Oceanus

American-Australian Bicentennial Issue

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GfBat Bartier R8Bf: Science & Management

ISSN 0029-8182

Oceanus

The International Magazine of Marine Science and Policy

Volume 29, Number 2, Summer 1986

Paul R. Ryan, Editor
James H. W. Hain, Assistant Editor
Eleanore D. Scavotto, Editorial Assistant
Kristen Kaliski, Spring Intern

Editorial Advisory Board

I930

Henry Charnock, Professor of Physical Oceanography, University of Southampton, England

Edward D. Goldberg, Professor of Chemistry, Scripps Institution of Oceanography

Gotthilf Hempel, Director of the Alfred Wegener Institute (or Polar Research, West Germany

Charles D. Hollister, Dean of Graduate Studies, Woods Hole Oceanographic Institution

John Imbrie, Henry L. Doherty Professor of Oceanography, Brown University

John A. Knauss, Provost (or Marine Affairs, University of Rhode Island

Arthur E. Maxwell, Director of the Institute for Geophysics, University of Texas

Timothy R. Parsons, Professor, Institute of Oceanography, University of British Columbia, Canada

Allan R. Robinson, Gordon McKay Professor of Geophysical Fluid Dynamics, Harvard University

David A. Ross, Chairman, Department of Geology and Geophysics, and Sea Grant Coordinator,

Woods Hole Oceanographic Institution

Published by Woods Hole Oceanographic Institution

Guy W. Nichols, Chairman, Board oi Trustees
Paul M. Fye, President of the Corporation
James S. Coles, President of the Associates

John H. Steele, Director of the Institution

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//

America Salutes Australia's Bicentennial

//

1788

1988

American-Australian Bicentennial Project

In 1988, Australians will celebrate 200 years of European
settlement. They have invited the United States to join in
their year-long celebration as Australians did in the U.S.
Bicentennial in 1976.

For this purpose, the U.S. Department of State formally
endorsed the creation of the American-Australian Bicen-
tennial Foundation. Its task is to develop a series of
commemorative projects worthy of America's close rela-
tionship with Australia. This issue of Oceanus is one of
the first of these projects.

America's participation in Australia's Bicentennial de-
pends on contributions from corporations doing business
in Australia. Contributions to the Foundation are tax de-
ductible: 1910 K Street, N.W., Suite 711, Washington,
D.C. 20006. Tel. (202)467-6988.

(SomGcemft

4 Introduction: The Great Barrier Reef: Science & Management

by Barry O. Jones, Australian Minister of Science

7 The Evolution of the Great Barrier Reef

by David Hopley, and Peter j. Davies

1 3 Managing the Great Barrier Reef

by Graeme Kelleher

20 Reef Metabolism

by David j. Barnes, Bruce E. Chalker, and Donald W. Kinsey
22 — Light and Corals

by Bruce E. Chalker, Walter C. Dunlap, and Paul L. Jokiel

27 Distribution of Reef-Building Corals

by ). E. N. Veron
28 — Coral Reproduction, Dispersal, and Survival

by Paul VV. Sammarco
31 — Coral Rings Give Clues to Past Climate

by Peter Isdale

33 Soft Corals: Chemistry and Ecology

by John C. Coll, and Paul VV. Sammarco

38 Sex on the Reef: Mass Spawning of Corals

by Carden C. Wallace, Russell C. Babcock, Peter L. Harrison, lames K. Oliver,
and Bette L. Willis

41 — Coral Genetics: New Directions
by James A. Stoddart

43 Historical Perspectives on Algae and Reefs: Have Reefs Been Misnamed?

by Llewellya Hillis-Colinvaux
45 — Halimeda — The Sand-Producing Alga
by Edward A. Drew

49 Reef Algae

by Michael A. Borowitzka, and Anthony VV. D. Larkum

55 The Crown of Thorns Starfish

by John Lucas

58 — The Significance of the Crown of Thorns Starfish

by T. J. Done
60 — Giant Clams

by Christine Crawford, and Warwick Nash
63 — Giant Clams as Pollution Indicators

by G. R. W. Denton, and L. Winsor

66 Photo Essay: Images From the Underwater Outback

68 The Nutritional Spectrum in Coral Reef Benthos
— or Sponging Off One Another for Dinner

by Clive R. Wilkinson

71 — Bioerosion of Coral Reefs

by Pat Hutchings, and William E. Kiene
74 — Pollution on the Reef

by Des Connell

76 Reef Fish: Large-Scale Distribution and Recruitment

by David McB. Williams, Garry Russ, and Peter /. Doherty
81 — Reef Fisheries
by Wendy Craik

83 Currents and Coral Reefs

by Eric Wolanski, David L. B. lupp, and George L. Pickard
86 — The Reef, Tides, and Flinders' Perspicacity
by Lance Bode

90 Remote Sensing: What Can It Offer Coral Reef Studies?

by D. A. Kuchler

94 Islands and Birds

by Harold Heatwole, and Peter Saenger
98 — Sea Turtles

by Colin J. Limpus

100 Dugongs and People

by Brydget f . 7. Hudson

102 — "Dugong Is Number One Tucker"

by Helene Marsh
105 — Human Exploitation of Shellfish

by Carla P. Catterall

107 Risk Analysis: Cyclones, and Shipping Accidents

by M. K. James, and K. P. Stark

109 Toxins and Beneficial Products from Reef Organisms

by I. T. Baker, and /. A. Williamson
111 — Sea Snakes

by Glen W. Burns

116 Research Stations on the Great Barrier Reef

Lizard Island
One Tree Island
Orpheus Island
Heron Island

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TORRES ^~3' STRAIT

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118 Joseph T. Baker

Early Man (3 a.m.)

Book Reviews: Books Received
122

Cover: Red harlequin tusk fish found on the Great Barrier Reef. Photo courtesy of Ron and Valerie Taylor/Great
Barrier Reef Marine Park Authority (GBRMPA).

Copyright® 1986 by the Woods Hole Oceanographic Institution. Oceanus (ISSN 0029-8182) is published in March,
June, September, and December by the Woods Hole Oceanographic Institution, 93 Water Street, Woods Hole,
Massachusetts 02543. Second-class postage paid at Falmouth, Massachusetts; Windsor, Ontario; and additional
mailing points. POSTMASTER: Send address changes to Oceanus Subscriber Service Center, P.O. Box 6419,
Syracuse, N.Y. 13217.

Introduction:

The Great Barrier Reef:

by Barry O. Jones

Australian Minister for Science

/Although man has ventured to the moon and
to outer space, developing sophisticated
satellite systems for communications and
remote sensing along the way, his
understanding and exploration of oceanic
space on Earth is relatively crude. The
application of science and technology to land-
based resources has resulted in highly
innovative agricultural, manufacturing, and
mining industries, whereas little attention has
been given to the utilization of marine
resources for aquaculture, mining, and
entrepreneurial developments.

These marine inadequacies are
highlighted at a time when the focus of world
trade and development shifts more and more
to nations in the Pacific and Southeast Asia.
Much of this area is tropical: many of the
shorelines of the numerous developing
countries are fringed by corals and/or
mangroves, and the marine living resources
appear barely able to support existing
population demands.

In this complex environment, Australia's
increased commitment to marine scientific and
technological research during the last 10 years
has produced results that are directly relevant
to a better understanding of its own tropical
resources. It also has provided a basis for
interactive development of marine resources
with other countries in these tropical seas.
Particular areas of collaboration include studies
of coral reefs, coastal zone management,
mangroves, oceanography, cyclones (typhoons/
hurricanes), and satellite imagery.

The Great Barrier Reef, which stretches

some 2,000 kilometers along the Australian
Pacific coast, has been a focal point for
international interest and tourism, as well as for
marine scientific and technological research. Its
unique status has been formally recognized by
its inclusion on the World Heritage List.
Publication of this special issue of Oceanus
recognizes this level of international interest
and of Australia's particular responsibility to
preserve for posterity this complex ecological
system with its wonderful diversity of species
and endless variety of color and form.

The Australian Marine Science and
Technology Advisory Committee (AMSTAC)
advises me on priorities for marine research in
general and has been instrumental in making
me increasingly aware of the need for a greater
research investment in the Reef region. The
Marine Research Allocations Advisory
Committee (MRAAC) administers the Marine
Sciences and Technologies (MST) Grants
Scheme and, in the initial years of the Scheme,
the greatest proportion of available funds has
been allocated to barrier reef research.
Evidence of the wide distribution of research
involvement on Great Barrier Reef topics can
be seen from the contents of this special issue,
where many of the major articles represent
joint authorship from people at two or more
Australian institutions.

There is a heavy concentration of
research effort at Townsville with interactive
programs undertaken at the Australian Institute
of Marine Science (AIMS), James Cook
University of North Queensland (JCUNQ), and
the Great Barrier Reef Marine Park Authority

Science & Management

(CBRMPA). Major studies involving all three
institutions include the Crown of Thorns
starfish research program, a collaborative
tripartite development of a three-dimensional
numerical modelling program to understand
the hydrodynamics of the water movements in
the reef region, and a proposal to develop a
satellite receiver station with image processing
facilities to analyze data from Landsat, and the
geostationary meteorological satellites.
Other research programs involve
collaboration with the Commonwealth
Scientific and Industrial Research Organization
(CSIRO), and the Bureau of Mineral Resources,
Geology and Geophysics (BMR). These studies
take advantage of a number of research
vessels: Lady Basten (28 meters, AIMS), Harry
Messel (21 meters, AIMS), James Kirby (17
meters, JCUNQ), and a large number of smaller
craft available along the coast, and the
oceanographic research vessel Franklin (55
meters, CSIRO), and the geologically equipped
research vessel Rig Seismic (72 meters, BMR).
These vessels conduct research programs
throughout Australian waters. The Inaugural
Great Barrier Reef Conference, held in
Townsville in 1983, provided evidence of the
extent of coral reef research. Significant
research discoveries were reported involving
coral spawning, weather records in corals,
ultra-violet-blocking agents in corals,
mariculture of prawns and clams, cyclone
impacts, coral regeneration, marine stingers,
the Crown of Thorns starfish, and
oceanography in the reef region. These
discoveries have provided for sound

management practices by the Great Barrier
Reef Marine Park Authority.

The mosaic of research presented in this
issue provides an exciting picture of Australia's
determination to unlock the scientific marvels
of this natural wonder, and also to preserve it
for posterity. This issue of Oceanus gives added
incentive to these aims.

Scientists and technologists from other
countries are always welcome to share in these
research programs. In 1988, the Sixth
International Coral Reef Congress will be held
in Townsville as part of that year's bicentennial
celebrations marking European settlement of
the continent. In addition, the Great Barrier
Reef Wonderland aquarium, designed to
represent a microcosm of the actual reef, will
be opened as a bicentennial project, also in
Townsville. This issue of Oceanus is therefore
most timely.

Acknowledgments

Oceanus magazine would like to thank the following
organizations for their support of this issue: the American-
Australian Bicentennial Foundation, Washington, D.C; the
Australian Marine Research Allocations Advisory Committee
(MARAAC); the Great Barrier Reef Marine Park Authority
(CBRMPA); the Australian Institute of Marine Science (AIMS);
the Sir George Fisher Centre for Tropical Marine Studies;
James Cook University of North Queensland; and Qantas
Airlines.

Oceanus also would like to thank Professor Michael
Champ for his advice and help in producing this issue. Dr.
Champ acted as co-editor. He is Senior Science Advisor at the
Environmental Protection Agency in Washington, D.C, and
was a Senior Queens Fellow in Australia in 1984/85.

Windward margin, Redbill Reef, central Great Barrier Reef. (Photo courtesy of David Hopley)

The Pompey Reef Complex comprises some of the largest and most complex reefs in the whole of the Great Barrier Reef
province. They are cut by narrow deep channels and contain numerous lagoons. (Photo courtesy of David Hopley)

The Evolution
of the

Great Barrier Reef

by David Hopley,
and Peter J. Davies

I he Great Barrier Reef is an immense, unique
environment of global aesthetic and scientific
significance comparable to any of the largest reef
structures that have existed in the last 450 million
years of the geological past. It is not a single reef, but
a whole series of individual reefs and reef complexes
occupying the Continental Shelf of northeastern
Australia for a distance of 2,300 kilometers over 14
degrees of latitude. Reef waters exceed 230,000
square kilometers. Almost 9 percent of the area is
occupied by reefs or submerged reef shoals.

Even within the area of the Great Barrier Reef
Marine Park, which extends only to the tip of Cape
York, there are 2,900 individual reefs, including 750
fringing reefs attached to the mainland or high
continental islands (inclusion of the Torres Strait reefs
would increase this figure by at ieast 30 percent).
Quite clearly from size alone the Great Barrier Reef
warrants the awe it has inspired since the first
descriptions of the early explorers:

A Reef such as one I now speak of is a thing scarcely
known in Europe or indeed anywhere but in these
seas.

— Joseph Banks on James Cook's voyage, 1 770.

However, the size and the morphological and
biological diversity of the Great Barrier Reef is not
matched by a lengthy geological history. Much of
the reef is young — little more than 2 million years
old. It has thus evolved during the Quaternary
period when ice advances and retreats in higher
latitudes caused major sea-level fluctuations,
probably the most important single factor in the
evolution of the Great Barrier Reef.

Morphological Diversity

Enormous regional diversity exists. Influence of
varying geological structures beneath the shelf is
probably paramount in producing macroscale
regional patterns, but even the modern environment
is sufficiently diverse to produce morphological
contrasts. For example, the incidence and severity of
tropical cyclones, the numbers of coral species, tidal
range, and water temperatures vary from north to

south. Equally important differences exist across the
shelf in the form of freshwater runoff and sediments,
and increasing influences of incursions of open
ocean waters.

The northern region of the reef has
developed on a narrow shelf, no more than 50
kilometers wide (Figure 1). Its most distinctive
features are the linear or ribbon reefs running
parallel to the edge of the Continental Shelf almost
as far south as Cairns. The ribbons are up to 25
kilometers long and rarely more than 500 meters
wide, are separated by narrow passes, and lie at the
very edge of a steep Continental Shelf. Water depths
exceed 1,000 meters within a few hundred meters of
the outer reefs. Inside many of the ribbon reefs are
large sand banks at depths of 20 to 40 meters. These
have been built by the calcium carbonate secreting
alga Halimeda (see pages 43, 45, and 49), which
appears to have built structures equal in size to
many of the coral reefs.

The middle shelf is occupied by large
platform reefs with extensive reef flats, some up to
25 kilometers in length. Closer to the shore is a more
open area of inner shelf, the main shipping channel
where a number of small reefs capped by distinctive
low, wooded (mangrove) islands are found.

In Torres Strait, the distinctive regional pattern
breaks down. The middle section of the shelf is
dominated by a mosaic of small reefs. Ribbon reefs
become shorter, and eventually alter into complex
splayed "deltaic" reefs with numerous passages,
reflecting the influence of the strong area tides. A
well defined line of larger reefs occurs northwards
from Cape York, including the Warrior Reefs, with
high seagrass-covered reef flats. Within Torres Strait,
the reefs are aligned east-west in response to the
high-velocity tidal currents.

As the Continental Shelf widens south of
Cairns, the Great Barrier Reef occupies only the
outer third of the shelf. Reefs are more widely
spaced and generally have less well developed reef
flats. Most reefs are irregular reef patches, or
crescentic features aligned toward the dominant
southeasterly tradewinds. Back reef areas and
lagoons can be large, but are frequently dominated

by sand. No ribbon reefs are found on the outer
shelf, but recent research has defined a more or less
continuous line of outer shoals rising from depths of
about 70 meters. Only fringing reefs on the high
continental islands are found on the inner shelf.

To the south, the Continental Shelf widens
even further to about 300 kilometers. From about 20
degrees South, reefs increase in size, and, with an
increase in tidal range (to more than 4 meters on
even the outermost reefs in the Pompey Complex),
narrow, well defined tidal channels up to 70 meters
deep intersect the reefs. Even the innermost reefs
are 100 kilometers from the mainland, but this is one
of the most spectacular parts of the Great Barrier
Reef. A series of submerged reefs occupies the shelf
edge, but about 10 kilometers back is an area
containing some of the largest and most intricate
reefs up to 100 square kilometers in area. This is the
Pompey Complex, stretching for 200 kilometers as a
solid mass of reefs and lagoons 15 kilometers wide
with narrow intricate channel systems. The southern
extent of the Pompey Complex is a distinctive T-line
junction of reefs to the south of which are the
contrasting Swains Reefs, smaller flat topped reefs,
closely spaced and with numerous sand cays. The
tidal range on the adjacent mainland reaches 10
meters in Broad Sound, but declines rapidly
seawards. The innermost reefs, however, still
experience ranges of up to 6 meters, and this results
in massive algal terraced rims that isolate internal
lagoons nearly 3 meters above the level of the
surrounding ocean at low tide.

South of the Capricorn Channel, the shelf
narrows again to less than 100 kilometers. The
Bunker-Capricorn Groups of reefs are the
southernmost of the Great Barrier Reef, a series of
22 reefs and 1 1 shoals of only moderate size and
with numerous vegetated cays. Corals do grow
further south, but the southern extent of the reef is
determined by the massive amounts of sand that
cross the shelf south of Lady Elliott Island. This sand
has moved northwards up the coast from southern
Queensland and, as the coast and shelf change
direction at about 25 degrees South, the sand
crosses the shelf obliquely via Fraser Island and
Breaksea Spit.

Origins of the Reef

In 1926, the first effective attempts to study the
origin of the Great Barrier Reef were made by the
Great Barrier Reef Committee when holes were
drilled to 183 meters at Michaelmas Cay in the
northern reef region. In 1934, holes were drilled on
Heron Island in the south to 223 meters. At the time,
these bores were considered disappointing as they
did not achieve the intended objective of proving
that Darwin's subsidence theory of coral reefs was
applicable to the Great Barrier Reef. This objective
clouded the interpretations of much crucial data in
the cores.

Both holes bottomed in sands, but their
significance was ignored as Darwin's theory
demanded volcanics; reef was therefore thought to
occur below the sands. The drill core from both
holes indicated the presence of unconformities
detectable on the basis of observation as well as

geochemical data. The now accepted possibility of
reef growth in superincumbent positions, many
times producing what are now seen as
unconformities related to sea-level changes, was not
recognized.

However, the initiation of the Great Barrier
Reef is related to the more recently developed ideas
of continental drift and sea-floor spreading (see
Oceanus, Vol. 22, No. 3). Until about 75 million
years ago, Australia and Antarctica were joined. Most
of Australia lay south of 40 degrees South, far from
waters warm enough for coral growth. About 65
million years ago, Australia began to split from
Antarctica and move northwards.

Subsequently, northeastern Australia was
formed by rifting between the Australian and Pacific
plates and, by the time a Continental Shelf had
formed, northern Australia lay close to 30 degrees
South latitude. Uplift, rifting, and volcanism
produced a complex rift basin system that has
controlled the location and form of the Continental
Shelf.

As Australia continued to move north, the first
development of ice in Antarctica caused worldwide
falls in sea level. Recent seismic investigations have
shown that shelf evolution was dominated by fluvial
sediment yield (current annual sediment input from
North Queensland rivers alone is estimated at 28
million tons). The relative height of sea level
provided the principal control of development
(Figure 2).

During periods of low sea level, alluvial
processes affected the shelf. At the shelf edge fluvial
and wave dominated deltaic progradation* took
place into deeper water. During the high sea-level
phases, sedimentation was generally restricted to
coastal deltaic progradation into the shallow water of
the inner shelf and onlap of the continental slope by
submarine fans together with extensive upper slope
erosion. This main phase of shelf construction from
the late Oligocene to the Pleistocene (11 to 2 million
years ago) produced about 10 kilometers of shelf
outbuilding off Cairns and about 50 kilometers off
Townsville, a sediment sequence 2.5 kilometers
thick.

The seismic records, with the exception of the
northernmost reef region, show a distinctive lack of
reef growth. Initially, this can be attributed to
Australia's latitudinal position and seawater
temperatures too cool for coral growth, but
subsequently high turbidity levels on the shelf during
high sea-level periods may have produced
conditions that were not conducive for reef building.
Earliest reef development was restricted to the Gulf
of Papua shelf area, which would have reached the
warm waters of the tropics earliest. By early and
middle Miocene times (12 million years ago), barrier
reefs had developed at the edge of a carbonate shelf
and platform reefs had developed on highs in front
of the shelf. However, following uplift and erosion,
they were rapidly buried by massive Pliocene to
Recent tide-dominated deltaic progradation.

* A seaward advance of the shelf resulting from the
nearshore deposition of sediments brought to the sea by
rivers.

8

Coastal wave dominated delta

Sea level

Base

Alluv
strea

Onlapping facies

Reefs and carbonate
build - ups

VV Volcanics

P4 Progradat lonal facies

Figure 2. The types of depositional systems in the development of the shelf of the central Creat Barrier Reef. (From Symonds and
others, 1983)

To the south, the reef sequence is thin, less
than 300 meters thick. It also is young, almost
certainly less than 2 million years — that is, mainly
Pleistocene in age and built during a period of
rapidly fluctuating worldwide sea levels. Reef growth
has occurred during short periods of high sea level.
During the intervening periods of low sea level, the
reefs were subaerially eroded. Continual
recolonization of sites throughout their growth
history has produced reefs that are composite
features made up of a series of remnant reefs
separated by unconformities.*

On a regional scale, there can be no doubt
that basement structure has exerted a profound
control on the development of major reef tracts.
Mid-shelf reefs in the central and northern areas are
coincident with a prominent mid-shelf fault line,
although the reason is obscure. Further, the
scattered reefs of the central Great Barrier Reef
border the fault-controlled confluence of the
Queensland and Townsville troughs. The ribbon
reefs in the north occur at the shelf edge, the
position of which is controlled by the western
boundary faults of the Queensland trough. Further
south, however, the seismic studies have shown that
the drowned ribbon reefs did not develop along the
paleoshelf break, but a few kilometers west of it.
Shelf edge reefs in the vicinity today have formed
their own shelf break feature through vertical
growth. These also have modified upper slope
deposition during periods of low sea level by
funneling fluvio-deltaic sediments through gaps in
the barrier reef, directly feeding upper slope canyons
and depositing submarine fans on the middle and
upper slopes.

* A surface of erosion or nondeposition, usually the former,
that separates younger strata from older strata.

Sea-Level Changes and Reef Growth

Once established, the layer-cake structure of most
reefs indicates that subsequent growth was usually
on the older reef surface during high sea level
phases. High sea levels approximating that of the
present time have had a periodicity of about 120,000
years during the Pleistocene. Individual reef growth
phases seem to have lasted from 4,000 to 14,000
years. Growth periods are clearly short compared to
low sea level phases of subaerial destruction.
Growth probably represents a maximum of 10 to 20
percent of time available. For the whole of the
Quaternary, (1.8 million years) actual growth
occurred for only 180,000 to 360,000 years.

The new reef veneer added at each high sea
level was draped over the older reef, which would
undoubtedly have undergone erosion while
subaerially exposed. The original aragonite and high
magnesium calcite deposits of the reef plants and
animals are subjected to diagenesis* in the subaerial
environment and revert to low magnesium calcite
clearly detectable, for example, beneath the
Holocene reefs at depths of between 4 meters and
more than 30 meters below modern reef flat level.
Soils and calcite stringers (horizontal layers of dense
calcium carbonate produced by soil processes on
limestone) also formed and also mark the position of
each unconformity.

The reefs are limestone and their subaerial
erosion has the potential to create karst landforms.**
Up to 15 meters of reef may have been removed
during the last low sea level period. Debate exists as
to whether it is the karst erosional forms, such as

* The process involving physical and chemical changes in
sediment after deposition that convert it to limestone.

** Marred by sinks, abrupt ridges, and channels.

enclosed solution depressions, that influence the
morphology of the modern reef, or the shape of the
earlier reef. In all probability both are important, and
occasional "blue holes" up to 40 meters deep in the
reefs attest to large scale karst collapse at least on a
local scale.

Maximum lowering of sea level at the height
of the last glaciation was about 1 50 meters. It is
probable that, based on ice volumes in previous
glaciations, this was close to the maximum glacio-
eustatic lowering during the Pleistocene. Although
the periods of absolute low sea level may have been
even more restricted than the interglacial highs, they
were important periods for reefs. World oceanic
temperatures were reduced on average by about 2.3
degrees Celsius, enough to restrict coral growth only
marginally. However, 150 meters of lowering of sea
level places the majority of world coastlines on the
slope of the Continental Shelf thus severely
restricting the available area of shallow (less than 40
meters) water for reef growth.

Recent research submersible dives off the
ribbon reefs near Cooktown have shown that from
depths of 90 to 210 meters there exists an almost
sheer wall on which no late Pleistocene reef growth
could have taken place. Increased cave
development in this wall between 130 and 150
meters depth may relate to the lowest sea levels. In
another dive off Myrmidon Reef near Townsville, the
slope at the critical 150 meters depth was 45 degrees
and consisted largely of unconsolidated scree, or
loose rock debris, which would provide too unstable
a substrate for reef growth. Apart from very
restricted local refuges, it has been hypothesized
that the major larval replenishment areas for
recolonization of the Great Barrier Reef during the
post-glacial transgression may have been the banks
of the Coral Sea plateaus. This could have played a
part in the delay between submergence of the older
reef foundations and initiation of Holocene growth.

Reef Growth During the Holocene

The rapid rise in sea level that accompanied the
melting of northern hemisphere ice sheets resulted
in the margins of the Great Barrier Reef shelf being
inundated 12,000 years ago. Most older reef
foundations were submerged 8 to 9,000 years ago,
when sea level was rising at a rate of 7 to 10 meters
per 1,000 years. Because of isostatic responses,
details of sea level change are regional in pattern and
modern sea level had been achieved on the Great
Barrier Reef by about 6,500 years Before Present
(BP), some 6,000 years earlier than for Caribbean
counterparts.

The modern reefs have thus had time to grow
up to present sea level. The thicknesses of Holocene
growth varies from as little as 5 meters in the
northern region reef to 8 meters on southern reefs,
and generally greater than 20 meters on the central
Great Barrier Reef. Considerable detail is available
for this latest phase of reef growth from a data base
collected by the authors during the last 10 years. The

data base consists of more than 100 drill holes in 30
reefs and more than 300 radiocarbon dates.

Five major biologic-sedimentary associations
comprise the Holocene reef: coralline facies, coral
head facies, branching coral facies, rubble/sand
facies, and terrigenous facies (Figure 3). Windward
margins of reefs show regional variation. In the
Cooktown region, both branching and coral head
facies occur on inner and outer shelf reefs. In the
central reef, coral head facies dominate particularly
in midshelf and fringing reefs, although on outer
shelf reefs both branching and head corals occur. In
the southern region, branching corals dominate all
windward margins except at One Tree Reef where a
mixed branching-head assemblage occurs.
Throughout the Great Barrier Reef the coralline
facies occurs as a crust on framework facies,
particularly in the upper 50 centimeters of reef.

Reef flat areas today are dominantly mixed
branching-head assemblages and have developed as
such throughout their history, although in some
examples a lower branching facies is replaced
upwards by a head facies. Leeward margins have
been dominated by branching framework facies
throughout their growth history.

The fabric of the midshelf reefs of the central
Great Barrier Reef is quite different to that of reefs in
higher energy areas. They are dominated by detrital
facies of sands, coral gravel, stick shingle, rubble, and
storm boulder beds. Some reefs are little more than
detrital piles with coral caps. Terrigenous facies are
limited to the fringing reefs and are normally minor
components.

Vertical accretion rates vary with facies type,
location of reef (inner, mid or outer shelf) and
location on reef. The modal rate for framework
accretion is 7 to 8 meters per 1,000 years, but higher
rates, up to 16 meters per 1,000 years are associated
with open branching coral framework and generally
lower rates for head dominated facies. Lowest rates
of about 2 meters per 1,000 years are associated
with coralline algae. Depositional rates for detrital
carbonate facies vary from 1 to 4 meters per 1,000
years for sand flat progradation to 13 to 18 meters
per 1,000 years for deposits associated with high-
energy, low-frequency events.

Despite the wide range of depths to the pre-
Holocene reef substrate, initiation of growth
ubiquitously appears to have been between 8,300
and 8,500 years BP, with earliest growth normally on
the windward margins. This means that water depths
of up to 20 meters existed over the reefs as they
grew upwards, although the greater the depth the
more optimal were the conditions for growth, as
fastest accretion rates are recorded for such reefs.
Thus, once sea level stabilized about 6,500 years
ago, reefs quickly caught up with sea level and the
majority were within 2 meters of modern sea level
between 6,500 and 4,500 years BP. In the final
approach to sea level, particularly where coralline or
head facies become dominant, the rates of accretion
slowed down significantly, possibly reflecting a
decrease in calcification accompanying
environmental change or a physical loss of calcium
carbonate in the high energy surface environment.

10

The outer edge of the northern Great Barrier Reef has an
almost continuous line of linear ribbon reefs rising from
oceanic depths of 1,000 meters or more. These are generally
narrow and have been at sea level for at least 5,000 years.
Sediment is swept from the reef top towards the lee side
where a significant sand slope can be seen. (All photos this
page courtesy of David Hopley)

The southern end of the Pompey Complex, showing the
deltaic-like pattern of channels that cut through these
massive reefs.

In the northern region, the reefs closest to shore are often
capped by low wooded islands. These consist of shingle
ridges around the windward margins that give protection for
the growth of reef flat mangroves. Small sand cays are
frequently found to the lee side. This example is Low Isles
near Cairns.

An almost circular blue hole on Molar Reef in the Pompey
Complex formed by the collapse of a subsurface cavern
developed by karst solution processes during Pleistocene low
sea levels.

A further example of the open, crescentic type reefs of the
central Great Barrier Reef. This example, Centipede Reef near
Townsville, has a secondary reef front and a deep lagoon
with a sand slope on the leeward side of the windward edge.

As the reef develops at sea level and grows horizontally, it
commences to develop a zonation in response to the
refracted wave fronts. In particular, sediments are swept from
the productive windward margins toward the lee of the reef.

11

~J Algal pavement "A Reef flat rubble ^j Sand

[■' '■' J Coral heads 1 Branching corals _] Pleistocene

I Encrusted coral heads M^;jj Encrusted branching corals

Figure 3. The distribution of
One Tree Reef fades, (from
Marshall and Davies, 1982)

The Final Details

For most of the Great Barrier Reef, sea level has not
varied significantly for the last 6,500 years. Only on
the fringing reefs of the inner shelf is there evidence
of a slightly higher (+ 1 meter) sea level. The reefs
that grew up to sea level 6,500 to 4,500 years ago
thus have had time to develop significant horizontal
growth expressed in the extension of reef flats.

Surface zonation* is a reflection of growth at
sea level. The coralline rim in windward margins is
usually only 50 centimeters thick and is a response
to high physical energy. The mixed coral
assemblages of the coral flat are likewise responses
to energy conditions, with the alignment of the
corals into "windrows" in this zone a response of
growth to the direction of energy dissipation.

A major effect of growth at sea level is reef
destruction, resulting in production of sediment and
its deposition as shingle banks, cays, prograding sand
flats, lagoon infills and leeside tails. These
accumulations result from erosional transport and
depositional processes associated not only with the
ambient southeasterly conditions, but also with
tropical cyclones. The end result of growth at sea
level is modification of the original zonation through
sedimentary infill, secondary coral growth as
microatolls in moated reef flat locations, and ultimate
loss of zonation. Finally, significant growth may be
confined only to the reef margins.

Conclusions

Although comparatively young, geologically, the
Great Barrier Reef contains such a diverse range of
environments that it may provide the model for
development, maintenance and management of
continental shelf reef systems on a global scale. Until
approximately 10 years ago the relatively small
amount of information available on reef
development came largely from locations outside

the Great Barrier Reef province. Work in the last 10
years has drastically changed this situation and
although many questions remain unanswered, an
understanding of the reef as a complex geological
system is closer. Recognition that the reef is
dynamic, not just during periods of rapid
environmental fluctuation such as sea-level changes,
but during for example the last 6,500 years of
relative sea-level and climatic stability, is important
for a more complete understanding of ecology, and
as the basis for management.

David Hopley is Head of the Sir George Fisher Centre for
Tropical Marine Studies at lames Cook University, Townsville,
Australia. Peter j. Davies is a geologist at the Bureau of
Mineral Resources, Canberra.

Selected Readings

Davies, P. J. 1983. Reef growth. In Barnes, D. ). (ed.) Perspectives on

Coral Reefs. Aust. Inst. Mar. Sci., 69-106.
Davies, P. ]. and D. Hopley. 1983. Growth facies and growth rates of

Holocene reefs in the Great Barrier Reef. B.M.R. /. Ausrr. Geo/.

andCeophys., 8, 237-251.
Davies, P. J., ). F. Marshall, and D. Hopley. 1985. Relationship

between reef growth and sea level in the Great Barrier Reef.

Proc. 5th Inter. Coral Reef Symp., 3, 95-103.
Hopley, D. 1982. The Geomorphology of the Great Barrier Reef:

Quaternary Development of Coral Reefs. Wiley-lnterscience N.Y.,

453 pp.
Marshall, ). F. and P. J. Davies. 1982. Internal structure and

Holocene evolution of One Tree Reef, southern Great Barrier

Reef. Coral Reefs, 1,21-28.
Symonds, P. A., P. ). Davies, and A. Parisi. 1983. Structure and

stratigraphy of the Great Barrier Reef. B.M.R. /. Austr. Geol. and

Ceophys.,8, 277-291.

* The condition of being arranged or distributed in bands or
zones, generally more or less parallel to the bedding.

12

Figure 7. Map of Great Barrier Reef.

The four research stations referred to on page 116 are

highlighted in red.

(Courtesy of David Hopley and Great Barrier Reef Marine

Park Authority)

Design and Production by Promotional Planning Service, Inc.

Terri Hare, Art Director

12

*m£m ,

Managing
The Great Barrier Reef

by Graeme Kelleher

How complex and unexpected are the checks and
relations between organic beings, which have to
struggle together in the same country.

—Charles Darwin, 1882.

A,

Australia has a federal system of government. The
complex relations between the federal and state
governments and their agencies are determined in
accordance with the provisions of a written consti-
tution, which was adopted when the six independ-
ent colonies became Australia on federation in
1901.

This constitution specifies the functions and
powers of the federal and state governments and
provides, as does the U.S. Constitution, that resid-
ual powers and responsibilities — those which are
not expressly provided for in the constitution — lie
with the states.

Before federation, the Great Barrier Reef
was administered by the colony of Queensland.
After federation, this arrangement continued largely
unchanged, except that the federal government
was given the responsibility for fisheries beyond
the 3-mile Territorial Sea and for navigation.

Serious conflict on and about the reef and its
management first arose in the 1960s when the peo-
ple of Australia became aware of, and objected to,
proposals to drill for oil and to mine limestone. The
ensuing controversy disclosed that the reef was
treasured by many Australians for its uniqueness,
biological diversity, beauty, and grandeur. The suc-
cessful management of the reef depends primarily
on maintaining and encouraging these values in the
hearts and minds of Australians.

The Great Barrier Reef

The Great Barrier Reef is the largest system of
corals and associated life forms anywhere in the
world. It is encompassed in a Marine Park within
the Great Barrier Reef region, covering an area of
about 350,000 square kilometers on the Australian
continental shelf — larger than the land mass of the
United Kingdom. The reef stretches for more than
2,000 kilometers along the northeastern coast of
Queensland in a complex maze of approximately
2,600 individual reefs, ranging in area from less
than 1 hectare (2.5 acres) to more than 100 square
kilometers. In the north, the reef is narrow and its

eastern edge is marked by a series of narrow
"ribbon" reefs, but in southern areas it broadens out
and presents a vast wilderness of "patch" reefs, many
in the shape of a boomerang.

The reef is diverse not only in the form and
size of its individual reefs and islands, but in its
inhabitants. Six species of turtle occur in the region
and it is believed that there are more than 1,500
species of fishes. The reef may be the last place on
earth in which dugong (Dugong dugon — an
endangered species) are still common and not in
jeopardy.

About 350 species of hard coral have been
identified on the reef and the islands are inhabited
or visited by more than 240 species of birds.

Human Use of the Reef

Commercial fishing and tourism, recreational
pursuits — including fishing, diving, and camping —
aboriginal fishing, scientific research, and shipping
all occur within the reef region.

Tourism is the largest commercial activity in
economic terms. In 1983-84, there were an
estimated 140,000 visitor trips to the 24 island
resorts in the region, resulting in 660,000 visitor
nights spent at the resorts, along with some A$60
million. Resort guests make extensive use of reefs
and waters for recreational activities, including
fishing, diving, and snorkeling, water sports,
sightseeing, reef-walking, and some shell collecting.

The popularity of the reef and adjacent coast
region as a tourist destination increased 40-fold
during the period from the 1940s to 1980 and is
continuing to increase. Recently, interest has been
expressed in building hotels directly on reefs. The
last five years have seen the introduction of several
large, stable, high-speed catamarans that provide
day trips to islands and outer reefs.

There is conflict between the various users
of the reef and those who wish to see it maintained
in its pristine state forever. Some uses of parts of
the reef have already reached levels that appear to

13

exploit fully the productive capacity of the
system — bottom trawling for prawns, for example.
Run-off from islands and the mainland contains
suspended solids, herbicides, pesticides, nutrients,
and other materials. They must have effects on the
reef, but the magnitude of the effects is not yet
known.

This description also applies to other reef
systems throughout the world's tropical seas. The
difficulties of managing uses of an ecosystem
"forever" are common to other reef systems.
Perhaps the system of management that has been
developed on the Great Barrier Reef could be
applied elsewhere, although the acceptability of
any management system is likely to be diminished
where there are very high levels of usage and
economic dependence on reef areas — for example,
in many parts of Asia.

Legislation and Administration

In 1973, Australia's federal Parliament passed the
Seas and Submerged Lands Act, which established
federal jurisdiction over, and title to, the seabed
below low-water mark outside state internal waters.
This act was challenged by some of the states, but
its constitutional validity was upheld by the High
Court in 1975.

Also in 1975, the federal Parliament passed,
with the support of all political parties, the Great
Barrier Reef Marine Park Act. This act provides the
legal basis for management of the reef. It has some
novel and critically important provisions in relation
to the establishment, control, care, and
development of a marine park in the region. They
include:

• Establishment of the Great Barrier Reef Marine Park
Authority, consisting of three members, one
nominated by the Queensland government and two
by the federal government. The Authority has a staff
of about 70, most of whom are headquartered in
Townsville.

• Establishment of a Consultative Committee — at least
a third of its members nominated by Queensland,
two-thirds by the federal government, with one
Authority representative.

• Specification of the Authority's functions —
recommending areas to be included in the Marine
Park, carrying out or arranging for research,
preparing zoning plans, the establishment of
education and management programs, and anything
incidental to these functions.

• Giving the Authority power to perform its functions
in co-operation with Queensland or its agencies.

• Prohibiting drilling or mining in the Marine Park,
except for approved research purposes.

• Providing that the Act, and zoning plans and
regulations made under it, prevail over conflicting
provisions of all state legislation and all federal
legislation, except in relation to the navigation of
ships and aircraft.

The Authority was established, and
continues to operate, in a situation of controversy
regarding federal and state powers and rights in the
Territorial Sea, within which lies a large part of the
Great Barrier Reef.

No other state of Australia is bordered by
reefs approaching the size, diversity, and splendour
of the Great Barrier Reef. The reef is regarded by
most as a national asset and by many as an
international asset. Many Australians, including
scientists, demand that the federal government
retain a dominant role in the management of the
reef. Others, not all in Queensland, maintain that
management of the reef, including the islands,
should be carried out by the state government.
Constitutionally, the Queensland government has
responsibility for all the islands within the outer
boundaries of the reef region above low-water
mark, except for those few that are owned by the
federal government. The latter, and all the waters,
reefs, and shoals below low-water mark are the
responsibility of the federal government.

Australia has a democratic system of
government, and action by the government is
frequently in response to public pressure. Much
that has been done so far to protect and manage
the reef has resulted from this process. Because
many of the pressures have been conflicting, as in
all controversial public areas, government action
has involved compromise.

The essence of the compromise has been
for the federal government to maintain over-riding
power in the region, while involving Queensland
co-operatively in all aspects of the establishment
and management of the Marine Park. The
Queensland National Parks and Wildlife Service
carries out day-to-day management of the Marine
Park for the Authority. The service also is
responsible for management of most of the islands
in the reef region. The two governments have
agreed to manage adjacent areas on a
complementary basis.

This arrangement recognizes that the islands,
reefs, and waters of the reef are a continuum, and
should be managed accordingly. The compromise
has been reflected in the creation and composition
of a Ministerial Council, which coordinates the
policies of Queensland and the federal government
on the reef, the Authority itself, and the
Consultative Committee.

The Authority

The Great Barrier Reef Marine Park Authority
(GBRMPA) has derived a primary goal and a set of
aims from the provisions of the Act and recognition
of the political, legal, economic, sociological, and
ecological environment in which it operates.

The Authority believes that any use of the
reef or associated areas should not threaten its
essential ecological characteristics and processes.
Activities depending on the reef's renewable
resources should generally be held at or below
maximum sustainable intensities indefinitely. This

14

People collecting on the rocky edge of Hardy Reef. (Photo courtesy of GBRMPA)

The Lizard Island resort, one of the fashionable tourist areas on the Great Barrier Reef. (Photo courtesy of GBRMPA)

15

belief has led the authority to adopt the following
primary goal:

To provide (or the protection, wise use, appreciation,
and enjoyment of the Great Barrier Reef in perpetuity
through the development and care of the Great Barrier
Reef Marine Park.

If the reef is to be protected, more than the
physical aspects of the reef need to be considered.
Administrative arrangements also must be durable.
In Australia, the major determinant of
administrative survivability of organizations like the
Authority is public support. In the long run,
government support flows from it. Recognizing that
the Authority and the Marine Park concept already
have a degree of public support, the Authority
must act in ways that sustain or increase that
support. What are those ways? It seems clear that
the ground work has been well established in the
Act through the formal requirements for public
participation, the provisions for a Consultative
Committee, the composition of the Authority itself
and its functions, as well as the ability to perform
those functions in association with Queensland or
its agents.

Generally speaking, the public is likely to
continue to support the Marine Park and the
Authority if the primary goal is perceived as being
achieved efficiently. For this to occur, the public
will have to be aware of what the Authority and its
day-to-day management agencies are doing and
the way they are doing it, the effectiveness and
costs of their programs and the reasons for them,
and, to the extent practicable, to be involved in the
establishment and management of the Marine Park.

The Park and the Zoning System

The Great Barrier Reef Marine Park is a multiple-
use protected natural area, fitting the definition of
Category VIM of the classification system used by
the International Union for the Conservation of
Nature and Natural Resources (IUCN). It also meets
the criteria for selection and management as a
Biosphere Reserve (Category IX), although it has
not been formally proposed or established as one.
The reef has been inscribed on the World Heritage
List as a natural site (Category X).

The concept of zoning was introduced as
the best solution to resolving the dual goals of
preservation and multiple use by possibly
conflicting activities. Through the use of zoning,
conflicting activities are separated, areas are
provided that are suitable for particular activities,
and some areas are protected from use. Levels of
protection within the park vary from almost
complete absence of restriction on activity in some
zones, to zones within which almost no human
activities are permitted. The only activities that are
prohibited throughout the park are oil exploration,
mining (other than for approved research
purposes), littering, spearfishing with SCUBA, and
the taking of large specimens of certain species of
fish.

In the zoning plans that have been

developed so far, there are three major categories.
They are:

• Preservation zones and scientific research zones

(equivalent to IUCN Category I, Scientific Reserve/
Strict Nature Reserve). The only human activity
permitted is strictly controlled scientific research.

• Three marine national park zones (equivalent to
IUCN Category II, National Park). The major uses
permitted are scientific, educational, and
recreational.

• Two general use zones (equivalent to IUCN
Categories IV, Managed Nature Reserve, and VI,
Resource Reserves). Uses are held at levels that do
not jeopardize the ecosystem or its major elements.
Commercial and recreational fishing are generally
permitted, although bottom trawling is prohibited in
one of these two zones.

The zoning plans for the Cairns and
Cormorant Pass sections of the Great Barrier Reef
Marine Park cover an area of 35,000 square
kilometers. The zones are fixed during the life of a
zoning plan (generally five years). They are
complemented by generally smaller areas that give
special protection from time to time to animal
breeding or nesting sites, to sites in general use and
other zones that are required to be protected to
allow appreciation of nature — free from fishing or
collecting, and to sites suitable for scientific
research.

The authority is progressively developing
zoning plans for sections of the Marine Park. We
expect the whole area to be zoned by Australia's
Bicentenary in 1988. Intensive and extensive
consultation with the general public and interest
groups will continue to be a feature of the process.

Zoning and Managing the Park

There are two principal categories of information
that are critical to making a zoning plan and
managing the park. These are:

• Resource Analysis — measuring and gaining an
understanding of the systems that make up the
Great Barrier Reef region, and, particularly the area
under consideration. The aims are to compile an
inventory of the physical, chemical, biological,
human, and human-built resources; to identify
processes; and to develop theoretical models that
will enable the processes occurring within the area
to be described, and will allow the authority to
make intelligent zoning and management decisions.

• Analysis of Use — defining the uses of the area: their
physical, chemical, and biological effects, their value
and economic importance; and measuring their
intensity and distribution. The aim also is to predict
future levels of use and their potential effects.

In preparing to make a zoning plan, both
categories of information are compiled on
transparent overlays. The base is an accurate map
of the section of park being zoned. The map shows
the location and shape of all reef and non-reef

16

r\ ^

Public participation and recreation is central to management goals. Several components in this conception of a recreational
facility already exist (sub, Reef Link, boardwalk) on John Brewer Reef.

structures to international cartographic standards of
accuracy.

The ability to produce such accurate maps
over such a large area is something of a
technological triumph. Collaboration between the
Authority and the Water and Land Resources
Division of the Commonwealth Scientific and
Industrial Research Organization (CSIRO) has
resulted in the ability to produce such maps from
Landsat data, with very little ground control (see
page 90). Cost savings over conventional survey
methods are estimated to be A$21 million for the
Authority.

The resource information included on
overlays comprises: distribution of fish and benthic
reef communities; dugong feeding grounds; turtle
nesting sites; significant land and water bird
breeding colonies; mangrove and seagrass
communities; and historic shipwrecks.

The usage information included on overlays
comprises: distribution of potential and actual
trawling areas for prawns, scallops, crayfish and
crabs; location and extent of areas for pelagic
(open water) fisheries; location and extent of areas
for demersal (bottom living) fisheries, both
commercial and recreational; areas where gill, drift
and bait netting occurs; areas where collecting of
coral, shell, and aquarium fish occurs; spearfishing
areas; diving areas where scientific research is
conducted; tourist resorts, camping areas and
possible offshore developments; charter vessel and
aircraft operating and landing areas; navigation,
shipping and defense areas; and adjacent land use
(national parks, aboriginal reserves, agricultural
areas, industrial or urban development).

The aim of zoning and management is to
provide for reasonable use of the Marine Park
consistent with conservation of the reef's natural
qualities. Reasonable use is taken to mean a usage
level that can be sustained forever.

Experience has shown that in many cases it
is not difficult to decide on the most appropriate
zoning for individual reef and inter-reef areas. The
combination of their natural qualities, location, and
present and predicted usage patterns often makes
the choice obvious.

An initial draft zoning plan is drawn up on
this basis and goes through many modifications and
adjustments before it is approved by the Authority
for release to the public for review.

The final zoning plan takes account of public
comments on the draft, as well as reactions from
government departments and agencies. Of course,
it would be naive to expect universal acclaim of a
plan — such as the completed zoning plan for the
Cairns Section — by all users, but it has been in
effect for two years and has received a high degree
of public acceptance.

The authority takes great care to avoid
inadvertently over-riding the provisions of other
legislation, whether state or federal, in making a
plan. It is equally careful not to interfere with
people's freedom unnecessarily or excessively. The
justification for any restriction must be clearly
specified in terms of the objectives of a zoning plan
and the authority's guidelines, goals, and aims.

Research and Monitoring

Adequate knowledge of the baseline (or reference)

17

Fishing fleet in port. (Photo courtesy of GBRMPA)

ecological characteristics of the reef is essential to
monitor the changes wrought by man's activities. It
also is necessary to be able to roughly predict the
type and scale of effect likely to be produced by
individual activities and combinations of them, so
that the intensity and distribution of usages can be
controlled — but not overcontrolled — in a manner
compatible with the conservation of the reef's
natural qualities.

The authority carries out, or funds, a
comprehensive research program in order to
manage the reef on the basis of knowledge. There
are three general areas of research (Table 1) — two
of them, resource analysis and analysis of use, are
necessary for supporting zoning and management
decisions. The third — information management — is
concerned with research leading to the
development of information systems that will allow
data to be stored and managed efficiently so that it
can be used in decision-making and in research
and education.

Oceanography

The basis of understanding the reef's processes can
fairly be attributed to studies in physical
oceanography. Knowledge of year-round water
quality characteristics throughout the region, and
of the small- to large-scale water movements that
transport chemicals, nutrients, and living organisms

Table 1. Research programs of the Great Barrier Reef Marine Park
Authority.

