanidae, Lethrinidae, Mullidae, Chaetodontidae, Pomacanthidae,
Pomacentridae, Labridae, Scaridae, Acanthuridae and Balistidae were abundant.

A key question in fishery management is the correspondence between adult stock size and the
number of each new cohort reaching the mean size of capture by the fishing gear. Recruitment to
the fishery is preceded by a pre-recruit phase from birth to recruitment to the ecosystem and
followed by a post recruit phase consisting of a pre-exploited phase. No study of larval
recruitment was carried out at Tikehau though the knowledge of this part of the life-cycle is
critical for understanding the dynamics of reef fish populations. Recruitment processes in coral
reef fishes are however well documented (reviews in Munro and Williams, 1985 ; Richards and
Lindeman, 1987) and much of the findings can apply to Tikehau.

Most reef fishes spawn externally in the water column above hard bottom structures. Off-shore
larval dispersal is thought to be an evolutionary response to intense predation pressure in the
adult habitat (Johannes, 1978). Fish community studies at Tikehau suggest that, adult fishes of
various species gather off or in the pass to release their offspring in oceanic water. Larvae or
fertilized eggs subsequently undergo oceanic advection and diffusion and juveniles enter the
lagoon through shallow channels of the eastern coast. Most coral reef fishes characteristically
present a two part life-cycle ; a pelagic larval phase during which extensive dispersal is
possible and a relatively site-attached phase during in which movements are somewhat
restricted. According to relevant data presented by Brothers et al. (1983), the duration of the
pelagic stage of the main families exploited in Tikehau is estimated to range from about one
month (Lethrinidae, Lutjanidae) to over three months in the case of Naso sp. (Acanthuridae).
Absolute survivalship during planktonic life stages is a function of highly complex interactions
among predation, oceanographic processes, growth and food availability. Mortality rates
through this phase are subject to tremendous variations which considerably affect the
availability of recruits to the atoll fish community. Although of a lesser order of magnitude,
additional losses in subsequent post-settlement life due to innapropriate habitat and predation
can in turn impact the number of recruit to the fishery. Variations in recruitment can also
contribute to significant shifts in species composition within the exploited stock as it does occur
in Tikehau.

Knowledge on the extent of fish population exchange between islands through the pelagic
phase is of particular importance to effectively manage a fishery. The management strategy
will vary greatly depending on the extent to which recruitment to the atoll is derived from
within the fished population or is spawned outside the system. Due to the close-spacing
pattern of the atoll of the Tuamotu archipelago, it might be expected that the stocks of species
having a long pelagic larval stage occurring in a given atoll may be recruited from parent stocks
living in areas further upstream. If the exploited stock of Tikehau is recruited largely from
atolls located upstream like Rangiroa and Arutua, regulations for the conservation of the
spawning stock will be ineffective and will be of benefit only to islands lying downstream
(Mataiva). We have yet insufficient information to determine any general patterns, but there
is an urgent need for further studies aiming to determine the potential limits of stock exchanges
between atolls and the unit stock of a given species.

29

ACKNOWLEDGEMENTS

Authors are deeply indebted to the support of the Tikehaun people. We are very grateful to
fishermen, for without their help, nothing would have been possible.

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32

Appendix 1 : Check-list of the fishes of Tikehau atoll (L : lagoon, P : pass, O : ocean)

CARCHARHINIDAE

Carcharhinus melanopterus (Quoy et Gaimard, 1824) JE,
ALBULIDAE

Albula oulpes (Linné, 1758) P
CHANIDAE

Chanos chanos (Forsskal, 1775) 12
MURAENIDAE

Echidna polyzona (Richardson, 1844)

Gymnothorax buroensis (Bleeker, 1857)

Gymnothorax fimbriatus (Bennett, 1831)

Gymnothorax javanicus (Bleeker, 1859)

Gymnothorax margaritophorus Bleeker, 1864

Gymnothorax zonipectis Seale, 1906

Gymnothorax sp.3

Gymnothorax sp. 16

Gymnothorax sp. 18

Uropterygius xanthopterus Bleeker, 1859
CONGRIDAE

Conger cinereus Riippell, 1828
OPHICHTHIDAE

Leiuranus semicinctus (Lay and Bennet, 1839)

Muraenichthys macropterus Bleeker, 1857
ATHERINIDAE

Atherinidae sp.
SYNODONTIDAE

Saurida gracilis (Quoy et Gaimard, 1824)

Synodus variegatus (Lacepéde, 1803)
ANTENNARIIDAE

Antennarius sp. (juv.)
OPHIDIIDAE

Brotula multibarbata Temminck and Schlegel, 1846
HEMIRAMPHIDAE

Hyporhamphus acutus (Gtnther, 1871)
HOLOCENTRIDAE

Myripristis kuntee Valenciennes, 1831

Myripristis murdjan Forsskal, 1775

Myripristis pralinia Cuvier, 1829

Myripristis violacea Bleeker, 1851

Myripristis sp.

Neoniphon argenteus (Valenciennes, 1831)

Neoniphon opercularis (Valenciennes, 1831)

Neoniphon sammara (Forsskal, 1775)

Sargocentron caudimaculatum (Ruppell, 1838)

Sargocentron diadema (Lacepéde, 1802)

Sargocentron microstoma (Gtinther, 1859)

Sargocentron spiniferum (Forsskal, 1775)
AULOSTOMIDAE

Aulostomus chinensis (Linné, 1766)
FISTULARIIDAE

Fistularia commersonii (Ruppell, 1838)
SYNGNATHIDAE

Corythoichthys flavofasciatus Ruppel, 1838 L
SCORPAENIDAE

Scorpaenodes parvipinnis (Garrett, 1863) L
SERRANIDAE

Anthias lori Randall and Lubbock, 1976

Anthias olivaceus Randall and Mc Cosker, 1892

Anthias pascalus (Jordan and Tanaka, 1927)

Anthias squamipinnis Peters, 1855

Cephalopholis argus (Bloch and Schneider, 1801) L

Cephalopholis urodelus (Bloch and Schneider, 1801)

Epinephelus fasciatus (Forsskal, 1775)

Epinephelus hexagonatus (Bloch and Schneider, 1801)

Epinephelus merra Bloch, 1793

Epinephelus microdon (Bleeker, 1856)

Epinephelus socialis (Giinther, 1873)

Epinephelus sp.

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OOO000000000

Appendix 1 (cont'd)

Gracila albomarginata (Fowler and Bean, 1930)

Grammistes sexlineatus (Thunberg, 1792)

Pseudogramma bilinearis (Schultz, 1943)

Pseudogramma polyacantha (Bleeker, 1856)

Variola louti (Forsskal, 1775)
KUHLIIDAE

Kuhlia marginata (Cuvier, 1829)
PRIACANTHIDAE

Priacanthus cruentatus (Lacepéde, 1801)
CIRRHITIDAE

Paracirrhites arcatus (Cuvier, 1829)

Paracirrhites forsteri (Bloch and Schneider, 1801)

Paracirrhites hemistictus (Gunther, 1874)
APOGONIDAE

Apogon angustatus (Smith and Radcliffe, 1911)

Apogon coccineus Ruppell, 1838

Apogon fraenatus Valenciennes, 1832

Apogonichthys ocellatus (Weber, 1913)

Cheilodipterus quinquelineatus Cuvier, 1828

Fowleria aurita (Valenciennes, 1831)

Fowleria marmorata (Alleyne and Macleay, 1876)

Ostorhynchus savayensis (Gtinther, 1871)

Pristiapogon snyderi Smith, 1961

Pseudamia gelatinosa Smith, 1955
MUGILIDAE

Liza vaigiensis (Quoy et Gaimard, 1825)

Mugil cephalus (Linné, 1758)
SPHYRAENIDAE

Sphyraena forsteri Cuvier, 1829
ECHENEIDIDAE

Echeneis naucrates Linné, 1758
CARANGIDAE

Alectis indicus (Ruippel, 1830)

Carangoides orthogrammus (Jordan and Gilbert, 1881)

Caranx ignobilis (Forsskal, 1775)

Caranx lugubris Poey, 1860

Caranx melampygus (Cuvier, 1833)

Caranx sp.

Decapterus macarellus (Valenciennes, 1833)

Elagatis bipinnulata (Quoy et Gaimard, 1825)

Scomberoides lysan (Forsskal, 1775)

Selar crumenophthalmus (Bloch, 1793)
LUTJANIDAE

Aphareus furca (Lacepéde, 1801)

Aprion virescens Valenciennes, 1830

Lutjanus bohar (Forsskal, 1775)

Lutjanus fulous (Bloch and Schneider, 1801)

Lutjanus gibbus (Forsskal, 1775)

Lutjanus kasmira (Forsskal, 1775)

Lutjanus monostigmus (Cuvier, 1828)
LETHRINIDAE

Gnathodentex aureolineatus (Lacepéde, 1802)

Lethrinus elongatus Valenciennes, 1830

Lethrinus mahsena (Forsskal, 1775)

Lethrinus miniatus Smith, 1959

Lethrinus variegatus Ehrenberg, 1830

Lethrinus xanthochilus Klunzinger, 1870

Monotaxis grandoculis (Forsskal, 1775)
MULLIDAE

Mulloides flavolineatus (Lacepéde, 1801)

Mulloides vanicolensis (Valenciennes, 1831)

Parupeneus barberinus (Lacepéde, 1801)

Parupeneus bifasciatus (Lacepéde, 1801)

Parupeneus ciliatus (Lacepéde, 1801)

Parupeneus multifasciatus (Quoy et Gaimard, 1825)

Parupeneus porphyreus (Jenkins, 1900)

Upeneus vittatus (Forskall, 1775)

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33

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Appendix 1 (cont'd)

PEMPHERIDAE

Pempheris oualensis Cuvier, 1831

KYPHOSIDAE

Kyphosus cinerascens (Forsskal, 1775)

CHAETODONTIDAE

Chaetodon auriga Forsskal, 1775
Chaetodon bennetti Cuvier, 1831
Chaetodon citrinellus Cuvier, 1831
Chaetodon ephippium Cuvier, 1831
Chaetodon lunula (Lacepéde, 1802)
Chaetodon ornatissimus Cuvier, 1831
Chaetodon pelewensis Kner, 1868
Chaetodon quadrimaculatus Gray, 1831
Chaetodon reticulatus Cuvier, 1831
Chaetodon trifasciatus Mungo Park, 1797
Chaetodon ulietensis Cuvier, 1831
Chaetodon unimaculatus Bloch, 1787
Forcipiger flavissimus Jordan and Mc Gregor, 1898
Forcipiger longirostris (Broussonet, 1782)
Hemitaurichthys polylepis (Bleeker, 1857)
Hemitaurichthys zoster (Bennett, 1831)
Heniochus acuminatus (Linné, 1758)
Heniochus chrysostomus Cuvier, 1831
Heniochus monoceros Cuvier, 1831

POMACANTHIDAE

Centropyge flavissimus (Cuvier, 1831)
Centropyge loriculus (Giinther, 1874)
Pomacanthus imperator (Bloch, 1787)
Pygoplites diacanthus (Boddaert, 1772)

POMACENTRIDAE

Abudefduf sexfasciatus (Lacepéde, 1801)

Abudefduf sordidus (Forsskal, 1775)

Amphiprion chrysopterus Cuvier, 1830

Chromis iomelas Jordan and Seale, 1906

Chromis margaritifer Fowler, 1946

Chromis vanderbilti (Fowler, 1941)

Chromis viridis (Cuvier, 1830)

Chromis xanthura (Bleeker, 1854)

Chrysiptera glauca (Cuvier, 1830)

Chrysiptera leucopoma (Lesson, 1830)

Dascyllus aruanus (Linné, 1758)

Dascyllus flavicaudus Randall et Allen, 1977
Dascyllus trimaculatus (Riippell, 1828)
Plectroglyphidodon dickii (Liénard, 1839)
Plectroglyphidodon johnstonianus Fowler and Ball, 1924
Pomacentrus fuscidorsalis Allen and Randall, 1974
Pomacentrus pavo (Bloch, 1787)

Stegastes albofasciatus (Schlegel and Miiller, 1839-44)
Stegastes aureus (Fowler, 1927)

Stegastes nigricans (Lacepéde, 1803)

LABRIDAE

Anampses caeruleopunctatus Rtippel, 1828
Bodianus axillaris (Bennett, 1831)

Bodianus loxozonus (Snyder, 1908)

Cheilinus chlorourus (Bloch, 1791)

Cheilinus trilobatus (Lacepéde, 1801)
Cheilinus undulatus Ruppel, 1835

Cirrhilabrus exquisitus Smith, 1957
Cirrhilabrus scottorum Randall and Pyle, 1856
Coris aygula Lacepéde, 1801

Coris gaimard (Quoy et Gaimard, 1824)
Cymolutes praetextatus (Quoy et Gaimard, 1824)
Epibulus insidiator (Pallas, 1770)

Gomphosus varius Lacepéde, 1801

Halichoeres hortulanus (Lacepéde, 1801)

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Halichoeres melasmapomus Randall, 1980
Halichoeres trimaculatus (Quoy et Gaimard, 1834)
Hemigymnus fasciatus (Bloch, 1792)
Labridae sp. (juv.)

Labridae sp. 8 (juv.)

Labroides bicolor Fowler and Bean, 1928
Labroides dimidiatus (Valenciennes, 1839)
Novaculichthys taeniourus (Lacepéde, 1801)
Pseudocheilinus hexataenia (Bleeker, 1857)
Pseudocheilinus octotaenia Jenkins, 1900
Stethojulis bandanensis (Bleeker, 1851)
Stethojulis strigiventer Bennett, 1832
Thalassoma amblycephalum (Bleeker, 1856)
Thalassoma hardwicke (Bennett, 1830).
Thalassoma purpureum (Forsskal, 1775)

Thalassoma quinquevittatum (Lay and Bennett, 1839)

Thalassoma trilobatum (Lacepéde, 1801)
Wetmorella ocellata Schultz and Marshall, 1954

SCARIDAE

Calotomus carolinus (Valenciennes, 1839)
Cetoscarus bicolor (Ruppell, 1829)
Hipposcarus harid (Forsskal, 1775)
Hipposcarus longiceps (Valenciennes, 1839)
Leptoscarus vaigiensis (Quoy et Gaimard, 1824)
Scarus altipinnis Steindachner, 1879
Scarus brevifilis (Giinther, 1909)

Scarus festious , Valenciennes, 1840
Scarus forsteri (Bleeker, 1861)

Scarus frenatus Lacepéde, 1802

Scarus frontalis Valenciennes, 1839
Scarus ghobban Forsskal, 1775

Scarus gibbus Rtippell, 1828

Scarus globiceps Valenciennes, 1840
Scarus niger Forsskal, 1775

Scarus oviceps Valenciennes, 1839
Scarus psittacus Forsskal, 1775

Scarus rubroviolaceus Bleeker, 1849
Scarus schlegeli Bleeker, 1861

Scarus sordidus Forsskal, 1775

Scarus sp. rayé (juv.)

Scarus sp. gris (juv.)

Scarus sp. marron (juv.)

Scarus sp. parc

Scarus sp. vert (juv.)

BLENNIIDAE

Enchelyurus ater (Gtinther, 1877)
Istiblennius periophthalmus (Valenciennes, 1836)
Plagiotremus tapeinosoma (Bleeker, 1857)

CALLIONYMIDAE

Callionymus simplicicornis Valenciennes, 1837

GOBIIDAE

Amblygobius phalaena (Valenciennes, 1837)
Asterropteryx ensiferus (Bleeker, 1874)
Asterropteryx semipunctatus (Ruppell, 1830)
Callogobius sclateri (Steindachner, 1880)
Eviota afelei Jordan and Seale, 1906

Eviota sp.

Fusigobius neophytus (Gunther, 1877)
Gnatholepis cauerensis (Bleeker, 1853)
Gobiidae sp. 5

Nemateleotris magnifica Fowler, 1938
Ptereleotris evides (Jordan and Hubbs, 1925)
Quisquilius eugenius (Valenciennes, 1836)

ISTIOPHORIDAE

Istiophorus platypterus (Shaw and Nodder, 1792)

ZANCLIDAE

Zanclus cornutus (Linné, 1758)

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Appendix 1 (cont'd)

ACANTHURIDAE
Acanthurus achilles Shaw, 1803
Acanthurus bleekeri Giinther, 1861
Acanthurus glaucopareius Cuvier, 1829
Acanthurus guttatus Bloch and Schneider, 1801
Acanthurus leucopareius (Jenkins, 1903)
Acanthurus lineatus (Linné, 1758)
Acanthurus mata (Cuvier, 1829)
Acanthurus nigricauda Duncker and Mohr, 1929
Acanthurus nigrofuscus (Forsskal, 1775)
Acanthurus nigroris (Valenciennes, 1835)
Acanthurus nubilus (Fowler and Bean, 1929)
Acanthurus olivaceus Bloch and Schneider, 1801
Acanthurus pyroferus Kittlitz, 1834
Acanthurus thompsoni (Fowler, 1923)
Acanthurus triostegus (Linné, 1758)
Acanthurus xanthopterus (Valenciennes, 1835)
Acanthurus sp. Juv.) jaune
Ctenochaetus striatus (Quoy et Gaimard, 1825)
Ctenochaetus strigosus (Bennett, 1828)
Naso annulatus (Quoy et Gaimard, 1825)
Naso brachycentron (Quoy et Gaimard, 1825)
Naso brevirostris (Valenciennes, 1835)
Naso hexacanthus (Bleeker, 1855)
Naso lituratus (Bloch and Schneider, 1801)
Naso unicornis (Forsskal, 1775)
Naso vlamingii (Valenciennes, 1835)
Zebrasoma rostratum (Giinther, 1873)
Zebrasoma scopas (Cuvier, 1829)
Zebrasoma veliferum (Bloch, 1795)
SIGANIDAE
Siganus argenteus (Quoy et Gaimard, 1825)
BOTHIDAE
Bothus mancus (Broussonet, 1782)
BALISTIDAE
Balistapus undulatus (Mungo Park, 1797)
Balistoides viridescens (Bloch and Schneider, 1801)
Melichthys niger (Bloch, 1786)
Melichthys vidua (Solander, 1844)
Odonus niger (Ruppell, 1837)
Rhinecanthus aculeatus (Linné, 1758)
Rhinecanthus rectangulus (Bloch and Schneider, 1801)
Sufflamen bursa (Bloch and Schneider, 1801)
Sufflamen fraenatus (Latreille, 1804)
Xanthichthys caeruleolineatus (Randall, Matsuura, Zama, 1978)
MONACANTHIDAE
Aluterus scriptus (Osbeck, 1765)
Amanses scopas (Cuvier, 1829)
Cantherhines dumerilii (Hollard, 1854)
OSTRACIIDAE
Ostracion cubicus Linné, 1758
Ostracion meleagris Shaw, 1796
TETRAODONTIDAE
Arothron hispidus (Linné, 1758)
Canthigaster bennetti (Bleeker, 1854)
Canthigaster solandri (Richardson, 1844)
Canthigaster valentini (Bleeker, 1853)

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ATOLL RESEARCH BULLETIN

NO. 416

COLONIZATION OF FISH LARVAE IN LAGOONS OF RANGIROA

(TUAMOTU ARCHIPELAGO) AND MOOREA (SOCIETY ARCHIPELAGO)

BY

V. DUFOUR

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

COLONIZATION OF FISH LARVAE IN LAGOONS OF RANGIROA
(TUAMOTU ARCHIPELAGO) AND MOOREA (SOCIETY ARCHIPELAGO)

BY

V. DUFOUR

ABSTRACT

The colonization of the lagoon by coral reef fish larvae was compared between
two islands of French Polynesia, the atoll of Rangiroa and the high volcanic island of
Moorea. In both cases the larval flux coming into the lagoon followed a daily cycle.
Larvae were mainly caught at dusk and during the night, and on both islands the
colonization was higher during moonless than moonlit periods. The larval flux did not
appear to be dependent on the waterflow in the lagoons. A comparison of larval
abundance and taxonomic lists indicates that Scarids and Labrids were dominant in
Rangiroa while Gobiidae was the major family on Moorea. This difference could be in
part related to the different sampling periods, but other environmental and biological
factors could also be important.

INTRODUCTION

Most reef fishes have a pelagic larval phase, ending with the colonization of the
reef (Leis, 1991). This recruitment of fish larvae on coral reefs is now studied in detail
“since it has been assumed that events occuring during this period determine the
characteristics of reef-fish stocks (Sale, 1980; Richards and Lindeman, 1987; Doherty
and Williams, 1988). Although some studies emphasized the importance of the
processes during the settlement of fish larvae among coral reefs (Sweatman, 1985,
1988; Victor, 1986), this phenomenon is not clearly understood. For fifteen years,
scientists have studied mechanisms of this return to the parental habitat. These studies
have been limited mainly to continental reefs (e. g.: reefs of Central America), or patch
reefs along continental platforms (e.g.: Great Barrier Reef of Australia) with very little
data available on recruitment of reef fish species in oceanic islands and in atolls. This is
a first attempt to compare some features of fish colonization of the lagoons of two
geomorphologically different islands located in French Polynesia.

Laboratoire d'‘Ichtyoécologie Tropicale et Méditerranéenne, Ecole Pratique des Hautes Etudes, URA
CNRS 1453, Université de Perpignan 66860 Perpignan Cedex France et
Antenne EPHE-Muséum Centre de l'Environnement BP 1013 Moorea Polynésie Frangaise

Manuscript received 14 October 1993; revised 2 June 1994

Although the data were not obtained simultaneously in both islands, it is still
useful to compare these two sets of data. It is also worth considering whether or not the
observed differences are due to the location, the geomorphological features of the
islands, or the time lag between sample collecting on the two islands.

MATERIAL AND METHODS
STUDY AREA

Rangiroa Atoll (figure 1) is one of the largest atolls in the world and the most
important of the Tuamotu Archipelago (Ricard, 1985). It is 70 km long, 30 km wide and
the peripheral rim is 225 km long. One third of the rim is above the sea surface and
consists of small cays separated by channels. The rim flat is generally wider in the
northern than in the southern part (800 m vs 500 m). The lagoon is biologically very
rich compared to the other atolls of Tuamotu and is one of the most important reef
fisheries centers of this Archipelago. The maximum estimated depth is 35 m and a lot of
pinnacles are evenly distributed on its surface. Two passes, 450 to 550 m wide and 14
to 35 m deep are located in the North coast and lagoon waters are flushed out through
these passes during ebb tides (35 cm to 60 cm tide range). Oceanic waters flow into the
lagoon through channels over the atoll rim and the two passes during flood tides and
also when trade winds blow. The fish larvae were collected in a channel, midway
between the two passes.

Moorea Island (figure 1) is located 25 km north-west of Tahiti (Galzin and
Pointier, 1985). This volcanic island has a triangular shape with a 61 km coastline and a
relief of 1200 m. The island is surrounded by a barrier reef, which encloses a lagoon,
800 to 1600 m wide. The reef is intersected by several passes. Two bays are located on
the northern part of the island. The lagoon is generally shallow (1 to 5 m), but deeper
near the passes. The oceanic water enters the lagoon by waves breaking over the outer
reef crest, and return to the ocean through the passes. The very weak tides on Moorea
(average range 15 cm) do not reverse the current in the passes. Sampling was carried out
on the outer reef crest, 600 m away from the pass.

METHODS

Samples were collected off the northern coasts of both islands. Fish larvae were
collected with an anchored net that filtered the waterflow coming into the lagoon. The
net with rectangular mouth (1 x 0.25 m) was of mesh size 0.5 mm. A General Oceanics
flowmeter was fixed in the mouth of the net.

On Rangiroa Atoll, the net filtered the water coming from the seaward reef flat to
the lagoon. It was located 500 m from the outer reef front. The channel was made of
gravel in a shallow area (0.5 m).

On Moorea Island, the fish larvae were collected on the outer reef crest. The net
was fixed on the reef substrate and filtered the water coming over the crest with the

3

breaking waves. Thus, the water flow was not constant but it was estimated over the
time period of each sample (10 minutes).

The time lag between two samples was lh or 2h. Two diel cycles were made in
February 1989 on Rangiroa. At Moorea, two diel cycles were made in April 1989 and a
third one was made in October 1989. At Rangiroa, the first cycle was 3 days before the
new moon and the second was around the first quarter. The diel cycles were made
during same lunar phases on Moorea.

The collected larvae were then fixed with 5% formalin seawater and identified
under a dissecting microscope at the lowest taxonomic level following the
recommendations of Leis and Rennis (1983) and Leis and Trnski (1989). This
correspond to a family-level identification for all the larvae but the Gobioids. In several
cases, genus-level identification was accomplished. Most of the larvae caught were in
the postflexion stage or in metamorphosis and were identified. Abundances of
unidentifiable preflexion larvae and juveniles were very low and were simply pooled
into preflexion and juveniles types. Results are expressed in larval abundance per
sample which represents the larval flux, i. e. the number of larvae for 1m of reef section
and for 10 minutes (Dufour, 1993).

RESULTS

DIEL CYCLES

The diel cycles from Rangiroa (figure 2) represent changes in larval composition
over a two night period. Although the samples do not cover 24 hours, they take into
account the two consecutive daily changes at dusk and dawn. Our data clearly indicate
that fish larvae were present only at night and during twilight. Because the waterflow
' may influence the larval flux, the volume filtered by the net was also presented. The

Kendall coefficient correlation rank calculated with Statview software (Abacus
Concepts, Inc, Berkeley, 1992) was significant for the comparison between the two
larval fluxes of the two cycles and also between the two water flows (Table I). But it
was positive between the larval fluxes (+0.524) while it was negative between the water
flows (-0.486). This result indicates that the change of the larval flux was somewhat
similar during the two sampling periods. But the water flow was negatively correlated
“between the two cycles. The Kendall coefficient correlation rank calculated between the
water flow and the larval flux for the two diel cycles made on Rangiroa was very small
and not significant (table II). However, the second cycle shows a strong decrease of the
water flow in the middle of the night and this decrease was also observed for the larval
abundance. These results indicate that there was no clear link between water flow and
larval flux, except for low water flow, which could hinden larval colonization in the
lagoon.

The diel cycles made on Moorea also show that most fish larvae were taken at
night and dusk (figure 2). The Kendall 's tau calculated between the larval flux and the
water flow (Table II) was not significant. The absence of significant correlation in the

4

four studied cycles confirms that larval flux did not seem to be quantitatively dependent
of the water flow.

The study of larval flux on the two islands reveals that the larval flux on Rangiroa
reached 3 times the value of 500 larvae per sample, which was obtained only once on
Moorea, despite a larger sampling effort. On both islands these larval peaks occured in
the early evening. A second peak was found just before dawn on the second cycle on
Rangiroa. The water flow during these larval peaks on Rangiroa was not very high and
similar to that found during larval peaks of Moorea. As a result, these high peaks of
larval colonization on Rangiroa and Moorea do not appear to be created by variation in
water flow over the reef of these islands. The comparison of the average larval flux
recorded on the two islands at different times indicates that this flux appears to be more
significant on Rangiroa than on Moorea (Table III). It was obvious that a high larval
flux from these islands was never recorded during full moon. However, during
moonlight periods of the first lunar quarter, the larval abundance on Rangiroa was
higher than the abundance on Moorea.

TAXONOMIC ANALYSIS OF THE SAMPLES

The number of larvae and the number of larval types were different between the
two islands (Table IV). The total number of larvae from Rangiroa was almost half the
number of those collected from Moorea during eleven months, although the number of
samples was higher. Based on the two studied periods, the average larval flux on
Rangiroa reached three times the average larval flux on Moorea. The number of larval
types on Moorea was 56 for the three cycles. The number of larval types on Rangiroa
during only two nights was 43. Several larval types from Moorea were not found on
Rangiroa, while only one larval type from Rangiroa was missing from Moorea. Some of
these types were represented by more than 50 larvae. The comparison between Rangiroa
and all the samples of Moorea indicates that the number of types was twice as less as
that found in all the samples of Moorea despite the fact that the number of samples
collected was eight times higher and the sample period was much longer in Moorea.
Therefore, the number of larval types caught in two nights on Rangiroa was
significantly higher that those caught off Moorea.

The list of the larval types and their abundance is presented for both Rangiroa and
Moorea (Fig. 3). The pie diagrams show the percentages of the main larval types for
each island. The abundance of the larvae from Moorea is presented for all the 358
samples made between March 1989 and November 1989 (grey bars) and for the three
diel cycles previously studied (black bars). The most abundant larval type on Rangiroa
was the Scaridae forming 52% of the total catch. The two most abundant larval types on
Moorea were Gobiidae (Gobiidae type 1 and Gobiidae type 56). The abundance of
Gobioid types on Moorea represents 63% of the total catch. Scaridae were the second
most abundant family on Moorea but they represented half the number of Scaridae
collected from Rangiroa. On Rangiroa Gobioid types were the second most important
group but their number were far below those of the Scaridae. The other significant larval
types were found in similar numbers on both islands although periods of sampling were

5

different. This was the case for the Labridae, the Callionymidae and the Schindleriidae.
It is apparent that the number of larvae of these families would have been much higher
on Rangiroa if the extent of sampling was similar to that carried out off Moorea. The
Apogonidae type 2 were more abundant on Rangiroa but the total number of
Apogonidae from both areas was not very different. Juvenile fishes were caught in both
islands in relatively high number. Different families were gathered in this type
(Mullidae, Holocentridae...). It is interesting to note that these juveniles were collected
at dusk despite the fact that daylight was supposed to assist in a higher avoidance of the
net. The Gobiidae type 8 was only collected at Rangiroa.

DISCUSSION

The daily patterns of the reef colonization by reef fish larvae have been
demonstrated only recently on coral reefs (Dufour, 1991, 1993). The fish larvae that
enter the lagoon were caught only at night and dusk. Their abundance was also found to
be higher during moonless periods. This pattern has been confirmed by samples over a
two years period. The data from Rangiroa in this study confirm this finding. Each cycle
made at Rangiroa demonstrated that fish larvae were abundant during the moonless
nights in the channel of the atoll. The larval abundance could reflect higher larval activity
above the reef at night (Hobson et Chess, 1978). However, the fixed nets could not
catch larvae that do not move into the lagoon. Hobson and Chess (1978, 1986) have
demonstrated that planktonic organisms drifted at night over the reef of Enewetak atoll to
enter the lagoon. Their appearence over the reef was related to a vertical migration at
night, followed by a passive drift in a current flow induced by breaking waves.
However, colonization by fish larvae at Rangiroa and at Moorea was only accomplished
by individuals ready to settle. The larval flux observations do not include preflexion
larvae because these larvae were scarce in samples, although they could have drifted
. more easily than postflexion larvae. It is known that postflexion larvae are able to swim
(Blaxter, 1986; Webb and Weihs, 1986). Moreover, reef fish larvae can avoid the reef
area until they are competent for metamorphosis (Kingsford and Choat, 1989). These
phenomena imply other mechanisms of colonization in addition to passive drift. The
larval flux in the lagoon could thus be viewed as an active process made nightly by
competent fish larvae. Night activity correllated to the darker phases of the moon cycle
has also been demonstrated for other planktonic organisms over reefs (Aldredge and
King, 1980, Tranter and al., 1981). These authors found that this moonless activity was
an adaptative advantage against predation. In a similar way, the colonization of fish
larvae occurs at night when predation is lower (Hobson, 1973, 1975). Therefore, larval
colonization of the lagoons at night could be viewed as an adaptative process against
predation, as predation plays a major role during the recruitment of reef fishes (Shulman
and Ogden, 1987, Victor, 1986, Hixton, 1991). Both the geomorphology of the reef
and hydrodynamic characteristics of the waters flushing into the lagoons appear to have
no significant control on larval colonization.

The difference of the abundance of fish larvae between the two islands can be
explained by the difference of the sampling periods. Although it has not been established
that fish larvae were more abundant in French Polynesia during February than during

6

April, the summer season was considered to be the recruitment season in other coral reef
areas (Williams, 1983, Victor, 1987). Thus, the lower abundance in samples from
Moorea could be explained by variations related to seasonal recruitment. The difference
in abundance and diversity of fishes during colonization between these two islands
could also be related to the size of the lagoon. The quotient of reef periphery to surface
of the lagoon is also much lower for Rangiroa than for Moorea. This is because the
lagoon of Moorea encloses the volcanic island and does not cover all the surface
delimited by the outer reef like an atoll. On Moorea, the quotient of the lagoon surface to
the reef length is around 0.86 km"! (60 km/70 km2), on Rangiroa it is 0.11 km-! (230
km/2100 km2), but the sand cays over one third of the reef lower this coefficient to
0.074. This last value is more than 10 times smaller than on Moorea. If we could
assume that the density of the larval flux per unit of lagoon surface over the crest was
related to this coefficient, the number of fish colonizing the lagoon should be
proportionally higher. This assumption could explain the higher rate of colonization for
Rangiroa. This hypothesis cannot be verified, however, because the larval flux over all
the reef rim has not been determined.

The difference between the major larval types from the two islands could also be
explained by other hypothesis. The composition and diversity of adult fishes in both
lagoons was probably not the same. It is possible that the number of fish species in the
lagoons of atoll is related to the surface area of these atolls (Galzin et al., 1994).
Scaridae and Labridae are among the most abundant fishes in atoll lagoons (Bouchon-
Navarro, 1983, Morize et.al., 1990), while Pomacentridae and Acanthuridae are more
abundant in Moorea lagoon (Galzin, 1987). Although we have no information about
their density in Rangiroa atoll, the higher abundance of Scaridae larvae on Rangiroa was
not surprising. But this higher abundance could be related to the low number of samples
collected in Rangiroa, and the period when they were collected. It is possible, however,
that the pattern of settlement of fish larvae on reefs could be relatively unpredictable and
chaotic and peaks of larvae have be described as randomly distributed at different time
scales (Doherty and Williams, 1988). Another explanation could be the reproduction
period of Scaridae, which could occur earlier. Larvae of Scaridae, however, were
caught on Moorea until the end of June and Scaridae and Labridae were also the most
abundant families in samples made in May and June 1988 on Moorea.

CONCLUSIONS

The study of the larval flux over the reef on Rangiroa and Moorea was useful to
the understanding of some aspects of the settlement processes of fish larvae in lagoons.
This study has confirmed some trends in the diel and lunar cycles of reef colonization by
fish larvae. The difference of larval abundance between samples on both islands can be
related to the time lag between the sampling periods of each island. The sizes of the two
lagoons could also play a role in this difference. It was more difficult to understand the
taxonomic difference. It could be explained by the difference in size of the two lagoons,
or by the period of fish reproduction or even by the density of the different families, but
few data were available to confirm these hypotheses.

REFERENCES

Alldredge A. L., King J. M., 1980. Effects of moonlight on the vertical migration
patterns of demersal zooplankton. J. exp. mar. Biol. Ecol., 44: 133-156.

Bouchon-Navarro Y., 1983. Distribution quantitative des principaux poissons
herbivores (Acanthuridae et Scaridae) de l'atoll de Takapoto (Polynésie frangaise).
J. Soc. Océan. 39(77): 43-54.

Blaxter J. H. S., 1986. Development of sense organs and behaviour of Teleost larvae
with special reference to feeding and predator avoidance. Trans. Am. Fish. Soc.
115(86): 98-114.

Doherty P.J., Williams D.McB., 1988.-The replenishment of coral reef fish
populations. Oceanogr. mar. Biol. Ann. Rev., 26: 487-551.

Dufour V., 1991. Variation d'abondance des larves de poissons en milieu récifal: effet
de la lumiére sur la colonisation larvaire. C.R. Acad. Sci., Paris, t.313, série III:
187-194.

Dufour V., Galzin R., 1993. Colonization patterns of reef fish larvae to the lagoon at
Moorea Island, French Polynesia. Marine Ecology Progress Serie, 102: 143-152.

Galzin R., 1987. Structure of fish community of French Polynesia coral reefs. 1/ Spatial
scales. Mar. Ecol. Prog. Ser., 41: 137-145.

Galzin R., Pointier J-P., 1985. Moorea Island, Society Archipelago. In: Proc. 5th int.
Coral Reef Congress, B. Delesalle, R. Galzin and B. Salvat (eds.), 1: 73-102.

. Galzin R., Planes S, Dufour V, Salvat B., in press. Variation in diversity of Coral reef
fishes among French Polynesian atolls. Coral Reefs.

Hixton , 1991. Predation as a process structuring coral reef fish communities. In : The
ecology of fish on coral reef, P. F. Sale (ed.), Academic Press : 475-508.

Hobson E. S., 1973. Diel feeding migrations in tropical reef fishes. Helgol. Meer. 24 :
361-370.

Hobson E. S., 1975. Feeding patterns among tropical reef fishes. Am. Scient., 63 :
382-392.

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Kingsford M. J., Choat J. M., 1989. Horizontal distribution patterns of presettlement
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8

Leis J. M., 1991 The pelagic stage of reef fishes: the larval biology of coral reef fishes. In: The
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230.

Leis J. M., Rennis D. S., 1983. The larvae of Indo-Pacific coral reef fishes. J. M. Leis
(ed.) NSW Univ. press & Univ. of Hawaii press, 269pp.

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Congress, B. Delesalle, R. Galzin and B. Salvat (eds.), 1: 159-210.

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Sweatman H. P. A., 1988. Field evidence that settling coral reef fish larvae detect
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163-174.

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Victor B. C., 1987. Growth, dispersal, and identification of planktonic labrid and
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of coral reef fishes. Mar. Ecol. Prog. Ser., 10: 231-237.

Table I: Values of the Kendall coefficient correlation rank for the larval flux and the
water flow between the two diel cycles from Rangiroa (n.s: not significant at 5%, s:
significant at 5%).

Comparison of the larval fluxes 0.524 s
Comparison of the Water flows -0.486 s

Table II: Values of the Kendall coefficient correlation rank between the water flow and
the larval flux (n.s: not significant at 5%).

[____JRangira 1 [Rangioa2 [Moowal [Moorea [Moorea

Kendall coefficient | 0.206 n.s -0.176 n.s_ |-0.109 n.s | -0.036 n.s| 0.345 n.s

Tableau III : Average values of the water flow and the larval flux for the cycles from
Rangiroa (R) and Moorea (M), standard deviation are in brackets.

water flow : -m3-sample-! | abundance : larves.sample-!

122.5 (156.4)

M 23.10 S50 (GID 38.1 (25.9)

Tableau IV : Abundance of larvae and larval types from Rangiroa and Moorea

| = SRangiroa | Moorea (3 cycles) | Moorea (all samples)
44

es

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Society Archipelago, Lec
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Study area

17°30S

Reef crest

Pacific Ocean

149°S0W

Figure 1. French Polynesia (above) with the atoll of Rangiroa, Tuamotu archipelago
(middle), and the high Island of Moorea, Society archipelago (below).

Larval flux
water flow

Rangiroa

Larval flux
water flow

New moon
Apr. 89

Water flow

%
3
Lamy
oS
fe
3
|

First quarter
Apr. 89
Moorea

Larval flux
Water flow

Larval flux
Water flow

Figure 2. Evolution of the larval flux expressed in number of larvae. sample7!
(bars) and the water flow in m*?. sample"! (line) during nycthemeral cycles made
on Rangiroa and on Moorea. The black thickness on the categories axis represents
the night hours, the white frame on the same axis represents moonlit hours.

Rangiroa

Moorea

Scaridae 1 Gobiidae 1

Labridae 1

OC 4

juveniles

Callionymidae Labridae 6

a i
SS

Schindleriidae leptocephalii ¥

El ES

Apogonidae 2 others

Gobiidae 2

OM oO

lopidae |
Blenniidae |
Pin BED wide

Rangiroa

abridae 3
Synodontidae
Apogonidae 1

bepocepbali
ridae 6

Apogonidae 2
Schindleriidae (ad.)_ =

Callionymidae
Labridae |
2229 Scaridae 1

0 100 200 300 400 500 0 500 1000 1500 2000

Figure 3. Percentage of the main larval types collected on Moorea and Rangiroa
(above) and diagram of larval abundance (below) for all the samples from Rangiroa
and for the three cycles of Moorea (black) and all the samples from Moorea (grey).
n.i.: not identified to lower taxonomic level; juv.: juvenile; ad.: adulte fishes are also
included in this neotenic family.

ATOLL RESEARCH BULLETIN

NO. 417

CAVES AND SPELEOGENESIS OF MANGAIA, COOK ISLANDS

BY

JOANNA C. ELLISON

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

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L002 LAvGRVEDT meEIPAOOLINNG ane:

CAVES AND SPELEOGENESIS OF MANGAIA, COOK ISLANDS
BY

JOANNA C. ELLISON

ABSTRACT

Ten caves in the makatea limestone of Mangaia, Cook Islands were
explored and mapped, totalling over 3.7 km of passage. Of these, there was
an apparent grouping by elevation that corresponds with previously
described sea-level terraces in the makatea. Four caves have major level
sections 10-20 m above sea-level, corresponding with a 14.5 m Pleistocene
terrace. The high dimensions of these caves indicate downcutting during
slow uplift, or multiple reoccupations by highstands of Pleistocene sea-
levels. One major cave has level passage 20-30 m above sea-level,
corresponding with a 26-27.5 m terrace. Three caves have level passage 40
m above sea-level, corresponding with a 34-39 m terrace. Active conduit
caves are developed at the present sea-level, but are closed with heavy clay
deposits from recent soil erosion.

INTRODUCTION

Mangaia is the second largest and most southerly of the Cook Islands
(21°54'S, 157°58'W), with a land area of 52 kmé@ (Fig. 1). The island is
divided into two concentric geological zones. The inner zone is a subdued
‘basaltic volcanic cone rising to 168 m, flattened at the summit possibly by
marine erosion prior to its uplift (Wood, 1967), dating between 17-19 m yr BP
(before present) (Dalrymple et al., 1975). The outer zone is a complete
raised limestone rim or makatea, 0.7 to 2 km wide, up to 70 m in height, with
erosional topography of steep terraces on the outer edge, and cliffs on the
inner edge (Stoddart et al., 1985).

Yonekura et al. (1988) showed from the identification of planktonic
foraminifera in makatea limestone that these are up to 17 m years old,
indicating that coral reefs developed shortly after the volcanic island formed.
While the major part of the limestone is Tertiary, Pleistocene deposits occur
on the seaward margins to an elevation of 14.5 m (Stoddart et al., 1985).
Emergence occurred in late Tertiary to Quaternary times, during which there
were two periods of stability in relative sea-level to cut marine terraces at 26-
27.5 m and 18-20 m (Stoddart et al., 1985).

Department of Biogeography and Geomorphology, Research School of Pacific Studies,
Australian National University, Canberra ACT 2601, Australia.

Manuscript received 25 January 1993; revised 14 September 1993

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3

Mangaia receives a mean annual rainfall of 1967 mm, with range in the
period 1914-1984 of 1024 to 2983 mm (Thompson, 1986). There is a
pronounced wet season from November to April, and dry season from May
to October. Drainage is radial, with deeply incised first and second order
streams off the central cone feeding lowland taro swamps collected against
the inner makatea cliff. Water from the swamps sinks beneath the makatea
limestone in radially draining cave systems. Stoddart et al. (1985) showed
that stream water entering the makatea limestone is aggressive, supporting
the interpretation that the cliffs of the inner makatea are erosional remnants
from a former complete cover of limestone to equivalent elevations on the
volcanic slopes (Stoddart and Spencer, 1987, Figure 4).

The purpose of this study is to investigate how these events are
expressed in the speleogenesis of Mangaia. Many cave entrances can be
seen in the makatea cliffs, and the topographic map of Mangaia shows 65
sink holes on the top of the makatea, which considering that the map was
made from air photographs of a heavily forested area must under-estimate
total numbers. The sinkholes are strongly clustered to indicate traces of cave
systems. A few are used for burials or settlement and hence are of
archaeological interest. As commented by Gill (1894), "the numerous and
extensive caves that honeycomb the makatea were formerly used as
habitations, cemeteries, places of refuge, and stores. Scores of them are
filled with dessicated human bodies".

While very little work has been done on the cave systems of makatea
islands, but the following principles on cave evolution are suggested from
the surface geomorphological work.

1. As cave development is most active at the water table, those that are
' presently under active development can be found at the vadose conduits
where streams enter the makatea. These decline slightly along their course,
similar to a stream.

2. Caves above these levels are fossil conduits, with a positive relationship
between elevation and age, resultant from uplift of Mangaia and general
decline in sea-levels from the Tertiary to the Quaternary (Haq et al., 1987).

3. Fossil conduit caves should decline slightly from the influent entrance at
the inner edge of the makatea to the coast, at an elevation that is slightly
above the sea-level position at the time of development. On low limestone
islands, such caves can be used as an indicator of former sea-leve! (Mylroie
and Carew, 1988).

4. Higher elevation caves should therefore show features of older caves,
with collapse, flowstone infill and large speleothem formations. Lower
elevation caves should show features of younger caves, with more even
walls and floor, and smaller formations.

5. A conduit cave could cut into its floor during uplift of the makatea,
developing a deeply rifted cave. Such caves could indicate a period of slow
uplift, while rapid uplift would result in abandonment of the former conduit
and development of a new cave at a lower level.

METHODS

In July 1991 ten caves were explored and surveyed, to the British Cave
Research Association Grade 5b standard, using a Suunto compass and
clinometer, and 50 m fibreglass tape. This standard requires a station- to-
station survey, with passage details recorded at the time (Ellis, 1976). Cave
maps produced are shown in plan view, so it must be remembered that
passages are not shown at their actual length unless they are horizontal. A
profile view is also shown of the cave passage. No vertical techniques were
possible in this study, and climbing risks not taken owing to lack of back-up
support.

Where possible, surface survey was continued to a known elevation to
give the altitude of the cave as indicated on the maps, otherwise it was
estimated from contours on the topographic map.

DESCRIPTIONS OF THE CAVES

Tuitini cave, Veitatei (Figure 2)

Tuitini is the largest cave explored in inis study, with two entrances about
100 m to the east of Lake Tiriara. It would have been the conduit cave for the
Veitatei drainage basin, which is the largest on Mangaia, when relative sea-
level was 20 m higher. Survey was continued to the water level of the lake to
establish the altitude. The main passage is large, with few formations, while
the upper passages to the south and east are well decorated with
formations. There are four burials in the cave, permission to explore should
be sought from the chief in Kaumata village (Oneroa).

The main passage indicates downcutting, with heights of 20 to 25 m,
while the upper passages have low ceilings of 10 m or less. There are
sections in the main passage with collapse, it is necessary to climb around
or over large boulders. At the end of the surveyed section the main passage
continues at the base of a 7 m pitch, at which point the cave is around 30 m
high.

KEY

TUITINI CAVE

Mangaia, Cook Islands + Skeleton
GR 21°S7'S; 15 7°S6'w » Column
bent ese m ni aE 8 > Stalactite
epth-13m =" : :
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entrance

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KEY
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+ L. Tiriara entrance

CAVE PROFILE | south upper passage

10 . %
main east passage

entrance

Depth (m)

0 100 200 300 400
Distance (m)

Figure 2.

6

To'uri cave, Tava'enga (Figure 3)

The entrance to To'uri is where the depression to the west of Tava'enga
swamp meets the makatea wall. A stream leads to the cave entrance, which
is approached by a steep climb down over boulders and ferns into a large
overhang. The cave is partially an active streamway, with heavy wet red clay
deposits throughout. A bank of red clay at the entrance has been incised by
headward erosion of the stream to create a 2 to 3 m profile.

The small stream follows the left hand side of the cave for 60 m, then
sinks into a hole. In the stream water are small black fish.

To'uri cave indicates recent stream flow that has downcut through older
clay deposits, leaving exposed mud sections along sections of the passage
wall. The cave is large in passage dimensions relative to others in Mangaia,
the roof a wide vertical fissure visible to 20-30 m, the passage 3-10 m wide.
There are occasional rocks fallen down, and occasional large stalagmite or
flowstone formations. Stalactites are the more common.

After 490 m of passage there is a clay bank 2.5 m down to flowing water,
which heads out through a tight passage to the north. The water tasted salty
and waves could be heard. Opposite, up a clay climb, the cave continues to
the west. This was not explored.

Elevations for Tou'ri and Teruarere caves are based on the salt water
being at sea-level.

Teruarere cave, Tava'enga (Figure 4)

This is the second largest cave explored in this study, located 40 m
above the entrance to To'uri Cave, along the makatea wall to the SW.

The cave is accessed from the top of the makatea. The entrance rift
trends east- west, and there is a 10 m climb down to the cave entrance 50 m
back from the makatea edge, assisted by roots. A large Hernandia
moerehroutiana tree grows out of entrance. Where the rift reaches the
makatea edge one can look down on entrance to To'uri cave, some 100 m to
the left. Strong winds come through the cleft. The cave entrance leads away
from makatea edge, under the entrance climb.

Cave is simple fossil streamway, 10-30 m high, 1-10 m wide, dry. It
contains at least 7 skeletons lying on the floor near the cave wall,
surrounded by stones. This is a burial cave, in the charge of Tuara George of
Oneroa village, from whom permission to explore the cave should be
obtained.

Cave has been studied by the ornothilogist D. Steadman, showing from
fossil bird bones that early Polynesian settlement caused extinction of many
species (Steadman, 1985, 1986).

The rift opens above to four daylight avens in the first 200 m of the cave.
Formations are mainly calcite cascades, curtains and flowstones, with
vandalism of whatever possible. The floor is hard red mud, with occasional
patches of rubble. Lower in the cave, calcite flows cover the floor, and there
are places where ridges on the floor indicate fossil pools. Towards the end
of the main passage of the cave, there are a couple of climbs down, then a

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pitch down that was not explored. Some daylight comes through high above
the pitch. The upper passage continues, but is a tricky climb past the pitch,
this was not explored.

Touropuru cave, Ivirua (Figure 5)

This is the third largest cave explored in this study. The entrance is 10 m
up the makatea wall adjacent to the small Kirikiri swamp, between the larger
Karanga and Ivirua taro swamps. Adjacent to the entrance to the south was
a large cave shelter used for habitation, which has unfortunately recently
collapsed.

This cave is the burial cave of the Totongaiti tribe, with 22 skeletons in
the main cave and 9 in a small cave above the lower entrance. Permission
to explore this cave must be obtained from a member of the tribe in Ivirua
village, such as Ma'ara Ora, Director of Forestry. Just inside the entrance is a
side passage to the right, 39 m long to a window 10 m up the makatea wall.
The passage is narrow and lined by 19 skeletons in open coffins, mostly of
planks (post-contact), but some canoes (pre-contact).

The main passage is a fossil vadose stream passage, generally 1-2 m
wide and 3 m high, but sections which widen to some 6 m, and sections
where the rift above is visible to some 15 m. After 350 m the passage forks,
the left passage closing up with flowstone after 150 m, the right fork leading
to the base of a doline entrance in Ivirua village, that has a 22.5 m pitch that
can be climbed (GR 21° 54' 45" S, 157° 54' 15" W). The main passage has
been closed in by flowstone deposits and some collapse, causing the route
to go up and down, but from the entrance to the fork over a distance of 350 m
there is no elevation change. There are three more skeletons at the start of
the main passage, then no more. Formations are mainly curtains and

.flowstones, though there are some large stalagmites and columns and more
smaller stalactites. There is less vandalism of formations in the final left
branch. After the fork, both passages climb some 4 m. There are some small
passages off the main route, some of which may have unexplored sections.

Erua Cave, Karanga (Figure 6)

The cave entrance is located some 200 m to the south of the Karanga
swamp conduit entrance, just north of where the path from Karanga village
descends the makatea to the Karanga swamp. The cave entrance is
conspicuous, 14 m above the base of the makatea, a rift 20 m tall, anda
strong through breeze can be felt. The passage of this cave is wide and
high, with few formations and a mud floor with frequent cobble-sized angular
rocks. It was used as a refuge during prehistoric wars, and several human
structures and midden deposits can be seen, but no burials. Like Tautua
cave, which was also used as a war refuge, Erua has light inside the cave,
from an aven. There is a debris slope from material which has fallen through
the aven, including some animal skeletons. The few formations are large

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stalactites and stalagmites, and there are two avens which could extend the
cave.

Taenoterau Cave, Karanga (Figure 7)

The cave entrance is located to the north of the Karanga swamp conduit
entrance, 20 m above the level of the swamp. Behind the large rock at the
entrance are trenches where a Japanese archaeological group dug in 1990.
The lighted entrance is some 25 m tall, but falls to 5-10 m as the cave
begins. Flowstone formations have blocked the passage twice in the first 20
m, so one has to climb over. The formations are all large, stalactites,
stalagmites and dripstones, and crystalline flowstone walls.

Tautua cave, Tamarua (Figure 8)

At the makatea wall where the East Tamarua swamp collects there is a
large cavern, over 30 m high and 100 m across (Plate 1). The floor is
covered by large boulders from collapse, and there are old, vertical
stalactites on the ceiling, indicating that the cavern has been exposed by
makatea retreat. The stream from the swamp enters the cavern and through
a conduit cave that is 15 to 20 m wide, mostly 1 to 2 m high, with extensive
wet clay deposits.

Above the conduit is the entrance to Tautua cave, up an 11 m climb. At
the entrance the cave is 15 to 20 m high, and this height continues along the
right branch just inside the entrance. This does not extend far, and has two
connections with the lower streamway.

On the left branch are habitation sites clustered around a window out of
the makatea wall. The cave is well known from oral traditions as the primary
refuge of the Tonga’iti tribe in times of war (Gill 1894, Buck 1934).
Permission to explore the cave should be obtained from a member of that
tribe, such as Noka Tumarama of Tamarua viilage. There are stone faced
platforms, a marae (worship place), a tupe disk pitch (for playing a bowling-
type game), and midden deposits. The site was analysed by P. Kirch and
other archaeologists from University of California at Berkeley in 1989, and
mapped by theodolite in 1991.

The site was a retreat in times of war as it is easily defended. The lower
entrance is a vertical climb, and defenders could bombard invaders with
rocks. Past the archaeological site is a T junction, where the left branch
leads up to a high makatea entrance, used as an escape route or otherwise
blocked with stones. The right branch leads down to the main part of the
cave, which was mapped here until a pitch down was reached.

TEANOTERAU CAVE CAVE EROFILE
Mangaia, Cook Islands

GR 21°54.5'S; 157°54.5'w
Length 5? m

Depth 5 m

Alt. 20 m

Depth (m})

20 40
Distance ¢m)

Grade 5b

archaeological
excavations
(Japanese, 1990)

KEY
oO Column
? Stalactite
& Stalagmite

: o Boulder

+18 mclimb a Ce ee
to entrance ; :

Scale: m Flowstone

Makatea
wall

Figure ?.

13

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16
Other Active Conduit Caves

Ivirua Conduit Cave

GR 21° 55' 30" S, 157° 54' 00" W. Where the Ivirua swamp drains
through the makatea is a cave entrance similar to Tautua cave in the East
Tamarua swamp. Above the stream is a large overhang some 25 m high,
with old stalactites. The stream has red clay banks, and in pools there are
many freshwater prawns (Macrobranchium lar). The conduit cave is wide
and low, with few and small formations, and heavy red clay deposits, similar
to East Tamarua. Neither of these active streamway caves were explored far
because of problems of sinking in the wet clay. A small raft is recommended,
as this could be dangerous.

To the north of the streamway, there is a cave entrance up a 10 m climb,
resembling the position of Tautua cave in Tamarua. The cave was not
explored.

Lake Tiriara Conduit

GR 21° 57' 00" S, 157° 56' 15" W. Lake Tiriara in Veitatei, adjacent to
Tuitini cave, drains through a large cave entrance (Plate 2). These
dimensions continue for some 50 m, with 2 m depth of water, then the cave
narrows and the roof meets the water level. Figure 2 shows that the main
passage of Tuitini cave trends towards the Lake Tiriara conduit, and it is
possible that they connect in the lower unexplored section of Tuitini cave.

On the makatea summit directly above where the Lake Tiriara conduit
enters the cliff, c. 10 m back from the cliff face, there is an arch some 15 m
high, and a pitch cave entrance in the south wall of the arch. The
topographic map shows a number of clustered cave entrances on the
makatea summit above the Tuitini and Lake Tiriara conduit cave systems.

Kauvava cave, Temakatea (Figure 9)

Kauvava and Piriteumeume caves both have doline entrances, rather
than makatea wall former streamway entrances. As they are of the highest
elevation of caves explored, they could have been formed before erosion
developed the makatea wall.

The southern entrance to this cave is the large doline to the N of
Temakatea village. Permission to explore the cave should be requested
from Papa Tua, who lives to the east of the cave entrance. At the base of the
doline is a 6 m climb down at the entrance, which is filled with boulders and
other debris. The entrance passage has rounded walls, indicating
meandering stream activity, but is presently dry. The cave is mostly a tall rift,
visible to 20 m. Some 60 m into the cave the passage descends and
narrows, indicating a sink which is now infilled by deposits of clay. This is the
lowest part of the cave between the two avens.

Towards the northern aven flowstone has closed the passage, but there
is a tight climb up the rift over this. The aven is 23 m high, the opening is
behind the Mormon church in Temakatea village. Below the aven the cave

17

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continues to the north, but this is down a pitch so could not be explored in
this study.

Pirituemeume cave, Temakatea (Figure 10)

The makatea summit is characterised by deep (5-10 m) dissection, with
"karst streets” that follow the joints (Stoddart, et al., 1985). The entrance to
Piriteumeume cave is a small doline in a karst corridor to the south of the
inland road from Temakatea village, opposite the quarry. There are old (dry)
flowstone walls at the entrance, and a strong draft.

The cave is relatively old, indicated by its elevation, collapse features
and large formations. It links three dolines, and has a low daylight aven
towards the northern end. The height varies from 4 to 15 m, and the floor is
irregular and filled with collapsed boulders. The flowstone walls are dry and
rough, indicating that they are no longer under formation. The southern
section of the cave has a cavern with large stalactites and dripstones, while
the northern section has several large columns.

Man 88 cave, Keia (Figure 11)

No name could be found for this cave, so it is described by the
archaeological site number of P. Kirch, who excavated both in the cave and
below its entrance in 1991. The entrance is 8 m from the makatea base, a
large lighted cavern adjacent to a pool of water further inside the cave, with
signs of occupation. The cave does not extend far, and seems to have been
Closed by calcite deposits.

SPELEOGENESIS

The ten caves described include the major caves of Mangaia, but many
more remain to be explored. However, there is an apparent grouping of
these caves according to elevation of major sections, as shown in Table 1.

The lowest caves are the present conduits, such as To'uri cave, and the
East Tamarua conduit below Tautua cave, as well as the Lake Tiriara and
Ivirua conduit caves described. These contain an active streamway, few
formations, and heavy clay deposits resulting from soil erosion off the
volcanic cone. The elevations are close to sea-level, and they resurge at the
coast as seen at Avarua landing, or on the reef flat as at Tamarua.

Tuitini, Touropouru, Tautua and Taenoterau caves all have major level
sections between 10 and 20 m above sea-level. This suggests that they
were conduit drainage caves corresponding with the 14.5 m elevation of
Pleistocene

20

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21

MAN 36 CAVE
Mangaia, Cook Islands
GR 21°55.7'S; 157°57.4'wW
Depth +3 m
Alt.c. 40 m
archaeological
excavations
(P. Kirch, 1991)

+7? 8mclimb
to entrance

Grade 5b

makatea
edge

CAYE PROFILE entrance

o

KEY M.N.
oO Column ]
° Boulder
& Pool

Depth (m)}

Oo

120 100 80 60 40
10
Ny Distance (m}

Scale: m

Figure 11.

22

Table 1. Dimensions and elevations of Mangaia caves (m)

Cave Length Altitude Depth Elevation of Height
explored _of entrance level sections __of rift
To'uri 489 3 -3 1 20-30
Tuitini 830 23 -13 10 & 20 20-25
Touropouru) 587 16 +4 10& 18 15
Tautua 335 fe) +6 15&19 10-20
Taenoterau 57 20 -5 Ue 5-10
Teruarere 791 43 -24 20 & 30 10-30
Erua 177 c. 40 -8 c. 40 20
Kauvava 358 c. 60 -38 c. 40 20+
Man 88 94 c. 40 +3 c. 40 10-15

Piriteumeume 136 c. 60 -9 ©2595 4-15

23

limestones, probably formed at the same time as a relative sea-level 20 m
higher than present (Woodroffe et al., 1991). Reef groove-and-spurs formed
at this time are now 2 to 11 m above sea-level (Stoddart et. al, 1985). Thus it
is indicated from three corresponding features that sea-level was in this
position for considerable time.

Teruarere cave is a major feature of Mangaia, a minimum of 791 m of
continuous level passage ranks with the spectacular find of Ana Maui by the
Tonga '87 caving expedition on 'Eua (the cave named after the Tongan
demi-god) (Lowe, 1988). It declines from 30 to 20 m above sea-level, a
simple fossil streamway, corresponding with the 26-27.5 terrace described
by Stoddart et al. (1985). The terrace is deeply dissected, and was believed
to represent a very old sea-level feature. Similarly, Teruarere cave has a
number of high daylight avens, indicating long-term dissolution and
collapse. The pitch at the end of the surveyed section indicates that one of
these cut down to a deeper level after uplift of the main passage.

Erua, Kauvava and Man 88 caves all occur at about 40 m above sea-
level, and could correspond with the 34-39 m terrace identified by Schofield
(1967), Wood and Hay (1970), and Ward et al., (1971), and shown by
several profiles of Stoddart et al., (1985). However, this feature is so old that
they must have eroded dowm from their formative elevation. While Erua and
Man 88 caves are closed by calcite deposits, the pitch beneath the 23 m
aven at the northern end of Kauvava cave indicates that flow through here
allowed the cave to cut down to a deeper level after uplift.

The highest elevation cave in this study is Piriteumeume, which has all
the features of an old cave, with large formations, collapse and irregularity,
and dryness. During development of the cave the dolines would have
drained a higher surface, and the karst corridors leading to the entrance
would also have been caves. The makatea surface has many such small
relic caves to be found in the karst corridors, though the caver will probably
- get lost finding them!

CONCLUSIONS

Cave systems are a relatively neglected aspect of study of raised
limestone islands, possibly owing to the specialised techniques of survey,
and potential dangers. This study shows that they can make a contribution to
the knowledge of limestone geomorphology and changes in relative sea-
level .

Features of the caves explored indicate the validity of the principles of
makatea cave development outlined in the introduction.

It is apparent that caves of lower elevation are of larger dimensions than
those higher. This could be because parts of the higher caves have been
lost with time, but as well as length the lower caves have higher rifts or
vadose slots. This could result from slower rates of island uplift that allowed
the streams to downcut their caves, or it could indicate the sea-level
changes of the Pleistocene that have caused multiple reoccupations of
these caves.

24

ACKNOWLEDGEMENTS

This research was carried out as part of the project "Anthropogenic
Environmental Change, Agricultural Intensification, and Socio-Political
Evolution in Polynesia", funded by the NSF Grant BNS-9020750, to Patrick
V. Kirch, Principal Investigator. | should like to thank P. V. Kirch and D. W.
Steadman for the opportunity to carry out this work, and their
encouragement and comments. Thanks are given to the Government of the
Cook Islands for their assistance in this project, particularly Tony Utanga,
and also to Ma'ara Ngu and Tuara George for field assistance in Mangaia.

REFERENCES
Buck, P.H., 1934. Mangaian Society. B.P. Bishop Museum Bulletin, 122.

Dalrymple, G.B., Jarrard, R.D. and Clague, D.A., 1975. K-Ar ages of some
volcanic rocks from the Cook and Austral Islands. Geol. Soc. Am. Bull., 86:
1463-1467.

Ellis, B.M., 1976. Cave surveys. In T.D. Ford and C.H.D. Cullingford (Editors),
The Science of Speleology. London, Academic Press, 1-10.

Gill, W.W., 1894. From Darkness to Light in Polynesia. London, The
Religious Tract Society, 383 p.

Haq, B.U., Hardenbol, J., and Vail, P.R., 1987. Chronology of fluctuating sea
levels since the Triassic. Science, 235, 1156-1167.

Lowe, D.J., 1988. ‘Eua Island Tonga ‘87 Expedition Report. Unpublished,
25);

Mylroie, J.E. and Carew, J.L., 1988. Solution conduits as indicators of Late
Quaternary sea level position. Quat. Sci. Rev., 7, 55-64.

Schofield, J.C., 1967. Pleistocene sea-level evidence from the Cook Islands.
J. Geosci. Osaka City Univ., 10, 118-120.

Steadman, D.W., 1985. Fossil birds from Mangaia, southern Cook Islands.
Bull. Br. Orn. Cl., 105, 58-66.

Steadman, D.W., 1986. Two new species of Rails (Aves: Rallidae) from
Mangaia, Southern Cook Islands. Pacific Science, 40, 27-43.

Stoddart, D.R., Spencer, T. and Scoffin, T.P., 1985. Reef growth and karst
erosion on Mangaia, Cook Islands: A reinterpretation. Z. Geomorph., N.F. ,
57, 121-140.

25

Thompson, C.S., 1986. The climate and weather of the southern Cook
Islands. N.Z. Met. Service Misc. Publ., 188 (2), 69 p.

Ward, W.T., Ross, P.J. and Colquhoun, D.J., 1971. Interglacial high sea-
levels, an absolute chronology derived from shoreline elevations.
Palaeogeogr., Palaeoclimatol., Palaeoecol., 9, 77-99.

Wood. B.L., 1967. Geology of the Cook Islands. N. Z. J. Geol. Geophys., 10,
1429-1445.

Wood, B.L. and Hay, R.F., 1970. Geology of the Cook Islands. N. Z. Geol.
Surv. Bull., n.s. 82, 103 p.

Woodroffe, C.D., Short, S.A., Stoddart, D.R., Spencer, T. and Harmon, R.S.,
1991. Stratigraphy and chronology of Late Pleistocene reefs in the southern
Cook Islands, South Pacific. Quat. Res., 35, 246-263.

Yonekura, N., Ishii, T., Saito, Y., Maeda, Y., Matsushima, Y., Matsumoto, E.,
and Kayanne, H., 1988. Holocene fringing reefs and sea-level change in
Mangaia Island, Southern Cook Islands. Palaeogeogr., Palaeoclimatol.
Palaeoecol., 68, 177-188.

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ATOLL RESEARCH BULLETIN

NO. 418

SHALLOW-WATER SCLERACTINIAN CORALS FROM KERMADEC ISLANDS

BY

VLADIMIR N. KOSMYNIN

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

v

WW MeOH VF SINIOATY

-

jay Yad AbesUA MORE BIAROD KA

SHALLOW-WATER SCLERACTINIAN CORALS FROM KERMADEC ISLANDS

BY

VLADIMIR N. KOSMYNIN

INTRODUCTION

Shallow-water scleractinian corals were collected in the Kermadecs (South-West Pacific) in April-
May of 1990 during the 18th cruise of the USSR Academy of Sciences’ R/V "Akademik Alexandr
Nesmeyanov", which sailed from Vladivostok to the Western Pacific. The objective of this expedition
was to study the influence of volcanic gas and hydrothermal activity on sublittoral communities.
Dredging operations were performed on the slopes of Kermadecs: underwater observations were
made near Curtis Island and corals were collected at several points near Raoul Island and nearby
islets using SCUBA (fig. 1).

Despite numerous previous visits to the Kermadec Islands by research vessels, very little
information has been reported on the scleractinian fauna. The presence of corals in bottom
communities in this area was mentioned by Nelson and Adams (1984) and coral communities were
noted when Shiel et al. (1986) described the sublittoral zonation, but neither publication provided
a list of species. The last publication dealt directly with corals from the Kermadec Islands was that
of Vaughan (1917). This paper was based on the material collected early this century by
R.W.B.Oliver, former director of the New Zealand National Museum of Natural History, who
described the Kermadecs in several publications. Material from this collection are deposited in the
Museum of New Zealand (MNZ) in Wellington and at National Museum of Natural History
(NMNH) in Washington. Some additional Kermadec corals collected and kept in the New Zealand
National Museum were identified by D.F.Squires. Soviet expeditions also worked there, but their
results are not yet published.

A SHORT DESCRIPTION OF SITES OF CORAL COLLECTING

Near Raoul Island two sublittoral areas were studied: one north of Blue Lake and another in the
southern part of Denham Bay. Meyers and Napier Islets were also studied and corals were collected
(Figure 1).

North of Blue Lake at the depth of 10-15 m the foreshore is characterized by a gently sloping
floor. The floor shows an alternation of areas covered by ripple sands with separate boulders and
patches of boulder pavement, among which some boulders that are 1-2 m high. Unlike the barren
ripple sands, bottom communities on large boulders are rich and include fleshy algae as well as
calcareous geniculated Corallina on upper surfaces and incrusting Lithothamnium under
overhangings, and many sea urchins that include at least two species. Corals are abundant there and
are mostly encrusting forms of Hydnophora, Goniastrea and Montastrea 50-60 mm in size on top
surfaces of boulders, and Dendrophyllia under overhangings (Tabl. 1). Life is less diverse on the

Moscow State University, Geographical Faculty, 119899 Moscow, Russia

Manuscript received 10 November 1993; revised 5 December 1993

2

surface of boulder pavement in comparison to that found on large boulders probably because of sand
abrasion.

The foreshore in the southern part of Denham Bay is considerably different from that described
above. It is steeper and at a distance of 50-70 m from the shoreline the depth is 15-20 m. The slope
is composed of large basalt blocks, each several cubic meters. They are arranged on the slope either
in dense groups or scattered individuals. Coarse-grained sand and gravel are accumulated between
boulders.

These boulders support rich flora and fauna on their tops, whereas at the base, where light is
weaker and sand-gravel erosion is stronger, the boulders are poorly inhabited. Along with
macrophytes, these rich communities contain a considerable number of corals, primarily colonies
of Turbinaria bifrons, which form large flat coralla up to 1.5 m in diameter. There are also abundant
encrusting colonies of Goniastrea australiensis with a corallum size up to 20 cm, and smaller coralla
of Montipora, Leptoseris and Cyphastrea. These corals cover no more than 10-20% of the surface
even at the top of boulders. The maximum number of corals appears to occur at depths of 13-15
m and decrease rapidly up the slope, probably because of the increasing abrasive effect of the
resuspended sediments.

The richest coral communities were discovered on the western side of the Meyers islets opposite
a channel separating them. Here at depth of 22-24m there is a terrace that looks like a wave cut
platform. It may be in fact a submerged coast-line. On the surface of the terrace there are thin
lenses of coarse-grained sand and gravel, as well as individual colonies of Turbinaria radicalis with
coralla up to 0.5m in diameter. Rocks of different height occur on the surface of the terrace, some
of them reach a depth of 10-12 m, while others extend up to almost the surface. The rocks contain
very rich communities in which corals play an important role sometimes covering up to 25% of the
surface. Life forms of corals are mainly encrusting such as Goniastrea, Leptoseris and Montipora,
or massive or columnar such as Hydnophora exesa. Branching forms are represented by sparse small
colonies of Pocillopora damicornis, which inhabit the tops of boulders. Turbinaria radicalis and
Turbinaria bifrons form the largest colonies and are more noticeable than other corals. Hydnophora
exesa form the second largest colonies, with coralla up to 40 cm in diameter.

On vertical cliffs there are frequent Dendrophyllia sp. together with gorgonian corals. The latter
grow abundantly at a depth of more than 25 m, and up the slope on more gently sloping areas there
are abundant alcyonarian corals. In the communities at the depths of less than 25 m other sedentary
animals are numerous along with the corals, including sponges, tunicates, hydroids, sea lilies, sea
urchins and the notorious sea-star Acanthaster planci. Similar communities were noted also near
Napier island.

The Kermadec Islands are also characterised by abundant deep water scleractinian corals at the
depth of 375-1000 m. In particular, a large quantity of fragments of Goniocorella dumosa
(Alcock,1902) were dredged from the depth of 1000 m by trawl at 30°28’0”S 178°37°2”’W, as well as
corals such as Madrepora vitiae Squires & Keyes,1967 and Flabellum gracile (Studer,1877).

DISCUSSION

The deep water scleractinian corals mentioned above are related to the fauna from New Zealand,
whereas the shallow water Kermadec corals are linked with the Tonga and Fiji Islands to the north
and the Norfolk Islands on the west. There is a certain affinity of the latter with the Great Barrier
Reef of Australia through the Norfolk and Lord Howe Islands but the diversity is considerably lower.
Further studies will undoubtedly increase the list of corals for the Kermadec Islands. Some fossil
corals were also noted by Vaughan (1917): Leptoria phrygia (Ellis & Solander,1786; USNM 93896),
Alveopora sp. (USNM 93898), Acropora sp.(sample I failed to find in USNM) and Cynarina

3

lacrymalis (Milne Edwards & Haime,1848) (USNM 93899), which may quite possibly be alive on
Kermadecs.

The low diversity of reef-building coral species off the Kermadecs is probably due to several
reasons. I tend to agree with Schiel et al.(1986) that it is not a result of competition for space with
other organisms, in particular algae. Among the main factors are the relative isolation of the islands,
their young age and recent activity of volcanic processes as well as wave erosion (abrasion). The
development of coral reefs near Raoul Island is limited not only by low water temperatures but more
by relief and coastal geomorphic processes. Quick wave erosion of volcanic shores and mobility of
floor substrates limit the possibilities for establishment of reef building corals. The coral fauna
adjacent to Raoul Island small islets is richer than the coral fauna of Raoul Island itself. The
precipitous rocky foreshores of small islets almost lack sediments. For corals it is more suitable to
settle and grow there than on the relativly gentle slopes of Raoul Island where the mobile coarse
bottom sediments limit coral growth.

The water temperatures near the Raoul Island are not optimal for reef corals but does not fall
to the lethal winter limit of 15°C for the majority of hermatypic corals. The summer temperatures,
which are about 24°C, is close to normal for coral reproduction.

The establishment/recruitment of new species of corals on Kermadec Islands is quite possible. It
can happen not only by the distribution of planula by but also by rafting, for example, by fragments
of pumice-stone carried by currents from northern volcanic islands. The discovery of fossil colony
fragments of such species as Acropora and Alveopora (Vaughan,1917) indicate that some species
could have established in this area but the conditions are not favorable for survival of new
populations. In particular, their survival is considerably limited by abrasion and mobility of sediment
material, and by volcanic activity.

ACKNOWLEDGMENTS

The author is grateful for the support provided to me: by Dr. Vitaly Tarasov, the head of the
expedition on the "Academik Alexandr Nesmeyanov"; Dr. Alan Baker, the director of MNZ,
Wellington; other collegues of the MNZ for the opportunity to work with their collection; Dr. Paul
Gillespie (Cawthron Institute, Nelson, NZ) for computer search of data on the corals from the
Kermadec Islands; Dr. Ian Macintyre and Mr.Chad Walter (NMNH) for reviewing of manuscript.
I would like to thank especially Dr. Stephen Cairns for reviewing of the article and for advice on
work with the NMNH coral collection.

LITERATURE

Nelson W.A.; Adams N.M. 1984: Marine algae of the Kermadec Islands. National Museum of New
Zealand occasional series 10: 1-29.

Schiel D.R., Kingsford M.J., Choat J.H. 1986: Depth distribution and abundance of benthic
organisms and fishes at the subtropical Kermadec Islands. New Zealand Journal of Marine
and Freshwater research. Vol. 20: 521-535.

Vaughan T.W. 1917: Some corals from Kermadec Islands. Trans. N.Z. Inst., vol.49: 275- 279.

Table 1. The list of shallow water scleractinian corals from Kermadec Islands.

Species name
Raoul

Hydnophora exesa (Pallas, 1766)
Goniastrea favulus (Dana,1848)*
Goniastrea australiensis

(Milne Edwards & Haime,1857) —18,19,23
Leptoseris mycetoseroides Wells,1954
Leptoseris hawatiensis Vaughan, 1907
Cyphastrea serailia (Forskal,1775)
Montastrea curta (Dana,1846) 1-10-3,8

Montipora cf. millepora Crossland,1952
Montipora cf. spumosa (Lamarck, 1816)**
Pocillopora damicornis (Linnaeus, 1758)
Plesiastrea versipora (Lamarck, 1816)**

Turbinaria radicalis Bernard,1896 1-10-22
Turbinaria bifrons Bruggemann, 1877
Dendrophyllia sp. 1-10-24

* according to Shiel et al.,1986.

North coast

1-10-4,5,6,7,9

1-10-4,7,17,

Denham
Bay

3-14-4,8,11,
13,14,17,18
3-14-7,15,16,24
3-14-4
3-14-5,6,9,12

3-14-22

Napier
Islet

2-22-1,2,6,11,13
2-22-3,15
2-22-10,12
2-22-3

2-22-4,9
2-22-8

2-22-5
2-22-14

** according to Vaughan,1917. Comments to some of these species see in text.

Meyers
Islets

4-5(15)-7,8
4-5(15)-1,2,15,19
4-5(15)-10
4-5(15)-13
4-5(15)-3
4-5(15)-12
4-5-30,31,32
4-5(15)-4,5,6,17

4-5(15)-14
4-5(15)-16

1-10-3 - Paleontological Museum of Moscow recent scleractinian corals collection number. First number is
the site of collecting (the same as on the chart, fig.1); second number is depth of collecting (if 5(15) - it means
range 5-15 meters); third is number of sample from this site. Dublicates of these spesimens with the same

indexation were transmitted to MNZ in Wellington.

New IN

Caledonia

Napier Isl

Hutchinson

Blue Lake @
(\

Raoul Island

29°18'S
Wok W

Figure 1.

A. The location of the Kermadec Islands, north of New Zealand.

B. Enlarged map of Raoul Island in the Kermadecs showing smaller
ISMeeS with, Sibesioer coral collecting (1) = 4).

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a

ATOLL RESEARCH BULLETIN

NO. 419

DESCRIPTION OF REEFS AND CORALS FOR THE 1988 PROTECTED AREA

SURVEY OF THE NORTHERN MARSHALL ISLANDS

BY

JAMES E. MARAGOS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

AATDSTOAT SRY TAT HOVE

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A902 OVS @RATAIO-Vi

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DESCRIPTION OF REEFS AND CORALS FOR THE 1988 PROTECTED AREA
SURVEY OF THE NORTHERN MARSHALL ISLANDS

BY

JAMES E. MARAGOS

Abstract

The Republic of the Marshall Islands requested a natural and cultural biodiversity
survey of 6 northern atolls (Bok-ak, Pikaar, Toke, Wotto, Rondik, Adkup) and one reef
island (Jemg) which was accomplished over 17 days in September 1988. This report
covers the results of the survey of the reefs and corals during the expedition. Ninety-five
marine sites were snorkeled and the shorelines of all island were surveyed during the
expedition. A total of 168 species and 55 genera and subgenera of stony corals were
reported including several new species and one new genus recorded (Polyphyllia) for the
Marshalls.

Bok-ak Atoll, the northernmost atoll, supports large giant clam populations, a
completely native flora, and the largest seabird populations in the Marshalls. Pikaar Atoll
also supports large giant clam populations and the largest sea turtle nesting populations
in the Marshalls. Both Bok-ak and Pikaar are isolated from other atolls and have shallow
lagoons elevated slightly above sea level due to their geomorphological configuration.
Toke Atoll is located about 10 km from inhabited Utrok Atoll, and supports healthy coral
reef habitats and giant clams. Jemg Island supports large seabird populations and is the
second most important sea turtle nesting site in the Marshalls. Boat access to Jemg,
Pikaar and Bok-ak is hazardous due to wave exposure or strong currents. Rondik Atoll
supports healthy coral reefs, blue coral habitats, pink foraminiferan sand beaches, and
large coconut crab populations. Adkup supports abundant seabird populations, sea turtle
nesting populations, and healthy coral reefs. Inhabited WOtto also supports healthy coral,
coconut crab, sea turtle and giant clam habitats and has beautiful beach, reef and lagoon
habitats.

On the basis of the surveys, Bok-ak, Pikaar and Jemg are recommended for
designation as limited entry ecological preserves. Toke is recommended as a national
park accessible to both tourists and residents. Limited sport diving and beach-going is
also suitable for Rofdik and Adkup. Assistance should be provided to the people of
Wotto Atoll to fulfill their desire for small scale adventure tourism.

Program on Environment, East-West Center
1777 East-West Road
Honolulu, Hawaii 96848 U.S.A.

Manuscript received 8 March 1990; revised 30 August 1994

II.

IV.

TABLE OF CONTENTS

Introduction

Materials and Methods

Results

Jemo Reef

Atoll Geomorphology and Oceanography
Bok-ak Atoll

Pikaar Atoll

Toke Atoll

Wotto Atoll

Rondik Atoll

Adkup Atoll

Corals: Combined Species List
Discussion

Marine Reserves

Marine Parks and Recreational Areas
Subsistence Activities

Radiological Contamination

Mariculture

Agriculture

Commercial Fishing

Small Scale Tourism

Variations in the Depths of Living Reef Flats
Rapid Marine Field Assessment Procedures
Summary

Acknowledgements

References

Appendix A

Appendix B

Appendix C

Appendix D

Table i.
Table 2.
Table 3.

Table 4.
Table 5.

Table 6.

Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.

Figure 6.
Figure 7.

Figure 8.
Figure 9.

Figure 10.
Figure 11.
Figure 12.

Figure 13.
Figure 14.
Figure 15.

Figure 16.
Figure 17.
Figure 18.
Figure 19.

Figure 20.
Figure 21.

LIST OF TABLES

Physiolographic data on the atolls and table reef visited
in 1988

Check list of corals observed in the Northern Marshalls,
1988

Relative diversity and distribution of stony coral genera and

species observed in 1988

Previous coral records from the RMI atolls studied in 1988

Criteria for evaluating candidate reef areas as marine
protected areas and parks in the RMI

Relationships between various types of resource uses for
Northern Marshalls reefs and atolls and the required
criteria for their feasibility

LIST OF FIGURES

Northern Marshall Islands

Map of Jemg Island and Table Reef

Reef features at Jemg Reef

Close up of Jemg Island and Nearby Reefs

Map of Bok-ak Atoll showing sites of Sept. 1988
marine surveys

Southern tip of Bok-ak Atoll

Bok-ak Atoll in the vicinity of the cluster of large
eastern islands

Bok-ak Atoll in the vicinity of the western passage

Bok-ak Atoll in the vicinity of the NW reef tip

Pikaar Atoll showing locations of marine survey sites

Detailed map of the single western passage at Pikaar Atoll

Pikaar Atoll in the vicinity of the southern tip and
island of Pikaar

Pikaar Atoll at the eastern end

Pikaar Atoll at the northwest tip

Shoreline changes between 1944 and 1978 at selected
locations at Toke and Pikaar atolls

Toke Atoll showing locations of marine survey sites

Toke Atoll, NW corner in the vicinity of a shipwreck

NE tip of Toke Atoll

SW side of Toke Atoll in the vicinity of 2 marine survey
sites and the deep passage

Detailed map of deep passage off western Toke Atoll

SW corner of Toke Atoll in the vicinity of the
largest islands

19
21
22
23

28
29

30
31
32
34
35

35
36
37

39
41
42
43

44,
44

45

Figure 272.
Figure 23
Figure 24.

Figures.

Figure 26.
Figure 27.

Figure 28.
Figure 29.
Figure 30.

Figure 31.
Figure 32.
Figure 33.
Figure 34.

Figure 35.
Figure 36.
Figure 37.

Figure 38.

Figure 39.

Figure A-1.
Figure A-2.
Figure A-3.
Figure A-4.
Figure A-5.
Figure A-6.
Figure A-7.
Figure A-8.
Figure A-9.

Figure A-10.

Figure A-11.
Figure A-12.

Figure A-13.
Figure A-14.

LIST OF FIGURES - cont’d

Map of Wotto Atoll

Defense Mapping Agency Chart of Wotto Atoll

Map of NE Wotto Atoll sketched from 1978 color
aerial photos

Map of southern Wotto Atoll sketched from 1978 color
aerial photos

Rondik Atoll showing locations of marine survey sites

SW corner of Rondik Atoll showing the main south passage
and the location of 2 marine survey sites

Western end of Rondik Atoll showing Bock Island

Main island cluster of NE Rofdik Atoll

Shoreline changes between 1944 and 1978 at selected
locations along NE Rondik Atoll

Map of Adkup Atoll

NE peripheral reef of Adkup Atoll

NE rim of Adkup Atoll near a windward passage

NW rim of Adkup Atoll in the vicinity of a pass and
one marine survey site

NW rim of Adkup Atoll near Aneko (Enego) Island

SE end of Adkup Atoll near the main islands and pass

Southeastern end of Adkup Atoll showing sites of some
marine surveys

Possible adverse effects of cutting channels through
semi-enclosed atoll lagoons

Progressive development of reef flat features on atolls

Bok-ak Atoll reef profiles: lagoon and pass reefs

Bok-ak Atoll reef profiles: eastern perimeter reefs

Bok-ak Atoll reef profiles: western perimeter reefs

Pikaar reef profiles: perimeter reefs

Pikaar reef profiles: lagoon reefs and perimeter reef

Toke Atoll reef profiles: perimeter reefs

Toke Atoll reef profiles: western perimeter and lagoon reefs

Jemg reef profiles: ocean slopes

Wotto Atoll reef profiles: north and eastern perimeter reefs
Wotto Atoll reef profiles: eastern and southern

perimeter reefs
Rondik Atoll reef profiles: southeast perimeter reefs
Rofdik Atoll reef profiles: northeast perimeter and
lagoon reefs

Adkup Atoll reef profiles: southern perimeter reefs
Adkup Atoll reef profiles: northern perimeter reefs

I. INTRODUCTION

Oceania represents one of the last frontiers for the assessment of biological
diversity, especially for shallow water marine ecosystems. Coral reefs are among the
most widely distributed ecosystems on the face of the earth, and within Micronesia they
dominate in terms of area. They also provide critical physical and ecological support to
most other ecosystems including those of low coral islands. Because of remote access,
geographic isolation, and the physical limitations of underwater surveying techniques,
most marine areas in Micronesia remain unstudied. Yet assessment of the ecological and
biological importance of reef areas for conservation, subsistence, recreation, visitor and
commercial uses must require on-site surveys to some extent. With many thousands of
reefs and islands yet to be evaluated, new techniques must be employed to allow a rapid
but technically adequate evaluation of reef sites. Existing regional evaluations (IUCN,
1989; 1988; Dahl, 1980) provided valuable information on many areas with respect to
park and reserve potential, but the emphasis has been placed on terrestrial (island)
ecosystems which are easier to visit and survey. The Marshall Islands study of September
1988 offered a unique opportunity to accomplish a marine oriented regional survey of
reefs using a non-conventional rapid field assessment technique relying on a combination
of field observations, teamwork, aerial photographs, underwater photographs, available
maps, and interviews with knowledgeable islanders.

The study is primarily based on the results of a three week expedition to six atolls
and one table reef in the northern Marshalls during September 1988. The areas surveyed
were the atolls of Bok-ak, (Taongi, Bokak, Pokak), Pikaar (Bikar), Toke (Taka), Adkup
(Erikub), Roidik (Rongerik), and Wotto (Wotho) and the table reef of Jemg (Table 1, Fig.
1). The name spellings used above reflect the most current official RMI linguistical
determinations. Those in parentheses above reflect spellings commonly used in the past.

The field expedition concentrated on evaluating the following categories of
resources with respect to potential justification and interest in protected area designation;
names in parentheses refer to the expedition team members responsible for collecting
information about the resources:

island vegetation (Derral Herbst),

seabird nesting, resting and feeding (James Juvik),

other terrestrial animals (James Juvik, Peter Thomas),

turtle nesting and feeding habits (John Naughton, James Maragos, Peter
Thomas),

nearshore reef fishes (John Naughton, R. Virgil Alfred and Paul Maddison),

giant clams and other edible shellfish (John Naughton, R. Virgil Alfred, James
Maragos),

* coral and reef features (James Maragos),

* pelagic fisheries and marine mammals (Paul Maddison, R. Virgil Alfred, and

John Naughton),

* * * =

See

* cultural historical and archaeological resources (Charles Streck Jr.), and
* tourism, park and reserve feasibility (Peter Thomas)

The present report describes the results of the surveys of reefs and corals with
emphasis on ecology and related oceanographic and geological characteristics. It is meant
to serve as a technical supplement to the report prepared by Thomas et al (1989), a
summary of all survey results.

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8
Il. MATERIALS AND METHODS

Limited field time required that maps, aerial photographs, underwater photographs,
and other sources of valuable information be consulted before the design and execution
of field observations. For one, the time available to cover such a large number of reef
areas was too short to warrant quantitative sampling surveys. Field work concentrated
on collecting qualitative information on several subjects for a broad number of sites.
During the 17 days of the expedition (7-24 September 1988), four days were spent in
transit between atolls leaving 13 days field time on station at the study sites, or an
average of about two days per atoll. Three days were spent on Bok-ak allowing 20
marine sites there to be surveyed. Elsewhere 12-13 sites were surveyed at the remaining
atolls and table reef. Only one day was spent at Jemg due to the small size of the reef
and lack of safe overnight anchorage. Field time at Rondik was cut short due to a
medical emergency. Thus the western half of Rondik could not be investigated. A total
of 95 marine sites were surveyed at the seven areas during the September 1988
expedition. Additional observations were also made on land, along sandy beaches
(especially for evidence of turtle nesting) and during small boat travel.

Most observations were made underwater using snorkeling equipment. SCUBA
diving was not possible. Notes and reef profiles were recorded in situ on waterproof
paper attached to clipboards, (See Appendix A), Underwater photographs of each site
were obtained using Nikonos cameras. Most coral species and all coral genera were
identified in situ by visual observation. A few specimens were collected to clarify or
confirm species identification. Major reference books on the taxonomy of reef corals
were brought on the expedition and include Veron (1986), Veron and Wallace (1984),
Veron and Pichon (1976, 1979, 1982), Veron et al (1977), Randall (1984), and Wells
(1954). At the end of each day’s field work, these reference guides were consulted to
finalize species assignments and to compile lists of corals for each station. Master coral
lists for the expedition and for each atoll were compiled (Tables 2 and 3).

Corals

Relative abundance of each coral species was visually estimated in the field and
assigned to one of the five following abundance categories:

D = dominant
A = abundant
C = common
O = occasional
R= tare

Definitions of each of these categories are provided in Appendix B. Previous
coral records from the region include 35 species reported in Wells (1954) based upon
collections and observations at Bok-ak and Rofidik (Table 4). There are no published
records of corals from the five other reefs visited in 1988. Thus, most compiled species

9

constitute new atoll records. Other important coral surveys in the Marshalls were
reviewed and include Wells (1951), Hiatt (1951), Titgen et al (1988), Devaney and Lang
(1987), Maragos and Lamberts (1989), Lamberts and Maragos (1989), Scanland (1977),
and Maragos, in preparation.

Reef Geomorphology

Previous geological studies of the Marshalls were consulted, including Wells
(1954), Fosberg (1988), MacNeil (1969), Fosberg et al (1956), Tracey et al (1948),
Nugent (1946), MacNeil (1954), Ladd et all (1953), and Emory (1948). A few of these
included descriptions of the atolls visited in September 1988. Observations on reef
features concentrated on confirming earlier evaluations, identifying trends or changes, and
describing features not previously reported (particularly underwater features).

Map Sources

The U.S. Army Mapping Service (AMS) compiled topographic maps at a scale of
1:25,000 for all of the seven visited areas, except WOtto whose maps were compiled at
a scale of 1:50,000. The AMS maps were based upon limited ground truthing and aerial
photo-interpretation of low altitude black and white imagery flown by the U.S. Army in
1944. Later the Defense Mapping Agency reviewed, updated, and corrected many of the
AMS maps and published navigation charts of all atolls at a smaller scale. A listing of
all maps of the seven areas within the DMA and AMS catalogues is found in Appendix
C.

Aerial Photographs

Copies of 1944 black and white Army aerial photographs were available for
inspection at the Bernice P. Bishop Museum Map Collection, Honolulu. In addition, the
U.S. Department of Energy sponsored complete coverage of 15 northern Marshall atolls
and collection of color aerial photographs at a scale of 1:30,000. A few additional
photographs were flown at a scale of 1:8,000 for the northern Marshall Atolls in 1978 (E
G & G, 1978). Unfortunately, Bok-ak was not surveyed. The 1978 photographs include
outstanding detail of all islands and most reef areas to depths of 15m or more. The 1978
photographs allowed photo interpretation and comparison to the earlier 1944 photographs
and maps to determine the extent of geomorphological changes to reefs and islands for
five of the seven visited areas (all except Bok-ak and Adkup). Appendix D provides a
listing of the 1944 and 1978 aerial photographs reported for the seven visited reef areas.

Marine Protected Area Evaluative Criteria

A number of criteria were used during evaluation of the marine sites surveyed
during the 1988 expedition (Table 5). These criteria were not assigned ranks or numerical
weights so that each site could be "quantitatively" evaluated. Such approaches are highly
subjective, and given the lack of quantitative data collected during field surveys,

10

quantitative comparisons are not justified. However, the gross number of positive criteria
identified for each site gave a good approximation of the value it serves a candidate
protected area. Most importantly, the criteria provide a useful checklist from which to
identify truly significant or substantial resource values and attributes.

Ship Itinerary

Figure 1 consists of a map of the northern Marshalls which shows the atolls
visited during the 1988 field expedition. The RMI government kindly made available
their fisheries patrol vessel Ionmeto I to provide transportation and lodging during the
expedition. With a top speed of 22 knots and modern navigation equipment, use of the
ship reduced travel time and increased survey time at each of the target study areas. The
maximum distance between Majuro (Majro) (port of departure) and the most outlying
atoll (Bok-ak) was nearly 500 miles. The 17 day expedition covered approximately 2,000
miles, including two unscheduled (medical and supply) stops at Kuwajleen (Kwajalein)
Atoll.

Digitizing of Maps

Original maps were prepared by CORIAL for presentation in this report. The
maps were digitized using Intergraph ® MGE and MapInfo ® software. Maps of all
atolls are being digitized as part of a geographic information system now being developed
for the Marshall Islands termed the Marshall Atoll Resource Information System
(MARIS).

11

Table 2. Check list of corals observed in the Northern Marshall Islands,
September 1988.

P = Pikaar Atoll, B = Bok-ak Atoll, T = Toke Atoll, J = Jemg Island, W = Wotto Atoll,
R = Rondik Atoll, and A = Adkup Atoll. Letters in parenthesis are additional records
reported in Wells (1954) at the same atolls.

Stony Corals (Scleractinia, calcified octocorals, calcified hydroids)
FAMILY ACROPORIDAE

petopera a abrotanoides (Lamarck) - P, B
aculeus (Dana) - P, B
acuminata Verrill - P, B, T, W, (R)
austera (Dana) - B, W, A
cerealis (Dana) - P, B
cytherea (Dana) - T, J, W,R, A
danai (Edwards and Haime) - B, (R)
digitifera (Dana) - P, B, T, J, W
diversa (Brook) - P
echinata (Dana) - (R)
formosa (Dana) - P, B, T, W, R, A
florida (Dana) - W, R, A
gemmifera (Brook) - P, B, W, A
grandis (Brook) - W
granulosa (Bernard) - B, W
glauca (Brook) - B, T, W
horrida (Dana) - W
humilis (Dana) - P, B, T, W, R, A
hyacinthus (Dana) - P, T, W
irregularis (Brook) - P, B, T, W
loripes - (R)
lovelli Veron and Wallace - P, B, W, A
microphthalma Verrill - B
millepora (Ehrenberg) - W
nasuta (Dana) - P, B, T, W, R, A
robusta (Dana) - A
nobilis (Dana) - B, W
polystoma (Brook) - P, B, T
selago (Studer) - P, B, T, W
striata - (R)
surculosa (Dana) - P, B, T, W, R, A
syringodes (Brook) - W
squarrosa (Ehrenberg) - P
tenuis (Dana) - B
vaughani Wells - P, B, T, W
yongei Veron and Wallace - P, B, W
spp (6)-P,R,A
Acropora (Isopora) palifera (Lamarck) - P, B,J, R, A
A. (1) brueggemanni (Brook) - P
A. (1) cuneata (Dana) - W, R
Anacropora forbesi Ridley - B
Astreopora explanata Veron - B, T, R, A
A. gracilis Bernard - P, B, T, J, W, A
IG listeri Bernard - B, a R

,W

Addai lela lest ER das

12

myriophthalma (Lamarck) - P, B, T, J, W, R, A
Spor) ATER A
fonti ora aequituberculata Bernard - P, B, J, W, R, A
caliculata (Dana) - B
foliosa (Pallas) - P, B, T, J
foveolata (Dana) - P, B, T, J, W,R
hoffmeisteri Wells - P, B, T, W,R
informis (Bernard) - T, W, R
marshallensis Wells - P, B
monasteriata (Forskal) - P
tuberculosa (Lamarck) - P, B, T, J, R, A
venosa (Ehrenberg) - B, T, W
verrucosa (Lamarck) - P, B, T, W,R, A
Spp\G) = Baik A

i

EN

ISISISISISISISISISISIS|

FAMILY ASTROCOENIIDAE

Stylocoeniella armata (Ehrenberg) - P, B, T

FAMILY POCILLOPORIDAE

| eepet a damicornis (Linnaeus) - P, B, W, R, A

brevicornis Lamarck - B

eydouxi Edwards and Haime - P, B, R

meandrina Dana - P, B, T, J, W, R, A

verrucosa (Ellis and Solander) - P, B, T, J, W, R, A
eriatopora . hystrix | Dana.- P; B, T; W, Rk; A

angulata Klunzinger - P, B, T; W,,R, A

tylophora pistillata (Esper) - P, B, 7 W, R,A

(ld

Abate WY

FAMILY PORITIDAE

Goniopora lobata Edward & Haime - B, A
columna Dana - T, W
Porites australiensis Vaughan - P, B, T, J, R, A

cylindrica Dana - P, B, T, W, R,A
lichen Dana - P, B, T, J, W, R, A
lobata Dana - P, B. T, J, W,R, A
lutea Edwards & Haime - P, B, T
murrayensis Vaughan - P, B, W
solida (Forskal) - P

superfusa Gardiner - B, R
SEG Wells - T, W, A

p (2)-R

Porites (Gunmen ens rus (Forskal) - T, W

Ie

oye ee

FAMILY SIDERASTREIDAE

Coscinaraea columna (Dana) - P, T, W,R, A
Psammocora haimeana Edwards & Haime - T
Pe nierstraszi Wan der Horst - B

PR. profundacella Gardiner - P, B, T, A

FAMILY AGARICIIDAE

Pavona clavus (Dana) - P, B, T

RS minuta Wells - P, B, J, W, R, A
iP varians Verrill - P, B, T, W, R, A
Ps venosa Ehrenberg - P

Pi maldivensis (Gardiner) - B, T

Leptoseris eris mycetoseroides Wells - P, B, T, A

FAMILY FUNGITDAE

pol

ungia fungites (Linnaeus) - P, B, W, A
(Danafungia) valida Verrill - P, B, T, W, A
(D) horrida Dana - A
(Pleuractis) paumotensis Stutchhbury - T, W, R, A
(P) scutaria Lamarck - P, B, T, R, A
(Verrillofungia) concinna Verrill - P, W,R
(V) repanda Dana - B, W, R, A
Cycloseris sp - W
Halomitra pileus (Linnaeus) - W
Herpolitha a limax (Houttyun) - P, B, T, W, A

Polyphyllia talpina Lamarck - W
Sandalolitha robusta (Quelch) - T, W

=! eel ates kas| fee

FAMILY MUSSIDAE

Acanthastrea echinata (Dana) - P

debacle hemprichii (Ehrenberg) - P, B, T

hataii Yabe, Sugiyama and Eguchi -
corymbosa (Forskal) - B, T,R

ymphvllia a radians Edwards & Haime - P, B, W,R, A
recta (Dana) - P, B, J, (R)

Zis\s

|y

FAMILY MERULINIDAE

Hydnophora microconos (Lamarck) - P, B, J, A
Scapophyllia ‘cylindrica ~ Edwards & Haime - P, B, T, W, R, A

FAMILY FAVIIDAE

Favia spp (2)-P, T, J, W, R,A
F. matthaii Renee - - Bay

pallida (Dana) - P, B, T, W,R
rotundata ee Pichon, & B
speciosa (Dana) - P, B, T, W, R,
stelligera (Dana) - P, B, T, W,A
vites flexuosa (Dana) - P, B, T, W,
halicora (Ehrenberg) - P, B, T,
B

oe

ay
2
re Pe

spp (2)-P, B,J, W,R
niastrea edwardsi Chevalier - P, B,
pectinata (Ehrenberg) - P, B,
retiformis (Lamarck) - P, B

Q|™|™
2)

mas}

13

14

Leptoria phrygia (Ellis & Solander) - P, B, W

Plesiastrea versipora (Lamarck) - R

Oulophyllia crispa (Lamarck) - B, T, W, R

Platygyra daedalea (Ellis & Solander) - P, B, T, J, W, R, A

Vea pini Chevalier - B, W

Re sinensis (Edwards & Haime) - B

P. Petals ee -B

P. pad)

Lep eres ee (Dana) - P, B, T, J, W, R, A
J vansverss (Klunzinger) PRA

L. pac Ee

eyenenes ees (Forskal) -P,R

Ip

microphthalma (Lamarck) - P, B, T, W, R, A
ee a lamellosa Nee - P, B, T, R,
pad Re R, A
meee ne (Dana) - P, B, T, W, R, A
valenciennesii (Edwards & Haime) - (R)

’

ot
A

Beas

FAMILY PECTINUIDAE

Pectinia lactuca (Pallas) - P

FAMILY DENDROPHYLLIDAE

Turbinaria frondens (Dana) -
Ms stellulata Lamarck - P, B, T, W, R, A
T. sp (1) -

FAMILY CARYOPHYLLIDAE

Euphyllia glabrescens Chamisso & Eysenhardt - A, (R)

FAMILY TUBIPORIDAE

Tubipora musica (Linnaeus) - B, W, R, A

FAMILY HELIOPORIDAE

Heliopora coerulea (Pallas) - P, B, T, J, W, R, A

FAMILY STYLASTERIDAE

Stylaster sp (1) - B,
Distichopora a violacea (balla P

FAMILY MILLEPORIDAE

Millepora platyphylla Hemprich & Ehrenberg - B, T, J, W, R, A
M. exaesa (Forskal) - B, T, W, R, A
M. dichotoma (Forskal) - P, B, R, A

SOFT CORALS

Sinularia sp (1) - P, B, T, J, W, R, A
Sarcophytum sp (1) -P, B, T, W, A
Xenia sp (1)-P, W

colonial clownfish anemones - A

Palythoa sp (1)-R
unidentified alcyonacean - A

TOTALS _ genera and (subgenera): 50 + 5 = 55
species: 164 (1988 surveys) + 4 (from Wells, 1954) = 168

15

16

Table 3. Relative diversity and distribution of major stony coral genera (and
subgenera) and species observed in shallow water at seven northern Marshall atolls in

Sep 1988.

NUMBER OF SPECIES AT EACH ATOLL
NAME OF vy
GENUS (OR) BOK-AK PIKAAR TOKE JEM9 WOTTO RONDIK ADKUP
—____ SUBGENUS ATOLL ATOLL ATOLL ISLAND ATOLL -_ATOLL ATOLL IJOTALS
Acropora 22 21 17 10 26 11 12 40
(Isopora) 1 2 1 1 2 2 ab 3
Anacropora 1 : 1
Astreopora 4 2 5 2 2 4 4 5
Montipora 8 8 8 4 6 7 6 al}
Stylocoeniella 1 1 1 1
Pocillopora 5 4 2 2 3 4 3 5
Seriatopora 2 2 2 2 2 2 2
Stylophora 1 1 1 1 1 1 1
Goniopora 1 1 al 1 2
Porites 7 a 6 3 7 7 1) 11
(Synaraea) al al 1
Coscinaraea 1 1 al 1 1 1
Psammocora 1 2 1 3
Pavona 3 4 3 1 2 2 2 5
Leptoseris 1 1 1 ? 1 1
Fungia at al 1 1 1 1
(Danafungia) 1 1 1 1 2 2
(Pleuractis) 1 al 2 1 2 2 2
(Verrillofungia) 1 1 2 2 1 2
Cycloseris 1 1
Halomitra 1 1
Herpolitha 1 1 al 1 at 1
Polyphyllia 1 1
Sandalolitha 1 1 1
Acanthastrea aye 1
Lobophyllia 2 2 2 1 3
Symphyllia 2 2 ? 5 1 1 1 2
Hydnophora al 1 ? a 1 al
Scapophyllia 1 1 1 1 1 at al
Favia 4 5 5 3 4 4 5 7
Favites 2 3 2 1 3 3 1 4
Goniastrea 2 3 <) ? 2 2 a 3
Leptoria 1 1 ? 1 1
Plesiastrea 1 1
Oulophyllia 1 1 1 1 1
Platygyra 3 3 al a 3 1 2 4
Leptastrea 1 3 2 al 1 me 2 3
Cyphastrea 1 1 1 1 2 i 2
Echinopora at Z at 2 734 2
Montastrea 1 at 1 1 1 1 1
Heliopora 1 1 al al 1 1 at 1
Millepora 3 2 2 al 2 3 3 3
Pectinia al a
Tubipora 1 1 1 1 1
Turbinaria al 2 1 1 1 2 pitee 3
Stylaster 1 ? ? 1 1
Distichopora 1 ? ? 1
h

TOTALS: GENERA 38 35 35 16 36 29 35

&

SPECIES PER ATOLL 93 93 93 33 88 74 75 158

17

TABLE 4, Previous coral records from the atolls studied during the September
1988 expedition to the Northern Marshall Islands. Compiled from Wells (1954).
R = Rondik, B = Bok-ak

NAMES OF SAME SPECIES
(NOW _ JUNIOR SYNONYMS)

PREFERRED NAME LISTED IN WELLS (1954) LOCATION
Stylophora pistillata Stylophora mordax R, B

w

Seriatopora hystrix

Pocillopora damicornis

P. verrucosa Pocillopora elegans
P. eydouxi

Acropora acuminata

cytherea Acropora cor sa
(I.) cuneata

nasuta A. cymbicyathus
echinata
humilis

(I.) palifera
danai A. rotumana
loripes A

striata

Astreopora myriophthalma

Fungia (P) scutaria

Porites cylindrica Porites andrewsi
P. lichen

P. lobata

Favia pallida

F. speciosa

a4
12)

°

ll ell al ll ll

°

w Ww

Montastrea valenciennesii Favites valenciennesii

Favites flexuosa Favites vireus

Goniastrea retiformis

Platygyra daedalea Platygyra yustica

Leptoria phrygia Leptcria gracilis

Hydnophora microconus

Echinopora lamellosa

Lobophyllia hemprichii Lobophyllia costata

Symphyllia recta Symphyliia nobilis , B

Euphyllia glabrescens
Tubipora musica
Heliopora coerulea

Millepora platyphylla

PADADAAWOWWWDWDWDDAWDDADDDDDADADDDADDAWDDDD

TOTALS 21 GENERA AND 35 SPECIES, 30 SPECIES OF WHICH WERE REPORTED FROM
RONDIK AND 11 SPECIES OF WHICH WERE REPORTED FROM BOK-AK

18

Table 5. Criteria for evaluating candidate reef areas as
marine protected areas and parks in the RMI.

high diversity of stony corals
high abundance of stony corals
high bathymetric relief for reef habitat
high abundance of reef fish
high diversity of reef fish
high abundance of giant clams
high diversity of giant clams
. presence of Tridacna gigas (the rarest & largest giant clam)
high abundance of large sand dwelling mollusks
10. high abundance of top shell and other reef dwelling mollusks
11. black coral and other precious corals
12. aesthetic stony corals (e.g. Stylasteridae)
13. aesthetic soft corals (e.g. Alcyonaria)
14. high abundance of sharks, skates, rays
15. absence of crown-of-thorns starfish infestations
16. absence of pollution or human damage
17. swimming or feeding sea turtles
18. resting sea turtles
19. nesting habitat for sea turtles
20. large populations of coconut crabs
21. coral and algal encrusted ship & plane wrecks
22. flourishing lagoon reef pinnacles
23. well developed patch reef system
24. overhanging ribbon reef formations
25. lagoon or ocean reef fingers and extensions
26. deep lagoon reef holes or sublagoons
27. unusual reef geomorphological features
a. perched lagoons
b. blue coral moats
c. coral-algae dams
d. restricted meandering passes
e. ocean reef pinnacles
28. wide reef flat with micro atoll zone
29. wide reef flat with coral moats
30. wide reef flat with room and pillar formations
31. wide reef flats with productive algal turf zones
32. seagrass beds or meadows
33. mangrove associations
34. tidal lagunas and inlets
35. complex emergent reef rock formations
36. marine mammal aggregation sites
37. sea snakes and crocodiles
38. back reef coral heads & blue coral zones
39. unique marine species or new records for the region (RMI)
40. safe ocean reef slope snorkeling sites
41. safe atoll reef pass snorkeling sites
42. accessible spur-and-groove formations
43. narrow reef isthmuses and indentations
44. sites’ of historic or cultural ‘significance

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Ill. RESULTS

General descriptions of the reef and island systems of the seven areas are found
in Fosberg (1988) and Fosberg et al (1956). Maps and additional geological information
are reported in MacNeil (1969). The six atolls (Bok-ak, Pikaar, Wotto, Toke, Rondik, and
Adkup) are generally small compared to the average size of atolls in the rest of the
Marshalls, in terms of island land area and lagoon area (Table 1). The island of Jemo iS
also smaller than the average size of islands on the other four table reefs in the Marshalls
(Mejit, Kili, Lib, Jabat). All areas visited are not permanently inhabited except WoOtto.
Jemg, Toke, and Adkup are occupied for brief periods during seasonal harvesting of fish,
turtles and their eggs, coconut crabs, or other resources. The other areas (Rofdik, Pikaar,
and Bok-ak) appear to be visited less frequently based upon our 1988 field observations.
A combination of factors discourages permanent occupation of the uninhabited areas,
including limited fresh water supplies and rainfall, poor soil conditions for cultivation,
remoteness from nearby population centers, difficult or hazardous boat access to main
islands, and perhaps greater vulnerability of the small islands to exposure from storm
waves and surges. General physiographic data on the seven areas are summarized in
Table 1. Reef profiles of most stations are found in Figures A-1 to 14 in Appendix A,
and maps of many reefs and islands constitute Figures 2 through 37 in the text.

Climate and Oceanography

The ocean in the region of the northern Marshalls is between 4,500 and 5,400m
deep (Fosberg et al, 1956). The northern Marshalls are semi arid and experience less than
average annual rainfall compared to atolls and islands more to the south. The two
northernmost atolls, Bok-ak and Pikaar are the driest Marshall atolls, (excluding Enen Kio
(Wake) which is under U.S. jurisdiction, drier still, and further to the north). Of the six
atolls and one island surveyed in September 1988, Adkup, which is situated in the central
Marshalls, is the wettest of the group. The dryness limits groundwater and vegetation
development, and Fosberg et al (1956) divides the Marshalls into several vegetative zones
(see Figure 1). The northern atolls are exposed to stronger tradewinds and associated
wave action. Although tropical storms and typhoons tend to spawn in lower latitudes
further to the west, sometimes the storms gain intensity, move into the Marshalls, usually
from the south, and cause extensive damage to shorelines, islands and some reefs. Even
infrequent storms can modify the distribution of islands on atoll reefs with long lasting
effects, as reported for Arno Atoll (Wells, 1951). The typhoon frequency in the Northern
Marshalls is of the order of 50 to 100 yrs, and the visible results of typhoons, especially
on atoll islands are the record of at least a thousand years or more (MacNeil, 1969).

The major tropical current system in the northern Marshalls is a large westward
flowing current between latitudes 10 and 20 degrees, north termed the North Pacific
Equatorial Current (NPEC). This current mostly affects deep ocean circulation patterns
off shore. Nearshore effects of the NPEC are masked by much stronger but localized
currents caused by the tides, winds, and wave action.

21
JEMO REEF (Figures 2-4, and A-8)

Jemo is the only reef of the seven visited that is classified as a table reef and is
one of only 5 table reefs (compared to 29 atolls) located in the Marshall Islands. A table
reef consists of an isolated flat topped coral reef which reaches the sea surface but which
lacks a lagoon (MacNeil, 1969). These reefs tend to be small, sometimes linear, and are
exposed to wave action due to the lack of sheltered lagoon reefs. The table reef
supporting Jemg Island is 8 km long, slightly arcuate, and is situated along a SW to NE
axis (Figure 2). Jemg Island is egg shaped and about one-third mile long.

Fig 2. Jemg Island and table reef showing

sites of marine surveys, September 1988

Stars indicate reef sites of special 40.7
s

interest. Scale: 1" = .5 mi. age

sate -“ Submerged reef... aoe

@stidllow reef flajy’

Exposure of the reefs and island to heavy waves and storms from virtually any
direction has controlled and shaped reef development at Jemg. Underwater observations,
published charts, and color aerial photographs all document that the flanks of the table
reef drop off near precipitously to great depths within a kilometer of the reef crest.
Shallow reef flats emerge at low tide only at the southwest end upon which rests the
single island of Jemo (Figures 2-4). Elsewhere, an extensive system of sand covered
surge channels (see Figures 3, 4) traverse the reef crest in a north-south axis and at depths
of 2-4m. At the NE end, which receives the most exposure from trade-wind waves, the
reef resembles a rounded knob in which the surge channels give way to well developed
spur-and-groove formations. Elsewhere the outer margin of the reef crest consists of flat
pavement-like and heavily scoured ramps descending at a moderate angle from a depth
of 2-3m to a drop off at a depth of about 6-8m. Below the drop off, the reefs are steep
vertical walls sometimes overhanging (Figure A-8, sites 4B, 4L, 4E, 4J, and 4D).