CATEGORY

PROGRAM

Resource
Analysis

Analysis of Use

Information Management

1. Bathymetry and Survey

2. Oceanography

3. Marine Geology

4. Marine Chemistry

5. Marine Ecology

6. Inventory of Uses

7. Impact of Uses

8. Management Strategies

9. Environmental Design

10. Great Barrier Reef Data Bases

1 1 . Mechanics of Information
Transfer

is necessary if we are to understand, and manage
the reef. The Authority is cooperating with other
research institutions in a physical oceanographic
research program that is aimed at developing a
computer-based predictive model of the
hydrodynamics of the reef region. Such information
is critical to zoning.

The extent to which activities that can take
place at one area within one zone can be regarded
as isolated from other zones must be determined.
The linkages within marine environments tend to
be much moresignificant than those in terrestrial
environments. Largely through tidal and wind
driven currents, the water mass is constantly
moving in three dimensions. The water mass brings
nutrients and recruits to the fauna and flora of the
reefs. These are essential inputs. In developing a
concept of zoning, the critical issue may thus be
the extent to which reefs can be regarded as
interconnected.

Of course, physical oceanographic
knowledge is useful only if it is complemented by
appropriate ecological knowledge. There has been
significant government expenditure in reef research
in the last two decades and this is continuing. A
large part of current research is ecological or
biological in nature.

The authority has developed a complex web
of arrangements with marine research agencies to
ensure that necessary studies are carried out by the
most appropriate agency and that the authority and
other institutions are aware of all relevant research
information, including research in progress.

Policies of the Authority

The Great Barrier Reef Marine Park Authority and
its programs are acceptable to most sectors of the
community because they are seen to be reasonable
and to avoid unnecessarily restricting the use and
enjoyment of the Great Barrier Reef. Without
public acceptance, the Authority and its programs
would be in jeopardy. But there is another factor
contributing to the success of the Marine Park
system. The Authority has a set of policies which,
in my view, greatly contribute to the system.

Decisions about zoning and management
are taken, and will always have to be taken, in the
absence of complete knowledge. Nevertheless, our
policy is to base decisions as far as possible on
scientifically-derived information. To this end, we
play a major role in the identification, coordination,
establishment, and use of scientific studies directed
toward answering management questions. Our
experience has been that much can be
accomplished without great expenditure of money.

The Authority does not make decisions
lightly that adversely affect existing commercial or
amateur activities. If those activities are already
consistent with conservation of the reef, then the
authority is likely to take decisions that support
them and which prevent them from becoming
destructive. As an example, we assist tourist
operators in the development of activity programs
that are conservationally and educationally focused
for visitors.

18

The Authority is a small agency, and wishes
to remain so. To the maximum extent practicable,
we work through other agencies and with their
officers. There are several reasons for this. We
believe that the flexibility and efficiency of an
organization tends to diminish with increasing size.
We do not expect the public to be impressed by
an agency which grows endlessly, absorbing vast
sums of public monies.

The public is not interested in bureaucratic
power struggles or in squabbles about precise
boundaries of jurisdiction. It is interested in using
and enjoying the Great Barrier Reef Marine Park,
free from conflicts with other users and
government officers. The Authority's policies are
designed to achieve that situation, consistent with
the primary aim of conservation.

Conclusion

The Great Barrier Reef is unique, and the
commitment of the Australian people to its
conservation is great. This commitment has led to
the establishment of legislation and a management
system in which conservation is the dominant
theme, with reasonable use of the reef's resources
being encouraged. The public participates in
decision-making, and is to a degree self-regulating.
The Authority acts as the trustee of the Great
Barrier Reef, on behalf of the people of Australia.

How applicable is the system to the
management of marine (or terrestrial) resources in
other places? Probably much of the methodology
could be applied with success in many parts of the
world. However, it should be recognized that
limitations on economic activities and on the
actions and powers of influential private and
government interests are essential if application of
the system is to achieve conservation. Therefore, a
strong public and government commitment to
sustainable use of a natural resource would appear
to be a necessary prerequisite to successful
application of the system anywhere.

Graeme Kelleher is Chairman and Chief Executive of the
Great Barrier Reef Marine Park Authority, a post he has
held since 1979. He holds a degree in civil engineering
from the University of Sydney and was awarded a Churchill
Fellowship in 1971 to study environmental engineering and
management in Canada and the United States. He has had
wide experience in formulating and implementing the
environmental policies of the Australian government.

Selected References

Darwin, Charles. 1882. The Illustrated Origin of Species. 1979.

Melbourne, Australia: Oxford University Press.
Nomination of the Great Barrier Reef by the Commonwealth of

Australia for inclusion in The World Heritage List. 1981.

Prepared by the Great Barrier Reef Marine Park Authority.
Bertram, G. C. L. 1979. Dugong numbers in retrospect and

prospect. In The Dugong, proceedings of a seminar workshop

held at lames Cook University 8-13 May, ed. by H. Marsh.

Townsville: lames Cook University.
International Union for the Conservation of Nature and Natural

Resources Areas. 1982. Categories, Objectives, and Criteria for

Protected Areas.
Harding, G., and |. Baden, eds. 1977. Managing the Commons.

San Francisco: W. H. Freeman.

Recreational fishing is one use of the Great Barrier Reef
Marine Park. (Photo courtesy of CBRMPA)

Commercial trawling for fish in the reef waters. (Photo
courtesy of CBRMPA)

Green turtles mating. (Photo courtesy of CBRMPA)

19

Reef Metabolism

by David J. Barnes, Bruce E. Chalker, and Donald W. Kinsey

V-^oral reefs are structures that encompass many
habitats, sheltering a huge diversity of organisms.
The reef structure is created by a relatively few,
simple organisms, which leave a skeleton of calcium
carbonate, commonly known as limestone. Only in
warm, essentially tropical, seas are these organisms
able to calcify faster than the physical, chemical, and
biological forces working to disperse the limestone
the organisms create.

The organisms that calcify fast enough to
create coral reef structures are either plants, or
animals that have developed a symbiotic relationship
with single-cell algae. The symbionts in reef-building
animals are dinoflagellate algae, often referred to by
the name of zooxanthellae. In all of the rapid
calcifiers of coral reefs, photosynthesis by the plant
leads to significantly increased rates of calcification.
Thus, the development and maintenance of reef
structure depends on photosynthesis — which in turn
depends on light. Consequently, reef development is
limited to relatively shallow water (essentially down
to 200 feet) in tropical seas.

Shallow, tropical seas are relatively low in
organic nutrients, and photosynthesis within reef
boundaries appears to provide the bulk of the
organic carbon required to sustain the organisms
living on and within reef structures. Coral reefs have
one of the highest rates of primary production of any
natural ecosystem. Still, the daytime primary
production is only just sufficient to sustain the
requirements of the huge numbers and varieties of
coral reef organisms over a whole day.

Measurements

Despite the complexity of reef structures,
communities, and ecology, it is possible to make
relatively simple measurements that explain how
these elements are maintained and sustained. Such
measurements are often referred to as
measurements of reef or community metabolism.
Although, in a strict sense, a reef or community does
not have a metabolism, it is possible to determine
the rates at which materials are imported, used,
turned over, and exported. Coral reefs have proved
very amenable ecosystems in which to make such
measurements. There are several reasons for this.
First, they have such sharp boundaries that it is easily
possible to define input and output. Second, inputs
and outputs must be through the overlying seawater,
and they are so large that, in shallower areas, they
measurably alter that seawater. Third, the shape of
many reefs is a response to the prevailing weather
conditions, the consequence is often that seawater

approaches, crosses, and leaves them in a relatively
simple, mostly single direction fashion. It is then
possible to measure alterations in the chemistry or
content of seawater flowing across a coral reef.

Sampling of seawater upstream and
downstream as it crosses a shallow coral reef area is
often known as flow respirometry. The name derives
from work in rivers and streams where upstream and
downstream sampling was first used. Indo-Pacific
coral reefs are most amenable to flow respirometry-
based measurements of community metabolism.
This is because, compared to Atlantic coral reefs,
they have wide areas of shallow reef flat that face
into the prevailing weather. It is not surprising that
most measurements of community metabolism
come from Pacific coral reefs. These reefs also have
proved the most suitable for whole system
measurements, providing estimates of rates of gain
or loss by whole reef systems. Such whole system
measurements are only possible when reef
physiography assists, as when all or most of the
water entering a reef system exits through a few
restricted passages or routes. Such measurements
have shown that reasonable approximations for
whole system gains and losses can be obtained by
appropriate integration of results from zonal studies.

Flow respirometry was first used, in
conjunction with measurements of oxygen
concentration, to determine the primary production
and respiration (day and night measurements) of
shallow reef areas. The oxygen content of water was
measured at an upstream point of a single directional
flow across a shallow area of coral reef. The
difference in oxygen concentration between this
point and some downstream point was then ascribed
to metabolism of benthic organisms in the area
between the two sampling points. The difference in
oxygen concentration was then adjusted for the
volume of water flowing per unit of time between
the sampling points and the area of benthos
between the points. The results could then be
expressed as the change in oxygen concentration
per unit volume of seawater multiplied by the
volume of seawater flowing over the area between
the sampling points per unit time (A02/m3 X m3/h/
m2 = A02/m2/h). Such estimates are possible if the
average depth and water velocity between the
sampling points are determined. Alternatively, a
sample can be taken and the patch of water marked
with dye. After the dye patch has moved a
significant distance across the reef (or resided for a
significant time), a second sample can be taken close
to the patch.

20

Figure 1 . A floating instrument package capable of providing
sophisticated, high-resolution measurements of reef flat
productivity and calcification, (a) The instrument package is
deployed from a small, inflatable boat moored in shallow
water on a reef flat, (b) The package floats across the reef flat
with the current and records changes in seawater pH, oxygen
content, and temperature, as well as the incident light
intensity. (Photo courtesy of the authors)

Oxygen-based Measurements

As already mentioned, early work on the
productivity and respiration of coral reefs was based
on changes in oxygen concentration. However,
these estimates had two major drawbacks. First,
oxygen readily exchanges between the water
column and the atmosphere, and allowance must be
made for oxygen exchange in measurements on
coral reefs. Initially, techniques were devised for
estimating the amount of exchange, but all of these
were based on risky assumptions. More recently,
sufficient understanding of exchange processes
together with sufficient measurements of exchange
in coral reefs have provided generalized data for
exchange rates over shallow reefs. It is now possible
to make reasonably accurate allowance for oxygen
exchange. The second drawback is that changes in
oxygen concentration do not directly measure the
amount of carbon dioxide fixed by photosynthesis or
released by respiration. Carbon, of course, is the
basic unit in which primary production and
respiration must be expressed. The majority of
studies based on oxygen concentration have
assumed a one-to-one relationship between oxygen
change and carbon dioxide change. Here again,
sufficient data has now accumulated to make
generalizations less risky than when studies of coral
reef productivity began.

Carbon Dioxide Measurements

In the early 1970s, Donald W. Kinsey and Steven V.
Smith independently introduced what has since
become known as the alkalinity anomaly technique.
This is a C02-based technique. It is not normally
subject to problems of air/sea exchange and it does
not require an estimate or measurement of
metabolic quotients. It has the additional major
advantage that it allows measurement of community
calcification (or dissolution). The technique requires
measurement of changes in seawater pH and total
alkalinity between upstream and downstream
sampling sites. Total alkalinity, essentially, is the
ability of the seawater to neutralize acid. Most of the
change in total alkalinity of seawater above coral

21

Light and Corals

When solar light penetrates the ocean, it
decreases in quantity and changes in spectral
quality. At any given wavelength, the amount of
light decreases exponentially with depth. There
also is a shift in quality toward the blue end of
the visible spectrum as red and ultraviolet light
are preferentially absorbed. These changes in
light quality and quantity profoundly influence
coral physiology.

Reef-building corals contain within their
cells large populations of the single cell brown
alga Symbiodinium microadriaticum. The
presence of these algae (zooxanthellae) confers
two major benefits to the coral. First, 95 to 98
percent of all the photosynthetically fixed carbon
produced by the algae is transported to the host,
where it is used as a major food source. Second,
the act of photosynthesis by the algae causes the
coral to grow its calcium carbonate skeleton two
to three times faster in the light than in the dark.

This light-enhanced calcification permits
modern coral reefs to grow faster than they are
eroded by physical and biological agents. Since
light directly influences both nutrition and
structural growth, it is the most important
physical factor influencing the metabolism and
ecology of coral reefs.

Hard coral Turbinaria peltata. (Photo courtesy of GBRMPA)

Hard coral Acropora sp. (Photo courtesy of GBRMPA)

Corals are common on reefs from the
surface down to about the 1 percent light level.
Successful growth over such a wide range of
irradiances occurs because corals have evolved a
variety of photoadaptive mechanisms. When
growing at increasingly low light intensities many
corals become progressively flattened. This
presumably increases the fraction of the colony
that is directly exposed to ambient light. Corals
also decrease the number of polyps per unit
surface area, which reduces coral respiration and
conserves the available resources.

The symbiotic algae within corals adapt to
decreasing light intensity by synthesizing
increasing amounts of chlorophyll -a and other
photosynthetic pigments. This increases the
efficiency of light-absorption at lower light levels.
In fact, at intermediate depths photoadaptation
has often occurred to a greater extent than the
available light has decreased. Thus, coral
photosynthesis may be higher at 10 to 20 meters
than at either shallower or deeper depths. For
relatively autotrophic coral species, the lower
limits of depth distribution will be reached when
photoadaptation is no longer sufficient to
compensate for decreasing irradiance. The precise
depth at which compensation occurs depends on
the availability and use of other food sources and
the clarity of the reef waters. In very clear water

reefs is the result of removal of calcium ions from
solution and their precipitation as calcium carbonate.
Changes in seawater pH essentially reflect changes
in the C02 concentration of the seawater. Thus, in
essence,

photosynthesis and respiration =

ApH — Atotal alkalinity

This equation is satisfied after pH and total alkalinity

change have been converted to equivalent units of
carbon. Present understanding of coral reef
productivity and respiration is largely based on
results obtained with this technique and present
understanding of coral reef calcification is almost
entirely due to the technique.

Combined Oxygen and C02 Measurements

The alkalinity anomaly and oxygen-based techniques
recently have been combined by David J. Barnes to

22

on the edge of the continental shelf, reef coral
community zonations are wide, and abundant
corals are found down to a depth of at least 85
meters. The zones become increasingly narrow
and more shallow as water turbidity increases on
reefs progressively toward the coast.

Ultraviolet Light

Until recent years it was a common
misconception that ultraviolet (UV) light was
attenuated within the first few centimeters of the
ocean surface and thus had little significance in
marine environments. On the contrary, ultraviolet
light is now recognized as an important attribute
of the shallow water environment of tropical
coral reefs. This is due to both higher levels of UV
light occurring at the ocean surface, resulting
from the thinness of the earth's ozone layer near
the equator, and to the general transparency of
tropical ocean waters.

UV light is frequently divided into three
bands: UV-C (200-280 nanometers), UV-B (280-
320 nm) and UV-A (320-400 nm). High energy,
ultraviolet light below 286 nm does not penetrate
the earth's atmosphere and thus is not
environmentally important. In contrast, solar UV-
B and the shorter wavelengths of UV-A light can
be physiologically and photosynthetically
damaging to many forms of reef life.

Only a limited variety of organisms survive
in the shallow waters of an Indo-Pacific reef flat.
These include some species of hard and soft
corals, sea mats (zooanthidians), sea anemones,
giant clams, and some algae. Most other marine
life, which may be abundant in deeper water or
in shade protected crevices on the reef flat, die
within a day when relocated to the intense
shallow-water sunlight of the reef flat. Death to
these organisms can often be prevented if they
are placed under a sheet of clear plastic that
filters ultraviolet, but not visible light. Thus,
ultraviolet light can be demonstrated as a
significant physical factor regulating the light
(depth) distribution of organisms on a coral reef.

Most of the organisms abundant on
shallow water reef flats are algae or are
invertebrates that contain within their cells large
populations of symbiotic algae. The tissues of
these animals are all relatively transparent to
facilitate transmission of photosynthetic sunlight
to their algae. This creates a difficult evolutionary
question. How can relatively transparent
organisms surviving in shallow waters protect

themselves from the damaging or lethal effects of
high-intensity ultraviolet light?

In each case, the solution appears to be
the synthesis of highly efficient, UV-absorbing
compounds found within both the algal cells and
that of the host animal tissue. At present, limited
information is available about the structure and
chemical distribution of these compounds in reef
organisms; however, hard corals have received
most attention. Extracts of coral tissue contain
chemical compounds absorbing strongly at a
wavelength of approximately 320 nanometers. In
studies at the Australian Institute of Marine
Science, we have separated and identified three
major compounds from the Pacific staghorn coral,
Acropora formosa, each of which has a UV-
absorption maximum in the region, 310 to 340
nanometers. In combination, these compounds
form a broad-band filter, intercepting potentially
damaging ultraviolet radiation without absorbing
photosynthetic visible light.

These compounds are produced in high
concentrations by corals growing on the reef flat
and concentrations decline in corals growing at
progressively deeper depths; minimal
concentrations occur at depths of 20 meters or
less. This observed photobiological adaptation
verifies the long dormant conclusion of the
pioneering optical oceanographer, N. G. jerlov
(1950):

This high transparency of the (tropical) oceans to
the biologically important ultra-violet radiation
would mean that the active region, where
photochemical processes can be carried out,
extends as far down as 20 meters.

Consideration should now be given to the
combined ecological significance of UV light,
photobiological mechanisms of chemical
protection, and propagation. Do the eggs and
larvae of reef invertebrates contain significant
concentrations of UV-absorbing materials? Do
environmental levels of ultraviolet light influence
the dispersal and survival of young coral reef
organisms? These questions and many others will
undoubtedly be answered as more researchers
become interested in UV-light and coral reefs.

—Bruce E. Chalker (AIMS),

Walter C. Dunlap (AIMS),

and Paul L. Jokiel (NMFS, Honolulu)

allow more or less continuous monitoring of changes
in the chemistry of a patch of seawater as it moves
across a shallow area of coral reef. The problem with
the alkalinity anomaly technique is that it cannot
easily be adapted to monitor changes in seawater
chemistry as they occur. This is because the
technique requires very precise laboratory work that
is not easily automated for remote use. However, by
combining pH measurements with oxygen
measurements it becomes possible to develop an

instrument package that will float across a reef with a
patch of water and monitor the chemical changes
induced in that patch of water by the reef benthos
(Figures 1a and 1b). The alkalinity anomaly equation
given earlier is rearranged to give:

calcification and solution = ApH — (A02 x Q),

where Q is the metabolic (photosynthetic or
respiratory) quotient. In fact, Q is more or less

23

constant for a particular community and is best
obtained by occasionally measuring changes in total
alkalinity, concurrently with changes in oxygen
concentration and pH. The beauty of a floating
instrument package is that it can measure changes in
seawater chemistry as the water moves as little as 1
meter across the reef benthos. Techniques based on
taking seawater samples usually require the water to
have moved over at least 100 meters of benthos.
Moreover, the technique allows monitoring the
response of relatively small areas of benthos with
respect to changes in light intensity. This means that
it permits investigation of the important relationships
between community metabolism and light intensity,
as well as allowing measurements at very fine spatial
and temporal scales.

The important parameters estimated in
studies of primary production, respiration, and
calcification on coral reefs are as follows:

• Cross productivity (P), that is, the gross photosynthetic
fixation of carbon. This is usually expressed as
gCarbon per m2 per day.

• Respiration (R); the respiratory utilization of fixed
carbon. This also is usually expressed as gCarbon per
m2 per day. Respiration of coral reef communities
must be measured at night (that is, in the dark when
photosynthesis is not taking place), and the nighttime
rate is assumed to apply throughout the day.

• Cross production to respiration ratio (P/R).

• The "net" gain in calcium carbonate (G). This is the
amount of calcium carbonate precipitated less losses
due to dissolution. It is usually expressed as kgCaCOi
per m2 per year. The "net" gain is a practical
measurement since changes in seawater chemistry
actually estimate precipitation less solution.

Problems exist in comparing data from
different workers for different reefs, often because
work was carried out where the geometry of a
particular reef made it most convenient. Thus, the
areas of reef reported in numerous studies of
community metabolism are not directly comparable
on any simple basis. Moreover, some workers have
provided results for community metabolism that are,
in essence, rates averaged over a whole year; other
workers have provided results that are applicable
only for the time of year and conditions under which
measurements were made.

Some workers have made attempts to allow
for daily changes in light intensity and, sometimes,
for changes in day length through the year. Other
workers have simply extended average rates
measured during the day (for example, for
productivity and calcification) over 12 hours and
nighttime rates (for example, for respiration and,
perhaps, solution of reef rock) have been extended
over 24 hours. Some recent results are based on
measurements of the light response curves for
community productivity and calcification (Figures 2
and 3). There have been several recent attempts to
pull together the varied and various results. Such
attempts make it likely that future workers will be
aware of the considerable problems that exist in
comparing data, and will attempt to make their work
fit with, and compare with, what has gone before.

Estimates of gross carbonate production on

coral reefs (that is, total precipitation) are in the
range 1-35 kilograms CaC03 per m2 per year, with
an average around 10 kilograms per m2 per year and
a most likely mean in the range 3-6 kilograms per m2
per year. Thus, coral reefs are biologically adding 12
to 24 tons of calcium carbonate an acre per year.
"Net" calcification measured from changes in
seawater chemistry fits well with these "growth
rate"-based estimates. Results suggest that fast
growing, but limited, areas of reef may achieve
deposition rates around 10 kilograms CaC03 per m2
per year; that reef flats may produce 4-5 kilograms
per m2 per year, and that lagoonal and sand-covered
areas produce 0.5-1.0 kilograms per m2 per year.
Estimates for whole reef systems suggest that 1 to 2
percent of the reef area achieves the higher rate; that
the intermediate rate covers 4 to 8 percent of the
reef area and the low rate is applicable to 90 to 95
percent of the reef area. Considering that living reefs
cover about 1 5 percent of the shallow seabed and
about 0.2 percent of the world's ocean area, these
rates for precipitation demonstrate that coral reefs
serve as an important buffer in the Earth's carbon
dioxide cycle. In general, the calcification rates
transform to upward growth rates for coral reefs of 1
millimeter per year in areas with slow calcification, 3
millimeters per year for intermediate areas and 7
millimeters per year in rapidly calcifying areas. These
values translate directly into 1, 3, and 7 meters per
1,000 years. This means that, as major geological
features on the earth's surface, coral reefs have
extraordinary growth rates and growth potential.

The mechanisms of calcification in reef
organisms — and, indeed, calcification and
ossification in general — are little understood. This is
perhaps surprising since such processes fall not far
behind photosynthesis and respiration in their
importance to the living world.

Perhaps the most important point to come
out of recent reviews of nearly four decades of work
on coral reef community metabolism is that
regardless of where measurements have been made,
particular coral reef environments appear to have
very similar rates of community metabolism.

Figures 2 and 3 show light response curves for
community metabolism across 300 meters of reef
flat. Productivity is highest toward the reef crest and
shows only a slight trend toward saturation with
increasing light intensity. This suggests overlapping
layers of primary producers and, since solution of
reef rock is at its highest in this region, it is likely that
a significant proportion of the primary production is
due to endolithic* as well as epilithic** algae. It
seems likely that high production by filamentous
algae is maintained in this region because of
continued disturbance of the substrate by waves.

The continual movement and turnover of the
substrate prevents colonization of the region by
longer-lived organisms, such as corals, or fragile
organisms, such as some of the calcareous algae.
With increasing distance across the reef flat, the

* Living within rocks or other stony substances, such as
mollusk shells or coral.

** Crowing upon stones or stonelike material (in contrast to
the above).

24

Figure 2. Light response curves for reef
flat community primary production
with distance across the reef flat. The
shape of the curves change from front
to back of the reef flat. At the front of
the reef flat, the essentially linear
response to light intensity reflects
overlapping layers of filamentous
algae on hard substrate. Toward the
rear of the reef flat productivity is
saturated at about half maximum light
intensity. This reflects the presence of
coral-dominated patches of hard
substrate toward the rear of the reef
flat. (Adapted from Barnes and
Devereux, 1984. Barnes and Chalker,
in press, Elsevier)

Figure 3. Community light response
curves for net calcification
(precipitation less dissolution) with
distance across the reef flat. More
negative values indicate higher rates of
calcification. Linear responses are
shown as this is the most appropriate
way to treat the "noisy" data for
community calcification. The response
curves probably tend toward
saturation at high light intensities.
There is an increase in calcification
rate and its dependence upon light
intensity with distance across the reef
flat. This shift in performance reflects a
shift toward coral-dominated
communities with distance across the
reef flat. (Adapted from Barnes and
Devereux, 1984. Barnes and Chalker,
in press, Elsevier)

o -io »

1000
Light Intensity
( pElnstelns m~* t"1 ) 2Q0

100
150
200

250 Distance ( m )

25

substrate becomes more stable and less subject to
disturbance. This allows establishment and
continued growth of calcareous algae, hard and soft
corals, sponges, and encrusting plants and animals.
As a consequence, community metabolic
performance tends toward that exhibited by these
organisms; productivity tends to saturate with
increasing light intensity and calcification increases
and becomes more light dependent.

Present understanding is limited for
seasonality in coral reef primary production and
calcification. Only seven studies have addressed
these topics and, unfortunately, most of these
studies have been on coral reefs growing in areas
approaching the latitudinal limits of reef
development (that is, where seasonal changes in
conditions are so marked that they have to be taken
into account). There appears to be a two-fold
summer to winter decrease in productivity and
respiration, with the greatest seasonal differences
occurring, surprisingly, at lower latitudes.
Calcification, on the other hand, shows little
seasonality at lower latitudes but considerable
seasonality as latitude approaches the limits for coral
reef development.

Studies of community metabolism on coral
reefs are fundamental to any understanding of how
such systems develop, grow, and are maintained.
The importance of calcification to reef development
is obvious. Metabolic studies are providing
information about the spatial variations in
calcification rate and on the environmental factors
that significantly affect reef growth. While the
inorganic gain in most reef systems is high, the
organic gain is around zero and may be slightly
positive or negative over periods of months to years.
The precise elucidation of the status of this delicate
balance is proving to be critical to our understanding
of the status of whole reef systems.

Reef flats, the areas most studied in terms of
community metabolism, appear to have a slight
excess of organic production. However, it is
becoming clear that such excess is probably due to
the short lived, filamentous algal communities.
Anything that alters the productivity of such
communities will greatly affect a whole range of
organisms: those that can quickly respond to greater
productivity, or those that will be quickly affected by
a lowered productivity.

The organisms that are most obvious on coral
reefs are those that have the metabolic reserves to
carry through weeks to months of lowered
productivity. However, the same drop in
productivity probably has catastrophic
consequences for the less obvious (but not
necessarily less important) reef communities, such as
those of bacteria and interstitial fauna. However, it is
already apparent that normal coral reef communities
are limited by the productivity of plants within the
communities, and that an unusual or excessive input
of organic nutrients seriously perturbs the
communities.

Perhaps the most important practical aspect
of metabolism studies is their potential to provide
vital information about the operation of reef systems
for people charged with managing such systems. The

literature on reef form and reef community structure
largely emphasizes the differences between reefs.
Even adjacent reefs can be very different in form and
community structure. Studies of reef metabolism
have emphasized that such apparently different reefs
and reef communities are likely to have very similar
metabolic performances. Reef systems that perform
outside "standards" of the sort already provided by
metabolic studies must be examined carefully to
determine whether the unusual performance reflects
perturbation by some outside agency. At present,
community metabolism studies on coral reefs are
defining the "normal" range of performance. Recent
studies are reaching a level of sophistication where
second order variations in community metabolism,
previously attributed to noise, are becoming
understood as important facets of system operation
(Figures 2 and 3).

Kaneohe Bay Studies

At present, there is only limited understanding of the
causes (that is, the meaning) of excursions outside of
"normal" metabolic performance. By far the best
studied metabolic responses to external perturbation
resulted from discharge of sewage and increased
terrigenous sedimentation in Kaneohe Bay, Hawaii.
Measurements were taken before and after sewage
was diverted from the bay in 1977 and early 1978.
Very clear temporal and spatial patterns emerged for
reef metabolic performance following the onset of
the perturbation. Generally speaking, the reefs
became less self-sufficient in organic production and
calcification decreased greatly. The perturbations
essentially shifted community structure away from
the sorts of organisms that characterize and maintain
coral reefs.

The Kaneohe Bay studies established that
marked shifts in community metabolism are
associated with equally marked and visually obvious
shifts in community structure and sedimentary
character. The real question is whether metabolism
studies can provide early warnings of impending or
potential catastrophic changes, and thus provide
time to take action before major, perhaps
irreversible, changes occur in community structure.

David I. Barnes and Bruce E. Chalker are biologists at the
Australian Institute of Marine Science. Donald W. Kinsey is
Executive Officer of the Great Barrier Reef Marine Park
Authority.

References

Barnes, D. J., and M. ). Devereux. 1984. Productivity and

calcification on a coral reef: a survey using pH and oxygen

electrode techniques. /. Exp. Mar. Biol. Ecol. 79:213-231.
Kinsey, D. W. 1983. Standards of performance in coral reef primary

production and carbon turnover. In: Perspectives on Coral

Reefs. Australian Institute of Marine Science, pp. 209-218.
Kinsey, D. W. 1985. Metabolism, calcification and carbon

production: I. System level studies. Proc. Fifth International Coral

Reef Congress, Tahiti. Seminar B.
Smith, S. V. 1978. Coral reef area and the contributions of reefs to

processes and resources of the world's oceans. Nature 273:225-

226.
Smith, S. V. 1983. Coral reef calcification. In: Perspectives on Coral

Reefs. Australian Institute of Marine Science, pp. 240-247.
Stoddart, D. R., and R. E. Johannes, eds. 1978. Coral Reefs: Research

Methods. UNESCO, Monographs on Oceanographic

Methodology. Paris. No. 5. 581 pp.

26

Distribution

of Reef-Building Corals

by J. E. N. Veron

J ust as the living reef forms a veneer on the
foundation structure below, so do recent studies
seek to layer new information onto the existing
foundation of coral reef studies begun by Charles
Darwin in 1842.

While Darwin's work remains a research
paradigm, recent findings in related fields have
contributed greatly. When Darwin wrote, he did not
enjoy the perspective gained from knowledge of 1)
plate tectonics, and 2) sea-level changes. Both have
played a major role in addressing a basic topic in
coral reef biology: the distribution of reef corals in
space and time.

Is the present distribution of corals correlated
with the present distribution of reefs? Are corals
found where they originally evolved, or have they
traveled (using their planktonic larvae) away from
their place of origin? Are present distribution patterns
mostly a matter of geological history, or are physical
environmental factors (like ocean currents and
temperatures), or biological factors (like species
interactions) more important? In short, why and how
do corals exist as they do?

Most of these questions and others like them
have no simple answers, for each involves an
intriguing mixture of geological history,
environmental and geological constraints,
evolutionary processes, and reproductive biology.

Coral Distribution Patterns

There are only about 500 species (88 genera) of reef-
building (or hermatypic) corals in the Indo-Pacific.
On the broad scale, hermatypic corals are
characterized by a low number of species, wide
species ranges, and a lack of endemics (species
native to a particular locality). As shown in Figure 1,

the numbers of genera of Indo-Pacific corals are
fairly evenly distributed across the tropical reefs of
the Indian Ocean, from the Red Sea to western
Australia and Indonesia. Further to the east, a north-
south belt of relatively high diversity (the Indo-West
Pacific Center) extends from the Philippines south to
the Great Barrier Reef. Further eastward across the
island archipelagoes of the South Pacific, diversity
gradually decreases, with only a few genera reaching
the west coast of the Americas.

Curiously, some species of coral span almost
the entire Indo-Pacific, while others are found only
in isolated areas.

The Great Barrier Reef is home to 350 named
species, hence most of these have wide distribution
ranges. For example, 89 percent of the species
recorded from japan's Ryukyu Islands, and 94
percent of the species recorded from western
Australia, also occur on the Great Barrier Reef. Over
these great distances, however, a species'
abundance, color, and range of growth forms may
change, sometimes making identification difficult or
doubtful.

Within the Great Barrier Reef, the distribution
and abundance of species is more uniform. Some
are more common in muddy waters near the
coastline, others are more common in the clear
waters of outer reefs. Only the southern-most
(Capricorn and Bunker) groups of reefs show a
significant reduction in the number of species
compared with the rest of the Great Barrier Reef.
South of the Great Barrier Reef, coral reefs are
widely spaced and the number of species decreases
rapidly. What then has determined the abundance
and distribution of corals on the Great Barrier Reef?

Figure -1. The diversity of reef-building coral. The index is compiled by adding the known distribution ranges of the individual
genera. The highest diversity occurs in the Indo-West Pacific, from the Great Barrier Reef to the Philippines.

27

Coral Reproduction,

C

r orals utilize a diverse set of reproductive
options, both sexual and asexual. The
propagules* associated with each have different
dispersal capabilities. When the propagules settle,
and growth begins, the physical and biological
forces of natural selection influence their survival.
While the average person envisions the coral reef
as waving fronds or massive structures, most of
the individuals in a coral community are small
(less than 500 microns), and not readily visible to
the naked eye. These members range from a few
days to a few years in age. Mortality rates at this
stage of development can be high.

Asexual Reproduction

At present, there are five known modes of asexual
reproduction, and each results in propagules
genetically identical to the parent colony. Most
have short dispersal capabilities, and remain near
the parent. The asexual modes are:

• Branch-breakage. Common in branching and

plating corals, such as Acropora spp. When
disturbed, either physically (storm) or
biologically (predatory fish), pieces may
break off and re-cement themselves to the
reef surface.

• Fission. A number of corals, among them the

motile fungiids or mushroom corals, may
split into two or more colonies during early
development.

• Polyp Bail-Out. In special cases, some brown

corals (for example Seriatopa hystrix,
Pocillopora damicornis) dissociate
individual polyps within a colony from
each other and the colony skeleton. These
polyps then drift to a new area of
settlement. This process has been
observed under conditions of
environmental stress.

* The parts of an organism capable of growing into a
new one; in plant life, for example, a spore, seed, or
cutting.

MODE
Sexual

TIMEFRAME

xternal fertilization and development ♦-^
brooded planulae

brooded planulae
polyp - balls

polyp bail- out
fission
breakage re cementa

Reproductive modes of coral.

Polyp-Balls. In Coniopora spp., for example, a
dissociation from the main colony occurs
in which a structure containing coral tissue
with a separate, primordial skeleton sets
adrift, falls to the reef surface near the
parent, and initates a new colony.

Asexual Brooded Planulae. As described by
James Stoddart (see page 41), the planulae,
or ciliated larvae, are now known to be
produced by a type of budding
mechanism, as well as sexually.

Sexual Reproduction

Sexual reproduction occurs in two forms:
fertilization and brooding of the larvae within the
polyp, and external fertilization and development.
Research reported by Garden Wallace and others
(see page 38) suggests that the sexual brooded
planulae may play a smaller role than previously
believed. The major mode of sexual reproduction
on the reef may be the spawning of eggs and
sperm into the water column, with fertilization
and embryonic development of the planulae
occurring while adrift in the plankton. The
additional time afforded the propagule for
development likely yields greater dispersal
capabilities.

Geological History

The discovery of continental drift has now shattered
most of the old Darwinian concept that species had
"centers of origin" and that old species were
displaced, or replaced, by more successful ones

evolving at the center. During the time period of the
evolution of most coral genera (the Tertiary Period —
70 million years before present), and probably that
of many of today's species, the continents of the

28

Dispersal, and Survival

[METRIC ]

Since space is a limiting factor for survival, competitive
interactions involving coral spat can be highly complex.
Here, an oyster is overgrowing an Acropora, which in turn is
overgrowing an encrusting foraminiferan, which in turn is
being overgrown by a coralline algae.

Larval Dispersal and Settling

Coral settlement and survival has been examined
by our laboratory in the recent Helix Experiment.
Successful dispersal and settlement appears tied
to both species and regional differences.

Although the larvae of some organisms
have high dispersal capabilities, the average
distances that they actually traverse can be
surprisingly short. For example, at times, pollen
seems almost ubiquitious in the lower
atmosphere. Yet most of the wind-dispersed
pollen of pine trees falls within a few meters of
the parent plant. Coral larvae exhibit a similar
pattern. Most settle directly on the reef, or within
600 meters of it— a fraction of the distance they
are capable of traversing. On a finer scale, the
pattern is genus-specific, and also tied to
reproductive mode, as described previously.
Planulae and fertilized eggs are certainly capable
of travelling much further, and many do, as others
haye suggested. These individuals are important
for the spread of coral populations, and the
question of actual dispersal distances of larvae
remains open at this time. It is an active area of
research.

Settlement geography also is important,
and cross-shelf differences are clear. Species that

Coral planulae often aggregate upon settlement. If two or
more spat abut in their initial growth phase, and if they are
histocompatible, fusion occurs. This can enhance survival
of both colonies by allowing them to grow into a size
refuge more rapidly — where they can better survive
predation, disturbance, or competition for space. (Photo
courtesy;. Exp. Mar. Biol. Ecoi, 1982)

successfully settled on an inshore reef were
different from those on mid- and outer-shelf reefs.
Mortality rates were higher inshore, suggesting
that high sedimentation and salinity variation
created a harsher environment, and in shallow
water on the outer shelf, where wave action
inhibits settlement. The optimal conditions for
settlement and survival of the coral appeared to
be on the mid-shelf.

Survival

After settlement, juvenile corals must survive the
rigors of not only their physical but also their
biological environment. Grazing by predators and
competition for space are the principal factors.
While these same factors continue to operate and
act on adult corals, mortality levels are greatly
reduced due to their refuge in size. Adult colonies
may be composed of thousands of polyps, each
capable of regeneration and regrowth, whereas
juveniles will have only a few. Thus, mortality to
several polyps would usually be fatal to the
juvenile, but insignificant to the adult — leaving
the adult to survive, reproduce, and begin the life
cycle anew.

— Paul W. Sammarco, AIMS

Southern Hemisphere — including Australia, India,
Africa, and South America — were well south of their
present positions, leaving a tropical/subtropical
circum-global seaway linking all of the world's great

oceans. This seaway, the ancient Tethys Sea, allowed
many groups of tropical marine organisms, including
corals, to range from the Atlantic to the central
Pacific. Today many groups of marine organisms

29

have this so-called "tethyian" distribution,
established before the closure of the Tethys Sea
more than 10 million years ago.

End of story for corals? Far from it. The mid-
Pliocene heralded the commencement of the Ice
Ages, the consequences of which, for coral reefs,
can hardly be overstated. The build-up of the polar
ice caps did not create a lethal temperature decrease
in most tropical regions. Rather, damaging effects of
the ice cap build-ups came from the lowering of sea
level that accompanied them. A drop in sea level of
1 meter would mean death for most reef flat corals,
and a drop of 100 meters would mean death to an
entire reef region. This is what happened,
repeatedly, during the Ice Ages. Vast areas of reef,
including the entire Great Barrier Reef, were
alternately left high-and-dry, then flooded, in a
continuing series of catastrophic cycles. This process
affects both the geomorphology of reefs and the
evolution of corals.

While the effects of the Ice Ages on the
evolution of corals are still being debated, the effects
on the distribution of corals are clearer. Lowered sea
level exposed and consequently killed most coral
communities, and created new barriers to
distribution. Many genera now restricted to the Indo-
Pacific were common in the Caribbean before the
final closure of the Panama Isthmus some 5 million
years ago. This area was severely affected by
glaciation as well as by sea-level change: all eastern
Pacific corals were probably entirely destroyed at
this time, with the present Caribbean fauna thus
coming from refuges along the east coast of South
America. Consequently, there are only a few species
of coral in the eastern Pacific, and all these have
their affinities with, or are the same species as, corals
in the western Pacific. Only a single species has
survived in both the Indo-Pacific and the Atlantic
and no hermatypic species has survived in the
Mediterranean.

Environmental and Ecological Controls

The combined effects of continental drift and sea-
level changes still leave a lot to explain about coral
distribution, reef distribution, and related subjects
like coral community composition. Why, for
example, does diversity decrease eastward and
southward from the Great Barrier Reef? Why does

the composition of coral communities vary from one
reef, or region, to the next?

Here we must consider the spatial scales
involved. The patterns of community types found on
a single reef primarily reflect patterns in the physical
environment, especially depth, wave action, light,
and sediment load. Within a whole region, such as
the entire east Australian coast, corals are distributed
primarily according to ocean currents and
temperatures, the availability of suitable sites for
colonization, and the capacity of larvae to get to
those sites. Within the entire Indo-Pacific, corals are
distributed according to a mosaic of regional
patterns, each with its own characteristics,
superimposed on a historical background of
continental drift and sea-level changes.

The effects of surface circulation patterns on
coral distributions are seen very clearly in the
western Pacific. Here, most tropical currents flow
toward the west, allowing rapid transport of larvae
toward the Indo-West Pacific center of high
diversity, not eastward away from it (Figure 2). Thus,
there is a "catch-all" effect in the west. Southward
from the Great Barrier Reef, the East Australia
Current flows unceasingly southward, and planktonic
larvae can only travel south on nonreturn journeys.
Thus, some coral species that are abundant on
eastern Australia's southernmost reefs are rare or
absent on the Great Barrier Reef: they have become
trapped in the south and will remain so as long as
the East Australia Current prevails. A very similar
situation also applies to the Northern Hemisphere
where the northward flowing Kuroshio Current flows
northward past Japan's Ryukyu Islands, bringing
planktonic larvae from tropical waters. It is not
surprising, therefore, that Japan and Australia have so
many coral species in common: both faunas have
dispersed from the same general (western Pacific)
region.

Temperature long has been considered the
primary factor limiting corals to tropical and
subtropical localities, and it has been generally
considered that it does so by affecting the
reproductive cycle. If this is so, it has yet to be
demonstrated. Alternatively, the effects of low
temperature may be indirect: it may slow the rate at
which corals can calcify, thus making light availability
(hence depth) more limiting. At high latitudes,

Figure 2. The world's major surface ocean currents. Westward flowing currents across the Pacific are one of the reasons why the
Indo-West Pacific has a high coral diversity. The dashed lines enclose about 75 percent of the world's coral reefs, another reason
why this region is so diverse.

30

therefore, the rate at which corals can construct
reefs may not be sufficient to outstrip the forces of
erosion.

There are several other environmental
constraints affecting hermatypic corals that may be
important in any particular region. Of course, most
of the world's oceans are too deep for reef growth.
Some regions are greatly affected by major rivers,
which decrease salinity to levels lethal to corals.
Others have substrates of soft terrigenous mud,
unsuitable for coral growth. Biological controls also
limit reef development. Important among these is
competition between corals and macro-algae (for
example, kelp and Sargassum), which are easily able
to out-grow corals. On coral reefs, algal growth is
held in check by herbivorous fish. However, where
reef development is poor, especially in the higher
latitudes, this is often not the case, and corals are
forced to compete directly with algae.

Dispersal and Speciation

Like most marine fauna, corals disperse by means of
tiny planktonic larvae, the fate of which depends on
prevailing ocean currents and the ability of the larvae
to settle and grow should they be able to find
suitable conditions. That corals are capable of long-
distance journeys has been disputed for some time,
and, for most species, still needs to be
experimentally demonstrated. However, taxonomic
evidence that most species do indeed make long
journeys is overwhelming. Most species are very
widespread, and few are endemic to any particular
region.

What, then, can be said of the origin of
species? Where in time and space did they originate?
Some claim that the sea-level changes earlier
described have created barriers to dispersal (barriers
to gene flow) which, as in the case of Darwin's
finches, have been a major cause of speciation. The
rise and fall of sea levels would have created and
removed all manner of barriers, especially land
bridges, causing separate species to form, then
allowing them to intermix. Others claim that sea-
level changes have acted to retard speciation. The
high frequency of sea-level fluctuations, combined
with the great longevity of corals and their capacity
for dispersal, has kept the gene pool mixed and the
number of species low.

The latter of the above two models now
appears to be the more likely for most hermatypic
corals that are indeed characterized by a low
number of species. Perhaps the very wide range of
growth forms displayed by most species also reflects
a lack of speciation. To find the origins of most
species, we should look back to an earlier time of
long-term climatic stability, perhaps late Tethyian
times, when tropical conditions prevailed over most
of the earth's surface and ocean currents did not
provide the communication between reefs that they
now do and would have done during the Ice Ages.

/. £. N. Veron is a researcher at the Australian Institute of
Marine Science, Townsville, Australia.

Coral Rings Give Clues
to Past Climate

^oral skeletons contain annual rings analogous to
tree rings. The rings are revealed as alternating light
and dark bands when coral skeletons are X-rayed.
A pair of these bands represents one year's growth.
The bands are best seen in large rounded coral
colonies that grow 0.5-1.5 centimeters in a year.
On the Great Barrier Reef, 600-year-old colonies
are frequent, and occasional colonies are older
than 1,000 years. Systematic changes in these rates
of coral growth have been found across the width
of the Great Barrier Reef from turbid coastal waters
to the clear waters of the Coral Sea.

Research in progress at the Australian
Institute of Marine Science in Townsville indicates
that growth patterns in coral skeletons are a
potentially important record of weather and
climate trends in the recent past.

The fundamental record in massive corals is
a marked annual variation in skeletal density. This
was first described in 1972, and is now recognized
as a characteristic of many species of coral. The
underlying causes of the annual density variation
have not been firmly established. The seasonal
timing of high and low density growth appears to
vary from one part of the world to another.

The density variations probably reflect
complex seasonal phenomena, such as cloud cover
and nutrition, rather than simple factors, such as
temperature. Nonetheless, the annual density
bands provide a reliable and accurate temporal
record of skeletal deposition. Research shows that
a resolution of about 14 days is possible from this
density record. The presence of an accurate
temporal record makes possible the deciphering of
a range of other environmental records that the
coral incorporates during growth.

Supra-annual peaks in skeletal density have
been found to coincide with El Nino years. Records
of the last 30 years can be easily obtained from
coral colonies collected from reefs. Longer records
can be obtained only by drilling a core sample
along the growth axis of larger colonies. We have
thus far obtained about 30 such cores from very
large colonies. These cores represent growth over
the last 200 to 600 years (shortest to longest cores).

Only one core has been analyzed in detail.
The core came from Pandora Reef and provided
information back to 1862. Pandora Reef lies inside
the Palm Islands, close to the mainland. Annual
density variations along this core showed a 60
percent correlation with atmospheric pressure at
Darwin from 1882 to the present (the extent of the
pressure record).

Whereas currently available models are
based on only several decades of conventionally
recorded weather and hydrological data, new
models resulting from our research will derive from
weather analogues in the form of bands in coral
cores that go back about 1,000 years. The goal is
to produce seasonal and other long-range
forecasts.

—Peter J. Isdale, AIMS

31

MAMNE

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A selection of papers

Roles of the oceans in the C02 question,

AJCRANE&PSLISS.

Oiled Magellanic penguins in Gulfo San

Jose, Argentina, J PERKINS.

Shell thickening in Crassostrea gigas:

organotin antifouling or sediment induced?

M J WALDOCK & J E THAIN.

Aerial flux of particulate hydrocarbons to

the Chesapeake Bay estuary, D B WEBBER.

A history of metal pollution in the Upper

Gulf of Thailand, M HUNGSPREUGS&

C YUANGTHONG.

Effects of metal on sea urchins

development — a rapid bioassay, H H LEE

&CHXU.

Comparative environmental chemistries of

metals and metalloids (viewpoint),

E D GOLDBERG.

Marine pollution research facilities in the

People's Republic of China (viewpoint),

DA WOLFE era/.

Estimates of oil concentrations in Aegean

waters (baseline), G P GABRIELIDES era/.

The influence of experimental sewage

pollution on the lagoon phytoplankton,

N FANUKO.

Reef-building coral skeletons as chemical

pollution (phosphorus) indicators,

RE DODGE era/.

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32

Soft Corals:
Chemistry and Ecology

by John C. Coll, and Paul W. Sammarco

Oot't corals (Coelenterata: Alcyonacea) are one of
the most important groups of animals on the Great
Barrier Reef. They are abundant over the 2,000
kilometers of this reef complex and are a most
diverse group, possessing hundreds of different
species. They occur as attached colonial organisms,
with each colony made up of thousands of
interconnected individual and identical polyps. They
vary widely in form from the soft and fleshy
members of the Xeniidae family to the very beautiful
but prickly members of the genus Dendronephthya,
and from the hard, leatherlike forms of the genus
Sinularia (S. dura) to other erect, tree-like forms of
the same genus (S. flexibilis) (Figures 1-4).

Soft corals produce natural compounds that
play important roles in their ecology — particularly in
their defense against predators, in competition for
space, and in reproduction. These secondary
compounds are novel in structure. The majority of
them belong to the chemical class called terpenes*,
and are responsible for the odors and distastefulness
of common plants and trees such as pines,
eucalyptus, sagebrush, and so on. These compounds
(and hence the organisms which produce them)
interest natural-products chemists because of their
potential application as pharmaceutical agents (for
example, antibiotics, antifungal agents, and
antitumoral agents).

These compounds appear to offer a distinct
adaptive advantage to the organisms that possess
them, helping them to survive in their natural
environment. In any community, particularly where
organisms are sessile (permanently attached to the
bottom), interactions between individuals can
become intense (Figure 5).

Toxicity As Protection Against Predation

In general, coral reefs possess many would-be
predators — fish, crustaceans, echinoderms, and so
on. Most common soft corals are fleshy in texture
and thus appear defenseless against predators.
Chemical analysis suggests that they are rich in
nutritionally important substances (such as protein,
fats, and carbohydrates) and could serve as a

* Any of certain types of organic compounds present in
essential oils of plants.

valuable food source to predators. Yet, recent
surveys show that the incidence of predation on this
group is low.