Perhaps due to the long NW facing axis of the reef oriented away from the
prevailing NE tradewinds, typical spur and groove formations are lacking along the reef
margin except at the NE end. These features, along with the prominent series of sand
bottomed surge channels across the reef crest, are clearly displayed in the 1978 color
aerial photographs of the island and reef at Jemg taken at scales of 1:30,000 and 1:8,000.

22

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24

There are no major accumulations of loose boulders strewn on the reef crest.
Small boulder beaches occur along the south and southeast facing shorelines of Jemo
Island. The reef margins off the elongate SE facing reef axis appear to be depositional
in character, with sand, gravel and other sedimentary materials apparently carried through
the surge channels over the crest of the reef from the other (NW) side. Thick
accumulations of sediments were observed at the base of canyons between steeply sloping
massive rounded reef buttresses along the SE reef margin. In contrast, the NW reef
margin lacked any loose sediment, and coral formations consisted of robust, low profile
colonies. The bare reef pavement ramps appeared heavily scoured. Ailuk Atoll affords
Jemo reef some protection from northeast swells, Likiep, provides protection from the
southwest, and Wotje and Adkup provide protection from the southeast, leaving the
northwest face of Jemg reef the most exposed to heavy seas. Movement of reef materials
appears to be from a northwest to southeast direction, with the northwest face of the reef
potentially more exposed to damage from wave energy.

Another unusual feature of Jemg reef is the truncated sheer face of the southwest
end of the reef adjacent to the island. This wall drops vertically from depths of 6m to
50m or more with some major overhangs (Figure A-8). The margin of the reef is nearly
perfectly straight along a northwest to southeast axis (see Figs. 3 & 4) as if a giant knife
had sliced away the reef mass further to the southwest. I can think of no explanation for
this unusual geomorphic feature, except that a previously existing extension of this reef
to the SE may have fractured and slumped down towards greater depths, leaving a vertical
face on the remaining reef.

Since none of the other table reefs in the Marshalls have been described in much
detail, it is impossible to compare Jemg’s features to them. It is possible that Jemg’s
table reef might be the peripheral remnant of a once larger atoll, the rest of which has
been displaced by faulting below the depths required for active upward reef growth.
Clearly Jemg’s reefs are unusual with features not having been previously reported in the
scientific literature.

Despite the abundance of hard reef surfaces and transparent well illuminated
waters, coral abundance and diversity were low. Coverage on the pavement terraces was
low and nearly absent from the walls of the sand channels. Highest coral development
occurred in a NW facing reef indentation near the NE end of Jemg reef. This indentation
apparently affords the reef slopes some protection from heavy wave action, allowing
luxuriant, three-dimensional coral development. Typical vertical profiles of all reef sites
sketched in the field are presented in Appendix A (Figure A-8 covers Jemo).

The absence of a more extensive and shallow reef flat and the presence of the
surge channels on the reef crest is curious. Perhaps the reef is too narrow or wave action
too severe to facilitate shallower reef flat development. Wave action was observed to be
approaching Jemg from all directions, although heaviest from the north during our visit.
The bulbous NE terminus of the reef was the zone of maximum wave action.

25

Landing on Jemg Island is extremely hazardous as noted in Fosberg et al (1956),
Fosberg (1988), and as experienced first-hand in 1988. The transition from deep to
shallow water is abrupt off the SW end (the only safe "access" point to the island) and
the spur and groove formations and unpredictable wave action renders boat navigation
dangerous. During our landing, the shaft of the outboard motor struck the reef and broke
off, causing our skiff to swamp. The lack of safe anchorage and access must have
contributed historically to the lack of permanent habitation on Jemg. During heavy surf
it would be impossible to land at the island from any direction.

Rare Marine Species at Jemo

Evidence of sea turtle nesting activity was high along Jemg Island’s sandy beaches
and the level of evidence (53 pairs of turtle tracks) was second only to Pikaar’s. Signs
of recent harvesting of green turtle was evident, and one nest with fresh eggs was
discovered. Although uninhabited, J emg lies close to inhabited Wotje, Likiep, and Ailuk
atolls. According to Fosberg (1988), Jemg was in pre-European times a turtle sanctuary,
and only infrequent visits were permitted; turtles and eggs were taken in limited numbers
under close supervision by priests (Jack Tobin, pers comm. to Ray Fosberg). Although
not rare species, numerous sharks also inhabit the reef waters off Jemg.

Jemg’s Corals

Jemg’s coral fauna is noticeably depauperate with only 33 species and 16 genera
reported after surveying 12 separate sites. These numbers compare to 74-93 species and
29-35 genera reported from atolls subject to the same sampling intensity (Table 2) during
the 1988 survey. The most common Jemg species were ramose stony corals (Acropora

(1) palifera, Pocillopora verrucosa, P. meandrina), robust firecorals (Millepora platyphylla),
encrusting colonies (Montipora spp) massive brain corals (Platygyra daedalea, Favia spp,

Hydnophora microconos) other reef corals (Symphyllia radians, Astreopora spp,
Turbinaria sp, Porites spp, the soft coral Sinularia, and the blue coral (Heliopora

coerulea). Maximum coral abundance and diversity occurred at depths between 7-10m
and especially where reef indentations afforded corals some protection from heavy wave
exposure. Free living forms such as the mushroom corals (Fungia and related genera)
were not reported. Coral coverage appeared lower along the southeast facing slopes
probably due to substrate instability of disturbance from moving sediment.

ATOLL GEOMORPHOLOGY AND OCEANOGRAPHY

Atolls are annular (perimeter) reefs enclosing lagoons which usually contain passes
through the reefs, islets on the reef, and lagoon reef formations (MacNeil, 1969). The six
remaining areas surveyed in 1988 are atolls with perimeter reefs affording protection and
surrounding semi-enclosed lagoons. At least five or more small to moderate sized islets
are situated on the shallow reef flats along the perimeter reefs of each atoll. All six atolls
include at least one natural deep passage through the perimeter reefs, allowing sub-tidal
exchange between ocean and lagoon waters. There are more islands and fewer passes on

26

the windward side than on the leeward side. The perimeter reefs of atolls in the
Marshalls are usually between 1,000 and 2,000 feet wide, with windward reefs usually
slightly higher in elevation. The six atolls can be divided into two major
geomorphological groups with gradients between one another along a north-south axis:

1) Small Northern Atolls. These have shallow lagoons with maximum depths
of 13mm or less, a very narrow single passage along the west side, and elevated (perched)
water levels in the lagoon during low tide. This category includes Bok-ak and Pikaar.
Toke Atoll is intermediate between the two groups. Wake (traditional Marshallese name
Enen Kio) is located further to the north of the Republic of the Marshalls, is under U.S.
military jurisdiction and is more closely allied to this group. The climate is dry and
prevailing trade winds are heavy. In addition, the semi-enclosed nature of the lagoons
of Ebon and Namorik (Namdik) Atolls and the two semi-enclosed sublagoons of Arno
Atoll, all in the southern Marshalls, show some functional resemblances to the first group.

2) Central Atolls. These have deeper, more open lagoons with maximum water
depths of 49m or more, larger, deeper or more numerous passages, and lagoon tidal
fluctuations more closely corresponding to those of the adjacent ocean areas. Included
in this category are Rondik, Wotto, and Adkup. These three atolls more closely resemble
most of the other atolls in the Marshalls.

Due to Wake’s proximity to Bok-ak and Pikaar, all three may have undergone a
similar geological evolution. Wake has no natural passage through its reef, and the
maximum depth of its lagoon is only 4m. Wake represents one extreme in the gradient
between the two groups of atolls in terms of small pass development, shallowness of
lagoon, and small lagoon area. At the other extreme would be the more typical atolls of
the Marshalls charactered by larger and more numerous passages and lagoons, well
developed perimeter reefs and islands, and passages generally concentrated along the
south and west rims (Wiens, 1963).

Toke Atoll, intermediate between the two extremes, most closely resembles nearby
Utrok Atoll, with comparable angular shape, size, moderate depth of the lagoon, and
small size and position of the single deep western passage.

The Perched Lagoons of Bok-ak and Pikaar:

The raised perimeter reefs and the single narrow western passage off both Bok-ak
and Pikaar atolls restrict tidal exchange between the lagoon and ocean (Fosberg et al,
1956). More water is pumped into the lagoon by wave action along the eastern
(windward) reefs than exits from the lagoon through the pass and over the reefs at low
tide along the western (leeward) side. This factor causes average lagoon water levels to
be higher compared to those on the ocean side. Since water levels in the lagoon never
get as low as the low tide levels outside the lagoon, perimeter reefs may have continued
to grow upward in response to the constant washing from higher lagoon water levels.

27

The raised nature of the peripheral reefs, especially along the leeward rim prevents tidal
exchange over the reefs except at moderate to high tide, further increasing the
accumulation of water pumped in the lagoon from the windward side wave action relative
to that which exits the lagoon. Coupled with the limited drainage of lagoon waters out
of the narrow pass of each atoll, the "low" tide water levels in the lagoon were observed
to be two - three feet higher than corresponding levels on the ocean side. Lagoon tidal
amplitude is very small and is nearly completely out of phase with ocean side tidal
fluctuations. During low tides on the ocean side, lagoon waters were observed to stream
out of the pass, dropping up to three feet and resembling white water "rapids" over a
distance of about 100m.

As a consequence, the leeward perimeter reefs of both Bok-ak and Pikaar atolls
serve as natural dams and spillways, ponding lagoon waters and dampening outside tidal
fluctuations. Only during the few hours of high tide do all perimeter and lagoon reef flats
completely submerge, allowing free exchange of lagoon and ocean waters over the reef.
At the time of highest tide (on the ocean tide) current flow out the channel reverses
direction, running into the lagoon for an hour or so. Perhaps in response to less water
level fluctuations in the lagoon, living corals and coralline algae grow to higher
elevations, displaying prominent overhanging reef wall formations.

In contrast, the central group of atolls (Adkup, Wotto, and Rofdik) display
localized oceanographic conditions more typical of the rest of the Marshalls. Wave action
along windward reefs pumps water over the perimeter reefs into the lagoon during
virtually all stages of the tide. Water also enters the lagoon during flooding tides through
all passes and over most shallow perimeter reefs. During ebb tide, water flow out of the
passes, and ebb flow over leeward reefs is likely to be strong (but not specifically
observed during the 1988 study). Lagoon and ocean tidal fluctuations appear more
closely synchronized and show similar amplitudes. Wave action inside the lagoons is
moderately high due to the more open configuration and larger size of the lagoons for the
central atolls compared to those of the small northern atolls.

BOK-AK ATOLL (Figures 5-9; A-1 through A-3)

Aelon-in Bok-ak (also called Taongi, Bokaak, or Pokak Atoll) is the Republic’s
most isolated atoll with the nearest reefs and islands located 150 NM to the southeast at
Pikaar Atoll and 300 NM to the north at Wake Atoll (Enen kio). Also an unnamed bank
at a depth of seven fathoms lies 100 NM south of Bok-ak (MacNeil, 1969). Bok-ak is
unusual from several respects, not the least of which is the elevated configuration of its
living lagoon reefs. The atoll is crescent shaped (Figure 5), curving to the west with reef
horns extending off the northern and southern tips of the atoll reef, and is about 11 miles
long from reef tip to reef tip. The 1988 team was able to spend three field days at Bok-
ak allowing 20 marine sites, including five leeward ocean reef sites to be surveyed
(Figure 5).

28

Fig 5. Bok-ak (Taongi) Atoll showing sites
of marine surveys September 1988. Stars
indicate reef sites of special interest.
Scale: 1" = 1.970 mi. :

: ne | Ane Jalto

Bokon-Ak
Bok-Dik

1R 7
Taongi Passag¢

29

Fig 6. Southern tip of Bok-ak (Taongi) Atoll
showing locations of some marine survey
sites. Stars indicate reef sites of special
interest. Scale: 1" = .6504 mi.

A near continuous string of islands (Figures 6, 7) extends along the SE windward
reefs. The NE windward reef and the entire western (leeward) reef lacks islands. Island
land area totals 1.45 square miles (3.8 km’) for Bok-ak, the second most of any of the
seven areas surveyed in 1988 after Wotto. There is no fresh water at Bok-ak and even
wells dug in the center of large islands are quite salty (Fosberg et al, 1956).

Bok-ak lies far enough north for tropical storms originating in the central
Marshalls to have gained full typhoon intensity, and the atoll’s islands and reefs display
extensive evidence of typhoon effects (MacNeil, 1969). Boulder ramparts, beaches, and
concentrations of strewn boulders are thought to have been formed during intense storms
and are most concentrated on the east and SE ocean facing sides of islands at Bok-ak
Atoll (MacNeil, 1969; Fosberg, 1988).

Many patch reefs throughout the lagoon are elongated into ribbon reefs with
vertical or overhanging walls. The lagoon averages seven fathoms (13m) in depth with
the greatest recorded depths being eight fathoms (15m), mostly in the western lagoon.
The tops of many lagoon patch and ribbon reefs are awash at low tide with overhangs of
profusely growing corals just below the surface. The tops of the shallowest reefs are
smooth pavements of living crustose coralline algae. Over a full tidal cycle, lagoon water

30

levels were observed to fluctuate less than one foot. At high tide all reefs and corals are
flooded to depths of a few inches or more. Water levels in the lagoon never dropped
below mean tide level. Sand deposits covered the floor of the lagoon while most elevated
surfaces were covered with live coral. Lagoon coral communities were very healthy with
only a few dead corals observed. Giant clam populations in the lagoon were huge,
including the species Tridacna maxima, T. squamosa, and Hippopus hippopus. Despite
an intensive search neither live or dead remains of the largest species Tridacna gigas were
reported. Neither were sea turtles observed at Bok-ak. Sharks were numerous, especially
black tips inside the lagoon and grey and white tip reef sharks outside the lagoon.

Fig 7. Bok-ak (Taongi)
Atoll in the vicinity of
the cluster of large
éastern islands.

Scale: 1"=.8953 mi.

Kiden-Kan

Ane Bokan

Bokon-Ak
Bok-Dik

Eastern (windward) perimeter reefs at Bok-ak are different in shape compared to
those of larger more open atolls to the south in the Marshalls. Observations at an
elevation of about 8m, from the deck of a recently wrecked Japanese longliner fishing
vessel on the windward reef (site 1-C), revealed that spur and groove formations are well
developed and typical. However, the coralline algal ridge was a wide irregular feature,
rather than a more typical elevated ridge measuring only a few meters in width (see also
Fosberg, 1988). The reef crest was generally flat but elevated 2 or more feet above mean

31

low water. The back lagoon edge of the reef abruptly drops as a pronounced step 1-2m
in depth. Elsewhere in the Marshalls back reef slopes towards the lagoon are generally
more gentle. Lagoonward water flow over the reef was also not as swift as reported for
many windward reef flats in the Marshalls. The higher observed lagoon water levels may
prevent more rapid "downhill" movement of waters from the ocean side.

Leeward perimeter reefs were
unusually narrow, averaging less than
100m in width (Figures 8, 9).
Except for a small coralline algal
ridge-like feature at the crest of the
Fig 8. Bok-ak (Taongi reef near its lagoon margin (see
Atoll in the vicinity of Fosberg, 1956; et al, 1988), the upper
the western passage. reef surface is smooth and covered
Scale: 1"=.7075 mi.@ © with living crustose coralline algae

1R and slopes down two to three feet
from the lagoon side to the ocean
side. This tiny ridge, up to 10-15 cm
in height, is also reported on
windward facing edges of patch reefs
in the lagoon and along the lagoon
shores of some islets. The living
reef flat serves as a coral-algal dam
and spillway, holding back higher
lagoon water levels except for excess water trickling downslope to the ocean margin.
Even at low tide (outside), water was seen constantly spilling over the dam and down the
spillway to the ocean, with flow presumably maintained by the constant wave action
pumping water into the lagoon from the windward side.

The ocean face of the leeward reefs resembled the steep slopes, reentrant/canyons,
high coral cover, and diversity typically reported for such environments elsewhere in the
Marshalls. Water currents were strong and turbulent off the leeward side of the southern
reef extension or horn (site 1-O). Loose sediment and sand were absent from the shallow
ocean reef slopes. Seven of the 20 sites surveyed at the atoll displayed exceptional or
unique coral reef features (Figs. 5, 6, 9, A-1, A-2, and A-3).

One unusual feature was an ocean patch reef (site 1-S) separated from the main
ocean reef slope by a deep chasm. Other exceptional sites included a windward reef flat
(site 1C), lagoon patch and ribbon reefs (sites 1K, IN, 11, 1G and 1H).

Corals of Bok-ak Atoll
Bok-ak was one of three atolls where the most species of corals were observed

during the expedition. Ninety-three species belonging to 38 genera and subgenera were
reported at Bok-ak based upon surveys at the 20 field sites, including five ocean sites.

32

In contrast, 93 species were reported at both Toke and Pikaar after surveys at only 13
sites which included no ocean sites at Toke and only two ocean sites at Pikaar. Thus,
despite the high number of coral species reported at Bok-ak, Toke and Pikaar would
appear to support high numbers of species, based upon equivalent sampling intensity.
The condition of the coral communities of Bok-ak was healthy and flourishing at all
observed lagoon and ocean reef sites. Thus a lower number of coral species does not
appear to be related to environmental stress.

Fig 9. Bok-ak (Taongi) Atoll in the vicinity
of the north western reef tip. Marine
survey sites shown with stars represent
reef sites of special interest.

Scale: 1" = .7149 mi.

Because of the elevated nature of the lagoon coral communities, they may be more
isolated from ocean reefs due to restricted tidal exchange. Furthermore, the remote
position of Bok-ak from its nearest reef neighbors may reduce the number of coral species
which can successfully migrate and establish at Bok-ak. Over prolonged periods this
might be reflected in fewer total species of coral that are established at Bok-ak.

Several reef genera which are common elsewhere in the Marshalls were absent
from Bok-ak: Porites (Synaraea), Coscinaraea and Distichopora. Some genera were
conspicuously more abundant at Bok-ak including Platygyra and to a lesser extent
Anacropora. These observations lend further support to the hypothesis of geographic
isolation of Bok-ak from nearby atolls.

However, coral communities at Bok-ak achieve an unprecedented level of
abundance and development. Lagoon habitats were complex three dimensional coral
dominated environments, with many overhangs, mounds, walls and elevated ledges. The

33

protected shallow lagoon environment appears to promote optimal coral growth due to
abundant light, transparent waters, lack of suspended sediment and only minor wave
action.

Along windward perimeter reefs, the stepped back reef margins included many
abundant corals: Acropora (J) palifera, other Acropora spp, Porites lobata, Cyphastrea
microphthalma, Goniastrea spp, Pavona minuta, Seriatopora aculeata, Heliopora coerulea,
Stylophora pistillata, encrusting Montipora spp, Pocillopora spp, Favia spp, Leptastrea
purpurea, Platygyra spp, Millepora spp, and Astreopora spp.

On the slopes of lagoon pinnacles, the following corals were common: Porites
cylindrica (fingercoral), Astreopora gracilis, Goniastrea pectinata, Favia pallida,

Stylophora pistillata, Porites spp, Fungia fungites, Lobophyllia hemprichii, Montipora spp,
Pocillopora spp, and Acropora spp, especially staghorn corals, and others.

On leeward ocean reef slopes and margins, the following corals achieved
prominence: Millepora spp, Acropora digitifera, A. palifera, Porites superfusa, Montipora
tuberculosa, Stylophora pistillata, Ecinopora lamellosa, Goniastrea retiformis, Favia
stelligera, Turbinaria stellulata, Symphyllia spp, Favia spp, other Acropora spp (tables),
Porites spp, and Cyphastrea microphthalma. Many other species were common, and the
leeward ocean reef slopes displayed the highest reef coral abundance and diversity
observed of any habitat at Bok-ak.

Rare Species at Bok-ak Atoll

The smaller giant clam species which were abundant in Bok-ak lagoon are
considered rare species. However, there was no evidence of the rarest and largest giant
clam species nor of sea turtles or coconut crabs. Bok-ak, along with Pikaar and Jemg
was regarded as a bird and turtle reserve by the Marshallese prior to the era of European
influence (Jack Tobin pers. comm. to Ray Fosberg, in Fosberg 1988), and in the early
1960’s Bok-ak was designated as a reserve by the then District Administrator of the
Marshalls.

PIKAAR ATOLL (Figures 10-15, A-4 to A-5)

Aelon-in Pikaar (also called Bikar Atoll) is the Republic’s second most isolated
atoll with the nearest reefs and islands being Utrok and Toke Atolls some 80 NM (146
km) to the south and Bok-ak Atoll some 150 NM (247 km) to the north. An unnamed
bank with a depth of seven fathoms lies about 50 NM (91 km) north of Pikaar Atoll.
Pikaar most closely resembled Bok-ak in geomorphology but has much less land area.
In fact, with only 0.19 square miles (0.49 km’) of land, Pikaar has the least amount of
land of any atoll in the Marshall Islands, and only the table reef at Jemo has less island
area. Storm generated boulder ramparts and concentrations of strewn boulders occur only
along the northwest shoreline of Jeliklik Island and along the lagoon face of northwestern

34

Fig 10. Pikaar (Bikar) Atoll
showing location of marine
survey sites. Stars indicate

reef sites of special interest.

Scale: 1" = 1.042 mi.

DS

ae

pe Almani

¢ Jeliklik

OB a4 Jobwero

Pikaar

35

perimeter reef flats (MacNeil 1969). Although no wells have been dug, the small size of
the largest islands and dryer climate argue against potable groundwater at Pikaar Atoll
(Figure 10).

Bikar Passage

lagoon
Jobwero

Fig 12. Pikaar (Bikar)
Atoll in the vicinity of the
southern tip and the
island of Pikaar (Bikar).
Stars indicate reef sites of
special interest.

Scale: 1" = 1 mi.

Fig. 11. Detail of the
single western
passage at Pikaar
(Bikar) Atoll.

Scale: 1"=.25 mi

The top of Pikaar’s
reef formations are living and
elevated some two to three
feet above mean low water.
Its one single pass (Fig. 11)
is narrow and forked to the
lagoon side along the western
rim of the atoll. Small boat
navigation through the pass at
low tide is extremely
hazardous, and many reef
sharks patrol its waters.
Pikaar Atoll’s largest island is
Pikaar Island, resting on the
widest section of _ the
perimeter reef at the southern
tip of the atoll (Figure 12).
Remaining islands are very
small or are only sand cays
(Figures 13-14). Pikaar’s
lagoon is deeper than Bok-
ak’s, varying in depth

36

between five and 13 fathoms (9-24m). The lagoon near the southern tip and western pass
region is shallower, averaging eight fathoms (15m), but most of the lagoon floor is
situated at depths between 10-11 fathoms (18-20m). As with the reefs of Bok-ak, the
tops of the shallowest reefs are smooth pavements of living crustose coralline algae.
Ribbon reefs fill the lagoon with the walls dominated by live coral and with pronounced
overhangs near the tops of the reefs. Sand deposits cover the floor of the lagoon.

Fig.13. Pikaar (Bikar) Atoll at the eastern
end showing locations of some of the
marine survey sites.

Scale: 1" = .8093 mi.

Tidal characteristics at Pikaar appear to be very similar to those of Bok-ak
although there was less time in the field (1-1/2 days) to observe them. At low tide, the
tops of lagoon reefs are awash but rest some two to three feet higher than the margin
along the ocean side of the reef at mean low water. Over a full tidal cycle lagoon water
levels were observed to fluctuate less than one foot. At high tide all living reefs and
corals are flooded to depths of one foot or more. Water levels in the lagoon never
dropped below mean tide level.

Huge populations of giant clams (especially Tridacna maxima, T. squamosa, and
Hippopus hippopus) were found throughout the lagoon, resembling those of Bok-ak.
Swimming green sea turtles were observed both inside and outside the lagoon, and
evidence of recent sea turtle nesting activity was evident along the sand beaches of most
islands, especially Pikaar.

Si]

Fig 14. Pikaar (Bikar) Atoll at the NW tip
showing locations of some of the marine
Survey sites. Scale: 1"= .5579 mi.

Saye e

eel
e 2F
numerous coral heads i
os
ee G
lagoon
ocean
e 2 o
2M
7) Oo

Se)

38

The windward, eastern facing perimeter reefs of Pikaar resembled those of Bok-ak
in terms of form and coral species composition. The back lagoon edge of the reef flat
drops down as a pronounced step one or more meters in depth. This feature shows up
well in the color aerial photographs, and the stepped or double reef feature is also marked
on available maps and charts. The fact that the stepped reefs were reported only from the
reefs of Bok-ak and Pikaar suggests that higher average lagoon water levels may have
something to do with the formation of the steps. Stepped reefs occur also along the
southwest and northwest lagoon faces at perimeter reefs at Pikaar atoll. Compared to
those of Bok-ak Atoll, leeward (western) perimeter reefs at Pikaar Atoll are generally
wider. Only the NW section to the north of the pass region shows narrow perimeter
reefs.

The perched lagoon water levels are maintained by wave action pumping water
into the lagoon at a rate faster than can drain out the deep western pass at low tide. The
water circulation dynamics in Pikaar’s lagoon appear very similar to those of Bok-ak
lagoon.

Several coral and reef habitats (sites 2A, 2B, 2C) at Pikaar displayed exceptional
or unique characteristics (Figs. 10, 11, A-4, and A-5). Site 2A is a deep reef flat moat
to the west of the main island (Pikaar). Site 2B is a back reef environment on the
windward side, and site 2L is an ocean reef slope along the leeward side of the atoll.

Comparison between 1944-based maps/aerial photographs and 1978 color aerial
photographs indicate that sandy beach habitat around Pikaar Island has increased
substantially during the 34 year period (Figure 15). Hence, suitable nesting habitat for
sea turtles may have increased during the interval.

Fosberg (1988) reports that Pikaar showed signs of extensive change from a
typhoon between 1945 and 1952 including possible loss of some of the small islets.
During our visit in 1988 there was extensive damage to the Pisonia forest on Pikaar and
near total destruction of it on Jobwero and Almani islands from high winds, possibly
during a recent tropical storm or typhoon.

Corals of Pikaar

Ninety-three species of corals belonging to 35 genera and subgenera were reported
from the surveys of Pikaar which encompassed 13 marine sites. Of interest was the
presence of the purple fan coral Distichopora on ocean reef environments at Pikaar. This
species was absent from Bok-ak although a related coral, Stylaster, was common.
Stylaster was absent from Pikaar, suggesting that these two different species are filling
the same niches in their respective atolls, occupying similar habitats. The presence of
Pectinia in Pikaar’s lagoon is only the second record of this coral from the Marshall
Islands. Other corals present at Pikaar but absent from nearby Bok-ak include
Coscinaraea and Acanthastrea. Curiously the common corals Oulophyllia and Goniopora
were absent at Pikaar although present at Bok-ak. Other "missing" corals from Pikaar

39

Ae eee PR RUC ye kas gates 10 fathom See
contour
a sandy
ca
=~ N mw reef line (MLLW) eal
eect feogsart sandy shoreline (1978)

—“—— island vegetation line
\ (1978)

9000 ce00e

island vegetation
line (1944)

~_—

FIGURE 15. Shoreline changes between 1944 and 1978 at selected locations in the
Northern Marshall Islands. A. sand cay at northeast corner of Toke Atoll.

B. Pikaar Island, southern Pikaar Atoll. Comparisons based upon U.S. Army 1944
black and white aerial photographs and E. G. & G. 1978 color aerial photographs.
Scale: 1:30,000.

cuprsinetoemt

40

which are normally common reef components include Psammocora, Porites (Synaraea),
Cycloseris, and Halomitra. It seems plausible that some of these and other widespread
genera would have been reported from surveys conducted at more sites and in deeper
water, especially along ocean facing reef slopes.

Common and abundant corals on reef flats and moat environments included the
fire corals Millepora spp, the blue coral Heliopora coerulea, the corals Favia stelligera,
Pocillopora spp, Pavona spp, Porites spp, Goniastrea retiformis, other Favia spp,
Montipora spp, Cyphastrea spp, Astreopora spp, Leptastrea spp, Acropora spp, Seriatopora
angulata, Stylophora pistillata, the soft corals Sinularia sp and Xenia sp, the free living
corals Herpolitha limax and Fungia spp, the brain corals Montastrea curta and Platygyra
sp, and the explanate corals Turbinaria spp and Echinopora sp.

Common and abundant corals on pinnacles and ribbon reefs included: the
fingercoral Porites cylindrica, the corals Stylophora pistillata, Favia stelligera, Cyphastrea

microphthalma, Acropora spp, Herpolitha limax, Millepora platyphylla, Scapophyllia
cylindrica, Favites halicora, other Favia spp, Fungia spp, and Seriatopora angulata.

Common and abundant corals along ocean facing reef slopes along the leeward
side of Pikaar include Pocillopora spp, Millepora spp, Acropora spp, Porites spp,

Goniastrea spp, Favia spp, Montipora spp, Platygyra sp, Lobophyllia spp, Symphyllia spp,
and Favites spp.

Rare Species at Pikaar

Pikaar is the most important sea turtle nesting area in the Marshall Islands. Over
264 sets of turtle nesting tracks were observed at the atoll around the perimeter of Pikaar
(176), Jobwero (74), and Almani (14) islands. One set of fresh tracks was probably those
of a hawksbill sea turtle while remaining tracks were of green sea turtles. One pair of
green sea turtles were observed to be mating in waters offshore from Pikaar Atoll (see
Thomas, 1989). Since pre-European times, the Marshallese have considered Pikaar to be
a turtle and bird sanctuary (Fosberg 1988).

TOKE ATOLL (Figures 16-21, A-6, and A-7)

At its closest point Aelon-in Toke (also called Taka Atoll) lies only 7.3 km
southwest of Utrdk (Utirik) Atoll. However, due to the position of Toke’s single deep
pass along the western atoll rim, it takes about 46 km by boat to travel from the largest
island of Utrdk Atoll to the largest island of Toke Atoll (Toke). Both atolls are roughly
triangular in shape. Although Toke has a larger lagoon area than Utrok (94 km’ vs. 57
km’), the land area of Toke is comparatively quite limited (0.57 km’ vs 2.4 km’). In fact,
Toke ranks only ahead of Pikaar with respect to land area for atolls in the Marshall
Islands. Toke’s land area consists of five islands of which only Toke and Allook are
large enough to support permanent vegetation. One centrally located well dug at Toke
Island yielded non-potable groundwater (chlorides 440-840 ppm). Two other peripherally

Watuwe-rok\ »

Jejakiki-kan milook

Fig 16. Toke (Taka) Atoll
showing locations of marine
Survey sites. Stars represent
reef sites of special interest.
Scale: 1" = 1.970 mi.

42

located wells yielded very salty non-potable water (Fosberg et al 1956). Although Toke’s
pass is deep and narrow, boat passage is not hazardous. Toke’s windward reefs are also
afforded some protection from the upwind position of Utrok Atoll. Storm generated
boulder beaches are not well developed along Toke Atoll’s island shorelines. They are
best developed along the eastern face of the southernmost island Watuwe-rok and the
western (lagoon) faces of Toke and Lojiron islands along the eastern perimeter (MacNeil,
1969). Fosberg (1988) also describes the effects of a typhoon which passed over Toke
inel9Ssile

Unlike the lagoons of Bok-ak and Pikaar, Toke’s lagoon is deeper (maximum
reported depth of 28 fathoms or 51m) and with many soundings between 18-22 fathoms
or 33-40m (Figures 16-18).

Jeig 17. Toke (Taka) Atoll,
NW corner in vicinity of a
recent shipwreck and one
marine survey station.
Dotted line represents

, submerged reef.
“. Scale: 1" = .8156 mi.

Toke’s lagoon has fewer pinnacles and patch reefs (less than 50 total) all of
circular shape and generally concentrated in the southern half of the lagoon and near the
deep western passage (Figures 16-18). Despite Utrok’s smaller size, its lagoon contains
over twice as many patch and pinnacle reefs. These factors help to explain why Toke is
not permanently inhabited. Land, water, and lagoon reef resources are larger and more
conveniently located on Utrok. Fishermen from inhabited Utrok Atoll occasionally visit
Toke to fish and to harvest shellfish and sea turtles. The land owners and managers of
Toke reside at Utrok, but the expedition was not able to visit Utrok because the limited
field time was cut short due to an unscheduled stop at Aelon-in Kuwajleen (Kwajalein
Atoll) for provisions.

43

Fig 18. NE tip of Toke (Taka) Atoll i
in the vicinity of Several September #3E
1988 marine survery stations. :

Dotted line represents submerged
reef. Stars represent reef e 3D
sites of special interest.

Scale: 1" = 1 mi

lagoon

The lagoon margins of Toke’s perimeter reefs are not elevated above mean low
water as is the case at Pikaar and Bok-ak atolls. Furthermore, lagoon tidal fluctuations
are more closely in phase and amplitude with those on the ocean side. At the most, water
levels in the lagoon at low tide were only a few inches higher than outside low tide
levels. Thus, Toke’s lagoon does not have the perched or elevated lagoon reefs and water
levels characterizing the other two atolls, and exchange of waters between the lagoon and
ocean is more pronounced. Besides the deep passage near Toke island with a depth of
12 fathoms (22m) and a width of over 100m (Figures 19-20), Toke Atoll also has several
other shallower passages through the western reef, three of which were visited during the
1988 surveys (sites 31, 3J, and 3L).

Four of the 13 marine sites surveyed at Toke displayed unique or exceptional reef
characteristics. All were situated along the lagoon margins of perimeter reefs, two near
the passes (sites 3K and 3L) and two in the northeast corner of the lagoon (sites 3G and
3E) where reef pinnacle and patch reef formations are slowly being buried under
accumulating sand deposits washing over the reef flats from windward directions (N &
E). The team was unable to visit any ocean reef slope sites at Toke due to safety and
time limitations. Observations from the ship indicate that live corals dominate the slopes
of ocean facing reefs and that sharks were numerous.

One of the largest sand cays visited during the expedition occurred at the northeast
corner (Figure 18) of Toke Atoll (site 3F). Comparison between Army maps based upon
1944 aerial photographs and 1978 color aerial photographs reveal the shape and position
of the sand cay has changed drastically. During the 34-year interval, the deposit
elongated and shifted 200m to the north. Our sea level observations in 1988 could not
determine whether additional changes had occurred since 1978. The instability of the
deposit and low elevation may explain the lack of vegetation on the sand cay.

44

Corals of Toke Atoll

Ninety-three species of
corals belonging to 35 genera

Fig. 19. SW side of Toke (Taka) and subgenera were reported

Atoll in the vicinity of 2 marine

survey sites and deep passage. collectively from the 13
Dotted line represents submerged marine sites at Toke Atoll.
reef. Stars represent reef sites of Of interest was the presence

special interest. .
Scale! Am 8456 mi: of Porites (Synaraea) and

Sandalolitha which were
absent from both Pikaar and

Bok-ak. The reported

lagoon absence of several common

ou reef genera from Toke may

Taka at be attributed to the lack of
Passage v

observations along ocean
facing reef slopes where
different and more diverse
coral assemblages are
expected. As a result, the
species diversity of corals at
Toke might be higher than
observed at Pikaar and Bok-
ak. The number of species
reported per site was also
relatively high at Toke, and
coral communities were well
developed and diverse.

In back reef environments
along windward (eastern) reefs,

the following corals were oy lagoon

abundant or common: Acropora Bi Fig 20. Passage off
spp, Cyphastrea microphthalma, western Toke (Taka)
Pavona varians, Montastrea Atoll. Dotted lines
curta, Tubipora musica, Favia Li submerged
“ae ieee reef.

spp, Platygyra daedalea, Fungia Seale: 1seadsornik

spp, Astreopora spp, Montipora
spp, Favites abdita, Pocillopora

verrucosa, Sinularia sp, Porites

: Taka
spp, Millepora spp, Echinopora Passage

lamellosa, Turbinaria stellulata,
Goniastrea spp, Heliopora

coerulea, Stylophora pistillata,
Psammocora profundacella, and Leptastrea purpurea.

45

Further offshore on shallow pinnacles and on the slopes of larger patch reefs the
following corals were common or abundant: Porites spp (both fingercoral and massive
forms), Pocillopora spp, Acropora spp, Montipora spp, Fungia spp, Goniopora lobata,
Astreopora spp, Pavona spp, Tubipora musica, Coscinaraea columna, Oulophyllia crispa,
Leptastrea purpurea, Seriatopora spp, Lobophyllia hemprichii, Millepora platyphylla,
Stylophora pistillata, Stylocoeniella armata, Goniastrea spp, Cyphastrea microphthalma,
Favia spp, Porites (Synaraea) rus, Montastrea curta, Psammocora profundacella,

Echinopora lamellosa, Herpolitha limax, Leptoseris mycetoseroides, Heliopora coerulea,
Scapophyllia cylindrica, Turbinaria stellulata and Favites russelli.

Rare Marine Species

Evidence of green sea turtle nesting activity was observed along the shorelines of
Toke Island (16 sets of tracks), Lojiron Island (4 sets of tracks), and Allook Island (4 sets
of tracks) (Figure 21). Of the seven areas visited Toke Atoll ranks fourth behind Pikaar,
Jemo, and Adkup with respect to the level of sea turtle nesting evidence. The only
sighting of a Hawksbill sea turtle during the expedition was off the NE sand cay at Toke
(site 3F). It was observed to be feeding and swimming at a depth of 2-3m off the
bottom.

lagoon / Toke Atoll was the
first in which live specimens
of the rare giant clam,

Lojiron Tridacna gigas were
observed, primarily in
Toke shallow lagoon environments

near islands or back reefs.
However, there were many
more dead shells of the
species observed on the reefs
(only 5 of 24 were alive).
Live individuals of the
smaller species were present

Fig 21. SE corner of Toke

(Taka) Atoll in the vicinity of
the largest islands. Dotted but in smaller numbers than

line represents submerged reported for Pikaar and Bok-
reef. ak. It was reported by

Allook Scale: 1" = 1.348 mi. islanders from Majro

(Majuro) and WoOtto that
overseas fishermen illegally
poach live individuals of T.
gigas to obtain the abductor muscles which fetch high prices in Asian markets. Evidence
obtained during our surveys suggest that uninhabited Toke Atoll may be an inviting target
for illegal poaching of the rare giant clam Tridacna gigas. Interviews with the residents
of Utrok might shed additional light on the extent of traditional harvesting and illegal
poaching of giant clams at Toke Atoll.

46

WOTTO ATOLL (Figures 22-25, A-9, and A-10)

Originally, uninhabited Ailinginae Atoll was to be visited during the expedition.
However, the failure to obtain approval to visit the atoll, and a subsequent invitation
extended by the leaders of Wotto Atoll, led the expedition to visit WOtto instead of
Ailinginae on 18-19 September 1988. Aelon-in WOtto (also referred to as Wotho Atoll)
is the only inhabited atoll surveyed during the 1988 expedition, and is only one of two
atolls visited within the Ralik (western or "sunset") chain of the Marshalls. W6tto is
relatively small in terms of lagoon area and is located within the dryer belt of the RMI.
However, land area is greater (4.2 km’), the most of any of the seven areas visited during
the 1988 expedition (Figures 22-23). Of the 22 inhabited atolls in the Marshalls though,
Wotto ranks only ahead of Utrok (Utirik) and Namdik (Namorik) in terms of land area.

Its population is about 100, the smallest of any inhabited atoll, and ranks ahead
of only Jabat and Lib which are inhabited table reefs. Of the 18 islands at Wotto, only
the largest (WOtto) is occupied (Figure 24). The atoll, including its islands, reefs, and
village setting, is very scenic, relatively undisturbed, and harbors considerable natural and
cultural diversity. Apparently, large land areas were never cleared and planted to
coconuts (Fosberg et al, 1956). The nearest atolls to WOtto are Kuwajleen (Kwajalein)
to the southeast; Ujae to the south; Bikini to the north; and Ailinginae, Ronlap
(Rongelap), and Rofdik (Rongerik) to the northeast. Due to the clustering of several
large atolls in the vicinity of WOtto, only the atoll’s southwest quadrant is considered
vulnerable or exposed to heavy open ocean seas.

Wotto Atoll is roughly triangular in shape with the widest reefs and the largest
islands situated at the apexes. WOtto Island, the atoll’s largest, is at the NE tip of the
atoll. The longest axis is the southwest facing side of the atoll, some 20 km between
Majur-wor Island at the NW tip and Kapen Island (Figure 25) at the south. Most of the
SW facing axis consists of several wide but shallow passages between smaller clusters
of shallow reefs. The main navigational passage occurs just north of Pik-en Island near
the northwest end of the axis. The three islets along the SW axis, Pik-en, Anbwil-en, and
Ane-aidik are very small. The rest of Wotto Atolls perimeter reefs along the N and E
facing axes are shallow and contain numerous islands and cays. The largest sand dune
reported by MacNeil (1969) in the northern Marshalls occurred along the lagoon side of
Ane-aidik Island, Wotto Atoll.

The three largest islands also display large boulder beaches and concentrations of
strewn boulders most likely tossed up on the reefs during storms. The boulder beaches
face seaward to the north on the two large northern islands (Majur-wor and Wotto) and
face seaward to the south off the southern islands of Kapen and Ane-jaito. A small
boulder beach also occurs on the north side of Kapen Island.

Ane-barbar
Ane-obnak
Majur-won

Anbwil-en

Ane-aidik

Fig 22. Wotto (Wotho) Atoll.
Numbers indicate marine survey
sites. Stars show reef sites

of special interest.

Scale: 1" = 2.058 mi.

48

Figure 23 . Defense Mapping Agency Chart of Wotto (Wotho) Atoll.
Scale 1:316,120. Soundings in fathoms.

WOTHO ATOLL

Medyeron I. @ , Lat. 10°10'36"N.—Long. 165°55/147E
SCALE 1:316,120
VAR 8°27°E (1980)
ANNUAL CHANGE 4°E

Lif Anchorese :
BeginI\ Aree &

Begin Chan **,

Nautical Miles

5
Meters

49

~ ee
_-—

O)5c BH
PON o>
”
5 ie
Figure 24. Wap of northeastern ie
WOtto (Wotho) Atoll sketched ne

from 1978 color aerial {
photographs. Scale 1:30,000. \
Numbers refer to Septembér 1988 i
marine survey sites. Underlined (
numbers represent reef sites of
special interest.

c y; Island vegetation am =
line
NT OG uv
y oy A Sand beach shore-
4 es } line

Reef line (MLW) = arm

10 fathom contour — — — ——

50

Figure 2:5, Map of Southern Wotto

(Wotho) Atoll sketched from 1978 color
aerial photographs. Scale 1:30,000.
Numbers refer to September 1988 marine
survey sites. Underlined numbers represent
reef sites of special interest.

XN
~—_ Island vegetations
line >

“se Cand beach shoreline

aT VTi, Reef line (MLW)

10 fathom contour

51

Patch reefs are not numerous in WoOtto’s lagoon and consist of three small clusters.
One cluster off Kapen island in the south lagoon includes five reefs. A second cluster
of seven reefs occurs in the south central lagoon east of Anbwil-en Island. The third and
largest cluster of 10 reefs in the north central lagoon occurs east of Pik-en Island. Our
limited time at WOtto did not permit field visits to patch reefs in the deeper lagoon.

There is very little easily available information about the depths and bathymetry
of Wotto’s lagoon. The only published soundings (Figure 22-23) show depths of at least
20 fathoms (37m) in the lagoon anchorage east of the main navigation channel which
shows a depth of 6 to 6-1/2 fathoms (11-12m). The channel south of Anbwil-en Island
shows a depth of 3-1/2 fathoms (6.4m). Some lagoon areas closest to Wotto Island may
be shallow, with published depths of 1-1/2 to 2-1/2 fathoms(3-4.6m). Inspection of 1978
color aerial photographs of WoOtto indicate that most of the lagoon appears deep and in
excess of 10 fathoms (18m) and probably close to 20 fathoms (37m) or more. Thirteen
field sites were visited at WOtto, all along perimeter reefs (Figure 22). Only site 5L was
on the ocean side of the reef.

Limited time did not permit more than cursory observations of water current and
circulation patterns at Wotto Atoll. During late afternoon fieldwork on 19 September
1988 on the shallow pass area between Ane-aidik and Anbwil-en islands (site 5L), a
strong 2 kt current coinciding with rising tide was flowing north through the channel and
into the lagoon. The depth of the top of reef varied from 2-3m. WoOtto’s lagoon appears
to be well flushed, based upon an analysis of the configuration of Wotto’s reefs and the
presence of wave action along the ocean sides of the north and eastern reefs. The wave
action continually pumps fresh ocean waters into the lagoon from the windward (NE)
sides during essentially all stages of the tide. This cooler water probably sinks to the
bottom of the lagoon displacing less dense water which exits the lagoon over the western
reef during ebbing tides. As noted during our limited field observations flood tide
currents are strong and ebb tide currents are expected to be strong if not stronger.
Although the western passes are shallow, their great width enhances the exchange of
lagoon and ocean waters during tidal fluctuations.

Corals of Wotto

A total of 88 species belonging to 36 genera and subgenera were reported from
WoOtto based upon surveys at 13 sites. However, time was very limited at several stations
where observations were hampered by low light conditions during a cloudy late afternoon.
In general, coral communities were diverse and in good health. Genera reported at Wotto
which were not observed elsewhere during the expedition were Cycloseris, Halomitra, and
Polyphyllia, all being free living mushroom corals. The last (Polyphyllia) is a new
generic record from the Marshall Islands. A few common coral genera should have been
reported but were not and include: Psammocora, Lobophyllia, Hydnophora, and
Echinopora. More extensive surveys on ocean facing reefs might have yielded some of
these genera as well as others.

a2

Four of the 13 stations surveyed displayed unique or exceptional characteristics
worthy of some mention. Three of these were lagoon reef slope habitats (sites 5A, 5G,
and 5K) and all supported live individuals of the rare giant clam Tridacna gigas. Three
of the sites (except 5G) had high live coral coverage of 60% or more. The single ocean
facing reef slope site surveyed showed spectacular relief and well developed coral
communities (site 5C), but numerous sharks and strong currents hampered the collection
of additional information. The slope was characterized by a series of large coral canyons
with flat scoured floors.

Abundant and common corals on the ocean reef slope site were Millepora
platyphylla, corymbose and table coral species of Acropora, Pocillopora spp, Turbinaria

stellulata, Porites lobata, Montipora spp, Stylohora pistillata, Platygyra pini, Favia spp,
Favites spp, Pavona minuta, Acropora palifera and Pavona spp.

Corals on a deep pinnacle along the western perimeter reef (site 5M) included
Acropora spp, Millepora spp, Stylophora pistillata, Pavona minuta, Pocillopora meandrina
and Montipora aequituberculata.

Abundant and common corals along the sheltered lagoon slopes (sites SA-5K) of

perimeter reefs included: Seriatopora hystrix, Acropora (many species), Astreopora spp,
Stylophora pistillata, Miullepora exaesa, Fungia spp, Porites spp, Montipora spp,
Oulophyllia crispa, Goniastrea retiformis, Pavona spp, Pocillopora spp, Scapophyllia
cylindrica, Acropora palifera, the blue coral Heliopora coerulea, Favia spp, Platygyra spp,
Porites (Synaraea) rus, Coscinaraea columna, Herpolitha limax, and Cyphastrea sp.

Rare Marine Species

Giant clams of several species were reported from WoOtto including the most living
specimens (15) of the largest and rarest species, Tridacna gigas. Some individuals were
very large, and WOtto was the only area where living specimens approached the numbers
of dead shells of the largest species (15 vs. 16). Interviews with the islanders revealed
the Taiwanese fishermen visited WoOtto "about six or eight years ago" to seek permission
to harvest T. gigas. After it was granted, the fishermen proceeded to harvest many clams
but taking only the abductor muscle and leaving the dead shells and remaining tissue "to
rot in the sun." This experience seemed to have shocked the islanders and made them
more conscious of the need to protect remaining giant clams. No doubt the presence of
the islanders discourages further harvesting. Despite recording the highest number of
living Tridacna gigas at Wotto Atoll, it is important to note that the ratio of dead to live
clams is still relatively high despite a hiatus on harvesting the species over a period of
six to eight years. This fact points to the vulnerability of such a population to
overexploitation, even from occasional or one-time harvests (Thomas 1989).

The smaller giant clam species are preferred by the islanders for consumption; for
one, they are easier to collect and shuck. Although all common species of giant clams

5/9

were observed on WoOtto’s reefs, the smaller species seemed less numerous than reported
at Pikaar, Bok-ak, and perhaps Toke.

Green turtles nest at WOtto but only in low numbers. The most pairs of tracks (4)
were spotted on the beaches of Pik-en, (Figure 22), with two pairs of tracks observed at
Long Island (Bokon-aetok) and two pairs at Kapen Island (Figure 25). During the night
of 18 September 1988, the ship’s crew captured a female Green sea turtle after it had laid
its eggs on Long Island, and gave it to the villagers. The WoOtto islanders harvest the
turtles only infrequently for special or ceremonial occasions, usually during the summer
months off the beaches of uninhabited islands. The villagers seem very conscious of the
vulnerability of the nesting turtle population and limit their harvesting practices
accordingly (Thomas, 1989).

Coconut crabs are heavily harvested by the islanders, primarily at Kapen Island,
and approximately 500 crabs per year are captured and consumed locally. The average
size of the crabs during our visit was about 0.5 kg, somewhat smaller than those observed
at Rondik. Harvesting pressure on coconut crabs at Wotto could be higher except that
a fuel shortage during most of 1988 prevented small boat travel and access to outer
islands including Kapen.

RONDIK ATOLL (Figures 26-30, A-11 and A-12)

Aelon-in Rondik (previously referred to as Rongerik Atoll) is moderately sized and
is located just east of Ronlap (Rongelap) and Ailinginae, northeast of Wotto, north of
Kuwajleen (Kwajalein), west of Toke and Utrok, and northwest of Jemg and Likiep. It
is generally afforded some protection from storms and large waves by the positions of
these atolls. However, Rofidik is exposed to open sea conditions from the north. Rofdik
is roughly circular in outline, has the second largest lagoon area (145 km’) and the third
largest land area (0.81 sq. mil) of the six atolls and one table reef visited in September
1988. All but one (Bok) of its 17 islands are located along the eastern perimeter of the
atoll (Figure 26).

Rondik’s lagoon is very open with major gaps in the perimeter reefs along the
northwest and west sectors. The navigation chart of Rofdik shows several major
navigable passes: Jeteptep and an unnamed passage to the north, Bok Passage to the west,
and Enewetak Pass (Ane-wetak) to the south (Figures 27-28). Bok Passage is over three
miles wide, and together with the lack of islands and shallow reefs along the west rim,
renders the lagoon and lagoon shorelines of islands facing to the southwest exposed to
heavy wave action.

54

6B 6C a
pa oe

Fig 26. Rondik (Rongerik
Atoll showing locations of
marine Survey sites. Stars
represent reef sites of special
interest. Scale: 1" = 2.335 mi.

Fig 27. Southwest corner of
Rondik (Rongerik) Atoll showing
the main south passage and the
location of 2 marine survey sites.
Scale: 1" = .3071 mi.

55

It is interesting to note that the
shorelines of several islands and sand cays
along the northeast rim of the atoll have
undergone considerable change between
1944 and 1978 comparing earlier and later
sets of aerial photographs. The island of

lagoon Rondik shows minor accretion of the beach

and vegetation along the SW facing lagoon

Fig 28. Western end shoreline. However, the W tip of Rondik,
of Rondik (Rongerik) the lagoon shorelines of two large islands

Atoll showing Bok Island.| (Patpat and Pikonaden), and several sand
mine Henn vegion\was cays between the islands have undergone
not visited during the ; :
1988 survey, Bok is a beach erosion and some receding of the
suspected turtle vegetation line, especially along W and SW
nesting site. facing shorelines. Perhaps large waves or
Seale: 1" = 9625 mi. storms traversing the lagoon from the
exposed W and SW directions were
responsible for these shoreline modifications.
Elsewhere on the atoll, beach and vegetation
lines along the shorelines of islands have
remained unchanged. The lagoon side of Ane-wetak Island has an unusually high sand
dune (Fosberg, et al, 1956). According to Fosberg (1988) the island was also much
disturbed by construction of a radio station involving bulldozing a strip across the center
and a road along the length of the seaward coast prior to 1956 (Figure 28).

Rondik’s lagoon is fairly deep (maximum reported sounding of 28 fathoms or
51m) with many pinnacles and patch reefs which breach the sea surface. Most shallow
lagoon reefs are patch reefs, circular or eliptical in shape and located in the eastern and
central lagoon. Primarily deeper lagoon pinnacles are found in the western lagoon and
are not as numerous or spatially dense. No soundings or bathymetric data are presented
for the north and southwest extremities of the lagoon.

The survey of Rofdik was cut short due to a sudden medical emergency and the
need to transport a sick seaman to the nearest hospital on Epja (Ebeye) island at
Kuwajleen (Kwajalein) Atoll. As a consequence, the western half of the atoll was not
surveyed including Bok (Bock) island and the extensive reef and lagoon areas to the NW
and SW of it. Small boat travel in the open lagoon was more turbulent the further away
from the upwind (NE) reefs, and most of the 12 marine survey sites were within the
lagoon shelter of the NE perimeter reef between Ane-wetak (Eniwetak) and Jeteptep
islands.

Six of the 12 marine survey sites demonstrated unique or exceptional natural
characteristics worthy of mention (sites 6F, 6G, 61, 6J, 6K, and 6A) and of possible
conservation importance (Figure 30). Site 6A was a shallow downwind lagoon reef

56

(» & Mot-lap

Fig 29. Main island cluster of NE Rondik

(Rongerik) Atoll. Numbers represent marine

survey sites, stars being reef sites of special interest.
Scale: 1" = .68 mi.

complex with table corals and gigantic spectacular colonies of the yellow foliaceous coral
Turbinaria. Site 6F was a shallow lagoon reef adjacent to Rondik island with exceptional
coral diversity. Also one live but six dead Tridacna gigas giant clams were reported
there. Site 6G was a spectacular deep reef flat moat environment on the windward side
of Rondik dominated by extensive platforms and microatolls of the blue coral Heliopora
coerulea. The high development of blue coral was unique and is probably maintained by
wave-generated water currents which constantly flush clean ocean water through the moat
system. Site 61 was the only deeper lagoon pinnacle reef surveyed and contained very
high coral abundance (over 90% live coral coverage) and diversity of reef fishes. Sharks,
however, were numerous and aggressive, preventing more detailed listing of corals. Sites
6J and 6K were shallow lagoon pinnacle habitats near the NE perimeter reef with fairly
high coral coverage and very high coral diversity. The blue coral back reef zone of site
6K was exceptional, and underwater visibility and relief were also excellent.

The expansive pink sand beaches of the NE islands of Rondik atoll are also
worthy of mention. The beaches are formed primarily of the remains of pink
foraminiferal tests. Although foraminiferal sand beaches are commonly observed in the
Marshalls, their extensive development and coloration at Rondik added substantially to
the natural beauty and aesthetics of the atoll’s island ecosystems.

"000°0€:1 eTeos ‘sydei30j0yd TeTaee azojTos

*) 9°95 *G pue syderaZ0joyud Tefiee ajtTym pue yIeTq HwHE, Awiy °S°p uodn
peseq suosfieduoj <‘T[[OIV (AFiesuoy) YF_puoy jo wea Yseoayjiou BuoTte
JaISN[O pue[S} upeW sSpueTs] TTeusieW ul IYyYIION 9y UF SUOTIeDOT

Pe eTOS 3e 8/6 puke HHEI Usemjeq SaeBueYD sUF[eACUS “QE eANsTY

8L61T JO FsSoYyA wor;
12JJEP YOFYM SQueuZes (761) FUFTe1OYsS Apues xew KM

8261 JO eSoy Wo1Z 19zZTP
YOFYM squseUses (HHE[) SUT[ UOTIEISBZOA PURTST ececcrcccce

(8461) 2UFT uoz3zeqeden pueTsST —~~__L

SUOF IIIS (8261) ouFfT9a0ys Apues ste eee c eens ees e.,

(MTT) auf, joo1r VAAL AA

“SI
MIGNOd Seas Anojuod woyyejJ OT —-— ——

58

Rare Marine Species

Evidence of substantial recent sea turtle nesting was observed along the lagoon
beaches of Ane-wetak (Eniwetak) island. A total of 33 pairs of tracks were observed
along Ane-wetak and one additional pair was observed on Kaarooka island.

A school of large bottlenose dolphins was seen swimming outside the reef on the
ocean side. Although bottlenose dolphins are common throughout the tropical Pacific,
marine mammals were observed only on this occasion during the 1988 expedition. There
is no obvious explanation for this curious lack of sightings of marine mammals elsewhere
during the northern Marshalls expedition.

The several smaller species and the rare larger species of giant clams were present
at Rondik but not common. Only four live individuals compared to 16 dead shells of
Tridacna gigas were observed on the reefs, suggesting heavy collection during the recent
past. Except during a brief period in 1946-1948, when Rondik was inhabited by the
displaced Bikinians, there are no other known periods of occupation of Rofidik during the
recent historical past. Hence the high mortality of giant clams may be best explained as
the consequence of unauthorized (and unobserved) poaching.

The largest concentration of coconut crabs observed during the expedition was
reported from Rondik islet. Other large islands at Rondik Atoll may also harbor large
coconut crab populations, but only Rofdik and Ane-wetak islands are said to be planted
in coconuts (Fosberg et al, 1956). Not only were the crabs very numerous, but many
individuals were large, exceeding two to three kg in weight. In a few hours time, several
of the ships crew were able to collect over 100 crabs without much effort, all of which
were 0.5 kg or more in weight.

The large population of coconut crabs at Rondik is best explained by infrequent
harvesting pressure by islanders (since Rondik is uninhabited), and the abundance of
coconut trees. Coconuts are the preferred food of the crabs. Although coconut crab is
a favorite delicacy of the Marshallese and other Pacific islanders, crab populations at
Rondik atoll may be contaminated with radionuclides.

In 1954, the U.S. accomplished BRAVO, the atmospheric testing of a large
thermonuclear device (H-Bomb) at Bikini Atoll, some 230 km west of Rondik. Due to
unanticipated adverse (westerly) wind conditions and higher than expected energy yields
from the detonation, radioactive fallout from the BRAVO blast penetrated the upper
atmosphere and drifted east. Fallout from BRAVO was observed to contaminate Bikini,
Ronlap (Rongelap) and Utrok (Utirik) Atolls and may have contaminated other nearby
atolls, some of which are uninhabited. Rofdik lies on a direct line between the
contaminated atolls of Utrdk and Rojlap, and thus it is likely to have been contaminated
by fallout from BRAVO. Radiological studies at Ane-wetak (Eniwetak) and Bikini Atolls
reveal that the radionuclides cesium-137 and strontium-90 are taken up and concentrated
in the tissues of coconut trees and nuts. The consumption of contaminated coconuts was

59

probably the most likely pathway explaining how returning Bikinians received excessive
dosage of these radionuclides during their aborted resettlement during the 1970’s (see
BARC, 1985; 1986; USACE, 1986). Coconut crabs can also become contaminated by
eating contaminated nuts, and in turn humans can become exposed to the radionuclides
by consuming effected coconut crabs or nuts. Although there has not been radiological
surveys of the trees and crabs of Rondik Atoll, the consumption of these foods poses a
potentially serious health risk, especially since the coconut crab population is very large
and since the crabs are a favored delicacy, in great demand.

Comparison of 1944 and 1978 shoreline configurations for NE Rondik Atoll did
not reveal significant changes (Figure 30).

Corals of Rondik

Only 74 species belonging to 29 genera and subgenera of corals were reported
from Rondik Atoll based upon the results of visits to 12 marine survey sites. These
numbers reflect lower levels and diversity of sampling at Rondik compared to the other
atolls. Only one lagoon pinnacle and no ocean reef sites were surveyed, and survey time
at the most northerly sites were shortened due to the need to leave Rondik earlier than
planned due to a medical emergency. The entire western lagoon of the atoll was also left
unsurveyed.

Many common coral species were not observed at Rondik, including
Stylocoeniella, Porites (Synaraea), Psammocora, Hydnophora and Leptoria. Most of these
would be expected on ocean reef slopes if they could have been examined.
Underrepresented during the survey were several genera and species of common free
living mushroom corals. Of interest was the recording of Plesiastrea versipora at Rondik,
the only atoll where this coral was reported during the 1988 study.

Abundant and common corals on lagoon pinnacle reef environments included:
Acropora spp (table and staghorn coral), Pavona spp, Stylophora pistillata, Montastrea
curta, Pocillopora spp, Cyphastrea spp, Astreopora spp, Montipora spp, the blue coral
Heliopora coerulea, Porites spp, the leafy yellow coral Turbinaria, the fire corals
Millepora spp, Fungia spp, and Seriatopora hystrix.

Abundant and common corals along the windward (NE) lagoon perimeter reef
slopes included: Heliopora coerulea, Acropora spp, Goniastrea retiformis, Fungia scutaria,
Astreopora spp, Pavona minuta, Stylophora pistillata, the conspicuous table coral
Acropora cytherea, Porites spp, Montipora spp, Leptastrea spp, Millepora spp, Montastrea
curta, Favia spp, Pavona minuta, Turbinaria stellulata, Platygyra daedalea, Pocillopora
spp, Goniastrea retiformis, Favites spp, the fingercoral Porites cylindrica, Seriatopora spp,
the soft coral Sinularia sp, Cyphastrea spp, and the organ pipe coral Tubipora musica.

Abundant and common corals within blue coral dominated reef moat and back reef
flat environments included: Heliopora coerulea, Stylophora pistillata, Seriatopora hystrix,

60

Jabonwod

Areto-jaion

° Aseto-jairok
7|

Fig 31. Adkup (Erikub) Atoll. Bokan-aik “SS

Numbers indicate marine survey Boke-lomjan ; Du Bokan-kowak
sites with stars showing reef sites

of special interest. Map created by

CORIAL using MARIS.

Scale: 1"= 3.146 mi.

61

Pocillopora damicornis, Acropora palifera, Porites spp, and Leptastrea purpurea. Giant
clams were abundant in these environments and along the slopes of perimeter reefs, but

most were dead and some stacked in piles - clear evidence of unauthorized poaching.
Nurse sharks (a harmless species) were also numerous.

ADKUP ATOLL (Figures 31-37; A-13, and A-14)

Aelon-in Adkup (also referred to as Erikub Atoll) has the form of an ellipse with
its long axis (about 27 km long) facing NE and SW (Figure 31). It is the largest and
most southerly of the atolls visited during the 1988 expedition. In comparison to the rest
of the Marshall Islands, Adkup is centrally located and of intermediate size in terms of
lagoon surface area (232 km’), ranking 15th of 28 atolls. In terms of land area (1.53 km’)
however, Adkup ranks much lower, 25th, and even the table reef of Mejit has more island
area. Due to its lower latitude, Adkup probably experiences a greater average annual
rainfall rate than the other six areas visited in 1988, and its islets are densely forested.

Adkup is clustered among several other atolls including Wotje just five NM to the
north, Maloelap and Aur to the southeast, and Likiep to the northwest. Perhaps due to
limited land and water area, Adkup is not permanently inhabited. However, residents of
nearly Wotje regularly visit Adkup to gather copra, fish, and other food. At the time of
our visit on 22-23 September 1988, there was evidence of a very recent visit to the main
island (Adkup) of the atoll probably to harvest sea turtles, fish, and crabs. Due to its
central location, Adkup is sheltered by other nearby atolls from heavy exposure to storms,
surges, and waves, except those approaching from the south.

There are no _ recent available
navigation charts of the atoll, and the 1978
aerial photography of the northern Marshalls
did not include Adkup. Eventually, after
considerable searching, a complete set of the
U.S. Army Map Service topographic series
maps of Adkup was obtained and analyzed
(Figures 32-37).

Fig 32. NE peripheral Adkup’s lagoon and reefs show some
reef of Adkup (Erikub) unusual features. Lagoon patch reefs and
Atoll showing marine pinnacles are rare, given the large size of the
SUNG SIO CVE SeE lagoon. Three clusters of patch reefs, each
interest. Pisce than DOMEEE a a atealhe
Scale: 1" = 8611 mi. of less than reeIs occur opposite three o

the atoll’s six passes (for example Figures
31, 36). Elsewhere in the lagoon there are
only a few isolated patch reefs (only seven could be counted from the AMS maps) and
reef pinnacles were only slightly more abundant (for example see Figures 31-34, 36).
Unfortunately, time did not permit the team to visit patch or pinnacle reefs in the deeper
lagoon. A limited number of soundings have been taken in Adkup’s lagoon, especially

62

near the passes, and reveal that the lagoon is deep. At least one lagoon area in the
vicinity of the west central lagoon shows depths of 30 fathoms (55m) or more.

‘ Six deep passes cut through
Adkup’s perimeter reefs (see Figures
Fig 33. Northeast rim of 31, 33, 34, and 36) and all are
Adkup (Erikub) Atoll near considered navigable. One pass to

pass and in vicinity of the north of Areto-jairok Island is on
several September 1988 the windward (eastern) side of the
marine survey sites, two atoll (site 7J; Figure 33) and is the
of which (stars) were of :

special interest only windward pass present at any of
Scale: 1"= 1.252 mi. the six atolls surveyed during the

1988 expedition. The AMS map lists
the depth of this pass at 3-3/4
fathoms (7m) and a width of about
60 m, but based upon my snorkeling
Areto-jairok )2 observations, the minimum depth of
this pass may be less (about 4m).
The other passes are deeper. For
example, the northwestern pass near
Looj Island is 12 to 23 fathoms (22-
42m) deep, and the southwest pass
closest to Adkup Island is 18-20
fathoms (33-37m) deep. Two
additional deep passes are located
just north of this latter pass.

The rest of the passes are
generally spaced out and are
probably effective in keeping
all portions of the lagoon well
flushed from tidal fluctuations
and currents. The northeast Rig St Notes sim

: : of Adkup (Erikub) Atoll
orientation of the atoll’s long in the vicinity of the pass.
reef axis maximizes the constant eS Scale: 1"= .6498 mi.
pumping of fresh ocean water .
into the lagoon from wave action
along the windward ocean reef lagoon
slopes. The lagoon gave the
impression of a well mixed open
system.

Fourteen islands occur at Adkup Atoll, but most are concentrated at the southern
end where most of the land area is also situated (Figures 36, 37). To the north of this

63

island cluster are found only three islands along the windward reef, and two islands along
the leeward reef throughout the rest of the atoll.

Rare Marine Species

Fig 35. Northwest rim of There was extensive evidence

Adkup (Erikub) Atoll in the of recent sea turtle nesting activity
vicinity of Aneko (Enego) on the beaches of several islands.
Island, an important sea Twenty-three pairs of sea turtle

turtle nesting site. tracks were reported from Aneko
Scale: 1" = 1.557 mi.

Island (Figure 35), a large island near
the northwest end of the atoll. Fewer
pairs of tracks were recorded on the
other islets: Adkup (13 pairs), Ijo-kan
(6), Areto-jairok (3), and Looj (4).
The collective totals for Adkup atoll
rank it third behind Pikaar and Jemo
with respect to the level of sea turtle
nesting activity recorded during the
1988 expedition. | However, the
nesting turtles and their eggs appear
to be subject to heavy harvesting
pressure. Recent human footprints
were found along all beaches where
turtle tracks were reported.
Numerous nest marker sticks, temporary camps, and the remains of sea turtles and their
eggs were also conspicuous. Most likely the turtle harvesting is accomplished by
residents of Wotje, but we were not able to visit Wotje and query its islanders.

Aneko Island

Fig 36. Southeast end of Adkup
(Erikub) Atoll near main islands
and pass. Scale: 1" = .95 mi.

lagoon

Bokan-aik — :
Boke-lomjan

Bokan-kowak i

64

Fig 37. Southeastern end of Adkup_ og, pe
(Erikub) Atoll showing sites of marine

surveys, with those of special interest

indicated by stars.

Scale: 1” = .9232 mi. Jaltoneej

7F

Bokan-kowak

Interviews with the crew and Marshallese from Majuro indicate that Adkup Island
is famous for its large coconut crab population. Indeed crabs were reported during the
survey, but most all were small. Only one crab approached the large (2 kg) size of the
many large crabs observed at Rondik Island (Rondik Atoll). The crabs were similar in
size as those observed at Kapen Island (WoOtto Atoll), but were not nearly as numerous.
We conclude that the Adkup crabs are also subject to intense harvesting pressure.

Giant clams of all four species were observed on the lagoon reefs of Adkup but
only Tridacna maxima and Hippopus hippopus were common. There were many more
dead shells than live clams, and only one live individual of Tridacna gigas was reported.
The lagoon slopes of the eastern perimeter reefs were unusually steep. These habitats
may be suboptimal for the giant clam T. gigas at Adkup due to substrate instability. It
is also possible that the giant clam populations at Adkup are subjected to heavy
harvesting pressure from islanders at nearby atolls.

Of the 13 marine sites surveyed at Adkup Atoll, four (7D, 7G, 71, and 7K) were
considered unique or exceptional with respect to natural characteristics. All of the sites

65

were lagoon facing sides of perimeter back reefs and reef slopes along the windward side.
All displayed complex three-dimensional coral communities on steep reef slopes
characterized by moderate to high fish abundance and high coral cover and diversity.
Live giant clams were present at all four sites and live coral coverage was 40% or more.
At site 7D underwater visibility on the lagoon slope (low tide) was 45 m. The slope at
site 7I consisted of a patch reef half buried by a sand talus where wave action and strong
currents constantly transport sand lagoonward and down the slope. Site 7K included
nurse sharks and several rarer corals among the 30+ species recorded.

The windward pass area (site 7J) was also of interest. At the time of my surveys
(morning of 23 September 1988) a strong flood tide of two to three kts was entering the
channel. The floor of the channel consisted of a hard reef pavement at a depth of 4m
which gradually deepened to 15m and transitioned to a sand bottom in a lagoonward
direction. The sides of the channel supported exceptional live coral development and
abundant reef fish populations.

Corals of Adkup

A total of 75 species belonging to 35 genera and subgenera were reported from
Adkup Atoll based upon observations at the 13 marine sites. The lower totals compared
to some of the other atolls reflect the lack of observations on ocean reef slopes, lagoon
pinnacles and other reef habitats expected to harbor additional species. One species
reported from Adkup at site 7E, Euphyllia glabrescens was not observed elsewhere during
the 1988 expedition and is a rare coral elsewhere in the Marshalls. Several common
genera or subgenera were not reported at Adkup, including Stylocoeniella, Porites
(Synaraea), several mushroom corals, Lobophyllia, Leptoria and others (Table 2). Some
of these would be expected to be seen after more intensive surveys.

Abundant and common species along Adkup’s back reef flats and shallow lagoon
reef slopes along windward perimeter reefs include: fingercoral (Porites cylindrica)
Acropora spp (tables), Stylophora pistillata, Favia spp, Montipora spp, Pavona spp, other
Porites spp, Acropora palifera, the soft corals Sinularia and Sarcophyton spp, Millepora
spp, Pocillopora spp, Astreopora myriophthalma, Echinopora lamellosa, Cyphastrea
microphthalma, Montastrea curta, Heliopora coerulea, Platygyra daedalea, Fungia spp,
Turbinaria stellulata, Seriatopora spp, Favites halicora, Scapophyllia cylindrica, Goniastrea

spp, and Leptastrea purpurea.

Abundant and common coral species along the windward facing lagoon reefs on
the western perimeter of the atoll include: staghorn and table coral species of Acropora,
Pavona minuta, Millepora platyphylla, Favia stelligera, Pocillopora spp, and Montipora
Spp.

66

CORALS: COMBINED SPECIES LIST

Prior to the 1988 surveys, coral records for the seven areas were extremely
limited, a combined 35 species from Bok-ak and Rondik (Wells, 1954) (Table 3). All but
four of these species were subsequently reported in 1988, and a total of 168 species
belonging to 55 genera and subgenera have now been recorded for the seven areas.
Several of the species and one genus (Polyphyllia) are new records for the Marshall
Islands. Despite limited deep water and ocean reef sampling, the 168 species is a sizable
total comparable to the faunas of Bikini, Ane-wetak (Enewetak), and Arno Atolls (Wells
1951, 1954; Maragos, 1989; Devaney and Lang, 1986), where much more extensive
surveys and sampling for corals was accomplished. The species totals for the individual
atolls surveyed in 1988 are lower than reported from each of Bikini, Arno, and Ane-wetak
Atolls due to the 1988 sampling limitations.

67
IV. DISCUSSION

An excellent overview of the feasibility, justification and procedures to establish
a system of protected areas in the Marshall Islands is found in Thomas (1989) and covers
terrestrial, cultural, and marine factors. The present report concentrates on marine
resources, and assesses the consequences of establishing marine parks and reserves (Table
5). The feasibility of other resource uses at the seven studied areas is also assessed since
atolls and islands that the RMI does not establish as preserves or parks may be earmarked
for other forms of development (Table 6).

Most of the Republic’s natural resources are marine resources, and the seven
studied areas represent a major proportion of the undisturbed reef systems in the country.
Although none of the study atolls is large, the RMI is home to the world’s largest atolls.
More atolls are found in the RMI (28) compared to any other country except the
Federated States of Micronesia (42) and French Polynesia. But unlike the FSM and
French Polynesia, the RMI is comprised of only atolls, table reefs, and low coral islands.
As such, the land resources are small and lack rich and abundant soil and groundwater
resources. Hence the RMI must look to marine and coastal environments for future
economic development. The RMI is also faced with rapid population growth and the
need to reduce balance of trade deficits and unemployment. Self reliance is the central
theme for the Republic’s future development goals.

Fully a quarter of the RMI’s atolls are uninhabited (including Ailinginae which
was not studied), and at least one or two others have been temporarily evacuated (Ronlap
and Bikini due to concerns over contamination from nuclear testing). Thus the RMI
perceives most of these uninhabited areas as major resource development opportunities.
The RMI government also recognizes and supports the traditional use of several of these
atolls as wildlife reserves or "pantry" reserves, and specifically requested the study team
to evaluate the uninhabited areas (and inhabited WoOtto) as possible parks and reserves.
Those areas which are not established as protected areas are theoretically open for
subsistence activities, resort development, small scale (nature based) tourism, agriculture,
mariculture, urbanization or settlement, and industry. However, the inaccessibility,
geographic isolation, small land areas, limited fresh water, and vulnerability to typhoons
and other natural hazards render most of the areas unfavorable for intensive development
(see Table 6).

Marine Reserves

At least portions of all seven areas visited harbor marine resources and sites
worthy of marine reserve and preserve status. The entire reef ecosystems (along with the
islands) of Bok-ak Atoll, Rikaar Atoll, and Jemo Island warrant reserve status, a
designation which would be entirely consistent with the traditional and cultural uses of
these reefs as practiced by the Marshallese for many centuries. All three areas are
acknowledged reserves for either nesting seabirds, nesting sea turtles, or both. All three
have unique coral reef features and habitats which have been little studied scientifically.

68

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69

The lagoons of Bok-ak and Pikaar also support huge populations of several of the smaller
species of giant clams which is perhaps the most important reason to establish them as
marine reserves. The lagoons also support exceptional populations of reef corals and reef
fishes and the whole ecosystems are in pristine condition. The designation of any area
for reserve or protected status will require the cooperation of persons with traditional
rights to these areas.

At a smaller scale there are unique or exceptional coral reef habitats at the other
atolls (Wotto, Adkup, Rondik, and Toke) that also merit marine reserve designation due
to the abundance, diversity or unique features of coral reef populations and reef features.
For example, the pink sand beaches and high dune systems, blue coral moats and
flourishing lagoon pinnacles at Rondik deserve special recognition as do other lagoon reef
formations at the other atolls.

Marine Parks and Recreational Areas

Several of the atolls offer major advantages with few disadvantages to support
marine park designation. The variety, accessibility, safety, and pristine condition of
lagoon reefs (and perhaps ocean reefs as well) at WOtto and Toke support the entire atolls
being designated as National Marine Parks. Portions of Adkup and Rofdik also contain
diverse and accessible reef habitats to support at least Regional Marine Park status. These
parks would serve both the residents of the RMI and visitors and would be oriented to
provide recreation and educational opportunities. Visiting tourists to these parks could
provide the fees to support park management, jobs, travel, and educational opportunities
for Marshallese residents, including school students.

Of the four areas, Wotto has the most potential to serve as a national park,
because of an onsite residential population interested in pursuing marine park and nature
based tourism. WOtto also contains food and water supplies, and its airstrip allows the
atoll to be serviced by weekly commuter flights from Majro or Kuwajleen (Kwajalein)
Atolls. The large population of American defense workers at Kwajalein may find the
opportunity to visit WOtto an attractive prospect. Many other people from the urban
settings of Majro and Kuwajleen may also be interested in experiencing the natural and
cultural resources of WOtto.

The atolls of Toke, Adkup, and Rondik are somewhat less accessible to serve park
visitors. The nearest airstrip and inhabited population from Toke is at Utrok atoll, and
the Utrok islanders need to be queried as to their interest in park designation for Toke.
Likewise, Adkup and Rojidik are close by other atolls (Wojte and Rofllap) where airstrips
are present. Wotje is inhabited while Ronlap has been temporarily evacuated. On a long
range basis, park designation and development is theoretically possible for these areas,
as well as for Ailinginae (which was not visited) which is also near Ronlap (see Figure
1). Park development at Pikaar, Bok-ak, and Jemg is not feasible due to hazardous
access, remoteness, vulnerability to large waves and typhoons, and lack of potable water.
Heavy visitation to these areas could also disturb wildlife resources (especially sea turtles,

70

sea birds, and possibly clam populations). Any form of physical development at these
atolls would compromise the value of a reserve, and could disrupt reef and island
ecosystems. As with any other proposed use, park designation of these areas will require
the cooperation of persons with traditional rights to these areas.

Subsistence Activities

Very limited harvest of sea turtles and seabirds for ceremonial purposes has been
traditionally practiced at Bok-ak, Pikaar, and Jemg. Such visits, if continued to be limited
to one or two per year, do not pose a danger to the vulnerable wildlife at these sites and
would be in keeping with long established cultural practices. However, harvesting of
larger numbers of wildlife for purely subsistence purposes would be disruptive to bird,
turtle and clam populations, and may endanger their status as the most important
populations in the RMI.

The remaining four areas are suitable for traditional level subsistence activities and
would be compatible with park reserve designations if planned properly. For example,
marine resources and sites at WOtto used for subsistence activities could be identified and
sustained for such uses, and visitor or recreation sites would be best located at separate
sites.

There should be controls established over the taking of rare marine species (sea
turtles, their eggs, and giant clams) from Rofdik and Adkup Atolls to ensure that
important breeding populations are not depleted or threatened. One way to accomplish
this is first to establish critical habitat areas as reserves.

Radiological Contamination

Consumption of coconuts or coconut crabs from Rondik Atoll may pose as health
hazards to islanders. In addition, subsistence use of terrestrial resources from Ailinginae,
if any, should likewise be discouraged until radiological surveys document that
consumption of these resources will not pose a hazard to public health. It is possible but
highly unlikely that consumption of marine resources from these two atolls as well as
from Toke would pose a health problem.

Resident coconuts, breadfruit, pandanus, and coconut crabs from Rondik Atoll may
be contaminated with the radionuclides cesium-137 and strontium-90. These
radionuclides were generated during the BRAVO hydrogen bomb test at Bikini in 1954
and carried with the nuclear fallout from the blast. Although Bikini is located over 125
NM west of Rofidik (and 100 NM west of Ailinginae and Romlap), fallout from BRAVO
was reported to have been carried into upper atmospheric winds and to the east, where
some of it eventually rained down on Rofilap and Utrok Atolls, which were inhabited at
the time. The fallout also probably rained down on other nearby atolls, but since they
were uninhabited, evidence of fallout must be derived from analysis of plants and soils.
Rojidik falls within a straight axis between Rofilap (25 NM to the west) and Utrok (140

yal

NM to the east) (see Figure 1). Thus it is highly likely that Rondik, and perhaps
Ailinginae were contaminated with the fallout.

Studies at Bikini and Ane-wetak Atolls after the nuclear testing period reveal that
coconut trees (especially the living nuts) and other crops take up and bioaccumulate
cesium-137 and strontium-90 in their tissues. The concentrated radiation levels in the
coconuts posed a much greater health risk than radiation in the soils, because resettled
Bikinians subsisted regularly off locally grown but contaminated coconuts between 1969-
1978. Excessive whole body dose counts of the Bikinians in 1978 measured by
Brookhaven National Laboratory prompted the evacuation of the Bikinians from their
home atoll on short notice in 1978.

Coconut crabs as well as humans subsist on coconuts, and the crabs can also
bioaccumulate Ce-137 and Sr-90 in their tissues by foraging off contaminated nuts, as
studies by Lawrence Livermore National Laboratory at Ane-wetak Atoll have
demonstrated (BARC, 1984; 1985; 1986). The radionuclides could then be passed up the
food chain to man if he eats contaminated coconut crabs. Unlike the small crab
populations at Bikini and Ane-wetak, Rofidik supports huge coconut crab populations.
This raises the possibility of a greater public health hazard since there may be many more
potentially contaminated crabs at Rondik. Regular consumption of coconuts, breadfruit
and other crops at Rondik is more likely and could also pose a risk.

Toke and Ailinginae Atolls were also within the fallout zone. Although Toke’s
edible vegetation and coconut crab populations are very small, the extent of Ailinginae’s
is not known since the team was unable to visit the latter atoll. Thus radiological surveys
may be warranted for Rondik as well as Toke and Ailinginae to document the extent of
radiation hazard from ingesting food crops and coconut crabs. Romnlap, and Utrok are
presently being monitored for radiation by Lawrence Livermore National Laboratory.

Mariculture

The shallow protected lagoons and broad reef flats and shelves within the Northern
Marshalls offer ideal locations for certain forms of mariculture development. Several
marine species with mariculture potential were observed during the expedition including:
giant clams (Tridacna, Hippopus), topshell (Trochus), black-lipped pearl oysters
(Pinctada), milkfish (Chanos), mullet (Mugil) and reef groupers (Epinephelus).
Mariculture would be more feasible within atoll reefs and lagoons accessible by air and
sea transportation and near population centers. Mariculture thus would be feasible at
WoOtto, with its airstrip, protected anchorage, resident population and proximity to urban
Kuwajleen. Toke is somewhat less feasible since the nearest airstrip and residential
population is at Utrdk. Similarly, Adkup is removed from Wotje, the nearest population
and airstrip. Mariculture would more likely be developed at the populated atolls (Utrok
and Wotje) rather than at their uninhabited neighbors (Toke and Adkup). Rojfidik is less
feasible for mariculture due to the lack of inhabited atolls nearby, although Ronlap, which

72

is serviced by an airstrip and protected anchorage was only recently evacuated and may
be eventually resettled (Rongelap Reassessment Project, 1989).

The remaining reef and atolls (Bok-ak, Pikaar, and Jemg) are not feasible due to
remoteness, lack of safe access, lack of safe anchorages, and relatively inhospitable living
conditions. Extensive mariculture development at Pikaar and Bok-ak might also conflict
with other values and uses such as protected reserves or preserves. The large giant clam
populations in the lagoons of Pikaar and Bok-ak may eventually serve as important brood
stock and a source of giant clam seed, if the smaller giant clam species become severely
depleted in the RMI. For this reason, the giant clam populations at the two atolls should
be maintained as reserves indefinitely.

Agriculture

Although the focus of this report is on marine resources, a few comments on the
feasibility of agriculture at the seven studied areas can be offered. Due to lack of water
and good soil, agriculture at Pikaar, Toke and Bok-ak is not feasible. Although Jemo
Island has thicker soil and more abundant water, agriculture is also difficult due to
hazardous access and limited land and settlement options. Rondik Atoll should not be
considered feasible for agriculture unless radiological surveys and analyses project it to
be safe. Subsistence level agriculture is already practiced on inhabited Wotto, including
some copra harvest. Likewise, Adkup is subject to limited copra harvest, but is small
land areas limit greater agricultural development.

Commercial Fishing

Commercial fishing activity by resident Marshallese would be feasible at inhabited
WoOtto, which has accessible ocean fishing grounds. Fishing vessels from Wotje, Utrok,
and Rofilap could also fish the coastal waters of Adkup, Toke, or Rofidik, especially for
game fish and tunas. Controlled commercial fishing in the lagoons of uninhabited atolls
is also possible unless it competes with the subsistence needs of the nearby inhabited
atolls which own or traditionally control lagoon fishing grounds. Commercial fishing is
less feasible at Pikaar and Bok-ak atolls due to remoteness. Fishing in the lagoons would
be further discouraged by numerous reefs and hazardous access through the single narrow
meandering passes. Permanent occupation of the atolls to promote commercial fishing
would be extremely disruptive to rare marine species, reef life and nesting seabirds.
Controlled commercial fishing for tunas and other migratory species along the ocean sides
(territorial waters) of all atolls is feasible but should be limited to Marshallese and
monitored to avoid poaching of turtles, giant clams, and other rare species within or near
designated marine reserves.

Small Scale Tourism

Small scale tourism in this report means small lodges or beach cabanas, limited
to about 20 rooms which take advantage of the natural features, scenic beauty, and

713

cultural resources within the vicinity of the tourism facilities (e.g. nature based tourism).
This style and level of tourism at Wotto is very feasible given the interests of the
islanders to pursue it and the host of natural amenities and attributes. Reliable sources
of water and food appear feasible to obtain and the major infrastructure requirements
would include the accommodations, power generation (for lights and refrigeration, ceiling
fans, etc.), catchment water storage, and waste disposal. WoOtto is already serviced by
weekly commuter air service and has a protected anchorage. Thomas et al (1989)
provides a detailed account of the feasibility of small scale tourism at Wotto Atoll. Many
existing marine resources and features could be incorporated into a tourism operation.
Visitor destination attractions include flourishing coral communities at safe and accessible
lagoon areas. Corals, fish, giant clams and other reef life could be observed via diving
and snorkeling. Mariculture and fishing activity at the atoll could provide fresh fish and
shellfish to feed visitors. Beaches and other coastal sites at islands away from the
existing village could also be visited. Interpretive and educational displays regarding
marine life could be established. Swimming, gamefishing, diving, some boating, and
sailing activities could also be included. The focus of small scale tourism at WoOtto
should be nature based, with considerable emphasis on marine resources.

Toke Atoll also has many attributes to support tourism visitation, but
accommodations for tourists would be best placed on Utrdk, subject to the views,
approvals and guidance of the Utrok people. The survey team could not find the time to
visit the Utrok islanders and obtain their views on tourism. The water and land resources
at Toke are too limited to support development of self-contained permanent tourism
accommodations. Toke would best serve as a day visitor area or for limited overnight
"rustic" camping. Access to the atoll would be gained by boat from Utrok. Land
resources at Toke are too limited to justify an airstrip, and dredging and filling to
construct a reef runway could have major adverse impacts on marine resources.

Similar limitations on tourism development apply at Rofidik and Adkup atolls.
Although land resources are more abundant, the lack of permanent residents would require
infrastructure development for accommodations, power, water supply and transportation.
Airfields would most likely be required to attract tourists to the atolls, and reef runways
would be needed. Tourism development would be expensive and would need to be well
planned to avoid serious socioeconomic and environmental impacts. Most importantly,
tourism development, if any, would require the approval and support of the traditional
land managers, owners, and users of both atolls.

Tourism development is not feasible at Jemo, Pikaar and Bok-ak due to
remoteness, hazardous accessibility, lack of reliable fresh water, lack of a permanent work
force, and the significant expected economic costs and environmental impacts. Of the
three areas, only Bok-ak has sufficient land for an airstrip, but substantial bird nesting on
the islands poses serious constraints. Disruption of nesting activity and collisions between
birds and airplanes are highly likely in nesting areas and contrary to the designation of
the atoll as a wildlife refuge. Safe boat access to either Bok-ak or Pikaar would require
major dredging and other coastal construction activity in the vicinity of the existing

74

passes. Additional lagoon reefs may also need to be dredged or knocked down to provide
safe access across the lagoons to the destination islands. The clearing of safe navigation
channels could have major adverse effects on coral reefs and giant clam populations, and
may also disturb some sea turtle nesting. Major widening or enlarging of the passes
could also lower lagoon water levels, exposing and killing many shallow reef flats,
disrupting lagoon circulation, and possibly degrading coral reef and giant clam habitat
(see Figure 38). For these reasons permanent occupation or settlement of Pikaar and Bok-
ak for tourism and other purposes (e.g. resettlement, industrial, development) would pose
serious threats to the natural resources of most value at the atolls and should be strongly
discouraged.

Variations in the depths of living reef flats: revisiting some widely held assumptions

It is generally thought that living reef flats on coral atolls and barrier reefs can
grow no higher than mean low water due to the requirement of the reef building
organisms (e.g. corals, coralline algae), to be regularly immersed in sea water for survival.
As growing coral reefs reach the sea surface, further upward growth is inhibited while
lateral growth lagoonward and seaward can continue (see Figure 39). Over time and with
stable sea level, cessation of upward growth and continued lateral reef expansion would
result in the formation of wide reef flats. Their widespread occurrence is indisputable
evidence on the limitation of marine organisms to grow above a level of regular exposure
to sea water.

One widely observed exception to the "mean low tide rule" is the presence of
elevated living coralline algal ridges along the margins of many windward reef flats of
many atolls, especially those of the RMI (Tracey et al, 1948. Wells, 1954; 1957a, b).
The fact that these ridges occur only along windward reef flats suggests a relationship
between the ridges and the wave action generated by the tradewinds. The most widely
supported hypothesis is that the constant wave action generates wave wash or splash that
constantly bathes the ridges, and keeping the reef building marine organisms (primarily
crustose coralline algae and some reef corals) alive. This wave wash can regularly
immerse surfaces up to two or three feet above mean low water during low tide
conditions on the ocean side of the reefs which explains why ridges at this elevation
remain alive. Wave wash passing over the ridge then moves downhill toward the lagoon
and mixes with lagoon waters, eventually exiting through the passes or over the tops of
reefs along leeward sides.

Another less widely known exception to the "mean low tide rule" became evident
after the visits to Bok-ak and Pikaar Atolls. Here, not only were windward algal ridges
found to be alive and growing above mean low water, but so were many other lagoon
reefs. The elevated living nature of some lagoon reefs were reported by Fosberg et al
(1956) and Fosberg (1988) at Pikaar and Bok-ak. These authors and the 1988 field team
also observed the elevated lagoon water levels at "low tide" at these atolls. Similar
elevated lagoon and leeward reef flats were also reported by Wells (1951) at Arno Atoll’s
northern sublagoon (Namdik), later corroborated by Maragos and Lamberts (1989). I also

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A. Reef Platform at lower sea level stand (during previous glaciation)
leeward side ¢—— windward side

sea level (s.I)
20,000 yrs before
present (b.p Me

B. Submerged Bank (during post-glaciation period of rising Re? level)
ABWAApRAIIeaerrr OOO Om
s.1. 8,000 -

10,000 yrs. A
b.p.

s.l. 20,000 growing coral reef
yrs. b.p.

mean high tide (MHO) wave action
present s.I-

mean low tide (MLW)

reef flat and
lagoon coralline algal
submerged ridge at MLW or
leeward reef slightly higher
oN pinnacle
s.l. 20,000 reef
yrs. b.p.
(W6tto, Rofidik, Kuwajleen Atolls)

wreamym reef line (MLW) I /1 1) raised living reef

| <em> Gage islands

KAAS j
.. submerged reef contour ROO raised dead reef
submerged bank or
100m contour

Figure 39. Progressive development of reef flat features on atolls.

D. Complete Atoll

E. Open Raised Atoll

S aeN~

MHW
MLW

present s.I.

leeward
reef flat

reaching MLW

s.1. 20,000 —*
yrs. b.p.

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dam & spill-
way above
MLW (living)

s.1. 20,000
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F. Nearly Closed Raised Atoll

2AM

raised (emergent)
reefs (dead)

windward

reef flat

projecting
patch above MLW

reef

(Toke, Utrok, Adkup Atolls)

stepped
reef massive
coral-algal

ridge (living)

ribbon
reef

(Bok-ak, Pikaar Atolls)

land blocking
lagoonward movement
of water pumped by
wave action

(Kanton Atoll, Phoenix Islands, Enen
Kio [Wake] Atoll)

78

observed elevated lagoon and leeward reefs at Namdik (Namorik) Atoll in 1971, and
former residents of nearby Ebon Atoll also noted the elevated nature of perimeter reefs
(pers. comm. to J. Maragos by N. Neimon). All five of these atoll lagoons have two
things in common: 1) exposure of windward reef flats to prevailing wave action generated
by the trade winds, and 2) restricted passages or no passages through the reef. These two
factors are interrelated in explaining the presence of elevated living lagoon and leeward
reefs (Figure 39). Progressive development of reef flat features on atolls explain how
contemporary reefs in the northern Marshalls can grow above low tide level without the
need for a higher "Holocene" sea stand. Stage A. Antecedent reef platform at the end
of the previous ice age. Stage B. Subsequent melting of the glaciers causes sea level to
rise, drowning the reef platform and renewing upward coral reef growth. Stage C.
Upward reef growth eventually reaches sea level (mean low tide) on the windward side.
Coralline algal ridges projecting above mean low tide may develop in response to
constant wave action. Stage D. All perimeter (annular) reefs grow upward to mean low
tide level except where passes cut through the reef. Coralline algal ridges and windward
reef flats continue to broaden. Stage E. Eventually the passes close off to the extent that
water pumped into the lagoon by constant windward wave action is greater than can exit
the passes at low tide, causing average lagoon water levels to rise. Remaining (leeward)
perimeter reefs, now constantly submerged, begin to grow upward, forming coral-algal
dams, spillways, and perched lagoon reefs. Stage F. Storms naturally cast sand and
rubble on top of windward reefs, forming cays, ramparts or islands, or man builds
causeways along windward reefs to connect islands. In either case they block the
pumping of seawater into the lagoon by wave action. As a result, water levels in the
lagoon drop, permanently exposing raised reefs which dry out and die, leaving intact
"fossil" raised reefs. The cutting or enlarging of passes through perimeter reefs can have
the same effect by draining lagoon waters more quickly and lowering average water levels
(see Figure 38).

The restricted passages result in more water entering the lagoon over windward
reefs than can exit through passes at low tide. In response to the restricted discharges,
average lagoon water levels increase with the excess water spilling over leeward reef flats
as well as through the passes. If the passes begin to close off, restrictions increase,
causing lagoon water levels to rise further. Higher water levels in the lagoon, especially
during low tide, result in more and more water spilling over the leeward reef flats until
the latter are constantly immersed even at low tide. Prolonged immersion may in turn
ultimately cause leeward reef flats to grow upward, since the reef organisms are no longer
limited by exposure at low tide (see Figure 39). Eventually, perimeter reefs along
leeward sides of the atoll grow upward. Supplementing the coralline algal ridges along
windward reef margins are smaller coralline algal ridges and coral-algal dams and
spillways along leeward reefs. Lagoon reefs also grow upward in response to the
progressively higher lagoon water levels.

Maximum upward reef growth depends upon the magnitude of prevailing wave
action and the extent of open reef flats along the windward side of the atoll. Some of the
kinetic energy of wave action is converted into potential energy by pumping water up on

TS,

higher reef flats. Wave action can constantly pump ocean waters into the lagoon over the
ridge and reef flats. If lagoonward water movement is blocked by the presence of islands
or rubble ramparts created during tropical storms, lagoon water levels could drop. Man’s
intervention, either by building causeways along windward reefs (which blocks wave
pumping of water into the lagoon), or by enlarging passes through leeward reefs (which
drains water more quickly from the lagoon), can also lower average lagoon water levels.
The lowered water levels could then result in the emergence and death of exposed reefs,
which may have occurred at Kanton Atoll, where a near continuous causeway was built
around the perimeter reefs of the atoll, and where recently exposed reefs were observed
(Jokiel and Maragos, 1978; Smith and Jokiel, 1978). The hypothetical evolution of atoll
reef flats based upon the above scenario is depicted in Figure 39.

Geologists often rely the elevation of previously intact fossil reef flats to estimate
the extent and age of relative sea level stands in various parts of the world. Two implicit
assumptions in many of these studies is that all or most modern living reef flats grow no
higher than mean low water elevation, and that intact previously living reef flats found
emerged on present day reefs must have formed when relative sea level was higher.
Based upon the 1988 observations at Bok-ak and Pikaar, supplemented by the
observations at other atolls (Arno and Namdik), the first, and perhaps both of these
assumptions may be incorrect. First, in the case of Bok-ak, Pikaar, Arno, Namdik, and
perhaps other atolls, many present day living reef flats occur above low tide level due to
factors other than a higher sea level stand. More importantly, some of these same reefs
may become reexposed due to natural factors, such as islands, cays, and rubble ramparts
forming on the windward sides of atolls with elevated leeward and lagoon reef flats,
thereby blocking lagoonward movement of water pumped by wave action.

As a consequence, the hypothesis of a higher Holocene sea level stand some
4,000-6,000 years ago that is based upon the evidence of higher stands of recent reefs less
than one meter above present sea level may need to be reexamined. The complex
interaction of prevailing wave action, restricted passages through reefs, open windward
reef flats, the frequency of storms, and other factors can alternatively explain the upward
growth of living reefs above normal low tide levels and their subsequent reemergence.
Reliance on evidence from prehistoric reef stands in support of hypotheses on previous
sea level stands must involve an examination of the geomorphology, oceanography, and
geological history of the reefs in question.

Rapid Marine Field Assessment Procedures

The results of the 17 day visit to 95 marine sites and other numerous shoreline
sites at seven atolls and reefs in the northern Marshall Islands demonstrate that qualitative
data gathering procedures can be very useful in describing marine areas. Preliminary
assessment of biological and ecological diversity can be accomplished without the need
for transect and quadrant surveys if the purposes and goals of such studies are clearly
identified in advance. With the primary emphasis of the 1988 expedition on evaluation
of natural diversity and feasibility for park and protected area development, it was

80

possible to collect valuable information on species, habitats, bathymetry, geomorphology,
and oceanography, relying primarily on shallow water snorkeling observations. Coupled
with the availability of aerial photographs, and previous map sources, field work was
designed to sample a greater variety of habitats than would have been otherwise possible.
Although the literature was scant and the opportunity to interview knowledgeable
informants limited (since all but one of the sites were uninhabited), good maps and aerial
photographs can be consulted to improve the efficiency of field work. Modern satellite
imagery from the French Satellite SPOT now has resolution (10m) which can supplement
photo interpretation of maps, especially where conventional aerial photographs are not
available.

Collectively these data acquisition strategies may become increasingly important
in evaluating the multitude of marine resources and habitats in the South Pacific. With
many thousands of reefs and islands, and hundreds of atolls, many of which are remote,
innovation will be required to allow rapid evaluation of particularly valuable areas. As
population levels and development pressures increase, more and more natural marine areas
will become vulnerable to exploitation and degradation. A systematic inventory and
evaluation of candidate marine protected and park areas throughout the tropical Pacific
will become an even more important goal of proponents of both conservation and
development.

81
V. SUMMARY

Six atolls: Bok-ak (Taongi), Pikaar (Bikar), Toke (Taka), Wotto (Wotho), Rofdik
(Rongerik), and Adkup (Erikub) and one table reef (Jemg) were surveyed during a 17-day
expedition in September 1988 to the Northern Marshall Islands to describe coral
communities and reef formations as part of a larger natural diversity survey. Only
observations using snorkeling gear, underwater writing slates and underwater cameras
were possible during the approximately 2-day visit to each atoll. A total of 95 sites were
surveyed, ranging from 12 to 20 sites per atoll. Additional observations were made
during boat travel and walks along shorelines of islands. Over 160 species of reef corals
belonging to 55 genera and sub genera were reported from the seven areas, including
several species and one genus as new records from the Marshall Islands. The abundance
and distribution of corals varied from one atoll to the next and may reflect geographic
isolation from adjacent reefs, limitations on habitat diversity (in the case of Jemo), and
limitations on larval recruitment (in the case of Bok-ak and Pikaar). Several of the coral
communities and habitats were unique or have not been previously described. Many sites
displayed exceptional coral development, and sites of special interest were identified on
maps and are highlighted in the report. The reef geomorphology of the seven areas is
also described and each belongs to one of three distinct physiographic categories:

1) small semi-enclosed atolls (Bok-ak, Pikaar, Toke)
ii) larger open atolls (Wotto, Rondik, Adkup)
iii) exposed table reef (Jemg)

Lagoon and adjacent perimeter reef formations at Bok-ak and Pikaar are elevated
two or more feet above mean low tide level. These elevated reefs are living and perhaps
growing, and are maintained by a combination of water being pumped into the lagoon
from wave action on the windward sides, and the inability of the narrow passes to drain
water from the lagoon at an equivalent rate during low tides. Unique features at both
atolls associated with the elevated reefs include overhanging ribbon reefs, coral-algal
dams, spillways and steep water level gradients in each atoll pass during low tide.
Navigation through the passes during low tide is treacherous due to the narrow and
meandering configuration of the passes, and the turbulent water flow caused by a two to
three foot drop from the higher lagoon water levels over a short distance. Huge
undisturbed giant clam populations (Hippopus sp. and Tridacna spp, but not the largest
species, T. gigas) occur extensively in the lagoons of both Bok-ak and Pikaar. The author
has never observed such high giant clam densities elsewhere in the central west Pacific.
Furthermore, extensive sea turtle nesting and swimming activity was reported at Pikaar.

Toke Atoll is more properly intermediate in form between the semi enclosed atoll
and open lagoon atoll groups. Like Bok-ak and Pikaar, Toke atoll has a single narrow
pass on the western side. Unlike the other two atolls, Toke’s lagoon is deep and lacks
the ribbon reef formations. Lagoon patch and pinnacle reefs are more circular in form,
and lagoon reefs are not elevated above mean low tide levels as noted for Bok-ak and
Pikaar. Giant clam populations at Toke are smaller but include live specimens of the rare

82

largest species, Tridacna gigas. The only sighting of a hawksbill sea turtle during the
expedition occurred in northeast Toke lagoon. Although uninhabited, Toke is near Utrdk
(Utirik) Atoll. The owners of Toke Atoll reside at Utrok, and Utrdk fishermen
occasionally visit Toke to harvest fish and shellfish. Small boat navigation through the
channel and landing small boats at islands along the lagoon shorelines are relatively safe.
Several important reef areas of special interest due to good coral development and
diversity were observed at Toke Atoll.

Jemo is one of only five table reefs in the Marshalis and the only one which was
visited. Due to the lack of a lagoon, and heavy exposure to ocean waves and swells from
virtually any direction, Jemo’s reefs have unusual geomorphology and limited coral
development. Only the southwestern end of the reef is shallow enough to form a reef flat
exposed at low tide, upon which Jemo Island is situated. Elsewhere, Jemo’s reef crest
does not emerge at mean low tide and is dominated by a curious but extensive network
of sand covered surge channels oriented in a north-south axis

The outer reef margins consist of scoured sloping pavements with limited coral
growth. Coral species diversity is low, less than half of that of the other areas surveyed,
and is probably controlled by exposure to heavy waves and limitations in habitat diversity
and abundance. The very steep, deeper reef slopes showed higher coral diversity. The
best coral development occurred within a semi-protected reef indentation on the north
side. Jemo’s beaches support the second largest sea turtle nesting population observed
in the Marshalls (only Pikaar’s population is reported to be larger). Jemo island itself is
relatively inaccessible due to hazardous reef conditions, lack of protection from waves,
and the lack of a safe approach to the island except during calm seas. The numerous
sharks and large swells would also discourage snorkeling and diving interest at Jemo.

Wotto, Rondik, and Adkup are the largest of the atolls visited during the
September 1988 expedition, but are relatively modest in size compared to many other
atolls in the Marshalls. All three have large passes, deep open lagoons, and a diverse set
of lagoon and ocean reef habitats. Wotto and Rofdik in particular have unique and
aesthetically interesting coral and beach habitats, including pink sand beaches. A blue
coral reef moat occurs at Rofidik, and diverse and flourishing coral and clam habitats
occur at Wotto. Boat passage through channels and lagoon access to islands are safe.
The inhabitants of Wotto have expressed strong interest in promoting tourism at their atoll
and prior to our expedition, requested financial and technical assistance to develop a
tourism facility.

From the standpoint of uniqueness of reef forms, Bok-ak, Pikaar, and Jemo all
warrant special recognition and research interest. The huge giant clam populations at
Bok-ak and Pikaar, and the large sea turtle nesting populations at Pikaar and Jemo also
argue for marine and island reserve designations. When coupled with the extraordinary
seabird nesting populations at Bok-ak and lesser but important bird populations at Pikaar
and Jemo, all three areas should be established as part of a system of national ecological
reserves (Thomas et al 1989). Such designation will require the cooperation of persons

83

with traditional rights to these areas. All three of these areas are unsafe with respect to
boat access and landing, which reinforces their preferred status as limited entry reserves.
In particular, the clam and turtle populations would be vulnerable to over exploitation,
and access to the three areas should be strictly controlled in any case.

Proposals to enlarge or widen the reef passes at Bok-ak and Pikaar to promote safe
boat access would result in major and perhaps catastrophic impact to lagoon reefs. Aside
from direct destruction of reefs, low tide water levels in the lagoons would probably drop,
exposing and killing the living tops of elevated reefs throughout the atolls’ lagoons.
Circulation in the lagoons would also change and possibly harm resident giant clam
populations.

Toke and Wotto Atolls seem well suited as possible national marine parks open
to both tourism and resident recreational use. Residents could manage and monitor the
areas as marine parks, perhaps as part of small scale tourism development. Access and
landing at both atolls is relatively safe, accessible snorkeling areas exist, and diversity and
development of coral reef environments is high. Although residents expressed strong
interest in tourism and marine park development at Wotto, it was not possible to query
the Utrok islanders on their views for similar development at Toke. Nature based tourism
and park use would benefit the natural and cultural resources in both areas if properly
planned and managed.

Adkup and Rofidik atolls likewise have many attributes supporting marine park
designation. Adkup, although uninhabited, is heavily utilized as a traditional harvest
("pantry") area by visiting fishermen and islanders from nearby Wotje Atoll. Any future
designation of portions of Adkup for marine park and sanctuary status should reflect the
coordination with and the views of the traditional resource users and owners. Although
specific areas of both Adkup and Rofidik are suitable candidates for marine parks or
reserves, there is less justification to designate the entire atolls as reserves or parks.

Western Rondik Atoll could not be surveyed, but Bok (Bock) island is suspected
as an important sea turtle nesting area due to its extensive white sand beaches. Follow-up
observations could confirm the importance of the island for turtle nesting. Rondik Atoll’s
pink sand beaches, blue coral moat, and luxuriant lagoon coral formations would be of
great recreational interest to both visitors and residents.

The large populations of coconut crabs at Rondik may eventually be heavily
harvested since coconut crab is a favorite islander delicacy. However, Rondik was
exposed to fallout from the "BRAVO" atmospheric thermonuclear detonation at nearby
Bikini Atoll in 1954. Fallout from the blast contaminated Bikini and the atolls of Ronlap
(Rongelap) and Utrok. Given the close proximity of Rondik to these other atolls, a
radiological survey of the atoll is warranted to determine possible health hazard from
ingestion of crabmeat and coconuts. Coconuts are known to concentrate the radionuclides
cesium-137 and strontium-90 in their tissues, based upon sampling of coconut trees at
both Bikini and Ane-wetak (Enewetak) Atolls conducted by Lawrence Livermore

84

Laboratories. Since coconut is the preferred food of the crabs, radiological contamination
of coconut crabs is a definite possibility. Consumption of Rofdik coconut crabs should
therefore be discouraged until radiological tests have determined the crabs are safe to eat.

85
VI. ACKNOWLEDGEMENTS

This study of reefs and corals was part of a joint project of the South Pacific
Regional Environment Programme (SPREP), the East-West Center Environment and
Policy Institute, the U.S. government, and the Republic of the Marshall Islands (RMI) to
assess the ecological and cultural conditions of selected reefs and islands in the Northern
Marshalls to determine their suitability as candidates for a system of the RMI protected
areas. The study was requested by the government of the RMI. Substantial financial
support for the project came from a grant from the John D. and Catherine T. MacArthur
Foundation, and matching support was provided in the form of scientific participation by
the U.S. Army Corps of Engineers, the East-West Center, the National Marine Fisheries
Service, and the U.S. Fish and Wildlife Service. This project also contributes to the RMI
Coastal Inventory and Atlas program supported by U.S. Congressional appropriations to
the U.S. Army Corps of Engineers and as described in the RMI Plan of Action for Water
Resources (OEA, 1989).

A number of officials in the Republic of the Marshall Islands provided critical
support for the project: we thank Peter Oliver, Special Assistant to the Chief Secretary;
Oscar De Brum, Chief Secretary; the late Stephen Muller, Director of the RMI Marine
Resources Authority; Larry Muller, Captain of the patrol vessel Ionmeto I, and the vessel
crew; Gerald Knight, Director of the Alele Museum; Alfred Capelle, RMI Resource
Protection Officer; Abacca Anjain, Acting Secretary of Interior and Outer Island Affairs;
and the atoll owners and land managers (alab) for granting access to their island and
reefs. We thank the project leader, Dr. Lawrence Hamilton, Research Associate, EAPI
for administrative support, and the late Dr. F. Raymond Fosberg of the Smithsonian
Institution for sharing his extensive experience and advice on the Marshall Islands.
Finally, I extend my appreciation to the other members of the expedition who assisted on
the marine surveys, especially Peter Thomas, Virgil Alfred, Paul Maddison, and John
Naughton; and to Linda Mizuguchi, Karen Tomoyasu, Chris Cabacungan, Jan Eber, Jody
Oyama, Jennifer Gorospe, Mary Hayano, Gidget Tsui, and Karin Z. Meier for word
processing and/or editing support. I thank Jim Laurel of Aspect Software Engineering
Inc. and Karin Z. Meier of CORIAL for digitizing the maps, and preparing most of the
map figures for this report. Finally, I thank Mr. Alfred Capelle for providing the correct
spellings of place names used in the text and added to the maps.

86
VII. REFERENCES

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Atoll: Feasibility and Estimated Cost of Meeting the Federal Radiation Protection
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Bikini Atoll Rehabilitation Committee, 1985. Report No. 2 FY 1985. Submitted to the
U.S. Congress, House and Senate Committees on Interior Appropriations.
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Bikini Atoll Rehabilitation Committee, 1986. Report No. 4 Status March 31, 1986.
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Dahl, A.L., 1980. Regional Ecosystem Survey of the South Pacific Area. Technical
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Devaney, D.M., and J.C. Lang, 1984. Scleractinia (Stony Corals) of Enewetak Atoll (pp.
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The Ecosystem: Environments, Biotas, and Processes. DOE/EV/007-03-TI-Vol
1: 228 pp.

Emery, K.O., 1948. Submarine geology of Bikini Atoll. Bull. geol. Soc. Am. 59:855-
860.

Emery, K.O., J.I. Tracey and H.S. Ladd, 1954. Geology of Bikini and Nearby Atolls.
U.S. Geol. Survey Prof. Pap. 260-A.

Fosberg, F.R., 1988. A review of the Natural History of the Marshall Islands. Prepared
for East-West Center/MacArthur Foundation Project, June 1988, unpubl. 115 pp.

Fosberg, F.R., T. Arnow, and F.S. MacNeil, 1956. Military Geography of the Northern
Marshalls. Prep. for the Chief of Engineers, U.S. Army by Intelligence Division,
Office of the Engineers, Headquarters, U.S. Army Forces Far East, Eighth United
States Army, and U.S. Geological Survey. Tokyo, 320 pp.

Ladd, H.S., J.I. Tracey, J.W. Wells, and K.O. Emery, 1950. Organic growth and
sedimentation on an atoll. J. Geol. 58(4):410-425.

87

MacNeil, F.S., 1969. Physical and Biological aspects of atolls in the Northern Marshalls.
Proc. Symp. Corals and Coral Reefs. Mar. biol. Assoc. India, pp 507-567.

Lamberts, A.E. and J.E. Maragos, 1989. Observations on the reefs and stony corals of
Majro Atoll, Republic of the Marshall Islands. In: Majro Coastal Resource
Inventory, prep by Univ. of Hawaii Sea Grant Extension Service and the U.S.
Army Corps of Engineers Pacific Ocean Division, Environmental Resources
Section, in press.

Maragos, J.E., 1990. Observations on the corals and reefs of Bikini Atoll 30 years after
termination of the U.S. nuclear weapons testing program, in preparation.