In contrast, hard corals constitute a major
food source for some common groups of reef fish:
parrotfish, starfish (crown-of-thorns), mollusks, and
crabs. Soft corals thus appear to possess defenses
not immediately obvious to the observer. Chemical
analyses have revealed high concentrations of
certain terpenoid compounds in many soft corals
that may serve as a defense mechanism.

Laboratory tests have been performed on the
mosquito-fish (Gambusia affinis) using aqueous
extracts of numerous soft corals collected over the
full range of the Great Barrier Reef. These tests show
that about 50 percent of the extracts are toxic. In
addition, the level of toxicity across families and
between species varies greatly, ranging from lethal to
harmless. Because toxicity does not seem to account
entirely for the very low levels of predation observed
in the field, other defenses are suspected.

Feeding Deterrence

Tests also were performed to determine whether
soft coral extracts possessed characteristics which
rendered them distasteful to fish. We impregnated
standard tropical fish food with soft coral extracts of
various concentrations and then tested them for
feeding deterrence in test fish. Almost 90 percent of
the samples possessing the highest amounts of
extract were found to deter from feeding. Even at
the lowest concentration, 55 percent of the samples
still elicited the same response — suggesting that
feeding deterrence is a common characteristic of soft
corals.

However, no easily definable link or positive
relationship was found between the incidence of
toxicity and that of feeding deterrence. Some very
unpalatable soft corals were shown to be harmless
while apparently palatable soft corals were lethal.
Thus, these characteristics, toxicity and feeding
deterrence, 1) probably evolved independently, 2)
may involve different sets of chemical compounds,
or 3) may represent adaptations that simply perform
different rather than dual functions in the organism.

33

Figure 1. The Xenia species is soft, like firm gelatin, with non-
retractile, fully exposed polyps. (All photos courtesy of John
Coll unless otherwise indicated.)

Figure 2. The colorful Dendronephthya species' polyps are
protected by small spicules composed of needle-like pieces
of calcium carbonate.

Predation

As mentioned previously, soft corals vary in structure
and form (morphology), particularly regarding
characteristics that protect either the polyps or the
colony as a whole from predation. Another type of
protection — toxicity — varies widely in both its
occurrence within species and its intensity. A
positive relationship has now been found between
the lack of physical defense characteristics and
toxicity to fish. Soft corals that bear physical defenses
against predators seem to be less likely to be toxic to
fish.

Soft corals, such as Sarcophyton can retract
their polyps completely inside the surface layer of
the colony (Figure 6), while the polyps of others,
such as Xenia and Cespitularia, are constantly
exposed (Figure 7). Another type of polyp and
colony defense involves small sharp calcium
carbonate spicules. These long, needle-like parts
often surround and protect the polyp-head in a
canopy-like fashion (Figure 8). In other colonies,
such as Sinularia dura, the spicules are tightly packed
throughout the body of the colony, and the polyps
can retract completely into a protected area. Other
species exhibit a combination of these
characteristics: Sinularia flexibilis possesses a heavily
spiculated base, devoid of polyps, but with soft
flexible branches into which polyps can completely
withdraw.

Neither these physical mechanisms nor
toxicity guarantees safety against predators. Some
specialized predators feed on highly toxic species of
soft corals. Examples of this type of coevolution may
also be found in the terrestrial environment. A
Chrysalina sp. beetle — immune to the effects of the
secondary compound hypericin — feeds largely on
the toxic fruit and leaves of Hypericum sp. This
opens up a food source to the species generally
unavailable to other predators. Mollusks are the
major group in the marine environment from which
several such predators have evolved. On the Great
Barrier Reef, the egg cowrie Ovula ovum feeds
almost exclusively on soft corals of the genus
Sarcophyton (Figure 9). This gastropod is capable of

transforming the highly toxic sarcophytoxide into a
less toxic compound without ill effects. A similar
example of predators modifying the toxins of their
prey may be found in other nudibranchs,* such as
Aplysia californica, which prey on algae.

Some predators even exploit the toxins of
their prey. Immune to the toxic molecules, they
store them in specialized glands in the outer surface
of their body. The aeolid nudibranch Phyllodesmium
longicirra selectively stores toxins from Sarcophyton
trocheliophorum in its cerata** but not in other parts
of its body. If predatory fish attack, the cerata may
be autotomized (voluntarily detached). In this way,
the predator is provided with an unpalatable if not
toxic sample of food. Similar examples may be found
in other nudibranchs, particularly Phyllidia.

Competition for Space

The use of chemicals is not limited to fending off
predators. They also are employed in competing for
living space with other species as well as with other
soft corals. Many sessile, colonial organisms on coral
reefs possess specialized mechanisms that allow
them to maintain and expand their living space, a
resource that can be limiting in a crowded
community. Hard corals possess elaborate
mechanisms, such as nematocysts or stinging cells on
their tentacles, to kill neighboring sessile organisms;
these long, specialized sweeper tentacles can extend
up to 15 centimeters — many times the length of the
polyp. Mesenterial filaments, digestive filaments that
extrude from the gut, are capable of extracoelenteric
digestion. Soft corals, on the other hand, possess
none of these apparatus and depend on other
adaptations, such as their chemical composition, to
maintain living space.

We hypothesized that the toxins present in
soft corals may help them compete for space, a
hypothesis supported by observations of retarded
growth and dead tissue in hard corals adjacent to

* Any mollusks of the order Nudibranchia.

** Long tubular projections on the backs of aeolid

nudibranchs.

34

Figure 3. Sinularia is an encrusting soft coral with hard tissue.
Common on the reef crest where wave action is intense, this
soft coral exhibits low relief profile.

toxic soft corals (Figure 10). Selecting several
common species of both soft and hard corals, we
performed manipulative relocation experiments,
demonstrating that this effect was indeed significant
and reproducible in the field. It first appeared that
soft corals were immune to the harmful effects of
hard corals, such as Pontes andrewsi and Pavona
cactus. A subsequent experiment, however, showed
that some soft corals do in fact suffer local mortality
from hard corals. Our most striking find was the
incidence of local mortality, tissue necrosis,* and
growth retardation in hard corals occurring without
contact. This is an example of allelopathy in the
marine environment — the influence of one living
organism on another due to secretion of toxic
substances.

To illustrate that the observed effect was
indeed caused by chemicals transmitted through the
water column from soft corals, a submersible water
sampling device was developed. It was selective for
organic molecules suspended or dissolved in
seawater. Compounds found in the water

* The pathologic death of living tissue in a plant or animal.

Figure 4. Sinularia flexibilis is one of the most common soft
corals found throughout the Indo-Pacific region especially in
areas with high currents.

surrounding one of the most toxic and most effective
allelopathic soft corals were identical to those within
the organism. To confirm that these toxins were
indeed the active allelopathic agents, pure crystalline
samples of chemicals from the soft corals were
dissolved in seawater and then tested in the
laboratory for potency. The pure compound killed
both Pontes andrewsi and Acropora formosa at
concentrations of less than or equal to 10 parts per
million.

Soft corals have other mechanisms that
protect them from the harmful effects of
scleractinian or hard corals. For example, some can
secrete a protective polysaccharide layer in areas
close to or in contact with the hard coral's tentacles
(Figure 1 1 ). This layer then allows soft corals to
overgrow living scleractinian tissue by providing a
base for colony attachment and expansion. Once
attachment is complete, movement across a living
scleractinian coral can occur through directional
growth. A good example of this is Nephthea brassica
moving across the plating scleractinian coral
Acropora hyacinthus.

Competition between soft corals also occurs

Predation

Defenses

Palatabilit
Morphology

Toxicity

Reproduction and growth

Sexual reproduction

External fertilization
- planktonic planulae

Figure 5. Summary of
ecological interactions in soft
corals that are chemically
mediated by secondary
compounds such as terpenes.

Specialists - coevolved predators

Phyllodesmlum longlclrra

Competition for space

External brooding
of planulae

35

for space. The same effects of local mortality and
tissue necrosis may be observed in the field, but at a
much lower frequency. Manipulative experiments
have confirmed that these effects are similarly
chemically mediated and are experimentally
reproducible in the field. Our experiments also
explained the apparent low frequency of
observations of these interactions in the field at any
one time. Upon contact with soft corals, localized
tissue necrosis occurs very rapidly, but within several
days an avoidance response occurs as the two
colonies bend away from each other. This is
followed by a somewhat slower but longer term
reaction whereby each colony moves away from the
other in a manner analogous to that in Nephthea
brassica. Soft corals can move and space themselves
in their environment, which helps them to decrease
the probability of contact with potential competitors.

Chemicals and Reproduction

Chemical ecology not only helps soft corals defend
themselves and their living space from others, but
also may play a role in reproduction. Although little
is known about the reproductive biology of the
Alcyonacea (soft corals), a number of interesting facts
have recently emerged. Soft corals are now known
to reproduce three ways: 1) externally fertilized eggs
are brooded on the surface of the soft coral, 2)
externally fertilized eggs develop planktonically in
the water column, and 3) asexual reproduction
occurs via colony growth and fragmentation. The last
of these includes production of stolons* and runners.

The concentration of major secondary
compounds in certain soft corals varies markedly
throughout their reproductive cycles. A recent study
covering the period immediately preceding and
subsequent to ovulation showed that certain toxic
metabolites increase markedly during the month
prior to ovulation. These same compounds also were
found in high concentrations in the eggs released
from the same colonies {Sinularia spp.) and were
virtually absent several months later after the peak
reproductive season.

Further insights into the complexity of the
terpenes' role in soft coral reproduction were
derived from the chemical composition of two
species of Lobophytum. In the case of L. compactum,
the story parallels that of Sinularia above, with one
compound found exclusively within the eggs of the
soft coral. In the other species, L. crassum, the major
terpene present in the soft coral was completely
absent in the eggs. Thus, the chemicals may possess
ecological functions that vary even between related
species.

* Stem-like structures from which new individuals within a
colony develop by budding.

Studies Under Way

Studies are presently under way to investigate three
possible roles these chemicals may play: 1) toxicity
or feeding deterrence in potential predators; 2)
chemotaxis — for these chemicals may play a role in
attracting sperm to the egg, and 3) accumulation of
the chemicals, acting as a stimulus, indicator, or
trigger for release of gametes.* At present, the
chemical ecology of soft corals is not fully
understood. Since 50 percent of the species possess
chemicals — in particular terpenes — that may be the
basis of important interactions both among
themselves and within the larger ecology of the
Great Barrier Reef, secondary compounds may be a
major contributing factor to the evolutionary success
and abundance of soft corals on the Great Barrier
Reef.

John C. Coll is a professor in the Department of Chemistry
and Biochemistry at lames Cook University in Townsville,
Australia. Paul W. Sammarco is a research scientist at the
Australian Institute of Marine Science, also in Townsville.

* A mature egg or sperm capable of participating in
fertilization.

Selected Readings

Bowden, B., J. C. Coll, D. Tapiolas, and R. Willis. 1985. Some

chemical aspects of spawing in alcyonacean corals. In: Proc. 5th
International Coral Reef Congress, Vol. 4, C. Gabrie and B. Salvat,
eds., Antenne Museum-Epha, Moorea, French Polynesia, pp.
325-329.

Brawley, S. H., and W. H. Adey. 1982. Coralliophila abbreviata: A
significant corallivore. Bull. Mar. 5c/., 32(2): 595-599.

Coll, J. C. 1981. Soft coral research at James Cook University of
North Queensland. Proc. 4th Asian Symp. Medicinal Plants and
Spices, Bangkok. UNESCO Spec. Publ., pp. 197-204.

Coll, J. C, B. F. Bowden, D. M. Tapiolas, R. H. Willis, P. Djura, M.
Streamer, and L. Trott. 1985. Studies of Australian soft corals —
XXXV. The terpenoid chemistry of soft corals and its
implications. Tetrahedron, 41(6): 1085-1092.

Coll, J. C, and P. W. Sammarco. 1983. Terpenoid toxins of soft
corals (Cnidaria: Octocorallia): Their nature, toxicity, and
ecological significance. Toxicon, Suppl. 3: 69-72.

Dinesen, Z. D. 1983. Patterns in the distribution of soft corals across
the central Great Barrier Reef. Coral Reefs, 1 : 229-236.

Jackson, J. B. C. 1977. Competition on marine hard substrata: The
adaptive significance of solitary and colonial strategies. Am. Nat.,
11 1(980): 743-767.

La Barre, S., and J. C. Coll. 1986. Movement in soft corals: An
interaction between Nephthea brassica (Coelenterata:
Octocorallia) and Acropora hyacinthus (Coelenterata:
Scleractinia). Mar. Biol. (Berlin), 72: 119-124.

La Barre, S., J. C. Coll, and P. W. Sammarco. 1986. Competitive
strategies of soft corals (Coelenterata: Octocorallia): III. Spacing
and aggressive interactions between alcyonaceans. Mar. Ecol.
Prog. Ser.

Muller, C. H. 1966. The role of chemical inhibition (allelopathy) in
vegetational composition. Bull. Torrey Bot. Club., 93: 332-351.

Sammarco, P. W., ). C. Coll, and S. C. La Barre. 1985. Competitive
strategies of soft corals (Coelenterata: Octocorallia): II. Variable
defensive response and susceptibility to scleractinian corals. /.
Exp. Mar. Biol. Ecol., 91: 199-215.

36

Figure 6. The Lobophytum species is commonly found on
reef crests and exhibits a colony form with low relief.

Figure 7. A species ofCespitularia exhibiting a soft flexible
body with polyps permanently exposed to potential
predators.

Figure 8. The tree-like Nephthea species has polyps that are
grouped at the ends of its branches; each polyp is protected
by micro-spicules.

Figure 9. The egg cowrie Ovula ovum can ingest and
assimilate some highly toxic soft corals without ill effects. The
shell is white, but when feeding, the mantle of the moilusk
covers the shell giving it a black appearance.

Figure 10. A large colony ofSinularia flexibilis releasing
chemicals into the surrounding water that can kill or inhibit
growth in the nearby hard coral Pavona cactus. (Photo
courtesy of Bette Willis.)

Figure 7 7. A colony of Nephthea brassica growing on live
Acropora hyacinthus. Note the dark brown cuticle secreted
by the soft coral. (Photo courtesy of Stephane LaBarre)

37

Sex on the Reef:

by Carden C. Wallace,
Russell C. Babcock,
Peter L Harrison,
James K. Oliver,
and Bette L Willis

/Vlany spawning events in the sea are linked to the
lunar cycle. Why then are recent discoveries on
coral spawning so remarkable? It's the scale — one
that is apparently unparalleled in the animal
kingdom.

At least one third of the 350 species of hard
corals occurring throughout the entire expanse of
the Great Barrier Reef concentrate their reproductive
activities for a year into the same few nights in late
spring or early summer. Eggs and sperm are released
en masse into the waters above the reefs, and the
next day slicks of eggs and developing embryos can
be seen on the sea surface.

It is a spectacle that can be observed by
divers, and its timing can be predicted from phases
of the moon. Its combination of brevity and
participation by so many species seems to be
unparalleled. Biologists are fascinated by an
occurrence that seems to defy ecological common
sense, for although it is advantageous for all the
individuals of one species in one place to spawn
together, thus ensuring that a large number of eggs
will be fertilized, spawning at the same time as many
other species would seemingly reduce the chances
of encountering the correct mate.

Textbook View

Many aspects of the massed spawning phenomenon
contradict previously-held notions of coral biology.
Until recently, all corals were thought to reproduce
throughout the year, and to release fully developed
larvae rather than eggs and sperm. This textbook
view of the way corals reproduce was based on a
few common coral species that could be observed
to spawn at any time of the year. Even for these, the
evidence was incomplete, but it seemed to indicate
that eggs were somehow fertilized while still inside
the parent polyp, and developed into larvae that
were brooded before being released. Such larvae
would not spend much time in the water before
settling to begin new coral colonies.

Some researchers, however, began to point
out that evidence for reproduction was lacking for
most corals. This resulted in the suggestion that

During spawning night, the sea surface becomes filled with
egg-sperm bundles. These soon break up, allowing
fertilization to occur.

A blizzard of egg-sperm bundles is created by the spawning
of Acropora tenuis just at dusk.

many corals rarely used sexual reproduction to
produce offspring — asexual reproduction being the
usual mode. Coral colonies develop by a process of
replication: a basic unit, the polyp, carries all the
features necessary for animal existence, and a colony
is formed by polyps dividing again and again while
maintaining tissue connections. This process is
regarded as growth. Coral colonies, however, can
sometimes be subdivided by breakage. The resulting
pieces can survive and exist independently. Thus, a
kind of reproduction without sex results in new coral
colonies. It was suggested that corals might typically
devote their energy resources to this type of
reproduction, sexual reproduction occurring only as
a rare event. The nagging fact remained, however,

38

Mass Spawning

of Corals

Red egg-sperm bundles lie beneath the tentacles of the hermaphroditic brain coral Platygyra sinensis, minutes before they will
be released. (All photos courtesy of authors).

that the natural history of corals had not really been
studied well enough to resolve this question.

Hints and Hypotheses

There were always hints of a major spawning event
for reef corals. Pink slicks appearing in the sea in late
spring or early summer were well known to
fishermen and coastal dwellers. Whenever such
slicks were investigated, they were found to be
composed of the alga Trichodesmium. Scientists
dismissed the possibility that they could ever be
composed of coral eggs. In Japan, however, certain
communities of coastal dwellers have observed for
many generations slicks of red eggs and larvae in the
sea during the days following spawning time. To
these folk it had a mythological significance as the
punitsu or "menstrual waters of the princess of the
dragon palace in the sea." Sadly, as Japan's coastal
reefs have diminished with encroaching
development, the punitsu has not appeared for some
years.

In the early 1970s, some reef ecologists
proposed that some modes of sexual reproduction

other than brooding of larvae must exist for corals,
and that spawning might be a regular, but brief,
event. Only by studying the natural history of
individual coral species could such a hypothesis be
tested. The challenge was quickly taken up by
workers at Heron Island, in the southern Great
Barrier Reef region. By combining field and
laboratory studies with great vigilance on the reef,
they were able to show that some corals do indeed
have an annual reproductive cycle and shed eggs
and sperm for external fertilization.

A Group Effort

Several post-graduate students at James Cook
University in Townsville independently began
research on the biology and ecology of various coral
species in 1979. Part of this research involved studies
of spawning in the corals. During 1 979 and 1 980,
evidence accumulated that most of the species had
annual reproductive cycles with ripe gonads
disappearing from the entire population in the
Austral spring. These initial results were tantalizing,
but despite intensive efforts, only one species was

39

observed to spawn, so we still knew nothing of the
degree of synchrony in spawning that existed for
these corals. In 1981, we decided to pool our time
and resources. We established a field camp at
Magnetic Island off Townsville so that we could
monitor the corals daily, both on the reef and in
aquaria.

The group effort was rewarded that year
when 14 species were recorded to spawn, after dark,
a few days after the full moon. Many of the species
spawned together on the same night. All released
eggs and sperm (gametes) into the water for external
fertilization, rather than expelling fully developed
larvae. This added further substantial evidence for
the recent suggestions of the Heron Island workers,
that the majority of coral species might not brood
larvae. One month later, we observed a second
spawning episode, at the same interval past full
moon, and after this no corals on the reef could be
found to contain ripe gametes.

We realized that we had happened on an
occurrence of great significance, and from that year
onwards our research efforts have concentrated on
exploring the events occurring in this narrow
window of time in late spring. We now believe that
this reproductive mechanism is used by the majority
of the corals on the Great Barrier Reef.

The Sexual Organs

Corals exist as colonies, not in the sense of
communities of individuals living together, but as
interconnected units (the polyps), each containing
the same organs. There is a mouth surrounded by
tentacles for food capture and defense, and a
cylindrical gut cavity divided by fleshy partitions
called mesenteries, which function as organs of
digestion. During part of the year this is the
mesenteries only role, but for some months they
contain the developing sexual organs (gonads). The
structure of the gonads and the type of sexuality of
the polyps varies with species. Many corals are
hermaphroditic, both female and male cells
developing in each polyp of the colony. Some
species have separate sexes (the gonochoric
condition). In this case, colonies have either all
female or all male polyps. Female gonads develop as
strings of eggs in the mesenteries, males as carrot-
shaped or rounded bundles in which sperm are
produced. In some hermaphroditic corals, eggs and
sperm develop in a single organ, but more
commonly testes and ovaries are separate,
developing in different mesenteries, or different
parts of the same mesenteries.

Development of eggs and sperm is called
gametogenesis, and for corals participating in the
massed spawning event this begins some time early
in the year. By early spring, large white eggs and
developing testes can be seen in the polyps. As the
waters around the reef become warmer, the eggs
become colored: usually pink or red, but sometimes
orange, purple, or green.

Onset of Spawning

We believe that spawning occurs in response to a
series of cues which operate on increasingly fine

time scales. Once the seawater temperatures have
climbed from winter low levels and gametes are
mature, the corals will spawn after the next full
moon. Sometimes when full moon occurs early with
respect to rising sea temperatures, some corals will
not be ready for spawning, and a "split spawning,"
such as that we saw in 1981, will occur. We know
that temperature is important, because corals
occurring inshore, where the sea water warms
earlier, spawn one month before those offshore.

Spawning "events" are spread over the third
to sixth nights after full moon. Lunar/tidal cycles
determine the date of spawning, which occurs
during the period of least difference between
successive high and low tides. This is a period of
very low water exchange over the reef and probably
is important to the spawning corals as a time during
which the high concentration of eggs and sperm
necessary for good fertilization rates is maintained
for the longest time possible. A period of darkness
must pass before the corals will release. We know
this because corals kept under artificial lighting delay
their spawning until an equivalent time after the
lights are switched off. Each species seems to have a
characteristic time during the evening when it
spawns, although many of these times overlap.
Nocturnal spawning is extremely important for corals
since the eggs and larvae are readily eaten by the
clouds of planktivorous fish which inhabit the reef
during the day.

What Does It Look Like?

Many people have now observed the mass spawning
event, and its features are becoming well known.
Shortly before releasing their reproductive products,
the polyps in the corals can be seen "setting." The
area around the polyp-mouth becomes distended by
the presence of eggs and sperm, which have been
gathered within the polyp, most often into a
compact ball. Since coral tissues are semi-
transparent, the brightly colored gamete ball can be
seen within the swelling. The coral can remain in this
setting state for about an hour. Then, suddenly in
some cases, rapidly in others, the bundle is pushed
through the polyp-mouth and released. Gamete
bundles begin to stream upward from the colony, to
join those released from other colonies nearby. In
corals with separate sexes, clouds of eggs or sperm
are released.

Development in the Sea

Shortly after reaching the surface of the sea, the egg-
sperm bundles break up. Sperm stream away from
the bundle and toward other eggs, which they may
penetrate and fertilize. Following fertilization, the
egg begins to develop until a free-swimming larva
(the planula) is formed. This drifts without feeding
until it is mature enough to settle, usually about 4 to
10 days after the spawning night. Then it descends
toward the hard reef surface, where it settles and
begins to take on the appearance of a coral polyp.
As the polyp is developing a mouth, tentacles, gut,
and mesenteries, it also is secreting a skeleton, in
which it sits. Then through a process of budding new

40

Coral Genetics: New Directions

It

he planula larva has been traditionally accepted as
the result of sexual reproduction in corals. Settlement
by planulae has been considered a diversifying force
within populations that balanced diversity-reducing,
asexual modes of reproduction, such as skeletal
fragmentation and tissue dissociation (see page 28). It
also has been considered to be a cohesive force
providing gene flow between geographically separate
populations.

Coral populations once were viewed as
heterogeneous, outbred aggregations recruited from a
diverse larval stock representing the output of many
reefs. Ecological and evolutionary models of corals
have been constructed using this assumption.
Recently, important exceptions to this view have
emerged, and the assumptions on how planulae are
produced are being tested.

Early studies of coral reproduction focused on
species that brooded their young. Brooded planulae
are pervasive reproductive features because of their
size, and the regularity and frequency of their
appearance. The temporal coincidence of sperm,
eggs, and planulae in the tissues of individual corals
convinced workers that the planulae were produced
sexually. However, embryogenesis was never
documented, and studies examining mechanisms by
which parental genes were passed to offspring were
deferred.

When research turned to genetic studies —
using electrophoretic techniques to examine the
enzymatic proteins, and thereby assign a genetic
basis — the results were surprising. When the analysis
was first applied to parent-offspring sets from the
common Indo-Pacific brown coral, Pocillopora
damicornis, the genetic modelling showed that the
probability that a meiotic process had occurred was
about I to 20 billion. These planulae were produced
asexually! Other populations of P. damicornis showed
the same pattern. Similar results have been
demonstrated for Tubastrea coccinea and T.

diaphana, two "daisy corals." (In the species of coral
that retain the ability to produce brooded planulae
sexually, the genetic analyses conform with
expectations of meiosis).

The genetic structure within populations of P.
damicornis suggests that, while most recruitment
originates from locally-produced asexual propagules, a
complementary production of sexually-produced
planulae also occurs. On the broad scale, the species
conforms to the evolutionary theories that predict
asexual propagules will settle close to their parent,
maximizing their chances of occupying an
environment in which their genotype has already
proven successful, and that the sexual propagules will
be more widely dispersed — encountering novel
environments.

The asexual production of planulae allows
each coral head to produce thousands of clonal
propagules. Localized propagation by fragmentation,
on the other hand, restricts each head to a few
effective propagules, and also implies a significant
chance of mortality to the parent. The ability to
produce these larger numbers of propagules of a
locally successful genotype confers an advantage to
corals subject to severe periodic mortalities caused
either by physical or biotic agents.

Techniques that examine in detail the genetic
structure of coral populations have wide application.
For example, studies will further our understanding of
the role reproductive tactics play in shaping the
complex evolutionary patterns of corals. Coupling
these tactics to the peculiar evolutionary patterns of
these modular organisms is central to interpreting the
ecological significance of coral life history data. Future
research must seek evolutionary paradigms more
appropriate to corals, rather than those drawn from
theories developed for organisms with population
structures in which individuals may be clearly defined.
— James A. Stoddart, AIMS

polyps, the change from single polyp to coral colony
is made.

As a consequence of mass spawning, most
new corals are recruited into reef communities at
about the same time every year. They grow very
slowly in the first year of life, being just visible to the
naked eye at about 8 months old. Between 3 and 6
years old, most are ready to begin the process of
sexual reproduction again. Coral colonies may live
for many decades, even centuries, and continue to
reproduce once a year.

Significance of Mass Spawning

Scientists and those concerned with preserving and
managing the Great Barrier Reef puzzle over the
degree to which reefs might be interdependent. The

prevailing view in the past was that the reefs of the
Great Barrier Reef were mainly self-seeded. In this
view, occasional larvae might be dispersed more
widely to colonize other reefs, but most new corals
on each reef are the offspring of local corals. Such a
situation might prevail if all or most corals brooded
larvae, which were ready to settle soon after release.
Now that we know most corals release buoyant
gametes and that development of larvae takes
several days, we favor the opposite view, that coral
larvae are most likely to be dispersed away from the
parent reef, and new corals on a reef must come
mainly from other reefs. Thus, each reef is
dependent on other reefs and on inter-reef waters
for its continued supply of new coral generations.
This has significant implications for the management

41

of the Great Barrier Reef Marine Park, since it
suggests that all reefs are functionally
interconnected, and individual reefs cannot be
managed in isolation.*

Why Multispecific Spawning?

Synchronized spawning by one species accrues
advantages in maximizing chances of fertilization and
avoiding wastage of gametes. There also are some
disadvantages, such as the possibility of complete
reproductive failure because of events on the
chosen night — for example, a rainstorm can kill the
eggs. When multispecific spawning occurs, many
eggs and sperm of different species, even of very
close relatives, are present in the water at the same
time. This might be expected to have a number of
accompanying problems, such as wastage of
gametes, the risk of hybridization, and competition
for settling sites when larvae settle a few days later.
Some powerful advantage must override these
difficulties.

What are the advantages of synchronized
multispecific spawning? In truth — we don't yet
know. We have, however, suggested two alternative
hypotheses. The first is that by spawning at the same
time as other corals, each species will reduce the
chances of its offspring being lost to predators.
Second, there may be a unique combination of
ecological and physiological factors that all the
participating corals require, and which occurs only
once a year. We are presently exploring both of
these avenues.

Geographic Extent of Mass Spawning

Corals in some areas, such as the Red Sea, the
Caribbean, and possibly Hawaii, do not seem to
exhibit mass spawning. There is evidence, however,
that areas other than the Great Barrier Reef do. We
have mentioned Japan; mass spawning also has
recently been observed in western Australia, Fiji, and
Vanuatu. By comparing time^of the year, lunar
phases, prevailing temperatures, and tides during
spawning at other locations with those on the Great
Barrier Reef, we should get further clues about the
factors that are important for the timing of the event.
By looking at differences between places with
and without mass spawning, we might gain insight
into how the phenomenon came to be. Many other
reef organisms may be mass spawners, and indeed
some other animals, such as soft corals and certain
polychaete worms, spawn at the same time as corals.
It seems the extent and significance of this event will
keep us and other biologists interested for many
years to come.

Garden C. Wallace is at the Bureau of Flora and Fauna in
Canberra. Russell C. Babcock, Peter L. Harrison, lames K.
Oliver, and Bette L. Willis are researchers at lames Cook
University, Townsville Australia.

* The question of the degree of interconnectedness of reef
coral populations is not yet answered, however, as results
of settlement experiments by P. W. Sammarco can be
interpreted as suggesting the opposite view, and indicating
only a limited dispersal away from reefs. Both research
groups plan to resolve this important problem.

Some polyps are "setting," some have released bundles, and
some are in the process of releasing in this colony of
Montastrea sp.

Fhe staghorn coral, Acropora formosa, is festooned with red
egg-sperm bundles just before they are released. This species
may have red, white, or pink eggs.

Letter Writers

The editor welcomes letters that comment on arti-
cles in this issue or that discuss other matters of
importance to the marine community.

Early responses to articles have the best chance of
being published. Please be concise and have your
letter double-spaced for easier reading and editing.

42

Historical Perspectives
on Algae and Reefs:

Have Reefs Been Misnamed?

by Llewellya Hillis-Colinvaux

Kain forests and coral reefs — the two most
productive, most species rich ecosystems of our
planet — are striking features of tropical latitudes.
Although vegetation is unmistakably the dominant
feature of the forest, plants seem almost absent from
the visual panorama of the reef. The stony and horny
edifices produced by the corals, and the many
colorful fish, blind the eye to traditional plant forms,
while other photosynthetic organisms are hidden in
the reef structure. The image of plantlessness, or else
of limited vegetation is induced, too, by the name:
coral reef. So the casual visitor and the armchair
reader, with good reason, are encouraged to regard
the reef as animal-based, and animal-created. Yet,
plants and photosynthesis are as much the basis of
the coral reef system as of the forest. Tropical reefs

could not exist were it not for a very large
photosynthetic component.

The Coral Reef Paradox

The coral structure characterizing tropical reef
systems is the skeletal frame of invertebrate animals
called cnidarians (the phylum containing jellyfish, sea
anemones, and corals). Naturalists, such as John Ray,
classified them as plants because of their vegetative
appearance. In the 18th century, Jean A. Peyssonnel
and John Ellis, the latter using a microscope he had
modified for aquatic work, discovered that animal

Above, an algal ridge. The framework in this region of strong
wave action is predominantly calcareous red algae. (Photo
from Enewetak Atoll)

43

polyps were part of many calcareous reef organisms,
and concluded they were animals. These tiny tube-
shaped animals, attached so as to produce massive
carbonate structures of many different shapes,
confirm their animal nature by filtering planktonic
food, using their crown of tentacles. The reef, as
viewed from a ship, distant shore, or by wading in
the shallows — essentially the only methods for reef
study in the 18th and 19th centuries apart from
dredging — would provide the same vast expanse of
life that a tropical forest does from the air. However,
from their vantage point, the "dominant" component
of a tropical reef was an animal! Consideration of the
reef as an ecosystem, and questions about the
energy support of the coral mass in a system where
plant numbers seemed low — the paradox of the
reef — had to await development of the field of
ecology and the research tools of the mid-20th
century.

Discoveries at Funafuti

In the 19th century, with the foundation laid of basic
knowledge about coral reefs, and ships of
exploration to traverse oceans, Charles Darwin was
able to take up one of the grand basic questions of
science: the origin of coral reefs. He also envisoned
a grand experiment to test his hypothesis of their
origin — a long core extending through the carbonate
of the reef, to its base.

It was close to the end of the century,
however, before the first long cores were obtained
from a reef in a project involving the British Royal
Society and the Australian province of New South
Wales. The site was Funafuti Atoll in the Ellice
Islands (1,800 nautical miles northeast of the Great
Barrier Reef) of the South Pacific. Although the first
hole had to be abandoned after about 25 meters of
drilling, two long cores were taken, the longest
penetrating 339 meters into the reef. It was a
spectacular achievement even though the base of
the reef was not reached. Nor was this goal attained
until the coring of Enewetak Atoll in the Marshall
Islands in the 1950s (2,000 nautical miles north-
northeast of the Great Barrier Reef).

The results from the analysis of the Funafuti
cores are an important benchmark in the study of
tropical reefs for they demonstrated that reefs are
built of organisms other than cnidarians. When the
Funafuti team ranked the reef organisms according
to their contribution of bulk during reef
development, they assigned corals to fourth place,
and foraminifera to third. Plants, represented by
calcareous red and green algae with Halimeda the
principal representative of the latter, were tied for
first place. They had, for example, discovered in the
core taken through the lagoon that 80 to 90 percent
of the material in the first 18 meters below the
lagoon floor was Halimeda debris. In the final
ranking, however, calcareous red algae, also known
as corallines, were listed first, because their greater
visibility to earth-bound scientists was equated with
greater importance.

Calcareous Algae

About 100 genera, or somewhat less than 10 percent
of the algal species calcify. Most calcareous algae

belong to the phyla Rhodophyta (red algae, -15
percent) and Chlorophyta (green algae, —10
percent). Among the Phaeophyta (brown algae) only
the genus Padina calcifies. Although now
unequivocably considered plants, for more than a
century the plant nature of a number of these genera
was controversial. Ellis, in his classic study of
calcareous organisms called "Corallines," then
defined as calcareous and horny sea organisms
(1 755), included calcareous algae along with corals.
He made brilliant microscopical studies of the
internal anatomy of some of the algae and observed
what he considered might prove to be "orifices for
polype-like suckers" when "magnifying glasses have
been improved." He also demonstrated by a public
chemical experiment that burning corallines smelled
not "like burnt vegetables," but had the "offensive
smell like that of burnt bones, or hair," so much so
that the door of the room "was obliged to be
opened, to dissipate the disagreeable scent and let in
fresh air." These investigations, outstanding for the
time, led him to conclude that organisms such as
Halimeda were animals, just as were the cnidarians
for which he had demonstrated an animal nature by
discovering polyps.

Such problems, however, were history by the
end of the 19th century. Perhaps the finest general
tropical algal collections of the first half of this
century were made during the Siboga Expedition.
The results, recorded in outstanding monographs,
have had an important influence on subsequent reef
botany, including studies of calcareous algae. The
"Lithothamnion ridge," a framework of
predominantly calcareous red algal construction, was
a prominent feature of reefs visited by the Siboga,
and undoubtedly contributed to the ready and
continuing acceptance of calcareous red algae as
major contributors to reef structure.

Prominent Lithothamnion ridge algae include
Neogoniolithon, Porolithon, and Lithophyllum, but
not the genus Lithothamnion. Hence the name of
this reef feature has been changed in recent years to
"algal ridge" to reflect more accurately its nature. But
whatever the taxonomy, the presence of these algae
at this very critical site, where the intense force of
the ocean regularly charges against the reef, serve in
the buttressing of the land, or in other words, the
providing of "reef." The ridge is most extensive in
reefs where the wave force is intense; there the
calcareous red algae, but not the corals, grow
successfully, and, in so doing, they secure the reef
environment for other reef organisms, including
corals.

In contrast, the discovery of the importance of
calcareous green algae in the tropical reef system of
Funafuti generally has been overlooked, especially
by biologists. The apparent fragility and
inconspicuousness of these algae when compared to
the massive and exposed algal ridge forms,
undoubtedly has contributed to this oversight.
However, with underwater exploration made
possible by skin and scuba diving techniques, and
especially submersibles, we have become
increasingly aware of extensive populations of green
algae, such as the Halimeda meadows of the Great

44

Barrier Reef and the wall populations of the deep
fore-reef of Enewetak Atoll.

Three genera — Halimeda, Penicillus, and
Tydemania — are of special interest in modern reef
structure, but Halimeda, a genus resembling a
cactus, is the only one of global importance.
Penicillus, the merman's shaving brush, is an
important sand former in the Caribbean; Tydemania,
which most commonly appears like a long string of
spherical brushes, may have a similar role in Indo-
Pacific reefs. All the calcareous green algae, with one
exception, are tropical or subtropical, but some
calcareous red algae also form massive calcareous
banks in subpolar waters.

New Perspectives on Halimeda

Halimeda has generally been characterized as a plant
of sand substrata, growing most prolifically in fairly
shallow lagoonal environments. Some species do
indeed grow in sand, where they are fixed by a large
holdfast, usually of one to several centimeters in
length. Halimeda incrassata is the classic example.
However, three quarters of the taxa have very
different habitats and growth forms. Several species,
attached by a single, small holdfast, usually 1
centimeter long or less, grow or hang from rock
surfaces that themselves may be buried under sand.
A third group of species sprawl across rock, sand, or
coarse algal and coral debris. Attachment is by
thread-like filaments produced at intervals along the
plant. Since most other algae are restricted to one of
these substrata, the ability of Halimeda to grow on a
very wide range is notable. This capability
undoubtedly contributes to the considerable success
of the alga in tropical reefs.

These different substrata are not restricted to
lagoons or back reefs. Just as they occur across the
entire reef system, so Halimeda appears able to
colonize successfully most zones of the reef,
including the region of spurs and grooves. Notable
exceptions are the very high energy algal ridges
where calcareous red algae flourish, and the region
of breaking waves.

There are three general regions, however,
where Halimeda populations may be exceptionally
large: the sands and pinnacles of the back reef or
lagoon, the H. opuntia zone behind the algal ridge,
and the fore-reef. In the first region, extensive
meadows of Halimeda grow over some of the flatter
areas while dense hangings or draperies are
associated with the more vertical surfaces of
bommies (large heads of coral), pinnacles, or patch
reefs. Shallow flat tops also may have sizeable
populations of the genus. All three categories of
species can occur, and members of the "rock"
growing group sometimes seem surprisingly
common on what would be casually classified as a
sandy environment. When extracted carefully,
however, they generally are found to be attached to
a small piece of rock.

The H. opuntia zone occurs where strong
currents flow over very shallow rock surfaces behind
the algal ridge, or the breaker zone if the ridge is not
present. Compact cushions, generally of H. opuntia,
frequently develop a three-dimensional cover so

Halimeda — The Sand
Producing Alga

Ideological studies in coral reef regions usually
mention Halimeda flakes, often as an important
component of the sediments. These flakes are in
fact the individual segments of a relatively small
and often cryptic green alga. Their preservation is
due to the large amounts of calcium carbonate
deposited internally as dense masses of
interlocking needle-like crystals of aragonite.
When the organic tissues decompose, the
calcium carbonate retains the shape of the
segments, often in sufficient detail to permit
identification of the fragments to species.

To contribute significantly to coral reef
sediments, Halimeda also must be productive. It
grows by producing discrete new segments at
branch tips and a complete but uncalcified
segment can be produced in a single night. This
initially consists of a flattened, white mass of
filaments, but as soon as chlorophyll has been
formed the next morning, and an outer layer of
swollen filament tips, the primary utricles, has
sealed the surface, calcium carbonate deposition
within the segment begins.

On reefs, only about 1 percent of the branches
grow actively, but as they may produce a new
segment every three to four days, production of
organic matter and accompanying calcification is
substantial. In the central Great Barrier Reef
(GBR), biomass of Halimeda vegetation can
double in 15 days with, on average, 7 grams dry
weight being produced per day per square meter
of solid substratum.

In the main species involved on these reefs, W
percent or less of this will be organic matter, the
rest calcium carbonate. It can be calculated that
a reef lagoon could accumulate 13 centimeters of
Halimeda flakes over 1,000 years.

—Edward A. Drew (AIMS)

dense that most other large organisms are excluded.
The morphologically distinct, tightly branched form
of the plants appears to be the parallel of the
compacted form of calcareous red algae growing in
highly turbulent waters.

The third region, the fore-reef, has
traditionally not been considered a habitat where
substantial populations of Halimeda would grow.
Recently, however, investigators using small
submersibles have discovered sizeable populations
on the fore-reefs of Pacific and Atlantic reefs. The
Enewetak Atoll project is the only one in which
some of the transects concentrated on this particular
genus. Halimeda populations were found to cover 10
to 50 percent or more of the atoll slope down to
greater than 1 10 meters, with at least a third of the

45

A sprawling species of Halimeda. Each unit, or segment,
follows another, as if strung on a thread. (Photo courtesy of
D.L. Meyer)

species growing to more than 90 meters. Sizeable
populations of Halimeda as well as calcareous red
algae also grew considerably deeper than
hermatypic corals, which at 90 meters were
estimated as covering less than 1 percent of the
region.

These data also have been important in
changing our concept of the vertical range over
which Halimeda can develop substantial
populations. Although the genus does not grow as
deeply as some calcareous red algae that extend to
268 meters, Halimeda was observed to 140 meters at
Enewetak, and to 150 meters in the Bahamas. For
the clear fore-reef waters of Enewetak Atoll, photon
flux densities at 140 and 150 meters were calculated
as 0.08 percent and 0.05 percent surface irradiance.
Growth therefore continues considerably deeper
than the 1 percent light level, or lower limit, of the
euphotic zone.

Impact of Calcareous Algae

The 1980s picture of calcareous algal distribution in
tropical reef systems provides a range for Halimeda
that is considerably more extensive, both
horizontally and vertically, than that of hermatypic
(reef-building) corals. Populations of at least two
other calcareous green algae also may be substantial
in some geographical regions. The genus Penicillus
produces extensive meadows in the Caribbean, and
may have a greater distribution in the Great Barrier
Reef than presently known. Tydemania also may
prove to be more widely dispersed in the Indo-
Pacific. This alga, once considered a rare "deep-
growing" plant was found growing abundantly in the
shallows of Indonesian reefs in the 1960s. It later was
discovered to be relatively common at 8 meters and
deeper in the lagoon of Enewetak Atoll.

The area of world reef occupied by sizeable
populations of calcareous green algae of the lagoon
and fore-reef, and calcareous red algae of the algal
ridge and fore-reef, can be very large. To understand
the reef building process and the functioning of the
reef ecosystem it is necessary to consider the
contributions of algae, especially calcareous species,

A sand-growing species of Halimeda. Whitish, dead,
segments about to be shed can be seen on the large tagged
plant in the center foreground. The fallen Halimeda
segments make up a large portion of the substratum. Since
Halimeda also provides a habitat, parts of the plants are
overgrown by other reef organisms. (The diameter of the
reference tag is about 2.5 centimeters) (Photo from Enewetak
Atoll)

to the carbonate and organic carbon budgets of
tropical reefs.

Primary Productivity

Primary productivity of the ocean historically has
been associated with phytoplankton. Although the
importance of these small organisms to open ocean
production of organic carbon is indisputable, in
tropical reef systems fleshy and calcareous
macroalgae, seagrasses, and zooxanthellae — the
dinoflagellate symbionts of corals and foraminifera —
are key participants in organic carbon production.
Since primary production is, in effect, the engine that
drives the entire reef system, awareness of the
potential of the macroalgal contribution is a prologue
to understanding reef ecosystems.

Primary productivity data for specific taxa are
very limited and often cannot meaningfully be
compared because of the different methods used, or
because there is too little information about the
quantity of biomass involved. Baseline net
productivity values for calcareous red algae on
Hawaiian reefs of 0.6-5.7 grams of carbon per
square meter per day, and for sand-growing
Halimeda of 2.3 grams of carbon per square meter
per day (conservative) indicate that contributions to
the organic carbon pool of the reef system by
sizeable populations of at least some species of
calcareous algae are far from negligible. A
perspective on this contribution is obtained by
comparing these net productivity values with those
for Nova Scotian kelps and tropical seagrass beds
which are of the order of 4.8 and 3.8 to 5.8 grams of
carbon per square meter per day, respectively.
Values for some of the least productive regions of
the oceans are of the order of 0.01 to 0.05 grams of
carbon per square meter per day.

Carbonate Productivity

The major contribution of calcareous algae,
however, is to the physical system of the reef itself,

46

Colonies of a sprawling species of Halimeda growing on the
fore-reef wall at a depth of about 100 meters. Size of the
colony in the center is about 0.6 by I meter. (Photo is from
Enewetak Atoll)

by the deposition of calcium carbonate. Red algae
provide framework and sand, and by their growth
promote the consolidation and cementing of algal
and coral frameworks. Segments, or growth units, of
Halimeda, discarded as part of the life history
strategy of this alga, add fill to lagoons and reef
framework, and produce extensive Halimeda banks
or bioherms. Finer materials from Halimeda and
other calcareous green algae produce sands and
muds.

Other researchers have underscored the
importance of loose carbonate sediments in reef
building, estimating that 4 to 5 times more loose
sediment is produced than is incorporated as reef
framework. The Funafuti borings implicated
Halimeda. The recent discoveries of large
populations of this alga in the lagoon and the deep
fore-reef, together with cores taken from lagoons
where the Halimeda contribution is likely to be large,
further implicate Halimeda as a major sediment
producer.

The extent of the contribution cannot be
assessed, however, without knowledge of the rate at
which sediments are produced. For this, we need to
know the rate of growth of the alga, and the size of
the contributing population. The first indication of
the rate of growth of Halimeda was an opportunistic
observation at Funafuti. A branch of Halimeda was
observed growing through a hole in a submerged
board of wood on the reefs. It was more than 60
years later before the next observations were made
by transplanting sand-growing species from
Caribbean reefs to aquaria, and the production and
loss of segments recorded regularly. Growth involves
the development of new segments (the primal
sediment material) as well as the loss of old segments
from the living plant, shed somewhat like leaves
from deciduous trees. Segments also are contributed
by the death of the plant itself. From such laboratory
work, as well as from field studies of growth and
population density, and the analysis of core samples,
baseline data on rates of vertical accretion have been
calculated. Most of the values lie between the
conservative figure of 0.5 centimeters per 1,000

A Halimeda meadow with mounds of sand created by
Callianassa shrimp, at a depth of 20 meters.

t*-

Two segments of a Halimeda with the calcium carbonate
removed, showing the filamentous construction of the
segments. Crystals of calcium carbonate develop in the
spaces between the filaments. Note the central medullary
filament, from which the others branch. The width of the
lower segment is about 0.5 centimeter. (Photo by Tom
Goreau)

years for a dense cover, by sand growing species, to
14 centimeters per 1,000 years for the very dense
covers provided by sprawling species in certain
regions of the Great Barrier Reef.

The extent to which Halimeda actually covers
reef surfaces with dead calcareous segments is
especially sensitive to the density of the population
and certain environmental conditions, such as
nutrient enrichment. A very few species generally
appear to provide the bulk of the sediments. The

47

accretion rates clearly demonstrate that Halimeda
produces significant quantities of sediments annually
in the Great Barrier Reef and in many other reef
systems. The Great Barrier Reef represents a sizeable
proportion of the world tropical reef area, however,
and so contributions of Halimeda to this one reef
system alone are a significant statement of this alga's
importance in the entire tropical reef system.

The role of calcareous green algae perhaps
can be best appreciated by considering the reef
ecosystem to be composed of two subsystems, the
reef ridges and the lagoonal or non-rigid framework
regions. Accordingly, the ultimate origin of the reef
mass depends on the relative rates of accretion by
the calcifiers of the two compartments. Where
lagoonal regions are large, as in some atolls and the
Great Barrier Reef, they may contribute most to the
mass of the reef. The lagoonal area has only to be
four to five times that of the reef ridges for its total
contribution to be the larger. Skeletal materials from
the calcareous algal populations of the fore reef
would mostly be contributed to the ridge system
where they are growing, as sand or framework,
unless moved into deeper water or carried away
from the reef system.

The evidence from the boring of the Funafuti
lagoon — that Halimeda and calcareous red algae are
major contributors to reef structure — has been
amplified in the past three decades by a series of
studies in the Great Barrier Reef, Enewetak, and the
Caribbean. Although the contribution by hermatypic
corals to the reef is important, as well as very
obvious, it is now possible to see the process of reef
building as more than the construction of coral
framework. The combined contribution of
calcareous green and red algae may account for
more than half the accretion of carbonates in some
of the world's reef systems. The recent discovery of
extensive Halimeda bioherms in the northern part of
the Great Barrier Reef emphasizes the need for
renewed attention to the nonframework portions of
tropical reefs.

"Coral" Reefs Reconsidered

Now well into the 1980s, we have accumulated and
refined our knowledge about coral reefs for more
than two centuries. What once appeared to be
predominantly an animal system and so was
appropriately named "coral" reef, is now
understood, by the solving of the paradox of the
coral reef, to be a system in which plant biomass
predominates just as in the similarly productive and
species-rich tropical rain forests.

Coral reefs are plant systems, and algae are
essential to the survival of the reef system in ways
beyond the accepted photosynthetic role. Not only
does the dinoflagellate symbiont of corals promote
calcification of its cnidarian host and consequently
make coral framework possible, but calcareous
plants are important contributors of reef framework
and sand.