Maragos, J.E. and A.E. Lamberts, 1989. Observations on the reefs and stony corals of
Arno Atoll, Republic of the Marshall Islands. In: Arno Atoll Coastal Resource
Inventory. prep by the Univ. of Hawaii Sea Grant Extension Service and the U.S.
Army Corps of Engineers, Pacific Ocean Division, Environmental Resources
Section, in press.

Odum, E.P. and H.T. Odum, 1956. Zonation of corals on Japtan Reef, Eniwetok Atoll,
Atoll Res. Bull 52:1-3.

Rongelap Assessment Project, 1989. Report, Corrected Edition March 1, 1989: prep
pursuant to the Compact of Free Association Act of 1985 and Administered by the
Republic of the Marshall Islands. 1203 Shattuck Ave., Berkeley, CA 94709 (this
is also the address for Bikini Atoll Rehab. Comm. reports).

Thomas, P.E.J. et. al., 1989. Report of the Northern Marshall Islands Natural Diversity
and Protected Areas Survey, 7-24 September 1988. South Pacific Regional
Environment Programme, Noumea, New Caledonia, and East-West Center,
Honolulu, Hawai, 133 pp.

Tracey, J.E. Jr., H.S. Ladd, and J.E. Hoffmeister, 1948. Reefs of Bikini, Marshall Islands
Bull. geol. Soc. Am. 59:861-878.

Veron, J.E.N., 1986. Corals of Australia and the Indo-Pacific. Australian Institute of
Marine Sciences, Townsville.

Veron, J.E.N. and M. Pichon, 1976. Scleractinia of Eastern Australia, Part 1: Families

Thamnasteriidae, Astrocoeniidae, Pocilloporidae, Austral. Inst. Mar. Sci. Monogr.
1:1-86.

Veron, J.E.N., and M. Pichon, 1980. Scleractinia of Eastern Australia. Part II]: Families
Agariciidae, Siderastreidae, Fungiidae, Oculinidae, Merulinidae, Mussidae,
Pectiniidae, Caryophylliidae, Dendrophylliidae, Austral. Inst. Mar. Sci. Monogr.
4:1-422.

88

Veron, J.E.N., and M. Pichon, 1982. Scleractinia of Eastern Australia, Part IV:
Family Poritidae, Austral. Inst. Mar. Sci. Monogr. 5:1-159.

Veron, J.E.N., M. Pichon, and M. Wijsman-Best, 1977. Scleractinia of Eastern
Australia. Part II: Families Faviidae, Trachyphyllidae. Austral. Inst. Mar.
Sci. Monogr. 3:1-233.

Veron, J.E.N., and C.C. Wallace, 1984. Scleractinia of Eastern Australia, Part V:
Family Acroporidae, Austral. Inst. Mar. Sci. Monogr. 6:1-485.

Wells, J.W., 1954. Recent Corals of the Marshall Islands, Bikini and Nearby
Atolls, Part 2, Oceanography (Biologic). Geological Survey Professional
Paper 260-I, U.S. Government Printing Office, Washington D.C., pp. 385-
486 + pls 94-187.

Wells, J.W., 1951. The coral reefs of Arno Atoll, Marshall Islands. Atoll Res.
Bull. 5:56 pp.

Wells, J.W., Coral Reefs, In: Treatise on Marine Ecology and Paleoecology. J.
Hedgepeth (ed.). Geological Soc. of Am. Memoir 67.

Wiens, H.J., 1962. Atoll Environment and Ecology. Yale University Press, New
Haven, Connecticut, 532 pp.

U.S. Dept. of Defense, Office of Economic Adjustment, 1989. Republic of the
Marshall Islands, Water Resources Plan of Action prepared by U.S. Army
Corps of Engineers Pacific Ocean Division, Honolulu, 64 pp + 21
appendices.

Appendix A.

Fig. A-1l
BOK - AK Atoll
REEF PROFILES: LAGOON AND PASS REEFS

+0.5m

Spondylis Es

hard abundant Tridacna spp

SITE 1B 4m coral reef & Hippopus
sand
sand
SITE 1D ee
large Tridacna spp hard reef &
Pa live coral
populations
3m
+0.5m
sand
hard coral
6m
live coral sand
SITE 1N
15m
TOP VIEW OF BOK-AK PASS
lagoon entrance
SITE 1R1 sire ik

gene (TOP VIEW)
scoured hard reef lagoon Ligne ss
interior from lagoon heads

1R2 Coral

scoured bottom
mid point
NORTH wae

0
REEF om )

1R3

reef

rubble

: . slump blocks
interior from ocean

ak ard hard reef rock
reef rock Beean
rubble trench

ocean entrance

1R5 ars

scour trenches of hard reef rock
& some rubble

CROSS SECTIONS OF BOK-AK PASS

FIG A-2

REEF PROFILES: EASTERN PERIMETER REEFS
BOK - AK Atoll

celagoon +1m ocean
NE SITE 1A sic sated Pa iat
coral head
sand pavement

pavement encrusting
SITE 1c

; corals
Holothuria at

rubble tract ztdge

SITE
eard live coral 1L
overhang
ocean ~» SITE 1M1
live coral
rubble XN coraliine SITE 1M3
ocean &
ocean» live
sand sand coral
overhang
dead
pane coral
ocean (southeast)
sand
SE 3-4m
Pinctada margarjti
mounds sand
; ocean >
Many Tridacna spp
microatolls
SITE 1F coral sand heads pabbie
sand head

SITE 1G

SITE 1H

reef wall

live coral

Halimeda

Bana sand sand
an

FIG. A-3
BOK - AK Atoll

SITE 1T

ocean

30m

25m

30m

SITE 19

REEF PROFILES: WESTERN PERIMETER REEFS

Coralline algal dam

spillway

coralline alage

live coral

SITE 1K

ribbon
reef

SITE 1J

Coralline
Canyon wall. ~ SITE 1S
YE algal
— canyon floor gamis
Y spillway
SITE 10

coralline algae +0.5m
spillway sacs
90% live coral cover on slopes
1m
SITE 1T eras
1P

coralline algae

90% live coral

on slopes

A-4

FIG. A-4
PIKAAR ATOLL REEF PROFILES: PERIMETER REEFS
NORTH
SS 1
= SITE 2F1 im 2F2 2F3
coral coral
overhangs
4m
live
reef pavement coral
pavement
WEST sand

SITE 2H

spillway sand chute

shingle

spillwa SITE 2L

coral-algal dam ‘
shallaw coralline algae
spurs &

grooyes~

Halimeda

live coral
SITE 2M

live cora

ocean (SE) —=

EAST 1m
reef pavement

SITE 2B
corals

hard reef
5m

sand
ocean (E)—>

1m
SITE 2D 1570
micro-atolls
reef
pavement

hard reef pavement
sand

0.5
as SITE 2E

pavement

F F corals
Dictyosphaeria

2.5m reef

hard pavement

FIG. A-5
PIKAAR ATOLL REEF PROFILES: LAGOON REEFS & PERIMETER REEF

LAGOON

2C i
STE coralline

algae

corals

; Qe
Dictyospheria

live finger coral

SITE 2G

live coral

SITE 21

coralline
15m
small Tridacna

abundant

ee

sand

SITE 23

dead cora

& live coral
<— lagoon

SITE 2K
talus
sand slope

5m

SOUTH (PERIMETER)
SITE 2A sw
~~ coral ocean reef flat
island
corals coral
sand

chute

FIG. A-6
2 REEF PROFILES: PERIMETER REEFS
TOKE ATOLL
a z Simoes
EAST Dictyosphaeria
(ocean)
SITE 3A pavement and rubble
coral
Culcita
_ 0.5m
7m
sand reef pavement
2m
SITE 3C ile taza rubble blue coral coral
OrSne es
2 XX
SITE 3D m . rubble
mixed corals pavement
staghorn
coral
< EAN aa
ee SITE 3F SE

sand cay
mixed coral &

reef pavement

hard coral beach
sand chute

lm sand

N—> (OCEAN)

NORTH
coralline algae
& corals

SITE 3G

live

live coral

SITE 3H

sand dune

WEST

live coral

Dictyosphaeria

SITE 31 coral

sand

FIG. A-7
- REEF PROFILES: WESTERN PERIMETER AND LAGOON REEFS
TOKE ATOLL
WEST
im
live coral staghorn
4m
staghorn coral
coral
ITE
3 Ses sand and
rubble eee
table coral
deep reef live coral
pool
SITE 3K
sand 10h
3m
coralline
, algae & live
SITE 3L Tavencoral coral

sand sand Bel ~ sand

LAGOON live coral
SITE 3B
Grane! im sand
live coral
SITE 3E

(Porites)

20m
20m

sand

A-8

FIG. A-8
JEMO REEF PROFILES: OCEAN SLOPES
3
hard reef pavement & Sens.
< NW
scattered corals
live corals
a
50% cover wy
3m
SITE 4C
Zi scoured reef pavement
45m 7 shallow channels
= W
SITE 4A 10-25% live coral cover

=o j[=e = isha =~ (SETE 4D
sand bottom
surge channels

scoured reef pavement

sharks

live coral

pavement

6 N 11m

high live trough

pavement
coral cover

SITE 4E
SITE 4F =< SE
coral terrace
4 pavement and live corals
<«s my ee

SITE 43

1

SITE 4H pavement

canyon /

“
4 5m

“ SITE 41

wall & some
live coral

overhang

aon pavement

20m

“ shallow SITE 4L-2
channels

ELS Cs corals & hard reef 40m

SITE 4L-1

FIG. A-9 REEF PROFILES: NORTH AND EASTERN PERIMETER
WOTTO ATOLL
REEFS
NORTH Ta RA IR Eee ELAS oS ST Ocean (N) ->

table and staghorn Caulerpa

Tridacna gigas corals en
Halimeda 50-60% coverage ee
sand
Bielad ate
—
Holothoria ere
edulis Bal
— — sand oPe
—— ew
10m —a SITE 5B
small Hippopus Se
3m 2m
coral
reef flat
(N) Ocean <&—
Holothuria
Dictyosphaeria Stichopus
Ba 10m cig SITE 5C
live reef rock coral
ba sand
coral aS nd
staghorn
rubble
———Yeéérf fiat rock
coralli

& coral — N (ocean)

corals

Dictyosphaeria

2m

s
SITE 5E and rubble

ey
SITE 5D om
sparse

corals

SITENSF 3m 2m hare reef pavement

A-10

FIG. A-10
WOTTO ATOLL REEF PROFILES: EASTERN AND SOUTHERN PERIMETER REEFS
EAST 2m lagoon (W)
8m eef rock
SITE 5G ovexys
and rubble turn XXX
10m
Coral
xe staghorn coral sand
3m ne
8m
SITE 5H coral mound
coral
sand
— lagoon (W)
am coral
und coral 2m In
te
mound over turned ——_— rubble

back re slope
eS

SOUTH

3m 2m coral

SITE 5J mound coral
fine sand

5m coralline aw

10m
SITE 5K
———
4m
Jp Se ee eee

coral

head corals, sand

& rubble
15m

A

A-11

FIG. A-11
RONDIK ATOLL REEF PROFILES: SOUTHEAST PERIMETER REEFS

SOUTH

SITE 6A <<— Ocean (S)

ck reef slope
Ss

hard coral x e staghorn
pavement head & coral

take coral sand

pinnacle

cpa ae See cp ~ (S) Ocean-=

SITE 6B (plex an
blue cora

hard

6m __ coral heads
= pavement

fine sand

Acropora palifera
(S) Island —7

Re hie beach

SReEUce coralline algae
beach rock
4m undercut lip
en coral heads
rubble & tables
sand
EIST trough avement
EAST g P
SITE 6D ee
rilled reef
2m
ere pavement
Am VA om sand SEO atoll
: y sand corals
eee coral heads
sand
Ocean (SE)=>
~~ coral head nie
SITE 6E rilled
SG lei Pavement
Ga gravels
4m \————_" staghorn
sand
coral
sand ripples table
corals
, . im canis
SITE 6F Tridacna & Hippopus beach

beack rock sand
sand

live
corals coral

sand

A-12

FIG. A-12

RONDIK ATOLL REEF PROFILES: NORTHEAST PERIMETER AND LAGOON REEFS

: SITE 6G1
lagoon (W) >

blue cora

sand &

mt rubble
SITE 6G2
bank
sand
aS sand channel
0.5m
SITE 6H
island

sand channel

island
SITE 6L coralline scoured
algae reef
corals
6
oH coral table sand ee ee
Sand
‘ mound corals
ripples
SITE 6I

crest of reef pinnacle

coralline algae

on 90% live coral

15m
SITE’ 6J

cover

15m

live coral mound

sand slope

back reef SITE 6K

pavement
2m microatolls

rubble corals

live corals

SITE 6K

6m coral

rubble
staghorn table

coral
mounds
sand

A-13

FIG. A-13
ADKUP ATOLL REEF PROFILES: SOUTHERN PERIMETER REEFS

coralline algae

SITE 7Al1
and corals

head

SITE 7A2

coralline algae and corals

sand staghorn sand

sts coral slope

BD Legions coral heads rubble beach rock

& mounds island
Halimeda

SITE 7B

lagoon (N)

—_——_____ i eastep ai == cin ne

reef pavement

SITE 7C

microatolls table rubble

coral

<— lagoon (N) Te eo Tae coe en ee —

3m

microatolls pavement SITE 7D

blue corals

steep sand Ocean (E) >»
slope -_-—— 2m

SITE 7E

steep mostly dead corals and rubble
table coral
sand dead)
slope (dea

Ocean (E)—>—

reef pavement

coral heads
SITE 7F

A-14

FIG. A-14
ADKUP ATOLL REEF PROFILES: NORTHERN PERIMETER REEFS
are oe a 0 | na ocean (NE)
SITE 7G1 =

coralline algal ocean (NE)>
a
staghorn pavement
coral

Halimeda
ee coralline algae

SITE 7G2
corals (40% cover rubble
on slope) coral coverage
finger coral
10m 20%
dead coral sane py go ie 0.3
ae ee OES

15m

sand talus

microatolls

SITE 7H 1.5m corals

rubble coral coverage 15%

reef flat corall

—> ocean (E)

F ~ algae Pass 4m
f 7
ingens aS SITE 7J3 =
sand
lagoon hard pavement
with scour, hard corals
SITE 71 and soft corals
talus
side to side cross section in pass
ocean end
corals
hard scoured pavement
with some corals
d igh
high lagoon en hig
corals
corals
SITE 7K

———

sand

staghorn coralline

coz coral algae & Porites lutea

Hippopus SITE 7L

dead coral coralline algae

high 50% coverage of the live corals
live
coral

sand talus

sandwedge

coral hora

coral

dead 1 Zupps avement
aie reef lip # SITE 7M

10% coverace of live corals

sand talus

Appendix B.

Definitions for relative abundance terms used in the field for corals

SYMBOL

D

TERM

dominant

abundant

common

occasional

rare

DEFINITION (WITHIN
A_ ZONE OR HABITAT

TYPE ON THE REEF)

the coral constitutes a
majority in abundance or
coverage (50% or more
of total)

the coral contributes
substantial abundance or
coverage, or 1S very
numerous

coral present as several or
more individuals or as a
few larger colonies

uncommon, present only
as a few individuals, or
present as a single
conspicuous individual

reported only once as a
single individual

DEFINITION (FOR THE
REEF SITE AS A

WHOLE)

the coral contributes
substantial abundance or
coverage (25% or more
of total) or is conspicuous
in all zones

coral is conspicuous in
most zones or is
dominant within a single
zone

coral conspicuous in only
one or a few zones or
locally substantial in a
single zone

present more than once
but not substantially
within a single zone

reported only once from
the reef

C-1
Appendix C.

Map sources for selected northern Marshall atolls.

AMS = Army Map Service Series W861 (all at scale 1:25,000, except Wotto which has
a scale of 1:50,000).

DMA = Defense Mapping Agency charts (various scales).

ADKUP (ERIK UB)
AMS - 8249 I SW, II NW, SW, III NE; IV NE, SE
DMA - none

BOK-AK (TAONGI)
AMS - 8066 III NE, SE; IV SE
DMA - 81626A (1:50, 190)

JEMO
AMS - 8152 III SW
DMA - none

PIKAAR (BIKAR)
AMS - 8258 IV NW, SW
DMA - 81626B, C (1:10,110; 1:50,200)

RONDIK (RONGERIK)
AMS - 7755 IV NE, NW, SE, SW
DMA - 81557A (1:50,000)

TOKE (Taka)
AMS - 8155 III NE, NW, SE, SW
DMA - 81616A (1:10,000; 1:50,310)

WOTTO (WOTHO)
AMS - 7352 II (1:50,000)
DMA - 81030C (1:316,120)

ALINGINAE
AMS - 7455 Il NW, SE, SW; III SE
DMA - 81557B (1:72,500)

Appendix D.

Index of aerial photographs consulted during the study from 1978 color (EG&G) and
1944-1945 black-and-white U.S. War Dept. (VD3) sources, the latter at the Bernice P.
Bishop Museum Map and aerial photo collections, Honolulu.

RONDIK (RONGERIK) ATOLL
EG&G Roll 8, perf 2234: frames 59-60, 62, 70-79, 82-90, 93-95, 101-110 (35 negatives,

scale 1:30,000; 16 Aug 1978)

VDB - oblique aerial photos only

TOKE (TAKA) ATOLL
EG&G Roll 7, perf 2205: frames 22-23, 102-106, 110-123, perf 2185: frames 208-216 (38

negatives, scale 1:30,000; 11 Aug 1978)

VDB - p. 40316-36 frames 1-14; VD3-AP47A figures 1-41; and VD3 - AP47B
photomosaic (55 negatives, scale unknown; 5 March 1944)

PIKAAR (BIKAR) ATOLL
EG&G Roll 12, perf 2305: frames 9-94, 98-103, 121, 123, 125, 137-139 (16 negatives,
scale 1:30,000; 8 Aug 1978)

VD3 - oblique aerial photos only

WOTTO (WOTHO) ATOLL
EG&G Roll 10, perf 2259: frames 4, 6, 8, 10, 54, 56-59, 108-109, 116-118, 134-138, 153-
157, (24 negatives, scale 1:30,000; 18 Aug 1978)

VD3 - AP41B frames 1-39 (39 negatives, unknown scale; 29 Feb 1944)

JEMO
EG&G Roll 1, perf 2096: frames 33, 35, 36 (3 negatives, scale 1:30,000; 29 July 1978),
Roll 2, perf 2122: frame 150 (1 negative, scale 1:8,000; 5 Aug 1978)

VD3 - oblique aerial photos only

ADKUP (ERIKUB) ATOLL
VD3 - AP16A frames 1-8 and VD3-AP16B frames 1-2 (10 negatives, unknown scale; 4

Feb 1944)

BOK-AK (TAONGI, POKAK) ATOLL
VD3-12, frames 1-10 (10 negatives, unknown scale; 28 Mar 1945)

Sey He PCTS: ii ats cig ee Nae at a eoes erent 12 pe “t

i ee ae AaeeS BA Ul a
FN Pte ea ‘6 i aaiiiet :
ae ie 2 aa aRR OT zi
yy mE) Fae | ’ A
A isa | se) ie > : ‘
: ¢ Fie - Tinne 2 we rr -
ved SESE SET A y af ‘ cf i eel YVxten Ny ' A oe $E-G Snrieket es eae
a) i soe hae pee te ni aD ert d ep ee : ciiry ARAL
. asi ESE RS STAN,
7 f = i ; A
Maik a4 D ‘a 7 e. : ee ; ae a
: ey ; - aes ra f c ‘URC aK ny ty ATIZR “ij wy
t - a a ve PoP "4 4 th ‘ a4 - sf ; ee i 4 “pi
is ‘ if — =
LIOTTA KOU
PEA BET-RED Bil -OEt MO aU) VEae pe wt 80 Sm ClsS ag,
EOE S UN Sai acl BL on Mok giaiyitia
f 4 é: ¥ ¢ -
' { 4 : 2 as ity rs | i . 4 Ji ) e) ' bv ER oD
5 tf 4 ;
% ; ° uf ‘ ;
% aris OEE toe (eerie ade EF assinat (a0Us +
’ sir ‘g
8 ~ ae
LIOTTA te

a ar So
F, AACS ay
(Pay vesrenyity Virose OEY eT |

ATOLL RESEARCH BULLETIN

NO. 420

QUATERNARY OOLITES IN THE INDIAN OCEAN

BY

C.J.R. BRAITHWAITE

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

~- 20cotra

=

- Sri Lanka
ee Swaine
Loe”

: ¢ Seychelles # Chagos

Cele Aldabra
* | Madagascar

WESTERN

INDIAN
OCEAN

> Mauritius.
2? ‘Rodrigues
Reunion

Fig. 1 General map of the Indian Ocean indicating positions of the principal locations
referred to in the text.

QUATERNARY OOLITES IN THE INDIAN OCEAN
BY

C. J. R. BRAITHWAITE
ABSTRACT

Aeolian calcarenites from Rodrigues in the Western Indian Ocean include oolites.
No recent oolites are recorded in the Indian Ocean and there is only one other Pleistocene
record. The calcarenites are compared with deposits in the Seychelles, East Africa, India,
and South Africa which consist of marine-derived bioclasts. In general they indicate critical
water depths over generating shelves and thus particular stages in sea-level change. They
are characteristic of both early phases of cooling and later stages of warming events. There
seems to be no explanation for the restricted distribution of oolites in the Indian Ocean.

INTRODUCTION

Aeolianites are widespread in the Pleistocene deposits of the Western Indian Ocean.
Those on Rodrigues are unusual in that those on the east coast consist of oolites with a
relatively small bioclastic component. With the exception of deposits in Kathianar in India,
described by Chapman (1900) and Evans (1900), these are the only oolitic deposits known
from the Pleistocene or Holocene of the Western Indian Ocean.

FIELD DESCRIPTION

Rodrigues lies about 650 km east of Mauritius, Lat. 19° 42' S, Long. 63° 25'E
(Fig. 1). It is approximately 18.3 km long and 6.3 km wide, consisting predominantly of
young undersaturated basalts erupted between 1.5 and 1.5 million years ago (McDougall et
al. 1965). The south-eastern and south-western margins of the island are blanketed by a
discontinuous cover of cross-bedded calcarenites (Fig. 2). These were known a hundred
years ago when they were described by Balfour (1879) and Slater (1879) who visited the
island during the Transit of Venus expedition to make observations on the general geology.
Their reports describe caves in these limestones in which the bones of the Solitaire and
other flightless birds were found.

Although Rodrigues has a surface area of only about 120 km? the platform on
which it rests is at least 1650 km2. The island surface slopes gently outwards to about 100
m depth before plunging into deeper water. The island is bordered on its south-western
coast by a fringing reef 4-8 km from the shore and Admiralty Charts show that the lagoon
area within this is generally very shallow (McDougall et al. 1965). However, the shallow
platform beneath extends a considerable distance both to the west and the east and, as will
be shown, probably played a significant part in the formation of the calcarenites.

Most of the calcarenites are bioclastic and were originally marine, but those in

Department of Geology and Applied Geology,
The University, Glasgow G12 8QQ, Scotland, U.K

Manuscript received 23 April 1993; revised 28 June 1994

2

south-eastern localities (Pointe Coton, Trou d'Argent) are clean-washed oolites. In both
south-eastern and south-western areas grains are well rounded and well sorted within
individual laminae. Cliff sections show well-defined high-angle cross bedding in sets of
up to 10 m, forming cosets locally of more than 20 m thickness (Figs. 3 and 4). Cross-
laminae dip at angles up to 30-35° and set-bounding surfaces generally dip a few degrees
in a seawards, (generally southerly) direction. In some areas the upper margins of dunes
are full of casts of branching root systems which imply colonization by substantial trees.
There are, however, no distinctive terra rossa or palaeosol deposits and plants must have
grown in unconsolidated sand before and perhaps during cementation. —

The thickness of the calcarenites is quite variable. In western localities they blanket
a gently undulating ramp, while in the east they occupy an erosional bench cut into the
underlying basalts. Significantly, in both areas basal surfaces appear to extend below
present sea-level. McDougall et al. (1965) recorded these limestones as occurring at more
than 60 m above present sea-level, while Snell and Tams (1920) claimed that they extend up
to 500 ft (165 m). Present observations suggest that the lower figure is more realistic. The
thickest sequences are found in the south-west of the island in the area of Caverne Patate
where Cave systems penetrate at least 30 m of limestone. Montaggioni (1973) suggested
that typical thicknesses are 15-20 m).

McDougall et al. (1965) thought that the depositional morphology of the calcarenites
had been obscured by recent erosion. In fact, low dune ridges can be seen in south-western
areas and air photographs reveal a spectacular series of parallel dune crests facing north and
north-east and having a wave length of from tens to hundreds of metres. These extend for
several kilometres from the present shoreline (Fig. 5). Groups of steep foreset laminae are
visible on air photographs and can be traced across outcrops. Interdune areas are less
conspicuous and are characterized in limited outcrops by low angle lamination and shallow
troughs.

PETROGRAPHY

The oolites have a mean diameter of about 300m (medium sand), many nuclei are
dark micritic peloids while others are bioclasts. Cortical layers have the tangential structure

typical of recent aragonitic ooids and may be more than 100um thick (Fig. 6). Bioclast
calcarenites consist predominantly of foraminifera, including Marginopora and
Heterostegina, together with echinoderm plates, calcareous algal fragments (cf. Goniolithon
and Halimeda), mollusc shell and coral fragments. In the samples examined grains have a

mean size of 400-800uUm. The marked contrast in grain typebetween oolitic and bioclastic
rocks are paralleled by differences in mineralogy and diagenetic history. The bioclastic
limestones include both aragonite and calcite (identified by X-ray diffraction) but have only
a sparse fine-grained blocky calcite cement. This is restricted to patches where it forms
meniscus bridges between grains and occasional pendant drops, suggesting deposition in
the vadose zone, although it lacks the fibrous or prismatic textures typical of such
environments. By contrast, in oolites, the ooliths themselves consist of aragonite and they
are commonly embedded in a coarse blocky calcite cement which may completely fill pores
and locally extends inwards from grain surfaces as a neomorphic replacement of the original
tangential structure.

INTERPRETATION

The distinctive high-angle lamination which characterizes the calcarenite deposits on
Rodrigues, and the occurrence of calcarenites over such a range of altitude, seems to

3

confirm an aeolian origin. Submarine sand-waves might be of similar size but would
generally be expected to have lower angle cross-bedding and are unlikely to have
accumulated over such a slope. They would, moreover, have had to be related to a sea-
level more than 60 m higher than at present. Deposition of these rocks must have occurred
at a time when sea-level stood lower than at present, perhaps by about 10 m. However,
the sediments were of marine origin and reflect generation in shelf environments. Thus,
sea-level must have been high enough to maintain a permanent water cover over a
sufficiently large area. The large area of gently-sloping surface beneath present reefs would
have ensured that a suitable shelf was present over a range of sealevels, although not during
the glacial maximum. Grains generated within the shelf were swept onshore by storm
waves and accumulated as beach and, ultimately, dune deposits, the latter probably
migrating several kilometres from the shoreline. Correlation with a lower sea-level implies
a general correlation with a cooler climate.

THE AGE OF THE DEPOSITS

Two different calcarenite types are present on Rodrigues and since lithological
variations are paralleled by diagenetic differences the rocks are likely to be of at least two
different ages. Montaggioni (1970) referred to three separate dune assemblies in the
eastern area but these have not been identified here. The calcarenites have not been
precisely dated but it is clear that they are not Recent. The active phase of accretion was
followed by a passive phase of colonization by trees, and the whole assemblage has been
dissected by a mature karst system which, judging from the included fauna, is at least late
Pleistocene (see again Slater, 1879). However, the ages inferred for these deposits have
been determined by reference to associated limestones. Montaggioni (1970) regarded them
as of the same age as calcarenites on Mauritius. In this interpretation they should equate
with high sealevel stand dates of 230Th/234U ages of 120 15-20 ka obtained by Battistini
(1976) for Pleistocene limestones on Mauritius, which were compared in turn with dates of
160 £40 ka and 110 +40 ka given by Veeh (1966) and of 114 £6-7 ka and 104 +4-6 ka
given by Elbez (1976). However, none of these ages was obtained from calcarenites and,
for reasons of environment, it is unlikely that the aeolian calcarenites on Rodrigues were
contemporary with the marine deposits from which the dates were obtained. There are no
observations of rocks overlying the Rodrigues calcarenites and this contrasts with the
relative positions of aeolianites in Kenya (Braithwaite, 1984) and on Aldabra (Braithwaite et
al., 1973) which are probably substantially older (see below).

OTHER INDO-PACIFIC DEPOSITS

Within the western Indian Ocean aeolianites (calcarenites with characteristics similar
to those described) have been identified in a number of areas. In northern Madagascar
Battistini (1976) recorded dune-bedded carbonate rocks low in the Pleistocene. These
overlie his Recif I but appear to be older than Recif II, dated at 160 £10-15 ka. This dune
assemblage is said to be more than 200 m thick but only about 15 m are shown on the
published synthetic section extending for 25 km in the south. It is considerably thinner on
the north and east coasts. Like the deposits on Rodrigues the top is marked by non-
deposition, in this case resulting in a dissected erosion surface and what are described as
"decalcified pockets”.

In East Africa, calcarenites with high angle cross-bedding and consisting of marine-
derived grains are exposed on the northern coast of Kenya, south of Malindi, and in the
extreme south, near Shimoni and Wasini Island (Braithwaite, 1984). In both of these areas
the deposits are believed to extend below present sea-level but are stratigraphically above

4

coral-bearing marine limestones which were apparently the source of material dated by
Battistini (1976) as 240 40-70 ka. They are overlain by younger limestones which have
been described by Crame (1980, 1981) and which appear similar to the youngest coral-
bearing limestones on Aldabra. Aldabra has a small area of calcarenites with high angle
cross-bedding exposed on the south coast (Braithwaite et al., 1973). These are overlain by
two marine limestones, the youngest of which has been dated by Thomson and Walton
(1972) as forming between 118-136 £9 ka. It is this which is equivalent to the younger
coral limestone in Kenya. These calcarenites, in which grains are entirely of marine
bioclasts, formed when Aldabra was a shallow marine platform with only small sand cays
accumulating along what is now the southern coast and in a relatively large area to the
north-east.

The aeolian calcarenites of southern India have already been referred to (Chapman,
1900, and Evans, 1900). Knox (1977) described other calcareous aeolian dune deposits of
supposed middle to late Pleistocene age from Saldanha Bay in South Africa. These average
30 m in thickness but are reported by Visser and Schoch (1973) to be as much as 88 m
locally. Once more they consist predominantly of marine bioclasts.

DISCUSSION

The descriptions given reinforce the view that aeolian deposits are a common, even
characteristic, feature of Pleistocene limestone successions in the Indian Ocean. They are of
a variety of ages but have commonly (although not exclusively) formed in areas which do
not have present day dunes. It might be argued that winds were stronger in the past and
that the absence of present-day dunes is a reflection of the inadequacy of present day winds.
However, this is unlikely, Bagnold (1941) and Wolman and Miller (1960) have indicated
that in dune formation the net transport of sands is controlled more by prevailing winds
above threshold velocity than by extreme wind events. In almost all of the Indian Ocean
examples the sands were of medium to fine grade and therefore do not reflect excessive
wind speeds. Elsewhere, in Bermuda (Mackenzie 1964), aeolianites show palaeowind
vectors which are essentially the same as present directions while in the Turks and Caicos
islands (Lloyd et al. 1987) palaeocurrents in both Pleistocene and recent aeolianites (which
include oolites) can be related to south-easterly Trade Winds.

The presence of oolites remains enigmatic. Their formation, and that of the
bioclasts, was probably critically dependent on water depths over the generating shelves. If
sealevel is too high shelves are deeply flooded and unlikely to reach the necessary saturation
conditions. If it is too low shelves are restricted (or dry) and again fail to generate
sediment. Thus it seems that the oolites and the aeolianites generally are characteristic of
early stages of cooling and later stages of warming events when sealevel was only
marginally below its present position. Why they were not more widespread in the Indian
Ocean, where there are several extensive shallow banks, is not known. Marine-deposited
oolites may be present but if they are it is likely that all lie beneath present-day shelves.

ACKNOWLEDGEMENTS

I wish to thank Prof. Gulam T. G. Mohammedbhai and Dr. André Chan Chim Yuk
of the University of Mauritius for guidance during visits to the Rodrigues deposits as part
of a programme financed by British Council. Work in Kenya was supported by the

5)
Carnegie Trust for the Universities of Scotland and that on Aldabra by the Royal Society,
and the Natural Environment Research Council, with logistical support and facilities
provided by the Seychelle Islands Foundation.

REFERENCES

Bagnold, R. A. 1941. The Physics of blown sand and desert dunes. Methuen, London,
265pp.

Balfour, I. B. 1897. The Physical features of Rodrigues. An account of the petrological,
botanical and zoological collections made in Kerguelen's Land and Rodrigues
during the Transit of Venus Expeditions 1874-5. Philosophical Transactions of the
Royal Society of London 168:289-292.

Battistini, R. 1976. Application des methodes Th239-Ur234 a la datation des depots marins
anciens de Madagascar et des iles voisines. Association Sénégal Etudes Quaternaire
Africain, Bulletin Liason Sénégal 49:79-95.

Braithwaite, C. J. R. 1984. Depositional history of the Late Pleistocene limestones of the
Kenya Coast. Journal of the Geological Society of London 141:685-699.

Braithwaite, C. J. R., Taylor, J. D. and Kennedy, W. J. 1973. The evolution of an
Atoll: the depositional and erosional history of Aldabra. Philosophical
Transactions of the Royal Society of London, Series B 266:307-340.

Chapman, F. 1900. Notes on the consolidated sands of Kathiawar. Quarterly Journal of
the Geological Society of London 56:584-588.

Crame, A. 1980. Succession and diversity in the Pleistocene coral reefs of the Kenya
Coast. Palaeontology 23:1-37.

Crame, A. 1981. Ecological stratification in the Pleistocene coral reefs of the Kenya Coast.
Palaeontology 24:609-646.

Elbez, G 1976. Application de la methode de datation 239Th/234U a la determination des
niveaux marins de Madagascar et des isles environmentes. Memoires Maitre
(Geophysique) soutenu a l'Universite de Paris-Sud, Centre Orsay.

Evans, J. W. 1900. Mechanically formed limestones from Junagarh (Kathiawar) and other
localities. Quarterly Journal of the Geological Society of London 56:559-583 and
588-589.

Knox, G. J. 1977. Caliche profile formation, Saldanha Bay (South Africa).
Sedimentology 24:657-674.

Lloyd, R. M., Perkins, R. D. and Kerr, S. D. 1987. Beach and shoreface ooid deposition
on shallow interior banks, Turks and Caicos islands, British West Indies. Journal
of Sedimentary Petrology 57:976-982.

Mackenzie, F. T. 1964. Bermuda Pleistocene eolianites and palaeowinds. Sedimentology
3352-64.

6

McDougall, I., Upton, B. G. J. and Wadsworth, W. J. 1965. A geological
reconnaissance of Rodrigues Island, Indian Ocean. Nature 206:26-27.

Montaggioni, L. 1970. Essai de reconstruction palaeogeographique de I'ile Rodrigue
(Archipel des Mascareignes, Ocean Indien). Compte Rendu de la Academie
Sciences de France, Paris 271:1741-1744.

Slater, H. S. 1879. Observations on the bone caves of Rodrigues. An account of the
petrological, botanical and zoological collections made in Kerguelen's Land and
Rodrigues during the Transit of Venus Expedition 1874-5. Philosophical
Transactions of the Royal Society of London 168:420-422.

Snell, H. J. and Tams, W. H. T. 1920. The Natural History of the island of Rodrigues.
Proceedings of the Cambridge Philosophical Society 1916-1919 19:420-422.

Thomson, J. and Walton, A. 1972. Redetermination of Chronology of Aldabra by
230Th/243U dating. Nature 240:145-146.

Veeh, H. H. 1966 Th239/U238 and U234/U238 ages of Pleistocene high sea-level stand.
Journal of Geophysical Research 71:3379-3386.

Visser, N. H. and Schoch, A. E. 1973. The geology and mineral resources of the
Saldanha Bay area. Republic of South Africa, Department of Mines, Geological
Survey Mememoir 63:150pp.

Wolman, M. G. and Miller, J. P. 1960. Magnitude and frequency of forces in
geomorphic processes. Journal of Geology 68:54-73.

63°30’ E

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Fig. 2 General map of Rodrigues showing distribution of main areas of calcarenites.
Based on air photographs and Montaggioni (1973).

Fig. 3. High angle dips in cross-laminae of calcarenites. Sante Francois, Rodrigues.
Metre rule gives scale.

Fig. 4 Two sets of high angle cross-laminae in calcarenites. Trou d'Argent, Rodrigues.
Sets about 10 m high. Note on the right hand side the abutment against the sloping surface
of the underlying volcanics.

‘sounp [Issoj Jofeul Jo UONRIO] Oy) pue ‘svUTWUR] SUIPpaq-ssoId ATTedt1ouud are YoTYM

soul] [emnjonys ‘s}yeseq SutApJopun ou} uM Arepunog say} ‘sdo19jno ayTUSIeITeD JO 3Ud1X9
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about 300u.m in diameter.

ATOLL RESEARCH BULLETIN

NO. 421

LARGE-SCALE, LONG-TERM MONITORING OF CARIBBEAN CORAL

REEFS: SIMPLE, QUICK, INEXPENSIVE TECHNIQUES

BY

RICHARD B. ARONSON, PETER J. EDMUNDS, WILLIAM F. PRECHT,
DIONE W. SWANSON, AND DON R. LEVITAN

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

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LARGE-SCALE, LONG-TERM MONITORING OF CARIBBEAN CORAL
REEFS: SIMPLE, QUICK, INEXPENSIVE TECHNIQUES
BY
RICHARD B. ARONSON!, PETER J. EDMUNDS’, WILLIAM F. PRECHT?,
DIONE W. SWANSON? AND DON R. LEVITAN*
ABSTRACT

With coral cover and diversity declining on many coral reefs, a clearer understanding
of large-scale reef dynamics is imperative. This paper presents a sampling program
designed to quantify the sessile biotas of Caribbean reefs on large spatiotemporal scales.
For each reef sampled, data are gathered along replicate, 25-m transects located within
the habitat of interest. Herbivore impact is estimated by fish and echinoid censuses along
the transects. High-resolution videotapes are used to estimate the percent cover of
corals, algae, and other substratum occupants, and to estimate coral diversity. Finally,
topographic complexity is measured along the transects. In at least some reef habitats,
this index of three-dimensional structure provides a measure of the total disturbance
regime, with flatter areas having been subjected to more intense, more frequent, and/or
more recent sources of coral mortality. The techniques and statistical analyses described
in this paper are simple, quick and inexpensive. Repeated sampling on multiple reefs
will enable the investigator to detect changes in community structure and to test
hypotheses of the causes of those changes.

INTRODUCTION

Coral reefs are complex, diverse, productive tropical ecosystems in which multiple
physical and biological processes covary in space and time (Huston 1985). Discerning
the contributions of those processes to the community structure of reefs has been and will
continue to be extremely difficult. The question of the appropriate scales at which to
search for pattern and process is fundamental to unraveling these multiple causal
connections (Jackson 1991, 1992; Karlson and Hurd 1993). Are ecological parameters
such as coral cover and diversity determined primarily by small-scale processes, such as
the local level of herbivore activity (Sammarco 1980; Lewis 1986), or are larger-scale,
regional disturbances more important? Such questions are becoming increasingly

‘Marine Environmental Sciences Consortium, Dauphin Island Sea Lab, Dauphin Island,
AL 36528; and Department of Invertebrate Zoology, National Museum of Natural
History, Smithsonian Institution, Washington, DC 20560.

*Department of Biology, California State University, Northridge, CA 91330.

’Reef Resources & Associates, 7310 Poinciana Court, Miami Lakes, FL 33014.
“Department of Biological Sciences, Florida State University, Tallahassee, FL 32306.

Manuscript received 14 October 1993; revised 22 July 1994

2

germane as we confront the possibility that human interference is altering coral reef
ecosystems (e.g., Brown 1987).

Over the past two decades, the "health" of many coral reefs worldwide has
deteriorated, as measured by indicators such as the diversity and abundance of reef-
building corals (Rogers 1985; Dustan and Halas 1987; Hatcher et al. 1989; Grigg and
Dollar 1990; Porter and Meier 1992; Ginsburg 1994). Hurricanes (Woodley et al. 1981;
Rogers et al. 1982, 1991; Edmunds and Witman 1991; Hubbard et al. 1991; Bythell et
al. 1993), coral bleaching (Oliver 1985; Brown and Suharsono 1990; Williams and
Bunkley-Williams 1990; Glynn 1993), coral diseases (Gladfelter 1982; Riitzler et al.
1983; Edmunds 1991), mortality of the sea urchin Diadema antillarum (Lessios et al.
1984; Levitan 1988; Lessios 1988; Carpenter 1990) and outbreaks of the seastar
Acanthaster planci (Moran 1986; Endean and Cameron 1991) may all be involved. At
present, it is unknown whether any or all of these problems are due to recent human
activities, or whether they are part of natural, long-term trends or cycles (Brown 1987;
Richards and Bohnsack 1990).

In addition, reefs are directly affected by human activities, particularly fishing,
sedimentation, eutrophication and pollution (Brown 1987, 1988; Hatcher et al. 1989;
Rogers 1990; Richmond 1993; Sebens 1994). These stresses reduce coral survivorship
and growth and may promote macroalgal growth. Furthermore, marine pollution may
increase the susceptibility of corals to disease (Brown 1988; Peters 1993).

Reef dynamics are governed by multiple causes operating on multiple scales (Grigg and
Dollar 1990). For example, the recent decline in coral cover and increase in macroalgal
cover on the well-studied reef at Discovery Bay, Jamaica appears to have resulted from
a variety of interacting processes: Hurricane Allen (1980), which opened substratum for
colonization; feeding by corallivorous snails, which increased the mortality of hurricane-
fragmented corals; the Diadema dieoff, which reduced herbivory drastically; and a
history of overfishing by humans, which had previously removed herbivorous reef fishes
(Hughes et al. 1987; Knowlton et al. 1990; Hughes 1994). Likewise, the catastrophic
effects of the 1982-83 El Nino event on eastern Pacific coral reefs were due to the
interaction of physical changes and a variety of biological processes (Glynn 1990).

One of the greatest challenges to ecology is determining the relative importance of
numerous causes to ecosystem structure and function (Quinn and Dunham 1983). Yet,
even choosing the correct range of scales on which to understand coral reef dynamics
seems a forbidding task. It is becoming increasingly clear that quadrat-scale observations
(square meters or smaller) have less explanatory power than larger-scale observations
(Jackson 1991). Those larger scales range from the landscape within a reef (hundreds
of m’ to hectares), to the area encompassing multiple reefs within a locality (hundreds
of km’), to an entire region such as the Caribbean.

The need for large-scale and long-term (>5 yr) monitoring programs for coral reefs

3

has been emphasized over the past few years (Rogers 1988, 1990; Ogden and Wicklund
1988; D’Elia et al. 1991; Jackson 1991; Ray and Grassle 1991; Smith and Buddemeier
1992; Bythell et al. 1993; Glynn 1993; Hughes 1994), although less attention has been
given to the hypotheses that should be driving the research (Hughes 1992). Few such
studies have been undertaken, in part because hypotheses are so difficult to formulate and
test (Hughes 1992). Such hypotheses might, for example, include an inverse relationship
between the degree of disturbance and coral cover; the intermediate disturbance
hypothesis (Connell 1978; Rogers 1993), which postulates that coral diversity should be
highest at intermediate frequencies and intensities of disturbance; and complex
relationships between herbivory, nutrients, coral and algal cover, and diversity (Littler
et al. 1991; Knowlton 1992; Hughes 1994). However, with so many possible causes of
community change, and with the ecological implications of each putative cause unknown,
highly variable and/or controversial, it is hard to know which variables to monitor in
order to test hypotheses adequately.

This paper outlines procedures for comparing coral reef community structure and
disturbance regimes across space and through time, with a view toward eventually testing
hypotheses such as those listed above. The methods were developed during continuing
studies of four western Atlantic coral reefs: Carrie Bow Cay, on the Belizean Barrier
Reef; Discovery Bay, Jamaica; and Conch and Carysfort Reefs, off Key Largo, Florida.
Since funding for monitoring programs is difficult to obtain and since field time is
usually limited, our goal was to create an accurate, relatively inexpensive, “rapid
assessment" sampling program for Caribbean coral reefs, with sufficient statistical power
to detect biologically meaningful differences. Video transects are used to describe the
sessile biota, and fish and echinoid censuses provide estimates of the intensity of
herbivory. Since the importance of each type of reef disturbance has not been
conclusively demonstrated, we advocate combining them in a single disturbance index,
topographic complexity. Topographic complexity reflects the total disturbance regime
in at least some reef habitats, integrated on a time scale of years.

METHODS

1. Sampling Design

Any study that compares reefs must be standardized with respect to habitat. The design
described here is for a common Caribbean fore-reef habitat: the spur-and-groove habitat
of windward-facing reefs at 12-15 m depth. Ten 25-m long transects are sampled at each
site. The transects are placed along the central axes of replicate, haphazardly chosen
spurs. Sandy areas and the edges of the spurs are avoided. In the present study, each
transect was placed on a different spur, except at Discovery Bay. A number of spurs at
Discovery Bay were >25 m wide; 2 transects, spaced >10 m apart, were surveyed on
some of those wide spurs. It is important to choose sites that will accommodate at least
25-30 transects, so that the transects sampled during different visits to a site will not be
identical.

4

The use of band transects is dictated in this particular application by the elongate shape
of the spurs, and in general by the desire to encompass as great an area as possible in
each sample. The 25-m transect length was chosen to be as great as possible while still
restricted to a narrow depth and habitat range on the spurs. A 25-m transect, when
extended over a 3-m depth range, requires spurs that slope at angles of no more than 7°.

For each transect, scuba divers unreel a 25-m fiberglass surveyor’s tape, laying it
taught along the center of the spur. The tape is left undisturbed for 3-5 min, at which
point the divers commence surveys of the mobile fauna.

2. Fish and Echinoid Censuses

Coral reef researchers have yet to agree on a single, reliable method for quantifying the
activity of herbivores (Steneck 1983). The simplest measure is the abundance of
herbivores, which correlates with their impact among habitats within reefs (Hay and
Goertemiller 1983; Lewis and Wainwright 1985). Therefore, before the fish are
disturbed further, a visual census is conducted along each transect. A diver swims along
the tape at a standard slow speed, recording the number of parrotfish (Labridae, formerly
Scaridae) and surgeonfish (Acanthuridae) within a visually-estimated 2 m on either side.
The fishes are classified as small (<10 cm Standard Length), medium (10-25 cm), or
large (>25 cm). The small transect width minimizes the underestimate of true fish
population density inherent in the transect method (Sale and Sharp 1983). Divers then
carefully explore the 100 m? area, recording the number and species identities of
damselfish (Pomacentridae), as well as censusing Diadema and other regular echinoid
species. The echinoids can be extracted from their shelters and measured (test diameter)
with calipers. Size distributions of echinoid species can then be used to estimate their
impacts on algal assemblages (Levitan 1988). It should be noted that daytime censuses
underestimate echinoid densities; more accurate estimates can be obtained by censusing
at night (e.g., Carpenter 1981, 1986).

An alternative approach is to examine the process of herbivory by counting the number
of bites that parrotfish and surgeonfish take per unit time from small areas of algal turf
(Steneck 1983). This technique is more time-consuming than counting fish. A more
serious concern is that some habitats on some reefs are currently so overgrown with
fleshy macroalgae that finding even a square meter of algal turf would be problematic.
For example, at Discovery Bay in 1992 macroalgal cover was >90 %, coral cover was
<3 %, and the cover of algal turfs, crustose coralline algae, and bare space combined
was <6 % at 15 m depth (as assessed by the video technique described below; Table 1,
p. 11). Large differences in the availability of algal turfs could lead to differences in fish
foraging behavior, independent of fish abundance. It is important to recognize that both
the abundance and bite frequency methods yield short-term "snapshots" of herbivory,
which may not adequately reflect longer-term variability.

3. Percent Cover and Scleractinian Diversity
Photography provides the only practical means of sampling large areas underwater,

5

given the time constraints of scuba diving. Littler (1980) discussed the advantages of
photography over recording data in situ. High-resolution video technology makes the
approach all the more attractive because videotaping is easier and less time-consuming
than still photography. While still photographs provide better resolution than videotapes,
the resolution of videotapes is adequate for work of the type described here. Videotapes
enable the investigator to cover a far greater area per unit sampling effort. In addition,
video exposures are automatic, continuous and do not require developing.

In this method, a diver swims slowly along the transect, videotaping a 40-cm wide
swath of reef from a height of approximately 40 cm, using a high-resolution (Hi-8) video
camera in an underwater housing, fitted with a wide-angle lens. A 15-cm gray plastic
bar is attached to a rod that projects forward from the video housing. The bar, which
is held at the level of the substratum during taping, provides scale in the videotaped
images and also ensures that the camera is held a constant distance from the bottom.

Individual video frames are displayed on a high-resolution monitor in the laboratory.
A clear plastic sheet with 10 random dots is laid over the monitor screen, and the sessile
organisms underlying the dots are recorded (Sebens and Johnson 1991; see Sample Sizes,
p. 8, for number of dots per frame). The videotape is then advanced to a new, non-
overlapping position. Each 25-m transect yields 50 video "quadrats", for a total of 500
points per transect. The point count data are used to calculate percent cover and the
Shannon-Wiener diversity index, H’, for each transect. Since this and similar sampling
methods tend to be biased against the inclusion of rare species, presence-absence data are
also gathered for coral species by viewing the entire videotape of each transect
(Chiappone and Sullivan 1991).

By holding the camera perpendicular to the substratum, swimming slowly along the
transect, and using a pair of video lights (50 or 100 watts each), it is possible to produce
clear stop-action images. Corals, sponges, and some gorgonians and macroalgae can be
identified to species, down to a diameter of approximately 5 cm. A drawback of this
method is the difficulty of distinguishing fine algal turfs, crustose coralline algae and
bare space from the tapes; these are lumped into a single category, which can be resolved
by closeup, still photography if desired.

Ecologists have devoted a great deal of effort to developing and comparing methods for
quantifying coral reef community structure, with variable results (e.g., Loya 1978;
Dodge et al. 1982; Ohlhorst et al. 1988; Chiappone and Sullivan 1991; Porter and Meier
1992). Porter and Meier (1992) examined some of the biases introduced to surface area
estimates by photographic and video techniques. Such errors include non-orthographic
projection, in which coral heads that stick up above the surrounding substratum are closer
to the camera lens and therefore artificially enlarged, and parallax. These problems are
difficult to correct (Porter and Meier 1992).

Whorff and Griffing (1992) found that point counts from video frames overestimated

6

the percent cover of intertidal barnacles and bivalves, compared to computer image-
processing of the video frames. More dots per frame yielded better percent cover
estimates. On the other hand, Foster et al. (1991) concluded that point counts from
photographs underestimated cover in multilayered, temperate subtidal assemblages,
compared to point counts done in the field. The point count method is not as accurate
as planimetry of the individual colonies in each frame or fully-automated image
processing. However, planimetry is so time-consuming as to be impractical. Image
processing is also difficult at present because subtle color and pattern differences must
be detected; most corals and algae are quite similar in color, and reasonably-priced,
hand-held video lights provide limited color saturation. The point count method is
capable of detecting significant among-site differences in percent coral cover and
diversity (see Sample Sizes, p. 8). Video has its problems and biases like other
techniques, but it remains a simple, cost-effective comparative method.

Another concern is the seasonality of macroalgal growth (Carpenter 1981; Hughes et
al. 1987). Seasonal changes within a site could change estimates of coral cover, as more
or less living coral is obscured by the algae (J. C. Lang, personal communication). The
constraints of time, logistics and funding do not always permit the investigator to
standardize sampling by season, and the error in coral cover estimates caused by seasonal
variations in algal growth are unknown. In the present study, Carrie Bow Cay was
sampled in the late spring, Discovery Bay in the winter, and Conch and Carysfort Reefs
in the fall of 1992. If algal growth is maximal in the summer and algal destruction by
storms is maximal in the winter, then, all other things being equal, macroalgal cover, and
the error in coral cover estimates due to macroalgal cover, should have been greatest in
Florida (after the summer’s algal growth), intermediate at Carrie Bow Cay (before the
summer’s growth), and least at Discovery Bay (during the stormy season). In fact,
macroalgal cover was highest at Discovery Bay, intermediate at Conch Reef and Carrie
Bow Cay, and lowest at Carysfort Reef (Table 1, p. 11). In this study, differences in
macroalgal cover among sites apparently outweighed any error in coral cover estimates
associated with seasonal differences.

The species diversity of scleractinian corals is evaluated as species richness, S, and as
the Shannon-Wiener index, H’. S is measured for each site as the asymptote of the
rarefaction curve (cumulative species numbers plotted against number of transects
videotaped). Species richness is not calculated for each transect since reefs with lower
coral cover are expected to have lower S per transect simply because fewer colonies are
sampled (Magurran 1988). The Shannon-Wiener index is calculated for each transect as
H’=-Y(p,[Inp,J), where p; is the proportion of the ith species in the sample. Vast size
differences among coral colonies and colony fragmentation and fusion obscure the
meaning of H’ calculated from numbers of "individuals". Unless the investigator is
prepared to establish the genetic identity of all ramets, we recommend H’ indices based
on areal coverage for a general characterization of reef communities.

4. An Integrated Measure of Disturbance

Historical records of disturbance do not exist for most coral reefs. Even where such
records are available, there is no obvious way to sum the different disturbances to reflect
the total disturbance regime; one cannot simply score three disturbance points for a
hurricane and two for a bleaching event. We present topographic complexity as a
technique for measuring disturbance, along with its rationale and sources of error, so that
the individual investigator can decide whether or not it will be useful.

Topographic complexity is measured by carefully conforming a 5-m length of fine brass
chain to the substratum adjacent to the central part of each transect tape. The chain is
conformed to the finest topographic features that the 17-mm links permit; it is carefully
inserted into small cavities and into the spaces within thickets of foliose and branching
corals. The 5-m chain length was chosen so that the procedure could be completed in
a reasonable length of time (10-15 min); the chain must be carefully straightened before
it is conformed to the substratum. A complexity index, C, is calculated as C=1-d/l,
where d is the horizontal distance covered by the conformed chain (measured against the
transect tape) and / is its length when fully extended (e.g., Risk 1972; Rogers et al.
1982; Aronson and Harms 1985; Hubbard et al. 1990; Connell and Jones 1991).

Disturbances that lead to the partial or complete mortality of coral colonies decrease
this topographic complexity. Hurricanes decrease complexity directly by toppling
branching and head corals (e.g., Rogers et al. 1982; Kaufman 1983), although this is not
true in all reef habitats (Rogers et al. 1991; see below). In addition, once dead coral
skeletons are exposed by a disturbance of any sort, they are colonized by bioeroders,
including bivalves, sponges, sipunculans, polychaetes and echinoids, which break down
the reef framework (Hutchings 1986). Disturbances that cause partial to complete
mortality of coral colonies, provide fresh substratum for bioeroders, and in fact lead to
increased bioerosion rates include hurricanes (Moran and Reaka-Kudla 1991), El Nifio-
induced coral bleaching (Glynn 1990) and damselfish territoriality (Kaufman 1977),
although damselfish can have a negative effect on bioerosion by excluding echinoids from
their territories (Eakin 1988; Glynn 1990). Naturally and artificially high levels of
nutrients on reefs also increase bioerosion rates (Highsmith 1980; Tomascik and Sander
1987; Hallock 1988). Overfishing off the coast of Kenya increased bioerosion and
decreased topographic complexity as well, by releasing burrowing echinoids from
predation (McClanahan and Shafir 1990). Furthermore, coralline algae, which are
important in cementing the reef framework (and thus important in maintaining
topographic complexity), are suppressed by macroalgae, which are promoted by nutrient
input and the removal of herbivores (Littler and Littler 1985; Lewis 1986; Carpenter
1990). Coral growth, by contrast, generally increases topographic complexity at the
scale under consideration (Dahl 1976). To a first approximation in certain situations,
the topographic complexity index should be inversely related to total disturbance, with
lower values indicating flatter terrain and suggesting more frequent, more recent and/or
more intense disturbance.

8

No measure of disturbance is free of bias, including topographic complexity. One
source of error is that coral mortality does not lead to the immediate loss of structure
because bioerosion takes time. In addition to this time lag, the relationship between coral
mortality and physical complexity is not always direct. Some coral species can survive
breakage in storms and even reproduce asexually as a result (Acropora spp.: Highsmith
et al. 1980; Tunnicliffe 1981); low complexity accompanied by high coral cover is a
possible consequence. Conversely, bioerosion following partial or complete mortality
of massive coral heads could initially increase complexity rather than decrease it.