The name "coral" reef, used to describe a
certain association of animals before there was an
understanding of communities or ecosystems, has
been outgrown. Just as the name "Lithothamnion

ridge" has been changed successfully in recent years,
it is perhaps time to exchange the epithet "coral" for
a more suitable one. Names such as "tropical" and
"biotic" have been introduced into the literature but
have a restricted following. Neither is as misleading
to scientist and nonscientist alike as the present one,
and yet neither indicates the reef's basic nature. A
more appropriate name is "algal" reef.

Llewellya Hillis-Colinvaux is Science Scholar at the Bunting
Institute, Radcliffe College, and Farlow Herbarium, Harvard
University. She is currently on leave from the Zoology
Department, The Ohio State University.

Selected References

Hillis-Colinvaux, Llewellya. 1980. Ecology and taxonomy of

Halimeda: primary producer of coral reefs. Advances in Marine

Biology 17: 1-327.
Odum, H. T., and E. P. Odum. 1955. Trophic structure and

productivity of a windward coral reef community on Enewetak

Atoll. Ecological Monographs 25: 291-320.
Proceedings of the Fifth International Coral Reef Congress, Tahiti,

1985.

48

Reef Algae

by Michael A. Borowitzka,
and Anthony W. D. Larkum

/xlgae may not be the most obvious members of
coral reef ecosystems, but they are a vital
component. They not only provide nearly all the
organic material for the other reef organisms, but
their calcification activities are essential to the
formation of the reefs. Figure 1 shows the general
distribution of algal species across part of One Tree
Reef. Each reef habitat has its distinct algal flora, as
well as its distinct fauna. In this article, we refer to
the algae of One Tree Reef, but the species and
habitats are common to most other offshore reefs
in the Great Barrier Reef region.

Distribution

The upper reef slope is dominated by encrusting
coralline algae, such as Paragoniolithon conicum on
the exposed (windward) side of reefs, and
Porolithon onkodes on the more sheltered reefs.
The deeper reef slopes are usually coral dominated
with many cryptic fleshy algae as well as turf algae.
In deeper waters, larger fleshy algae also may be
found.

The reef crest of One Tree Island consists of
an extensive layer of the crustose coralline alga
Porolithon onkodes, which may be overgrown by
mat-forming algae, such as Laurencia sp. and
Caulerpa racemosa. Unlike most central Pacific and
Caribbean reefs, the reefs of the Great Barrier Reef
(GBR) do not have a raised algal ridge of P. onkodes
(sometimes called a Lithothamnion ridge). This
absence of a distinct raised ridge is presumed to be
the result of the high tidal range and the periodic
absence of ocean swells in the GBR region, which
leave the reef crest exposed for long periods.

Inshore of the Porolithon zone is a region
consisting usually of extensive rubble deposits that
are fully exposed at low tide. Except for shallow
pools where algae, such as Yamadaella coenomyce
and Caulerpa sp. grow, there is little algal growth
other than various blue-green algae that grow
within the limestone rubble giving it a characteristic
black-green color.

Behind this rubble crest is the outer reef flat,
which is largely exposed at lagoon low water and
consists of small, 5 to 50-centimeter high, coral
lumps interspersed by sand patches. This zone
progrades into the deeper inner reef flat with larger
coral bommies.* The algal flora in this region is very

* Large coral masses rising from the lagoon floor up to 20
meters high.

diverse and consists of many "turf" algae (Figure 1)
as well as the very conspicuous Chlorodesmis, and
fleshier algae, such as Caulerpa spp., Padina,
Dictyota, Halimeda and Laurencia. Underneath
these macrophytes smaller algae, such as Valonia
and Dictyosphaeria may be found. During spring,
this zone may be dominated by large brown algae,
such as Turbinaria, Sargassum, Hydroclathrus, and
Chnoospora. The latter often form a thick matt
which eventually sloughs away in clumps of up to
0.1 square meters and up to 1 kilogram fresh
weight. The clumps are swept by currents into the
lagoon, where for a short time they "litter" the floor
before they are rapidly degraded by bacteria and
eaten by detrivores. At the lagoon rim and near the
upper edges of the coral bommies, branched
unarticulated coralline algae, such as Lithophyllum
kotchyanum and L molluccense, are also very
common.

One Tree Reef has a 3 to 6 meter deep
central lagoon with extensive coral bommies
reaching from the sandy lagoon floor to the low
water mark. A definite zonation of algae can be
observed on the vertical sides of these bommies
(Figure 2). The shallow pools within these bommies
have a flora similar to that of the outer reef flat.
The sand floor of the lagoon also has a distinct algal
flora of filamentous blue-green algae, such as
Hormidium and Oscillatoria, which grow over and
through the sand, forming distinct purplish patches.
Loosely attached algae, such as Hydroclathrus
clathratus and stoloniferous algae, such as Caulerpa
serrulata and Halimeda cylindricea, are also locally
abundant.

Near the shore of the island, especially in
the area where beach rock occurs, three definite
algal zones usually can be distinguished. This is
more obvious on sand cays, such as Heron Island.
At the intertidal fringe there is a band of the small
rhodophyte Gelidiella bornetii obscured by a layer
of loose sediment. In winter, this band may appear
greenish because of the seasonal development of
Enteromorpha spp. Above this band in the lower
eulittoral, there is a pale pink to white band of
various blue-green algae firmly entrapping fine
sediment, and above this, near the high tide mark,
is a black to brown band of the blue-green
Entophysalis deusta.

Inter-Reef Areas

Interestingly, the reefs themselves are largely free

49

Lagoon

Reef slope

Paragoniolithon con/cum
Porolithon onkodes

i rim
Porolithon onkodes
Laurencia spp.
Caulerpa racemosa

Rubble ( rest
Caulerpa racemosa
Yamadaella coenomyce
endolithic cyanophytes
{tnteromorpha sp.)
Celidiella acerosa

Figure 1 . One Tree Reef (not
to scale), showing major algal
habitats and listing some of
the major algal species found
there. Below, the reef has all
the classic features of a
platform structure including a
lagoon. One Tree Reef is in
the southern Great Barrier
Reef region, east of Gladstone.

Reel flat '"mW?/.

Halimeda discoidea
Halimeda opuntia
Caulerpa racemosa
Boodlea composita
Ch/orodesmis fastigiata
Dictyosphaena spp.
Padina australis
Lobophora variegata
Dictyota barlayresii
Chnoospora fastigiata
Hydroclathrus clathrus

Turbinara ornata

Sargassum spp.

Caulerpa cupressoides

Valonia ventricosa

Hypnea spp.

Laurencia spp

Gliffordia spp.

Feldmannia spp.

Ceramium spp.

Celidiella acerosa

Bryopsis sp.

Polysiphonia spp.

Leveillea jungermannoide

Lophosiphonia spp

Calothrix Crustacea
Ralfsia sp.
Peyssonellia sp.
Lyngbya spp.

Lagoon

I lormothamnion enteromorpnoides
Oscillatoria bonnemaisonii

sand species

Halimeda cylmdracea

Caulerpa serrulata

Caulerpa sertularioides

Ceratodictyon spongiosum

Ldhophyllum molluccense 1 on bommies

Uthophyllum kotchyanum J

and most of the species listed lor the reef flat

• Turf spec ies

One Tree Reef

leeward coral flat sancj wedge
algal rim

agoon

lagoonal patch reef

reef flat

v.-.:-r

scarp

'^"•\" "-".y^ pleistocene cliff

spur and groove

moat

windward algal flat

One Tree Island

50

Turf Algae

^ .<**

* G^V"* ^ C^V^C^>*>eV%

50

100

150

1 00%

Pert ent Cover

Figure 2. The vertical face of a "bommie" in One Tree Lagoon, showing the relative abundance of the benthic algae and
coral (Redrawn from Borowitzka, 1981).

of large fleshy algae, and seagrasses are rare.
However, in the deeper waters of the inter-reef
areas, extensive beds of larger algae may be found.
These may consist of algae, such as Hallmeda spp.,
or may be mixed with seagrass. A new species of
Halophila (hi. tricostata) was discovered by
dredging in the northern section of the Great
Barrier Reef as recently as 1980. To date, little is
known of these plant communities or why they
occur there.

Inshore Reefs

There also is a marked difference between the algal
communities of the offshore reefs and the inshore
fringing reefs along the mainland, or those
bordering large continental islands, such as
Magnetic Island near Townsville. Large algae are
much more common in the more turbid waters of
these inshore reefs than on the outer reefs where
the terrigenous influence is absent. In spring, a very
diverse and extremely abundant algal flora may
develop on the inshore reefs with larger algae, such
as Sargassum spp., Lobophora variegata, Calaxaura
spp., Taonia sp., Botryocladia sp., and many others,
growing there. These algae achieve a quite large
biomass, but they usually die back in late summer
and are almost completely absent in winter.

Algal Roles

As indicated already, algae are an essential
component of coral reefs and they play a crucial
role in coral reef ecosystems. The various functions
of algae in reef systems are illustrated in Figure 3.

Primary Producers

Algae, like all plants, capture light energy
and use this to convert C02 into organic carbon in
photosynthesis. Thus they are the primary
producers in coral reefs. This organic carbon enters
the reef food chain by a number of paths. Many of
the algae are consumed by herbivorous
zooplankton, crabs, fish, or echinoderms, while the
symbiotic algae of corals and sponges release some
of their photosynthetically fixed carbon directly to
their animal partner. The organic carbon released
by the algae into the water also is consumed by
heterotrophic bacteria, which in turn may be
consumed by a wide range of filter feeders. The
algae are thus the primary source of energy for all
other reef organisms.

Estimates of primary production on One
Tree Reef have shown that three algal communities
make the major contribution to the primary
production of this reef. These are 1) the "turf algae"
(that is, the small filamentous and fleshy algae
growing over most of the dead coral and rubble on
the reef), 2) the "sand algae" growing on the
surface of the sand, and 3) the "symbiotic algae,"
such as the symbiotic dinoflagellates found in
corals and clams, or the blue-green symbionts of
sponges.

The rich animal life of coral reefs means that
much of the algal biomass is consumed by various
herbivores almost as fast as it grows, so that large
accumulations of algae are rarely seen except in
shallow waters where grazing pressure is reduced,

51

Fleshy
macrophytes

Turf algae +
Sand flora

Calcareous
macrophytes

Boring algae

PRIMARY PRODUCERS

NITROGEN FIXERS-* — |4Phytoplankton

f \

NUTRIENT SINKS &
/ RECYCLERS

SEDIMENT FORMERS«-^Symbiotic algae

REEF BUILDERS &
CONSOLIDATORS

► REEF MODIFIERS

Figure 3. The main algal groups and their roles in the coral
reef ecosystem. The thickness of the lines is an indication of
the relative importance of that algal group to a particular
process. Dashed lines indicate a possible role for that algal
group.

or in spring, when algal growth can outstrip
consumption by herbivores. The importance of
grazing in structuring reef algal communities can be
seen in experiments, such as when algae are
protected from fish grazing by cages.

If patches of reef are caged, thick growths of
algae soon develop. Similarly, algal growth is
always more extensive in the territories of
Pomacentrid fish, which actively defend their
territories against other fish, thereby reducing the
grazing pressure on the algae. The extent of fish
grazing also can be seen in transplantation
experiments. In one experiment, plants of
Sargassum were transplanted from the reef flat,
where grazing pressure is lower as a result of the
lack of water at low tide, to the reef slope, where
fish have access to the algae throughout the day.
Transplanted Sargassum plants that were
unprotected from grazing were all eaten within 24
hours, whereas Sargassum plants protected by
cages remained intact.

The high grazing pressure in coral reefs
maintains the algal community, especially the turf
algal community, in a state of high productivity.
Repeated grazing selects for fast-growing plants
and prevents the build-up of dead plants that
would shade actively growing plants and thus
reduce their growth. Regular grazing also means
that nutrients are not tied up in nonproductive
biomass, but are made available to the growing
plants via the excretory products of the herbivores.

Nitrogen Fixers
Primary production by algae not only
involves the fixation of carbon but also the
incorporation of inorganic nitrogen from dissolved
nitrates and ammonium. While carbon dioxide
forms a plentiful supply of carbon, there is no such
ready supply of nitrogen.

The tropical ocean waters in which coral
reefs occur are characteristically low in organic
nitrogen sources. This has led to the well known
anomaly first commented on by Charles Darwin of
extremely rich and diverse coral reef ecosystems
existing side-by-side with ocean ecosystems that
are the marine equivalent of deserts.

During the last decade, the activity of
nitrogen-fixing blue-green algae (Calothrix
Crustacea) on coral reefs has been widely studied.
These microscopic members of the "turf" algae had
previously been largely overlooked but in fact they
fix considerable quantities of atmospheric nitrogen
into ammonia, which is then used by the blue-
green algae themselves to build organic matter.
Because of the rapid turnover of these algae and
the intense grazing on coral reefs, the organic
nitrogen derived from nitrogen fixation is quickly
distributed throughout the reef ecosystem.

At One Tree Reef, the mean nitrogen
fixation activity is high by any standards: being not
far short of that occurring in paddy fields or in
fields of leguminous crops (Table 1). Is this, then,
the answer to Darwin's anomaly? The answer is
probably "only in part." The algae of One Tree Reef
have carbon to nitrogen ratios of between 10:1 and
20:1. From this and the data on primary
production, the annual budget for nitrogen can be
computed: it turns out that nitrogen fixation
accounts for only 20 to 40 percent of the overall
annual need for nitrogen. The role of algae as
nutrient sinks and recyclers is therefore important
to further understanding of this apparent shortfall.

Nutrient Sinks and Recyclers

As shown previously, nitrogen fixation alone
cannot account for the nitrogen needs of reef
algae. Studies elsewhere have shown that algae are
very adept at taking up available nutrients, such as
phosphate and nitrogen, and converting this into
algal biomass, or storing it in times of excess for
later use when the nutrient supply is limited. If
algae do this efficiently on reefs, then the nitrogen
excreted by animals or released from dead remains
of plants and animals would be recycled and not
lost by tidal currents to the surrounding oceans.
Thus, nitrogen fixation by blue-green algae would
merely "top up" the system as some inevitable
losses occurred to the ocean.

Alternatively, the surrounding ocean itself
may be a source of nitrogen. Recent evidence
suggests that the rich life of coral reefs may be
partly dependent on periodic upwellings of
nutrient-rich deep water. The algae would be the
likely traps for these nutrients, releasing them later
to the other reef organisms either by grazing or

Table 1. Rates of nitrogen fixation by various biological systems.
The rates quoted are for maximum rates under ideal conditions,
with the exception of the estimate for One Tree Reef, which is
based on seasonal changes and includes areas of poor nitrogen
fixation, such as the lagoon floor.

Kg Nha_1yr_1

Azolla associations

Red clover

Other leguminous crops

Polar/subpolar soil cyanophytes

Rice paddies, soil cyanophytes

Trichodesmium phytoplankton blooms

Coral reef cyanophyte communities

Annual mean, One Tree Reef

80-600
80-300
20-100
20-100
10-80
5-30
1-330

8-12

52

remineralization following death. The algae thus act
as nutrient "sinks" and recyclers.

The various symbiotic algae in coral reefs
also conserve the nitrogen reserves of their animal
partners by taking up waste nitrogen products,
such as urea and ammonia, and eventually re-
releasing it to the animal partner in the form of
amino acids and other N-containing compounds.

Reef Formers

The algae are an essential component of that
group of organisms that actually forms the physical
limestone structure of these biotic reefs. The reef
formers can be separated into three functional
groups: the cementers, the structural element
formers, and the sediment formers.

The cementers are crustose red coralline
algae, such as Porolithon onkodes, Hydrolithon
megacystum, and Paragoniolithon spp., which have
cell walls that are heavily impregnated with the
calcite crystal isomorph of CaC03. These algae
grow over the reef structure and cement it, forming
a hard skin over the softer limestone. They are
most developed in areas of high wave energy, such
as the upper reef slopes and reef crest, where they
form a solid barrier resisting the erosive action of
the ocean swells. Cores through the reef crest of a
number of reefs have shown that the coralline algal
layer may be many meters thick. Without the solid
limestone barrier formed by these algae, the
structure of the reef would soon be worn away by
the pounding of the ocean swells.

The structural element formers are the
dinoflagellate symbionts (zooxanthellae) found in
almost all corals. Together with their animal
partner, these algae form complex skeletons of
aragonite, another crystal form of CaC03. Although
not as hard as the calcite produced by the coralline
algae, the branching aragonite skeletons of corals
form the basic three-dimensional structure of coral
reefs and provide the necessary habitats for many
other plants and animals.

The spaces between the coral skeletons are
filled with the smaller skeletal remains of many
other calcareous organisms, such as foraminifera,
echinoderm spicules, mollusk shells, and so on. A
large component of this sand is made up of the fine
needle-like aragonite deposits of calcareous green
algae, such as Halimeda and Udotea, and red algae,
such as Calaxaura and Nemalion. Up to 80 percent
of the sand fraction of portions of reefs, such as
Heron Reef, may consist of the skeletal remains of
algae.

Reef Modifiers
The algae not only participate in the
formation of new reef limestone, but some of the
algae also contribute to the breakdown processes
of the reef limestone. These are the boring algae,
which penetrate into the dead skeletons of corals
and other limestone forming organisms, and slowly
break these down into smaller fragments. These
smaller fragments become part of the sand fraction
and fill the interstitial spaces between coral
skeletons thus modifying and consolidating the reef
structure.

Symbiotic Algae

Symbiotic algae are ubiquitous on coral reefs.
Associations occur with all kinds of animals and the
list appears to be by no means complete since
discoveries of new associations are being made
every year. Reef-forming corals are functionally
dependent on dinoflagellate algae (zooxanthellae),
which provide organic carbon from photosynthesis
and aid in nitrogen conservation. Zooxanthellae
also are found in the mantles of the giant clam
Tridacna, and a wide variety of other reef animals.
Blue-green, green and red algae, diatoms, and
cryptomonads have all been found in symbiotic
associations and the list of algal groups involved
continues to grow.

Recent work in this area has even brought to
light an alga which could not be placed in any
known algal group. For this reason, Ralph Lewin of
the Scripps Institution of Oceanography in
California created a new division, the
Prochlorophyta, to accommodate the find. The alga
is Prochloron sp., a large, single cell prokaryote,
differing from blue-green algae in having no
phycobiliprotein pigments but possessing
chlorophyll b, in addition to chlorophyll a. It is
found in a number of didemnid ascidians, which
are common on reef crests and outer reef slopes.

Phytoplankton

Phytoplankton are generally not very abundant in
coral reef ecosystems with the exception of the
blue-green Trichodesmium spp., which forms large
brownish windrows of many kilometers in length
floating at the surface of the ocean. Trichodesmium
remains an enigma in that it is abundant in all
tropical areas of the world yet little is known of its
biology. The algae grows from small filaments that
appear to develop deep in the water column and
which only aggregate and float to the surface as
they age. The floating accumulations observed
consist largely of senescent colonies.
Trichodesmium has been reported to fix nitrogen,
despite the fact that it does not contain
heterocysts; however little is known of its role in
coral reef systems.

Other common phytoplankters are
dinoflagellates and diatoms, many of which also
harbor symbiotic blue-green algae.

Algae and Man

Aside from the importance of algae in the
formation and maintenance of coral reef
ecosystems and thus to man, the algae also affect
man in other ways.

The food-poisoning called ciguatera, which
is contracted by eating affected fish, has its origins
in a small benthic, single celled dinoflagellate
Gambierodiscus, which produces a potent toxin,
ciguatoxin, that fish accumulate. Similarly, a fatal
poisoning called paralytic shellfish poisoning, is
caused by the accumulation of cells of the toxic
dinoflagellate Gonyaulax by shellfish. When these
shellfish are consumed, poisoning, which is often
lethal, occurs. At this time, no cases of paralytic
shellfish poisoning have been reported in

53

Chlorodesmis fastigiata, growing on the side of a bommie
in One Tree Lagoon. (Photo courtesy of A. W. D. Larkum)

The ascidean Didemnum molle, growing on dead
Acropora among the turf algae covering the coral skeleton.
(Photo courtesy of R. Lethbridge)

Australian waters, although cases have been
reported in New Guinea and elsewhere.

The algae also are a potentially important
source of new chemicals and drugs. Many of the
algae produce a unique range of biologically active
molecules that have been found to act as
antibiotics, pharmacologically active substances
and possible anti-cancer compounds. Therefore,
there is extensive study of the chemistry of tropical
algae in various parts of the world to isolate these
compounds and to test their efficiency in human
and animal medicine. Tropical reef algae seem to
be particularly good sources of such substances.

The possible reason for this is the high
grazing pressure. Algae can reduce grazing pressure
by either growing in habitats inaccessible to many
grazers, or by producing grazing-deterring
substances. Many of the biologically active
molecules seem to belong to the latter category.
For example, the conspicuous green alga
Chlorodesmis fastigiata produces an acyclic
diterpene that causes avoidance behavior in
herbivorous fishes and which also is quite toxic.
Similar substances have been isolated from some of
the larger reef algae, such as Udotea, Halimeda,
Caulerpa, and Laurencia. The algal symbionts of
sponges, such as the Oscillatoria symbiotica found
in the common sponge Dysidea herbacea have
been implicated in the synthesis of the toxic
halogenated metabolites produced by sponges.

Conclusions

Algae are an integral component of "coral" reefs. A
better term for these reefs, therefore, might be
"biotic" reefs. In a basic sense, reefs such as those
of the Great Barrier Reef can be considered to be
driven by the photosynthetic activity of the algae.
Corals should be considered to be just as much
plants as they are animals. Although reef algae are
not normally as spectacular as the animals on coral
reefs, nor as large as their temperate counterparts,
they are an important and major part of reefs.

Michael A. Borowitzka is a Lecturer in Phycology in the
School of Environmental and Life Sciences, Murdoch
University, Perth, Western Australia. Anthony W. D. Larkum
is Associate Professor in the School of Biological Sciences,
University of Sydney, New South Wales, Australia.

Selected References

Borowitzka, M. A. 1981. Algae and grazing in coral reef

ecosystems. Endeavour, N. S., 5: 99-106.
Borowitzka, M. A. 1983. Calcium carbonate deposition by reef

algae; morphological and physiological aspects. In:

Perspectives on Coral Reefs, D. ). Barnes, ed. pp. 16-28.

Australian Institute of Marine Science: Townsville.
Hatcher, B. C, and A. W. D. Larkum. 1983. An experimental

analysis of factors controlling the standing crop of the epilithic

algal community on a coral reef. /. Exp. Mar. Biol. Ecol. 69: 61-

84.
Hillis-Colinvaux, L. 1980. Ecology and taxonomy of Halimeda:

primary producer of coral reefs. Adv. Mar. Biol. 17: 1-327.

At left, Prochloron didemnii, the unique prokaryotic
symbiont of the ascidean Didemnum molle. (Photo
courtesy of A. W. D. Larkum)

54

The Crown
of Thorns
Starfish

by John Lucas

I he Crown of Thorns starfish is (he major scientific
and management issue of the reef. Because of recent
publicity, one could be forgiven for thinking that the
Crown of Thorns starfish is a very recent species, and
that it suddenly appeared a few decades ago as a
coral predator causing widespread consternation and
fear for the future of coral reefs, including the Great
Barrier Reef. In fact, however, this is far from the
truth. The Crown of Thorns starfish (Acanthaster
plane!) has been known to scientists since the 1 7th
century. Long before this, it was undoubtedly known
to the people of the tropical Indo-Pacific region,
some of whom have special names for the starfish.
For instance, the Japanese call it "One-hito-de" (devil
starfish), obviously referring to its poisonous spines,
and their painful effect on anyone unfortunate
enough to get pierced by them.

The Crown of Thorns starfish is a normal
member of the coral reef communities of the Great
Barrier Reef and throughout the tropical and
subtropical regions of the Indian and Pacific Oceans.
It also is found in the Red Sea and in the Gulf of
California (Sea of Cortez). It does not occur in the
Atlantic Ocean; the Caribbean coral reefs are free of
this predator. Thus, there was recent concern that
proposed enlargement of the Panama Canal could
allow the starfish's planktonic larvae to be carried
through to the Caribbean, where it probably would
become established.

An Extraordinary Starfish

Although a typical member of reef communities, the
Crown of Thorns starfish is not an ordinary starfish: it
has some extraordinary features. First, its size: adult
starfish are typically 30 to 40 centimeters in
diameter, but some very large specimens are seen
occasionally on the Great Barrier Reef. There have
been accounts of specimens five feet (160
centimeters) in diameter, but the largest specimens
officially reported are about 70 centimeters in
diameter. Second, the Crown of Thorns starfish has
numerous arms — usually about 15 — but ranging
from 7 to 23 arms. Other starfish typically have 5

The author, gingerly holding a Crown of Thorns starfish.

arms, with body organs, guts, gonads, nerves, and so
on, repeated in each arm — a body pattern known as
pentamerous symmetry. The Crown of Thorns briefly
passes through a phase of being a tiny 5-armed
starfish, but as it develops, it adds arms and reaches
its adult arm number at about 6 months of age.
Third, there are long poisonous spines covering its
upper surface. Other starfish have spines, but they
are usually short and blunt, while those of the Crown
of Thorns are long, sharp, and spear-like.

There are other unusual features of this
starfish that are not as obvious as the previous three.
These include its very high fecundity (reproductive
output of eggs) and the presence of strong wax-
digesting enzymes in its stomach. The high fecundity
is partly a function of its large size; for example,
female starfish of 35 and 40 centimeters diameter
release more than 20 and 50 million eggs,
respectively, each breeding season. These are
enormous outputs of eggs for starfish. The presence
of strong wax-digesting enzymes relates to the
Crown of Thorns' diet of corals, which store waxes
(for example, cetyl palmitate) as a major energy
reserve.

Morphology

Other external features of the Crown of Thorns
starfish are a large central mouth, rows of tube feet

55

The underside of an arm showing the tube-feet used in
locomotion. (Photos by the author unless otherwise
indicated)

with suckers down a groove on each arm, and rows
of blunt spines along each arm on the undersurface.
On the upper surface are a number of structures that
can only be seen by careful examination. Among
these are an anus, situated near the middle of the
central body region (the disk), a number of
madreporites (small stony bodies occurring around
the outer portion of the disk) and numerous
pedicellaria (pairs of tiny pincer-like spines that are
used to clean the surface). Papulae are small finger-
like sacs that project through the surface and are
used for respiration. Then, at the tip of the arms,
there are small, pink, light-sensitive structures
surrounded by specialized tube feet, the sensory
tentacles that wave about and detect chemical
stimuli. The color of the Crown of Thorns starfish
varies from subdued green-red combinations to
grey-green.

As a group, starfish are noted for their
regenerative powers after damage. Crown of Thorns
starfish, however, have limited powers of
regeneration. Its internal skeleton is not as strong as
is that of many other starfish. Therefore, when badly
damaged, they are inclined to fall apart and become
diseased. Damaged individuals with regenerating
arms are common, and two halves may survive when
an individual is bisected, but fragments and
detached arms will not regenerate to whole Crown
of Thorns starfish.

Behavior

Because the Crown of Thorns starfish is radially
symmetrical (its structures are repeated around a

central vertical axis), it has no front or back and
moves with any of its arms leading. The hundreds of
tube feet under its arms moves the animal slowly, at
a rate of centimeters per minute. Each tube foot
reaches forward and attaches to the substrate by its
sucker. The tube foot contracts, pulling the starfish
forward, then it detaches and reaches forward again.
How the literally brainless starfish coordinates these
movements of hundreds of tube feet working at
various angles to the arms is a puzzle.

The starfish feeds by forcing its convoluted
stomach out through its mouth. The starfish locates
itself on some suitable coral, everts its stomach, and
then spreads it out over the coral to cover an area
almost equal its own diameter. It secretes digestive
enzymes onto the coral tissue and then absorbs the
digested tissue as it withdraws its stomach. As the
process takes hours, the Crown of Thorns feeds just
once or twice a day even when coral is plentiful.
Since reef-building corals consist of a thin veneer of
tissue on a calcareous skeleton, the feeding process
removes the veneer of tissue and leaves an area of
white skeleton. White feeding scars are often the
first evidence observed of the presence of Crown of
Thorns starfish in an area of coral.

Most likely, the Crown of Thorns starfish
perceives its environment mainly through chemicals
in the water. Although there are light receptor organs
(optic cushions) at the tip of each arm and probably
light sensitive cells over its body surface, none of
these are capable of producing visual images. These
light receptors indicate light intensity, enabling the
starfish to detect daylight.

The starfish detects its food, perhaps the
presence of other starfish, and certainly the presence
of spawn from other starfish, by chemoreception.
Chemoreceptors are concentrated in the sensory
tentacles at the tips of the arms and these wave
actively on the leading arms as the starfish moves.
They can pick up the presence of a feeding starfish
several meters or more away.

Typically, the starfish remains hidden beneath
coral during the day and is active at night. This
behavior changes when the starfish are numerous
and competition for coral food forces them to seek
food day and night. At times the starfish aggregate,
perhaps because they are attracted to other feeding
starfish by the chemicals released from coral during
feeding or, perhaps they release chemical attractants
for other starfish.

Chemical Defenses

All the soft tissues of the Crown of Thorns starfish
contain saponins, surface-active or detergent-like
substances. In fact, saponins are present throughout
the life-cycle in the eggs, larvae, and juvenile starfish,
serving as a chemical defense. Saponins are toxic at
low concentrations in solution, but their presence in
the starfish is not to poison predators, but rather to
discourage them. Saponins impart a bad taste and
irritate wounds caused by the starfish's spines.
Human injuries from punctures by the Crown of
Thorns spines are more painful than would be
expected from the puncture alone because the
spines are coated with saponin-containing tissue. In

56

Early brachiolaria

\,,':T f ' '■- J ; ' , ,' Spawning

Adult

Australian Institute o( Marine Science

Early starfish

The life-cycle of the Crown of Thorns starfish. (®1985 Australian Institute of Marine Science; used with permission)

addition, the brittle spines often break off in the
wound if they penetrate deeply.

Coral Predation

The Crown of Thorns starfish is not the only species
that eats corals. The coral predators include a variety
of fishes (belonging to at least 12 families), crabs,
nudibranch, and gastropod mollusks, an encrusting
sponge (Terpios sp.), worms, and at least one other
starfish, the pincushion starfish {Culcita
novaeguineae). What distinguishes the Crown of
Thorns from these other coral predators is the extent
of coral deaths that it causes during phases of high
population densities. None of the other coral
predators has been reported to cause significant
levels of coral damage in the Great Barrier Reef
region. Only two of them, the gastropod Drupella
and the starfish Culcita, have been observed to kill
even small coral colonies.

This is a little surprising when one considers
that corals represent a major food resource. It is not
unreasonable to think of "meadows" of corals on the
surfaces of coral reefs. It would seem then that more
animals should be engaged in harvesting these
"meadows." The reason they are not may be
because the coral tissue is a thin veneer on the
surface of and within a massive calcareous skeleton.
A starfish is well-suited to feeding on a surface
veneer of tissue by virtue of its mode of feeding:
everting the stomach over the surface and digesting
the tissue in situ. The problems of this mode of
feeding in a coral reef environment are that it is a
slow process and that, while engaged in feeding, the
starfish exposes itself to a range of predators,

especially bottom-feeding predatory fishes. A variety
of starfishes inhabit coral reefs, but only three of
them — Culcita, Linckia, and the Crown of Thorns —
live conspicuously. Each of these has particular
adaptations to deal with potential predators, those of
the Crown of Thorns being its battery of long, sharp
spines and saponins.

Reproduction

There are about equal numbers of males and
females in Crown of Thorns populations. Males and
females are identical in external appearance. Their
gonads develop from late winter (August) as water
temperature rises and they breed in mid-summer
(January) in Great Barrier Reef waters. Spawning has
been observed only infrequently. The starfish climbs
up onto high points, such as the upper branches of
corals, where they shed their eggs or sperm into the
water through pores on the upper surfaces of their
arms. Many starfish in a group will spawn
simultaneously as they are stimulated by the
presence of spawn from other animals.

Tens of millions of the tiny eggs (1 .2
millimeters in diameter) are released by large
females. Sperm swim to locate eggs. As each egg is
penetrated by a sperm, its membrane swells away
from the yolk to prevent further sperm from
entering. The eggs float in the water and are carried
away from the breeding site by water currents. The
eggs and the larvae that soon develop from them are
temporary members of the plankton of the Great
Barrier Reef waters. Thus, they are carried away by
water currents; sometimes traveling over the surfaces

57

The Significance of the

C

■ orals are to a coral reef what trees, shrubs,
herbs, rocks, and local topography are to a forest.
Much more than vegetation, which simply covers a
landscape, corals are both the clothing of the reef
and the architects of its complex form — the very
foundation of its teeming abundance and diversity
of life.

Or are they? These same corals that are so
fundamental to the reef ecosystems of the Great
Barrier Reef are presently being eaten in vast
numbers by the large, coral-feeding Acanthaster
planci, the Crown of Thorns starfish. What
becomes of the coral community, the reef
structures, and the dependent biotic communities?
And how should we view the Crown of Thorns
starfish? As a demolition team that tears down the
national heritage, or as renovators which strip off a
veneer before it gets too shabby? To address these
questions, it is necessary to consider the impact of
the starfish in the context of both the reef-building
process and the types of disturbances that occur in
the absence of feeding outbreaks.

Coral Dynamics

The contribution of corals to growth of reef features
is not a simple additive process, where successive
generations of corals merely grow on the dead
skeletons of their predecessors. This simple picture
is true in few situations. Rather, coral communities
exhibit all the short- and long-term changes of
recruitment, growth, interaction, and death typical
of any natural community. More often than not, an
individual or piece of coral is not incorporated into
the framework of the reef, evidence that the forces
of destruction are always present on reefs. Some
corals are broken off by storm waves, especially
when a multitude of different boring organisms
have weakened their limestone skeletons. Others
(slower-growing corals) are overgrown or
overtopped by faster-growing species, which may
cause death through either interference or shading.
A whole catalogue of other causes of death could
be given.

Whether or not the dead skeleton is
dislodged from its place of growth, it is seldom
long before the area becomes reoccupied by a
succession of algae, other sessile organisms, and
then, perhaps, by various species of coral. These
coral may derive from planulae that settle in the
area, from adjacent corals, or from attached or
unattached fragments of colonies that regenerate in
the area. The "rules" of succession and the role of
chance in such situations vary, depending on the
size of the disturbed area, the intensity of the
disturbance, the location on the reef, and the coral
species involved.

Against this background of chronic patchy
disturbance and localized secondary succession,
there is a component of coral communities that, in
human time scales, seems to transcend such fluxes.
This component consists of large corals of a
hemispherical or other massive form that can live
for centuries. The larger they grow, the less
vulnerable they seem to become to natural
mortality. Such corals sometimes are numerically
dominant, and if they are of great size, contribute
more than any other living or non-living
component to local topographic relief. Elsewhere,
they are scattered sparsely, or perhaps in small
local aggregations, throughout communities
consisting primarily of more ephemeral corals with
life expectancies measured in years to decades. In
these situations, they constitute striking exceptions
to the usual cycle of short-term localized
disturbance and secondary succession.

Crown of Thorns

Twice in recent years, the Crown of Thorns
population explosions have inflicted enormous
levels of coral mortality over large areas of reefs in
the Great Barrier Reef. The ecological significance
of the phenomenon is not clear, and is the subject
of both investigation and dispute among reef
scientists. Crown of Thorns starfish moving through
coral communities at densities of thousands per
hectare can reduce the quantity of living coral
tissue to only a few percent of the normal — 90

of coral reefs, other times being in open ocean far
from reefs.

Life Cycle

Within a day, the fertilized egg hatches and a
gastrula larva emerges. This is an extremely simple
sack-like larva with the beginnings of a gut and cilia,
beating hair-like structures, by which it swims. The
gastrula develops into a bipinnaria larva that in turn
develops into a brachiolaria larvae, both

characteristic larval stages of starfish. The larvae are
about 1 millimeter long; they are transparent and
they swim with their long axis vertical, rotating slowly
about the axis. They swim and feed using cilia,
which are organized into bands, and their food is
microscopic algal cells (phytoplankton). In the latter
part of development, an opaque structure develops
at the posterior of the brachiolaria larva. This is the
developing starfish or starfish primordium.

After several weeks in the plankton, if

58

Crown of Thorns Starfish

percent devastation is not uncommon. In Japan,
bounties have been paid to divers to protect reefs.
In some areas of the GBR, copper sulfate injections
have been used to kill the starfish.

This widespread, intense, and synchronous
disturbance contrasts markedly with the patchy,
chronic, and localized disturbances previously
described and changes the essential ecological
character of the affected areas. Where reef-building
corals formerly prevailed, a swift shift to algal
dominance follows. Scientists have seen in the 15-
year interval between the two recent outbreaks
(the late 1960s and the early 1980s) that high coral
cover can be re-established in that time. What is
not known, however, makes a far longer list:

• Are outbreaks a normal part of the population
dynamics of A. planci, and if so, is the recently
observed 1 5-year interval also normal?

• Do outbreaks affect the diversity of hard corals
present? (Both an increase and a decrease in diversity
may be argued on theoretical grounds.)

• Are reef-building activities of corals affected by
outbreaks? Again, both a suppression and an
acceleration of localized reef growth may be argued.

• Can the massive corals sustain the levels of damage
observed in recent outbreaks, given that the
replacement time for individual corals may be as high
as several centuries?

• Are there secondary effects on other reef biota, such
as favoring of other benthic groups that are free to
settle and grow without interference from a high
cover of corals, or disappearance of fish that
previously depended on live coral to provide
microhabitats and/or food?

The damage caused by A. planci may be
compared to the destruction caused by a forest fire.
Most observers would assess the severity of a forest
fire by the level of damage to the trees, giving a

lesser value to an undergrowth that can regenerate
itself relatively quickly from dormant seeds,
rootstock, and the like. Like the forest
undergrowth, the more ephemeral coral species
regain their dominance, in this case from growth of
new individuals derived from planktonic larvae,
and from regeneration of an abundance of
surviving remnants. And, as with the forest fire,
scientists attribute a greater significance to the
death or damage of the very old, large, and slow-
growing corals, some so huge that they must have
already been giants when Captain Cook first
explored these waters more than 200 years ago.
Although they seem to be among the least
preferred foods of A. planci, (he populations of
these corals do bear the scars of the outbreaks,
with some large colonies killed and many injured.

Assessing the ecological significance of the
impact on coral communities is complex. Many
characteristics of species involved need to be taken
into account: an apparently sporadic success in
colony establishment despite an enormous and
regular reproductive output; an impressive ability
of some species to regenerate entire colonies from
small remnants of living tissue; the protection
which the size of large species seems to confer
against starfish predation; the interactions with
competitors, predators, and symbionts; and, very
likely, the intervention of further disturbances.
Ecological theory and recent coral research on the
Great Barrier Reef have provided an unsurpassed
foundation for the important and exciting
ecological research that is now underway.

The Crown of Thorns starfish is usually cast
in the role of the villain. Maybe the benefit of
hindsight will confirm this view, when we are left
with a reef that is but a poor caricature of what
once was. Or maybe time will decide that what we
really saw was a passing renovator, making a
terrible mess in the short-term, on the way to
home improvements in the longer term. For it is
the long-term persistence of the system with all its
richness and complexity that really matters.

—by T. J. Done, AIMS

development has been successful, the larva has a
large starfish primordium on its posterior. At this
stage, the larva must be carried over the surface of a
coral reef, where it will attach to algae-coated
surfaces, such as coralline algae. There follows a
most dramatic metamorphosis over several days,
when all the larval structures are absorbed into the
tiny starfish.

The initial starfish is cream-colored, has five

arms, and is about 0.7 millimeters in diameter. It is
far too tiny to feed on coral. In fact, coral polyps
would feed on it, or damage it with their
nematocysts. Instead, the starfish feeds on algae,
especially the abundant coralline algae. It feeds by
extruding its stomach over the algae in the same
manner as the adult starfish feeds on coral.

The juvenile starfish feeds on algae for about
six months while growing to about 10 millimeters in

59

Giant Clams

L-Jne of the most spectacular and enthralling
sights when diving on the Great Barrier Reef is a
giant clam, its brilliantly-colored mantle fully
exposed over the convoluted edges of the
massive shell. These clams are the largest bivalve
mollusks in the world, some growing over a
meter long and weighing more than 300
kilograms.

Seven species of giant clams (family
Tridacnidae) inhabit the tropical Indo-Pacific
region, and six of these are found on the Great
Barrier Reef. All species need clear, warm,
shallow waters that have a high salinity content.
Typically, they live among the corals or on sand
and coral rubble. The largest giant clam, Tridacna
gigas, can live in 20-meter-deep waters, but also
can be exposed at low tide. Tridacna derasa, the
second largest tridacnid, grows to more than 50
centimeters in length, and is common in oceanic
environments, particularly in the 4 to 10 meter
deep waters of the outer reef edges.

The scaley or fluted clam, T. squamosa,
usually inhabits sheltered environments, such as
back-reef lagoons, in depths to 15 meters. T.
maxima, one of the most common species, is
found on reeftops and slopes, often partially
embedded in coral. The latter two species grow
to a maximum of about 40 centimeters long. The
boring clam, T. crocea, is the smallest of the giant
clams. Fully embedded in coral boulders, just the
top edge of its shell and its mantle are visible. The
most abundant on the interior reef flat, it may
reach 15 centimeters in length. Hippopus
hippopus, the horse's hoof clam, resides on reef
flats down to 6 meters deep and grows about 45
centimeters long.

Life Cycle

All giant clams are hermaphrodites, releasing
both eggs and sperm into the seawater, where
fertilization takes place. Sperm are spawned first,
followed by hundreds of millions of microscopic
eggs. The release of gonadal products from one
clam apparently triggers spawning by others
nearby, thus ensuring cross-fertilization.
Reproductive success, therefore, most likely
depends on a critical minimum population
density of breeding adults.

The early life histories of all clam species
are similar. Fertilized eggs develop into
planktonic trochophore larvae, which later
become free-swimming veliger larvae. The larval
life span is comparatively short; after 7 to 12 days,

An adult Tridacna gigas. The largest of the giant clam
species, it may grow to more than 1 meter in length.

they settle onto the reef substrate, where they
metamorphose into juvenile clams 0.2 millimeters
in length. Initially, the juveniles are mobile,
crawling by means of a well-developed foot until
they find a suitable substrate for attachment by
byssal threads. These threads gradually are lost in
the largest three species, which then rely on their
own weight to maintain position.

Food Sources

Giant clams have two sources of food. They filter-
feed in phytoplankton from the surrounding
seawater and also obtain nutrients from
specialized algae, the Symbiodinium species.
These algae, commonly called zooxanthellae, live
symbiotically within the exposed mantle tissue of
the clam. They obtain both energy from the sun
and nutrients from the seawater, and
photosynthetically produce carbohydrates, which
are released directly into the tissues of the clam.
In turn, the zooxanthellae use the clam's waste
products.

Only larvae and newly-metamorphosed
juveniles are entirely dependent on exogenous
phytoplankton as a food source. During these
early life-cycle stages, the zooxanthellae are
ingested from the surrounding seawater and

60

move by unknown means to the enlarged mantle
tissues. Once the symbiotic relationship has been
established, giant clams obtain almost all of their
nutritional requirements from the zooxanthellae.
Therefore, they are capable of a high degree of
autotrophy (self-feeding) and can thrive in the
nutrient-deficient waters of the reef. This
symbiotic relationship explains both the large size
attained by the giant clam and its restriction to
shallow, sunlit waters.

Recent studies have shown that, contrary
to previous beliefs, giant clams are relatively fast-
growing. Growth rates of juveniles are rapid after
they have established symbiosis; T. gigas can
reach more than 10 centimeters in length in the
first year, with annual growth increments of 8 to
12 centimeters during the next few years. The
clam may even attain a length of more than 60
centimeters in 10 years. Other species are slower-
growing, such as T. derasa, which reaches 5
centimeters after the first year.

Because the sedentary giant clam is
conspicuous in shallow water, it is easily
harvested, making it vulnerable to over-
exploitation. Stocks of giant clams have been
severely depleted throughout much of their
range, becoming extinct in some areas. The two
largest species, T. gigas and T. derasa, are listed
as threatened by the International Union for the
Conservation of Nature.

The principal causes of the population
decrease are over-fishing by local peoples and
poaching by foreigners. Clam meat, an important
component of the diets of Indo-Pacific Islanders,
has been harvested on a subsistence level for
centuries. The adductor muscle, which comprises
10 percent of the flesh weight, is in high demand
in Southeast Asia as a high-priced delicacy. In
addition, the shell is coveted as a decoration.

In Australia, giant clams are protected by
law, making population densities on the Great

Barrier Reef much higher than those of other
countries. Several reefs support more than 30 T.
gigas or T. derasa per hectare, with T. crocea
densities regularly exceeding 100 animals per
square meter. Even so, giant clams occasionally
are taken in enormous quantities by Taiwanese
fishermen.

Commercial Cultivation

Research on giant clam biology in recent years
has highlighted the mollusk's potential for
commercial cultivation: it spawns prol ideally, the
larvae and juveniles are amenable to high density
cultivation in artificial conditions, growth rates of
the larger species are high, it does not require
supplementary feeding after the first month, and
well-established markets already exist.

Significant advances in mass culture
techniques, particularly for T. derasa, have been
made at the Micronesian Mariculture
Demonstration Center in Patau, where more than
100,000 juveniles were produced in 1 984. On
the Great Barrier Reef, research into giant clam
mariculture techniques is underway at Orpheus
Island, near Townsville, and is funded by the
Australian Center for International Agricultural
Research. A commercial hatchery also has been
established on Fitzroy Island, off Cairns.

Giant clam farming currently is receiving
enormous interest, and, if it proves to be
economically feasible, a new industry
undoubtedly will arise in the Western Pacific
region. Many depleted reefs possibly can be
restocked with farm-reared juveniles, thus
reversing the increasing trend toward extinction
of this important component of coral reef
communities. If this does not occur, then the
Great Barrier Reef may well be the last bastion for
the largest bivalves ever to exist.

— Christine Crawford and Warwick Nash,
James Cook University, Townsville.

diameter and adding arms to reach its adult number.
Then, it begins to feed on coral polyps.

Feeding on coral it grows rapidly, reaching
about 5 centimeters at one year of age, 20
centimeters at two years of age, and 30 plus
centimeters at three years of age. However, if it
cannot find coral to feed on, it remains very stunted
in size.

Crown of Thorns starfish reach sexual
maturity at 2 to 3 years of age. Growth rate slows
down after they reach sexual maturity because of
the diversion of energy from body growth to
production of gametes. In laboratory studies, the
starfish ceased growing after 3 years of age, and

finally went into a senescent phase after 5 years. In
the senescent phase, they ceased gonad
development and actually shrank somewhat in size.
Most died before 8 years of age. It has not been
possible yet to confirm these observations of
cessation of growth and senescence in the field. A
major problem for growth studies and population
studies in the field is that no effective tagging
method has been developed. The Crown of Thorns
starfish is a master of getting rid of foreign objects
from its body.

What are we to make of the occasional 70-
centimeter starfish that occur on the Great Barrier
Reef? Are they very old animals that kept growing or

61

White coral skeleton remaining after Crown of Thorns
starfish have fed on the coral tissue.

Undersurface of Crown of Thorns starfish showing its
stomach partly everted through its mouth.

Young juvenile Crown of Thorns feeding on coralline algae
and leaving circular white feeding scars on the pink alga
(Photo courtesy of L. Zann).

are they starfish that grew especially rapidly during
the years of growth? The relationship between size
and age is a loose one because of the strong
influence of food on growth rate: thus bigger animals
may not be older animals.

Mortality

One may ask: "What happens to the millions of eggs
that are released by each female each summer?" The
Crown of Thorns starfish is exceptional among
starfish in its fecundity, but other marine
invertebrates also release millions of eggs. The usual
pattern of survival in these cases is for extremely
heavy mortality of the eggs and early developmental
stages, so that only a very small proportion survive
even a few weeks of development. This is likely to
be the case for the Crown of Thorns, but there are
no field observations of larvae and early juvenile
starfish to confirm this.

There are considerable problems connected
with obtaining observations. The larvae are localized
in time and space, and an extensive sampling
program in Great Barrier Reef waters failed to locate
more than a few, if any, larvae. The occurrence of
juvenile starfish is also very localized, and looking for
them in a coral reef community is like "looking for
needles in a haystack," without being sure that the
needles are there in the first place.

Eggs and Larvae

One of the first factors in mortality is whether the
eggs are fertilized or not. Where starfish are
aggregated it is likely that there will be high levels of
fertilization as clouds of eggs and sperm are released
in close proximity. However, where the starfish are
at low densities, tens of meters and more apart,
starfish may spawn without any other individual
detecting gametes in the water. In this way, whole
spawnings of eggs may suffer total or near total
mortality.

The eggs are carried away from where they
were spawned over the coral reef. Benthic
predators, such as coral polyps and feather starfish,
may feed on them. Also, the reef community
contains small schools of plankton-eating fishes,
which may prey on the eggs. Small fishes have been
observed to eat the eggs, but, as described earlier,
the eggs have chemical defenses that discourage
predation.

The eggs will be carried off the reef into the
open waters of the Great Barrier Reef region and
subsequently develop into larvae. There are further
potential predators in this open water plankton
community — predatory copepods, medusae, arrow
worms, larval fishes, and so on, but nothing is known
of the severity of this predation.