While these problems introduce error to estimates of disturbance, that error should be
minimal in the spur-and-groove down to 15 m depth. Throughout Florida and the
Caribbean, those habitats are now or were formerly (before disturbance) dominated by
branching or other delicate coral species, including Acropora cervicornis (Belize,
Jamaica, the Florida Keys and many other localities), branching Porites spp. (some reefs
in St. Croix, U. S. Virgin Islands), and Agaricia tenuifolia (Belize). For all of these
corals, complexity in their habitats should decline rapidly following mortality.
Topographic complexity would not be as useful an indicator of disturbance in certain
other reef habitats, such as shallow-water hardground areas, which are characterized by
isolated head corals on limestone pavements. Similarly, deep-reef areas dominated by
corals with a plating morphology could have high coral cover but low topographic
complexity.

Another potential complication in separating disturbance and herbivory effects is an
observed positive correlation of fish abundance and topographic complexity.
Herbivorous (and other) fish avoid low-relief areas, including those which have been
disturbed (Hay and Goertemiller 1983; Kaufman 1983). Areas with fewer herbivores
may experience increased algal cover, decreased coral cover, and increased bioerosion,
leading to even flatter topography (reviewed in Hutchings 1986). This feedback loop
does not appear to be a problem in the reefs studied (see Sample Sizes).

SAMPLE SIZES

The techniques outlined above are intended for testing hypotheses on large scales,
ranging from a landscape scale (among spurs in the spur-and-groove habitat within reefs),
to a subregional scale (among reefs within an area such as the Florida Keys), to a
regional scale (among reefs throughout the Caribbean). In order to determine the
appropriate sample sizes for statistical comparisons among reefs, preliminary surveys
were conducted during 1992-93 in the spur-and-groove habitats of the four sites
mentioned in the Introduction. Ten transects were completed at each site, and an
additional 10 transects were videotaped only (see comments below on species richness).
Two investigators can sample a site in 3-4 days, assuming 2-3 "full" transects per dive
and 2 dives per day. Where funding and equipment are available, the use of nitrox
diving techniques increases bottom time substantially, increasing the number of transects
that can be completed per dive.

9

Percent cover and H’ are estimated by point counts from each of 10 video transects per
site. Fifty non-overlapping, video frame "quadrats" cover most of the length of the
transect videotape. The question is how many random dots to use per video frame. For
each of the 50 frames in each of the 10 Carrie Bow Cay and 10 Discovery Bay transects
that were analyzed, the substratum occupants under 25 random dots were recorded, in
groups of 5 dots. The means and standard deviations of percent cover of hard corals and
H’ for scleractinians remained virtually unchanged when the number of dots used was
=10 (Figs. 1, 2). Therefore, an appropriate sampling protocol is 50 video frame
"quadrats" per transect and 10 random dots per video frame. Each 500-dot data set
constitutes a single sample, requiring 2-3 hours for trained personnel to extract from the
videotaped transect. Because each video transect is a single sample, increasing the
number of random dots per frame yields no advantage in terms of statistical power.

The only parameter for which more than 10 video transects per reef are required is
species richness, S. Plots of cumulative § for Conch Reef and Discovery Bay reach their
asymptotes after 9 and 15 transects, respectively, and the curves for Carysfort Reef and
Carrie Bow Cay both asymptote after 13 transects (Fig. 3). The difference in sample
sizes required to estimate H’ and S is due to rare species, which add little to the coral
cover from which H’ is calculated. We recommend 20 transects to estimate species
richness for a site.

The percent cover and topographic complexity data were arcsine-transformed and the
fish census data logarithmically transformed, so that they conformed to the assumptions
of parametric statistics (Sokal and Rohlf 1981). The square root transformation, often
recommended for data in the form of counts (Sokal and Rohlf 1981), was not used on
the census data. This transformation assumes that the data in question are Poisson
distributed, but count data are not necessarily so distributed. Transformation of the H’
‘data was unnecessary because H’ is normally distributed (Magurran 1988) and the data
collected in this study were homoscedastic. (See Clarke and Green [1988] for a detailed
discussion of data transformations.)

A one-way analysis of variance (ANOVA) on the arcsine-transformed percent coral
cover data showed significant among-site differences (p< 0.0005; Table 1). Tukey HSD
multiple comparisons revealed the following differences between sites, listed in order of
increasing cover (<, significantly less than; =, not significantly different from at
a=0.05):

Discovery Bay < Conch Reef < Carrie Bow Cay = Carysfort Reef.
The ANOVA results were used to estimate the minimum detectable difference, 6, in
transformed percent cover at a significance level of ~=0.05 with a power of 1-8 =0.90
(Zar 1984; Clarke and Green 1988). For an ANOVA comparing 4 sites, 5=0.13. This
calculated 6 was then used to estimate the range of the minimum detectable difference
in actual (untransformed) percent cover by the following procedure:

1. adding 6 to the (transformed) lowest mean, back-transforming that value to
actual percent cover, and taking the difference between the back-transformed value and

10
—®— Discovery Bay
25 ]|—o— Carrie Bow Cay

20
15

10

Percent Cover

0 5 10 15 20 25

Number of Dots

Fig. 1. Percent cover of hard corals as a function of the number of random dots used
per video frame in transects from Discovery Bay, Jamaica and Carrie Bow Cay, Belize.

Fifty frames were analyzed in each of 10 transects for each site. Error bars represent
standard deviations.

—®8—_ Discovery Bay
2.57|—o— Carrie Bow Cay

2.0

Ww 1S
1.0
0.5
0.0
0 5 10 15 20 25

Number of Dots

Figure 2, Shannon-Wiener diversity of Scleractinia, H’, as a function of the number of
random dots per video frame in transects from Discovery Bay and Carrie Bow Cay.
Sample sizes as in Fig. 1. Error bars represent standard deviations.

11

Discovery Bay
—oO— Carrie Bow Cay
Conch Reef

Carysfort Reef

0 5 10 15 20
Number of Transects

Figure 3. Cumulative species richness curves for scleractinian corals in video transects
from the four sites surveyed.

Table 1. Means + standard deviations of parameters measured in 1992 at four coral reef
sites.

Field Site
Parameter § Discovery Bay Carrie Bow Cay Conch Reef Carysfort Reef
A. Percent Cover
Hard corals 2.8+1.5 16.74+3.8 6.4+4.0 DNAse i)
Macroalgae 91.2+4.3 63.2+6.9 65.7+8.8 40.9+12.0
B. Scleractinian Diversity
1’ 1.22+0.28 1.81+0.29 1.04+0.55 1.21+40.58
C. Integrated Disturbance Index
C 0.184+0.078 0.403+0.089 0.194+0.077 0.335+0.106

D. Fish Abundance (number/transect)
Parrotfish 31.5+10.0 24.6+7.4 17.0+8.3 34.24+15.8
Damselfish 7.5+4.5 38.5+7.9 58.5+14.2 18.5+7.8

12

the observed (untransformed) lowest mean, and

2. subtracting 6 from the (transformed) highest mean, back-transforming that
value to actual percent cover, and taking the difference between the observed
(untransformed) highest mean and the back-transformed value.
The minimum detectable difference ranged from 5.2 % where coral cover is minimal (a
few percent cover) to 9.8 % at high values of coral cover (approximately 20 % cover;
Table 1). In fact, a posteriori comparisons after ANOVA on the arcsine-transformed
percent cover data detected a significant difference between the sites with the two lowest
means, Discovery Bay and Conch Reef, which differed by only 3.6 % cover (Table 1).
If the study were expanded to include surveys of 10 sites instead of just 4, the minimum
detectable difference would range from 6.3 to 11.1 % cover.

A one-way ANOVA on the H’ data also revealed significant differences among sites
(p<0.005), which are listed in the same format as for percent coral cover:
Conch Reef = Carysfort Reef = Discovery Bay < Carrie Bow Cay.
A power analysis gave 6=0.81 for an ANOVA comparing 4 sites and 6=0.93 for an
ANOVA comparing 10 sites, at a=0.05 and 1-8=0.90. A posteriori comparisons
detected a significant difference between the sites with the two highest means, Carrie
Bow Cay and Discovery Bay, which actually differed in mean H’ by only 0.57. The
video method thus provides a statistically powerful tool for detecting differences in coral
cover and diversity among sites.

The estimates of percent cover and H’ for Discovery Bay were compared to estimates
obtained independently at the same time (during the winter of 1992) by the linear point-
intercept (LPI) method (Ohlhorst et al. 1988). A 10-m surveyor’s tape was positioned
randomly at 15 m depth, and the sessile organisms underlying the tape were recorded
every 10 cm, for a total of 100 points per transect. The LPI method gave a higher
estimate of coral cover (mean 4.4+0.9 SD, based on 5 transects) than the video transects
(Table 1), but the two estimates were not significantly different by Student’s f-test
(t,=2.207, df=13, 0.05<p<0.10). In contrast, the LPI method underestimated H’
(mean 0.72+0.18 SD) compared to the video transects (t,=3.577, df=13, p<0.005).
The significant difference in species diversity obtained by the two methods is largely an
artifact of the number of points used to calculate H’. Since coral cover was so low at
Discovery Bay, the H’ value calculated for each 100-point LPI transect was based on a
maximum of only 5 points overlying coral. With 5 times as many points per sample,
undersampling corals was not a problem in the video transects (Fig. 2).

Hughes (1994) employed line-intercept transects to document reef dynamics at
Discovery Bay at 10 m depth. Using a 10-m surveyor’s tape, he recorded the lengths
of tape overlying different species. His value for coral cover in 1993, approximately 3
%, agrees with the mean reported for 15 m depth in Table 1. In addition, Hughes
(1994) monitored permanent photoquadrats at a site near Discovery Bay. In 1993, he
obtained values of coral and macroalgal cover at 15-20 m depth that are nearly identical
to those listed in Table 1 for Discovery Bay.

13

Analysis of the topographic complexity data showed that the chain method is capable
of detecting significant differences among sites (ANOVA, p<0.0005):

Discovery Bay = Conch Reef < Carysfort Reef = Carrie Bow Cay.
Interestingly, the four sites display the same qualitative differences in topographic
complexity that they do in coral cover. Jackson (1991) used coral cover as a proxy for
disturbance, with higher coral cover indicating a lower level of disturbance. Our
suggested measure of disturbance, topographic complexity, agrees with Jackson’s (1991)
for the reefs studied. We prefer the complexity index, because it avoids the circularity
of using Jackson’s (1991) method to test for a causal relationship between disturbance
and coral cover.

The log-transformed abundance of damselfish differed from site to site (ANOVA,
p <0.0005):

Discovery Bay < Carysfort Reef < Carrie Bow Cay = Conch Reef.

Apart from damselfish, which actually promote algal growth, parrotfish were by far the
most abundant herbivorous fishes in the spur-and-groove habitat (Lewis and Wainwright
1985); 82-98 % of the herbivores were parrotfish in censuses at the four sites.
Surgeonfish and echinoids were virtually absent, and they were ignored in this analysis.
Among-site differences were also detected in log-transformed parrotfish abundance
(ANOVA, p<0.0005):

Conch Reef < Carrie Bow Cay = Discovery Bay = Carysfort Reef.
Multiplying parrotfish abundance in the three size classes by average length to calculate
"biomass" did not alter these patterns. As suggested in the section on fish and echinoid
censuses, parrotfish and surgeonfish abundance can be highly variable, and counts of
these mobile herbivores should be interpreted with caution.

For long-term studies of particular reefs, our protocol has distinct advantages over the
‘traditional approach of permanent transects or quadrats. The marine environment is
highly variable, and independent sampling during each site visit (factorial, with time as
a factor; Green 1979) encompasses more of that variation than a permanent transect
approach (repeated measures). While it is true that independent sampling makes it more
difficult to detect significant effects, conclusions are not bound to the particular histories
of individual organisms and the particular areas of reef framework on which they live.
An independent/factorial approach thus gives investigators increased scientific confidence
in the signals detected, but less statistical power to detect those signals, than a
permanent/repeated measures approach. Furthermore, since the independent sampling
approach avoids the expensive and time-consuming procedures involved in permanently
marking study areas, it is more practical for reef monitoring in developing countries.

CONCLUSION
The methods outlined in this paper were developed to combine logistical ease, low cost

and statistical power. The point-count data extracted from the videotapes can be taken
beyond univariate statistical treatments to more sophisticated, multivariate ordinations and

14

tests. Differences in species composition among reefs can then be considered in light of
differences in geomorphology and oceanography as well as differences in disturbance
regime.

Coral reefs have been central to the development of ecological theory (Connell 1978),
yet we still need basic information on their dynamics (Jackson 1991; Ginsburg 1994).
As reef ecosystems become increasingly threatened, commitment to large-scale
management is growing in the United States and abroad. However, effective
management policy cannot be created without an understanding of reef dynamics and the
effects of disturbance. The methods described in this paper can provide the necessary
information. Large-scale and long-term data collected now will be of particular value
if and when conditions change (e.g., recovery of Diadema populations, future
hurricanes).

ACKNOWLEDGEMENTS

This research was supported by the Smithsonian Institution’s Caribbean Coral Reef
Ecosystems (CCRE) Program and by NOAA’s National Undersea Research Center at the
University of North Carolina, Wilmington (NURC-UNCW). Additional support was
provided by the Institute of Marine and Coastal Sciences (IMCS) at Rutgers University,
the Smithsonian Institution Women’s Committee and Northeastern University’s East/West
Program. Sony Corporation of America generously provided an underwater video
system, and S. L. Miller lent us his personal video equipment. G. Sternschein invented
a superb little device to hold the video scale rod and manufactured it in his machine shop
in Glasgow, Scotland. We thank M. A. Buzas, J. C. Bythell, J. H. Connell, G. D.
Dennis III, P. Dustan, C. M. Eakin, L.-A. Hayek, J. C. Lang, M. M. Littler, J. B. C.
Jackson, I. G. Macintyre, S. L. Ohlhorst, S. R. Smith and R. S. Steneck for their advice
and comments. We are also grateful to S. L. Miller and the staff of NURC-UNCW’s
Florida Research Program, K. Ruetzler, and J. D. Woodley for providing laboratory
space and logistical support in the Florida Keys, Belize, and Jamaica, respectively.
Research in the Florida Keys was conducted under National Marine Sanctuary Permits
KLNMS-19-92 and FKNMS-14-93. This is CCRE Contribution No. 417, IMCS
Contribution No. 94-21, and Contribution No. 560 of the Discovery Bay Marine
Laboratory, University of the West Indies.

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ATOLL RESEARCH BULLETIN

NO. 422

CHANGES IN THE COASTAL FISH COMMUNITIES FOLLOWING

HURRICANE HUGO IN GUADELOPE ISLAND (FRENCH WEST INDIES)

BY

CLAUDE BOUCHON, YOLANDE BOUCHON-NAVARO, AND MAX LOUIS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

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CHANGES IN THE COASTAL FISH COMMUNITIES FOLLOWING
HURRICANE HUGO IN GUADELOUPE ISLAND (FRENCH WEST INDIES)

BY

CLAUDE BOUCHON, YOLANDE BOUCHON-NAVARO AND MAX LOUIS

ABSTRACT

Hurricane Hugo swept the island of Guadeloupe (French West Indies) on 16 and 17
September 1989. Sustained winds were of 140 knots and gusts exceeded 160 knots. This
hurricane was one of the most devastating of the century for the Lesser Antilles.

The mangroves were completely defoliated and anoxic conditions of the water
induced considerable fish mortality. Consequently, the fish community was modified in
terms of species composition, structure and biomass. Four months later, the fish assemblages
of the mangroves returned to conditions previous to the hurricane in species composition
and community structure.

The impact on the marine phanerogams was more destructive on the Syringodium
filiforme seagrass beds than on those of Thalassia testudinum. In this ecosystem, the effect
of the hurricane was minor on the fish community. Changes in the fish community occurred
four months later in the seagrass beds and were apparently induced by a delayed mortality
of the Thalassia testudinum.

In the coral reef environment, the impact of the hurricane surge on the coral
_ community mainly affected the branched coral species located between the surface and 15
m deep. The fish assemblages were not modified concerning their species composition.
However, the proportion of juveniles in the community drastically dropped after the
hurricane. Four months later, the proportion of juvenile fishes was still reduced.

The overall effects of hurricane Hugo on the coastal fish communities of the island
of Guadeloupe were minor considering the magnitude of the hurricane.

I. INTRODUCTION

In the Lesser Antilles, hurricanes are considered one of the major factors controlling
the coastal marine ecosystems. In the island of Guadeloupe, these are represented by
mangrove, seagrass beds and coral reefs.

Hurricane Hugo reached Guadeloupe in the night of 16 September 1989, travelled the
length of the island until the following morning, with the 37 Km-diameter eye passing over

Université des Antilles et de la Guyane, Laboratoire de Biologie et Physiologie Animales, B.P. 592, 97167
Pointe-a-Pitre, Guadeloupe (F. W. I.)
Manuscript received 20 June 1991; revised 4 August 1994

2

the Grande Terre (Fig. 1). The atmospheric pressure dropped to 941,5 millibars and the
wind was recorded at 140 knots with squalls exceeding 160 knots. In some areas, rainfall
reached 300 mm in one day. Such a rainfall rate has a probability of occurence lower than
1 per 50 years (Anon., 1990).

Figure 1 : Guadeloupe Island. Track of the hurricane. Location of the study areas.

Only few observations were available concerning the effects of the hurricane on the
sea conditions.The theoretical calculation of the storm tide predicted a 3 m rise of the mean
sea level (Anon., 1990). Our examination of the high-water marks after the storm indicated
that the tide did not exceed 1,5 m. Offshore, the predicted amplitude of the swell was 5 m
(Anon., 1990). On the shore, the structure of the waves is normally variable and depends
on the morphology of the sea bottom and the incidence of surge along the coast.
Unfortunately, no observations were made during the hurricane. However, the amplitude
of the waves observed for similar hurricanes in the Caribbean area varied between 10 and
12 m (Stoddart, 1974 ; Woodley et al., 1981 ; Kjerfve et Dinnel, 1983).

3

The general impact of Hurricane Hugo on the different coastal communities of the
island of Guadeloupe was previously reported by Bouchon et al. (1991). The present work
summarizes the observations made on the changes in the fish communities during the
months preceding and following the hurricane.

Il. STUDY AREAS AND METHODS

Observations were made in the Grand Cul-de-Sac Marin bay, for the fish in the
mangrove and the seagrass beds. The coral reef fish community was studied near Pigeon
Island, on the west coast of Guadeloupe (Fig. 1). These areas were chosen because previous
data were available for them and provided a basis for comparison.

After the hurricane, the first observations were made on 24 September, 1989 at Pigeon
Island and on 25 September in Grand Cul-de-Sac Marin.

The fish communities were studied with different sampling techniques because of the
varied habitat. In the mangrove, where the water was turbid, fishes were sampled with a
special fishing net called “capéchade”. This device consisted of a fence net (45 mlong and
2 m high), placed perpendicular to the mangrove front and three hoop-nets that trap the
fishes. From the mouth to the extremity of the hoop-nets, the mesh-size decreased from 13.8
mm to 6mm (Fig. 2). The sampling station was located in the “Manche a Eau", a mangrove
lagoon (Fig. 3) and important nursery zone for the fishes in Guadeloupe (Louis et Guyard,
1982). In the seagrass beds, fishes were collected with a seine net, 50 m long and 2 m high,
used to encircle the sampling area. Two stations were chosen in Grand Cul-de-Sac Marin :
one at Lambis Point and the other at Christophe Islet (Fig. 3).

mangrove

hoop net
U CEO 04

Figure 2 : A “capéchade” : the fishing device used in the mangrove.

The sampling area for the coral reef fish community was located near Pigeon Island
at 15 m deep (Fig. 1). The fishes were counted, by SCUBA diving, inside a quadrat of 300
m? (150 m long, 2 m wide) defined by transect lines on the bottom. The water column
investigated was about 3m high. Each fish censused was assigned one of three size-classes
(juvenile, medium-size, big-size) based on the size range of each species (Bouchon-Navaro
and Harmelin-Vivien, 1981).

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Figure 3 : Location of the sampling stations in Grand Cul-de-Sac Marin Bay.

5

From the data, several biological indices were computed such as species richness,
species diversity (H’) calculated according to Shannon and Weaver (1948), and evenness
index (E) of Pielou (1969) that gives an indication on the community structure. E fluctuates
between 0 (only one species in the community) and 1 (all the species of the community have
the same importance). These indices were calculated using biomass values for the
mangrove and seagrass fishes and the number of individuals for the reef fishes.

Data did not fit a gaussian distribution, even when using current transformation
techniques (Log, square root, hyperbolic...). Three non parametric statistical tests were used
to analyse the data : the Wilcoxon signed-ranks test, the Spearman rank correlation and the
Friedman two-way analysis of variance by ranks (Siegel, 1956). Results are given with their
exact probability of occurence. We considered that the results of the tests were statistically
significant when probabilities were < 0.05.

lil. RESULTS
A. Mangrove areas

The hurricane was accompanied by a storm tide which was followed by arise in sea
level of at least one meter. The mud from the bottom in shallow waters was stirred up by
the waves. Considerable amounts of freshwater runoff flushed the mangroves. These
phenomena induced a drop in salinity (to 7%o) and quite anoxic conditions (0.2 mg.02.1")
that lasted several days (Bouchon et al., 1991).

After the hurricane, numerous dead fishes were floating at the surface of the water in
the mangrove. Some fishes were observed dead on the substrate between the mangrove
roots and up to 20 m inshore. The dead fish species were the following : Gerres cinereus,
Eucinostomus gula, Eugerres brasilianus, Bairdiellaronchus, Lutjanus apodus, Haemulon
' bonariense, Mugil curema, Sphyraena barracuda, Chaetodipterus faber, Archosargus
rhomboidalis, Diodon holacanthus and Sphoeroides testudineus.

Fish surveys were conducted from 24th September 1989 (one week after the
hurricane) and the data could be compared to data acquired previously at the same station.
In the Manche-a-Eau lagoon, the results were compared to data from June 1989 (3 months
before the hurricane) and additional samples made in January 1990 (4 months after the
hurricane) and in March 1990 (6 months later) (Annex I).

The Friedman two-way analysis of variance by ranks was used to compare the fish
biomass among the four samples. A global statistical significant difference was found
between the samples (X?= 11.709 ; p = 0.0084).

The Wilcoxon signed-ranks test was used to compare the samples pairwise (Tab. 1).
The results show that the fish community observed before the hurricane (June 1989) was
different from the one observed after the hurricane (September 1989). Surveys conducted
in January and March 1990 were also different from the September 1989 sample. But in
January and March 1990, 4 and 6 months after the hurricane, fish biomass returned to the
previous situation of June 1989.

A drop in fish biomass was observed just after the hurricane. In January 1990, fish
biomass had returned to the pre-hurricane values. Decreases in the number of species and

6

number of individuals, as well as the diversity indices, were also noticed one week after the
hurricane.

The fish community observed in the mangrove lagoon during the study period
comprised 32 species. A Spearman rank- correlation coefficient calculated with the pre and
post-hurricane data showed a significant inverse correlation between the quantitative fish
dominances (Z = -2.817, p = 0.048). Before the hurricane, the dominant species in biomass
were : Sphoeroides testudineus, Bairdiella ronchus, Archosargus rhomboidalis,
Eucinostomus argenteus and Eucinostomus gula. These species usually correspond to the
fishes permanently residing in the mangrove (Louis and Guyard, 1982). After the hurricane,
these species were no longer present in the surveys, except for A. rhomboidalis (three
individuals collected). Moreover, gobiid fishes which were not commonly sampled in the
mangrove (chiefly Gobionellus oceanicus) were dominant in the community.

Thus, significant changes in the fish community were observed just after the hurricane
in the mangrove : 4 and 6 months later, the community had returned to its previous situation.

Table 1 : Results of the Wilcoxon tests concerning the fishes of Manche-a-Eau lagoon
( Z = values of the Wilcoxon test ; p = probability of realization of Ho ; * = significant values).

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B. Seagrass beds

In seagrass areas, a total of 50 fish species were collected in October 1988 (one year
before the hurricane), in October 1989 (10 days after), in January 1990 (4 months after) and
in March 1990 (6 months after the hurricane) (Annex II).

At Christophe Islet, the Friedman analysis of variance revealed a significant difference
between the fish biomass in the four samples ( X?= 17.891 ; p = 0.0013).

The Wilcoxon test was used to test the difference between the samples pairwise (Tab.
2). Only samples collected in January 1990 appeared significantly different from those of
October 1989 and March 1990. No significant difference was found in biomass between the
samples collected in October 1988 and the 3 samples collected after the hurricane. Thus,
there was no change in fish biomass immediately after the hurricane.

Table 2 : Results of the Wilcoxon tests on the fish community of Christophe Islet
(Z = values of Wilcoxon test ; p = probability of realization of Ho ; * = significant values).

jae Werranaruies October 1989 January 1990 March 1990
| October 1988 aa Z =- 1.589 Z =- 1.663 Z = 0.368

January 1990 p=0.0964 | p=0.0001 * per aeeeae bn 2 =-3.346
March 1990 p=0.7132 | p=0.1919 p = 0.0008 * eae

At Lambis Point, the Friedman test also revealed a significant difference between the
samples (X?= 13.05 ; p= 0.011). The Wilcoxon test showed a significant difference only
between the samples of October 1988 and January 1990, and between those of January 1990
and March 1990 (Tab. 3). As for the previous station, there was no change in fish biomass
just after the hurricane.

Conversely, a comparison of the Spearman rank correlation coefficients (rs)indicated
that the fish community structure differed significantly before and after the hurricane in
both stations (1s = -1.086, p = 0.277 at Christophe Islet and rs = 0.311, p = 0.756 at Lambis
Point). These differences are partly due to the appearance in the samples of schooling
transient fishes (Anchoa lyolepis, Diapterus rhombeus). Their suppression from the analysis
increased the values of the correlation coefficients.

October 1988

Table 3 : Results of the Wilcoxon tests on the fish community of Lambis Point.
(Z = values of Wilcoxon test ; p = probability of realization of Ho ; * = significant values).

[eso [omen [amine |

C. The coral reef areas

Pigeon island, a volcanic formation, is devoid of true coral reefs, but its steep slopes
support the most flourishing hermatypic coral community of Guadeloupe. Concerning the
fish communities, the results presented hereafter cover a 9 month period from April 1989
to January 1990. During this period, 12 censuses were made respectively before and after
the hurricane. These censuses were separated by a 12-day interval. A total of 89 fish species
were observed (Annex III).

The Wilcoxon signed-rank test was used to compare the biological parameters
obtained from the data collected before and after the hurricane, i. e., species richness, the
total density of fishes; the number of juveniles; the number of medium-size fishes; the
number of big-size fishes; the number of species possessing juveniles; the Shannon- Weaver
diversity and the evenness index (Tab. 4).

A significant difference was found for the total density of fishes, the number of
juveniles, H' and the Pielou evenness. The other parameters such as the species richness,
the number of big and medium-size fishes were not significantly different before and after
the hurricane. Since there were no significant changes in the amount of medium and large
fishes, only the juveniles were responsible for the observed changes in total abundance.

Table 4 : Results of the Wilcoxon test concerning the fish community of Pigeon Island ( Z = values of
the Wilcoxon test ; p = probability of realization of Ho ; * = significant values).

a ets aera end
a
ee
ee
a
ee

Pielou evenness

Moreover, a Spearman ranks correlation coefficient was computed between the
profiles of fish abundances before and after the hurricane. The correlation was highly
significant showing that there were no noticeable changes in the species composition or
their dominance ranks within the community.

Figure 4 shows the change in numbers of juveniles for the 24 samples distributed
before and after the hurricane. An important drop in the abundance of juveniles can be
observed just after the hurricane. The density observed remained low even four months
after the hurricane and these conditions would probably persist until the next period of
recruitment that occurs in summer.

Number of juveniles

We 20 3 4.56 7 8 29) JO) MN) 12,13) 14) 15) N67, 18) 19) 120) (21) 22) 23) 24.

Samples

Figure 4 : Change in number of juvenile fishes before and after the hurricane.

IV. DISCUSSION AND CONCLUSION

The effects of severe storms or hurricanes on the fish communities have been
documented from many parts of the world. For the Atlantic region, reports can be found for
Florida (Robins, 1957 ; Breder, 1962 ; Springer and McErlean, 1962 ; Tabb and Jones,
1962 ; Beecher, 1973 ; Bortone, 1976 ), Jamaica (Woodley et al., 1981 ; Kaufman, 1983 ;
Williams, 1984 ), Puerto Rico (Glynn et al., 1964 ) and Texas (Hubbs, 1962. For the Indo-
_ Pacific region, observations have been reported for Hawaii (Walsh, 1983), the Great Barrier
Reef of Australia (Lassig, 1983), the Fiji Islands (Cooper, 1966), Japan (Araga and Tanase,
1966 ; Tribble et al., 1982 ) and Reunion Island (Letourneur, 1991). However, as pointed
out by Walsh (1983), the effects of catastrophic storms on fish communities is still unclear.
Some authors reported a high fish mortality after a hurricane, while others observed
noticeable changes in the fish communities. Some did not observe any significant
alterations in the community due to the storm.

Among the authors who did not find noticeable changes in the fish communities after
a hurricane are Springer and McErlean (1962) and Bortone (1976) in Florida. Springer and
McErlean (1962) noticed that reef fish populations were not much disturbed after a
hurricane although reef formations were destroyed. However, their observations occurred
one month after the hurricane. Bortone (1976) concluded that no major changes occurred
in the fish community as a result of Hurricane Eloise. He related this to the location of the
study area (well oxygenated waters and not directly affected by the surge) and to the possible
presence of protective shelters for the fishes.

Robins (1957) was the first to report on the effects of a severe storm on fishes. He
observed numerous dead specimens washed onshore after a severe storm in Florida. In the
same region, Hurricane Donna also caused a high fish mortality (Tabb and Jones, 1962).
After Hurricane Edith at Puerto Rico, Glynn et al. (1964) reported dead fishes floating near

10

the coast. Cooper (1966) presented a dismal picture of the reefs of Fiji Islands after the
hurricane of February 1965 ; dead fishes were floating on the water and thousands were
washed up on the beach. High fish mortality was also recorded in Japan after typhoons
(Araga and Tanase, 1966; Tribble et al., 1982). Araga and Tanase (1966) made quantitative
observations on the stranded fishes and noticed that about 84 % of the species and 98 % of
the individuals were inshore inhabitants. In general, the fish communities from the shallow
coastal waters are mostly affected.

In the mangrove areas of Grand-Cul-de-Sac Marin, the trees were completely
defiolated after the hurricane. However, the loss of wood biomass was variable according
to the area. In the part of the mangrove areas dominated by the red mangrove, the estimation
of the loss of biomass fluctuated between 25 and75 % (Bouchon etal., 1991). Fish mortality
mainly occured in the mangrove areas where the fishes were exposed to low salinity, high
levels of suspended sediments and oxygen depletion. The post-hurricane fish community
was significantly different to the pre-hurricane community.

The impact of Hurricane Hugo on the seagrass beds was varied. The Thalassia
testudinum beds, even those situated in shallow waters, were only slightly affected by the
direct impact of the cyclonic surge. On the contrary, the Syringodium filiforme beds were
much more affected. A large amount of S. filiforme leaves and roots were washed onshore.
In the months following the hurricane, a delayed mortality of the T. testudinum meadows
was observed in the Grand Cul-de-Sac Marin. In some places, T. testudinum was progressively
replaced by S. filiforme (Bouchon et al., 1991). In the seagrass beds, the observed changes
in the fish community were more complex. They only appeared a few months after the
hurricane. This may be related to the delayed mortality of Thalassia testudinum.

In the coral reef environment the observed changes were less important than would be
expected from the strength of the hurricane. For the benthic community, the damage due to
the cyclonic surge mostly affected branching species of corals, such as Millepora alcicornis
(especially in shallow waters), Madracis mirabilis, Acropora cervicornis, Porites porites
and Eusmilia fastigiata. These colonies, broken and tossed by the waves, smashed the other
benthic organisms. Massive corals withstood the hurricane better than branching corals.
The soft benthic organisms, such as sponges and gorgonians were greatly damaged
especially in shallow waters (Bouchoneral., 1991). During the weeks following the hurricane,
a “bleaching” phenomenon affected many coral colonies. This bleaching consisted in the
loss of their symbiotic unicellular algae (zooxanthellae). This is generally linked to a state
of stress of the animals. Most of these corals finally died. Three months after the hurricane,
the bleaching phenomenon progressively disappeared. Before the hurricane a dense algal
community, dominated by species belonging to the genus Dictyota, were present at Pigeon
Island. These algae were washed ashore by the storm waves. A few weeks after, an outbreak
of a red algae belonging to the genus Liagora occurred. Three months after, the Liagora
population disappeared and the Dictyota resettled (Bouchon et al., 1991).

In the study area, Hurricane Hugo mainly affected the juvenile fishes. Their density
on the study reef drastically decreased the week following the hurricane. The same
observations were made by Lassig (1983) on the Great Barrier Reef of Australia who noted
that “the cyclone had little effects on adults but caused high juvenile mortality and re-
distribution of sub-adult individuals”. Beecher (1973) also reported a high mortality of

11

juveniles of a Pomacentrid fish, Pomacentrus (=Stegastes) variabilis, after Hurricane Agnes
in Florida.

In Guadeloupe, no specific changes in reef fish behavior were noticed after the
hurricane. This is contrary to what had been described in Jamaica after Hurricane Allen
(Woodley et al., 1981 ; Kaufman, 1983) where cryptic species were observed in the open
waters and planktivorous species swam near the bottom. The territorial fishes such as
Stegastes planifrons became more aggressive and schools of parrotfish were reduced in
size. In Hawaii, Walsh (1983) reported that fishes from the reef flats moved down to the
deeper zones.

During the weeks following the hurricane in Guadeloupe, some acanthurid species
(Acanthurus bahianus and A. coeruleus) were observed browsing the algae belonging to the
genus Liagora that abnormally proliferated in the coral community. Nevertheless,
examination of the survey results showed that the density of herbivorous fishes in the study
areas did not increase significantly after the hurricane. This is contrary to what had been
noticed in Martinique following the proliferation of Sargassum (Bouchon et al., 1988). In
Jamaica, Williams (1984) and Kaufman (1983) had reported an increase in the number of
Stegastes planifrons, an herbivorous species, after Hurricane Allen.

The consequences of a hurricane on fish communities depend on various factors: the
violence of the phenomenon ; the geographical location of the study areas ; the reef
topography ; the depth location of the observations ; and above all, the magnitude of the
damage on the reef associated benthic communities. In the island of Guadeloupe, the
immediate impact of Hurricane Hugo was important for the fish communities situated in the
mangrove. However, in this habitat, the fish community is well adapted to variations in
environmental factors and apparently recovered within a few months. The changes which
occurred in the seagrass beds reflect a long term decay of this habitat. As for the reef fishes,
' the drastic drop of juveniles may have an influence in the structuring of the fish community
in the long term.

ACKNOWLEDGEMENTS

This research was funded by the Commission d’ Organisation de la Recherche dans
les Départements et Territoires d’ Outre-Mer (C.O.R.D.E.T.) of the French Government.

BIBLIOGRAPHY

Anon., 1990. L’ouragan Hugo. Pub. Service Météorologique Interrégional Antilles Guyane.
Météo France, 32 pp.

Araga A., Tanase H., 1966. Fish stranding caused by a typhoon in the vicinity of Seto. Publ.
Seto Mar. Biol. Lab., 14 : 155-160.

Beecher H.A., 1973. Effects of a hurricane on a shallow-water population of damselfish,
Pomacentrus variabilis. Copeia, 3 : 613-615.

12

Bortone S.A., 1976. Effects of a hurricane on the fish fauna at Destin, Florida. Fla. Sci., 39 :
245-248.

Bouchon C., Bouchon-Navaro Y., Louis M., 1988. A firstrecord of a Sargassum (Pheophyta,
Algae) outbreak in a Caribbean coral reef ecosystem. Com. oe Gulf Carib. Fish.
Inst. Congress, St Thomas : 452-468.

Bouchon C., Bouchon-Navaro Y., Imbert D., Louis M., 1991. Effets de l’ouragan Hugo
sur les communautés cotiéres de Guadeloupe (Antilles frangaises). Ann. Inst. océanogr.,
Paris, 67 (1) : 5-33.

Bouchon-Navaro Y., Harmelin- Vivien M., 1981. Quantitative distribution of herbivorous
reef fishes in the gulf of Aqaba (Red Sea). Mar. Biol., 63 : 79-86.

Breder C.M., 1962. Effects of a hurricane on the small fishes of a shallow bay. Copeia, 2 :
459-248.

Cooper M.J., 1966. Destruction of marine flora and fauna in Fiji caused by the hurricane
of February 1965. Pac. Sci., 20 : 137-141.

Glynn P.W., AldomovarL.R., Gonzales J.G., 1964. Effects of hurricane Edith on the marine
life in La Parguera, Puerto Rico. Carib. J. Sci., 4 : 335-345.

Hubbs C., 1962. Effects of a hurricane on the fish fauna of a coastal pool and drainage ditch.
Tex. J. Sci. , 14 : 289-296.

Kaufman L.S., 1983. Effects of Hurricane Allen on reef fish assemblages near Discovery
Bay, Jamaica. Coral reefs, 2 : 43-47.

Kjerfve B., Dinnel S.P., 1983. Hindcast hurricane characteristics on the Belize barrier reef.
Coral reefs, 1(4) : 203-207.

Lassig B.R., 1983. The effects of a cyclonic storm on coral reef fish assemblages. Envir.
Biol. fish, 9 (1) : 55-63.

Letourneur Y., 1991. Modifications du peuplement de poissons du platier récifal de Saint-
Pierre (ile de La réunion, Océan Indien) consécutives au passage du cyclone Firinga.
Cybium, 15 (2) : 159-170.

Louis M., Guyard A., 1982. Contribution al’ étude des peuplements ichtyologiques dans les
mangroves de Guadeloupe (Antilles frangaises). Bull. Ecol., 13 (1) : 9-24.

Pielou E.G., 1969. An introduction to mathematical ecology. Wiley, Interscience, New-
York : 286 pp.

Robins C.R., 1957. Effects of storms on the shallow-water fish fauna of Southern Florida
with new records of fishes from Florida. Bull. Mar. Sci. Gulf and Caribbean, 7 (3) :
266-275.

Shannon C.E., Weaver W., 1948. The mathematical theory of Communication. Urbana
Univ. Press, Illinois : 117 pp.

Siegel S., 1956. Nonparametric statistics for the behavioral sciences. Mc Graw-Hill, New
York : 312 pp.

Springer V.G., McErlean A.J., 1962. A study of the behavior of some tagged South Florida
coral reef fishes. Am. Mid. Nat., 67 : 386-397.

Stoddart D.R., 1974. Post-hurricane changes on the British Honduras reefs : resurvey of
1972. Proc. 2nd Inter. Coral Reef Symp., Brisbane, 2 : 473-483.

Tabb D.C., Jones A.C., 1962. Effects of Hurricane Donna on the aquatic fauna of North
Florida Bay. Trans. Am. Fish. Soc., 91 : 375-378.

13

Tribble G.W., Bell J.L., Moyer J.T., 1982. Subtidal effects of a large typhoon on Miyake-
Jima, Japan. Publ. Seto Mar. Biol. Lab., 27 : 1-10.

Walsh W.J., 1983. Stability of a coral reef fish community following a catastrophic storm.
Coral reefs, 2 : 49-63.

Williams A.H., 1984. The effects of Hurricane Allen on back reef populations of Discovery
bay, Jamaica. J. Exp. Mar. Biol. Ecol., 75 : 233-243.

Woodley J.D., Chornesky E.A., Clifford P.A., Jackson J.B.C., Kaufman L.S., Knowlton N.,
Lang J.C., Pearson M.P., Porter J.W., Rooney M.C., Rylaarsdam K.W., Tunnicliffe
V.J., Whale C.M., Wulff J.L., Curtis A.S.G., Dallmeyer M.D., Jupp B.P., Koehl
M.A.R., Neigel J., Sides E.M., 1981. Hurricane Allen’s impact on Jamaican coral
reefs. Science, 214 : 749-755.

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Annex II (continued) : Numbers (N), biomass (W) and diversity indices for the fish samples collected with a seine net in the

FAMILY

LUTJANIDAE

POMADASYIDAE

SPARIDAE

SCIAENIDAE
GERREIDAE

BOTHIDAE
SOLEIDAE

SCORPAENIDAE
CHAETODONTIDAE
LABRIDAE
SCARIDAE

GOBIDAE

ACANTHURIDAE

MONACANTHIDAE
TETRODONTIDAE

DIODONTIDAE

Total

Species richness
Shannon Index
Pielou Index

SPECIES

Harengula clupeola
Anchoa cf lyolepis
Cosmocampus elucens
Syngnathus sp
Holocentrus rufus
Sphyraena barracuda
Hypoplectrus puella
Serranus flaviventris
Caranx latus

Oligoplites saurus
Selene vomer

Lutjanus analis

Lutjanus apodus
Lutjanus griseus
Lutjanus synagris
Ocyurus chrysurus
Haemulon aurolineatum
Haemulon bonariense
Haemulon chrysargyreum
Haemulon flavolineatum
Haemutlon plumieri
Haemulon sciurus
Archosar gus rhomboidalis
Calamus sp

Bairdiella ronchus
Diapterus rhombeus
Eucinostomus argenteus
Eucinostomus gula
Gerres cinereus
Citharichthys spilopterus
Achirus lineatus
Pseudupeneus maculatus
Scorpaena grandicornis
Chaetodon capistratus
Lachnolaimus maximus
Sparisoma chrysopterum
Sparisoma radians
Gobidae sp.1

Gobidae sp. 2

Gobidae sp.3
Gobionellus oceanicus
Acanthurus bahianus
Acanthurus chirurgus
Monacanthus ciliatus
Sphoeroides nephelus
Sphoeroides greeleyi
Sphoeroides spengleri
Sphoeroides testudineus
Diodon holacanthus

50 species

138

215

W (g) N
81
97 5
32.3 2
31.3 2
he)
4
633.7 90
12.3 3
2
2
10.5 i
9
1.5
85.5 34
42
88.2 2
0.4 4
3.3
1.4 1
43.2 1
85 2
1045.7 2A5
16
2.14
0.54

922.2

28.1
6.3

287.5

151.7

15.1

LAMBIS POINT
Oct. 89
W (g)
Albula vulpes

98

Jan. 90
W(g)

309.1

85.3

193.3

60.4
157.3
152.2

3.1
0.8

seagrass beds of Grand Cul-de-Sac Marin Bay.

March 90
N W (g)
6 27.1
3 6.1
10 37.3
1 15

153 396
Wi 14.2
7 42.4
9 57.3
12 83.9
1 2.6
2 20.4
3 12.8
2 0.3
1 23.8
4 3.1
2 1.6
1 5.2
1 293.8

225 1042.9

18
2.7

Annex II : Numbers (N), biomass (W) and diversity indices for the fish samples collected with a seine net in the
seagrass beds of Grand Cul-de-Sac Marin Bay.

CHRISTOPHE ISLET

FAMILY SPECIES Oct. 88 Oct. 89 Jan. 90 March 90
N W (g) N W (g) N Wg), NN W(g)
ALBULIDAE Albula vulpes 1 5.8 1 20.3
CLUPEIDAE Harengula clupeola 27 81
ENGRAULIDAE Anchoa cf lyolepis 8 13.9 347 995.3 360 550.5
SYNGNATHIDAE Cosmocampus elucens
Syngnathus sp
HOLOCENTRIDAE Holocentrus rufus 1 43.6
SPHYRAENIDAE Sphyraena barracuda 2 143.5 6 8.9 4 134.5
SERRANIDAE Hypoplectrus puella 1 2.8 8 77 2 14.7
Serranus flaviventris 10 42.7 3 3.8 17 51.6 4 13.1
CARANGIDAE Caranx latus 1 2 1 6
Oligoplites saurus
Selene vomer 5 11.9 1 5
LUTJANIDAE Lutjanus analis 1 21.9
Lutjanus apodus 3 13 1 74.1
Lutjanus griseus
Lutjanus synagris 75 55 43 278.2 12 88.5
Ocyurus chrysurus 152 595.2 9 69.3 115 583.8 5 18.1
POMADASYIDAE Haemulon aurolineatum 4 4.5
Haemulon bonariense 1 8.8 1 5.1 2 10.1
Haemulon chrysargyreum 2 17.6
Haemulon flavolineatum 13 18.2 2 5.2
Haemulon plumieri 14 114.1
Haemulon sciurus
SPARIDAE Archosar gus rhomboidalis 2 81.7 1 31.8 2 45.5
Calamus sp
SCIAENIDAE Bairdiella ronchus 3 16.9
GERREIDAE Diapterus rhombeus 128 945.3 398 1173.6 99 344.9
Eucinostomus argenteus 12 23.5 31 135.4
Eucinostomus gula 70 293.7 258 358.6 200 609.9 103 472
Gerres cinereus 2 8.6 8 63.4
BOTHIDAE Citharichthys spilopterus 1 15.7 9 23.7 4 19.1
SOLEIDAE Achirus lineatus 20 355.7 11 4
Pseudupeneus maculatus 1 14.3
SCORPAENIDAE Scorpaena grandicornis
CHAETODONTIDAE Chaetodon capistratus 7 14.6 1 6.6
LABRIDAE Lachnolaimus maximus 1 49
SCARIDAE Sparisoma chrysopterum 1 58.3
Sparisoma radians 5 51.6
GOBIDAE Gobidae sp.1 17 57
Gobidae sp. 2 2 0.4
Gobidae sp.3 4 0.9 1 0.1
Gobionellus oceanicus 5 1:5
ACANTHURIDAE Acanthurus bahianus 1 17.2 1 2.9
Acanthurus chirurgus 1 8.4 1 1.2
MONACANTHIDAE Monacanthus ciliatus
TETRODONTIDAE Sphoeroides nephelus 1 0.2
Sphoeroides greeleyi 1 4.3 2 0.9
Sphoeroides spengleri 1 12 1 0.6 1 0.5
Sphoeroides testudineus 1 0.5 2 9 1 1
DIODONTIDAE Diodon holacanthus 2 139 4 987.9
Species richness 50 species 19 17 29 20
Shannon Index 2.98 1.83 3.29 2.66

Pielou Index 0.7 0.45 0.68 0.61

land.

igeon is

Number of indivuals per species observed before (1 to 12) and after (13 to 24) the hurricane at P

Annex III

23-24

16 17

15

12

10

Lycodontis moringa

Muraena miliaris

Synodus intermedius

10

Neoniphon marianus

Holocentrus rufus

Myripristis Jacobus

14 «(14

14

22

13

36 22 2

BS G3 e214 2222013

17 17

16

Aulostomus maculatus
Fistularia tabacaria

Scorpaena plumieri

14

Cephalopholis cruentatus
Cephalopholis fulva

Epinephelus adscensionis

Hypoplectrus chlorurus

Hypoplectrus cf guttavarius
Hypoplectrus nigricans

11

Hypoplectrus puella

Hypoplectrus sp. 1

Mycteroperca interstitialis
Paranthias furcifer

Serranus tabacarius

Serranus tigrinus

1

Heteropriacanthus cruentatus
Carangoides ruber
Caranx latus

0

0 275 4

0

Selar crumenophthalmus

Inermia vittata

0 115

40

0

0

0 20 20

Lutjanus apodus
Lutjanus jocu

Lutjanus mahogoni

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ATOLL RESEARCH BULLETIN

NO. 423

THE SIAN KA'AN BIOSPHERE RESERVE CORAL REEF SYSTEM,

YUCATAN PENINSULA, MEXICO

BY

ERIC JORDAN-DAHLGREN, EDUARDO MARTIN-CHA VEZ,
MARTIN SANCHEZ-SEGURA, AND ALEJANDRO GONZALEZ DE LA PARRA

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

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THE SIAN KA'AN BIOSPHERE RESERVE CORAL REEF SYSTEM,
YUCATAN PENINSULA, MEXICO

BY

ERIC JORDAN-DAHLGREN’*, EDUARDO MARTIN-CHAVEZ”,
MARTIN SANCHEZ-SEGURA™, AND ALEJANDRO GONZALEZ
DE LA PARRA™

ABSTRACT

The coastal shelf of the Sian Ka’an Biosphere Reserve was
surveyed in order to determine the distribution and
composition of coral reefs, and to assess the nature and
relative cover of coralline biota along the Reserve shelf,

both in reef and non-reef habitats. A census of 11 living
morphological attributes (including stony corals, sponges,
algae and gorgonians), and 3 non-living ones, was

quantitatively estimated by means of line-transects at 30
sampling stations. Well developed coral reef structures, are
mostly restricted to shallow Acropora palmata reefs, forming
a fringing-barrier reef bordering the shoreline. A relatively
high proportion of dead A. palmata was found in these reefs,
both in the crest and in the shallow fore reef zone. The
cause of A. palmata mortality is unknown. In deeper waters,
isolated raised karstic features are colonized by a rich and
diverse coral community. However, the majority of the bottom
of the shallow shelf consists of hardgrounds with sparse coral
cover. Coral community composition and relative degree of
development seems to be influenced principally by the
magnitude of the submarine topographical relief and depth.

INTRODUCTION

As part of the effort to preserve and protect natural systems
threatened by the development of modern society, a large Bios-
phere Reserve was established in the eastern margin of the
Yucatan Peninsula, México, in 1986. The Sian Ka’an Biosphere
Reserve encompasses a complex set of environments and commu-
nities, ranging from tropical forests, wetlands, estuarine and
marine coastal lagoons, to coral reefs. The environment of

* Instituto de Ciencias del Mar, UNAM. Ap. Postal 1152, Canctin 77500, Q. Roo. Mexico.
** Parque Eco-Arqueolégico Xcaret, Ap. Post. 833, Canctin 77500, Q. Roo. México

Manuscript received 20 May 1992; revised 22 October 1993

the Sian Ka’an reserve has been studied with a strong emphasis
on terrestrial topics (see CIQRO, 1983; Navarro and Robinson,
1990). No similar comprehensive studies of the marine systems
in the Sian Ka’an Reserve have been carried out. Long term
studies have been restricted to the biology and fishery of
spiny lobsters (Lozano-Alvarez, et al., 1991), while other
published studies mostly consist of taxonomic lists from the
northern part of the reserve or from other nearby, accessible
areas (Navarro and Robinson, 1990).

This study was conducted in order to contribute to the
understanding of the broad ecological framework of the benthic
coastal marine ecosystems in the Sian Ka’an Reserve. Because
of the expanse of the reef and coastal system of the Sian
Ka’‘an Reserve, this first work is by necessity a preliminary,
general approach.

STUDY AREA

The Sian Ka’an Biosphere Reserve is located on the eastern
side of the Yucatan Peninsula, facing the Caribbean Sea (Fig.
1). The Reserve covers an area of approximately 4,500 km’, of
which some 1,200 km? correspond to lagoon and marine
environments. The marine coastline extends for more than 100
km, and a nearly continuous reef system is found along it.

The Yucatan Peninsula is a large platform formed by extensive
carbonate and evaporite deposition, since the lower Cretaceous
to the Present (Weidie, 1985). On the eastern margin of the
Peninsula are a series of NNE to NE trending ridges and
depressions, reflecting the occurrence of the horst and
grabben blocks of the Rio Hondo fault zone. The bays of
Ascenci6n and Espiritu Santo, the major geomorphological
features in the eastern continental margin, are a result of
this fault system (Fig. 1). The shelf is covered by carbonate
rocks and sediments of Tertiary to Holocene age. In the Sian
Ka’an coastal zone, Quaternary sediments predominate from
Punta Tupac (section V, Fig. 1) to the north; while older
sediments predominate south of Punta Herrero (section VI, Fig.
1; Lopez Ramos, 1973).

The Sian Ka’an Biosphere Reserve has a low relief carbonate
coastline of alternating rocky outcrops and sandy beaches,
interrupted by the mouths of the two large, shallow bays, and
the Boca Paila inlet. The shoreline of the bays and inlets is
bordered by a well-developed mangrove forest (Olmsted and
Durdn, 1990), while the bottoms are predominantly covered by
the seagrass Thalassia testudinum. The coastal shelf extends
offshore from about 1000m to almost 4000m, gently sloping
seaward. At the shelf edge, the shelf abruptly drops to depths

3

in excess of 400m (Fig. 2). The morphology of the shelf is
locally modified by erosional terraces and small escarpments.
The escarpments are relatively steep (20° to 30°) as compared
with the average slope of the shelf (3° to 5°), and they are
found in two depth ranges in almost all sections of the shelf.
The first escarpment is found at depths of -7 to -10m from
sections I to V, and slightly deeper (-9 to -14m) in sections
VII to VIII. The second escarpment is found between -33 to -
39m in sections IV to VI, and slightly deeper in section VII
(Gserton—45miy) Fag.) 2))r.

The climate on the Sian Ka’an Reserve is warm and subhumid.
Mean air temperature is 25.4 °C, although in the coastal zone
air temperature is strongly influenced by predominant winds
(pers. obs.). Trade winds predominate from March to September,
and colder north winds from November to March. Average
rainfall for a fifteen year period (1967-1982) was 1023.3 +
320.6 mm per year (Lopez-Ornat, 1983). Seventy percent of the
yearly rainfall occurs from May to October, with precipitation
peaks in June and September.

Hydrological data from both the marine and estuarine-lagoonal
environments are scarce, since no systematic survey has been
done. The few available data indicate surface salinities in
the outer areas of the bays are in the order of 35-36 ppt, and
sea surface temperatures range from 31°C in summer, to 23°C in
winter (Briones, pers. com.). These values are comparable
with those of the Belizean shelf (Purdy et. al., 1975) and
with those noted in the northeast end of the Yucatan Peninsula
at Puerto Morelos (Merino and Otero, 1991). Run-off and
underground seepage may provide enough fresh and brackish
water to reach the fringing reefs (particularly at Boca Paila
inlet, Section II; Fig. 1). During ebb tide we have observed
Slightly brownish (mangrove tanins ?) and colder superficial
waters flowing through channels in localities III and VI (Fig.
1). Sediment runoff however, is limited due to the karstic
nature of the terrestrial substrate and the scarcity of soil
on the land. In the case of the banks and barrier reefs that
border the two large bays, fresh water influence is perhaps
lower due to dilution in the large, predominantly marine,
water mass of the bays (pers. obs.).

METHODS

Reef crests and other coastal shallow features were mapped by
using LANDSAT color enhanced satellite imagery and low level
black and white aerial photography (Fig. 1). The surveyed
sections, encompassing the coastline of the reserve (I to
VIII, Fig. 1; Table 1) were determined by systematic sampling
criteria and to a certain extent by remarkable features of
both coast and reef morphology.

4

Precise geographical positioning of the sections to be sampled
(Fig. 1, I to VIII) was obtained by means of satellite
navigation system (GPS). The precision of the "fix" was in the
order of tens of meters. The same GPS system together with
radar bearing checks was utilized to control the registers of
the bathymetric profiler on each section. ‘The bathymetric
transects were orthogonal to the shoreline, from the edge of
the shelf to the shore, and were done in two parts: The first
one was made with high resolution echosounders on board the
research vessel, from the edge of the shelf to approximately -
10m (ship’s draft approximately 5m). The second one was made
with a portable echosounder, on a small boat following a
compass course. Drift and speed of the small boat were tracked
by radar from the research vessel.

In each section, a qualitative survey was carried out by means
of drift diving at depths of -10m, -20m, -30m and -40m (marked
by anchored buoys). Each drift dive extended at least one km
north and south from the buoys. A much wider survey of the
shallow reef areaS was carried out by snorkeling, including
important shallow reef structures that were not covered by the
Giving (Localities A, B and C; Fig. 1). In all qualitative
surveys an estimation of the reef structure (dimensions, depth
ranges, morphology and setting) was carefully noted on
underwater slates and by still photography. The most abundant
(relative bottom coverage) species of corals, sponges,
gorgonians and macroalgae colonizing all types of substrata
were recorded (Jordan, 1990).

The quantitative sampling of the coral communities was
designed to provide a global coverage perspective rather than
a detailed study of isolated points. The method was based on
the estimation of the relative coverage of the sessile coral
reef macrobiota as well as substrata apparently devoid of
biota. The biota was classified by means of attributes related
to biotic substrate control and its relative importance as
reef builders (Table 1; see Bradbury et. al., 1986; Reichelt
eG aliagin1986)) «

For the sampling, we used multiple chain transects (Loya,
1978). At each sampling station five 20m chain transects were
randomly laid parallel to the bathymetric profile. This sample
size was arbitrarily determined based on previous experiences
in a similar environment (Jordan et al., 1981; Jordan, 1989a),
because limited ship time, did not allow us to estimate
specific sample sizes for the different habitats. The relative
importance of each attribute was determined by summing the
number of links that covered the biota and non-biotic surfaces
under a given transect-chain. The data of the five transects
were pooled together to obtain a single value per attribute
and per station, and expressed as lineal cm of cover (1
link=3.32cm; Table 2).