Lowered salinity improves the survival of
larvae which require particular levels of algal food
(phytoplankton) for optimal development and
survival. At low levels of phytoplankton, the larvae
starve; at high levels, they literally choke on surfeits
of algae because they cannot control their feeding
rate. The larvae have very narrow temperature
tolerances, in the range 26-30 degrees Celsius. This
is the water temperature range in the Great Barrier
Reef region where the starfish breed.

Juveniles

The small starfish have chemical defenses, but they
lack the battery of spines of the larger starfish. Thus,

62

Giant Clams as Pollution Indicators

In addition to their commercial importance, the
tridacnid clams appear to have applications in
environmental research, specifically in monitoring
heavy metal pollution. These bivalves accumulate
metals such as zinc, copper, cadmium, lead, and
mercury to levels which are dependent on, and
therefore reflective of, concentrations available to
them from their surroundings.

The bio-indicator capacity of the
Tridacnidae is confined primarily to their kidneys.
The large tridacnid kidney forms a single mass of
brown pigmented tissue that represents up to 15
percent of the total wet flesh weight. Thus, the
kidney is easily sampled and provides an
abundance of tissue for analysis. Apart from their
size, the Tridacnid kidneys appear similar in
structure to those of other bivalve mollusks. It is
the spongy internal structure of the kidney that is
of greatest interest. Here, the tissues form a mass
of fine irregular tubules. Each tubule opens to the
renal lumen and is lined by secretory and ciliated
columnar cells (nephrocytes). These cells have a
basal nucleus and a highly vacuolated cytoplasm
which may contain granular, laminate
concretions, termed nephroliths. The nephroliths,
which are excreted via the nephridiopore, are
highly mineralized, spherical bodies composed
primarily of calcium phosphate on a
mucopolysaccharide matrix. They are the major
sites of trace metal deposition in the kidney and
are considered to play a prominent role in metal
detoxification and excretion. Moreover, they are
known to increase in quantity and in trace metal
content in response to trace metal pollution and,
therefore, are of central importance to the
kidney's indicator capabilities.

Tridacnid clams from pristine or near
pristine environments normally contain fairly low
renal concentrations of cadmium and zinc,
although rapid and substantial increases can

occur in response to elevated ambient levels. For
example, T. crocea, held in Townsville Harbor (or
two months, accumulated zinc to 2000
micrograms per gram (dry weight) in their
kidneys, where a range of 1 to 10 is normal.
Clearly, clams are useful where episodic trace
metal inputs are to be measured. Once bound
within the clam's kidneys, most trace elements
are lost very slowly. The biological half-lives
(BI/2) for zinc, cobalt, and lead, in the kidneys of
T. crocea, are in the order of 1 to 1.5, 2, and 4
years, respectively. Preliminary results indicate
that the BI/2 for cadmium and mercury are of
similar magnitude while copper, on the other
hand, has a fairly rapid turnover (Bl/2 = 60 days).
With the exception of copper, the tridacnid
kidney records and retains changes in the
ambient availability of many elements over
comparatively long periods. It is therefore
particularly useful in multiple-year monitoring
surveys, as it provides the investigator with
information that would otherwise be lost using
bio-indicators with shorter time-integrating
capacities.

Clearly, tridacnid clams show considerable
promise as indicators of trace metal pollution in
tropical waters. As phototrophic organisms, they
are especially well suited for such purposes in the
clear, relatively barren, waters of the Great Barrier
Reef where other bivalve indicator species may
fail to survive. The considerable scientific interest
now centered on the culture of Tridacnia can
only add to our knowledge of the biology of
these organisms, and facilitate a better
understanding of their role in marine pollution
studies.

— G. R. W. Denton and L Winsor,

James Cook University,

Townsville.

they are "fair game" for any predator that can locate
them and stand their bad taste. A crab and at least
one fish species are known to prey on juvenile
Crown of Thorns starfish, but it is probable that
many other predators attack them.

After six months of feeding on algae, the
juvenile starfish is ready to transfer to coral feeding.
This requires that suitable coral species be available
in the near vicinity, which is not guaranteed because
the settling of the juvenile starfish at this stage is
limited by its small size (10 millimeters) and need to
remain concealed. Thus, it may be months before
the juvenile locates suitable coral, or it may never
locate sufficient coral to enable it to get into the
rapid growth phase that takes it out of its vulnerable
small-size range.

Adults

Some fishes, such as toad fish and trigger fish, have
been observed to feed on adult Crown of Thorns
starfish. The fish avoid the spiny defenses of the
starfish by turning it over and attacking its
undersurface. The giant triton (Charonia tritonis) and
the painted shrimp (Hymenocera picta) also are
starfish predators. However, none of these predators
has been observed to increase in numbers in
response to outbreaks of Crown of Thorns starfish in
the Great Barrier Reef region. In fact, it is probable
that starfish populations increase and then decline
on individual reefs at rates too rapid to allow for
corresponding recruitment of predators. Even when
these predators attack large Crown of Thorns starfish,

63

they need not kill them. The predator may be
satisfied with part of the starfish; the remaining
portion then regenerates the lost tissue. Crown of
Thorns with groups of regenerating arms are
common in Great Barrier Reef populations. Thus, it
seems that Crown of Thorns starfish reach a "size-
refuge" — that is, by virtue of their large size in
combination with their defenses they are relatively
free of predation.

Disease

Another factor that may cause damage and mortality
in Crown of Thorns populations is disease. I first
observed a bacterial disease in an aquarium system
that caused widespread rotting of the starfish and
rapid mortality. Interestingly, the disease only
affected Crown of Thorns among the various
starfishes that were held in the aquarium. I
controlled the disease by injecting the starfish with
antibiotics.

Disease now has been observed in the field
and is being studied by microbiologists and
pathologists at James Cook University. Diseased
individuals tend to occur in populations of "old"
starfish or stressed starfish. It is not clear yet whether
the bacteria are the cause or a consequence of the
poor condition of the animals. The possibility exists
that the high density populations of Crown of Thorns
starfish are short-lived because at high density they
are prone to epidemics of pathogenic bacteria.

Mathematics

The mathematics of fecundity and survival are
interesting. If a female starfish reproduces for three
of four successive breeding seasons, its total egg
release will be in the order of 100 million. To replace
itself and a male starfish, two individuals out of 100
million need to reach sexual maturity, a survival rate
of 0.000002 percent. If, instead, the survival rate is
0.001 percent, still a very low rate of survival (one
individual surviving from 100,000 eggs), there will be
a population outbreak of 1,000 starfish where
previously there were two. This gives an
appreciation of the potential for starfish population
fluctuations resulting from changes in the survival
rates of the very abundant early stages of the life
cycle.

It is not surprising that there should be
marked fluctuations in the populations of Crown of
Thorns starfish on various reefs of the Great Barrier
Reef. However, this is not to say that the recently
observed population outbreaks are "natural." Both
"natural" and "unnatural" (human interference)
factors may produce profound changes in starfish
numbers through their effects on the survival of
larvae and juvenile starfish.

Recruitment

Considering recruitment, as in the above example of
1,000 starfish instead of two: it is likely that juveniles
recruit to reefs other than the reef from which the
larvae were liberated. Over the period of several
weeks of planktonic development the larvae will
travel a considerable distance depending on the
ocean currents. For example, in a prevailing current

of 0.1 meters per second (approximately one quarter
of a knot), the larvae will be transported more than
170 kilometers in 20 days of planktonic life. Thus,
unless there are particular circumstances, such as
gyral current systems or alternating current systems,
it is likely that the larvae will be carried and recruited
to reefs away from that of the parent population. In
the two recent periods of Crown of Thorns starfish
outbreaks in the central region of the Great Barrier
Reef, in 1960/70 and 1970/80, the starfish were
abundant on reefs off Cairns (1 7 degrees South),
such as Green Island, several years before they were
abundant off Townsville (19 degrees South). The
prevailing currents are southerly in this region during
the summer breeding season. It is thus reasonable to
attribute the large populations off Townsville to
southerly transport of larvae from the more northern
populations near Cairns.

Conclusion

This article does not address the controversy
surrounding the Crown of Thorns starfish — whether
recent population outbreaks on the Great Barrier
Reef and elsewhere are unique events caused by the
unprecedented level of human interference in the
marine environment or whether they are recurring
natural events that simply have not been witnessed
by marine biologists prior to the 1960s. There is no
compelling evidence to support either viewpoint
(see box page 58).

Contrary to the popular view which sees the
Crown of Thorns starfish as an arch villain, I see it as
a magnificent creature, beautifully adapted to its role
as a coral predator. This is not to say that we can be
complacent about the large populations of the
Crown of Thorns starfish currently on reefs of the
Great Barrier Reef. These populations are having a
profound effect on the coral communities of many
reefs. Undoubtedly, the Crown of Thorns starfish is
the major scientific and management issue of the
reef at this time. If the recent population outbreaks
are not a unique event, and if they continue, then
we face the prospect of long-term changes in the
coral reef communities. The reef will not be "eaten
away" as has been suggested. It will remain, but the
coral communities and all the other reef organisms
that depend on them will be changed. Obviously,
the Crown of Thorns phenomenon needs to be
treated very seriously, as the Australian government
is doing, having recently allocated A$3 million for
research on the starfish over the next few years.

lohn Lucas is a biologist and professor at lames Cook
University of North Queensland in Townsville, Australia.

Suggested Readings

Branham, ). M. 1985. The Crown of Thorns on coral reefs.

BioScience 23(4): 219-226.
Lucas, J. S. 1984. Growth, maturation and effects of diet in

Acanthaster planci (L.) (Asteroidea) and hybrids reared in the

laboratory, journal of Experimental Marine Biology and Ecology

79: 129-147.
Lucas, ]. S, W. J. Nash, and M. Nishida. 1 985. Aspects of the

evolution of Acanthaster planci (L.) (Echinodermata, Asteroidea).

Proceedings of the Fifth International Coral Reef Congress, Tahiti.

64

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Goldman's sweetlip (CBRMPA)

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Images From the

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White-tipped shark (CBRMPA)

All photos unless otherwise indicated by James K. Oliver

66

Underwater Outback

Potato cod being fed

Feather star, Himerometra robustipinni

Corgonian, Subergorgia sp.

Coral clam siphon, Tridacna derasa

Gold-flecked ascidian, Phalusia julinea

Featherworm, Spirobranchus sp.

67

The Nutritional Spectrum
of Coral Reef Benthos

or Sponging Off
One Another
for Dinner

by Clive R. Wilkinson

v_vne feature that distinguishes coral reefs from all
other ecosystems is that a significant portion of the
primary production occurs within animals. Indeed,
this production occurs, in conjunction with
heterotrophic consumption, within animals which
constitute the bulk of the animal biomass on coral
reefs.

Nutrition in most ecosystems is derived from
photosynthetic primary production, with the
secondary production being consumed by organisms
ranging from the smallest of bacteria to the largest of
whales. In coral reef ecosystems, as in other systems,
there are approximate balances between primary
production and consumption. In coral reefs, though,
the demarcation between the primary and the
secondary producers is narrower, and a nutritional
symbiosis* is characteristic.

Coral Reefs

The latitudinal range of coral reefs is relatively broad,
roughly 25 degrees north and south of the equator.
The reefs occur principally on the eastern coastlines
of continents and around seamounts, in waters
shallower than 30 to 40 meters. The reef ecosystems
come under two different influences: the continental
land mass, which contributes fresh water, nutrients,
and sediments; and oceanic waters, which are clear
and have low concentrations of nutrients. The only
eastern continental shelf that does not feature coral
reefs is that of South America, where the strong

* Two dissimilar organisms living together in a stable
association which sometimes is mutually beneficial to both.

influences of the Amazon River preclude the growth
of reef-forming corals.

Coral reefs occur along a spectrum from the
relatively high terrestrial influences near the
mangroves, to the oceanic environment at the outer
edge of the continental shelf. Although all fit within
the definition of coral reefs, the nature of the animal
communities, their nutrition, and the nutritional
balance of the reef itself may be quite different.
Coral reefs nearer land masses are likely to be
slightly heterotrophic, requiring additional nutrition
from the surrounding environment, whereas reefs
further offshore may be more autotrophic,
generating all their own nutrition, and even
exporting some organic matter.

Reef Studies

The area where the relationship between nutrition
and the environment has been studied most
intensively is a section of continental shelf extending
from the coast near Townsville out to the Coral Sea
(Figure 1a). This section is about 220 kilometers long,
encompasses 2 degrees of longitude, and is at I8V2
degrees south latitude. Within this section are
contained considerable ranges in the critical
environmental parameters (Figure 1b).

Populations of Halimeda algae, hard corals,
soft corals, sponges, crinoids, and fishes have been
examined on 1 1 reefs within this section. The fish
studies are described by David Williams and co-
authors on page 76. The description of benthic
nutrition is based largely on work with sponges,
done by our laboratory, and on the coral research of
Terrence J. Done at the Australian Institute of Marine
Science (AIMS).

These studies of nutrition and environment
have sought to identify the factors that determine
community development, and to build both
explanatory and predictive models of coral reef
ecosystems.

Nutrition of Benthic Animals

Sessile (permanently attached) animals are faced
with a dilemma — to survive they depend on currents
to provide sufficient dissolved or particulate food
material. The problem confronting coral reef benthos
is that the water around the reefs is usually clear,
signaling that food matter is scarce. Unable to move
and seek out other concentrations of food, the most
prominent benthic animals have evolved an
augmentative system of providing energy-rich
carbon compounds. They "generate" food internally.

68

(a)

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Figure 1 (a). The transect used in studies of benthic nutrition, showing the location of reefs across the continental shelf of the
central Great Barrier Reef region and out to the Coral Sea. (b) The major environmental parameters along the transect. POC =
particulate organic carbon and DOC = dissolved organic carbon.

69

The photosynthetic symbionts in tridacnid
clams, most scleractinian and alcyonacian corals, and
many sponges and colonial ascidians (sea squirts)
provide their animal hosts with an additional source
of nutrient carbon not available to their relatives that
lack symbionts. This combination of phototrophic
and heterotrophic nutrition delineates coral reefs
from other ecosystems — particularly as it relates to
the system's major framework builders, the corals.
Coral reefs and the animals associated with them
owe their existence to this balance of nutrition.

Photosynthetic symbionts and their host
animals have co-evolved over hundreds of millions
of years, so that one partner or often both are totally
dependent on the symbiosis for survival. Where light
levels are adequate, the symbionts produce an
excess of organic carbon photosynthate, some of
which is translocated to the host. The success of
phototrophic nutrition depends on the ability of the
host to enhance the low levels of natural leakage
from the symbiont. Corals induce a greater supply of
photosynthate by causing the zooxanthellae* to
become "leaky," and augment this by reducing the
rate at which the symbionts grow and divide.
Indeed, in some corals, as much as 95 percent of the
carbon fixed by zooxanthellae is made available to
the host. Similar levels of translocation are suggested
for some sponges, tridacnid clams, and possibly
some ascidians.

There are two groups of symbionts. In
sponges and colonial ascidians, the photosynthetic
symbionts are prokaryotic** — cyanobacteria and
Prochloron; whereas in corals and tridacnid clams,
the symbionts are eukaryotic*** brown algae — the
zooxanthellae.

This phototrophic nutrition augments (or in
another perspective — is augmented by)
heterotrophic nutrition. Sponges, clams, and
ascidians are filter feeders removing particulate
matter from the ambient water. Sponges operate in
the range of smaller particle size, being able to
remove about 99 percent of bacteria less than 1
micron in diameter. The bacteria, however, are
probably a minor constituent of the diet. In a
detailed study of sponge nutrition on coral reefs,

* Zooxanthellae are alga-like brownish or greenish-brown
plant cells found in the tissues of marine animals of diverse
groups. They use much of the nitrogenous wastes and
carbon dioxide from the host before these substances enter
the water. In turn, they liberate oxygen and food materials.
Of vital importance to the host, there may be as many as 3
million zooxanthellae cells per square centimeter. In the
spawning of some corals, when the planula larvae are
discharged into the water, many already contain
zooxanthellae.

** Prokaryotic cells have the genetic material in the form of
simple filaments of DNA, and not separated from the
cytoplasm by a nuclear membrane.

** Eukaryotic cells are more complex in that the nucleus is
separated from the cytoplasm by a nuclear membrane, and
the genetic material is borne on chromosomes. This cell
type is common to all organisms except bacteria and blue-
green algae.

Henry M. Reiswig, writing in the Biological Bulletin,
showed that the bulk of food intake was fine detritus
of unknown origin, possibly algal fragments, animal
feces, and the like. Particles in the larger size ranges,
including algal cells and zooplankton, are apparently
removed by clams and ascidians.

Some corals also may act as filter feeders by
trapping detritus in waving tentacles, or on mucus
mats produced by the coral and subsequently
retrieved. Corals, however, are best known as
predators of small prey animals, such as copepods,
various larvae, and fish. Often, these prey are killed
by toxin-bearing cells on the tentacles.

Recent studies have confirmed that many
marine invertebrates are able to incorporate
dissolved organic carbon (for example, sugars, amino
acids, and short chain fatty acids) directly from
seawater. The importance of this form of nutrition in
the total energy balance of these invertebrates has
yet to be determined. It is certain, however, that its
role will vary among individuals and species.

A Nutritional Spectrum

The concept I wish to advance is that of a
continuous nutritional spectrum involving corals,
sponges, clams, and ascidians — a spectrum ranging
from total dependence on heterotrophy for those
animals without symbionts to almost total
dependence on phototrophy. The "phototrophs"
host large populations of photosynthetic symbionts,
and have reduced capability for heterotrophic
feeding. The opposite is true for the "heterotrophs."
Between these extremes lie a broad band of
organisms with various mixtures of feeding modes,
and often with a high degree of "nutritional
plasticity" (described later in this article). All of the
afore-mentioned groups fit on this spectrum (Figure
2).

Distribution and Nutrition

In considering a cross-shelf situation, one would
expect animal communities on coral reefs to vary
across the shelf with respect to distinct
environmental variations. In theory, the more
heterotrophic animals will predominate on the turbid
inner shelf, whereas animals nearer the phototrophic
end of the spectrum will be more prevalent on the
outer shelf. In recent research, using coral reef
sponges, I sought to test this hypothesis — that
distribution is related to position on the nutritional
spectrum.

Like the other groups, the sponges span the
nutritional spectrum. Some sponges on the Great
Barrier Reef can obtain most of their nutrition from
symbiotic cyanobacteria. In some cases, the
production of fixed carbon in the whole animal may
be 3 to 4 times respiration.

First, I divided sponge species into three
nutritional categories: heterotrophs contain no
photosynthetic symbionts, and obtain energy from
the environment; phototrophs, which are generally
flattened, obtain 50 percent or more of normal
energy requirements from the symbionts; and a
mixed category, where the principal mode of
nutrition is heterotrophic feeding, with a small (less

70

Bioerosion of Coral Reefs

I he structure and form of ancient and modern
coral reefs is the result of the interaction between
growth and destruction. Considerable
information on the mechanisms and rates of reef
growth in a variety of reef environments is
available. By contrast, information on destructive
processes is scant, especially data on rates of
destruction and the variation occurring between
and within environments. Yet boulder tracts,
eroded reef flats, islands, and lagoon sediments
are visible reminders that destructive processes
are continually operative, and are substantially
affecting reefs.

Reef destructive processes include
physical, chemical, and biological erosion of the
hard skeletons of corals and other organisms on
the reef. Studies have shown that biological
erosion, termed bioerosion, may be the primary
destructive process on modern day reefs and
evidence from fossil reefs indicates bioerosion has
been present in reef environments for millions of
years.

Bioeroders can be conveniently divided
into borers and grazers, and within each of these
groups a wide variety of organisms are involved.
Borers include micro-borers, such as algae,
bacteria, and fungi; and macro-borers, such as
polychaetes and sipunculan worms, bivalve
mollusks, and sponges. Borers have a pelagic
larval stage. They initially penetrate coral
substrates as juveniles, and spend their adult lives
in the coral skeleton. The majority of borers are
restricted to dead coral substrates, as live corals
are carnivorous and eat the juvenile boring
organisms as they attempt to settle on the coral.
The grazers are animals which rasp, scrape, or
bite the surface of the reef feeding on algae.
While removing the algae, grazers also remove a
fine layer of hard substrate, which is expelled as
detritus. Important grazers include a wide variety
offish, such as parrot fish with their beak-like
jaws made for scraping, and sea urchins. Like the
borers, most grazers attack dead substrates,
however, some will graze live coral.

Studies from other areas pointed to the
large destructive potential of boring and grazing
organisms on coral reefs. In 1980, we undertook
experiments to measure rates of bioerosion in a
variety of reef environments on the Great Barrier
Reef. Substrates, made from recently killed
colonies of the coral Porites* were exposed in a
variety of reef environments for varying lengths of
time ranging from a few months to several years.
These substrates imitate the natural process

* Many coral genera have characteristic shapes that give
rise to a common name, but the familiar and often
dominant Porites have none — due to a variable color
and shape (massive domes, encrusting plates, or lobed
clumps).

occurring on reefs where colonies of live coral are
killed by such factors as predation, storms, 01

diseases.

Borers occurred at all sites studied on the
Great Barrier Reef. Initially, mk ro-borers, such as
algae, colonized the newly available substrate.
Polychaetes also are important borers in the early
stages of exposure. After about 12 months oi
exposure on the reef, sipunculans (peanut
worms), sponges, and bivalve mollusks begin to
appear. Although polychaetes are still common
after 5 years, the dominant borers by this time are
the sponges, sipunculans, and bivalves — due to
their larger size.

Grazers begin to erode substrates soon
after algal communities develop on their surfaces.
Substrates exposed in reef slope environments
experience large amounts of erosion because of
grazing. In this environment, as well as in some
lagoon habitats, grazers are the dominant
bioeroders. In other environments, such as the
reef flat, grazing is not as important, and borers
are the main bioeroders. Environmental
conditions that control the type and size offish
populations in various reef habitats are most
likely responsible for these differences in grazing.
Erosion by sea urchins, although significant in
some parts of the world, is not as important on
the Great Barrier Reef.

High rates of bioerosion in particular reef
environments have important implications to the
overall growth of reefs. On reef slopes, high rates
of growth are matched by high rates of
bioerosion that may limit the ability of this
environment to build up. The skeletons of dead
coral colonies are rapidly reduced to rubble and
sand by bioeroders. Waves and currents
redistribute this debris and deposit it on the reef
flat, in the lagoon, or carry it away from the reef
altogether. In this way, the process of erosion
helps reefs to grow, through the accumulation of
sediment bodies that subsequently provide a base
for colonization by more reef-building organisms.
The sediment and debris can also build up into
the sand cays so characteristic of the reef
environment. These cays are unstable initially,
but if vegetated, can become permanent features.

The balance between growth and
destruction processes in the reef community is a
fundamental part of its development.
Understanding the relationship between these
processes is vital to the interpretation of many
biological and geological features on reefs. In
gaining this understanding, it also may be
possible to predict the consequences of natural
and unnatural disturbances to the coral reef
ecosystem.

— Pat Hutchings, The Australian Museum,

Sydney, and William E. Kiene, Australian

National University, Canberra.

71

Heterotrophy
POC

Phototrophy

DOC

Figure 2. The Heterotrophy: Phototrophy Spectrum. The range
of benthic animal nutrition from phototrophy to
heterotrophy, with the three major sources of carbon
acquisition in the latter — live particle capture (C), filter
feeding of particulate organic carbon (POC), and direct
incorporation of dissolved organic carbon (DOC). Animals
without photosynthetic symbionts are totally heterotrophic,
whereas those with symbionts will occupy a position or a
span of the spectrum. The width of the span will depend on
the plasticity of the animal's nutrition. Three examples are
shown — X is a true heterotroph, such as a non-symbiotic
coral that derives its nutrition from particle capture and DOC
uptake; Y is a predominantly heterotrophic animal feeding on
DOC and POC with a small phototrophic contribution; Z is
predominantly phototrophic like a shallow water, symbiotic
coral which obtains some nutrition from particle capture. It is
unlikely that any animal has totally phototrophic nutrition.

than 50 percent) contribution from phototrophic
nutrition. In general, sponge species in the mixed
category are more heterotrophic, with the
contribution from phototrophic nutrition estimated
at less than 10 percent.* The three categories do not
necessarily relate to taxonomy. For example,
different species of the same family may be grouped
into different nutritional categories.

When the distribution of sponges relative to
these nutritional categories was summarized, it
appeared that the initial hypothesis — distribution is
related to position on the nutritional spectrum — was
supported (Figure 3, next page). The largest sponge
biomass occurred on the higher nutrient, and lower
light, inner shelf reefs. All species were heterotrophs
or mixed, indicating there was sufficient particulate
and dissolved nutrient matter to sustain a population
that averaged 500 grams wet weight per square
meter. In contrast, a much lower biomass was found
on the high light, and lower nutrient, reefs of the
outer shelf and Coral Sea. Here, phototrophs were
predominant. On the southeastern slope of the Coral
Sea reefs, for example, the population consists of
more than 85 percent phototrophs at depths down
to 20 meters.

The link between light, nutrition, and
distribution was further demonstrated in the vertical
plane. Sponge populations were studied to a depth
of 40 meters on nearby Davies Reef. Here, the
sponge biomass peaked at a depth of 20 meters. At
this depth, a large phototrophic component was

* Although this is true for adults, juvenile or freshly settled
sponges in this category may have a larger nutrient
contribution from the symbionts because of their larger
surface area (relative to volume) for receiving light energy.

present that was absent at 40 meters. Physiological
experiments on specimens from 20 meters showed
that these sponges were particularly efficient at using
ambient light energy. At 40 meters, however, light
levels were too low, and capable of supplying less
than 10 percent of total energy requirements. As
shown in Figure 4, overall biomass, as well as
percentage of phototrophy decreases at these
depths. Although light would appear not to be
limiting in shallow water, another factor may be.
Because sponges have soft tissues, sponge
colonization in shallow water is likely limited by
water turbulence.

Studies on coral distribution by Terrence J.
Done at AIMS seem to corroborate the sponge data.
The pattern of coral distribution, based on the nature
of coral community structure, likewise shows a
distinct cross-shelf gradient. The major factors
causing this variation were considered to be light
and degree of turbulence. Whether this
distributional pattern is related to the nutritional
spectrum of the corals is unknown, but, after

Heterotrophs

Mixed
Phototrophs

100

200

BIOMASS

(wet wt. grams sq. meter )

Figure 4. Sponge biomass with respect to depth on the
southeast side of Davies Reef. Similar methods were
employed as for the cross-shelf reefs. The peak in population
between 15 and 30 meters also is paralleled by peaks in
numbers of species and individual sponges. In this depth
range, there is a corresponding decrease in the extent of live
coral cover.

72

600 r

I

Heterotrophs

Mixed
Phototrophs

100

V)

-C

Q.
O

O

50 100 150

Distance from shore (km

200

Figure 3. Biomass (wet weight) of sponges at 15 meter depth on the southeast sides of reefs along the cross-shelf transects. The
histograms represent the mean biomass of triplicate 40-square-meter transects with sponges divided into nutritional categories
on the reef. The distance from the shore is represented on the x axis. Superimposed on this is the proportion (as percentage) of
phototrophic sponges within the total biomass at each reef (circles, R axis, dashed line). The regression lines are included to
indicate that there are distinct trends in both biomass and proportion of phototrophy, however, they should not be taken
literally or extrapolated as the shape of the curves will probably vary at different locations on the Great Barrier Reef.

consideration of the sponge data, I would not be
surprised if inner-shelf corals are more
heterotrophic, and those on the outer shelf more
phototrophic.

Nutritional Plasticity

The coral reef is populated by animals that can be
considered nutritionally "plastic." What does this
mean, and why is it so?

Contrary to a popular concept, most of the
coral reef animals are not specialists — either in
nutrition or in choice of habitat. They are, in fact,
generalists, or opportunists. This is true for the
benthos, as well as many of the fishes.

By plastic, I mean animals that can obtain
their nutrition from a wide variety of sources, subject
to availability. These sources include dissolved
organic carbon (DOC), particulate organic carbon
(POC), predatory capture of small animals (all
heterotrophy), and phototrophy. Such plastic
nutrition is exploited by the most prominent animals
on the reef, the same groups addressed
throughout — corals, sponges, tridacnid clams, and
colonial ascidians. This plasticity is less common at
the extremes of the nutritional spectrum, and more
common/important in the large central "mixed" area.

Plasticity as a concept may be applied to
different species in a phylum, or to individual
animals within a species. The breadth of the span

also will vary on a qualitative scale: survival of an
individual would presumably encompass a broader
span of the spectrum than growth and reproductive
success of the species.

If, for instance, water transparency is reduced
through input of particulate nutrients during flood
runoff or storms, some species will be able to
compensate for the reduction in phototrophic
nutrition by shifting in the direction of heterotrophy,
and exploiting the particulate food. The opposite
would occur when normally turbid environments
experience periods of water clarity.

How does the concept of nutritional plasticity
affect our concept of the nutritional spectrum? In this
way: the placement of an organism within the
spectrum is rarely fixed. Rather, shifts in feeding
mode along the spectrum are common. In general,
however, the assignment of species to one of three
broad nutritional categories remains valid.

Integrating Environmental Factors

In seeking to understand the factors that determine
the distribution of benthic populations on the reef,
one must look not only at present conditions,
(including perhaps previously unconsidered
secondary factors), but also back to the historical.
The major present environmental conditions alone
may not adequately explain a distribution. For
example, recent transplant experiments conducted
by Janice E. Thompson, Stanford University, showed

73

Pollution on the Reef

Will the waters of the Great Barrier Reef,
because of their vast size, dilute any pollution to
the point where it will simply disappear without
effect or trace? This has been the thinking of
some. Added to this is the notion that a sparse
mainland population of some 300,000 people,
distributed along 2,000 kilometers of coast, leads
to relatively low runoff discharges. Some
rethinking is now taking place, and perhaps a less
sanguine view is in order.

One event that precipitated this revised
thinking occurred in 1970. The near wreck of the
oil tanker Oceanic Grandeur in the Torres Strait
raised the question of oil spills. In fact, at that
time, this question was the subject of scientific
debate, and a public controversy, since oil
exploration had been proposed — with the
potential for oil field development. To clarify the
dangers to the reef, the Australian government
initiated an inquiry which took the form of a
Royal Commission (consisting of a presiding
judge and two scientific commissioners). The
commission took evidence from witnesses
representing the oil industry, as well as scientific
and environmental organizations from many
countries. In 1974, a commission report
suggested a variety of safeguards to protect the
reef. In 1975, when the Great Barrier Reef Marine
Park Act was passed, oil drilling was specifically
forbidden in the park. Nevertheless, the risk of
the spillage of oil from tankers and other craft in
the area remains.

Recent surveys of various types of
petroleum hydrocarbons in the reef area have
been carried out by the School of Australian
Environmental Studies at Griffith University, and
also by the University of Melbourne. As expected,
only boat harbors were found to contain
significant trace levels. But, very low
concentrations also were found in various biota in
the Capricorn Group at the southern extremity of
the reef. This could have originated from
industrial activities on the adjacent mainland such
as alumina refining, aluminum smelting, coal
exporting, and electricity generation.
Alternatively, natural seeps could be a factor,
since the area has some of the largest oil shale
deposits in the world.

In intensive surveys of the reef,
investigators from the Australian Institute for
Marine Science near Townsville were able to
detect trace amounts of lindane, and some other
pesticides, in various reef organisms over
extensive areas. They suggested these residues
originated from pesticide useage in the sugar
industry that operates along most of the reef
coast. The levels were below those known to
have any biological impact, but nevertheless, the
vast dilution did not cause these residues to
disappear.

The Oceanic Grandeur awash in Torres Strait after
striking an isolated reef in 1970. The oil released from
the ruptured tanks was fortunately washed to open
waters towards the Coral Sea. (Photo courtesy of the
Courier Mail, Brisbane).

Other work at La Trobe University in
Melbourne has suggested that polyclorinated
biphenols (PCBs) may also be present in reef
organisms. This is another example of
bioconcentration of trace amounts in the
environment by organisms. The possible origin of
these substances is unknown, since they are
usually associated with large urban centers.
However the nearest large urban center,
Brisbane, lies around 400 kilometers to the south.

Entry routes to the reef have not been
investigated. The contaminants mentioned above
would be expected to be strongly adsorbed onto
sediments. There is a movement of sediments
from mainland estuaries — the focus of urban,
industrial, and agricultural activities — out towards
the reef. The establishment of equilibrium with
seawater in the reef zone could release
contaminants into water, which would then be
bioconcentrated by organisms.

At present, pollution seems to present a
low level threat to the reef. But, accidents with
tankers carrying hazardous cargoes are possible,
and spills in remote areas would pose a
particularly difficult problem. Probably the low
level pollution from activities on the mainland,
which shows an incremental creep up in intensity
with the passing years, is a more serious problem.
The present low levels of contaminants represent
a danger signal that contaminants do not
disappear through dilution. Continued, careful
monitoring of contaminants, and their possible
effects, is essential, coupled with wastewater
treatment and control of other contaminant
sources. Preventative action is required at this
stage. This course is preferred over an attack on a
crisis situation in the future.

— Des Connell, Griffith University, Brisbane

74

that sponge species occurring on mid-shelf reefs
would survive and grow on inner-shelf reefs where
they do not appear to occur naturally. Their absence
may be caused by larvae never reaching the inner-
shelf reefs.

There also may be a caveat to considering
historical factors. Rather than consider a continuum
of stable or evolving environmental conditions,
"spikes" also may play a role. Joseph H. Connell,
University of California at Santa Barbara, has
proposed that periodic catastrophic disturbances
were a major factor in determining the species
composition of natural populations. For example,
cyclones or floods during prolonged monsoon
periods may inundate the reefs with large volumes of
low salinity, very muddy, water. These type of
events may wipe out those species unable to
tolerate the conditions.

As described by Peter Isdale (see p. 31), the
environmental history of hard corals is locked up in
the skeleton. Information on past rainfall and solar
illumination is now available for hundreds of years.
We likewise can use a knowledge of benthic
community structure to hindcast the environmental
conditions in the immediate past. What we require is
additional information on the physiology of the
animals, and how this varies with environmental
parameters.

Management Questions

If we understand the present and the past, then our
second type of modelling — predictive — can be used
to look into the future. It is hoped that predictive
models of coral reef communities may be an aid in
reef management. With knowledge and
understanding, we may be able to predict what will
happen to coral reef communities if conditions vary.

The variations might relate to increased
farming, land clearing, or large influxes of residents
or tourists. This, in turn, could cause added sediment
or sewage loads, leading to a shift from
phototrophic-dominated communities to
heterotrophic-dominated communities (provided
suitable larval stocks existed in the vicinity). This
would presumably be the case within the Great
Barrier Reef region. However, if a supply of
adaptable or specialized larvae is unavailable, the
outcome might be different. A shift, therefore, in the
environmental parameters of isolated atolls and
islands could result in large-scale depletions of
benthic communities.

Give R. Wilkinson is a Senior Research Scientist, and Coral
Reef Ecology Croup leader at the Australian Institute of
Marine Science (AIMS), Townsville.

Selected References

Done, T. J. 1982. Patterns in the distribution of coral communities

across the central Great Barrier Reef. Coral Reefs 1: 95-107.
Isdale, P. 1984. Fluorescent bands in massive corals record centuries

of coastal rainfall. Nature 310: 578-579.
Reiswig, H. M. 1971. Particle feeding in natural populations of three

marine demosponges. Biological Bulletin (Woods Hole) 41 : 568-

591.
Wilkinson, C. R. 1983. Net primary productivity in coral reef

sponges. Science 219: 410-412.

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75

Reef Fish:

by David McB. Williams,
Garry Russ, and Peter J. Doherty

Raccoon butterfly fish, Chaetodon lunula. (GBRMPA)

I he approximately 1,500 species of fish on the
Great Barrier Reef are spread among an immense
array of more than 2,400 individual coral reefs.
These reefs, usually thousands of meters in length,
range from nearshore reefs fringing the Australian
mainland to those perched on the outer edge of the
continental shelf.

The species composition of reef fish
communities varies significantly from reef to reef,
and also from one time period to the next. Some of
this variation can be attributed to chance
replenishment of benthic populations by pelagic
larvae, but this factor cannot explain all, or even
most, of the variation observed among coral reefs.
Recent surveys have shown that at certain scales of
space and time there are consistent patterns in fish
communities which reflect deterministic factors,
such as cross-shelf (longitudinal) gradients in the
physico-chemical and biological environment. The
research also has provided some insight into feeding
habits and trophic relationships.

Cross-Shelf Distributions

Intensive studies offish communities on nearshore,
mid-shelf, and outer-shelf reefs (see Figure 1 for
station locations) using quantitative (explosive)
collections have disclosed fundamental differences
in the structure of fish communities on the outer
slopes of these reefs. In addition to species
composition, the major differences include the
density of species per reef (mid-shelf highest, outer-
shelf next, and nearshore least) and the trophic
structure of the communities. The most striking
variation in trophic structure is in the abundance of
the herbivorous grazers and the planktivores.

Visual censuses by SCUBA divers of more
than 100 species of fish covering a wide range of
ecological types have demonstrated significant
differences in fish abundances on adjacent reefs, but
far greater differences among reefs at different cross-
shelf locations: nearshore, mid-shelf, and outer-shelf

(Figure 2). This trend has been confirmed in eight
different cross-shelf transects spanning more than 10
degrees of latitude. These surveys also revealed a
significant north-south variation in both species
abundances and community structure. The amount
of this variation, however, is small relative to the
changes across the shelf. The abundance of some
species on any given reef also varies considerably
with time (over years), but again this temporal
variation is small relative to the cross-shelf variation.
The physical environment of the central reef
region ranges from the highly turbid and sheltered
waters typical of the nearshore zone, to the clear,
exposed waters typical of the outer-shelf. Not only
the distributions of fishes, but also those of algae,
plankton, corals, and other organisms on which fish
are dependent, vary greatly across the shelf (see
article by Clive R. Wilkinson, page 68). This physical
and biological heterogeneity provides an ideal
environment in which to generate and test
hypotheses concerning factors determining the
large-scale distribution of fishes and to assist in
establishing the significance of this variation for other
reef organisms, and for the dynamics of the reef
communities as a whole.

Fish and Algae: Lawnmowers

One of the most characteristic features of coral reefs
is their high-standing crops of herbivorous fishes and
their generally low-standing crops of algae. It is not
uncommon to see great numbers of herbivorous
fishes feeding in areas that appear almost devoid of
algae. Closer examination reveals that these fishes
are exploiting a very light cover of small filamentous
and microscopic turf algae that grows on almost all
illuminated surfaces not covered by living corals.
How does such a small amount of algae support
such a large amount of fish flesh? The answer is that
although the small filamentous algal turfs have a low
standing crop, they also have a very high rate of
productivity and are possibly the largest trophic flux
on coral reefs.

76

Large-Scale
Distribution
and
Recruitment

The saddled butterflyfish. (CBRMPA)

Visual censuses and quantitative (explosive)
collections made in the central region of the Great
Barrier Reef have shown that there are significantly
more herbivorous grazing fishes on the coral reefs of
the mid- and outer-shelf than on reefs nearshore.
These patterns of distribution and abundance can be
viewed from an additional perspective. How do the
fish affect the benthos, and how does the benthos
affect the fish?

To answer the first question, it is necessary to
quantify the amount of algae eaten by the
herbivores. This has been done by comparing the
standing crops of algae (as grams per square meter
per day of carbon produced) on dead coral surfaces,
some of which were caged to exclude the common
herbivorous fishes for short periods of time. Results
show that the rate of trophic exchange between algal
turfs and grazers is 6 to 7 times higher on mid- and
outer-shelf reefs compared to those nearshore, and

that this is correlated with standing crops (average
fish wet weights per 150 square meters of reef) of
herbivorous fishes that are three to five times higher
on mid- and outer-shelf reefs compared with those
nearshore (Figure 3).

This significant difference in intensity of
grazing between the nearshore reefs and those reefs
further from the coast appears to have some
important implications. First, some algae grow faster
when they are cropped, so that increased grazing
pressure can actually enhance rates of production of
algal tissue. Thus, the different grazing regimes
across the shelf may enhance or retard production of
the algal turfs.

Second, increased grazing of the algal
community allows certain species, notably blue-
green algae, to increase in relative abundance. This
could be important, since the blue-greens are one of
few groups of organisms capable of nitrogen fixation
(the conversion of inorganic nitrogen to organic

Figure I. Location of nearshore
(N1, N2), mid-shelf (Ml -MA),
and outer-shelf (01-03) reefs
and zooplankton stations (I, III,
2 and 4) across the central
region of Great Barrier Reef.

-^y —

*3$ -2 & V

* 01 Coral Sea

03

0

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77

Caesionidae

Caeslo cunlng

C. caerulaureus

Pterocaeslc dlagrmmma

Nearshore
N1 N2

Mid-shelf

M1 M2 M3

Outer-shelf
01 02 03

► ►

Figure 2. Distribution of the most abundant species of fusilier (Caesionidae) across the central transect. Reef codes as in Figure 1.
Five sectors in each circle represent five non-overlapping censuses on each reef. The radius of each sector is proportional to the
log-abundance category of the given species in a particular census. Each of the three species has a characteristic and distinct
distribution relative to the three shelf regions.

nitrogen — required by plants and animals for
growth). Differential grazing intensity may help to
explain why rates of nitrogen fixation have been
observed (by Wilkinson and others at AIMS) to be
higher on mid- and outer-shelf reefs than on reefs
closer to the coast.

Third, increased grazing may reduce the
survivorship of young corals by removing coral spat
(recently settled young coral larvae) along with the
algae, thereby enhancing the survival of corals and
spat by reducing the likelihood of overgrowth of
corals by algae. In other words, the effect of grazers
may result in differential survivorship of juvenile
corals at different locations across the shelf.

Finally, grazing is a major form of bioerosion.
Consequently, cross-shelf differences in the
abundance of grazing fishes may be responsible for
different levels of bioerosion across the continental
shelf.

The greater productivity of algal turfs on
offshore reefs means that more food is available to
grazers on mid- and outer-shelf reefs, relative to
nearshore ones. Thus, there is a positive correlation
between food availability and standing crop of
herbivorous fishes along the cross-shelf transect, but
it is not yet clear to what extent fish are determining
algal productivity or vice versa.

Fish and Plankton: A Wall of Mouths

The clouds of planktivorous fishes found on the
outer reef slope during the day form a major link
between the reef communities and the surrounding
waters. These fishes, acting as a wall of mouths or a
giant plankton net, filter plankton from the waters
impinging on the reef and convert this external
source of energy into feces, which are deposited
within the benthic system. Although the relatively
small proportion of inter-reef plankton production
lost to reef fishes is not likely to have a major
influence on the plankton communities, it is of
considerable significance to the reef communities,
and particularly to the fishes.

Herbivorous grazers

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Nearshore Mid-shelf Outer-shelf

Figure 3. Cross-shelf distribution of a) standing crop of algal-
grazing fishes, b) rates of trophic exchange from algae to
grazers, c) rates of nitrogen fixation by algae. The herbivorous
grazers are most abundant on the outer-shelf reefs.

78

Recent studies have demonstrated that the
average summer biomass of plankton is significantly
higher in mid- than in outer-shelf waters (Figure 4); a
difference that is at least partly explained by
phytoplankton blooms following intrusions into the
reef area of cold, nutrient-rich water from the deep
waters of the Coral Sea (through upwelling).
Planktivores also are significantly more abundant on
mid-shelf reefs than elsewhere (Figure 4), and hence
fish are likely to import a greater amount of external
energy to the mid-shelf reefs than to other reefs.

The high biomass of plankton feeding fish on
the mid-shelf relative to the outer-shelf may well be
the result of a greater availability of planktonic food
on the mid-shelf. The lower biomass of planktivores
nearshore relative to the mid shelf is clearly not
because of a lower availability of food nearshore,
however, since there is more plankton in the coastal
waters. The decrease in planktivores nearshore may
relate to the difficulties of feeding on plankton in
very turbid waters, or, may be a response to an
entirely different factor such as larval survival.

Corals and Fish: a Natural Experiment

Reef fishes use corals directly for both food and
shelter, and indirectly, because many of their prey
also are dependent (to some degree) on corals for
food and shelter. The structure (species composition
and growth forms) of coral communities varies from
nearshore waters to the outer-shelf as much as fish
communities. On the central reef transect, it is quite
possible for an experienced observer to accurately
predict the fish community in a particular area given
only knowledge of the coral community, and vice-
versa. This, however, does not demonstrate an
invariable, or even a causal, relationship between
these two taxa.

Comparisons of fish and coral communities
on other transects with those of the central reef
region suggest that the overall correspondence
between fish and coral communities is not
necessarily close, and that different factors are likely
to be affecting the large-scale distributions of both.
For example, the coral communities on the inner
reefs of the Pompeys complex in the southern GBR
are similar to those of the central mid-shelf and
outer-shelf, but the fish communities are more
similar to those on nearshore reefs in the central
region.

A large-scale natural experiment testing the
significance of corals for fish communities occurred
recently in the central region when Crown of Thorns
starfish, Acanthaster planci, caused extensive
destruction of the hard-coral cover on several mid-
shelf reefs (see article by John Lucas on page 55).
The starfish digest away the thin veneer of living
coral tissue and leave behind the carbonate skeleton
which is overgrown rapidly by filamentous algae.
Large infestations of these starfish are able to remove
up to 90 percent or more of the live coral on the
outer slopes of average-sized reefs within six
months.

Of four reefs where fish communities had
been examined previously three suffered extensive
mortality of coral and the fourth did not (Figure 5).

Planktivores

30

20

10

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I

300 r

200

100

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4

20

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Nearshore

Mid-shelf Outer-shelf

Figure 4. Cross-shelf distribution of a) standing crop of
planktivorous fishes, b) mean summer biomass of plankton
(from Williams and P. Dixon, unpublished data). The
plankton-eating reef fish have their greatest biomass in the
mid-shelf region.

By comparing the composition of fish communities
before and after Acanthaster infestation on affected
reefs and unaffected reefs, a relatively direct test was
made of the significance of living coral communities
for fishes. Within 12 to 18 months of the major
decrease in live coral cover, species of previously
abundant coral-feeding butterflyfish (Chaetodon
spp.) had decreased in abundance by an order of
magnitude. During the same time period, no other
species, including algal grazers and planktivores,
showed any obvious effects. Ongoing studies
suggest that death of the coral may have a long-term
more than several years) effect on the fish
communities by modifying recruitment patterns of
different species, in addition to the relatively short-
term effect on coral-feeding species.

Recruitment Patterns: The Larval Connection

Recent studies of coral reef fishes have drawn
attention to the fact that while they are relatively
sedentary as adults (most do not move between
reefs and some may not move more than a few
meters during juvenile and adult life), the vast
majority of species have a pelagic larval phase during
which there is a potential for extensive dispersal, and
during which there is enormous mortality. After a
period of pelagic life lasting from a week to 3
months, competent larvae settle to the reef surface,
gain pigmentation, and recruit to the community of
reef residents. There is evidence that fewer than one
recruit is returned for every 100 thousand to 1
million eggs cast into the sea.

79

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100

S 50
O

B

■

A

n_

'80 '84
M3

m

'80 '84 '80 '84

M2 Ml

'80 '84
M4

Figure 5. Changes in live coral cover on four mid-shelf reefs, 3
of them affected by Crown of Thorns starfish (MI-M3) and
relative abundances of obligate coral-feeding butterflyfishes
(Chaetodontidae), and other butterflyfishes. B = estimated
coral cover before starfish infestation, A = coral cover after
infestation. Fish abundances shown are in 1 980 (prior to
infestation), and in 1984 (18 months after infestation). Both
live coral and fish abundance decreased dramatically
following the starfish infestation.

Patterns of distribution could be determined
at any one, or more, of three stages in the life-cycle
of a fish: a) prior to settlement (larval stage), b) at the
time of settlement, or c) post-settlement. To
determine which of these stages is most important,
patterns of recruitment across the central transect
were examined. For 16 out of 18 species, there was
a close relationship between the distributions of
recruits and adults. Despite variation in recruitment
on any given reef from year to year and differences
in recruitment to different reefs at the same shelf
location during the same year, species which
occurred nearshore as adults tended to recruit only
to nearshore reefs. The same was true for species
characteristic of mid- and outer-shelf habitats (see
Figure 6, which presents the number of individuals
per 750 square meters of reef for 3 species of fish). It
appears that (for those species studied) cross-shelf
distributions of adults are determined largely at, or
by, the time of settlement into the reef
environments. Therefore, hypothesis c (post-
settlement) can be eliminated as a determining
factor.

Additionally, two sets of observations suggest
the distributions may be determined before (during
the larval phase of the life cycle), rather than at,
settlement. First, patterns of recruitment of fishes to
identical coral heads placed across the shelf, and
from which all fishes were removed frequently,
appear as clearly defined as those to the natural

substratum of reef slopes. Second, sampling of
mature larvae attracted to lights suspended from a
boat at night yielded primarily larvae of nearshore
species in nearshore waters, and mid-shelf species in
mid-shelf waters.