5

Four sampling stations on each section were quantitatively
surveyed: a) Rear Reef-Crest (RR-C, shallow reefs); b) -10m
Slope (associated with the first main escarpment); c) -20m
Slope (mainly flat hard grounds), and -30m Slope (associated
with the main second escarpment). The attribute data were
classified by means of cluster analysis (Bradbury et al.,
1986), pooling data of sampling stations after logarithmic
transformation to eliminate size and abundance effects and to
ensure independence of scales (Gower, 1986; Gauch, 1982). The
cluster analysis was performed using Euclidean distance as a
measure of similarity and average linkage.

RESULTS
I. Reef Morphology

Two main coral reef types can be recognized in the Sian Ka’an
Biosphere Reserve: I) Crest Reefs. Shallow, mostly emergent
reefs, fringing the land margin or forming narrow barriers
offshore. I1) Slope Reefs. Deeper reefs associated with the
discontinuous shelf escarpments. Both reef types are strongly
influenced by the local coastal and shelf morphology and there
was great variability within any particular section. Here, we
will describe only the main reef features.

Crest Reefs: A submerged consolidated calcareous crest runs
almost continuously, roughly parallel to the coastline at
average depths of less than -1 to more than -3m. The
consolidated crest, perhaps a former shoreline, is separated
from the shore by a shallow lagoon, a few hundred meters wide
at most (except in front of the bays). Dense stands of
Acropora palmata grow upon this crest forming reefs whose
morphology appears to be strongly influenced by the bottom
topography. In the majority of the sections, the crest reef
structures are better developed lagoonward than seaward (Fig.
3), and there is great variability in the degree of
development of the Acropora reefs from one locality to
another, mostly as a function of local water depth (Fig. 4).

In sections I, II and V (Fig. 3), the crest reef comprises
isolated, elongated coral patches of varying dimensions
growing along the submerged crest rarely more than 1.5 to 2m
high. The size and relative degree of development of these
patches decreases in shallower water. In these localities, A.
palmata stands crown the submerged crest and sturdy Millepora
complanata colonies may fringe the stands to seaward. In
general though, abundant coral growth does not extend much
beyond the crest. A relatively poorly developed rear reef
community mostly composed of isolated colonies of Montastrea
annularis and Agaricia tenuifolia, may extend the patches
toward the lagoon. Many other, less abundant, coral species

6

can be found here. The lagoon bottom is sandy and normally
covered by Thalassia testudinum seagrass beds. In localities
IV and B (Fig. 3), the calcareous pavement is very shallow
(less than 1m) and very close to the shore line, sparsely
covered by small colonies of M. complanata and A. palmata..

The most developed A. palmata reefs in the Sian Ka’an area are
found in sections III and IV. The reef in section III, unlike
all others, rises from a relatively deep bottom (2m) and
extends seaward to 5m depth from the submerged crest through
large, well developed, and irregular spurs (30 to 100m long;
20 to 50m wide at the base; 2 to 3.5m high; Fig. 3). At the
time of the survey most of the A. palmata colonies in this
formation were dead with few signs that recovery was underway,
although encrustation and bioerosion on these colonies was not
readily evident. The bottom of the grooves between the spurs,
is a flat pavement, covered with a thin layer of sand and
colonized by Gorgonia flabellum. A similarly well-developed
Acropora reef is found in section VI, and in contrast with the
former one A. palmata colonies appear quite healthy. In this
reef there are no spurs, starting from a crest crowned with
sturdy M. complanata colonies, many large A. palmata colonies
form a loose matrix down to -5 to -7m. On the lagoon side,
reefs of both sections drop abruptly forming an almost
vertical wall of A. palmata, up to 3m high where large
colonies of Agaricia tenuifolia and Porites are also abundant.
In section VI, large colonies of Montastrea annularis and
abundant patches of Acropora cervicornis are found close to
this rear wall.

The mouth of Ascencion Bay is framed by a chain of small reef
banks, prograding southward from locality A (Fig. 1). The bank
reefs are well developed A. palmata formations growing upon a
raised platform (-2 to -2.5m). Nicchehabim reef (locality A),
has a cuspate shape with the lateral tips deeply curved
inside, almost encircling an internal shallow lagoon (Fig. 3).
The reef is formed by well developed external belt of
partially dead A. palmata, with many large dendritic
protrusions extending toward the inner "lagoon". Here, large
colonies of M. annularis, Dendrogyra cylindrus, and relatively
large patches of Agaricia tenuifolia and Acropora cervicornis
predominate. As the banks approach the southern tip of the
bay’s mouth, the bottom becomes shallower, and they give way
to a series of isolated stands, as in section IV.

Espiritu Santo Bay is bordered by a continuous A. palmata
barrier, interrupted in only two places by moderately wide
channels (Fig. 1). The reefs are similar to those described
above, and their degree of development is apparently regulated
by the depth of the lagoonal floor, in the sense that the
shallower the bottom, both the vertical and horizontal
extension of the living reef is smaller. No extensive coverage

7

of reef flats are found here. The bottom is very shallow close
to section V and gradually deepens toward the central part of
the Bay’s mouth (locality C). On the edge of the channels very
well developed reefs are found, not unlike those at localities
III and VI.

In sections VII and VIII, the submerged crest is absent.
Instead a flat calcareous platform, less than 2m deep, extends
for several hundred meters offshore (Fig. 3). The seaward part
is colonized by gorgonians, mostly Gorgonia flabellum and
Plexaura flexuosa, while on the inner part A. palmata stands
flourish, together with colonies of A. tenuifolia. In section
VIII the seaward section of the platform pavement is deeply
pitted, and colonies of Siderastrea siderea roll freely in the
bottom of some pits. In the southern end of section VII, at
depths of -4 to -8m, a submerged reef is composed of a mixture
of large interlocked M. annularis pinnacles, topped in places
by large A. palmata colonies and many other coral species.
The pinnacles and isolated colonies constitute a rather solid
structure, a few hundred meters long.

Fore Reef Slope. Two types of diverse coral communities grow
upon well consolidated, raised features associated with small
escarpments on the fore reef slope. Plataform reefs are mostly
associated with the first escarpment (-7 to -14m), and spur-
block reefs are mostly related with a deeper escarpment (=33
to -45m).

Plataform reefs. Coral communities inhabit reefs formed by
relatively extensive platforms (more than one hundred meters
long) rising from 1 to more than 3m above the mostly denuded
basal pavement. This gives the reef the morphology of a raised
platform with spur-like extensions on the seaward side, but
not on the shoreward margin (Fig. 3).

In section III, a well developed A. palmata reef colonizes the
platform (noticeable on the shoreward margin), at depths of -8
to -10m. The reef has irregular spurs, 10 to 12m wide at the
base, and often over 3m in height, extending for some 20m to
almost 100m meters seaward. As in the shallow crest reefs of
section III, most of the A. palmata colonies of the platform
reef, were dead. Other coral species, such as A. tenuifolia,
M. annularis, P. porites and a few stands of A. cervicornis,
are found mostly on the central and back parts of the reef.

In section IV at a depth of -7 to -9m, is another platform
reef similar to that described above, however, large colonies
of A. tenuifolia dominate on the edge of the spurs and
platform. Although many other coral species are present, they
are not as abundant; and on the upper part of the platform
gorgonians are conspicuous. The platform rises for 2 or 3m on

8

the seaward margin, and in several places erosional notches
are found at the base of the spur-like extensions.

At about -17m in section III, a platform reef has irregular
spur-like seaward prolongations that are part of the
consolidated platform, with a relief of up to 4m above the
basal pavement (Fig. 3 and 4). An interesting feature of this
platform reef is the presence of inner, fracture-like channels
which seem to follow the alignment of the spur-like features.
These inner channels are found inside the platform and
seldomly reach the edge of the reef platform, they may be
former surge channels. The channels are narrow (1 to 1.5m),
shallow (-1 to -2m) and of variable longitude, the bottom is
more or less flat and mostly covered with sand. The walls of
these channels are vertical and in places the channels are
blocked by M. annularis colonies growing from the bottom, or
are covered by colonies of the same species. The coral
community of this platform reef is rich, dominated by massive
and encrusting corals, colonizing the upper parts of the
platform edges.

Spur-block Reefs. These reefs are mostly found at a depth of
approximately 30m, associated with the main second escarpment
(Fig. 4). They consist of a nearly parallel series of
irregular and mostly discontinuous raised blocks and elongate
domes, running at orthogonal angles to the general trend of
the shoreline alternating with sandy grooves. The overall
impression is that of a set of independent, eroded spurs (Fig.
Bes

Each spur-block can be formed by several smaller blocks with
roughly the same orientation. In contrast with the platform
reefs, the sides of the blocks descend at a shallow angle
toward the basal pavement. Dimensions of these structures are
highly variable from one section to the other. In sections VI
and VII the width of the blocks varies between 8 and 12m. They
rise for 1 to 2m above the sea floor and are separated by
narrow grooves 1 to 2m wide. In sections IV and V the blocks
range in length from less than 10m to more than 40m, rise to
more than 3m high, and the grooves vary from 3 to 5m wide. The
community that colonizes the deep spur-blocks is different
from that found on the shallow platform reefs. Consisting of
a rich assemblage of gorgonians, sponges, sea whips, and
macroalgae. Scleractinians are poorly represented, mostly by
encrusting forms of Agaricia agaricites, and small colonies of

A. fragilis, Mycetophyllia spp., and Scolymia lacera.

In sections VII, the shallowest spur-block reefs are found at
a depth of 9m. The blocks rise up 2 or 3m high, and are 8 to
12m wide, with gently sloping sides and narrow grooves of 1 to
3m width. An abundant coral community grows on top, including
some large colonies of A. palmata and M. annularis (Fig. 4).

9

Non-Reefed substrata. In sections IV and VII, the surface of
the escarpment is deeply pitted with a relatively sparse
community of small gorgonians and sponges. Most of the
substrate is covered by the brown alga Lobophora variegata. On
the bottom of sections I and II, no escarpments were detected
in the -20 to -30m range (Fig. 4). The bottom is covered by a
layer of sand and colonized by calcareous macroalgae of the
genera Avrainvillia, Udotea, Rhipocephallus, and Penicillus.

Below -40m the bottom is covered by small, rounded coral patch
reefs, 1 to 2.5m in diameter and rising to 1 to 1.5m above the
pavement (sections IV to VIII). In some of these sections a
mixture of flat hard grounds and poorly developed spur-block
reefs are found (sections IV and VII; Fig. 4).

II. Coral Community

The quantitative sampling of benthic macrobiota covered the
principal biotic environments in the exposed Sian Ka’an shelf,
to depths of 30m. Most of the sampled space corresponded to
denuded hard grounds, sand and rubble with no apparent
macrobiota (68%), with a relatively low percentage of biotic
cover (17%). Dead coral, mostly in growth position, accounted
for the remaining 5% (Table 2). Non-living attributes were
excluded from the analysis to produce a cluster classification
based solely on biotic components.

The resulting dendrogram (Fig. 5) suggests two main groups:
I) A High-Cover cluster, corresponding mostly to the crest and
platform reef stations, with a relatively high average percent
biotic cover (33%; Fig. 6). II) A Low-Cover cluster, mostly
composed of slope stations with a relatively low average
percent biotic cover (11%; Fig. 6). These two main groups are
further divided in sub-clusters, which reflect different
secondary patterns. The High-Cover cluster is composed of two
main sub-groups: The RR-C group, mainly formed by rear reef-
crest stations (six out of eight), and the P-R group mostly
composed by platform reefs. The Low-Cover cluster is divided
into three sub-groups: The N-C group is composed of stations
with sandy substrates and without scleractinians (Table 2);
The MIDDLE group corresponds mostly to stations at -10m and -
20m levels, where prominent reef features are scarce (Fig. 4).
The DEEP group, mostly contains the -30m stations and spur-
block communities. Although there are some discrepancies in
the classification (for example -10m stations in the DEEP
cluster, or reef crest stations in the P-R cluster), the
resulting grouping seems coherent with the observed
distribution patterns of the coral communities.

Presumably the differences in reef morphology and physiography
determine different environments along the shelf, and thus the

10

dendrogram reflects the structural changes of the coral
community from one environment to another. Thus, the main
patterns indicate that there are two main community types: a)
A shallow water community colonizing raised features (platform
reef communities are included in here), strongly dominated by
scleractinian corals in both sub-clusters (RR-C and P-R) of
the High-cover group. The other three main biotic attributes
follow a similar relative abundance pattern in both sub-
clusters (Fig. 7). b) A deeper water community colonizing
raised features, or a shallow environment without raised
features, corresponding to the Low-cover group stations. Here
scleractinian corals are the least important component and the
community is dominated by gorgonians. In this Low-cover group
secondary relative abundance patterns are different for each
subcluster (Fig. 7). Variability within the main attributes
is considerable as indicated by the large standard deviations
(Fig. 7), in both High and Low cover groups. These relatively
large values reflect both a high level of patchiness and the
substantial variability in reef morphology even on similar
reef types. A practical consideration emerging from these
results is that censuses at a small spatial scales may provide
quite different results from site to site.

Scleractinians. The scleractinian coral community of the
High-cover group shows a different structure in the two sub-
clusters (Fig. 8). In terms of mean linear coverage, in the
shallower RR-C group the dominance of A. palmata is evidently
high (mean=1744cm; CV=74%), in comparison to the other main
coral attributes: encrusting corals (mean=193cm; CV=101%), and
massive corals (mean= 90cm; CV=97%). In contrast, in the P-R
cluster, dominance among the main coral attributes is low:
encrusting corals (mean=495cm; CV=74%); M. annularis
(mean=455cm;CV=103%); A. palmata (mean=407cm; CV=88%). In this
High-cover group, the proportion of dead coral is high in
terms of average percentage (up to 20%), resulting mostly from
the A. palmata reefs, that have a large proportion of dead
Corals ‘(Bigs 6);

A. palmata is by far the most abundant coral attribute in the
shallow reefs. Other branching corals such as A. cervicornis
or Porites spp. tend to be scarce in all clusters and seem to
be the least important coral component in all sampled reefs.
In contrast, leafy corals such as A. tenuifolia are important
in both High-cover clusters. Massive M. annularis and other
massive coral species as Diploria clivosa, D. strigosa and
Colpophyllia natans, and encrusting corals (mostly forms of
Agaricia agaricites) are more abundant in well-developed reef
structures, and are rather scarce on hard ground (Table 3).

Gorgonians. In general, gorgonians are important throughout
the study area, including the shallow water communities. Their
proportion is similar in both High-cover clusters: RR-C (mean=

ibe

207cm; CV=138%); P-R (mean=169cm; CV=88%), but more variable
in the RR-C cluster (Fig. 7). In the Low-cover cluster
gorgonians are relatively more abundant: N-C (mean=373cm;
CV=70%); MIDD (mean=228cm; CV=103%); DEEP (mean=168cm;
CV=89%). However, the relative importance of gorgonians with
respect to the other main biotic attributes is probably
underestimated because the chain method is not efficient in
recording small gorgonian colonies (Jordan, 1989).

The gorgonian zonation patterns are similar to those found on
the NE shelf of the Yucatan peninsula, where gorgonians are a
very conspicuous component of the community (Jordan, 1989a;

1990). Gorgonian communities in shallow areas are dominated
by Gorgonia flabellum, Plexaura flexuosa and Eunicea
tournefortii in exposed areas, and by G. flabellun,

Pseudopterogorgia americana, and Plexaura homomalla in
protected or rear reef areas, where species richness is much
higher. On the slope, the same species that dominate on
exposed shallow environments are found, and again species
richness increases as moderate depths are reached. On the
deeper -30m level (Spur-block reefs) Pseudopterogorgia
elizabethae, Plexaurella dichotoma and Muricea muricata are
usually dominant. Non-zooxanthellate species are found
occasionally on deeper locations including isolated colonies
of Iciligorgia schrammi, and less commonly colonies of
Elisella barbadensis and Nicella sp. in heavily shaded areas
(Table 3). In many areas, hydroids are abundant either forming
dense stands (Gynangium longicauda) or as isolated colonies
(mainly species of Sertularella).

Sponges. Sponges show relatively similar proportions in both
the High-cover group (RR-C: mean= 98cm; CV=79%; P-R: mean=
67cm; CV=132%), and in the Low-cover groups: (N-C: mean=105cm;
CV=118%; MIDD: mean=14lcm; CV=113%; DEEP: mean=140cm;
CV=100%), as observed in Fig. 7. As with the other attributes
the variability of the sponge community is relatively high.

Sponges in the High-cover cluster are mostly encrusting
species (RR-C=98%; P-R=85%) of mainly boring sponges growing
upon dead coral heads or hard ground patches, primarily
Anthosigmella sp. and Cliona spp. In contrast in the Low-cover
cluster, erect sponges are more important (N-C= 87%; MIDD=
63%; DEEP= 49%), especially at the -10m and -20m levels.
Apparently, the erect sponge composition of a given site is
influenced by changes in substrate type. On flat, hard
ground, massive vase sponges, mainly of the genera
Xestospongia and Ircinia, are abundant. In a more rugose
substrate a multi-species sponge assemblage is found, mostly
vase and tubular sponges of the genera Agelus, Verongia and
Haliclona. In areas where gorgonians dominate, the sponges
Haliclona hogarthi and Iotrochota virotulata typically grow
amongst the gorgonian fronds.

12

Algae. Algal cover is relatively constant in proportion among
the different clusters in both cover groups. Mean values are
less variable in the High-cover group (RR-C: mean=184cm;
CV=105%; P-R: mean=120cm; CV=98%), than in the Low-cover
groups: (N-C: mean=243cm; CV=83%; MIDD: mean=23cm; CV=228%;
DEEP: mean=119cm; CV=112%), as observed in Fig. 7. Fleshy
macroalgae are more abundant in the deeper stations (N-C= 85%;
MIDD= 76%; DEEP= 62%), than in the shallower ones (RR-C=13%;
P-R=23%), where turf algae become more important. However,
this may be a biased estimate because loosely integrated
filamentous algae that do not form turfs, were included into
the hard ground attribute. In the N-C cluster where the
highest macroalgae abundance is found the substrate is mostly
covered by sand. Here, the dominant species are calcareous
green algae oof the genera Udotea, Penicillus and
Rhipocephallus. In other areas the macroalgae set comprises a
multi-species mixture of brown and green algae species. The
most abundant are Lobophora variegata and species of
Stypopodium and Dictyota, and also species of Halimeda and
Caulerpa. In many areas of hard grounds the brown algae
Sargassum spp. and fTurbinaria turbinata are extremely
abundant.

DISCUSSION

Perhaps the most striking characteristic of the reef system of
the Sian Ka’an Biosphere Reserve is the paucity of reef growth
upon the shelf compared to other Caribbean localities such as
the Belizean reefs a hundred km south (RUtzler and Macintyre,
1982). In fact, well-developed shelf reefs are found a few
tens of kilometers south of the Sian Ka’an area, both along
the continental margin (Jordan, in press) and on insular
shelves (Jordan and Martin, 1988). On the other hand, poorly-
developed reefs on the shelf are the dominant feature along
the Yucatan eastern margin, north of the Sian Ka’an Reserve
(Jordan et al., 1989a; Jordan, 1989b). Although a few, well-
developed reefs of limited extension can be found on several
localities, both on the northern eastern Yucatan shelf
(Jordan, 1989b) and in the central part of the eastern shelf
(this work), it appears that a characteristic of the gently
sloping shelf of the eastern Yucatan is the scarcity of well-
developed reefs. This observation coincides with that of
Stoddart (1976) and others, and seems to be the case as well
for the Honduras and Nicaraguan shelves.

The presence of well-developed coral communities in the Sian
Ka’an shelf seems to be linked to the relatively few, raised
topographic features, such as terraces and scarpments. The
shelf physiography suggests that there was both karst erosion
and bevelling during low sea level stands as has been found in
many other shelves in the Caribbean region (Logan, 1969).

iS)

This idea is further strengthened by our finding of erosional
notches at the base of the spur-like extensions of the
platform reefs in section IV. Therefore, we speculate that the
raised features upon which the crest and platform reefs are
developed may be remnants of pre-Holocene calcareous
platforms, or consolidated shorelines, karstified by rainfall
and percolating water. The shape of these structures, mostly
those of the small sized platform (and internal, dead end
channels), and spur-block reefs, would thus result from
subaerial processes and not from reef building (Purdy, 1974).
However, coral growth upon them will maintain and perhaps
enhance the old structures, as observed in the spurs of
platform reefs, or over the spur-block reefs.

Well-developed A. palmata reefs growing upon a submerged
consolidated crest are found on the NE margin of the Yucatan
peninsula (Jordan et al., 1981). Most likely, their
development in the Sian Ka’an area, as in the northern region,
is influenced by topography, water depth and wave action
(Geister, 1977). A striking example of this situation may be
found in the rich development of the crest reefs near gaps
and channels in front of the Espiritu Santo and Ascencidén
Bays. The submerged crest together with the coral reef growth
upon it, effectively isolates the bays from the oceanic regime
and constitute a barrier to free water movement between the
bays and the open sea. Thus, relatively strong currents are
found in the tidal channels and gaps, in spite of the low tide
range within the region (Kjerve, 1982). The relatively intense
tidal flux together with the greater depths in the gaps may
enhance the growth of the coral reef builders. Since most of
the gaps and channels are at least a few hundred meters wide
‘(see locality A), wave refraction could intensify the water
movement over the reefs, further stimulating the growth of A.
palmata colonies (Geister, 1977).

The coral communities growing upon the raised features on the
shelf (platform reefs, spur-block reefs and the pinnacle reefs
at section VII), are considerable more developed in species
richness and relative abundances, than those over the reefless
hard bottoms. These well-developed, but isolated, coral
communities indicate that the environmental setting is
Suitable for the growth of reef biota in the shelf, in spite
of the extensive un-reefed areas, and also that raised
topographical features are an important factor in the eventual
success of these communities. Jordan (1989b) has observed that
well-developed reef communities in the northern continental
shelf of the Yucatan, are also dependent on bottom relief; as
well as those on the eastern Cozumel island (see also Boyd et.
al., 1963; on coralline microatolls in the seaward margin of
Cozumel Island).

14

The scarcity of well developed coral communities on the
hardgrounds of the shelf according to Jordan et al., (1981)
and Jordan (1989b), is possibly related to the low slope of
the shelf and wave action. According to this hypothesis, the
gentle slope contributes to a stressful environment for corals
by a more or less continuous accumulation of unconsolidated
sediments over the hardgrounds. This sediments are also
continuously re-suspended and re-deposited by wave action,
thus affecting individual corals in different ways. This
ecological condition may reduce the coral growth rates
(Hubbard and Pockock, 1972; Cortés and Risk, 1985), generate
lethal conditions (Rogers, 1983) and diminish the surface
available for larvae settlement (Babcock and Davies, 1991) of
key reef-building coral species. Under this stress coral
colonies may also be handicapped to successfully cope with
competitors and predators (Loya, 1976; Cortés and Risk, 1985).
Isolated colonies able of attaining larger sizes and thus
"escape" from the stressful bottom environment (Connell, 1975;
Jackson, 1982) on the exposed and almost featureless shelf,
Still have a high probability of being broken and detached by
high energy waves from storms and hurricanes (Jordan, 1989b).
This situation is partially the result of weak colonies due to
extensive internal bioerosion of the corallum (pers. obs.;
Hutchings, 1986). In contrast, on crests, platforms and spur-
blocks, survival and success of coral colonies is more likely,
because these features moderate the effects of wave action.

Another possible source of stress for these coral communities
is that of occasional up-wellings, that result from the
Yucatan current running northward along the _ eastern
continental slope. Whenever an upwelling occur there is a
possibility of colder and nutrient-rich waters spreading over
the shelf. Such waters could stress or kill scleractinian
corals, and temporarily contribute the ecological success of
macroalgae, further stressing scleractinians and other slow
growers. The relatively large proportion of brown macroalgae
colonizing the deep spur-block systems, suggests that this is
another possibility.

Other events of biological nature, triggered or not by
physical forcing, such as Diadema mass mortalities (Lessios et
al., 1984), unrecorded widespread bleachings (Glynn, 1993) or
unrecorded widespread diseases such as white and black band
disease (Antonius, 1985; Edmunds, 1991), may also have played
in the past and present times, an important role in shaping
this reef system. The complexity of biological and physico-
biological interactions in the reef community are further
confounded by the lack of appropriate historical records. For
example, the cause of the relatively large mortality of A.
palmata colonies in the more developed Acropora reefs of the
Sian Ka’an is unknown, and at the time of the survey (summer
of 1987) there were few signs of recovery. This however, is

15

not a unique situation. Several reports in the Caribbean
region have shown that large areas of previously healthy
Acropora reefs have suffered widespread mortality for largely
unknown reasons (Davies, 1982; Dustan and Halas, 1987; Jordan,
1992).

Finally, a Biosphere Reserve is designed as a series of zones
ranging from controlled utilization to total conservation.
Both the coast line and shelf of Sian Ka’an fall under the
controlled utilization category. At the moment, fishery
activities are the only intense activity and this is carried
out mostly by trapping in the seagrass areas (Lozano-Alvarez
Gieialis:, 0 991),. However, with the enormous expansion of
tourism in the Mexican Caribbean, the coastal areas may soon
be affected by "non-damaging" recreational activities. Thus,
we strongly advise that total conservation zones should also
be implemented in the marine environment of the Reserve. Based
on the findings of this study, Punta Allen (section III), the
Nicchehabim and nearby bank reefs (locality A), and Punta
Herrero (section VI), should be the first areas where total
conservation should be implemented.

ACKNOWLEDGEMENTS

Many people were involved in this survey and we are grateful
to all of them. In particular to Francisco Escobar, Astrid
Frisch, José Fuertes, Susana Kulhuac, Guillermo Olguin, Luzma
Guzman and Felipe Cat, for their enthusiastic support both in
Giving activities and general field work. Special thanks are
given to Captain Luis Osuna (B/O "Justo Sierra"), whose daring
and skillful seamanship allowed us to survey the uncharted
Sian Ka’an shelf. In this sense, we are also very grateful to
Inigo Sistiaga, for his friendship and seamanship, on a second
complementary survey on the sailing vessel "Sul-Ik". Amapola
Otero kindly provided the satellite imagery. We also express
our gratitude to Drs. T. Done, J. Ogden, I. Olmsted and to S.
Wells, and two anonymous reviewers for their contribution
toward improving this work. This study was partially supported
by a CONACyT grant PCCBBNA-021928 to the first author, and by
Instituto de Ciencias del Mar, UNAM., through extensive ship
time and logistic support.

16
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18

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Scleractinia

1 A. palmata
2 M. annularis
3 Massive
4 Branching
5 Encrusting
6

Leaffy

Sponges
7 Encrusting
8 Erect

Octocorallia
9 Gorgonians

Algae
10 Turf algae
11 Macroalgae

Other
12 Dead coral

Non—biotic
13 Sand/rubble
14 Hard ground

TABLE 1. Structural Attributes utilized
on the quantitative sampling.

. palmata
. annul.

. massive
. branch.
. encrust.
leaffy

. encrust.
. erect
Gorgonians
Turf algae
Macroalgae
Dead coral
Sand/rubble
Hard ground

mM AaAADAaA = -&

A. palmata
M. annul.
C. massive
C. branch.
C. encrust.
C. leaffy
S. encrust.
S. erect
Gorgonians
Turf algae
Macroalgae
Dead coral
Sand/rubble
Hard ground

II

a

287 0
187 0
33 0
37 0
oy 0
333 0
0 80
20 0
110 400
307, 217
PAS eeel43
737 0
2016 1300
5763 7859
ree Lh

Cc Cc

0 0

99 0
71 0
0 0

0 0

20 0
137 0
183 400
37 ~—- 100
323 0
24307397)
i 0
1067 7799
7813 1303

REAR REEF-CREST

PTS ely V
a a a
1816 =213'«- 1517
0 0 0
See el 213
230 7 0
400 20 40
460 360 93
V7 98333) 337
17 0 0
133 3 180
403-23 410
1309117, 0
5036 440 = 193
0 430 0
1123 8036 7016

FORE SLOPE (-20m)

Pie TV,
Cc Cc
57 0
1157 0
623 100
770 7
5Milite 13
537 0
97 aa 5S
53a 60
110 183
10 0
170 0
1830 0
243 0
3796 9562

243
8972

Vio Vit Vill

a a a
3840 1363 717
O50 127

40° 97 0
33 0 0
ASS 1S 250
633) is 150.
SLO Tio
0 0 0

Ve eS UT
MEM = 7A) EY
17 0 3
202617350) mel,
13 0 0
2466 6829 6876
VES VEE® VEE
Cc Cc C

0 0 0

13 Q- 83

OR 06S

0 3 0
2010 0

0 0 7

OCW nese OS
50052975198
SO S27 Moi

0 110 0
TaepAsy 1423

7 eB

SOI 6607 e877
9462 8499 8279

I
d

0
31
77

3
35

0
13
87
20

247
97
0
177
9212

FORE SLOPE (-10m)

LE ay LV Via VE
b D b b b

Or903) 2 ScOnme25 0
Om 203 a 28h e227 0
Bes SAS Cay Ve CANS) MO
LOO eo Ore sok ec0 0
33 943 267433) 3283 0
Q7 523) s21575 30 0
373333 eel eG SOO, 60
107 0 Sige ane 6/7
7770507390) Se 6280, 10
0 0 0 20 0
ine te SVae213 3 0
70 4606 247 #17 0
373". 150 OF. 463 0
1503 7003 8579 9716

FORE SLOPE (-30n)

TOL 583) 5 427 20027
900 7919 7926 8892

Table 2. Attributes sustrate coverage in linear cm per station. The number in the code
above each data set indicates the corresponding section and the letter the depth level
of the station.

VIII
b

SPECIES RR-C

Gorgonians

Briareum asbestinum
Erythropodium caribaeorum
Gorgonia flabellum

G. mariae
Pseudopterogorgia americana
P. bipinnata

P. acerosa

P. rigida

P. kallos

Pterogorgia anceps

P. guadalupensis

P. citrina
Lophogorgia sanguinolenta
Ellisella barbadensis
Nicella sp.
Iciligorgia schrammi
Plexaura homomalla

P. flexuosa
Pseudoplexaura porosa
P. flagellosa
Plexaurella dichotoma
P. nutans

P. grisea

Eunicea mammosa

E. succinea

E. calyculata

E. tournefortii

E. laciniata

E. fusca

E. laxispica

Muricea atlantica

M. muricata

M. elongata
Muriceopsis flavida

Hydrocorals

Millepora complanata
M. alcicornis

PSR

QK «MK DD KOKDOKKDDDPIKKKQANKDAKAKAKPY PN

yd

PAQAAMIADAAKAPADAADADPAKKKAPAADAAQAWDAADPAO

SB-R

QAKXDADQADDAQPADQADIAPKADAKQAIQIAKANAQIAAKAD

Qn

H.G.

DK KD KRM MKD KK KOK KOK KAD ADDW dK

Scleractinians

Stephanocoenia michelini
Oculina diffusa
Madracis decactis
Acropora palmata

A. cervicornis
Agaricia agaricites
A. humilis

A. fragilis

A. lamarcki
Leptoseris cucullata
Siderastrea siderea
S. radians

Porites porites

Pe Lurcaca

P. divaricata

P. astreoides

Favia fragum
Diploria clivosa

D. strigosa

D. labyrinthiformis
Manicina aereolata
Colpophyllia natans
Solenastrea bournoni
Montastrea annularis
M. cavernosa
Meandrina meandrites
Dichocoenia stokessi
Dendrogyra cilindrus
Mussa angulosa
Scolymia lacera
Isophyllia sinuosa
Isophyllastrea rigida
Mycetophyllia lamarckiana
M. aliciae

M. ferox

Eusmilia fastigiata

DAXKKMQAQAKAADADQKXHDAKXADQAPQAADAKXDADAKXKXQNADYP KAM
AXKAAQQAADAADAPAQAQKANIAPDADAQQAQAKXAAPAAAADAD
DPHDDAADQQAADQQAADADAKAQAKAKXANHDQQADADYP*XKAKN
PS OS PSO KOO KK ODD OK OK KD KK KKK

Table 3. Commonly found gorgonian, hydrocoral and scleracti-
nian species of the coral reef environment on the Sian Ka’an
Biosphere Reserve. RR-C: Rear reef-Reef crest; P-R: Platform-
reefs; SB-R: Spur Block reefs; H.G.: Hardgrounds. A: Abundant;
Cs: Common; R: Rare; X: Not found.

VILLAS BOCA PAILA

(1)

GULF OF MEXICO

BOCA PAILA
(1)

P. ALLEN
(1)

P. PAJAROS
(Iv)

Sian Ka ‘an: en | os P. TUPAC
Biosphere ey?
Reserve

3) ESPIRITU s \

SANTO ’

(VI)

P. TAMPALAM
(vil)

P. PULTICUB
(vill)

87°10'

Figure 1. Map showing the geographical position of the Sian Ka’an
Biosphere Reserve and location of the sampling sections. Roman
numerals below correspond to code numbers.

ooot

0002

OOOE

SY31L3N

DEPTH (m)

DEPTH (Mm) DEPTH (m)

Zz
09

> LS)
fo} (o} fo)

09
Ov
0

ooo!
ooot

Al

0002
0002

IA

OOOE
ooo€e

1SW
sw
Wt
1SW

SuY3aLaw
SY¥313~N

Figure 2. Bathymetric profiles for each section. The horizontal

line at the
observations.

-40m level marks the deeper limit of underwater

*“squsueinsesu jo

sqes Tereaes Jo sebereae jueseidei pue ajzemtxoidde erie suoTsueuTd
-paze Apnys euR ut punoj sedAQ joer uTew ey FO saudqexs °€ eanbty

GuvMv3as

-— 30-70m —H

3YNOHS ite
SNOOT1E-HYNdS

SYOHS

wooe-002 ——————>

Wa

SALAS

——— wosi-0sS ——}{

3YOHS
1

—_——— wos- ofr

CLL Y/

WS

\\

ee Ole INO) ive

(RICE FC Yank fond 2)

On = NO Se i),

(™) H1d3G (w) H1id30

(“) Hid30

TUK ie SUMP
2 &

S4335Y VYOdOYNOV

EEO FOiry a:
fh 50- 100m —

S4535H WHOALV Id

3YOHS
-— wos:-00!1 ———4

ornmw ww

3y¥OHS a
wosi-o001 —— 4 rs

Soy es Z
=u
0

(YW) Hid3ad (w) H1d 30

(Ww) H1d30

DEPTH Slope Sections

Platform Spur block
Reefs Reefs

Acropora
Reefs

Hard

Sand
grounds

Figure 4. Main reef and substrata distribution on the shelf of Sian
Ka’an.

Wi-a

Vi-a

IV— @ REAR REEF-
Vil-—@ crest

y-a HIGH COVER

Vil-a

Wi-c

i —b PLATFORM
iV - b REEFS
l-a
W-c
ll-d NON-CORAL
ll-a

Vil-c¢

Vi-b

IV—'c MIDDLE
V-c SLOPE

Vi-c
ll!-—b
= 2 LOW COVER
ec
Ii-d
VII|—d DEEP SLOPE
Vill-—c
Vi-d
V-b
V-d
Vil-d
Vi-d

(Sec ar ee OA SO Nee an SL

2.0 EUCLIDEAN OISTANCE 0.0

Figure 5. Dendrogram of cover attributes (excluding
hard ground and sand). Cluster analysis of log-
transformed cover data with average linkage.

“fo

100

80 |

60

40

20

Oo <= -
RR-C P-R {MIDD DEEP N-C |
High Cover Low Cover
LZABiotic Gi Dead coral
C=JSand/rubble (J Hard ground

Figure 6. Percentage of cover for biota, dead coral,
hard ground and sand, for each of the clusters
suggested by the dendrogram in Fig. 5.

cm

Lineal

800

600

400+ Et ul
i \

200 5 NN % 3 \\ ‘NN
TNT] EEL \ NN NY
4 | NA eT AA \ NN N
SCtNN “| NN N NN NN
= \\ PENN IN 8 NN WN

LEE NS aLLN : rN, ERE
RR-C P-R N-C MIDD DEEP

High Cover Low Cover

ESS Coral EJ Sponge MSSGorgo [2] Algae

Figure 7. Mean lineal cover of the main biotic

attributes, for each of the clusters suggested by the

dendrogram in Fig. 5. The vertical line indicates one
standard deviation.

cm

Lineal

LOCLSS

CORES

CAS
OSS

x
2x

Cx xX

Cx xX

ras

TORO Oe
3050 g-9-6:0%

Pas

oi
yas

500

<2

yas

x

Bess

O
RR-C P-R MIDD DEEP
High Cover Low Cover
(XX A.palmata M8 M. annularis EZ]] Massive
Branching L_lEncrusting CA eatty

Figure 8. Mean lineal cover of the coral attributes
for each of the clusters suggested by the

dendrogram in Fig. 5. The vertical line indicates
one standard deviation.

i a

4" ; } T5 eee
& : e a Fee)! ‘ " * “ * Le! ‘ ee
ry > ‘ ’ ‘ h 24 i ; a * Pe
- 3 pee Ne mtyer'é rg sy Han + et : iv +h) fees 16% fi
= ctr 7 i i fe ‘s » t J " wy
Sao bas. Ay Leo) SB TP tty f helena
, ‘

yt CY eae Var eee ; Aol teivet Syrah aes: er _ / ee

ATOLL RESEARCH BULLETIN

NO. 424

| A PRELIMINARY EVALUATION OF THE COMERCIAL SPONGE
RESOURCES OF BELIZE WITH REFERENCE TO THE LOCATION OF THE

TURNEFFE ISLANDS SPONGE FARM

BY

J.M. STEVELY AND D.E. SWEAT

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

ete aan i a

——

iE LT SNR A TG a

|

,

err

Peewee Shuma Vs

; 4
i -
” -
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Dey 1
= - -
° re vi y 7 Meet ATR ty
nH 4 Vi J AMGTT AV
; eS ak ;
H y y it : WAURE I
-- Sa eee x = #
ate Te iye i Fs
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ba
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a mi
Pe
~ {~
i
j aj

A PRELIMINARY EVALUATION OF THE COMMERCIAL SPONGE
RESOURCES OF BELIZE WITH REFERENCE TO THE LOCATION OF THE
TURNEFFE ISLANDS SPONGE FARM

BY

J.M. STEVELY AND D.E. SWEAT

SUMMARY OF FINDINGS

Our discovery of concrete disks used for planting sponge cuttings confirms the
location of the Turneffe Island sponge farm activities as described by Smith (1941). It
is hoped that this information will be useful to the Government of Belize in identifying
potentially historic or unique marine resources.

We here also report the occurrence of the velvet sponge, Hippospongia
gossypina, at Turneffe Islands. The occurrence of the velvet sponge is particularity
worthy of note since a devastating commercial sponge mortality in 1938-39 drastically
reduced velvet sponge abundance throughout a portion of its geographic distribution.
We observed that the attachment substrate of the Turneffe Islands velvet sponge,
mangrove peat, was different than that reported for sheepswool sponge, Hippospongia
lachne, and different than the attachment substrate previously reported for velvet
sponge.

The quality of the Turneffe Islands velvet sponge is such that it is commercially
marketable, but would be less valuable than the sheepswool sponge. The velvet
sponge is sufficiently abundant at one location to support commercial fishing activity.
However, our survey work was not adequate to establish whether the abundance of
velvet sponges was sufficiently extensive to support a sustainable sponge fishery. The
lack of more extensive data on abundance and the historical accounts indicating the
effects of past sponge disease and fishing pressure on velvet sponge distribution
warrant a conservative approach to managing velvet sponges as a commercial! fishery
resource. Additional survey work will be required to more fully understand the
commercial sponge resources of Belize.

Florida Sea Grant College Program
University of Florida
P.O. Box 110400
Gainesville, Florida 32611-0341

Manuscript received 5 January 1993; revised 5 June 1994

INTRODUCTION

The usefulness of commercial sponges is based on their soft, compressible
nature and their ability to absorb and hold water. Sponges from the genera Spongia
and Hippospongia have been used for personal bathing and household cleaning for
thousands of years. The taking of sponges for commercial purposes was first practiced
in the Mediterranean Sea and the sponge fishery was often noted in early Greek
literature (Moore, 1951). More recently, commercial sponges have been used in
manufacturing pottery and ceramics, and in a variety of applications in surgery,
painting, polishing, printing, horse grooming, and professional cleaning services.
Synthetic sponges have replaced natural sponges for many of these uses because they
are cheaper and more readily available. Today, natural sponges are principally used for
bathing (Josupeit, 1991) and the application of cosmetics by people in westernized
communities because these people prefer a natural product (Wilkinson, unpub. mans.).
Although synthetic sponges are less expensive, they cannot equal the softness and
absorbency of natural sponges, and, importantly, natural sponges can be more easily
and thoroughly cleaned due to the truly porous nature of the sponge skeleton.

Until the 1840’s the world’s sponge supply was derived solely from the waters
of the Mediterranean. However, the discovery of quality commercial sponges in the
Bahamas and Florida Keys led to the rapid development of sponge fisheries in
Caribbean and Gulf of Mexico waters. During the early part of the 20th century (1900 -
1940's) the commercial sponge fishery was the most economically important fishery
in Florida, U.S.A. (Stevely, et al., 1978). Cuba produced 440,000 Ib (198,000 kg) of
sponges, the Bahamas 670,000 (302,000 kg), while U.S. production totaled 610,000
Ib (275,000 kg) (Moore, 1951). The large-scale attempts to culture sponges in the
Bahamas (Storr, 1964), Belize (Smith, 1939) and Florida (Moore, 1910a; Shubow, I969)
further attest to the importance of sponges as a fishery resource during this period.

A sponge disease swept through the Caribbean and Gulf of Mexico in 1938-39
and dramatically reduced commercial sponge abundance. The decline in supply caused
by the disease and the outbreak of World War II, which curtailed production in the
Mediterranean, resulted in dramatically higher prices. Although production in Florida
declined precipitously in the 1940’s, rapidly escalating prices were sufficient to increase
fishing effort and actually increase the total value of the fishery. The result was
increased fishing effort at a time when fishing effort probably should have been
curtailed to allow the commercial sponge populations to recover (Storr, 1964). The
Florida commercial sponge grounds were depleted to the point of causing the virtual
economic extinction of the fishery and many years were required for commercial
sponges to increase to abundances that approached those found before the sponge
disease epidemic. The effects of the sponge blight were similar throughout the
Caribbean. The cause of the disease has been confused somewhat by the presence
of bacteria including symbionts, that live in close association with sponge tissue
(Lauckner, 1980).

Although the Caribbean sponge disease and introduction of synthetic sponges
in the post World War II era has resulted in reducing the world sponge trade to a
fraction of its former importance, a significant sponge trade still exists. Prior to WW
Il (1927-1936), world sponge production annually averaged 1,346.1 MT, and in more

3

recent times (1977-I986) it has annually averaged 222.1 MT (Josupeit, 1991). The
world’s supply of bath sponges comes from the lesser-developed countries of the
Mediterranean and Caribbean: Tunisia (48%), Greece (17%) and Cuba (26%) are the
principal suppliers. Countries importing the largest volume of natural sponges are
France (37%), USA (26%), Japan (10%), and Italy (9%) (Josupeit, 1991). In terms of
the quantity landed by weight, most fishery managers would consider the world
sponge fishery to be insignificant. However, it must be noted that the highest grade
of commercial sponge can command a price of over U.S. $50.00/lb ($110.00/kg) in
the export market.

Currently, market demand for natural sponges is such that the opportunity
exists for expanded production from the Caribbean and Gulf of Mexico. A decline in
commercial sponge abundance caused by disease (Gaino and Pronzato), 1989), and
pollution and overfishing (Verdenal and Verdenal, 1986) has significantly reduced the
supply of Mediterranean sponges. Reduced supply has resulted in higher commercial
sponge prices and focused attention on increasing sponge production on other areas
of the world. For example, Josupeit (1991) reported that, in France, the reduced
sponge supply, as well as a general trend for increased use of natural products,
resulted in retail sponge prices doubling and even trebling. During |988, Florida sponge
prices more than doubled and fishing effort and production significantly increased
(Stevely, pers. obs.). Although Florida sponge prices have stabilized below the peak
prices of 1988, they are still substantially higher than pre-I988 prices.

Increased market demand and the consequent higher prices for Caribbean
sponges has resulted in a need to carefully assess sponge fishery potential and fishery
management needs throughout the region. The objectives of this project were to (1)
evaluate the fishery potential for harvesting commercial sponges in the marine waters
of Belize, (2) provide the Belizean Fisheries Unit with information pertinent to
management of a commercial sponge fishery, and, (3) establish the location of the
historic Turneffe Islands commercial sponge farm before its location was lost to
posterity in general, and to the fisheries heritage of Belize in particular. Project funding
was provided by the Smithsonian Institution’s Caribbean Coral Reef Ecosystem
Program (CCRE Contribution No. 402).

METHODS AND MATERIALS

Field surveys to determine the distributions and abundance of commerical
sponges were conducted from !l4 May to 30 May, 1989. These surveys were
performed using dive mask, snorkel and fins. To cover large areas, a diver was towed
by boat for 30 to 90 minutes. Three locations were surveyed (Figure 1): Carrie Bow
Cay, Ambergris Cay, and Turneffe Islands. The maximum and minimum diameters of
commercial sponges were measured with a pair of large calipers. Field notes on
duration of tow and habitat type were recorded. Plans to collect commercial sponge
abundance within quantifiable transect lines had to be aborted due to inclement
weather and contractual problems with a local fishing guide.

Surveys at Carrie Bow Cay, capitalizing on the Smithsonian Institute facilities
there, were conducted to field-test survey procedures, and collect information on the
distribution of commercial sponges in the vicinity of the barrier reef and associated

Belize

30 mi

40 km ,7~

MEXICO ¢

/. TURNEFFE
B3/ ISLANDS
yah
)

/

=<
—
<=
=
Ld
—
<
=>
[aie]

CARIBBEAN
SEA

Figure 1. Location of commercial sponge survey sites (Carrie Bow Cay, Ambergris
Cay, and Turneffe Islands).

5

habitats. Ambergris Cay was chosen as a survey site because anecdotal observations
suggested that commercial sponges could be found there and because a fishery
cooperative was located at San Pedro. Turneffe Island was selected as a survey area
because it was the reputed site of a large scale sponge farm in the 1930’s and
interviews with fishermen indicated that Turneffe Islands was the most likely area
where commercial sponges could be found. To assist with the Turneffe Islands field
work, the services of two fishermen were contracted, one of which was old enough
to have personal knowledge of the sponge farm location. Fisheries Unit personnel,
commercial fishermen and fishing guides were interviewed to obtain information prior
to conducting the field work in each area.

RESULTS

A total of 19 locations were surveyed by either towing a diver or by having the
boat follow 2 divers. These surveys represent a total of 24 hours of underwater
observations.

Distribution and Abundance of Commercial Sponges

Carrie Bow Cay

No commercial sponges of the genera Spongia and Hippospongia were found.
Habitats surveyed included: seagrass beds surrounding Twin Cayes (occasional
loggerhead sponges, Spheciospongia vesparium, were seen), seagrass beds west of
South Water Cay, Barrier Reef sand/rubble zone, and Barrier Reef habitat accessible by
snorkeling from South Water Cay through South Water Cut (Figure 2). Strong winds
precluded surveying exposed areas, and, by necessity, surveys had to be conducted
in nearby protected locations. The inability to travel appreciable distances limited the
thoroughness of the survey. In general, the Carrie Bow Cay vicinity did not appear to
be a productive area for commercial sponges. However, one of the authors (Stevely)
has observed the presence of the reef sponge (Spongia obliqua) in patch reef areas
located between the mainland and barrier reef during field work on a different project.
The reef sponge is generally not considered to be of sufficient quality to support
commercial harvest.

Ambergris Cay

No commercial sponges were found. Based on conversations with local fishing
guides, five potential sponge habitat areas in the vicinity of Ambergris Cay were
surveyed. These included: north of San Pedro, south of San Pedro, offshore of Laguna
de Boca Ciega, seagrass beds near Congrejo Cay, and Cayo Romero (Figure 3). Survey
sites north of San Pedro, south of San Pedro, and offshore of Laguna de Boca Ciega
were "hard bottom" habitats with numerous "loggerhead" sponges (Spheciospongia
vesparium), and represented habitat in which commercial sponges are sometimes found
in Florida.

. Tobacco E 2" Tobacco
Sr daGay,
Coco Plum:
Cay

Tobacco
Reef

Blue Grounds): eae i

Range: o¢ Sp fae x
. 8 — >. South Water Cay
Ee OS Se
8 ut . ; :

CARRIE BOW CAY

Figure 2. Carrie Bow Cay commercial sponge survey sites.

Key: G= survey site

Laguna
de Boca Ciegat

y Boca Chica

Congrejo Cay

/ Barrier
} Reef
J

CARIBBEAN
SEA

Figure 3. Ambergris Cay survey sites. A - north of San Pedro, B - south of San
Pedro, C - offshore of Laguna de Boca Ciega, D - seagrass beds near
Congrejo Cay, E - Cayo Romero.

Key: f = survey site

8

Turneffe Island

A total of 9 areas within the Turneffe Islands lagoon were surveyed, but velvet
sponges, Hippospongia gossypina, were found only in one location, the "Crooked
Creek" area (Figure 4). Velvet sponges were abundant in water 3-6 ft (1-2 m) deep,
400-500 ft (400-500 m) north of the Crooked Creek entrance into the Turneffe Islands
lagoon (a tidal cut between mangrove islands). Ircinia sp. and Spheciospongia
vesparium, were also present at this location. Additional field observations made on
October 19, 1991, as part of a different survey project, documented the presence of
velvet sponges in other areas within the Turneffe Island lagoon. These areas included:
the eastern shoreline of Soldier Bight and shallow waters near mangrove islands and
mangrove shoreline in the vicinity of the western opening of Grand Bogue Creek into
the main lagoonal area. The October I9th, 1991 observations did not include measuring
the sponges or recording quantifiable data on whether the sponges were attached to
the substrate.

Data on maximum and minimum sponge diameter and type of attachment to the
substrate was recorded for a total of |5 velvet sponges (Table 1). The velvet sponges
were growing on a mangrove/seagrass peat substrate. A considerable percentage of
these sponges had broken free from their attachment to the substrate, with only 53%
found growing attached to the substrate.

A species of Spongia, probably a variety of sponge that would commonly be
referred to as "yellow sponge" in the commercial trade (Spongia barbara, sensu de
Laubenfels and Storr, 1958), was found in patch reef habitat to the west of Douglas
Cay (outside the lagoon environment). This sponge did not appear to have significant
value for commercial trade. Unfortunately, the collected specimens were lost in the
process of having the specimens shipped.

Evaluation of Commercial Sponge Fishery Potential

A commercially valuable grade of velvet sponge (Hippospongia gossypina) was
found at Turneffe Islands (Figure 5). After evaluating a sample of I3 Turneffe Island
sponges, tarpon Springs, Florida sponge buyers indicated that they would pay US
$2.00-3.00 per sponge. The velvet sponge quality was such that it would be
considered to be somewhat inferior to the sheepswool sponge (Hippospongia lachne),
but would have a market value greater than that of other commercial sponge varieties.
Velvet sponges tear more easily than sheepswool sponges, partially because of the
characteristic presence of large pseudoscula or vents on the upper surface (Moore,
1910b).

Based on our experience with sponge fisheries in Florida and the Bahamas, we
estimate that the value and quantity of sponges at Turneffe Islands were sufficient to
support sponge fishing activities. Field observations indicated that it would not be
unreasonable for a 2-man fishing team to produce in excess of 100 sponges per day.
For example, we collected 15 sponges in | hour, and this included time taken to
measure each sponge and record data. However, there are several important factors
and limitations which must be considered before the fishery potential can be properly
evaluated. These are considered in detail in the following discussion section.

Norierit Ho Ne
; Turneffe Flats
Resort

Crickozeen Creek &
Cc ay

£
Z

RESEARCH =
BASE CAMP244

fCrooked “=
Creek =x}.
Ambergris £

Joe’s Hole :

¢ &
RIVA’S KEY \-
SPONGE .
FARM RELICT
Blue Creek

© RESEARCH BASE CAMP
Grand Point “2
“ vo Turneffe Island Lodge

Figure 4. Turneffe Islands survey sites and approximate location of the sponge
farming area (stipled area).

10

Table 1. Maximum and minimum sponge diameters and category of attachment to the
substrate for 15 velvet sponges (Hippospongia gossypina) collected at Turneffe Islands,
Belize, May 24, 1989.

Maximum Diameter Minimum Diameter Attachment to
in (cm) in (cm) Substrate
10.8 (27) 9.6 (24)

11.2 (28) 10.8 (27)
10.8 (271 8.8 (22)

ps 48.6000) 5]. n0.otze1 7/7 Tineteechoa aa
ee eee ee

Mean Maximum Minimum Percent
Diameter 10.6 (27) 9.6 (24) Attached 53%

Location of the commercial sponge farm

Information provided by local fishermen (Mr. Joseph Garbutt, Mr. Carl Carbal)
indicated the approximate location of sponge planting areas in the Turneffe Islands
lagoon (Figure 4). The approximate location of the sponge planting area in the
southern portion of the lagoon was verified by finding the concrete disks used to
"plant" sponges (Figure 6) on the western side of Riva’s Cay, approximately 200 m
south of the northern tip of the island (Figure 4). The disks found along the mangrove
shorline and in the water immediately adjacent to the shoreline. This site marked the
location where sponge farm workers docked a live-aboard boat. No navigation charts
that located Rivas Cay could be found. However, the approximate location, as
determined by triangulation on the open water is shown in Figure 4. Smith (1941) did
not describe the precise location of the sponge farm but his figure showing the

11

Figure 5. Live velvet sponge (Hippospongia gossypina) removed from water. Note
pseudoscula described by Moore, I9IOb.

Figure 6. Concrete disks used to "plant" sponge cuttings at the Turneffe Islands
sponge farm.

12

progression of sponge disease throughout the large planting areas is consistent with
our location of the sponge planting areas.

The area where sponges were planted was extensively surveyed, but no
concrete disks were found. Wood stakes were found which the local guide (Joseph
Garbutt) claimed were marking the sponge planting area. These wood stakes were
obviously much older than stakes used to mark lobster traps (they were covered with
an extensive growth of fire coral). Although all of Mr. Garbutt’s comments during the
expedition proved to be accurate, the verification of these stakes as artifacts from the
sponge farm was impossible.

DISCUSSION

Inclement weather (sustained 25-30 mph winds) and failure of a local guide to
provide contracted services (a new Turneffe Islands expedition team had to be
organized) reduced opportunities to conduct more extensive surveys. These factors
prevented the collection of quantitative data on sponge density and population
structure. However, two significant goals were realized: useful ecological and fishery
information was collected on the velvet sponge, Hippospongia gossypina, in the marine
waters of Belize and the location of the Turneffe Islands sponge farm was documented.
These observations increase the information available for understanding and managing
the marine biological and fishery resources of Belize.

Distribution and Abundance of Commercial Sponges

Within the Turneffe Island lagoon (the only location where commercially valuable
sponges were found), velvet sponge were found growing on a mangrove peat
substrate. Although the mangrove peat provides a substrate for sponge attachment
(Figure 7), it crumbles easily and is sufficiently soft to allow the establishment of the
seagrass Thallassia testudinum. Our observations indicate that, although this substrate
is adequate for the attachment of sponges, many of the sponges eventually break loose
(Table 1). Sponges that break loose from the substrate but continue to survive and
grow are commonly called "rollers" in the commercial trade (Figure 8). The percentage
of rollers was much higher than the percentage observed in the Florida commercial
sponge harvest (Stevely, pers. obs). The occurrence of commercial sponge growing
on a non-rock substrate was a new observation for us. In our extensive field
observations in both the Gulf of Mexico and the Bahamas, we have found commercial
sponge species (Hippospongia and Spongia growing either attached to rock
outcroppings or to any suitable hard surface (coral/rock fragments, gorgonians, etc).
De Laubenfels (1948) reported that sheepswool and velvet sponge were common on
these substrates, often in precisely the same localities.