If cross-shelf distributions of adults are
determined by larval distributions, what determines
larval distributions at this scale? Our hypotheses are
becoming more and more speculative as our line of
questioning gets further from the available data, but
it would appear that passive dispersal of larvae from
the adult habitat is not an adequate explanation for,
say, larvae produced on the outer-shelf recruiting
only to the outer-shelf. There are many physical

Pomactntrua taanlomutmpon numbers 750 m 2
30

adult density

recruit density

Labrlchthys unlllntata
15

adult density

0L —

9r

recruit density

Plmctroglyphldodon dlckll

100r

adult density

recruit density

N1

M3 M2

Figure 6. Densities (average number of individuals per 750
square meters of reef) of three reef fish species (both adults
and recruits) for three successive years on one nearshore (N1),
three mid-shelf (Ml -M3) and one outer-shelf (Ol) reef of the
central transect.

80

Reef Fisheries

I he Great Barrier Reef region supports a number
of significant recreational and commercial
fisheries. These fisheries, which extend along the
2,000 kilometer length of the Great Barrier Reef
off Queensland, include otter trawling for prawns,
shovel-nosed lobsters (known as "bugs"), and
scallops; trolling, gill, and drift netting for
mackerel and other pelagic species; handlining
for reef fish; gill netting for coastal pelagic fishes
such as trevally (mackerel), queenfish, and
threadfin salmon; mudcrabbing; collection of
aquarium fishes, coral, beche-de-mer (edible sea
cucumber), and trochus (mother-of-pearl); and
trolling for big and small game species, such as
martin, sailfish, and tuna. The commercial catch
in the region in 1 979-80, the most recent year for
which data are available, was estimated at about
8,000 tons, worth an estimated A$27 million,
about half the Queensland fisheries production.
This can be compared with the total Australian
catch of 150,000 tons (live weight), valued at
A$360 million in 1980-81. In 1980, commercial
fishing in Queensland was estimated to be less
important to the Queensland economy than
sugar, beef, grains, wool, and dairying, but ahead
of tobacco, cotton, barley, eggs, and other
primary industries.

Recreational fishing in 1980/81 was more
important than commercial fishing — both in
monies invested, and in percentage of catch. The
recreational fishing population in the Great
Barrier Reef region in 1980 consisted of about
15,000 motorboats (about 5 meters in length),
making about 197,000 fishing trips, and averaging
2.6 fishermen per boat. Recreational fishermen
also used charter and party boats (carrying 5 to
25 anglers), or fished from the beach. In 1980,
these fishermen took about 70 to 80 percent of
the finfish caught in the Great Barrier Reef region.
As always seems to be the case, the majority of
the non-commercial reef fish catch was taken by
a small percentage of the fisherman. About 10
percent of the fishermen took about 40 percent
of the catch; the least successful 50 percent of the
anglers took 10 to 20 percent of the catch. The
reef fishing may have had some effects on the
stocks. The average size of reef fish landed from
charterboats in the Townsville area has declined
from 2.5 kilograms in 1957 to 1.4 kilograms.
There also have been reports of increases in catch
with increasing distance from shore —
attributable in part perhaps to nearshore fishing
pressure.

Game fish, large and small, also occur in
the region — and form the basis for a substantial

Black Martin being weighed in. (GBRMPA)

recreational fishery. Starting initially off Gairns in
1966, for black martin (Makaira indica), the big
game fishery, from about Gairns to just north of
Lizard Island, now involves about 40 vessels.
Most marlin are tagged and released, although an
angler's first fish, potential record fish, and fish
over 1,000 pounds may be weighed in (usually
about 5 percent of the season's catches). It has
been suggested that the marlin grounds off the
outer reef off Lizard Island may be a spawning
area for black marlin, as the large marlin caught
are gravid females. Light game recreational fishing
for small marlin, tunas, queenfish, and others also
is a rapidly expanding fishery along the
Queensland coast. Game fishing clubs in most
major coastal centers conduct annual
tournaments.

Minor recreational fisheries also exist for
the collection of aquarium fishes and shells. The
extent of the recreational aquarium fishery is
unknown, although it is believed to be more
intensive in areas where the reef is close to the
coast. Recreational shell collectors operate
throughout the Great Barrier Reef, with active
shell clubs in Yeppoon, the Whitsunday area,
Townsville, Innisfail, and Cairns.

—Wendy Craik, GBRMPA,
Townsville.

81

processes (wind, tides, currents) operating in the sea
that ought to promote the widespread dispersal of
planktonic larvae. The mixing potential of these
processes is such that larvae should be far more
mixed in their cross-shelf distribution than is
suggested by the patterns of recruitment. Thus it
would appear necessary to invoke either some
habitat selection by larvae at the cross-shelf scale, or
a differential survivorship of larvae in coastal and
oceanic waters. At this time, we have no reason to
prefer either of these hypotheses ahead of the other.

Summary

Large scale variations in the structure of fish
communities on the Great Barrier Reef and trophic
interactions related to this variation are
extraordinarily complex. Nevertheless, considerable
pattern does occur, and a number of plausible
hypotheses have been forwarded to account for this
pattern. Variations in the biomass of trophic groups
in some, but not all, cases is correlated with the
availability of resources in the reef environment,
although causal relationships have yet to be
established. Species distributions, on the other hand,

may be determined largely by factors influencing egg
and larval fish distribution, and survival.

David McB. Williams and Carry Russ are researchers at the
Australian Institute of Marine Science, Townsville. Peter I.
Doherty is at the School of Australian Environmental Studies,
Griffith University, in Nathan. Both institutions are in
Queensland, Australia.

Selected References

Done, T. J. 1 982. Patterns in the distribution of coral communities
across the central Great Barrier Reef. Coral Reefs 1: 95-107.

Russ, G. 1984. Distribution and abundance of herbivorous grazing
fishes in the central Great Barrier Reef I. Levels of variability
across the entire continental shelf. Mar. Ecol. Prog. Ser. 20: 23-
34.

Wilkinson, C. R., D. McB. Williams, P. W. Sammarco, R. W. Hogg,
and L. A. Trott. 1984. Rates of nitrogen fixation on coral reefs
across the continental shelf of the central Great Barrier Reef.
Mar. Biol. 80: 255-262.

Williams, D. McB. 1982. Patterns in the distribution of fish

communities across the central Great Barrier Reef. Coral Reefs 1 :
33-43.

Williams, D. Mc.B., and A. I. Hatcher. 1983. Structure of fish
communities on outer slopes of inshore, mid-shelf, and outer
shelf reefs of the Great Barrier Reef. Mar. Ecol. Prog. Ser. 10:
239-250.

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82

Currents and Coral Reefs

by Eric Wolanski, David L B. Jupp, and George L Pickard

I he Great Barrier Reef incorporates several
thousand coral reefs spread over the continental
shelf of northeast Australia for more than 2,000
kilometers in a longshore direction, from roughly 23
degrees South to 9 degrees South. In the north, long
"ribbon" reefs are spread over the length of the shelf
break, separated by reef passages typically 1
kilometer wide. In addition, there are a large number
of reefs scattered, often very densely, over the width
of the shelf. The inner shelf, or what is known as the
lagoon, is thus restricted to the shallow, turbid,
coastal zone. Near Barrow Point (Figure 1), the shelf
width is about 30 kilometers (its narrowest point) and
the reef-free lagoon is only 8 kilometers wide,
offering a tortuous and shallow (less than 20 meters
deep) passage.

In the central region, roughly between 15.5
degrees and 20 degrees South, the reef consists of a
loose matrix of individual reefs widely scattered on
the mid- to outer shelf, and the inner shelf forms a
reef-free lagoon (Figure 2). Further south, the lagoon
is much wider (up to 100 kilometers) and the outer
shelf is a dense matrix of reefs up to 50 kilometers
wide and separated by passages typically 10
kilometers in width.

The water circulation over the Great Barrier
Reef is primarily directed by wind conditions, tides,
and oceanic currents, and other events in the
adjacent Coral Sea. The water circulation over the
shelf responds to these force factors, but the
response is strongly dependent on the blocking
effect of the reefs. Hence, reef density within the
matrix is an all-important parameter in the analysis of
water circulation patterns. In this manner, one can
distinguish between features of water circulation that
are typical of reef-free continental shelves elsewhere
in the world, and features unique to a reef-studded
continental shelf.

Classical Continental Shelf Circulation

In the central and the southern regions of the Great
Barrier Reef, the lagoon is essentially reef-free. The
large-scale, wind-driven circulation in the lagoon is
typical of that of a classical continental shelf. There
exists a southward current (the East Australian
Current [EAC]) which runs typically 30 to 50
centimeters per second over the continental shelf
slope. This current is a near-surface phenomenon, as
there is a return flo.w in deeper water. The surface

current thickness is largest (about 250 meters) in the
ocean, and smallest (100 meters or so) on the upper
continental slope. Hence, the zone of return flow
creeps up on the upper slope, as is typical of other
shelves, for example in California. Thus, the current
is a 100-meter-thick feature near the shelf break.

Because the East Australian Current is
accompanied by a longshore pressure gradient, a
southward drift also is felt on the continental shelf of
the Great Barrier Reef, but, because of bottom
friction, the strength of this southward drift
decreases with increasing distance from the shelf
break. The lateral shear of this current can be very
large near the shelf break. As a result, hydrodynamic
instabilities can develop and generate eddies such as
those observed, for example, in the Gulf Stream.
Such eddies have indeed been observed to exist on
the shelf slope of the Great Barrier Reef, either
directly from satellite images (Figure 3), or indirectly
from moored current meter data.

These eddies presumably have the thickness
of the East Australian Current, that is, 100 to 200
meters, so that they are deep enough to touch the
seafloor of the upper continental slope and the outer
shelf, should they drift there. In that case, they
generate considerable suction near the bottom,
resulting in major upwelling events.

Another classical upwelling event that can
occur is caused by wind-forced long waves that
cause density changes on the continental slope. The
longshore wind-stress r with frequency on drives a
bottom friction-limited longshore current over the
vertically quite well-mixed Great Barrier Reef shelf of
typical depth on the order of 40 to 60 meters. This
current rarely exceeds 50 centimeters per second,
and results in mean sea-level fluctuations of up to 35
centimeters peak to trough. Near the shelf break,
these sea-level fluctuations are much smaller (on the
order of a few centimeters) and the cross-shelf
currents are small enough (on the order of a few
centimeters per second), that, over the long periods
of a normal wind event (typically 5 to 20 days), the
shelf waters remain hydrodynamically coupled to the
ocean waters.

The coupling implies that both the sea-level
and the cross-shelf water fluxes are the same on
both sides of the shelf break. The effect of the
blockage of the flow through the Great Barrier Reef

83

Figure 1 . False color LANDSAT view of the area around
Barrow Point.

matrix near the shelf break is to slow down the
coupling somewhat, but, at the long periods of the
wind (typically one to a few weeks), the density of
reefs is unable to prevent the ocean-shelf coupling.
As a result of this coupling, the thermocline*
separating the mixed layer (typically 80 meters thick
in winter) from the nutrient-rich deeper waters is

raised or lowered by a given amount. It appears that
these vertical oscillations, confined to the vicinity of
the shelf break, may be sufficient at times for
nutrient-rich water from below the thermocline to
spill onto the continental shelf.

In the central region and northern regions, the
Great Barrier Reef matrix is sufficiently porous so
that at least the dominant daily tides are able to
propagate through the reef matrix with only small or
moderate changes in phase and amplitude. In those
cases, classical continental shelf oceanographic
processes roughly prevail, and the topography of the
shelf (that is, the longshore-dependent shelf width
and bottom slope) largely controls the distortion of
the tidal wave and the generation of longshore
currents over the shelf.

Reef-Controlled Shelf Circulation

In the southern region, extremely large tides of up to
10 meters amplitude of vertical oscillation are
experienced at the coast near 22 degrees South at
Broad Sound. Yet the tidal range near the shelf break
is only a third as large with small longshore gradients
in phase and amplitude.* Two effects combine to
generate this tidal enhancement. First, the shelf
width is the largest in that area. About 200
kilometers to the north, the shelf width is about half

* A vertical temperature gradient, negative with respect to
depth and appreciably greater than the gradients above and
below it.

* The vertical distance from low water level to tide crest.
Phase is the time of the wave crest at a given point.

T

Mud Concentratio

n %&** -

Burdekin Rive

~T~TT~J

Surface Salinity $*£

Figure 2. Simplified distribution,
on the left, of the
concentration of terrigenous
mud on the seafloor in the
central region of the Great
Barrier Reef, and, on the right,
of the minimal surface salinity
measured during the January,
1981, flood event.

84

as large, and, about 200 kilometers to the south, the
shelf width decreases abruptly and the reef-free
isobaths* run nearly perpendicular to the coastline. It
may thus be "easier," in terms of bottom friction
effects, for the tidal wave to converge toward Broad
Sound from both north and south.

The second effect compounds the first one, in
that the density of reefs offshore from Broad Sound
is much greater than that both further north and
south. In fact, the reef density is so large that, at the
twice-daily frequencies, the tide is measurably
blocked by the reef matrix. This blocking is
illustrated in Figure 3, which is a Coastal Zone Color
Scanner (CZCS) satellite image of the reef matrix.
This figure shows tidal jets in front of reef entrances.
Such current features significantly enhance the
overall friction of the prevailing currents by
dissipating a large fraction of the kinetic energy of
the incoming flow in the eddies. This energy loss is
most prevalent for strong prevailing currents, such as
exist at tidal frequencies. In this way, the southern
Great Barrier Reef matrix helps decouple the shelf
from ocean tides.

The large tides in Broad Sound can then be
explained as the result of the convergence of two
tidal waves propagating toward the Broad Sound
area from both north and south. This property results
also from numerical and analytical models of the
tidal circulation in the southern reef region. In such
models, the complex water circulation introduced
near reef passages is neglected, but the overall
obstruction of the currents by the Great Barrier Reef
is still included by modelling the reefs as weir-type
structures.

Another example of reefs blocking the water
circulation occurs near Barrow Point (Figure 1),
where the reefs are so densely packed across the
shelf width that only a narrow and shallow lagoon
remains. As a result, there is so little water transport
through this passage that for all practical purposes
the northern and the central regions of the Great
Barrier Reef are hydraulically disconnected. A similar
situation occurs in the shelf region of the Torres
Strait, north of Cape York, making this region a
backwater of the Gulf of Papua. In this case, the bulk
friction coefficient at low frequencies is enhanced
further by the very strong tidal currents through the
Strait.

The increased friction resulting from the
interaction of currents and reefs is the result of at
least two hydraulic phenomena, namely the island
wake effect (when there is only one obstacle), and
the tidal jet effect (when there are two obstacles in
close proximity).

The Island Wake Effect

One of the most dramatic effects of the circulation
around islands and coral reefs is the generation of
recirculating flows downstream. LANDSAT views
(computer-enhanced for depth of penetration using
the techniques discussed by D. A. Kuchler page 90)
and aerial observations show that such recirculating
flows are visible when sufficiently strong currents are

* Contours of equal depth.

Figure 3. CZCS view, enhanced to emphasize chlorophyll, of
the central reef region. Note the two eddies at the shelf break
in the north and a complex jet-vortex system in the south.

present, and whenever there exists in the water a
natural "dye" (such as mud on the seafloor, or
particulates released from a reef). Topographically-
shed eddies are visible near the coast, in relatively
shallow (15 to 30 meter depth) waters around coral
reefs and islands, and around coral reefs in deeper
waters (60 meters depth) see Figure 4.

An intensive field experiment was carried out
to measure the recirculating flow around Rattray
Island at 20 degrees South. The shape of the wake
resembled that obtained in two-dimensional
laboratory investigations at low values (of the order
10 to 30) of the Reynolds number (a parameter
expressing the ratio of inertia to viscous forces).
However, the field data disclosed that there is no
valid analogy between the island wakes in two-
dimensional laboratory experiments and those
observed in nature. Indeed, the eddy in the
laboratory is composed of a mass of water that is
nearly stagnant, while at Rattray Island the waters in
the eddy are under very rapid rotation. Further, the
Reynolds number of Rattray Island, based on the
turbulent eddy viscosity, is a thousand times larger
than in the laboratory.

Figure 4. Aerial view of the eddies shed by coral reefs in 60-
meter-deep waters.

85

In 1802, one of Australia's foremost maritime
explorers, Captain Matthew Flinders was charged
with the first circumnavigation and charting of the
Australian coastline in the ship H.M.S.
Investigator. During this expedition, he noted the
unusual nature of the tides in the southern region
of the Great Barrier Reef.

Commenting on his observations in the
vicinity of Broad Sound, Flinders stated in his
journal, published in 1814: "On the west side of
the sound, . . . the rise at spring tides is not less
than 30, and perhaps reaches to 35 feet. " He
remarked on currents associated with "a tide
which ran at the strongest between 4 and 5 knots
and that the flood came in, 6 or 8 inches
perpendicular with a roaring noise, " presumably
a reference to the tidal bore that is known to exist
in the sound. Flinders also noted the unusual
phase of the tides, stating that "the time of high
water is nearly 1 1 hours after the noon's passage
over and under the meridian."

Flinders' observations have been
confirmed by direct measurement in recent times.
What is more remarkable is the perspicacity that
Flinders displayed in deducing a convincing
physical explanation for tides that are both very
much higher and later than those in neighboring
reef waters to both the south and north, and
which peak in Broad Sound itself.

The Reef, Tides, and

Flinders went on to write of a "super-
adding cause ... a vast mass of reefs which lie
from 20 to 30 leagues [100 to 150 kilometers]
from the coast. These reefs, being mostly dry at
low water will impede the free access of the tide;
and the greater proportion will come in between
Break-sea Spit [to the south] and the reefs, and be
late in reaching the remoter parts; and if we
suppose the reefs to terminate to the north, or
northwest of the Sound, or that a large opening
in them there exists, another flood tide will come
from the northward, and meet the former; and
the accumulation of water from this meeting will
cause an extraordinary rise in Broad Sound and
the neighboring bays. . . . I am disposed to think
that it is at the entrance of Broad Sound where
the two floods meet each other."

The map after page 8 gives some idea of
the density of these reefs (between 1 9 degrees
and 22 degrees South), in both the longshore and
cross-shelf directions. After considerable
difficulties (during a period of more than two
weeks), Flinders eventually found a passage,
subsequently named after him, out into the Coral
Sea. It must have been most unnerving to explore
for possible passages among reefs that are more
often than not invisible, especially given the
presence of such strong currents, in a small and
unwieldy sailing vessel — the Investigator was

To reconcile these observational differences,
it is believed, as is shown in Figure 5, that there
exists a mass of water in solid body rotation
separated by a dividing streamline from the
surrounding waters. Rotation in the eddy is
maintained by the large vorticity flux at the
separation point at the tip of the island. By analogy
with the circulation in a tea cup, the combined
effects of bottom friction and of rotation in the eddy,
generate a self-driven bottom benthic boundary
layer. As a result, water is sucked downwards from
the eddy to the bottom layer and upwelled near the
center. The upwelling process near the eddy center,
which brings fine particulates to the surface, makes
the eddy often readily visible from the air. The
downwelling controls the time and length scales of
the eddy.

The secondary circulation in the island wake
also is reflected in the sediment size distribution on
the seafloor, with less mud and more sand near the
eddy center than elsewhere.

The island wake parameter (P) determines the
wake shape; satellite and aerial views indicate that,
for increasing values of P, the downstream flow

becomes perturbed by meanders even very far
downstream. For higher values of the island wake
parameter, these meanders can become unstable
and form small eddies at their troughs and crests. For
very high values of P, the wake is fully turbulent with
no organized recirculating flow structure.

The "standard" depth-averaged numerical
models, developed for open waters, are generally
unable to yield a wake effect and predict a quasi-
potential flow pattern. A numerical scheme that
accounts for flow separation effects has been
developed recently. The resulting predicted currents
agree closely with the currents measured with
current meters moored at 26 sites.

It is now feasible to reliably model eddies and
their fate, when the eddies detach themselves from
their natal reefs. Two important properties of these
topographically-shed eddies are that they generate
patchiness and hence control the rates of diffusion
and dispersion through the reef matrix, they also
dissipate much of the kinetic energy of the incoming
flow facing the island, so that they greatly enhance
the bulk friction coefficient of the prevailing current.

If the water column is vertically stratified in

86

Flinders' Perspicacity

condemned the following year as unseaworthy!
Only in the last year has the charting and
marking of a navigational channel
(Hydrographer's Passage) for large cargo vessels
from the port of Mackay been accomplished.
From personal observation, tidal currents near
individual large reefs (for example, White Tip Reef
at the seaward entrance of this passage) can be as
high as 8 knots!

Present-day marine scientists may find it
sobering to read these extracts from Flinders'
account. They are a tribute, not only to his
navigational and cartographic skills (many of his
maps still form the basis of today's charts), but
also to his ability to conceptualize this large-scale
and unusual tidal flow pattern, along with the
active involvement of the reef itself, from only a
few key observations — all of this from a man of
only 26, recently given command of his first ship.

Essentially, Flinders' hypothesis was that
the tides are inhibited in their cross-shelf passage
by the high density of coral reefs in this vicinity.
As a consequence, the major streams flow
through the very large passages that exist to the
north and south (Flinders' Passage and the
Capricorn Channel, respectively), to converge
near Broad Sound. The position and geometry of
the sound results in further local amplification of
the tides. The considerable heads of water that

are induced by this inhibition result in very large
currents in the gaps between reefs, although the
actual proportion of water that crosses the reef
matrix is relatively small.

Interestingly, Flinders' hypothesis came to
light only recently, after a number of
investigators, using both analytical and numerical
models, had come to similar conclusions (roughly
160 years later). Of course, the Broad Sound area
is just one portion of the reef; Flinders' description
does not apply universally. How then do reef
structures elsewhere affect tidal as well as other
flows, given the contrasting geometric reef
patterns that exist? North of the dense reef
pattern, the reefs of the central reef region,
centered on Townsville, are relatively sparse.
They have little effect on the large-scale tidal
pattern. Farther north, the "ribbon" reefs exist,
with often 90 percent linear coverage along the
edge of the continental shelf, over large
distances. There, in contrast with the Mackay/
Broad Sound area, reefs are effectively transparent
to the tides, although the almost unbroken reef
chain does appear to act as a semi-permeable
barrier, modifying both the amplitude and phase
of the tidal wave passing "through" it.

— Lance Bode,
James Cook University

density, the flow separation at the tip of the island or
headland will still generate an eddy downstream.
However, and such is the case in the deep waters
near the shelf break, the strong current may be only
a near-surface phenomenon, and the eddy may be
confined to the well-mixed layer. The interfacial
stresses between the well-mixed layer and the
deeper water are small, so that the eddy in the well-
mixed layer does not have a tendency to be spun
down rapidly by suction. Hence, flow disturbances
are introduced and felt very far downstream. The
thermocline can take the shape of a dome in such
near-surface eddies. If the thermal dome of an eddy
comes in contact with the seafloor, considerable
suction and upwelling result.

The Tidal jet Effect

In the northern and southern regions, strong tidal
currents can exist in the reef passages between long
ribbon-shaped reefs spread along the shelf break.
When the currents are small, the density (thermal)
stratification results in selective withdrawal, as in a
stratified water reservoir, and, at rising tide (Figure 6),
only nutrient-poor water from the mixed layer is

flowing in the passage, the water from below the
thermocline being at rest. However, when the tidal
currents are very strong (say on the order of 100
centimeters per second), nutrient-rich deep water
can be entrained vertically up to 100 meters into the
reef passage (Figure 7). This water mass, and the
nutrients it contains, is then entrained by the tidal jet
effect into the shelf.

In calculating the bulk properties of such jet
flows, we determined that these eddies are basically
vortices which are self-propelled, that is, they tend
to move together away from the reef passage. These
eddies are not sucked back into the reef entrance at
the following falling tide. The mass of jet-injected
water will spin down by friction, but does not return
to the ocean and indeed stays roughly in the same
area for a very long time, giving plenty of time for
nutrient uptake at tidal frequencies nearly every day
of the year.

This phenomenon is believed to account for
the profuse meadows of the calcareous green alga,
Halimeda (see page 45), in the areas where the tidal
jet-vortex pair system appears to penetrate on the
shelf. These meadows are most prevalent near reef

87

Reef passage

Side view
Figure 5. The three-dimensional circulation in an island wake.

passages forming a small canyon, hence where
upwelling is facilitated, and appear not to exist in
areas where the shelf elevation is too high for
nutient-rich deep water to be upwelled by tidal jets.
The vortices dissipate much of the kinetic energy of
the incoming flow, and this may explain the blocking
effect by ribbon reefs on tidal propagation.

Surface Gravity Waves

Every sailor who takes shelter from the wind behind
a coral reef knows that reefs also measurably affect
surface gravity waves. Reefs provide a platform for
wave-breaking, diffraction and refraction. These
processes also control the formation and migration
of sand cays by establishing a zone of wave
convergence in the weather lee of platform reefs.
Wave breaking also raises sea level. This
combination can drive a net unidirectional current
over long thin reefs, such as the "ribbon" reefs. On
the other hand, a strong, two-dimensional flow
prevails over platform reefs near the shelf break with

^Continental^
"**" shelf 4^

i' ■■-"'.

Figure 6. The upwelling by tidal jet pumping at a reef
passage.

areas of higher elevation where waves break
preferentially, and areas of slightly lower elevation
where the return flow occurs after wave breaking. In
more sheltered reefs, one commonly finds a
submerged coral seawall, with occasional gaps,
running parallel to the reef it protects, and separated
from the reef by a drainage channel that
accommodates the return flow of the breaking wave.

Wave data from a site offshore of the Great
Barrier Reef show the presence of a classical oceanic
saturated wave spectrum under strong winds, with
the 10-second period wave (swell) dominating the
energy spectrum. On the other hand, inshore wave
data show that the swell is much smaller, and local
wind-sea, 4-second waves predominate. Thus, the
Great Barrier Reef matrix does indeed shelter the
lagoon.

In the lagoon, the 4-second wave introduces
pressure and current fluctuations near the bottom
that are too small to move the sediment except in
the nearshore zone. As a result, terrigenous
sediments may accumulate in the lagoon. This
hypothesis also is suggested from a comparison of
the distribution in the central region of the reef of
terrigenous mud on the seafloor, with that of the
minimal surface salinity during major river floods
(Figure 2). The shape of the salinity and mud
distributions is quite similar, except for a tongue of
mud through the reef matrix off the Burdekin River

88

mouth. That tongue is believed to be a relic one,
attributed to the old mouth of the river as the sea
level started to rise 10,000 years ago. The Burdekin
river plume, by buoyancy and effects of the Earth's
rotation, moves northward along the coastline and
against the prevailing weak southward currents. The
width of the river plume increases with distance
from the mouth of the Burdekin river, as a result of
both lateral mixing and of the additional freshwater
input from the Ross, Herbert, Tully, and Johnstone
Rivers. The Burdekin River, however, has by far the
largest freshwater discharge. Along the way,
terrigenous mud falls from suspension and
accumulates at the bottom. This mud may be quite
stable on the seafloor, since the swell is unable to
penetrate the lagoon, and because tidal and wind-
driven currents are quite small.

Conclusions

The large-scale water circulation on the continental
shelf of the Great Barrier Reef is complex, driven
mostly by currents, tides, and the wind. A full
understanding of this circulation still eludes us. On a
small scale, the presence of coral reefs and islands
serves to substantially modify the general water
circulation by increasing the overall friction, as well
as the wave climate of the Great Barrier Reef. The
existence of tidal jets and large eddies downstream
of a reef has profound effects on 1) the formation of
fronts, 2) the trapping of water and particulates, 3)
the mixing rates in inter-reef shelf seas (by creating
patchiness), 4) the overall water circulation (by
increasing the overall friction coefficient), and 5) the
sedimentology (by forming tidal banks and shoals
and possibly helping shape the reefs during
geological time).

The topographically directed flows around
reefs are believed to influence the aggregation of
plankton, fish eggs and larvae, benthic invertebrates,
and, possibly, the location of fisheries. These
complex flows are probably the dominant physical
process producing patchiness (advection and
diffusion in the inter-reef shelf seas of reef-born
suspended particulates once they drift away, as a
patch, from their natal reef). Hence, they help to
determine the level of biological exchange between
reefs. Collecting statistics on this exchange may be
the most useful information that physical
oceanographers can provide to the users and the
managers of the Great Barrier Reef. The tool for
understanding such information may be a recently
developed numerical model that can, with very
reasonable assumptions, reproduce such complex
flows.

Continental shelf

\

Ribbon Reef

- 0.5 m/s
1 km

Ocean

Ribbon Reef

Reef passage

Figure 7. Predicted depth-averaged velocity field over the
continental shelf in front of a reef passage at slack high tide.
The tidal current through the passage has a peak velocity of
100 centimeters per second. The shelf is assumed to be flat;
water depth = 37 meters.

Eric Wolanski is a principal research scientist at the Australian
Institute of Marine Science, Townsville, Qld., Australia. David
LB. jupp is a principal research scientist at the CSIRO
Division of Water and Land Resources, in Canberra, ACT,
Australia. George L. Pickard is Emeritus Professor of
Oceanography at the University of British Columbia,
Vancouver, B.C., Canada.

Selected Readings

Wolanski, E., G. L. Pickard, and D. L. B. Jupp. 1984. River plumes,
coral reefs and mixing in the Gulf of Papua and the Northern
Great Barrier Reef. Estuarine, Coastal and Shelf Science 18, 291-
314.

Wolanski, E., J. Imberger, and M. L. Heron. 1984. Island wakes in
shallow coastal waters, journal of Geophysical Research 89 (C6),
10553-10569.

Falconer, R. A., E. Wolanski, and L. Mardapitta-Hadjipandeli. 1986.
Modelling tidal circulation in an island's wake, journal of
Waterway, Port, Coastal and Ocean Engineering, Amer. Soc. Civil
Engineers 112 (2), 234-254.

Onishi. 1984. Study of Vortex Structure in water surface jets by
means of remote sensing. In: Remote sensing of Shelf Sea
Hydrodynamics, ). C. ). Nihoul, ed. Elsevier Publ., Amsterdam,
pp. 107-132.

89

Remote Sensing: What Can It

by D. A. Kuchler

Ounlight reflected from shallow seas and
submerged features is providing a wealth of
information on coral reef ecosystems. Until recently,
recording and interpreting this data on a routine
basis was not economically feasible. The advent of
the space age, however, ushered in the
development of advanced sensor systems and the
platforms that support them. These technological
gains now have made remote sensing a viable
method of collecting data for coral management and
research. For the Great Barrier Reef, remote sensing
has saved researchers and management both time
and money by providing information that is
otherwise unavailable.

Remote sensing's main advantage is that it can
collect some coral reef information faster and less
expensively than ground-based techniques. In
addition, it can measure uniformly the abundance
and distribution of phenomena in time and space.
Land- or ship-based measurements are only capable
of patchy sampling. While methods for deriving
chemical information from remotely-sensed coral
reef and oceanic data are still being designed,
research into the nature of remotely-sensed physical
and biological data is comparatively well advanced.
Among information gathered from the latter group
are data on reef geography, form, cover, and
vegetation.

Reef Geography

The geography of reefs is of extreme importance to
mariners, researchers, and administrators who assess
coral reef resources, plan shipping routes, and locate
potential fishing grounds. Until the processing of 24
Landsat Multispectral Scanner (MSS) images in 1985,
however, maps giving such information were not
available. Rectified satellite images, taken from the
Landsat satellite now provide such maps at scales of
1:250,000 and 1:100,000.

Once image distortions have been removed,
the map is accurate to within 200 to 500 meters.
While sufficient for many applications, this level of
accuracy is not precise enough for navigation,
cartographic, or environmental monitoring purposes.
By registering the images with a cartographic base,
higher map accuracies (± 64 meters) that meet the

National Map Accuracy Standard have been
achieved.

In addition to maps of a relatively small area,
satellites can produce much larger views as well. Just
two Coastal Zone Color images taken aboard the
Nimbus 7 satellite provide a total perspective of the
1 , 900-kilometer extent of the Great Barrier Reef,
while a regional perspective is available from images
taken aboard the space shuttle.

Reef Form

The form of a reef and its surroundings contains an
abundance of information that is key to innumerable
scientific and administrative concerns. Because reef
topography is virtually unseen from a land-based
perspective and at best obscure when viewed on a
raw Landsat image, a reef exposure image has been
devised to enhance images of topographic features.
It uses a technique of relief shading to clarify reef
features.

Through this relief shading, the exposure
images provide information on reef form that can be
used to:

• plan geophysical field programs on individual reefs;

• update site morphology;

• give clues to structural or stratigraphic features; and,

• show relationships between structure and site,
important in determining areas for research.

The exposure image also gives increased edge
enhancement for both the detection and mapping of
paleochannels and for an indication of a reef's
exposure to weather.

A further understanding of reef form is gained
from submergence and turbidity levels. These can be
estimated using remotely-sensed data of reflected
light from the sea, since depth of light penetration
tells us approximate water depths and turbidity
levels. The Landsat satellite has recorded water
depths varying from just below the sea surface down
to 20 meters. Factors affecting the satellite's ability to
get such information include the conditions of both

90

Offer Coral Reef Studies?

the sky and the water, and the absorption of light by
the water at the wavelength received by the satellite.

Reef Cover

A basic goal of research is to both understand and
explain the abundance and distribution of reef cover
types over time and space. With the availability of
Landsat data in 1972 (originally called ERTS-1 data),
the speed and sophistication of taking an inventory
of reef covers have increased significantly. Methods
of analysis range from visually interpreted maps to
advanced computer interpretations.

Variations in light reflected from a submerged
reef surface can be interpreted and utilized for a
number of different mapping purposes. This is
possible because a computer statistically classifies
digital image data into a number of classes. One
study determined the extent to which Landsat
mapped classes cross-compare with reef cover
classes on the ground. At most, classes showed 85
percent cross-comparison with reef zones, 82
percent with reef features, and 64 percent with reef
feature components. The results illustrate that
Landsat data can be used as a surrogate source of
ground information and that mapping precision
increases with smaller mapping scales (large area,
small detail).

Overseas, two successful projects are using
large scale (small area, large detail) remotely-sensed
data to map reef covers. For coral reefs in the Red
Sea, digitized aerial photographic data are being
used to make periodical surveys of seasonal change.
In New Caledonia, simulated SPOT satellite* images
are mapping possible trochus shell (Trochus niloticus)
habitats on offshore coral reefs.

The higher spatial resolution of a SPOT image
can be seen by comparing it with an aerial
photograph. Such resolution could be used to map
the devastating effects of Crown of Thorns starfish
(Acanthaster planci) on some corals of the Great
Barrier Reef (see page 58).

Vegetation & Micro-studies

Studies often are conducted to provide reef
vegetation cover maps either for management
inventories, research projects, or environmental

* The SPOT satellite is a high resolution (10 and 20 meters)
data collection system from which data will be available in
mid-1986.

impact assessments. Conventional field mapping
takes weeks to produce such maps, but processing
remotely-sensed data with computers can take only
a few hours.

Maps showing the dispersion of vegetated
coral cays and algal vegetation on shallow reef flats
can be produced from Landsat data. Digitized aerial
photographic data or SPOT satellite data can map
vegetation diversity and human or natural
interferences with vegetation cover.

Coral calcification and accretion studies also
can rely on remote sensing technology. Coral cross-
sections are digitized, and growth bands within the
resulting images are classified, contoured, and
measured using image processing techniques.

Remote sensing is providing another broader
view of the recently discovered coral spawning
phenomena. After the spectral reflectance
characteristics of coral spawn are determined, the
dynamics of coral spawn dispersal and settlement
are examined using a multistage remote-sensing
approach involving sensors aboard boats, aircrafts,
and satellites.

A Broader Look

Since coral reefs are a small subsystem of a much
larger oceanic system, they are often studied in this
context. Scientists have used remotely-sensed data
to study the oceans for many years. Typically, the
studies are at synoptic scales because oceanic
processes interact over wide ranges of space and
time.

Ocean color studies on the Great Barrier Reef
have concentrated on utilizing back-scattered
radiation in the visible part of the spectrum. Nimbus
7 Coastal Zone Color Scanner data have been used
to conduct synoptic surveys of phytoplankton
concentrations, to study mesoscale circulation
structures, and to map eddies and wakes. Other
researchers investigating ocean color have used
Landsat data to view sediment plumes and to
monitor high concentrations of material, such as
Trichodesmium blooms. Remotely-sensed
information on such blooms has been plentiful:
recordings have been made from the Landsat
satellite, from a NOAA satellite, and from the space
shuttle.

Not An Automatic Process

Interpreting remotely-sensed coral reef data is by no

91

Aerial photograph of Tetembia Reef, New Caledonia.

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WILDLIFE

FUND-US.

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means an automatic process. Rather, it involves
unravelling the spectral and spatial relationships
within the data, requiring much more basic research.
Consequently, researchers are focusing their efforts
on the collection and analysis of reflected surface
radiation from reef cover types.

Such emissions will provide the trained
interpreter with a vast amount of information about
the spectral composition of a coral reef. This
knowledge, coupled with the new generation of
sensors optimized for oceanographic applications,
will mean that coral reef and oceanic studies will
adopt newer, more precise, and more extensive
applications of remote sensing technology.

Deborah A. Kuchler is a research scientist at the
Commonwealth Scientific and Industrial Research
Organization (CSIRO), Division of Water and Land Resources,
Canberra, Australia.

Acknowledgments

The Great Barrier Reef research reported in this article was
supervised by Dr. D. L. B. Jupp, CSIRO Division of Water
and Land Resources, Canberra, and funded by the Great
Barrier Reef Marine Park Authority and Marine Science and
Technology Grants Scheme, Australia. Dr. Jupp, GBRMPA
(Australia), and GDTA, IFREMER, and IGN (France)
provided some of the satellite imagery.

References and Selected Readings

Bina, R. T., K. Carpenter, W. Zacher, R. Jara, and ). B. Lim. 1978.
Coral reef mapping using Landsat data: follow-up studies.
Proceedings Twelfth International Symposium Remote Sensing
Environment. Ann Arbor, Michigan. 2051-2070.

Bour, W., L. Loubersac, and P. Rual. 1985. Thematic mapping of
reefs by processing of simulated SPOT satellite data —
application to the Trochus niloticus biotope on Tetembia reef,
New Caledonia. Marine Ecology.

jupp, D. L. B. 1985. Report on the application and potential of
remote sensing in the Great Barrier Reef region. GBRMPA
Research Publication.

Jupp, D. L. B., P. Cuerin, and W. Lamond. 1982. Rectification of
Landsat imagery to cartographic bases with application to the
Great Barrier Reef. Proceedings URPIS 10, Sydney, NSW, Dec,
ed. K. R. Nash. 131-147.

Jupp, D. L. B., K. K. Mayo, D. A. Kuchler, S. J. Heggen, and S. W.
Kendall. 1981. Remote sensing by Landsat as support for
management of the Great Barrier Reef. "Landsat 81," Proceedings
2nd Australasian Remote Sensing Conference, Canberra, 9.5.1-
9.5.6.

Jupp, D. L. B„ K. K. Mayo, D. A. Kuchler, S. J. Heggen, S. W.
Kendall, B. M. Radke, and T. Ayling. 1985. Landsat based
interpretation of the Cairns section of the Great Barrier Reef
Marine Park. CSIRO Division of Water and Land Resources,
Natural Resource Series No. 4, 51 p.

Jupp, D. L. B., K. K. Mayo, D. A. Kuchler, D. V. R. Classen, R. A.
Kenchington, and P. R. Guerin. 1985. The application and
potential of remote sensing to planning and managing the Great
Barrier Reef of Australia. Photogrammetria, 40. 21-42.

Kuchler, D. A. 1985. Geomorphological separability Landsat MSS
and aerial photographic data: Heron Island Reef, Great Barrier
Reef, Australia. Ph.D. Thesis, Department of Geography, James
Cook University of North Queensland, Australia.

Maniere, R., and J. Jaubert. 1984. Coral reef mapping in the Gulf of
Aqaba (Red Sea) using computer image processing techniques.
Proceedings Symposium on Coral Reef Environment of Red Sea.
Jeddah, Saudi Arabia.

92

Landsat satellite image of Heron Island and
Wistari Reefs on the Great Barrier Reef. Red is
the spectral response to vegetation, white is
the beach around the cays. (Image courtesy of
D.A. Kuchler)

Ilslaimdl:

by Harold Heatwole,
and Peter Saenger

I he islands of the Great Barrier Reef range from
tiny sand patches so small you can barely stand on
them to mountainous islands more than 150 square
miles long with rocky peaks rising 3,650 feet above
sea level. Some are remote and visited only by an
occasional, lone scientist or beachcomber; others are
built-up tourist resorts with helicopters constantly
flying people in and out. The islands are also a haven
for birds.

Islands and birds go together. Birds deposit
guano on islands, which not only forms phosphate
rock (or cay rock), but also fertilizes the soil and thus
stimulates plant colonization. Birds also bring seeds
to islands. In turn, the islands provide birds with a
place to breed and/or nest without the disturbance
of humans or mainland predators, such as rats, foxes,
snakes, monitor lizards, and raptorial birds.

Although there are many species of birds on
the islands, there are only two kinds of islands on the
Great Barrier Reef: continental islands and cays.*
Continental islands are located on continental
shelves that were once part of the mainland
geological formation, but became isolated as either
the land sank, the sea level rose, or a combination of
the two occurred. Cays are formed in situ as the sea
and wind act on local sediments. While cays may lie
on continental shelves or on remote reefs, they were
never part of the mainland.

Along the Great Barrier Reef, the prevalence
of these two types of island changes. The northern
and southern parts of the reef contain numerous
cays, whereas the central region has few.
Throughout there are more than 240 cays. By
contrast, the continental islands are located primarily
in the central section of the reef. All in all, more than
2,100 individual reefs make up the main barrier, with
540 continental islands closer inshore supporting
fringing reefs.

Cays

On the Great Barrier Reef, sand cays are composed
primarily of the remains of marine organisms, such as

* Keys is the American spelling. Cays is used elsewhere in
the English speaking world.

A view of the Swain Reefs showing two small sand cays,
Bacchi Cay in foreground, Thomas Cay in background.
(Photo courtesy of Menna lones)

coral, mollusk shell, calcareous algae, and
foraminiferans. These organisms may be ground into
small particles to form sand; water currents then
deposit them on the top of the reef. A cay evolves as
enough sand accumulates to be exposed at low tide
and winds add more sand on top. Since cays are
formed at the surface, they can date only from the
time the coral reached present sea level; those on
the Great Barrier Reef are only about 4,000 years
old.

In addition to currents and winds, storms also
are a potent force in cay development. Hurricanes
can tear pieces of coral from the reef front and hurl
them onto the reef. These large pieces of shingle
may accumulate and form a shingle cay. On some
islands, successive storms have left their mark in
concentric ridges of shingle, the most recent storm
composing the outer ridge and earlier ones forming
the inner ridges.

Once formed, cays often change their shape.
One way this occurs is through the formation of
beach rock. Beach rock develops below the sand
surface at the periphery of a cay. How it forms is still
not completely understood, but it seems to involve
the precipitation of calcium salts among the sand
grains, consolidating them into rock. This can occur
very rapidly. When the beach subsequently erodes,
the exposed beach rock is left as an outcrop.

Cays are not only unstable, but because of
the various ways they are formed, they are quite
diverse: they can be all sand, all shingle,
combinations of both, or have large outcrops of
beach rock or cay rock.

Occurring only on the northern Great Barrier
Reef, low-wooded islands form from a combination
of a sand cay on the leeward side of a reef platform
and a shingle cay on the windward side. The

94

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A colony of Crested Terns nesting on Bell Cay, Swain Reef. (Photo courtesy of H. Heatwole)

depression between the two is then colonized by
mangrove trees which, in turn, result in deposition of
organic materials and the build-up of sediment.
Thus, low-wooded islands often are composed of
sand, shingle, and organic sediment.

Colonization of Islands

Amazing though it is, even tiny, remote islands
support plants and animals. Continental islands have
a head start in this regard since some of their species
may have been stranded when the island formed,
and have simply persisted there ever since. For coral
cays, the situation is quite different. When cays
emerge from the sea, they contain no terrestrial life:
all their plants and animals must reach them across a
seawater barrier.

The ways that life arrives are varied. Many
insular plants have seeds or fruits that can float for
weeks or even months and remain viable in seawater
for long periods of time. Such plants are dispersed
long distances by sea currents. Others have hooks or
sticky secretions on their fruits, or seeds that adhere
to feathers; these plants are widely dispersed by
birds as they fly from island to island. Still other
plants reach the islands inside birds' digestive
systems.

On One Tree Island, 48 percent of the plant
species were sea dispersed and 22 percent bird
dispersed. The rest were distributed either by the
wind, humans, or unknown means. Curiously, few
species of plants seem to reach the islands by wind.
In general, the pioneer plants on small and/or new
islands are sea dispersed while plants in the center
are bird dispersed.

Along with plants come insects, many of
which reach the islands through offshore winds.
When the winds are right, many insects reach tiny,
remote Willis Island, 280 miles from Australia; some
are even blown from as far away as New Guinea, a
distance of more than 370 miles. Although nearly 97
species of insects were carried to this island in a
single season, most did not become established.
Even small, weakly flying insects can be passively
wafted by winds. Such strong flyers as butterflies and
dragonflies, however, can cover long distances under
their own power.

Another way that small, terrestrial
invertebrates — insects, spiders, centipedes, and
mites — reach islands is by flotsam. Logs or other
debris cast adrift from beaches or flooded rivers
carry on or within them a surprising variety of such
animals, and help colonize distant islands.

Even after these invertebrates and plants
reach the islands, they still must survive the hot,
salty, waterless, and nutrient-poor conditions of
newly formed sand cays. Thus, only the hardiest
species persist on newer islands. As cays grow large
enough to retain freshwater, and the interiors are
further removed from the effects of salt spray,
conditions become more benign, and more
immigrant species become established. Plants help
both stabilize the substrate and enrich the soil with
organic matter as they die and decay. These
improved conditions allow additional species of
plants to colonize. The variety of plants increases
from four or five species to as many as 40 species on
older cays. These insects and plants change the

95

¥2***5*"':K, ..U

Beach near lighthouse bordered by shrubs (Octopus Bush,
Argusia argenteaj on North Reef Cay, Capricornia Reefs.
(Photo courtesy of H. Heatwole)

The forested interior of a cay in the Capricorn Islands,
Masthead Island. (Photo courtesy of H. Heatwole)

environment. For example, plants cast shade and
lower the ground temperature, form leaf litter which
serves as cover for invertebrates, and add organic
matter to the soil.

On very small or newly formed cays, the food
basis for the terrestrial community is not the plants
that colonize, but the marine community. The first
truly terrestrial organisms that become established
on new islands are scavengers feeding on dead fish,
other marine organisms that wash up onshore, and
on guano and the carcasses of dead seabirds. These
include earwigs, beetles, and flies. Next to settle on
the cays are predators such as spiders, centipedes,
and other invertebrates that feed on scavengers.
Proof of this is the number of sand cays, completely
devoid of vegetation, that have been found to have
scavenger-based communities, complete with
predators, of up to 1 1 species of terrestrial
invertebrates. The final colonization phase involves
the establishment of green plants, and the
subsequent herbivores and additional species of
predators. As the islands grow and contain increasing
numbers of plant species, the local plants become
the principal food base for the community, which
thus depends progressively less on the marine
community.

Insular Instability

Continental islands are more stable than cays
because of their rocky substrate, high topography,
and relatively large size; cays, in contrast, are usually
small, flat, and sandy. While some cays remain in the
same place for a long time, others have only a stable
center and the edges, particularly the ends, shift
back and forth with temporal changes in currents.
Varying currents and storms can build and erode
cays. Some cays tend to move in a continuous
direction, eroding from wave action on the
windward side, and redepositing sand on the
leeward side. Cays can creep progressively across
the reef seemingly destined to disappear over the
reef edge into deep water.

Instability is related partly to cay size. The
smaller, lower cays are generally less stable than the

larger ones. Successive aerial photographs can map
the changes of an island such as Bylund Cay in the
Swain Reefs section of the Great Barrier Reef. In 20
years, this cay moved across its reef so much that
only about a fourth of it overlapped in photographs
taken in 1964 and again in 1984.

Insular Vegetation

As an island changes, so does its vegetation. Cay
vegetation relates to an island's size, age, and
stability. Generally, the larger the island, the greater
the number of species of plants. Large cays are less
susceptible to washover by the sea, except on the
edges, and the intensity of salt spray diminishes
toward the interior. Many islands have a ring of
shrubs, especially Argusia argentea and Scaevola
sericea, around the edge. A comparison of the levels
of salt spray on the seaward and interior sides of the
shrubs demonstrates that they form an effective
barrier against air borne salt and thus ameliorate
conditions inside the shrub ring. This permits plants
that could not otherwise survive to grow, increasing
the number of species that can eventually culminate
in a forest.

In these ways, the cay and its vegetation
develop together in five stages. In the first Pioneer
Stage, only low, hardy plants cover the entire island
sparsely. Next the Herb Flat Stage contains two
vegetation zones: 1) the pioneer vegetation around
the edge where conditions are harsh and unstable;
and 2) a denser, lusher cover with more species in
the milder interior conditions. The third stage is the
Shrub-Ring Stage which differs from the second one
by the presence of shrubs separating the beach and
interior zones. In the fourth Parkland Stage, shrubs
and trees occur in the interior herb flat forming an
open woodland. Finally, the Forested Stage features
a series of concentric vegetation zones: the pioneer
vegetation on the edge followed by a ring of shrubs
with a forest replacing herb flat and parkland in the
center.

Although many islands on the Great Barrier
Reef conform to these stages, many do not, but
instead are affected by local conditions. Shrub rings

96

Mangroves (Rhizohora stylosa) with their graceful stilt roots
form part of the vegetation of low wooded isles. (Photo
courtesy of Peter Saenger)

A pair of Brown Boobies and their chick on Bylur
Swain Reefs. (Photo courtesy of H. Heatwole)

may be incomplete or the interior may have
parkland in some places and forest in others. Low
areas with brackish water seepages may have a mat
of succulents, and mangroves may produce different
conditions.

Composite islands with mangroves are a
special case. The vegetation of sand and shingle
sections often resembles that of sand cays and
shingle cays, respectively. However, the parts of
islands with mangroves are unique and consist of
many species of mangrove trees. In the leeward
sites, the mangroves are divided into two
communities. In one, mature woodlands of up to six
species of trees occur on the higher, more protected
sediments. The second community, peripheral to
woodland on the leeward reef margin, is a mangrove
forest, primarily of the stilt-rooted Rhizophora
stylosa, but occasionally containing other species.
This mangrove forest extends out to the edge of the
sediment zone where live corals begin. The more
exposed windward sites support dwarfed mangrove
shrubs in small, outlying patches.

Mangrove or otherwise, the development of
islands is often reversed by a degradational process
of deterioration. Since cays usually erode only on
one side, a lopsided vegetational pattern occurs:
while the sea eats away the beaches and encroaches
directly on the later-stage vegetation on one side,
the Pioneer zone is still intact between the sea and
the mature vegetation on the other side. In other
words, when erosion and sand deposition occur on
opposite sides, the central type of vegetation is left
as a remnant near the eroding edge, and the newer
part of the island is covered with pioneer vegetation.

Seabirds and Vegetation

Island vegetation and seabirds are intimately
associated. Not only do birds carry seeds to the
islands and fertilize the soil, but they also affect
plants by trampling on them. Heavy birds such as
gannets can break off parts of plants and compact
soil. Where bird densities are high, this effect causes
some cays to appear bare when, in fact, live roots
are in the soil.

For example, Gannet Cay was once heavily
vegetated with Tah-vine (Boerhavia diffusa). Now the
large fleshy roots send up shoots, but they seldom
get more than a half inch tall with a few small leaves
before birds destroy them. Eventually, if this situation
continues, the roots use up their stored energy
reserves and die. In this extreme case, birds virtually
strip a cay. Wire-mesh cages that exclude seabirds
have been built around several small plots on
Gannet Cay, and the vegetation growing inside
shows the effect of the absence of birds.

Another way seabirds adversely affect plants
is by producing excessive guano. Although guano is
beneficial as fertilizer, too much can burn plants.
Although some species of plants on coral cays can
tolerate levels of guano that would kill other plants,
even these plants can succumb to both the
trampling and excess guano prevalent immediately
around nests.

Sometimes, however, another cycle occurs:
birds nesting on bare sand improve the soil and
permit plants to grow. This provides suitable nesting
sites for additional species of birds that, in turn, kill
the plants, opening up bare patches. When these
birds leave and the vegetation recovers, this cycle
continues as birds return to nest on the sand.

Birds on the Islands

Continental islands have a wide variety of land birds
living in habitats similar to those they occupy on the
mainland. Cays, in contrast, have fewer such habitats
and thus more seabirds than land birds.

Seabirds are mainly associated with coral cays
where they breed. The Great Barrier Reef, with its
abundance of cays and coral reefs is one of the
richest areas in the world for tropical and subtropical
seabirds. Twenty-nine species of seabirds from seven
different families, including gulls, terns, gannets,
shearwaters, herons, and frigatebirds are distributed
throughout this region. Of these, 19 species breed
there with colonies occurring on at least 78 different
islands.

97

Sea Turtles

I he Great Barrier Reef is one of the few places
in the world where several species of sea turtles
still abound. Although vast numbers of immature
and adult green turtles, Chelonia mydas, live year
round within the Great Barrier Reef, most that
breed there actually live in the waters of
neighboring countries. Green turtles, for example,
inhabiting the Coral Sea/Arafura Sea region,
usually migrate to breed on a few coral cays such
as Raine Island and Pandora Cay in the north and
the Capricornia Islands in the south.

The Hawksbill turtles, Eretmochelys
imbricata, live sparsely on every coral and rocky
reef, and also migrate to specific nesting
beaches-small sand cays on the inner shelf in the
far northern section and in Torres Strait. Some,
however, migrate internationally to breed as far
afield as the Solomon Islands. Most loggerhead
turtles, Caretta caretta, living in the Coral Sea/
Arafura Sea region breed on the small sand cays
of the Capricornia Section and the surf beaches of
the adjacent mainland in the south. Loggerheads
live principally in the sandy lagoons of the reefs
and in the inshore bays.

While green and loggerhead turtles
migrate across deep oceanic waters, the flatback,
Natator depressa, never leaves the shallow
waters of the continental shelf. Within the Great
Barrier Reef, flatbacks migrate to the southern
end to nest on continental islands such as Peak
and Wild Duck Islands. Small numbers of olive
ridley turtles, Lepidochelys olivacea, also live in
the inshore turbid waters along the reef, but it is
not known where they breed, only that they have
not been found breeding within the Great Barrier
Reef.

Each turtle has a home feeding ground,
probably encompassing 100,000 square meters,
where it can be found for many years. At
breeding time, the adults migrate to their own
specific breeding areas. The peak breeding season
lasts from October to February, but may occur
less frequently at other times of the year.
Courtship occurs in the sea; each female mates
with a series of different males for a few days. In
this way, she acquires enough sperm to fertilize
the hundreds of eggs she lays in the following
weeks. The males return home after a month of
courtship while the females move to their inter-
nesting habitat, usually quiet, shallow areas near
the nesting beaches.

During one nesting season, each female
will lay three to five clutches of approximately
120 eggs (with flatbacks averaging 50 eggs to the
clutch) in two weekly intervals. According to
estimates of growth rates, the turtles appear to be
about 50 years old when they mature for first
breeding. After a breeding season, female turtles

Many green turtles, Chelonia mydas, nest on Raine Island,
one of the few remaining green turtle rookeries in the
world and the only one in the southern Pacific Ocean.
(Photo courtesy of Colin Limpus)

return immediately to their home feeding ground
where they remain for many years before
migrating again, usually to breed at the same
beach.

When sea turtles nest, they dig a large pit
in the sand in which they lay their eggs. In so
doing, they break vegetation and tear up whole
plants by the roots. On small islands, the nesting
area may cover the entire island, and be heavily
pitted throughout. Only the pioneer plants,
especially the vines and those that send out
runners, survive; thus, sea turtles tend to keep the
parts of the islands where they nest in the pioneer
stage.

Sea turtles require specific nest
temperatures. Temperature at nest depth
determines the location of major turtle rookeries.
Turtle eggs will not hatch if the nest sand is
cooler than 24 degrees Celsius or warmer than 34
degrees Celsius. The beaches of the Great Barrier
Reef are a suitable temperature for successful year
round breeding in the north, but are suitable only
for summer breeding in the south.

The nest temperature during the middle
50 percent of incubation determines the sex of
the hatchlings. Each species has a temperature
that determines sex and uses nesting beaches that
provide the range of temperatures necessary to
ensure hatchlings of both sexes. However, the
number of turtles that survive from hatchlings to
breeding adults is extremely low, perhaps as low
as a few hatchlings per 10,000.

Sea turtles and their eggs long have been
the traditional food of coastal and island peoples.
Unfortunately, turtle and egg harvests have

98

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Feeding ground recaptures of female turtles, Chelonia
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numbers denote multiple recaptures.

escalated in the 20th century with the use of
more efficient catching techniques and improved
transport facilities. This, along with the
degradation of many turtle habitats, now
threatens sea turtles. Positive conservation
management by both Australia and her neighbors
is required to ensure the survival of turtles, which
by their intrinsic biology, cannot adapt to long-
term intensive harvests or rapid alteration of their
environment.

— Colin Limpus, Australian
National Parks and Wildlife Service

Along with the seabirds, many shorebirds and
waders, such as sandpipers, plovers, curlews,
whimbrels, and tattlers inhabit the beaches of cays.
These birds are closely linked with the sea, but are
not usually considered true seabirds. Some remain
only seasonally or during pauses in their migratory
flights. The reefs and beaches of some of the Great
Barrier Reef islands have become important habitats
for their feeding and roosting since estuaries and
continental shores have either been destroyed or
populated by humans.

Land birds are a less conspicuous part of the
avifauna of cays, although a few species such as the
Silvereye (Zosterops lateralis), Buff-breasted Rail
(Rallus philippensis) and Bar-shouldered Dove
(Geopelia humeralis) breed on the more heavily
vegetated cays. Many land birds that are lost, blown
offshore by storms, or merely stop during migration
are non-breeding transients on cays. For example, 18
transient species of land birds have been sighted on
One Tree Island.

As long as there are islands, birds probably
will inhabit them. Continental islands and cays attract
different species of birds because of their varying
resources. As cays and their vegetation change, so
does the bird fauna. Some of the islands and cays
are already national parks, a situation that will
protect the birds and encourage them to continue
nesting there.

Harold F. Heatwole is Associate Professor in Zoology at the
University of New England, New South Wales. Peter Saenger
is a Research Fellow with the Department of Zoology,
University of New England, New South Wales.

Some of the colonies are large: 20,000 Sooty
Terns (Sterna fuscata) nest on Michaelmas Cay and
10,000 on Raine Island (along with M other species);
70,000 Black Noddies (Anous minutus) nest on
Heron Island and 160,000 on North West Island. In
addition, 8,000 Common Noddies (Anous stolidus)
nest on Michaelmas Cay and 6,000 on North Reef
Cay on Frederick Reef; 750,000 Wedge-tailed
Shearwaters (Puffinus pacificus) nest on North West
Island. The amounts and types of seabirds that breed
on any particular island usually depend on the
accessibility to their hunting grounds and the
presence of suitable habitats for nesting.

Some islands are more important breeding
sites than others. The 10 most important ones in
descending order are: Raine, Bramble, Michaelmas,
Swain Reefs (a number of small cays), Masthead,
North West, One Tree, Wilson, Pipon, and Fairfax.
Many more are collectively important nesting areas
such as the Capricorn group of islands. Including
both breeding and non-breeding birds that use the
cays for roosting, there are an estimated 1.5 million
Wedge-tailed Shearwaters, half a million Black
Noddies, more than 3,000 each of Crested Terns and
Bridled Terns, and 2,000 each of Black-naped Terns
and Roseate Terns in the Capricorn area.

Suggested Readings

Bennett, I. 1971. The Great Barrier Reef. Lansdowne: Dee Why West.
Farrow, R. A. 1984. Detection of transoceanic migration of insects to

a remote island in the Coral Sea, Willis Island. Australian lournal

of Ecology, 9: 253-272.
Fosberg, F. R. 1976. Coral island vegetation. In Biology and Geology

of Coral Reefs, eds. O. A. Jones and R. Endean, Vol. 3, Chapter 8,

pp. 255-277. New York: Academic Press.
Heatwole, H. 1976. The ecology and biogeography of coral cays. In

The Biology and Geology of Coral Reefs, eds. O. A. Jones and R.

Endean, Vol. 3, Chapter 11, pp. 369-387. New York: Academic

Press.
Heatwole, H. 1981. A Coral Island. Sydney: Collins
Heatwole, H., T. Done, and E. Cameron. 1981. Community Ecology

of a Coral Cay. The Hague: Dr. W. Junk.
Heatwole, H. 1984. Island and plant and animal life: biological

microcosms. Reader's Digest Book of the Great Barrier Reef, ed. F.

Talbot, pp. 324-353. Sydney: Mead & Beckett.
Hopley, D. 1982. The Geomorphology of the Great Barrier Reef:

Quaternary Development of Coral Reefs. New York: John Wiley

& Sons.
Kikkawa, J. 1976. The birds of the Great Barrier Reef. In Biology and

Geology of Corals Reefs, eds. O. A. Jones and R. Endean, Vol. 3,

Chapter 9, pp. 279-341. New York: Academic Press.
Maxwell, W. G. H. 1968. At/as of the Great Barrier Reef. Amsterdam:

Elsevier.

99

Dugongs
and People

by Brydget E. T. Hudson

^)ealore has it that the appearance of one or more
of the species of sea cows, or Sirenians, gave rise to
mariners' tales of mermaids. One species within this
taxonomic order is now extinct (the Stellar sea cow),
and most others are threatened. In the Indo-Pacific,
the dugong has likewise come under increased
hunting and environmental pressures. In the Great
Barrier Reef region, steps are being taken to ensure
its survival.

The dugong fishery has followed a path
paralleled by other of the world's fisheries. A current
Northern Hemisphere example is the bowhead
whale fishery of western Alaska (see Oceanus, Vol.
29, No. 1 , pp. 81-84). In these and other cases, the
pattern is similar: a traditional fishery exists on a
small scale, largely in balance with the resource, and

Dugongs. (Photo courtesy David Parer)

is self-regulating. Due to economic factors and
technological improvements, the fishery changes in
nature and scope. As the resource is depleted,
concerns surface (often belatedly), and management
plans are called for. These plans are difficult to
design, implement, and enforce (for reasons
described later). When modern management plans
are successful, it is often found that many of their
components resemble elements of the self-regulating
system contained within the former traditional
fishery.

The difficulties in effective management stem
from the duality of purpose. That is, while it is clear
that a species needs protection, and that commercial
hunting should be restricted or banned, it is not that
easy. There also is a compelling argument in favor of

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Location of traditional
communities, hunting reefs,
and major dugong habitats.
Circled highlight numbers
indicate (1) Daru, capital of the
Western province of PNG. A
site of hunting, research, and
management; (2) Warrior Reefs
hunting area; (3) Orman Reefs
hunting area; and (4) Lockhart
River and Hopevale Aboriginal
communities.

100

traditional hunting by indigenous peoples, and a
maintenance of their culture and traditions. With
these dual goals, conflicts are inherent, and an
agreeable compromise is often difficult to attain.

The dugong fishery in and around the Torres
Strait region is illustrative of the pattern, the issues,
and the attempts at resolution. Its management is a
complex biological and sociological undertaking,
with both economic and political implications. The
principal peoples involved are the Kiwai of the
Western Province of Papua New Guinea (PNG), to
the north of the Torres Strait; the Torres Strait
Islanders; and the Aboriginal people of eastern
Australia.

Modern Management Regimes

As the dugong were depleted, management plans
were set into place. At present, there are several
levels: international, national, and local (for example,
specific to the Great Barrier Reef). Although the
general goals are similar, there are incongruities in
the mechanisms, and in the definition of terms.

In Papua New Guinea, the Fauna Protection
and Control Act of 1968 enables protection of
species declared as "National Animals." Such species
may not be commercially exploited, but may be
taken by indigenous people if they use "traditional"
techniques, and hunt for "traditional" purposes. The
act also enables creation of "Wildlife Management
Areas," where a community may designate an area
for local management.

Across the straits in Queensland, fisheries
legislation prohibits the taking of dugongs except by
indigenous people living on reserves. There is no
restriction on hunting techniques.

On the international level, a treaty between
Australia and Papua New Guinea, commonly called
the "Torres Strait Agreement," was ratified at the
beginning of 1985. It defines traditional fishing
liberally — in light of prevailing custom. It institutes an
"International Conservation Area" and establishes
reciprocal rights for traditional fishing and use within
the defined area.

Lastly, the Great Barrier Reef Marine Park
Authority (GBRMPA), under its legislation and
through consultation with the public, includes in its
management two groups of indigenous people living
on reserves within the park: the Hopevale and
Lockhart River Aboriginal communities. At present,
the people of the Hopevale Community, in the
Cairns Section of the park, are required to apply for
a restricted number of permits to hunt dugongs
within their traditional hunting area. Presumably, this
system will be extended to the Lockhart community,
in the Far Northern Section, at a later date.

Traditional Hunting

Before 1920, the people of the Torres Strait used
two methods for hunting dugong. The first and
perhaps oldest method was the use of a platform set
over the seagrass beds where dugongs came to feed
at night. In the second, dugongs were hunted from
single-outrigger canoes using harpoons. The Kiwai
have an intimate knowledge of the movements of
the dugong relative to the moon-phase and tidal

A dugong herd in Moreton Bay, near Brisbane. (Photo
courtesy of George Heinsohn)

state — a knowledge vital to the positioning of the
platforms and the canoes. Hunting was only possible
in the season at the end of the year when the
northeasterly winds were light, the seas calm, and
the dugongs fat and near calving.

The number of hunters was limited by access
to the knowledge of the best hunting locations, the
useable reef areas, access to the magic stones and
other charms needed, and the technical skill and
courage needed for such hunting.

Prowess as a dugong hunter earned the
hunters great prestige within the community. Each
village had only a few skilled "dugong-men". The
rights to hunt on certain reefs were jealously
guarded, and the "home reefs" close to each village
were sacrosanct. Dugong hunting had a role in
training young men for adulthood, in maintaining the
social position of women, and in the social
organization of the villages.

The human population was small and kept in
check by limited resources, disease, and infanticide.
While the hunting technology was effective, the
numbers taken were limited by the difficulties of
transporting such a large animal back to the village
for the ritual butchering that appears to have been a
feature of all these societies. Dugong meat was
typically used only for special occasions such as
traditional feasts. However, these occurred
infrequently, and although several dugongs could be
eaten at each feast, excessive hunting beyond the
needs of the community was unthinkable.

This general pattern was repeated by

101

'Dugong Is Number One Tucker'

I f you ask a coastal Aborigine or Islander from
the Great Barrier Reef region to nominate his
favorite food, he will probably tell you that
"dugong is number one tucker" (outback word
for food). Dugong meat is delicious tasting —
rather like beef or veal, and is typically reserved
for special, often religious, occasions — much like
turkey at Thanksgiving in the United States.
Dugong oil is also valued for its medicinal
properties.

The dugong is one of only four surviving
species of sirenians, or sea cows. The other
existing sirenians are the three species of manatee
that occur in the Caribbean region and the
southeastern United States, the Amazon River
Basin, and West Africa, respectively.

Manatees tend to be riverine or estuarine,
and are believed to be physiologically dependent
on fresh water. In contrast, the dugong is the only
herbivorous mammal that is strictly marine. It is
usually seen in shallow, sheltered bays that
support extensive beds of the seagrasses on
which it feeds. Within the Great Barrier Reef
lagoon, dugongs have been sighted up to 55
kilometers from land. Often, the dugongs form
herds, consisting sometimes of up to several
hundred animals. The Aborigines believe that
these herds are controlled by animals known as
"whistlers." Unlike dolphins, dugongs are not
known to echolocate. The only sounds recorded
to date are bird-like chirps.

Historically, the dugong's range extended
throughout the tropical and sub-tropical coastal
and island waters of the Indo-West Pacific from
East Africa to Vanuatu (an independent nation of
some 70 islands, 1,200 miles east of the Great
Barrier Reef). It is now considered rare over much
of this range.

On the other hand, aerial surveys
conducted in northern Australia since the mid-
1970s have shown that substantial numbers of
dugongs still occur in this area. It may be that a
major portion of the world's remaining dugong
stock is located in these waters. On a still more
localized level, up to 600 dugongs have been
seen from survey aircraft near the mouth of the
Starcke River, in the Cairns Section of the Great
Barrier Reef Marine Park, making this the most
important dugong habitat yet identified.

Recent studies of dugong life history have
been based on more than 600 dugongs caught
by Aborigines or Islanders, or killed accidentally

Although the dugong looks like a rotund dolphin, it is an
herbivore feeding on seagrasses. Its nearest non-sirenian
relative is thought to be the elephant. Dugongs grow to
about 3 meters and weigh from 250 to 400 kilograms.
(Photo counesy of Tony Preen)

in the shark nets set for bather protection. The
results show that the dugong life span may be
greater than 70 years, and that females do not
bear their first calf until they are at least 10. A
single calf is produced at intervals of from 3 to 7
years. Most calves are born between September
and January — just before the seagrasses are at
their most nutritious. Calves remain with their
mothers for at least two years, and suckle for at
least 18 months. The cow-calf bond appears to
be extremely well-developed.

Because dugongs are such slow breeders,
they are vulnerable to over-exploitation.
Population models indicate that, even with the
most optimistic combination of life history
parameters and a low level of natural mortality, a
dugong population is unlikely to increase by
more than 5 percent per year. This means that at
least 200 dugongs are needed to be able to
harvest five females per year without causing the
population to decline. Plummeting catches
suggest that the level of harvest in the Torres
Strait Region in the late 1970s far exceeded this
level.

— Helene Marsh
James Cook University, Townsville.

aboriginal people throughout the region — as far
south as Botany Bay, near Sidney.

A Changing Technology

The changes that have taken place in the technology

relating to dugong hunting underline the complexity
of management in such situations.

In the 1920s, the use of the hunting platforms
ceased, and a new form of double-outrigger canoe
was developed by the Kiwai. Where previously their

102

Kiwai hunter with harpoon on the bow of a double-outrigger canoe. (Photo courtesy of Elizabeth Parer-Cook)

single-outrigger canoes could only be used as
nearshore craft, the new canoes — up to 30 feet in
length, and requiring 9 to 1 1 men to sail them —
made longer visits to the reef possible, and thus
extended their hunting range. The number of
dugongs that could be carried in these boats also
was increased to four or more.

In recent times, the canoes have been
replaced by dinghies powered by outboard motors.
Some trawlers and other commerical fishing boats
also have appeared. A few indigenous trawler
owners have used their boats as "mother-ships"
when hunting dugongs on the reefs in quasi-
traditional fashion.

There also was a change in the outlet for
dugong meat. In 1957, a market was established at
Daru (provincial capital, Western Province, PNG).
The Kiwai requested permission to hunt dugongs
and turtles to provide meat for the expanding
population. This commercial outlet for dugong meat
increased their annual kill from about 25 to 75
dugongs per year.

The take of dugong next became linked to
other developing fisheries. In the 1970s, efforts were
made to develop economically the Western
Province of PNG. Two high-value marine resources,
the barramundi (perch-like fish) along the coast, and
crayfish (or lobsters) on the reefs, became the basis
of fishing industries. The Kiwai soon discovered that
the nets introduced for barramundi fishing also
caught dugongs very efficiently. They considered
this particularly beneficial in the southwest wind
season, when other forms of hunting and fishing
were impossible because of the rough sea

conditions. During this time, the dugongs came close
to Daru Island and residents, often people with other
forms of income, constructed bigger nets. The
dugong kill increased dramatically.

Likewise, because of the cray fishing, longer
periods of time were spent at the reef, where the
focus of hunting could easily switch from craying to
dugong hunting. As more money was injected into
the community, more people bought outboard
motors and dinghies. The hunting became easier and
more efficient.

In a very short period, many traditional
restrictions on hunting were altered. The new boats
and motors meant that hunting could be undertaken
at almost any time. There was a large demand for

A dead dugong on a canoe. (Photo courtesy of Brydget
Hudson)

103

220
200
180
160H

! Data from
■
! J Interviews

1920 1960 1977 1978 1979 1980 1981 1982

Narato Double- Netting Introduced

A outrigger

Canoes Cano#s

Developed

The effect of changing
technology and
commercialization of dugong
hunting by the Kiwai.

dugong meat among the nearly 8,000 residents of
Daru, and for the money this highly profitable
hunting could provide. Detailed knowledge and
magic were no longer required, as the reefs could be
patrolled until a dugong was sighted. Butchering on
the reef also meant that more than one animal could
be brought to the market at once. A few facets of
traditional practice remained: traditional reef usage
was maintained, as was the dipping of the harpoon
in the water to bring luck.

The rapidity of these changes was
phenomenal. It precluded management by
education (concerning the need for conservation). At
the same time, the regulation of hunting by
legislation was politically untenable, and would have
been unenforceable if enacted.

Management Initiatives

In 1978, the Kiwai formed the Maza Wildlife
Management Area. Rules were enacted to reduce
the kill by limiting the gear to canoes and harpoons
(banning nets and dinghies). Animals had to be
brought whole to the market — in keeping with
custom — to 1) restrict the kill per trip, and 2) enable
the collection of biological data which in turn would
aid further management. The capture of juveniles
and mothers with calves also was banned. Lastly, an
education program emphasizing dialogue with the
hunters was established.

Modern Threats

Despite early efforts, financial pressures and the
demand for meat caused the local stocks of dugong
to be precipitously depleted. From 1978 through
1982, hunting was directed further and further down
the Warrior Reefs. In 1982, a ban on the sale of
dugong meat was instituted.

Turtles now appear to be the major target for
hunting, and their decline as the result of

commercial fishing pressures exerted by people of
the Torres Strait and Indonesia may occur in the not
too distant future. Since the dugong and turtle
harpoons are usually carried on any fishing
expedition, a classical multispecies fishery situation is
now occurring. The focus of hunting can change
between commercial and traditional, with the danger
of depleting all stocks below economic and
sustainable levels.

In addition to directed hunting, incidental kills
do occur. Trawlers occasionally catch dugongs, and
the barramundi nets are responsible for a presently
unquantified dugong kill. Nets set to protect
swimmers from sharks have killed significant
numbers of dugongs off Townsville. Lastly, mining is
a possible threat because of the increased silt
burden in certain areas.

Can Traditional Practices Help Management?

Active participation involving all members of the
community was a feature of traditional management.
An understanding of the environment and duty
toward its management also were a part of the
traditional education system. The people considered
themselves stewards of their environment for
perpetuity. These facets are required in management
today as in the past.

The conservation of human societies as well
as marine species should likewise be an aim of
management. Many human societies, too, are
endangered. Our world would be poorer without
their contribution, as it would without the dugong.

Other members of modern society also need
to use the resources of the Great Barrier Reef.
Commercial fisherman need to make their living
economically, efficiently, and in an ecologically
sound manner. The aims of the manager and the
fisherman should coincide. The goals of all —
commercial fisherman, traditional hunter, and

104

Human Exploitation of Shellfish

I numerous shell-midden deposits along the
northeastern coast of Australia testify to the
frequent consumption of shellfish by Aboriginal
groups in the Great Barrier Reef region. Shellfish
constitute a dependable source of protein,
important during periods when other animal
food sources are scarce.

Recent studies by archaeologists and
anthropologists in northern Australia and Papua
New Guinea have demonstrated that a wide
range of gastropod and bivalve species have
been harvested by traditional gatherers (usually
women and children) from the extensive
intertidal back-reef areas in the region. A
particular locality frequently yielded from 20 to
50 shellfish species from more than 10 families.
The shellfish could be gathered from a variety of
habitats, including reef flat and coral platform
areas, sand or mud flats, seagrass beds,
mangroves, and rocks.

Many of the preferred species are found
mainly in soft-sediment areas, either buried or
on the surface. Unfortunately, there has been
little documentation of traditional Aboriginal
knowledge of shellfish or their harvesting
methods, possibly because coastal researchers
have focused mainly on the hunting of turtle,
dugong, and fish by men. Furthermore, shell-
gathering has rapidly declined in groups that
have adopted a more Westernized lifestyle, so
that a large amount of traditional knowledge of
reef shellfish — poorly known by white
Australians, including scientists — will soon have
disappeared.

Despite the wide range of species
gathered, a few species from particular families
often make up a large proportion of the catch.
In clear water reef areas, there is often a
predominance of conchs, Strombus, and spider
shells, Lambis, and members of the giant clam
family (Tridacnidae). In more estuarine areas,
mudwhelks (family Potamididae) and large
bivalves, family Corbiculidae, are more
common. Various members of the bivalve
families Arcidae (particularly Anadara spp.),
Veneridae (particularly Tapes spp.), and
Ostreidae (oysters) may be common in either

type of area, as may periwinkles of the family
Neritidae.

Most contemporary white Australians eat
very few shellfish other than scallops and
cultured oysters, even though there are major
commercial Anadara and giant clam fisheries in
the Asia/Pacific region. Pinctada (pearlshell) and
Trochus (topshell) species are commercially
exploited in restricted sections of the Great
Barrier Reef and Torres Strait for mother-of-
pearl.

The present shellfish communities may
be different from those existing several hundred
years ago in the times of heaviest Aboriginal
exploitation. The exploited communities may
have been more heavily dominated by species
whose life-histories enabled populations to
persist in the face of gathering, perhaps
attributable to a propensity to bury in the
substrate, a highly mobile adult stage, a well
developed swimming larva, or the existence of
subtidal populations. Certain species, such as
some Strombus, Anadara, and Tapes, are
exceptionally common in some midden
deposits, and the little available information on
the biology of these species shows that they
share many of these characteristics, making
them resilient to gathering.

Contemporary shell-gathering and
harvesting practices may have different effects
on shellfish populations and communities. For
example, many Strombus gigas (queen conch)
populations in the Caribbean have recently
been overfished following the use of SCUBA
equipment and outboard motors by collectors,
together with the introduction of export
markets. Since the biology of shellfish on the
Great Barrier Reef has been largely overlooked
by scientists, it will be difficult to assess the
effects of similar impacts. This will have to
change if sound conclusions about the effects of
past, present, and future exploitation are to be
drawn.

— Carla P. Catterall,

Griffith University,

Brisbane

manager — should be in maintaining a sustainable
environment. Each has much to give the other. The
fisherman and hunter work continuously in coastal
waters and can provide information needed for
management. The professional manager, in turn, can
aid in advising on gear selection and hunting areas
that will minimize accidental catch of non-target
species.

The recreational users of the reef are
fascinated by its unique creatures — such as the

dugong. They too need information about how they
can assist in conservation and management; as user
involvement programs demonstrate, they are eager
to participate in the reef's management.

The Great Barrier Reef Marine Park Authority
is active in these areas — through its funding and
support of management research, liason with all
users, and through its excellent educational
programs. Thus, a convergence between traditional
and modern management has occurred. But, even

105

A double-outrigger canoe under sail. When these larger canoes were developed in the 7 920s, they extended the range and time
on the reef of the Kiwai hunters. (Photo courtesy of John Mason)

so, complacency with regard to the management of
the dugong would be unfounded. The precipitous
decline of a dugong population has been recorded,
and what might be regarded as minor changes in
technology and the environment require careful
monitoring to ensure that our already reduced herds
are not threatened further.

Brydget E. T. Hudson is a researcher with the Department of
Biological Sciences, lames Cook University, Townsville,
Australia.

^f **r»

Selected References

Baldwin, C. 1985. Management of dugong: An endangered species of
traditional significance. Technical Report GBRMPA-TR-1, Great
Barrier Reef Marine Park Authority.

Chase, A. 1 981 . Dugongs and indigenous cultural systems: some
introductory remarks. In The Dugong, pp. 112-123, James Cook
University.

Fisher, M. 1985. Aboriginal customary law: The recognition of

traditional hunting, fishing, and gathering rights. The Recognition
of Traditional Fishing Proposals for Change. Sydney: The Law
Reform Commission.

Laade, W. 1971. Oral Traditions and Written Documents on the
History and Ethnography of the Northern Torres Strait Islands,
Saibai-Dauan-Boigu. Weisbaden: Franz Steiner Verlag.

A meeting of the Maza Wildlife Management Area
Committee. Here rules were enacted to reduce the dugong
kill. (Photo courtesy of Elizabeth Parer-Cook)

106

Risk Analysis: Cyclones,
and Shipping Accidents

by M. K. James, and K. P. Stark

I he Great Barrier Reef stands as a bulwark along
the Queensland coast and in some places is
impenetrable to ships. Between the reef and the
coast, the waters provide protected shipping routes
and ideal sites for developing tourism facilities,
offshore structures, and port and harbor facilities.
Sea conditions within this area are dominated by
prevailing winds so that the worst conditions usually
anticipated are 30 knot winds and 3 meter waves;
however, three or four times a year, tropical
cyclones — called hurricanes or typhoons
elsewhere — cross the reef from the Coral Sea and
approach the coast. Along with the risk of cyclones,
the reef area also is vulnerable to shipping accidents,
both rare, but potential threats.

However rare, both nature and man must
develop mechanisms to cope with disastrous events.
Many corals, such as foliaceous Leptoseris cucullata,
have adapted to this environment by developing
high mobility and rapid growth. Man, on the other
hand, has developed risk analysis techniques so that
rare events, possibly those for which no local
experience exists, can be simulated to provide an
appreciation of how best to adapt and cope. Risk
analysis for cyclonic effects and for shipping
accidents help us predict the probability and
consequences of disasters.

Risk Analysis of Cyclones

Cyclone paths have no simple pattern, as shown in
Figure 1 . Many cyclones affect the areas they
traverse very little because their central pressure
ranges from 980 to 1,000 millibars. However, under
particular circumstances, the cyclone can intensify
and create widespread, disastrous consequences.
Cyclones with a central pressure below 950
millibars are classified under the Saffir-Simpson scale
as severe; if the central pressure is below 915
millibars, the classification becomes very severe. A
very severe cyclone in the Great Barrier Reef region
would have the following characteristics:
1) a maximum wind gust of 270 to 300 kilometers
per hour or 145 to 160 knots; 2) a coastal storm
surge greater than 6 meters; and 3) a wave height in
open ocean greater than 8 meters. Such conditions
damage coral reefs, create extreme shipping hazards,
and impose excessive loads on both natural and
man-made structures. Fortunately, the probability of

Figure 1. Tropical cyclone tracks in the Great Barrier Reef
region (1910-1969).

a very severe cyclone passing over any selected
point in the oceans is quite low.

Using the meterological details associated
with the tracks in Figure 1, a statistical extreme value
analysis can be used to provide a stochastic
simulation of anticipated cyclonic strengths over
time. From the air-sea interaction produced in each
cyclone, the complex wind field generates
wind-waves that can be deduced.

Simultaneously, the wind will create
hydrodynamically an oceanic tidal surge that, when
superimposed on the predicted tide level, produces
abnormal water levels. If the cyclone landfalls at high
tide, then the combined tide and storm surge can
penetrate inland with disastrous consequences.
Buildings in the path of such storm surges would
require evacuation.

There are two mitigating circumstances on the
reef. First, away from the coastline, storm surge
development is restricted to the inverted barometer
effect, and abnormal water levels for the very severe
cyclone should not exceed 1.0 to 1.5 meters.
Second, if both man-made and natural structures are
within a lagoon protected by coral at mean sea level,
then wave heights will be weakened as they break
over the coral; thus, maximum waves within the
lagoon are unlikely to exceed 3 meters. Of course,
since maximum winds will persist within the lagoon,

107

160 knot or 300 kilometers per hour winds must be
considered in designing reef structures to survive
such extreme events. Detailed computer simulations
can now be done before any offshore structures—
whether floating hotel, drilling rig, navigation
beacon, or artificial reef — are built.

Risk Analysis for Navigation

The increasing use of Great Barrier Reef waters for
navigating large vessels raises concerns over the risks
and repercussions of shipping accidents. The higher
traffic densities have already resulted in many close
encounters and the sinking of at least one trawler.
The potential clearly exists for more serious
accidents that could possibly lead to major oil spills.

Risk analysis is concerned with estimating the
probabilities of shipping accidents — collisions and
groundings — and the distribution of that risk over a
region, that is, the likelihood of accidents at different
locations. These accident statistics are then used to
determine the geographical distribution of spills and
to provide input to various areas: navigation
management in the area, spill trajectory models to
determine impact zones, and logistic analyses to plan
the location and movement of materials, equipment,
and personnel for dealing with spills.

Since no statistical data exist to estimate
probabilities of these events and statistical estimation
techniques cannot be applied, an approach based
on computer simulation of the navigation process is
used. A computer program models the passage of
vessels through the restricted waters of the region as
well as close-quarters situations where ships must
maneuver to avoid collision or grounding. The risk

analysis model allows important causal factors to be
considered, such as environmental conditions (poor
visibility), mechanical conditions (steering failure),
and human error (positioning errors). The outcome
of an encounter between two ships depends on the
interaction of these factors.

Accident scenarios are represented by fault-
trees (Figure 2) used extensively to assess safety. The
accident appears as the top event and is linked to
more basic fault events by various logic gates. An
accident occurs when one or more basic failures
occur, enabling a causal path that leads to the
accident. Some methods from fuzzy set theory are
also employed to model mariners' decision
processes and their compliance with the Collision
Regulations.

Many years of shipping experience can be
simulated this way, and many potential accident
situations analyzed to give statistical estimates of
accident probabilities. These results are expressed
on risk distribution maps that highlight the areas
most likely to receive pollution from dangerous
chemical spills. The analysis thus contributes to the
knowledge of human influences on the environment
in the Great Barrier Reef Marine Park.

Risk analyses of navigation and cyclones
demonstrate the dynamic processes influencing the
Great Barrier Reef. The more that is known about
the potential risks to the area, the more likely they
can be either avoided or monitored safely.

M. K. James is Senior Lecturer in Systems Engineering
at lames Cook University, Townsville. K. P. Stark is
Head of the Department of Civil and Systems
Engineering at lames Cook University.

GROUNDING

iOR

SHIP TURNED
TOWARDS REEF

SHIP DID NOT TURN TO AVOID
REEF

OR

OR

WRONG
MANEUVER

EXTERNAL
CONDITIONS
(E.G. STRONG

CURRENT)

NOT AWARE OF REEF

COULD NOT TURN

(E.G. STEERING

FAILURE)

f\ AND

POSITION
ERROR

DID NOT SEE REEF |

Figure 2. Example of fault tree.
108

Toxins

and Beneficial Products

from Reef Organisms

by J. T. Baker, and J. A. Williamson

I he diversity of a tropical reef's fauna and flora has
attracted significant attention from those interested
in characterizing the active compounds of the often
complex venoms transmitted by several marine
species. In addition to the obviously venomous
marine animals, many other species of tropical fauna
and flora offer potential for scientific investigation.
Ninety percent of all species of living organisms live
in the ocean in totally different biosynthetic
conditions than terrestrial fauna and flora. Thus, it is
highly probable that the oceans will yield as yet
unknown chemical substances with novel structures
and a wide range of biological activities.

Since the mid-1960s, scientific literature has
reviewed many new substances available from
marine organisms, but to this day, only a few
biologically active compounds have attracted the
interest of major pharmaceutical companies as
potentially marketable drugs. Future advances in the
medical aspects of marine venoms require research
into effective methods of immediate pain relief and
prevention of scarring, such as with jellyfish stings,
and the immunological characterization of marine
toxins.

Marine animals with toxic compounds are
often put into three broad categories based on their
potential threat to human life or health: 1) marine
animals that have caused documented death in
northeastern Australian seas by envenomation or
poisoning; 2) marine animals that produce either
common or serious envenomations, but currently
have not caused documented death; and 3) marine
animals that have caused allergic reactions.

The Box-Jellyfish

The two closely related box-jellyfish species,
Chironex fleckeri and Chiropsalmus quadrigatus* are
distinguished morphologically by experts, but from

* Recent field work has thrown doubt on the accuracy ot
this naming for the Australian version.

Figure 1. An adult box-jellyfish (Chironex fleckeri]. Its sting
can be fatal. (Photo courtesy of J. A. Williamson)

the practical medical viewpoint, their distinction is
unnecessary. However, the latter may be slightly less
dangerous. These box-jellyfish occur in the summer
months only in northern Australia, dwell and breed
on the coast, and are often found in tidal streams or
near-shore waters (Figure 1).

Although the box-jellyfish is not encountered
on the reef, it is responsible for at least 64
documented Australian deaths since 1884, and many
other undocumented deaths due to the remoteness
of the northern Australian coast. Thirty-four of these
deaths happened in the coastal regions adjacent to,
but not on, the Great Barrier Reef.

An intensive marine biological and medical
research program has existed in North Queensland
since the animal's identification in 1956. Details of
serious envenomations, progress with management
and prevention, research into the envenomation
process and into the life-cycle have been published
elsewhere.

The venom of Chironex fleckeri is a mixture of
high molecular weight proteins, containing

109

cardiotoxic and haemolytic components to small
experimental animals, and capable of killing human
skin. The precise pharmacology of its lethal action in
humans is still uncertain, but direct, central
neurological toxicity is suspected. The venom
probably disrupts cell membrane stability by
inhibiting calcium ion re-uptake of the sarcoplasmic
reticulum. Further characterization of this venom,
together with other Australian and world jellyfish
venoms of clinical significance, using immunological
techniques, is already under way, and therapeutic
advances are expected.

The venom produces immediate, savage pain,
and skin destruction (Figure 2) that may result in
scarring if untreated. A specific anti-venom,
concentrated immunoglobulins from
hyperimmunized sheep, has been available since
1970, and is dramatically effective in life threatening
situations, for pain relief, and probably also
prevention of scars. Any clothing, including
pantyhose and the Townsville stinger suit, can
prevent jellyfish tentacle stings.

Ciguateric Fish

Ciguatera poisoning is caused when ciguatoxin, a
complex toxin whose structure has been extensively
studied, contaminates the flesh of fish. One of the
most potent toxins known, it remains active even
after the fish is cooked. Its detection in fish is
presently impossible, although researchers in Hawaii
claim to have developed a stick test for field
detection of toxin. The toxin does not affect the
fish's health or appearance, but causes 1,200 annual
cases of disease, and death in the Pacific region
where fish is a staple diet.

Ciguatoxin, thought to be transmitted via the
marine food chain, affects pelagic reef fish,
appearing and disappearing unpredictably in a wide
range of edible species. However, certain species
are believed to be more commonly affected than
others, such as chinaman, Symphorus nematophorus,
red bass, Lutjanus bohar, moray eels, and the larger
predatory reef fish, such as Spanish or grey
mackerel.

The toxin predominantly induces gastro-
intestinal symptoms, but more seriously affected
persons demonstrate peripheral neurological
features. Potentially fatal cases show central
neurological depression with coma, convulsions,
and respiratory failure. Without resuscitation and
medical assistance, death may occur from hypoxia.*

Blue-ringed Octopus and Cone Shells

The toxin of the blue-ringed octopus is tetrodotoxin,
one of the few marine toxins whose structure and
action are known. With a molecular weight of 319, it
is non-antigenic and causes selective inhibition of
sodium ion transport across cell membranes. Thus it
has proved useful as a neurophysiological research
tool. It is distributed naturally, notably in the puffer
fish — the "fugu" of Japan. Cone shell venoms, by
contrast, produce post-synaptic neuromuscular

* Deficiency in the amount of oxygen reaching bodily
tissues.

Figure 2. A large Chironex fleckeri sting after 24 hours
showing skin death. (Photo courtesy of I. A. Williamson)

inhibition, have a higher molecular weight, and offer
the promise of anti-venom production (Conus
geographus venom).

These cone shell toxins act peripherally at the
human somatic neuromuscular junction (Figure 3),
and death results from respiratory failure and
consequent hypoxis; assisted ventilation, such as
expired air resuscitation (E.A.R.) is life saving. First-
aid for blue-ringed octopus or cone shell venom is of
life-saving importance in seriously affected persons,
and is identical to that used now for Australian snake
bites. Full recovery of muscle power can be
expected in 6 to 10 hours in severely poisoned
patients who are protected from hypoxia.

Sea Snakes

Australia possesses the world's most formidable array
of venomous sea snakes; at least 12 species of sea
snakes, most of them venomous, are found in
tropical Queensland waters alone. They have an
efficient fang mechanism with very toxic venoms.
The beaked sea snake, Enhydrina schistosa, is
considered one of the most dangerous to man, and
the Commonwealth Serum Laboratories sea snake
anti-venom is based on this venom, along with that
of the Australian terrestrial tiger snake, Notechis
scutatus. Since the anti-venom works with all
Australian sea snakes, precise identification of the
offending species is unnecessary.

Sea snake venoms act neurologically, affecting
both the peripheral and central nervous systems.
They consist of extremely complex protein mixtures
that can produce haemolysis, muscle cell
breakdown, and blood coagulation, possibly
resulting in attendant renal and electrolyte
complications in seriously affected patients. Near
fatalities from sea snake bites have occurred
increasingly in Australian waters.

Non-fatal Jellyfish

Nowhere is the present ignorance of marine
envenomation better illustrated than by the
fragmentary knowledge of tropical stinging jellyfish
species and their toxins. As well as genera common
to many other parts of the world (Physalia, Pelagia,
Cyanea, Catostylus), the Great Barrier Reef houses an
extraordinary group of Cubozoan jellyfish

110

Sea Snakes

I he Australian sea snakes (family Hydro-
phiidae) share several morphological char-
acteristics with the venomous terrestrial fam-
ily Elapidae, from which they have probably
evolved.

At least 32 species of sea snakes in-
habit Australian waters, 76 of which are
found on the Great Barrier Reef. One spe-
cies, Aipysurus laevis, the olive sea snake,
has been the subject of a 5-year study con-
ducted by researchers from the University of
New England in New South Wales. The
study has centered on the Swain Reefs area
at the southern end of the Great Barrier Reef.
Researchers have conducted an ongoing
mark and recapture program, using a pop-
ulation of A. laevis found at Mystery Reef
within the Swain Reefs complex.

At Mystery Reef, it has been esti-
mated that between 2,000 and 3,000 adult
olive sea snakes reside in the 1 square kil-
ometer that comprises the reef's lagoon. This
figure is typical of most of the reefs in the
Swains complex that support A. laevis pop-
ulations. Although neighboring reefs seem
ecologically similar, only 22 reefs of the 40
examined to date support resident popula-
tions. This patchy distribution is consistent
yearly and has not been accounted for in
terms of either physical or biological factors.
Neither water temperature, salinity, distri-
bution of prey, nor numbers of predators has
been shown to affect the distribution of Ai-
pysurus laevis along Australia's Great Barrier
Reef.

Sonic tracking equipment has been
used to monitor movements of individual
snakes for periods of up to 7 days. This

Sea Snakes
courting.

technique has provided information on for-
aging behavior and range size. Males have
exhibited a slightly smaller mean range size
(1,500 square meters) than have females
(1,800 square meters). Movement is gener-
ally centered on a section of reef edge less
than 150 meters in length. Neighboring
ranges may overlap by as much as 85 per-
cent, with snakes occupying the same range
for three consecutive years.

Additional studies have found that
males and females have synchronous, sea-
sonal reproductive cycles. Courtship and
mating occur during winter, after which the
female stores sperm in the uterus until ovu-
lation occurs in the spring. Following a 6-
month gestation, the young are born at the
end of summer. Mature female A. laevis in
the southern areas of the Great Barrier Reef
reproduce biennially, producing two or
three young per clutch. There is evidence of
geographical variation in the reproductive
cycle.

Several species of Australian sea
snakes possess attractively patterned skin
that is coveted for shoes, belts, handbags,
and a variety of other clothing accessories.
Potential overseas markets include lapan,
the United States, and Italy. Sea snakes are
not protected in Queensland waters. How-
ever, the Australian government has refused
to grant export permits until the effects of
large-scale harvesting (30,000 skins or more)
on natural sea snake populations have been
assessed.

—Glen W. Burns,

University of New England,

New South Wales.

collectively known as the family Carybdeidae. The
three identified species of this family are very
venomous. Many other as yet unidentified species
exist, but nothing is known about the structure or
pharmacology of their toxins.

Two species of these simple, four-tentacled
jellyfish with which painful encounters have
occurred in Queensland and other Australian waters
are "Irukandji," Carukia barnesi, and "Morbakka,"
Tamoya spp. Irukandji is a tiny jellyfish, invisible
under natural conditions, whose initially painful sting
subsides in about 30 minutes, only to be replaced by
prostrating muscular pain, nausea, vomiting, and

incapacitating headache. Hospitalization and
intravenous analgesia provide relief from these
symptoms which last 12 to 24 hours.

The existing confusion concerning the precise
identification of different Tamoya species is such that
the nickname Morbakka has been suggested and is
pending world wide clarification of this group's
taxonomy. Tamoya is a larger, four-tentacled, open-
water jellyfish (Figure 4) aptly nicknamed "fire jelly"
for its painful sting that can cause generalized effects.
Unconfirmed fatalities in the western Pacific exist,
but Australian cases of exhaustion and mental
confusion have occurred.

111

Figure 3. A somatic neuromuscular junction, showing sites of
action of various zoo-toxins. (Courtesy of V. Callanan)

Stonefish

The venomous stonefish is not rare in northeastern
Australia. Since the painful encounter invariably
results from the fish's superb camouflage, most
wounds occur on the sole of the foot, or
occasionally, on the palm of the hand. At least one
of the 13 erectile dorsal spines, each with its own
venom sac, penetrates deeply, depositing venom in
the wound. The venom is a high molecular weight,
heat-labile protein for which a specific anti-venom,
horse anti-serum, exists.

Immediate pain is followed quickly by a
bluish discoloration of tissues near the venom
deposit. Pain can be reduced by immersing the
poisoned part in hot water. Despite repeated,
contrary statements, no documented death from a
stonefish exists in Australia to date, although more
than 80 cases have reportedly received hospital
treatment. Medical attention for a stonefish sting is

Figure 4. A large Morbakka jellyfish of the Ta'moya species.
Note the four solitary tentacles, and the papules of
nematocysts on the bell. (Photo courtesy of Ben Cropp, Port
Douglas)

always necessary to relieve pain and prevent local
complications.

Stinging Corals, Starfish, and Sea Urchins

These less dramatic, but troublesome stingers are
more frequently encountered because of the
popularity of snorkeling and SCUBA diving. The
stings are nematocyst-mediated, as with all stinging
Coelenterates, and treatment is symptomatic, but
effective. Little is known about their toxins.

The Crown of Thorns starfish is of special
interest as it is present from time to time in plague
densities on parts of the Great Barrier Reef. The
starfish's venom is contained in the lining of the
spines, and the calcified core of the spine tip
commonly breaks off in the wound. The nature of
the toxin is presently unknown. Localized allergic
reactions to this venom occur in susceptible
individuals, and treatment is largely symptomatic,
but helpful.