Although the previously noted additional field observations taken on October 19,
1991 were extremely cursory, they did confirm the observation that the velvet sponge
was found growing on mangrove peat/seagrass substrate. Also, there was a general
impression that the percentage of "roller" sponges varied considerably from site to site.
In some areas it seemed that most sponges were found growing attached to the
substrate. In the Soldier Bight area it appeared as if almost all the velvet sponges were
rollers and that they had accumulated along the eastern shoreline as a result of

Gere ss tere ee ee

Figure 7.

Figure 8.

13

Live velvet sponge (Hippospongia gossypina) removed from water to
show growth habit of attachment to mangrove peat substrate.

Live velvet sponge (Hippospongia gossypina) removed from water to
show growth habit of "roller sponge". Former point of attachment to
substrate is now covered by ectosome.

14

tidal and/or wind driven currents. However, these observations need to be verified by
more detailed field work.

Smith (1941), in describing the Turneffe Islands lagoon sediments, stated that
"the floor of the lagoon consists of calcarious mud, with admixed shell and coral sand
predominate near the eastern entrances, and with organic matter formed from the
detritus of eel-grass and mangrove roots present in varying degree throughout the
lagoon". Mangrove/seagrass peat substrate was observed in several areas in the
Crooked Creek and Chickozeen vicinity. The depth of the mangrove peat appeared to
be considerable. On one occasion crevices were seen in the mangrove peat which
extended 6-8 ft (2-2.5 m) in depth. Observations made while snorkeling Crooked
Creek (a channel between mangrove islands carved boy tidal currents) indicate the
depth of the mangrove peat deposits extended to at least 30 ft (10 m). These
observations suggest that the Turneffe Islands represent an atoll formation consisting
of mangrove peat and suggest that mangrove peat formation has kept pace with
seamount subsidence/and or sea level rise.

Prior to the 1938-39 sponge mortality, the velvet sponge was known for its
commercial value and was considered to be the most valuable commercial sponge after
the sheepswool sponge (Moore, 1910b). Although it was considered to be less
compressible, absorbent, and durable compared to the sheepswool sponge, velvet
sponges from some area (e.g., the Bahamas) were regarded as almost equivalent in
quality to the sheepswool sponge.

Moore (1910b) reported the velvet sponges were found in the straits of Florida,
the Caribbean Sea, and the Bahamas. De Laubenfels and Storr (1958) stated that
velvet sponges had been common around Florida and the west Indies. In Florida,
velvet sponge was harvested from the fishing grounds between Key West and Cape
Florida (Moore, !9I0b) in living coral areas at depths of 3-25 ft (1-8 m) (Storr, 1964).
Florida sponge fishermen produced 8,000 Ib (3,600 m) of velvet sponge in 1899
(Moore, I9I0b). Although velvet sponges were sufficiently abundant to sometimes be
reported in Florida commercial sponge landings, they were the least abundant of the
commercial sponges (Smith, 1898). The best quality of velvet sponge was regarded to
be from the Bahamas (Moore, 19IOb), and at one time it was the principal commercial
sponge of the Bahamas (de Laubenfels and Storr, 1958). Moore (I9I0b) noted some
commercial sponge production from the British Honduras, including velvet sponge.
Moore also reported that sheepswool, velvet and grass sponges (Spongia sp.) were
found along the entire coast of British Honduras, in the shallow waters about the
numerous islands, rocks, and banks, and that many commercial sponge varieties grow
"attached to staghorn corals and gorogonians". No mention was made of either
sponges at Turneffe Islands or velvet sponges found growing attached to mangrove
peat substrate. Cresswell (1935) mentioned an effort by commercial sponge fishermen
in 1895 to explore the waters of British Honduras and reported that velvet sponge was
the most common sponge harvested.

After the devastating sponge mortality, the velvet sponge was thought to be
essentially extinct in areas that had been known to produce commercial quantities,
although many years later a few were reported from Cuba (de Laubenfels and Storr,
1958; Storr 1964). An extensive survey of the Florida sponge grounds in 1947 and 1948

15

was conducted to evaluate the condition of the sponge grounds following the effects
of the sponge disease and overfishing during the early 1940’s. The resulting fishery
report did not report the occurrence of any velvet sponge (Dawson and Smith, 1953).
However, later taxonomic study of the sponges collected during the survey reported
a velvet sponge specimen collected from a station in the northern Gulf of Mexico (de
Laubenfels, 1953). Storr (1964) stated that the velvet sponge had not been reported in
the Bahamas since the disease. In 1975 a report on the Bahamian sponge fishery
indicated that the fishery was based on the harvest of sheepswool and grass sponge
and contained no reference to velvet sponge (Thompson, unpubls. mans.).
Wiedenmayer (1977) surveyed the shallow-water sponges of the western Bahamas and
reported eighty-two sponge species, including 3 commercial species of the genus
Spongia but no velvet sponge (his study was not intended as a survey of commercial
varieties). Repeated communication with Florida sponge fishermen and sponge buyers
has failed to indicate even the rare occurrence of the velvet sponge. The effects of
disease and overfishing were apparently sufficiently severe to drastically reduce velvet
sponge abundance throughout a major portion of its geographic range. In view of the
long-term change in distribution and abundance of the velvet sponge and a lack of
knowledge of its current distribution, the apparently healthy population at Turneffe
Islands is worthy of note to fishery managers and scientists.

The Turneffe Island’s velvet sponge population may represent a relatively small
genetically isolated population. Storr (1964) indicated that the sheepswool sponge
(Hippospongia lachne) larval state is short-lived (I-2 days) and does not have strong
swimming capabilities. The Turneffe Islands atoll is separated from other shallow
water habitats by waters at least 250 fathoms in depth. Prevailing surface current
patterns (Hartshorn et al., 1984: Figure 9, this report) support the idea that larval
recruitment (i.e., genetic exchange) may be limited between Turneffe Islands and other
shallow water Caribbean sponge populations. If the prevailing surface currents
depicted in Figure 9 accurately indicate a likely transport mechanism for velvet sponge
larvae, then the larvae would have to traverse open Caribbean Sea waters in a
relatively short time.

The ability of the velvet sponge to grow attached to a mangrove peat substrate,
and possibly the ability to utilize a food source enriched with detrital particles may help
to explain to future investigators subtle differences and commonalities in the ecological
niches occupied by commercial sponge species. Although speculative, field
observations may suggest that seagrass/mangrove derived detrital particles may
contribute to velvet sponge nutrition. On windy days, waves and currents agitated the
shallow water where the velvet sponges were found, and, in effect, produced a
suspension of detrital material consisting of decaying seagrass leaves and eroding
mangrove peat. The detrital suspension was sufficient to noticeably reduce water
clarity in mangrove peat areas exposed to windy conditions. Sponges are efficient
filter feeders, evidently capable of filtering bacteria size food particles. It is possible
that fine detrital particles in the water column could either directly or indirectly, by
promoting bacterial growth or elevating the level of dissolved organic, contribute to
nutritional intake. Lauckner (1980) reviewed data that suggest the presence of
symbiotic bacteria associated with several sponge genera, including Spongia and
Hippospongia, which possibly could assist the sponge in utilizing dissolved organic
substances.

16

Belize
30 mi
AO sake

d anette
} "y Pe Sab
rl (teathe

“ky

/ ighthouse

Figure 9. Prevailing surface currents for waters of Belize (adapted from Hartshorn
et al., 1984).

17

Evaluation of Commercial Sponge Fishery Potential

Although a commercially valuable grade of velvet sponge was found to occur
at a density capable of supporting fishery activities, several important factors must be
considered before the fishery potential can be properly evaluated. Most importantly,
the extent of sponge producing areas within the Turneffe Islands lagoon must be
assessed more thoroughly. Although the additional field work conducted on October
19,1991 found more areas that supported velvet sponge growth, the areas were limited
in size and might be easily depleted by continuous intensive fishing effort. The
comments by Moore (I9lOb) indicating the presence of several varieties of commercial
sponges from the coast of British Honduras suggest that additional surveys are required
to more fully define the commercial sponge resources of Belize.

The unique substrate to which the Turneffe Islands sponges are attached may
not be conductive to allowing long-term harvest. Sponge fisheries in Florida and the
Bahamas are supported by harvesting sponges that grow attached principally to
carbonate rock outcroppings. Field observations in the Bahamas (Stevely, pers. obs.)
and experimental work in the Florida Keys (Stevely and Sweat, 1985) indicate that
when sponges are either cut or torn from such substrate, a significant quantity of
sponge tissue sometimes remains attached to the substrate. This tissue is capable of
regenerating to produce another viable sponge. In Florida, survival of harvested
sponges ranged from 30% for sponges torn free using a sponge hook to 70% for
sponges cut free with a knife. In Turneffe Islands, where sponges are anchored only
to mangrove peat, it is likely that all the sponge tissue would be taken when the
sponges were harvested by either hooking or cutting and that no attached sponge
tissue would remain for regeneration. The same would be true for harvested roller
sponges.

The large size of the Turneffe Islands velvet sponges (Table 1) may suggest that
the legal size for sheepswool sponge required by either Florida (5 in, 12.5 cm, minimum
diameter) or Bahamian law (7 in, 17.5 cm, minimum diameter) would provide little
protection for the resource if sponge harvesting was economically feasible. Only one
of the |5 sponges measured (Table 1) would have been protected by a law requiring a
minimum harvest size of 5 in (12.5 cm). However, may more sponges from several
areas should be measured before fishery management regulations are suggested. Also,
consideration must be given to managing a regularly harvested resource compared to
harvesting a virgin stock. A conservative approach that insures adequate protection
of the resource should be taken in managing Turneffe Islands sponge fishery
development until more complete information is available. Establishing an enforceable
minimum legal size of 8-9 in (20-22.5 cm) exemplifies such a conservative approach.

Conservative management of the Turneffe Islands sponge fishery requires
protection of reproductive stocks. Historically, research on reproduction in commercial
sponges has focused on the more valuable sheepswool sponge, and essentially no
information on velvet sponge biology is available. The sheepswool sponge attains
reproductive maturity at a size of from 3 in (7.5 cm) in the Florida Keys to 5.5 in (14
cm) in the northernmost Florida west coast sponge grounds; reproductive maturity is
attained at a smaller size in the warmer portions of its geographic range (Storr, 1964).
Assuming a similar trend in the size of maturation in the velvet sponge it is reasonable

18

to assume that a minimum size of 8 or 9 inches (20-22.5 cm) in Belizean waters would
protect sponges capable of a significant contribution to larval production.

The physical remoteness of Turneffe Islands presents transportation problems
for sponge fishermen. Most likely, it would be necessary to store sponges
accumulated for several weeks before transport to the mainland. Fortunately, cured
and dried sponges do not require refrigeration and could be collected over weeks or
months while intermittently pursuing other fishing activities. Storage of cleaned
sponges would require some shelter to prevent rotting and long-term exposure to the
sun. Cleaned sponges are also lightweight and can be easily transported by small
boats.

Proper cleaning of sponges is hard work, but it is critical for receiving top price;
improperly or incompletely cleaned sponge are either worthless or are worth only a
fraction of their true value. In addition to time allotted for sponge harvesting, the
sponge fishermen must commit an equal proportion of effort to cleaning, storing, and
transporting the catch.

Conversations with fishery cooperative manager indicated some lack of interest
in exporting sponges for two reasons: they were unfamiliar with the current value of
commercial sponge in the export market and they did not know whether sponges were
sufficiently abundant to support fishery development. The fishery cooperatives are the
obvious focal points for collecting and exporting sponges. Belizean fishery
cooperatives routinely ship seafood to Florida. Sponges are a highly valuable
commodity (e.g., US $20.00-50.00/lb; $44.00-110.00/kg), and reasonable shipping
costs (e.g. US $l.00-2.00/lb; $2.00-4.00/kg) would not be prohibitively expensive.
Thus, sponge exports may significantly increase the cash flow and profitability of
fishery cooperatives. For example, a 5,000 Ib (2250 kg) annual shipment could easily
result in an annual cash flow of $100,000 based on an estimated minimum price of US
$20.00/lb ($44.00/kg) for velvet sponge. If a reliable supply of quality velvet sponges
was established, it is reasonable to expect that the price paid for sponge to further
increase.

Location of the Commercial Sponge Farm

A significant amount of historical information exists for sponge culture work in
the Florida Keys, Bahamas, and Pacific Ocean (Stevely et. al., 1978). However, only
sparse notes in the literature, referring principally to the occurrence of sponge disease
and briefly describing sponge farm operations and location are available for the
Turneffe Islands sponge farm (Smith, 1941). Smith (1941) stated, "Cultivation consists
of cutting the sponge into small pieces, attaching these to stone or cement disks and
allowing them to grow to market size on areas of the lagoon bottom most favorable to
fast and healthy development". In the Bahamas, a length of palmetto string made from
splitting a palmetto palm leaf was used to tie the cut sponge pieces to the concrete
disk (Storr, 1964). One of the sponge disks found during our investigation still had a
piece of aluminum wire attached through the small hole in the disk, suggesting that
aluminum wire was at least sometimes used to attach sponge cuttings at Turneffe
Islands. Aluminum wire also was used in sponge farming attempts in the Florida Keys
(Stevely, et. al., 1978). The Turneffe Islands concrete sponge planting disks (Figure 6)

19

were similar in appearance to those used in both the Bahamas (Storr, 1964; Figure 9)
and Florida Keys (Stevely et al., 1978, Figure I5).

Smith (1941) stated that the farm was run by concessionaires (Messers. R.E.
Foote and H.T. Grant) licensed by the British Honduras Government. At the time of the
sponge disease mortality, approximately 700,000 sponges were under cultivation
(225,000sheepswool sponges, and 475,000velvet sponges). Mortality of the densely
planted sponge cuttings (in some places one per square meter) was estimated to be
95%.

Some of the geographical advantages of attempting sponge farming in the
Turneffe Islands lagoon are readily apparent. The lagoon contains extensive shallow
areas 3-I2 ft (1-4 m) deep that are reasonably protected by mangrove islands.
Sheltered and relatively clear waters would permit sponge farm operations to proceed
in all but the most severe weather conditions. The remoteness of the Turneffe Islands
would probably assist in enforcing security of the farm. Difficulty with protecting
sponge plantings from theft has been a major problem for sponge farming attempts in
many areas (Stevely et al, 1978). However, Turneffe Islands sponge farm workers
living in the immediate vicinity of the farm could serve as security guards in the area.
Potential thieves interested in stealing sponges from the farm would have to establish
a camp for harvesting, cleaning, and storing a sufficient number of sponges to justify
transport back to mainland. In general, it would be difficult for a potential sponge
poacher to escape notice in these remote surroundings populated principally with
sponge farm workers.

Finally, the abundance of "wild" sponge stock in the lagoon may have played
a key role in the decision to attempt sponge farming. The natural sponge populations
may have been insufficient to support a fishery harvesting hundreds-of-thousands of
sponges, but capable of producing tens-of-thousands of "seed" sponges for
‘ propagation.

LITERATURE CITED

Dawson, C.E., and F.G. Walton Smith 1953.
The Gulf of Mexico sponge investigation. State of Florida Board of
Conservation Technical Series No. 1. Marine Laboratory, Univ. of Miami, FL
28p.

Cresswell, E.J, 1935.
Sponges: their nature, history, modes of fishing, varieties, cultivation, etc.
Pitmen’s common Commodities and Industries Series. Sir Isaac Pitman and
Sons, Ltd. London. 126p.

de Laubenfels, M.W. 1948.
The order Keratosa of the phylum Porifera - a monographic study. Occ. Pap.
Allan Hancock Fdn. (3):1-217.

20

de Laubenfels, and J.F. Storr. 1958.

The taxonomy of American Commercial sponges. Bull. Mar. Sci. Gulf and Carib.
8(2):99-117.

Gaino, E. and R. Pronzato. 1989.
Ultrastructural evidence of bacterial damage to Spongia officinalis fibers
(Porifera, Demospongiae). Dis. Aquat. Org. 6:67-74.

Hartshorn, G. 1984.

Belize country environmental profile. San Jose: Trejos. Hnos. Sucs. S.A. p.
XVI-152.

Josupeit, H. I99I.
Sponges: world production and markets. INFOFISH International, Kuala
Lumpura, Malaysia. I99I, No. 2, p. 21-27.

Lauckner, G. 1991. .
Diseases of Porifera. In: Kinne, O. (ed) Diseases of Marine animals, Vol. I,
General aspects, Protozoa to Gastropoda. Wiley and Sons, Chichester, p. 139-
165.

Moore, H.F. and P.S. Galtsoff. 1951.
Commercial Sponges. In: Marine Products of Commerce, R.K. Tressler and J.M.
Lemon eds. Rheinhold Publishing Corp. N.Y., N.Y. p. 733-751.

Moore, H.F. 19l0a.
A practical method of sponge culture. Bull. U.S. Bur. Fish., Vol. 28, 1908 Part
|, p. 545-585.

Moore, H.F. I9IOb.

The commercial sponges and the sponge fisheries. Bull. U.S. Bur. Fish. Vol. 28,
1908. Part |, p. 399-511.

Shubow, D. 1969.

The Florida sponge industry. Master’s Thesis, Univ. Miami, Coral Gables, FL.
123 p.

Smith, H.M. 1898.
The Florida commercial sponge. In: Proceedings and papers of the National
Fishery Congress held in Tampa, FL. Jan. 19-4, 1898. p. 225-250.

Smith, F.G.W. 1941.
Sponge disease in British Honduras and its transmission by water currents.
Ecology 22(4): 415-421.

Stevely, J.M., Thompson, and R.E. Warner. 1978.
The biology and utilization of Florida’s commercial sponges. Florida Sea Grant
College Program Tech. Rept. No. 8. 45p.

21

Stevely, J.M., and D. Sweat. 1985.
Survival and growth of cut vs. hooked commercial sponges in the Florida Keys.
Florida Sea Grant College Program Tech. Rept. No. 38. 12p.

Storr, J.F. 1964.
Ecology of the Gulf of Mexico commercial sponges and its relation to the
fishery. U.S. Dept, Interior, Fish. Wildl. Serv., Spec. Sci. Rept. No. 466. 73p.

Thompson, R.W. Unpubl. mans.
Report on the sponge industry. Bahamas Ministry of Agriculture Fisheries and
Local Government. 4p.

Verdenal, B. and M. Verdenal. 1987.
Evaluation de I’Interet Economique de la Culture d’ Esponges Commerciales sur
les Cotes Meditereenes Francaises. Aquaculture, 64:9-29.

Wiedenmayer, F. 1977.
Shallow-water sponges of the western Bahamas. Birkhauser Verlog, Basel and
Stuttgart. p. 1-287, pls. 1-43.

Wilkinson, C.R. Unpubls. mans.
Consultants report on the potential for commercial sponge farming in Pohnpei,
Federated States of Micronesia. Prepared for Marine Resources Division,
Federated States of Micronesia. FAO South Pacific Aquaculture Development
Project, Suva, Fiji, 31p.

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ATOLL RESEARCH BULLETIN

NO. 425

SPATIAL AND TEMPORAL VARIATIONS IN GRAZING PRESSURE BY

HERBIVOROUS FISHES: TOBACCO REEF, BELIZE

BY

PETER N. REINTHAL AND IAN G. MACINTYRE

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

5
o
Y
c
io}
o
—lo)
20
=
1.0]
U

) if South Water
: Cay

South Water Cut
ve 2 Carrie Bow
a “Lagoon ao S Cay
lsu Reefs :/

cf Curlew
Bank

Curlew Cut

FIGURE 1 - Index map showing location of study transect on Tobacco

Reef.

SPATIAL AND TEMPORAL VARIATIONS IN GRAZING
PRESSURE BY HERBIVOROUS FISHES:
TOBACCO REEF, BELIZE
BY
PETER N. REINTHAL!
and

IAN G. MACINTYREZ

ABSTRACT

Fish herbivory appears to play an important role in the pattern of macrophyte
zones running parallel to the crest of the Belizean barrier reef. The experimental
relocation's of reef macrophytes seaward of the reef in 1984 and 1989 revealed that
algal species with herbivore-resistant strategies are predominant in the zones of
strongest herbivory near the reef crest, whereas those highly susceptible to fish grazing
occur well lagoonward of the reef crest. The foraging ranges of herbivorous fish are
thought to depend in large part on their proximity to suitable shelter. These trends in
herbivore activity were observed in both 1984 and 1989, although the grazing pressure
was uniformly less for all algal species studied in 1989. These findings may be related
to seasonal (May 1984 versus March 1989) or annual variations in grazing pressure, or
to a general decrease in grazing pressure over the five-year study period.

INTRODUCTION

The patterns of abundance and distribution of coral reef macrophytes are well
known to be influenced by grazing activities of herbivorous fishes (Stephenson and
Searles 1960, Randall 1961, 1965, John and Pope 1973, Wanders 1977, Hay 1981a,
b, Hay et al. 1983, Hay 1984, Lewis 1986, Horn 1989, Choat 1991, Hay 1991) and
urchins (Ogden et al. 1973, Sammarco et al. 1974, Sammarco 1980, Lawerence and
Sammarco 1982, Hay 1981a, b, 1984). However, only recently have studies been
conducted on spatial variation in herbivore activity patterns and the effects of spatial
patterns of herbivory on macrophyte distributions (Hay et al. 1983, Lewis 1986,
Macintyre et al.. 1987, Morrison 1988; Hay 1991). Spatial heterogeneity in grazing
intensity has been found to contribute to regional diversity among and within tropical
reef habitats (e.g. Lewis 1986) and fishes appear to play a major role in structuring
shallow water macrophyte communities (e.g. Morrison 1988).

Department of Biology, Eastern Michigan University, Ypsilanti, Michigan 48197, and

2Department of Paleobiology, National Museum of Natural History, Smithsonian
Institution, Washington D.C. 20560
Manuscript received 11 May 1994; revised 30 August 1994

FIGURE 2 — Aerial view of Tobacco Reef looking south towards South
Water and Carrie Bow Cays. Note location of study transect and
biogeological zones on sediment apron. (1. Coralline-Coral-Dictyota
pavement; 2. Turbinaria-Sargassum rubble; 3. Laurencia-Acanthophora
sand and gravel; 4. Bare sand; 5. Thalassia sand.) Emergent reef crest
and deep fore-reef on left.

3

In this study we used transplanted samples of various reef macrophytes as a
bioassay for an assessment of fish grazing in the backreef habitat. The grazing activity
was then compared to observed patterns of macrophyte zonation and evaluated to
determine relative grazing pressures on various macrophytes as a function of distance
from the reef crest. Varying selective pressures from fish herbivory and substrate
requirements appear to be important factors in determining the distribution and zonation
patterns of reef macrophytes (Macintyre et al. 1987).

Preliminary results found in 1984 (Macintyre et al. 1987) prompted us to repeat
similar experiments in 1989 when we were able to replicate the treatments at three
separate locations (versus one location in 1984) and provide a caged control treatment at
one of the locations. This approach allowed us to look at spatial variation in grazing as
both a function of distance from the reef crest and variation along the reef crest. The
results raise a number of interesting questions concerning spatial and temporal variation
in fish grazing activity in the back reef habitat.

MATERIALS AND METHODS

This study was conducted during May 1984 and March 1989 in the backreef
habitat at Tobacco Reef, north of the Smithsonian Institution's field station at Carrie
Bow Cay, Belize, Central America (16948' N, 88°05' W; Fig. 1). The topography,
geology and zonation of the region and the floristic and fish distribution patterns are
described in detail elsewhere (Rutzler and Macintyre 1982, Norris and Bucher 1982,
Lewis and Wainwright 1985, Macintyre et al. 1987). A primary study site
representative of the reef was identified on the sediment apron of Tobacco Reef
approximately 1 km north of South Water Cay (Fig. 1). Three sites that were separated
approximately 100 m (north, middle and south) were used as replicate localities.

We transplanted samples of eight reef macrophytes to 0 m., 40 m., 90 m. and
150 m. from the reef crest to determine fish grazing activity as a function of distance
from the reef crest. The distances were related to the observed patterns of macrophyte
_ zonation and five distinct biogeological zones (Fig. 2): (1) 0 m: coralline-coral-Dictyota

pavement, (2) 40 m: Turbinaria-Sargassum rubble, (3) 90 m: Laurencia-Acanthophora
sand and gravel, (4) 150 m: bare sand and (5) Thalassia sand. These zonation patterns
and various abiotic factors affecting macrophyte distribution are discussed elsewhere
(Macintyre et al. 1987).

The eight macrophytes used in the grazing assay were Turbinaria turbinata,
Sargassum polyceratium, Thalassia testudinum, Padina jamaicensis, Acanthophora
spicifera, Laurencia papillosa, Laurencia intricata and Dictyota sp. The T. testudinum
blades and other species were free of epiphytes as were all macrophytes. These
macrophytes were chosen because they are common and abundant members of the
backreef community and show variation in distribution patterns. A mixed assay
allowed us to determine grazing intensity with respect to the variety of herbivore groups
observed to be active in this area. For example, previous studies (Lewis 1985) have
shown that T. turbinata, S. polyceratium, T. testudinum and P. jamaicensis are
preferred and primarily consumed by parrotfish (Sparisoma and Scarus spp.). In
contrast the red algal species, A. spicifera, L. papillosa and L. intricata, are preferred
and primarily consumed by acanthurid species (Acanthurus bahianus, A. coeruleus and
A. chirugus) (Lewis 1985). Another herbivore, Diadema antillarum, was not
considered in this study because it had undergone a massive die-off throughout the
Caribbean (Lessios et al. 1983) and was never common on this back-reef sediment
apron of Tobacco Reef. Moreover, fish are considered to be the grazers of prominent

FIGURE 3 - Before and after photographs of test set of four macrophytes
(left to right: Turbinaria turbinata, Sargassum polyceratium, Padina
jamaicensis, and Thalassia testudinum) at reef crest site.

5

importance on many tropical reefs (Hay 1984, Lewis 1986, Morrison 1988). No other
organisms were found grazing on any of the assays.

The pattern of herbivore pressure as a function of distance from the reef crest
was measured by placing complete spin dried and weighed sets of the assay in the back
reef at distances of 0, 40, 90 and 150 m behind the reef crest. Samples of each of the
macrophyte species were held in wooden clothespins attached to metal rods (Fig. 3).
All trials were run for 8 h from 0830 to 1630 h at each experimental grazing site. The
samples were then spin dried and reweighed. In 1984, four trials were conducted at
each distance at one location each on different days. The amount of macrophyte used in
the assays was consistent with the size of macrophytes observed in the study area. In
all trials a small piece of the macrophyte remained in the clothespins where it was
inaccessible to herbivores. The remaining macrophytes, grazing scars and field
observations indicated that macrophytes were not lost by wave action.

In 1989 the trials were replicated on different days three times at each of three
locations approximately 100 m apart for all four distances from the reef crest. The
middle site was approximately at the same location as that used in 1984. At the
northern most locality, 1 m3 cages constructed from 1/4" wire mesh were placed at
each distance from the reef crest. Grazing assays with the eight macrophytes were
placed in the cages as controls for the amount of macrophyte lost due to wave action
when fish grazers are excluded. Special care was taken to avoid placing macrophyte
assays near the guarded territories of damselfish.

Fish counts were made in 1984 along a series of four replicated visual line
transect censuses (50 m x 2 m) between 0800 and 1600 h at each experimental grazing
site. All parrotfish (Scarus and Sparisoma spp.) and surgeonfish (Acanthuridae) were
counted to determine distribution patterns and densities. The methodology applied here
is similar to that used by Lewis and Wainwright (1985) in their study of distributions of
herbivores among reef habitats.

RESULTS

1984 Experiments

In 1984, a distinct fish-grazing pattern emerges from the data on percent weight
loss for the macrophyte species used in this study. Average percent weight loss
generally decreases with distance from the reef crest for seven of the macrophytes
studied (the exception being Dictyota sp.) and shows highly significant weight-loss
differences with respect to distance from the reef crest (ANOVA, P < 0.005 in all
cases) (Table 1).

For all macrophytes except Dictyota divaricata, grazing pressure was
homogeneously heavy in 1984 at 0 and 40 m from the reef crest as indicated by Duncan
multiple range tests (Table 1): the average percent weight loss at 0 and 40 m are
included in the same homogeneous subset whose highest and lowest means do not
differ by more than the shortest significant (.05 level) range for a subset of that size.
For two macrophyte species, Padina jamaicensis and Thalassia testudinum, the
homogeneity of heavy grazing pressure extends to 90 m. These two macrophyte
species are highly preferred by parrotfish in field feeding trials (Lewis 1985, Lewis and
Reinthal in prep.). Turbinaria turbinata and Sargassum polyceratium, also preferred by
parrotfish, appear to be subject to the same heavy grazing pressure at 0 and 40 m, but
little or moderate grazing pressure at 90 and 150 m.

The situation was similar for the macrophytes preferred by surgeonfish
(Acanthuridae) (Lewis 1985, Lewis and Reinthal, in prep.). The grazing pressure on
Acanthophora spicifera and Laurencia papillosa is homogeneously heavy at 0 and 40 m,

moderate at 90 m, and light at 150 m as indicated by the homogeneous subsets in the
Duncan's Multiple range test (Table 1). Heavy grazing pressure is also observed at 0
and 40 m for L. intricata but grazing is homogeneously moderate to weak at 90-150 m.

In the case of Dictyota divaricata sp., grazing pressure was homogeneously light
and no significant differences were found between average weight loss at various
distances (ANOVA, P = 0.68) (Table 1). The Duncan's Multiple range test included
all distances in the same homogeneous subset. The weight loss in this case is thought
to be due primarily to experimental error caused by the removal of small fragments
through wave action and this was the only macrophyte that proved difficult to retain as
one piece in a clothespin.

Distribution patterns identified for herbivorous fish (Table 2) coincide with
grazing patterns identified here. Fish densities were highest at 0 and 40 m, the areas
with the greatest grazing pressure. Even though most of the fish observed at 90 m
were juvenile Acanthurus bahianus, the sighting of a large heterospecific school of
adult herbivorous fish outside the transect area (approximately 60 A. bahianus, 10 A.
chirugus, 4A. coeruleus and 13 Sparisoma chrysopterum) indicates these fish do
extend their foraging to 90 m. Many heterospecific schools were also observed at 0
and 40 m. No schools were sighted at 150 m and only 1 individual was counted in the
transects.

1989 Experiments

There were no significant differences between the three replicate locations for all
eight macrophytes nor were there any significant distance*location interaction effects
(ANOVA p > .05 in all cases). Thus, the three locations were grouped together for
purposes of analyses.

The caged treatment showed no significant distance effects for macrophyte loss
due to wave action (ANOVA p > .05 in all cases) and all distances were included in the
same homogeneous subset (Table 1).

For the experimental assays, a similar pattern of spatial variation in grazing
intensity emerges with respect to distance from the reef crest as that found in 1984
(Table 1) but grazing pressure was uniformly weaker. At all distances, for all
macrophyte species, the percent weight loss was less in 1989 than that found in 1984
(ANOVA; p<.01). For six of the eight macrophytes there was a significant difference
between the distances (ANOVA; p < .0005; Table 1). Only Turbinaria turbinata and
Dictyota sp. showed no significant differences between distances.

The grazing intensity observed in 1989 appears to be uniformly less than that
found for all macrophytes in 1984. The Duncan's multiple range tests for 1989 show
the same grazing pattern but a fairly consistent shift in the grazing pressure toward the
reef crest and in no cases was grazing pressure heavier nor further extended than that
found in 1984 (Table 1).

DISCUSSION

Spatial Patterns of Herbivory

The data presented here show distinct spatial grazing patterns on the macrophyte
species under study. For all macrophyte species, except Dictyota divaricata, the
grazing pressure in 1984 is heavy at 0 and 40 m from the reef crest, moderate to light
at 90 m and absent at 150 m. The same general results were found in 1989 but the
grazing pressure was uniformly less. These results are associated with zonation
patterns and biogeologic zones observed for this backreef habitat and the distribution of
_ biological assemblages appears to be controlled mainly by a combination of grazing

7

pressure of herbivorous fish, which is a function of distance from the reef crest, and
both physical factors and hydrodynamic conditions which are discussed elsewhere
(Macintyre et al. 1987). Thus, while spatial heterogeneity in herbivore grazing
represents a biotically generated mechanism contributing to high regional diversity
among reef habitats (Lewis 1986, Hay 1981a, 1985; Morrison 1988), the patterns of
zonation and habitat diversity within the Tobacco Reef backreef appear to be under a
similar mechanistic control.

Dictyota spp. in general, probably because they contain noxious chemical
compounds (Gerwick 1981, Norris and Fenical 1982), are notably avoided by
herbivorous fish (Montgomery 1980, Hay 1981a, Littler et al. 1983). Surgeonfish
were occasionally observed taking single bites of D. divaricata but would not continue
to feed or graze with the same intensity as they did on Laurencia papillosa or
Acanthophora spicifera.

The grazing pressure may be determining the zonation pattern through either
direct effects or an indirect effect by inhibiting an efficient competitor. Lewis (1986)
directly compared grazed backreef versus ungrazed backreef and found that
Sargassium, Padina and Turbinaria did increase significantly in the absence of fish
herbivory and outcompeted corals and other slow-growing benthic species. Hay
(1981a, b) and Hay et al. (1983) showed that algal species characteristic of the deep
sand plains and intertidal reef flats may be restricted from the reef slope by herbivory,
and suggested that these species would represent potentially dominant competitors on
the reef slope in the absence of herbivory. The same may be true for the Tobacco Reef
backreef habitat.

Macroalgae species found at the greatest distances from the reef crest and found
in low-herbivory habitats were found to be the macrophytes most highly susceptible to
grazing by herbivorous fishes. Other studies have indicated that many algal species
characteristic of habitats with high grazing intensities are resistant to herbivorous fish
grazing and, conversely, algae in habitats with low grazing intensity are susceptible to
herbivory (Hay 1981b, 1984, Littler et al. 1983, Lewis 1985, 1986). For example, the
coralline-coral-Dictyota zone (Macintyre et al. 1987) is the zone in which we measured
the highest levels of herbivory. The dominant biota have well-documented herbivore
. defense strategies (Norris and Fennical 1982, Paul and Hay 1986).

Fish grazing intensity has been found to decrease with depth on forereefs and
exhibits an inverse relationship to algal abundance (Morrison 1988). The decreasing
herbivory is thought to be the result of diminishing trophic carrying capacity and
increased risk of predation (Hay and Goertemiller 1983, Steneck 1983, Lewis 1986).
The latter may well apply to the habitat studied here but the argument concerning
trophic carrying capacity is not applicable in the shallow back-reef.

Proximity to suitable shelter has long been recognized as a critical factor in
determining herbivore foraging ranges on patch reefs in tropical seagrass beds (Randall
1965), on deep sand plains adjoining reef slopes (Earle 1972, Hay 1981a, b) and in the
backreef areas remote from the reef crest (Lewis 1986, Lewis and Wainwright 1985).
Although we have no experimental evidence to explain why herbivorous fish do not
graze further from the reef crest, they may be constrained by predatory piscivorous
fishes (Ogden et al. 1973) and birds. Barracuda (Sphyraenidae), jacks (Carangidae)
and snapper (Lutjanidae) were often seen swimming in the study area. This might also
explain why only heterospecific schools of fishes, not solitary adult individuals, were
seen at the 90 m site. Heterospecific schooling is considered to provide predator
avoidance advantages to participants (see Morse 1977 for review).

All three study areas for 1989 showed the same pattern of herbivory and no
significant differences were found between the different locations for all macrophytes.
Thus, while the data clearly indicates that herbivore pressure varies perpendicular to the
reef crest, it is also consistent along the reef at any one distance from the crest.

Temporal Patterns of Herbivory

In 1989, the grazing pressure for all macrophytes was homogeneously less than
the grazing pressure found in 1984. These differences could represent seasonal
fluctuations in herbivory pressure or resource availability (May versus March) or longer
term patterns of variation (1984 versus 1989). The seasonal patterns could be the result
of differences in productivity or resource availability to the herbivorous fish.
Unfortunately, seasonal variation in grazing pressure or herbivore diets has been
largely ignored and warrants further research. There may also be seasonal differences
in fish movement patterns or community composition that may influence herbivory
patterns.

Alternatively the long term effects could be the result of the Diadema die-off
(Lessios et al. 1983) such that there is less competition for resources among
herbivores. Morrison (1988) demonstrated that fish grazing intensity tripled after the
Diadema die-off. Thus the increased herbivore pressure in 1984 could be the fish
responding to the lack of a competition and a new equilibrium is established by 1989.
An alternative explanation could be that in 1984, the macrophytes had not yet
responded to the overall decrease in grazing and the fish were showing the same
grazing pattern had Diadema been present. By 1989 the fish were no longer required to
venture as far into the backreef to graze on macrophytes since they were no longer
competing with Diadema.

Fish grazing intensity has also been found to vary between reefs because of
heavy fishing pressure (Hay 1984). Thus the decrease in grazing pressure from 1984
to 1989 could also be the result of a decrease in the fish populations through an increase
in fishing pressure.

CONCLUSION

From these data we may conclude that herbivorous fish have a strong impact on
the distribution patterns of various reef macrophytes and this impact is a function of the
distance from the reef crest. The data also indicate that there is temporal variation in
herbivory patterns. While grazing pressure did not vary at three locations along the reef
crest, it appears effective in preventing the establishment of many macrophytes within
90 m of the reef crest in the backreef habitat. The herbivory patterns found here are
consistent with the macrophyte distribution patterns and suggests that fish grazers are
of primary importance in controlling these distributional patterns. These patterns are, in
turn, directly correlated with the distance from the reef crest.

ACKNOWLEDGEMENTS

Special thanks go to Cindy Stackhouse, Anthony Macintyre and Allan Macintyre
for their assistance in the field. Sara Lewis made helpful comments in her review of an
earlier version of this manuscript. Part of this work was done while PR was a
postdoctoral Research Fellow at the American Museum of Natural History. This work
was supported by grants from the Caribbean Coral Reef Ecosystem Program, National
Museum of Natural History, American Museum of Natural History and Exon
Corporation (CCRE Contribution No. 351).

REFERENCES

Choat, J.H. (1991). The biology of herbivorous fishes on coral reefs. Pages 120-155
in P.F. Sale, editor. The ecology of fishes on coral reefs. Academic Press, Inc.
Harcourt Brace Jovanovich, San Diego.

Earle, S.A. (1972). The influence of herbivores on the marine plants of Great
Lameshur Bay, with an annotated list of plants. Results of the Tektite Program:
ecology of coral reef fishes. Sci. Bull. 14:17-44.

Gerwick, W.H. (1981). The natural products chemistry of the Dictyotacae. Ph.D.
dissertation, University of California, San Diego, Calif.

Hay, M.E. (1981a). Herbivory, algal distribution, and the maintenance of between-
habitat diversity on a tropical fringing reef. American Naturalist 118:520-540.

Hay, M.E. (1981b). Spatial patterns and grazing intensity on a Caribbean barrier reef:
herbivory and algal distribution. Aquatic Botany 11:97-109.

Hay, M.E. (1984). Patterns of fish and urchin grazing on Caribbean coral reefs: are
previous results typical? Ecology 65(2):446-454.

Hay, M.E. (1985). Spatial patterns of herbivore impact and their importance in
maintaining algal species richness. Pages 29-34 in Proceedings of the Fifth
International Coral Reef Congress, Tahiti 1985. Volume 4. Antenne Museum-Ephe,
Moorea, French Polynesia.

Hay, M.E. (1991). Fish-seaweed interactions on coral reefs: Effects of herbivorous
fishes and adaptations of their prey. Pages 96-119 in P.F. Sale, editor. The ecology of
fishes on coral reefs. Academic Press, Inc. Harcourt Brace Jovanovich, San Diego.

Hay, M.E., Colburn, T., Downing, D. (1983). Spatial and temporal patterns in
herbivory on a Caribbean fringing reef: the effects on plant distribution. Oecologia
(Berlin) 58:299-308.

Hay, M.E., Goertemiller, T. (1983). Between-habitat differences in herbivore impact
on Caribbean coral reefs. Pages 97-102 in M.L. Reaka, editor. The ecology of deep
and shallow coral reefs. Symposia series for undersea research. Volume 1. Office of
Undersea Research, National Oceanic and Atmospheric Administration, Rockville
Maryland, USA.

Horn, M. (1989). Biology of marine herbivorous fishes. Oceanography and Marine
Biology Annual Review, 27:167-272.

John, D.M., Pope, W. (1973). The fish grazing of rocky shore algae in the Gulf of
Guinea. Journal of Experimental Marine Biology and Ecology 11:81-90.

Lawrence, J.M., Sammarco, P.W. (1982). Effect of feeding on the environment:
Echinoidea. Pages 499-519 in M. Jangoux and J.M. Lawrence (eds.), Echinoderm
nutrition. A.A. Balkema Press, Rotterdam, The Netherlands.

10

Lewis, S.M. (1985). Herbivory on coral reefs: algal susceptibility to herbivorous
fishes. Oecologia (Berlin) 65:370-375.

Lewis, S.M. (1986). The role of herbivorous fishes in the organization of a Caribbean
reef community. Ecological Monographs 56(3):183-200.

Lewis, S.M., Wainwright, P.C. (1985). Herbivore abundance and grazing intensity on
a Caribbean coral reef. Journal Experimental Marine Biology and Ecology 87:215-228.

Lessios, H.A., Glynn, P.W., Robertson, D.R. (1983). Mass mortality of coral reef
organisms. Science 222:715.

Littler, M.M., Littler, D.S., Taylor, P. (1983). Algal resistance to herbivory on a
Caribbean barrier reef. Coral Reefs 2:111-118.

Macintyre, I.G., Graus, R.R., Reinthal, P.N., Littler, M.M., Littler, D.S. (1987). The
Barrier Reef sediment apron: Tobacco Reef, Belize. Coral Reefs 6:1-12.

Montgomery, W.L. (1980). The impact of non-selective grazing by the giant blue
damselfish Microspathodon dorsalis on algal communities in the Gulf of California,
Mexico. Bulletin Marine Science 30:290-303.

Morrison, D. (1988). Comparing fish and urchin grazing in shallow and deeper reef
algal communities. Ecology 69(5):1367-1382.

Morse, D.H. (1977). Feeding behavior and predator avoidance in heterospecific
groups. BioScience 27(5):332-338.

Norris, J.N., Bucher, K.E. (1982). Marine algae and sea grasses from Carrie Bow
Cay, Belize. In: Rutzler, K. & I.G. Macintyre (eds.) The Atlantic Barrier Reef
ecosystem at Carrie Bow Cay, Belize. Smithsonian Institution Press, Washington, DC
(Smithson. Contrib. Mar. Sci. 12:167-238).

Norris, J.N., Fenical, W. (1982). Chemical defenses in tropical marine algae. In:
Rutzler, K. & I.G. Macintyre (eds.) The Atlantic Barrier Reef ecosystem at Carrie Bow
Cay, Belize. Smithsonian Institution Press, Washington, DC (Smithson Contrib Mar
Sci 12:417-431).

Ogden, J.C., Brown, R.A., Salesky, N. (1973). Grazing by the echinoid Diadema
antillarum Philippi: formation of halos around West Indian patch reefs. Science
182:715-717.

Paul, V.J., Hay, M.E. (1986). Seaweed susceptibility to herbivory: chemical and
morphological correlates. Marine Ecology Progress Series, 33:255-264.

Randall, J.E. (1961). Overgrazing of algae by herbivorous marine fishes. Ecology
42:812.

Randall, J.E. (1965). Grazing effect on seagrass by herbivorous reef fish in the West
Indies. Ecology 46:255-260.

Rutzler, K., Macintyre, I.G. (1982). The habitat distribution and community structure
of the barrier reef complex at Carrie Bow Cay, Belize. In: Rutzler, K. & 1.G.

11

Macintyre (eds.) The Atlantic Barrier Reef ecosystem at Carrie Bow Cay, Belize. 1.
Structure and communities. Smithsonian Institution Press, Washington, DC
(Smithson. Contrib. Mar. Sci. 12:9-45).

Sammarco, P.W. (1980). Diadema and its relationship to coral spat mortality: grazing,
competition, and biological disturbance. Journal of Experimental Marine Biology and
Ecology 45:245-272.

Sammarco, P.W., Levinton, J.S., Ogden, J.C. (1974). Grazing and control of coral
reef community structure by Diadema antillarum (Philippi) (Echinodermata:
Echinoidea): a preliminary study. Journal of Marine Research 32:47-53.

Steneck, R.S. (1983). Quantifying herbivory on coral reefs: just scratching the surface
and still biting off more than we can chew. Pages 103-111 in M.L. Reaka, editor. The
ecology of deep and shallow coral reefs. Symposia series for undersea research.
Volume 1. Office of Undersea Research, National Oceanic and Atmospheric
Administration, Rockville Maryland, USA.

Stephenson, W., Searles, R.B. (1960). Experimental studies on the ecology of
intertidal environments at Heron Island. Australian Journal of Marine and Freshwater
Research 11:241-267.

Wanders, J.B.W. (1977). The role of benthic algae in the shallow reef of Curacao
(Netherlands Antilles) II: The significance of grazing. Aquatic Botany 3:357-390.

Table 1. Results of macroalgal transplant experiments: mean percentage macrophyte
weight loss (+ standard deviation) after exposure to or caging from herbivores at
varying distances from the reef crest in the Tobacco Reef backreef habitat for 8-h
trials. Four replicate trials were conducted at one location at each distance in 1984
(N=4) and three replicate trials were conducted at each of three locations in 1989 with
no differences found between locations (N=9). 1989 Cage are the results from three
replicate trials placed in fish exclusion cages at one location (N=3). Groupings
between distances are based on Duncan's multiple range test.

SPECIES MEAN PERCENT WEIGHT LOSS (4 S.D.) ANOVA
Om 40 m 90 m 150 m F P
Thalassia testudinum

1984 83.4 (6.2) 76.4 (10.7) 78.7 (6. > ae) (23: ») 24.98 <.0001
|
1989" 27 7-35(67) 2 9 (40. ) 0.0 (0.0) 0.0 (0. ») 30.39 <.0001
|
1989 0.0 (0.0) 2:31:33) 0.0 (0.0) 0.0 (0. ») 1.00 <.4411

Cage _ |------------------------------------------------------------------

Padina jamaicensis
1984 an 8 (3.0) 91.5, G31) 87.8 (9. =) 11.8 (6. 8) 142.2 <.0001

1989 81.3 (29. ? 42.4 (33. ey 6.4 (6.4) 11.0 (6. i 21.17 <.0001
|

1989 10.3 (5.6) 15.0 (6.4) 14.0 (4.5) 11.3 (8. “ 0.23 <.8707
Oe

Turbinaria turbinata
1984 86.4 (25.3) 61.1 (44. ? 8.9 (3.5) TUG) » 9.37 <.0018
|

1989) 21.8 (28.5) 6.9 (4.5) 5.4 (5. 2 3.8 (2.0) 2.26 <.1031
|

1989 4.3 (0.9) Sle) 4.7 (2.9) 4.0 (0. oh 0.35 <.7934
CAC lonnana ans n rama nnn ar nn a nnn

Sargassum polyceratium
1984 97.3 (2.0) 61.2 (42. “ 31.2 (36.1) 10.0 (4. _ 7.40 <.0046
|

1989 sie 730; HY i 4 (5.4) 5.8 (3.6) 7.4 (4. Z 9.32 <.0002

1989 = 4.7 (3.3) 10.7 (4.6) 8.0 (6.2) 6.3 (3. i 0.65 <.6023
Cage _ |-----------------------------------------------------------------

Table 1 (cont.).

SPECIES

MEAN PERCENT WEIGHT LOSS (z S.D.)

Om

Acanthophora spicifera
1984 93.3 (2.8)

1989

1989
Cage

74.8 (26.7)
|

ee

Laurencia intricata
1984 73.6 (19.7)

1989
Cage

19.7 (7.0)

Laurencia papillosa

1984

1989
Cage

93.4 (3.1)

13.0 (8.5)

Dictyota sp.

1984

1989

1989
Cage

28.5 (11.7)
|

40 m

89.1 (11. »

90 m

712) Gi. )
|

150 m

4.0 (6. y
|

ANOVA
F P

87.14 <.0001

31.22 <.0001

2.79 <.1090

12.35 <.0006

8.13 <.0005

0.25 <.8621

30.20 <.0001

85.65 <.0001

0.98 <.4477

0.52 <.6778

0.28 <.8371

0.00 <.9998

Table 2. Mean fish counts (densities per 100 m2, N=4) along line transects (50 x 2
m) at the four distances (m) from the reef crest (herbivory test sites) (from
Macintyre et al. 1987). The Acanthuridae juveniles (Juv) and adults (Ad) were both
counted and the species represented are Bah. = A. bahianus, Coe. = A. coeruleus
and Chi. = A. chirugus. All Scaridae individuals were included in counts and
species represented are Ise. = S. iserti, Chr. = S. chrysopterum, Rub. = S.
rubripinne, Vir. = S. viride and Rad. = S. radians

ACANTHURIDAE SCARIDAE
Dist. Bah. Coe? Chi. ise. Chr Rubs) Vir | Rad?
(m) Juv Ad Juv Ad Juv Ad
150 0.0 0:.0---40220 OF25- 7.0 0 0 0
90 6) 3054 40,0 108.0 0.50 0O 0 0 Pt /S)
40 23 45 On 2it i313 5:00 “0250 0 0 0.25
0 14.15 0:5.22.5-1010:8 LOS) (12541-0325 0

* U.S. GOVERNMENT PRINTING OFFICE: 1994-383-509

os

NEWS AND COMMENTS

F. RAYMOND FOSBERG (1908-1993)

A CELEBRATION

On May 19 1994, just a day before what would have been Ray Fosberg's
86th birthday we held a celebration in his honor in the Learning Center of the
National Museum of Natural History. Approximately 60 people participated in
this commemoration of Ray's life achievements, including several members of
his family.

The activities began with Warren Wagner, Chairman of the Department
of Botany, who welcomed everybody to this celebration of Francis Raymond
Fosberg's life and introduced the Guest Speaker David R. Stoddart from the
University of California at Berkeley. Along with a general biographical review
of both Ray Fosberg and David Stoddart, Warren, in a lighter vein, mentioned
Ray's comment in a letter to Dr. William Stearn of the British Museum, that
despite the poor quality of David's initial plant collection, David, unlike "most
geographers" was capable of learning how to collect botanical specimens.

Warren Wagner introduces the Guest Speaker. (photo by Bill Boykins)

In reviewing Ray Fosberg's career, David Stoddart made particular
mention of the early stage of development of the Coral Atoll Program and the
initiation of the Atoll Research Bulletin. He also talked about Ray's wide range
of interests in natural history, which extended well beyond his specialty in
floristic and taxonomic studies. In addition, he described Ray's profound
influence on his own career, starting with those first lessons in plant collecting.
Finally he discussed Ray's strong commitment to conservation, highlighted with
the successful preservation of Aldabra, in the western Indian Ocean -- an island
that was scheduled to be converted into a military base in the mid-1960s. David
worked very closely with Ray on this crusade.

David Stoddart gives the Guest Speaker's address. (photo by Bill Boykins)

Ian Macintyre followed with a report on the current status of one of Ray's
major legacies -- the Atoll Research Bulletin. He indicated that there has been
a considerable increase in the editorial board in the hope of attracting
manuscripts from a wider variety of disciplines. The new members include Steve
Cairns (Invertebrate Zoology), Brian Kensley (Invertebrate Zoology), Wayne
Mathis (Entomology), Victor Springer (Vertebrate Zoology), Warren Wagner
(Botany), and Roger Clapp (National Biological Survey). Ian also mentioned
that three Special Issues of the Bulletin are in press, including a Fosberg
Commemorative Issue along with issues on Caroline Atoll and the Cocos
(Keeling) Islands. With another regular issue in preparation, he suggested that
Ray would be rather pleased with our progress.

Ian Macintyre reports on the status of the Atoll Research Bulletin.
(photo by Bill Boykins)

The last speaker was Dan Nicolson, who read a few letters that he had
recently received from some of Ray's former colleagues. He then went on to cite
Statistics on Ray's work that he had assembled for the Fosberg Commemorative
Issue. At least 51 plants were named for Ray and each year for about 60 years

Ne \ —< wa

Dan Nicolson cites statistics on Ray Fosberg's work. (photo by Bill Boykins)

Ray named about 20 new taxa, with a total of about 1,000. His publication
record was even more impressive, with an average of about 10 papers a year,
resulting in 625 papers to date with still more to come. Most spectacular of his
achievements was his average yearly collection of 1,000 plants, with a total of
66,369. |

After thanking the many people who had worked on Ray's backlog and
assisted with the organization of this event, Dan asked the audience if anybody
wanted to make a statement. At least 6 people responded, including Frank
Whitmore, who hired Ray to work in the US Geological Survey to work on the
Pacific Geologic Mapping Program; Elbert Little, who was one of the Cinchona
Mission collectors who Ray lead during the Second World War; and Lee Talbot,
who talked about Ray's contribution to conservation.

A member of the audience, Frank Whitmore comments on his past
association with Ray Fosberg. (photo by Bill Boykins)

After about an hour of talking, all of which was recorded by the
Smithsonian Institution Archives staff, the participants socialized over a light
serving of food and drinks. It was at this time that Ray's family mentioned that
they had just spent the moming driving out to the Blue Ridge Mountains where
they scattered Ray's ashes in places where he used to love visiting with them.

ATOLL RESEARCH BULLETIN

NOS. 415-425

NO. 415.

NO.

NO.

NO.

NO.

NO.

NO.

NO.

NO.

NO.

NO.

417.
418.

419.

420.

421.

422.

423.

424.

425.

TIKEHAU
AN ATOLL OF THE TUAMOTU ARCHIPELAGO (FRENCH POLYNESIA)

PART I. ENVIRONMENT AND BIOTA OF THE TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)
BY A. INTES AND B. CAILLART

PART II. NUTRIENTS, PARTICULATE ORGANIC MATTER, AND PLANKTONIC AND
BENTHIC PRODUCTION OF THE TIKEHAU ATOLL (TUAMOTU ARCHIPELAGO,
FRENCH POLYNESIA)
BY C.J. CHARPY-ROUBAUD AND L. CHARPY

PART III. © REEF FISH COMMUNITIES AND FISHERY YIELDS OF TIKEHAU ATOLL (TUAMOTU
ARCHIPELAGO, FRENCH POLYNESIA)
BY B. CAILLART, M.L. HARMELIN-VIVIEN, R. GALZIN, AND E. MORIZE

COLONIZATION OF FISH LARVAE IN LAGOONS OF RANGIROA (TUAMOTU
ARCHIPELAGO) AND MOOREA (SOCIETY ARCHIPELAGO)
BY V. DUFOUR

CAVES AND SPELEOGENESIS OF MANGAIA, COOK ISLANDS
BY JOANNA C. ELLISON

SHALLOW-WATER SCLERACTINIAN CORALS FROM KERMADEC ISLANDS
BY VLADIMIR N. KOSMYNIN

DESCRIPTION OF REEFS AND CORALS FOR THE 1988 PROTECTED AREA SURVEY
OF THE NORTHERN MARSHALL ISLANDS
BY JAMES E. MARAGOS

QUATERNARY OOLITES IN THE INDIAN OCEAN
BY C.J.R. BRAITHWAITE

LARGE-SCALE, LONG-TERM MONITORING OF CARIBBEAN CORAL REEFS: SIMPLE,
QUICK, INEXPENSIVE TECHNIQUES BY RICHARD B. ARONSON, PETER J. EDMUNDS,
WILLIAM F. PRECHT, DIONE W. SWANSON, AND DON R. LEVITAN

CHANGES IN THE COASTAL FISH COMMUNITIES FOLLOWING HURRICANE HUGO IN
GUADELOPE ISLAND (FRENCH WEST INDIES)
BY CLAUDE BOUCHON, YOLANDE BOUCHON-NAVARO, AND MAX LOUIS

THE SIAN KA’AN BIOSPHERE RESERVE CORAL REEF SYSTEM, YUCATAN
PENINSULA, MEXICO

BY ERIC JORDAN-DAHLGREN, EDUARDO MARTIN-CHAVEZ, MARTIN SANCHEZ-
SEGURA, AND ALEJANDRO GONZALEZ DE LA PARRA

A PRELIMINARY EVALUATION OF THE COMMERCIAL SPONGE RESOURCES
OF BELIZE WITH REFERENCE TO THE LOCATION OF THE TURNEFFE ISLANDS
SPONGE FARM

BY J.M. STEVELY AND D.E. SWEAT

SPATIAL AND TEMPORAL VARIATIONS IN GRAZING PRESSURE BY HERBIVOROUS
FISHES: TOBACCO REEF, BELIZE
BY PETER N. REINTHAL AND IAN G. MACINTYRE

NEWS AND COMMENTS

ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
AUGUST 1994

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