Injuries from sea urchins are similar to those
from the Crown of Thorns. The sea urchins are
widely dispersed over the reef and nothing is known
about the toxin which at least one species,
Toxopneustes, possesses.

Stingrays

Although lurid stories relate the threat of these
animals, injuries are relatively uncommon, and are
invariably the result of man disturbing the animal,
either accidentally or intentionally. Stingrays are seen
commonly in northeastern Australian water, and are
speedy swimmers. Injuries are sustained from the
one or two barbed spines located halfway along the
dorsum of the muscular tail. The spines are used in
defense and can penetrate powerfully. Most injuries
occur on the lower limb and are severely painful.
Two-thirds of Australian species inject a protein
venom via their spine that can kill local tissue and
may require surgical excision. No anti-venom exists,
but there have been no confirmed Australian
fatalities to date.

Allergic Reactions

Although clinicians have long observed puzzling or
unusual reactions to marine envenomations, it is only
recently that it has become understood that many of
these could be allergic reactions to the foreign
venom material. These reactions include localized
inflammation, either immediate or delayed for up to
two weeks, or a hypersensitive systemic reaction,
anaphylaxis. Such reactions have detectable sero-
immunological markers.

Delayed allergic reactions, still serologically
unproven, have been connected to envenomations
or contacts with Chironex flecker! , Acanthaster plana ,
and a toxic marine sponge. The swelling, itching,
blister formation, weeping skin, and burning pain
that can characterize delayed reactions occur in
patients with a personal history of allergies, even
without further contact with the offending marine
animal or its venom. Such reactions are effectively
controlled by systemic steroids. Medical attention of
the fortunately rare, but life-threatening anaphylactic
reactions is crucial to the survival of the patient.

112

Promising Therapeutic Substances

Scientific work on marine toxins has concentrated on
organisms that are visible and obtainable in high
biomass. Scientists have ignored the enormous
variety of novel bacteria, microalgae, and fungi in
marine waters; dedicated research in this area could
yield an even more spectacular array of novel
metabolites than have thus far been obtained from
the marine macroorganisms. In addition, marine
microorganisms lend themselves more readily to
genetic engineering and manipulation than more
complex macroorganisms.

In our limited work, we have been impressed
by the wide variety of metabolites obtainable from
marine bacteria and the interesting pharmacological
properties of substances and extracts. An interesting
biological effect has been noted in the macroalgae
species, Chlorodesmis fastigata, which produces a
metabolite containing enol acetate grouping. In the
north, one acquires a different metabolite than from
the south, but both compounds appear to act as fish
repellants. Brown algae, which have been isolated
often, contain phenolic compounds, initially
indicating strong antibiotic activity; but, so far, no
commercially viable substances have been isolated.

By far the widest range of organisms studied
in the Great Barrier Reef are the sponges. One of the
most interesting single species is Dysidea herbacea
which, depending on where it is collected and
whether it is associated with symbiotic blue-green
algae, may yield metabolites with a predominance of
chlorinated substances, or in another instance, there
may be no chlorinated compounds, but brominated
metabolites, or metabolites containing neither
chlorine nor bromine. This series of metabolites,
although including in one case a very active topical
antiseptic, has not produced a single, commercially
therapeutic substance.

The Great Barrier Reef sponge Aplysinopsis
reticulata yielded a metabolite, methylaplysinopsin,
that was very active in reversing ptosis caused in
mice by preadministration of tetrabenazine — a test
which preliminarily indicates that an active substance
may show human antidepressant activity. Tests on
this compound were conducted for seven years,
reaching the penultimate stage prior to human

administration, before adverse side-effects caused
the end of the study. This factor alone indi< ates the
cost and necessary commitment for therapeutic ally
marketable substances to be available from marine
organisms.

In tests conducted at the Suntory Institute for
Biomedical Research, crude extracts were applied to
screens for antimicrobial assay, cytotoxicity assay,
coronary vasodilation assay, cardiotonic assay,
antiulcer assay, angiotensin converting enzyme
inhibition assay, and platelet aggregation inhibition
assay. Many of the crude extracts showed strong
pharmacological activities and then were purified
further. Table 1 indicates the summary results where
a check indicates that activity was detected. The
actual results provided a more detailed analysis of
the significance of the activities obtained.

The Future

The development of any pharmaceutical product is
risky. An initial activity may result in many years of
work before a final decision can be made to proceed
to commercial development or to end work.
Additional problems exist with marine organisms and
many of these relate to the fact that the metabolites
obtained will be different from those traditionally
available to the microbiologist and pharmacologist
whose results are so important in interpreting an
activity, and determining whether further tests
should be done. The metabolites often have halogen
substitution with a high probability that marine-
derived metabolites will act differently than those of
existing drugs. The traditional screens of the
pharmaceutical industry may not be adequate to
detect novel substances with novel mechanisms of
action.

The move by many innovative drug evaluators
to test the molecular mechanism of action is
probably the greatest chance of success for marine-
derived metabolites. Studies of receptor binding,
displacement, and tissue culture may provide more
reliable evaluations of potential therapeutic
application than conventional screens. In addition,
before a new product can enter the market in all
developed countries, it must show a significant
therapeutic advantage over those already available.

Table 1. Activities noted with marine species.

antimicrobial* o c ^

S.a. B.s. M.I. M.s. E.c. P.a. A.f. C.a. f S 2

sponges V V V V V V V V

algae V V V V V V

corals V -J V V II

sea cucumbers — — — — vv v v

higher plants — — — — — *

gastropod mollusks "". ^

sea urchins — — — — — / /

tunicates — — — — ^

sea anemones — V ■*

others V -J — — si v' V V

* Abbreviations of microorganisms:

B.s. = Bacillus subtilis P.a. = Pseudomonas aeruginosa S.a. = Staphylococcus aureus

M.s. = Mycobacterium smegmatis C.a. = Candida albicans M.I. = Micrococcus luteus

^ a * fffs

„ < .E a "5 ■-

V V

V V

V -

V" -

- V

7 -

■J -

E.c.

A.f.

= Escherichia coli
— Aspergillus flavus

113

Nevertheless, the sea's potential to produce
novel biological compounds, coupled with human
perception of interaction between species, should
lead to new therapeutically valuable substances to
apply to health, agriculture, veterinary science, and
the production of fine chemicals. The road to
success could be underwater.

/. T. Baker is Director of the Australian Institute of Marine
Science at Cape Ferguson outside Townsville. /. A.
Williamson is a Consultant in Diving Medicine in Townsville.

Selected Readings

Baker, J. R., B. Brooks, A. Hinder, R. Pollard, K. P. Stark, J. A.

Williamson, B. Zerner. 1984. Task Force Report, Chironex

fleckeri (Southcott). Government of Queensland.
Barss, P. 1984. Wound necrosis caused by the venom of stingrays.

Med. I.Aust. 141:854-855.
Endean, R., C. Duchemin, D. McColm, E. H. Fraser. 1969. A study of

the biological activity of toxic material derived from nematocysts

of the cubomedusan Chironex fleckeri. Toxicon 6: 179-204.
Endo, M., M. Nakagawa, Y. Hamamoto, M. Ishihama. 1985.

Pharmacologically active subtsances from southern Pacific

marine invertebrates. Paper presented at the IUPAC Symposium

on Marine Natural Products, Paris.
Fenner, P. J., P. F. Fitzpatrick, R. F. Hartwick, R. Skinner. 1985.

"Morbakka": another cubomedusan. Med. /. Aust. (In press)
Hartwick, R., V. Callanan, |. Williamson. 1980. Disarming the box-
jellyfish: nematocyst inhibition in Chironex fleckeri. Med. /. Aust.

1: 15-20.
Olson, C. E., M. C. Heard, G. J. Calton, ). W. Burnett. 1985.

Interrelationships between toxins: studies on the crossreactivity

between bacterial or animal toxins and monoclonal antibodies to

two jellyfish venoms. Toxicon 23: 307-316.
Southcott, R. V. 1956. Studies in Australian cubomedusae, including

a new genus and species apparently harmful to man. Aust. /.

Marine Freshw. Res. 7: 254-263.
Sutherland, S. K. 1983. Australian animal toxins: the creatures, their

toxins, and care of the poisoned patients, 359-373. Melbourne:

Oxford University Press
Togias, A. O, J. W. Burnett, A. Kagey-Sobotka, M. Lichtenstein.

1985. Anaphylaxis after contact with a jellyfish. /. Allergy Clin.

Immunol. 75: 672-675.
Williamson, ). A. 1984. The blue-ringed octopus. Med. /. Aust. 140:

308-309.
Williamson, |. A., V. I. Callanan, M. L. Unwin, R. F. Hartwick. 1984.

Box-jellyfish venom and humans. Med. /. Aust. 140: 444-445.
Williamson, |. A. 1985. The Marine Stinger Book. Brisbane, Qld. State

Centre, Surf Life Saving Association of Australia.
Williamson, J. A., L. LeRay, M. Wolfhart, P. Fenner. 1984. Acute

management of serious envenomation by box-jellyfish (Chironex

fleckeri). Med. /. Aust. 141: 851-853.

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'. o XI.

Great Barrier Reef Echinoderms

This drawing is from the first scientific study of the reef detailed in the book The Great Barrier Reef by E. Saville-Kent, 1893.

Research Stations on the

Lizard Island

I he Lizard Island Research Station, situated at
the center of one of the richest coral reef regions
known, is a facility of the Australian Museum. The
laboratory provides access to a wide range of
tropical habitats including sand and mud flats,
mangrove swamps along the mainland coast, sea
grass beds, fringing reefs, platform reefs,
continental islands, raised limestone islands,
vegetated and bare coral cays, outer barrier or
ribbon reefs, and oceanic habitats outside the
reefs with depths to 5,000 meters only 10 miles
away. True atolls in the Coral Sea (such as Osprey
Reef) are also within easy access. Lizard Island
itself is a high (370 meters), granitic, continental
island, covering 7 square kilometers with
permanent fresh water and a variety of terrestrial
habitats. The island is fringed by a coral reef
which also encompasses two nearby islands
(Palfry and South), and encloses a 10-meter-deep
lagoon.

The objectives of the Lizard Island
Research Station are to provide optimal logistic
support for a maximum of 14 visiting researchers.
Tacilities include four, fully self-contained
bungalows, diving equipment, sea-water aquaria,
laboratory space, equipment, and services. The
laboratory also operates 10 small, aluminum,
outboard-powered boats which can be used by
visitors around the island, in the lagoon, or
further afield, depending on experience. For
extended voyages, the research station operates a
14 meter motor-sailing catamaran research
vessel — R.V. SUNBIRD, powered by twin diesel
engines and sail, and accommodating two crew
and up to 5 researchers.

Researchers from anywhere in the world
are welcome to come and pursue their research
at the Lizard Island Research Station. An all-
inclusive bench fee is charged. This fee covers
accommodation and use of all laboratory
facilities. Post-graduate students are invited to
enquire about the Doctoral Fellowships which
are awarded each year to support field studies at
Lizard Island.

For more information, a more detailed
brochure on the station's facilities, current bench
fee rates, and booking forms, please write to:

The Secretary

Lizard Island Research Station

P.M.B. 37

Cairns, Queensland

Australia 4870

— Barry Goldman,
Lizard Island Research Station

One Tree Island

O,

'ne Tree Island is a four-hectare (10-acre) cay
situated on the Tropic of Capricorn at the
seaward (southeast) end of a biologically rich reef
5.5 x 3.5 kilometers in size. It lies in the center of
the Capricorn Group about 20 kilometers east of
Heron Island and about 100 kilometers off the
Queensland coast. The nearest mainland port is
Gladstone.

The Australian Museum began research at
One Tree Reef in 1965. Three primitive buildings
were completed by 1972. Ownership and
operation of the station was transferred to the
University of Sydney at the end of 1974. In the 1 1
years since, there have been substantial
improvements to the quality of the station,
including a fourth building, but the station has
been kept small and dedicated to field as
opposed to laboratory research. The University
has sole occupancy of the island under a lease
from the Queensland Department of Lands and
operates the station under a permit from the
Great Barrier Reef Marine Park Authority
(GBRMPA).

The station provides basic accommodation
for up to 8 scientists, and excellent facilities for
field research. The whole of One Tree Reef and
surrounding waters to a distance of 1 kilometer
from the reef edge is a Scientific Zone within the
Capricornia Section of the Great Barrier Reef
Marine Park. This zone is off-limits to all parties
except scientists with research permits.

The station, although owned by the
University of Sydney, is accessible to scientists
from all institutions, and provides immediate
access to a biologically rich lagoon which
provides ideal sheltered waters for many kinds of
research. The station is equipped with boats and
diving gear. There is limited laboratory space and
some instrumentation.

Scientists interested in working at the
station should write to:

The Executive Officer,

One Tree Island Field Station,

School of Biological Sciences,

University of Sydney,

Sydney, N.S.W., Australia 2006.

Access to the station is via the port of
Gladstone and thence Heron Island. Transport
from Heron Island to One Tree Island is included
in the standard fee for accommodation and use of
the station's facilities, which is presently A$40 per
day.

— Peter F. Sale,
University of Sydney

116

Great Barrier Reef

Tt

Orpheus Island

he Orpheus Island Research Station is located
at Pioneer Bay on the western side of Orpheus
Island, a 1 70-meter-high continental island in the
Palm Islands Group, 30 kilometers north of
Townsville. The Bay faces northwest, providing
excellent shelter from the prevailing southeasterly
winds.

The island is mainly granite, with some
volcanic material. Vegetation is mainly dry
sclerophyll (scrub) forest, with some vine thickets
and palms in the gullies, and grassland on the
eastern side. Strand vegetation is evident, and
there are several areas of mangrove on the
western side of the island with Rhizophora
especially well represented. Aboriginal middens
and ceremonial sites remain from pre-European
times at various sites around the island.

Sandy shores are found at several locations
along the western side, while the many
promontories provide a variety of rocky shore
habitats. Orpheus Island is surrounded by an
excellent fringing reef with extensive reef flats
developed in both north and south Pioneer Bay,
Hazard Bay, and on the northeast and southeast
ends of the island. Reef flats are walkable at low
tide. The combination of coastal proximity and
shelter from strong wave action provides
opportunity for great diversity of marine and
benthic plants and animals.

The facilities at the station include a four-
bedroom house for use by visiting scientists
(capacity 20). Also available is a laboratory
equipped with seawater aquaria and laboratory
equipment, which includes balances,
microscopes, freeze drier, ovens, and other
laboratory equipment. The laboratory is divided
into wet and dry sections, and is partially air-
conditioned. Power (240 v) is provided on a 24
hour basis, as is filtered seawater. Diving facilities
include compressor and dive tanks, and there are
four small boats available. All food and provisions
must be brought to the Island.

All inquiries and bookings relating to the
Marine Research Station at Orpheus Island
should be directed to:

The Director,

Sir George Fisher Centre for Tropical Marine

Studies,
James Cook University
Townsville, Queensland
Australia 4811

Heron Island

I he Heron Island Research Station was
established in 1951 by the Great Barrier Reef
Committee. It was the first permanent, land-
based center for coral reef studies on the Great
Barrier Reef and has grown steadily since that
time to become the largest coral island research
facility in Australia.

In 1 980, the ownership of the station was
transferred to the University of Queensland. It is
now a fully integrated research and teaching
center of that university.

The station's facilities are available to
scientists and students throughout the world to
pursue independent studies in any discipline, and
on any subject pertaining to coral reefs. The
major attractions of the station for researchers
and educational groups are:

• Its unique location on a coral sand cay,
surrounded by a large (9.5-kilometer long,
3.5-kilometer wide) and flourishing lagoon
platform reef.

• The space and the staff to support several
research projects simultaneously.
Educational groups are provided with
completely separate laboratory facilities.

• The close proximity of Heron Island to
other reef systems in the Capricorn and
Bunker Groups for comparative and inter-
reef studies.

• The proximity of the southern capital cities
of Australia, which serves to reduce traveling
time and costs. It is possible to stand on the
reef at Heron Island within 2Vi hours of
leaving Brisbane, using scheduled air services
to the island.

The site of 2 hectares (5 acres) contains 29
buildings occupying a floor area in excess of
2,000 square meters, approximately 900 square
meters of which consists of space for research and
teaching. A total of 21 buildings is related to
accommodation and the others are used for
research, teaching, administration, and technical
services.

Scientists interested in working at the
station should write:

Director

Heron Island Research Station
University of Queensland
Gladstone, Queensland
Australia 4680

— I. D. Lawn,
University of Queensland

117

o

DXrXQ

0

Joseph T. Baker

Early Man (3 a.m.)

It is not uncommon when seeking
an appointment with Joseph Thomas
Baker, the Director of the Australian

118

by Barbara E. Kinsey

Institute of Marine Science (AIMS),
for him to suggest 3 a.m. "You must
be kidding," might be a natural

reaction. He would not be.

Joe (he is widely known by
his Christian name) thrives on a busy

schedule, which he packs into a 20-
hour working day. I know because I
worked for Joe on a number of
projects when he was head of the Sir
George Fisher Centre for Tropical
Marine Studies at James Cook
University in Townsville. I found him
to be exceptionally pleasant — with a
rare capacity for bringing scientists,
policy- and decision-makers together
to exchange viewpoints. I also know
him as a dedicated family man —
proud of his wife, Val, and four
children (two sons and two
daughters). However, I knew very
little about his "off duty" life. Thus it
was a challenge to write this profile
and to discover the "other Joe
Baker."

A Struggle Early On

Joe Baker was born in Warwick, in
the south of Queensland, in 1932.
He attended the local primary and
high schools in that town. His father
was a railway worker. During the war
years, his father was transferred north
to Townsville, which was at that time
a large base for U.S. military forces in
northern Australia. Young Joe
continued his schooling at South
Townsville and Railway Estate
schools. This was to be a very
valuable introduction for him in later
years.

The family could not afford to
support Joe as a full-time student at
university, and at that time there
were only a few scholarships
available. He started out in 1950 as a
laboratory cadet with the
Commonwealth Scientific and
Industrial Research Organization
(CSIRO), working full time during the
day as a histologist cum dishwasher,
and attending classes five nights a
week. The situation improved in later
years, as the course requirements
dropped to three or four nights a
week, but doing it this way meant
that it took him 6 years to complete
his basic degree. This is, of course,
standard for part-time students, in
contrast to 3 years for full-time
students.

Joe's father had played Rugby
League for Queensland, in the state
team. Joe grew up close to football,
playing Rugby Union for his school in
Warwick and on Sundays playing
Rugby League in the local
competition. He first played A grade
in the Warwick Representative Team
at the very young age of 16, as a
fullback.

Turning up for Rugby Union
training, when he started at
university, he was asked by the
coach if he was in either the School

of Medicine or Law (Rugby Union
being the "gentlemen's game" in
distinction to Rugby League, which
was professional). On learning that
Joe was a Science student, the coach
asked him at which college (Hall of
Residence) he was living. "None, I
am an evening student." Having filled
none of the social requirements, he
was told by the coach that there was
no point in him turning up for
training for the university team.

Joe then decided that he
would play Rugby League for Easts,
one of the major Brisbane teams. He
captained the Brisbane team, and in
the year he was working as a Senior
Demonstrator at the university, was
selected for the State Team of
Queensland. At this point, the
registrar called him in to explain why
he, a member of staff, was not
playing Rugby Union for the
university. Joe had much delight in
telling him. He advanced the case for
Rugby League, and after two years it
was reintroduced to the university as
a team sport.

Of course, being
Joe Baker, these were
hardly conventional
fishing trips.

His habit of a long working
day developed in these first two
years, when he never returned home
from university before 1 1 at night. As
he was then too tired to start
studying, he would go to bed, getting
up at 3 a.m. to continue his studies.
Finding that practice to be perfectly
satisfactory for him, he has
maintained it ever since. He
considers that while such a work
practice was forced on him initially,
that he is not a workaholic. Others
do tend to view him in that light.

Joe's entry into marine
science was indirect. Australia is a
large continent, with most of its
major population centers lying on the
coastal fringes. So most Australian
children grow up with memories of
seaside vacations, surf and sand,
exploring rockpools, and fishing.
Every year a large number of our
student intake to the universities is
spurred on by the hope that they will
be able to work in the field of marine
science. The selection process is
quite intense, because entry to
university is highly competitive.
There are comparatively few
openings for such students, and

when they do obtain tertiary

qualifications, very few positions are
available.

After doing honors in organic,
inorganu , and physic al < hemistry,
because Joe was not sure in which
aspect of Chemistry he wished t< i
specialize, he did his Master's degree
on the essential oils of Australian
eucalypts. Then, fate intervened; he
met his future wife, Val, a dedicated
angler. He maintains that the only
way he could get near her was to
become interested in fishing himself.
He also involved his supervisor,
Maurice Sutherland, in some of his
fishing expeditions.

The Dye Is Cast

Of course, being Joe Baker, these
were hardly conventional fishing
trips. They would set out from
Brisbane at 2 a.m. and head for
Currumbin, 60 to 65 miles away, fish
for tailor (American bluefish,
Pomatomus saltatrix), then return to
the University of Brisbane by 9 a.m.
at the latest.

One particular morning,
having exhausted their regular bait
on a very substantial run of tailor, and
not wanting to leave when the fish
were in such plentiful supply, they
decided to try some nearby
gastropods as bait. Joe broke them
out of their shells and handed them
to Maurice Sutherland to try. This
was an extremely successful ploy.
They went home with the best catch
of fish they had ever had.

On the return trip, however,
they began to feel uncomfortable. A
foul smell pervaded the car. Each was
reticent to comment until they
noticed their hands developing a
decided greenish cast, and then an
indelible purple coloration, and that
their hands were the source of the
odor.

A literature search provided
the clue to what had happened. The
dye was Tyrian purple, the royal
purple of antiquity. Nobody had ever
characterized the colorless precursor,
and this search became Joe Baker's
doctoral topic. He comments on his
felicitous choice of organism
Dicathais orbita Gmelin: "I was very
lucky because the Australian species
has only one precursor to the purple
dye, unlike Mediterranean
gastropods, which may have as many
as three." With the technology and
instrumentation available in the late
1950s, a more complex pathway
could not have been as readily
elucidated.

In 1961, before he had
completed his doctorate, he was

119

offered the lectureship in chemistry
at the new University College at
Townsville. University Colleges were
set up from parent universities in the
state capital cities in a few large
country towns throughout Australia;
they became autonomous later, as in
the case of James Cook University in
1970). His versatility was an asset
here because, where there could
only be one lecturer in chemistry in
the new college, it was an advantage
to have someone who had a
reasonable breadth in all three major
sections of chemistry. Recognizing
the problems of isolation in a town so
far from the academic centers of the
south, he enlisted the aid of the
professor of chemistry at Brisbane
University in starting a visiting
lecturer system to broaden the
student's exposure to a variety of
topics. This practice is still
maintained.

The new college to which he
reported consisted of some pegs laid
out on the ground. Eight weeks
before lectures were to commence,
there was no building, and the first
term's lectures were conducted in
Pimlico High School, just across the
road. Having very little time for
research, but a lot of time for
collecting, he developed the practice
of collecting during the academic
year. During his summer vacation, his
family and he would go south and
while his family vacationed at the
Gold Coast, he would work
intensively on his research. Because
of the photosensitivity of the material
and his minor need for sleep, much
of the work was done at night.

In the first year, Joe Baker
was the Chemistry Department. Not
entirely comfortable with physical
chemistry as a discipline, he took the
recommended text and worked out
every problem, so that he would be
able to understand any difficulties his
students might have. Determined to
have the new school produce quality
graduates, he ran tutorials for those
finding difficulties with the subject.
Friends remember with awe that not
only were some of those tutorials
held in the small hours of the
morning, but that the students
actually attended them!

As if his commitments to
teaching and research were not
enough to more than fill the day,
there was football. His love for the
game stood him in good stead in
Townsville. It was a bridge between
the townspeople and the new
University College, at a time when
each was wary of the other. His big
straw hat, which he wore every
Sunday when he went as coach with

the fledgling university team, was his
trademark. He is particularly proud of
the fact that his hat, raffled to assist in
defraying the medical costs of an
injured player, earned $208 and sat
for many years in the bar of one of
the local pubs. To this day, friends
are awed when people everywhere
know him, especially cabbies and
airport staff. Many of the senior
politicians in the Queensland
Government are either friends from
his football days or former players,
students, or supporters of clubs for
whom he played and this has often
been helpful in establishing a
dialogue. The University team
reached A grade status in 1970. The
North Queensland team he coached
in 1971-1972 won the State
Championships in 1971.

In one night,
he can probably do
more work than a
conventional staff
can do in a week.

Each year, an additional
member of staff was added to the
new School of Chemistry, and an
additional year of course work
instituted, so there was no hiatus in
graduating for that first intake of
students. In 1962, he was appointed
Senior Lecturer (Associate Professor
in the U.S. system), and in 1970
Associate Professor (Full Professor in
the U.S. system). He was involved
with the architectural planning of the
Chemistry School and is credited
with much of the planning of a
comprehensive curriculum for it.

In the late 1960s and early
1970s Joe's work on Tyrian Purple
became recognized. He went
overseas, on a sabbatical to the
United States and to Italy, where he
worked on those Mediterranean
mollusks which are sources of the
dye. Developing an international
reputation, he was retained as a
consultant to the Roche Institute in
Switzerland in the early 1970s.

His consultancy with
Hoffman-La Roche, Switzerland, led
to him being asked in 1974 to set up
the Roche Research Institute of
Marine Pharmacology (RRIMP) in
Sydney. As a now well-recognized
marine scientist, appointments to a
variety of committees followed. He
became a member of the Heron
Island Research Station Board in
1974 and a member of the Great

Barrier Reef Marine Park Authority in
1976, a position he has held ever
since, and of which he is very proud.
The Authority is basically a
triumvirate, each member
representing different concerns. The
Chairman, Graeme Kelleher,
represents the Commonwealth
Government, Sir Sydney Schubert is
the nominee of the Queensland
Government, and Joe Baker
represents the independent
viewpoint.

Stands Up for Staff

The period at RRIMP established Joe
Baker as a marine scientist. As
distinct from a marine chemist, he
had to develop a broad base of
knowledge on all aspects of marine
science, physiology, and
pharmacology. It was an active,
productive institute in 1981, when
the parent company decided that
their research efforts should lie in
other directions and that RRIMP
would close its doors. On the staff of
80 was one of Joe's original students
and he recounted the stand that Joe
made, on behalf of his staff, so that
they did not suffer from the closure
to the extent that was initially
considered likely. Joe maintained that
he would, if they could not find
alternative employment, look for
appropriate openings for them
himself. And he did.

Joe Baker returned to
Townsville in 1981 to set up the Sir
George Fisher Center for Tropical
Marine Studies at James Cook
University. This is a multidisciplinary,
marine oriented center charged with
the responsibility of developing
research programs within the center,
maintaining contact with other
research organizations locally and
overseas, coordinating the use of the
university's research vessel, the lames
Kirby, and administering the Orpheus
Island Research Station. The center
houses the RRIMP Collection of
marine microorganisms, and has an
active microbiological research
program with cross disciplinary ties to
other university departments.

The involvement with
advisory committees built up to an
even greater commitment in the late
1970s, often to the point that one
meeting would conflict with another.
Joe became a latter day "flying
doctor." He developed the habit of
making the airplane his office. This is
rather hard on his secretary, because
he is quite capable of dictating more
in one night's flight than she can
transcribe in a day (and he has had
some extremely competent
secretaries). In fact, in a single night,

120

he can probably suggest more work
than the laboratory staff can add into
their busy week's schedule. Because
his time scale is so radically different
to that of most people, he sometimes
fails to comprehend the reasons for
the hiatus between his suggestion
and another person's implementation
of it.

Joe Baker accepts all
commitments, declining none, but he
has not yet solved the problem of
how to be in two different places at
the same time. A colleague recalls
that a meeting of the Marine
Research Allocation Advisory Council
had been scheduled in Darwin, and
was to be followed by a further
meeting of the Council on the
following day at an aboriginal reserve
situated in one of the most remote
areas of Australia, the Cobourg
Peninsula, well to the North. While
the council was in Darwin, Joe
received a telephone call from the
Minister for Arts, Heritage, and the
Environment asking him to go to
Canberra. His presence was also
expected at the Cobourg Peninsula
meeting. He solved the problem that
time by going to Canberra. However,
as no direct flights were available at
that time his route was via Perth and
Melbourne, thousands of extra miles
and a very long flight time (because
of the limited number of flights). And
how to occupy oneself on such a
flight? No problem. En route to
Canberra flying over the middle of
nowhere, a message for the Advisory
Council was sent via the airline radio.
Joe had sent his comments on all the
papers on the agenda for the
meeting. The transmission was
equivalent to six handwritten pages.

Joe is also a Member of the
Great Barrier Reef Marine Park
Authority, the Chairman of the
Committee of Directors of Island
Research Stations, the immediate
past President of the Australian
Marine Science Association, the Vice-
Chairman of the World Wildlife Fund
(Australia), the past President of the
Australian Museum Trust, and a
member of the Advisory Committee
to the Federal Minister for Science
and Technology on Grants for Marine
Science. He also is the immediate
past Chairman of both the Australian
Special Programme Committee for
the World Heritage Convention and
of the Australian Committee for the
World Heritage Commission, a
position he had to relinquish on
taking up the appointment as
Director of AIMS last fall. AIMS,
located near Townsville, is one of the
largest and best institutions dedicated
to tropical marine science today. Joe

was awarded the OBE (Officer ot the
Order of the British Empire) in 1982
for services to marine science. It is
the first to be given to an Australian
in this category. He is very pleased to
have been part of the Australian
delegation that earned the
nomination of the Great Barrier Keel
to the World I lentage Committee foi
listing in 1981.

Joe had ties to AIMS long
before he was appointed to the
directorship. In 1972-73, he was a
member of the Scientific Advisory
Committee to the interim AIMS
Council and Ken Back, the Vice
Chancellor of James Cook University,
was on that council. Sites had been
examined for the new laboratory
complex, but the decision had not
been made. The Cape Ferguson site,
30 miles from Townsville, had been
inspected from the air, but not at
ground level. The day for the council
meeting dawned, and the Vice
Chancellor suggested that, before the
meeting, they should take a four-
wheel drive vehicle out and have a
look at the area from the land
approach. The roads were poor to
nonexistent, and the jeep became
bogged. Forgetting he had on his
best shirt in preparation for the
meeting, Joe leaped out in the mud
and lifted the rear of the vehicle at

the same time thai Ken put his loot
on the a< i elerator. |oe was i overed
from he, id to loe with mud Ins first
physical contact with the site.

And how does he see the

future for AIMS? Basic .illy, rather
similar to the tried and true approa< h
which has worked so well for it, but
with some additional input and
output. He would like to see the
institute with a more informative role,
exposing it to greater public scrutiny.
He favors an open door approat h.
with visiting scientists and students
filling some of the gaps in the staff's
areas of research. He would like to
see aspects of mariculture examined,
complementary to that of other
institutions, and aimed toward
solving some of the problems
inherent to high-density stocking.

He hopes to be able to bring
in some staff who are skilled in
finding practical uses for pure
research, so that there will be an
applied component without losing
that very special advantage of free
ranging thought that is the hallmark
of pure science. At its present level of
staffing and support, Joe believes that
the Australian Institute of Marine
Science must concentrate the
majority of its research in a few
specialized fields in which it can
establish world leadership.

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121

h)@(S)k F®WD(g\W:

The Art of Captain Cook's Voyages by Riidiger
Joppien and Bernard Smith. 1985. Two volumes.
Volume One, The Voyage of the Endeavour, 1768-
1771. Volume Two, The Voyage of the Resolution &
Adventure, 1772-1775. Published for the Paul
Mellon Centre for Studies in British Art by Yale
University Press, New Haven and London. Volumes
$50.00 each.

The Art of Captain Cook's Voyages provides an
opportunity to observe Europeans in the initial
process of discovering, interpreting, and mastering "a
new world in the Pacific." Captain James Cook's
three voyages to the Pacific, 1 768-1 780, were the
first of the great European voyages of discovery to
carry professional artists. These two handsome
volumes (with a third forthcoming) are published in
support of the high value Cook and his famous
colleague Sir Joseph Banks placed on visual
description to supplement the verbal records of the
journals. Each volume is devoted to a separate
voyage; together they describe in detail and illustrate
all the known drawings and paintings that relate to
the peoples of the Pacific, the lands and islands they
inhabited, and the artifacts they used in daily life.

The first section of each volume includes a
critical and analytical account of the professional
artists associated with the relevant voyage: Parkinson
(first voyage), Hodges (second voyage), Webber
(third voyage). The work of important amateur artists,
such as Herman Sporing and William Ellis, is also
discussed in detail.

The second section of each volume provides
a full descriptive catalogue of the drawings and
paintings associated with the voyage. It is arranged
chronologically. Within this framework, items of
similar subject matter are brought together so that
the progress from a field sketch to a developed
painting or published engraving can be observed.

The first objective of the Endeavour's voyage
was to observe the 1 769 transit of Venus across the
face of the sun at Tahiti, and then to seek the great
then unknown southern continent of Australia. Any
relationships established with the peoples
encountered in the Pacific area were secondary to
these goals.

The tradition of drawing for informational
purposes that Banks brought to the Endeavour's
varied undertakings consisted of three main
divisions: that which served the purposes of

^ T"*"

^ -

[fete -:' ,*

Portrait of an Australian Aborigine by Charles Praval, 1 770.

navigation, that which served the purposes of natural
history, and drawings of places visited, people
encountered, and artifacts noted. It is the last
division that is the focus of the first volume.

The second volume of The Art of Captain
Cook's Voyages depicts visits by the Resolution and
Adventure to New Zealand, the Society Islands, the
New Hebrides, New Caledonia, Antarctica, Eastern
Island, and elsewhere. It also details the
circumstances in which William Hodges took over
from Banks as chief artist on the voyages, an
interesting tale in and of itself.

These volumes will be of interest to historians,
geographers, and anthropologists. They also will be
of importance to anyone interested in the study of
the Pacific region in its widest context, or in the
study of European art, ideas, and attitudes in the
latter 18th century. The scholarship is exceptional.

Paul R. Ryan,
Editor, Oceanus

122

Books Received

Aquaculture

Mussel Aquaculture in Puget Sound
by Douglas Skidmore and Kenneth K.
Chew. 1985. Washington Sea Grant
Program, Seattle, WA. 57 pp. + viii.
$5.00

Recent Advances in Aquaculture:
Volume 2, James F. Muir and Ronald
J. Roberts, eds. 1985. Westview
Press, Boulder, CO. 282 pp. $42.00.

Biology

Basic Marine Biology by A. A.
Fincham. 1984. Cambridge
University Press, New York, NY. 157
pp. $37.50.

The Behavior of Teleost Fishes, Tony
J. Pitcher, ed. 1986. The Johns
Hopkins University Press, Baltimore,
MD. 553 pp. $57.50

Biotechnology of Marine
Polysaccharides, Rita R. Colwell, E. R.
Pariser, and Anthony J. Sinskey, eds.
1985. Hemisphere Publishing Corp.,
New York, NY. 559 pp. + xi. $79.95.

Proceedings of the Nineteenth
European Marine Biology
Symposium, P. E. Gibbs, ed. 1984.
Cambridge University Press, New
York, NY. 541 pp. + viii. $99.00.

Chemistry

Geochemistry of Marine Humic
Compounds by M. A. Rashid. 1985.
Springer- Verlag, New York, NY. 300
pp. + xii. $68.00

Diving

Living and Working in the Sea by
James W. Miller and Ian G. Kablick.
1984. Jones and Bartlett, Boston, MA.
433 pp. + xiv. $32.50.

The Professional Diver's Handbook,
David Sisman, ed. 1985. Gulf
Publishing Company, Houston, TX.
304 pp. $48.00.

Engineering

Introduction to Naval Engineering by
David A. Blank, Arthur E. Bock, and
David J. Richardson. 1985. Naval
Institute Press, Annapolis, MD. 545
pp. + x.$ 17.95.

Environment/Ecology

California's Battered Coast by Jim
McGrath. 1985. California Coastal
Commission, San Diego, CA. 403 pp.
+ v. $6.00.

Coastal Wetlands, Harold H. Prince
and Frank M. D'ltri, eds. 1985. Lewis
Publishers, Inc., Chelsea, Ml. 286 pp.
+ xvii. $39.95.

Dwellers in the Land: The
Bioregional Vision by Kirkpatrick
Sale. 1985. Sierra Club Books, San
Francisco, CA. 217 pp. + x. $14.95.

Early Life Histories of Fishes: New
Development, Ecological and
Evolutionary Perspectives, Eugene K.
Balon, ed. 1985. Kluwer Academic
Publishers Group, Boston, MA. 280
pp. $75.00

The Ecology of Rocky Coasts, P. G.
Moore and R. Seed, eds. 1986.
Columbia University Press, New
York, NY. 467 pp. + xi. $45.00.

El Nino North: El Nino Effects in the
Eastern Subarctic Pacific Ocean,
Warren S. Wooster and David L.
Fluharty, eds. 1985. Washington Sea
Grant Program, Washington, D.C.
312 pp. + v. $10.00.

Key Environments: Western
Mediterranean, Ramon Margalef, ed.
1985. Pergamon Press Ltd., Elmsford,
NY. 363 pp. + ix. $23.95.

Lake Stechlin: A Temperate
Oligotrophic Lake, S. Jost Casper, ed.
1985. Dr W. Junk Publishers, The
Netherlands. 553 pp. -I- xiii. $95.00.

Marine and Estuarine Geochemistry,
A. C. Sigleo and A. Hattori, eds.
1985. Lewis Publishers, Inc., Chelsea,
Ml. 331 pp. $39.50.

Marine Mammals & Fisheries, J. R.
Beddington, R. J .H. Beverton, and D.
M. Lavigne, eds. 1985. Allen &
Unwin, Inc., Winchester, MA. 354
pp. + xxi. $55.00.

The Oregon Oceanbook by Tish
Parmenter and Robert Bailey. 1985.
Oregon Department of Land
Conservation and Development,
Salem, OR. 85 pp. $6.00 (+ $1.25
shipping & handling).

Practical Estuarine Chemistry, P. C.
Head, ed. 1985. Cambridge
University Press, New York, NY. 337
pp. + x. $54.50.

Reefs and Banks of the Northwestern
Gulf of Mexico: Their Geological,
Biological, and Physical Dynamics by
Richard Rezak, Thomas J. Bright, and
David W. McGrail. 1985. John Wiley
& Sons Inc., New York, NY. 259 pp.
+ xvii. $48.95.

Sea Fog by Wang Binhua. 1985.
Springer-Verlag. New York, NY. 330
pp. + iv. $79.00.

Field Guide

Alaska's Saltwater Fishes and Other
Sea Life by Doyne W. Kessler. 1985.
Alaska Northwest Publishing Co.,
Anchorage, AK. 358 pp. + xxvi.
$19.95.

The Bunker Climate Atlas of the
North Atlantic Ocean-Volume 1:
Observations by Hans-Jorg Isemer
and Lutz Hasse. 1985. Springer-
Verlag, New York, NY. 218 pp. + vii.
no listed price.

Dangerous Marine Animals of the
Pacific Coast by Christina Parsons.

123

1986. Sea Challengers, Monterey,
CA. 96 pp. $4.95.

Marine Fauna and Flora of Bermuda:
A Systematic Guide to the
Identification of Marine Organisms,
Wolfgang Sterrer, ed. 1986. John
Wiley & Sons, New York, NY. 742
pp. + xxx. $99.95.

The Marine Mammals of Virginia
with Notes on Identification and
Natural History by Robert A.
Blaylock. 1985. Virginia Sea Grant
College Program, Gloucester Point,
VA. 34 pp. + iii. $1.00.

Plant Lore of an Alaskan Island by
Frances Kelso Graham and The
Ouzinkie Botanical Society. 1985.
Alaska Northwest Publishing Co.,
Anchorage, AK. 194 pp. + xvi. $9.95.

Fisheries

Fish Catching Methods of the World
by Andres von Brandt. 1984. Avon
Litho Ltd., Warwickshire, England.
Distributed in U.S.A. by Unipub,
New York, NY. 418 pp. + xiv.
$66.00.

General Reading

The Antarctic Circumpolar Ocean by
George Deacon. 1984. Cambridge
University Press, New York, NY. 180
pp. + viii. $24.95.

Dame by H. Greeley Thornhill. 1985.
Coolidge Press. Chattanooga, TN.
270 pp. $15.95.

Pacific Fxplorer: The Life of Jean-
Francois de La Perouse 1741-1788
by John Dunmore. 1985. The Naval
Institute Press, Annapolis, MD. 318
pp. $19.95.

The Sea Peoples: Warriors of the
Ancient Mediterranean by N. K.
Sandars. 1985. Thames and Hudson,
New York, NY. 224 pp. $10.95.

Seven Clues to the Origin of Life by
A. G. Cairns-Smith. 1985. Cambridge
University Press, New York, NY. 131
pp. + xii. $17.95.

Trails of an Alaska Game Warden by
Ray Tremblay. 1985. Alaska

Northwest Publishing Co.,
Anchorage, AK. 176 pp. + xv. $9.95.

Underwater Acoustics: A Linear
Systems Theory Approach by
Lawrence J. Ziomek. 1985. Academic
Press, Inc., New York, NY. 290 pp. +
xi. $45.00.

Geology

General Bathymetric Chart of the
Oceans. 1984. Canadian
Government Publishing Center,
Ottawa, Canada. $100 (Canada),
$120.00 (Other Countries).

The Ocean Basins and Margins:
Volume 7 A The Pacific Ocean, Alan
E. M. Nairn, Francis G. Stehli, and
Seiya Uyeda, eds. 1985. Plenum
Press, New York, NY. 733 pp. + xiv.
$95.00.

Great Barrier Reef

A Coral Island: The Story of One
Tree Reef By Harold Heatwole. 1981.
William Collins Pty Ltd., Sydney,
Australia. 200 pp. A$ 10.00. Available
through H. Heatwole, The University
of New England, Armidale, N. S. W.
2351, Australia.

A Coral Reef Handbook, Patricia
Mather and Isobel Bennett eds. 1984.
The Australian Coral Reef Society,
Brisbane, Australia. 144 pp. A$ 11.00.

The Great Barrier Reef: The World's
Wild Places /Time-Life Books by
Craig McGregor and the editors of
Time-Life Books. 1974. Time-Life
Books, Amsterdam. 184 pp. A$22.95.

The Mysterious Undersea World by
Jan Leslie Cook 1980. National
Geographic Society, Washington DC.
104 pp.

Perspectives on Coral Reefs, D. J.
Barnes, ed. 1983. The Australian
Institute of Marine Science, Manuka,
Australia. 277 pp. +ix.

Proceedings of the Great Barrier Reef
Conference, J. T. Baker, R. M. Carter,
P. W. Sammarco, K. P. Stark, eds.
1983. James Cook University of
North Queensland, Queensland,
Australia. 545 pp. + xviii.

History

Secrets of the Bible Seas: An
Underwater Archaeologist in the
Bible Seas by Alexander Flinder.
1985. Severn House Publishers Ltd.,
London, England. 174 pp. £10.95.

South Atlantic Paleoceanography, K.
J. Hsu and J. J. Weissert, eds. 1985.
Cambridge University Press, New
York, NY. 350 pp. + vi. $69.50

Marine Policy

Marine Mining: A New Beginning,
Peter B. Humphrey, ed. 1985.
Department of Planning and
Economic Development, Honolulu,
Hawaii. 319 pp. $10.00.

Ocean Yearbook 5, Elisabeth Mann
Borgese and Norton Ginsburg, eds.
1985. The University of Chicago
Press, Chicago, IL. 544 pp. + xvi.
$49.00.

Wastes in the Ocean Volume 5:
Deep-Sea Waste Disposal, Dana R.
Kester, Wayne V. Burt, Judith M.
Capuzzo, P. Kilho Park, Bostwick H.
Ketchum, and Iver W. Duedall, eds.
1985. John Wiley & Sons, Inc., New
York, NY. 346 pp. + xvii. $79.95.

Wastes in the Ocean Volume 6:
Nearshore Waste Disposal, Bostwick
H. Ketchum, Judith M. Capuzzo,
Wayne V. Burt, Iver W. Duedall, P.
Kilho Park, and Dana R. Kester, eds.
1985. John Wiley & Sons, Inc., New
York, NY. 534 pp. + xx. $95.00.

Physical Science

Intrinsic Geodesy by Antonio
Marussi. 1985. Springer- Verlag, New
York, NY. 219 pp. + xvii. $56.00.

Storm Surges — Meteorological
Ocean Tides by T. S. Murty. 1984.
Friesen Printers Ltd., Manitoba,
Canada. 897 pp. + ix. $34.95
(Canada), $41.95 (Other Countries).

Ships and Sailing

Ships of the Panama Canal by James
L. Shaw. 1985. Naval Institute Press,
Annapolis, MD. 269 pp. + x. $29.95.

124

MM. W IK >l I I lilt \in

Oceanus

Oceanus

The

Arctic Ocean

Vol. 29:1, Spring I986 It's
frozen. It's remote. But
sc ientists, the military, law-
yers, corporations, govern
ments, and investors are
pa\ ing partk ular attention to
the Arctic. Sonic call it ,i
stampede. Find out who,
why, and what it means.
l~opi< s inc lude exploration,
U.S. and Soviet sec unt\ , sea
ice, climate, shipping, pollu-
tion, and poli< \

UH 1A2N /

The Titanic:
Lost and Found

Vol 28:4 Wintei 1985/86
I he inosi , omprehensive
a< < ounl available ol the h
tank s loss in 1912 and re
i enl dis( over) ln< ludes .1

detailed a< < ount ol how the

ship was found .1 profile ol
discoverei Robert Ballard,

dct. nls (it the Argo system
used to find the ship, as well
.is artu les < ontaining mam
new historic al details ol the
wre< k.

Beaches,

Bioluminescence,
Pollution, and
Reefs

Vol. 28:3, Fall 1985— Arti-
cles deal with topics of great
current interest, such as lat-
est scientific perspectives on
oil pollution, threats to the
beaches of the U.S. East
Coast, the strangely lit world
of the deep ocean, and the
unique ecosystems of Aus-
tralia's Great Barrier Reef.

The Oceans and
National Security

Vol. 28:2, Summei 1985

The U.S. Nav\ 's effei tive
ness relies on proper use ol
strategy, tec hnology, ,\n(\
marine s< ien< e. I his issue
looks at all these areas from
details ot spe< iii* weapons
systems, to the proper role
ol the I l.S \a\\ . to the mi
portant e of marine si ienc e
resean h. Additional artk les
examine the Soviet Navy
and the U.S. (oast Guard.

• Marine Archaeology,

Vol. 28: 1 . Spring 1985 —History and s< lence beneath I he waves

• The Exclusive Economic Zone,

Vol. 27:4, Winter 1984/85 Options tor the U S. EEZ

• Deep-Sea Hot Springs and Cold Seeps,

Vol. 27: 3, Fall 1984 A full report on vent s< ienc e.

• El Nino,

Vol. 27:2, Summer 1984 — An atmospheric phenomenon analyzed.

• Industry and the Oceans,

Vol. 27 1. Spring 19H4

• Oceanography in China,

Vol. 26:4, Winter 198 5/84

• Offshore Oil and Gas,

Vol. 26 :3, Fall 198 5

• Summer Issue,

1985, Vol. 26:2— C02, mussel watch, warm-core rings, MIZEX, the U.S EEZ

• Summer Issue,

1982, Vol. 25:2 — Coastal resource management, acoustic tomography aqua

culture, radioactive waste

• Summer Issue,

1981 .Vol 24:2 <\quati< plants seabirds oil and gas

• The Oceans as Waste Space,

Vol. 24:1, Spring 1981

• Senses of the Sea,

Vol 23 i, Fall 1980

• Summer Issue,

198H, Vol 2 1 2 Plankton, El Nino and African fisheries hot springs I
Bank, and more

• A Decade of Big Ocean Science,

Vol 2 I I spring 1980

• Ocean Energy,

Vol 22:4 Winter 1979/80

• Ocean/Continent Boundaries,

Vol 22 i Fall 19^9

• The Deep Sea,

Vol 21:1, Winter 1978

• Summer Issue,

1977 Vol 20 I rhe 200 mile limit, the Galapagos nit discovers nitrogen
fixation, sh.nk senses

Issues not listed here, including those published prior to 1977, are out of print. Oceanography Institution Foreign orders musl be accompanied by ached
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P.O. Box 6419
Syracuse, NY 13217

Be there for
the America^

back,
Yanks,
lake it
back!'

At first, it might seem a bit disloyal
for Yanks to fly to the America's Cup races
with Qantas, the Australian airline.

But the fact is, no one knows
Australia like we do. So no
other airline can offer you 44TJlke it
everything we can.

To start with, Qantas is
the only airline with through
service from the United States
to Perth, where the races will
be held. That means you won't
have to change airlines on the
way. And neither will any valuable sailing gear
or equipment you might be bringing with you.

We can also arrange all-inclusive tours that
give you everything you're likely to want on your
Australian trip: stopovers and sightseeing in Sydney,
plus accommodations, ground transport, and
spectator arrangements for the races in Perth. We
can even offer a free stopover to see the Great Barrier
Reef, if your interests extend below the waterline.

For more information about Qantas flights and
tours to the America's Cup, just fill out the coupon below

i.

I want to be there! Tell me more about Qantas flights and tours to the America's Cup.
Name.

Address.

City.

L

Qantas, Dept., OC, P.O. Box 476, San Francisco, CA 94101

State.

Zip_

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