ATOLL RESEARCH BULLETIN

NO. 549

COMMUNITY STRUCTURE OF HERMATYPIC CORALS AT PEARLAND
HERMES ATOLL, NORTHWESTERN HAWAIIAN ISLANDS: UNIQUE
CONSERVATION CHALLENGES WITHIN THE HAWAIIAN ARCHIPELAGO

BY

JEAN C. KENYON, MATTHEW J. DUNLAP, CASEY B. WILKINSON,
KIMBERLY N. PAGE, PETER S. VROOM, and GRETA S. AEBY

ISSUED BY

NATIONAL MUSEUM OF NATURAL HISTORY
SMITHSONIAN INSTITUTION
WASHINGTON, D.C. U.S.A.
DECEMBER 2007

175'W 170°W tes^w 160“W ISS^W

Figure 1. The Hawaiian Archipelago. NWHI = Northwestern Hawaiian Islands; MHI = main Hawaiian
Islands. Lightly shaded areas represent 100-fathom isobaths.

COMMUNITY STRUCTURE OF HERMATYPIC CORALS AT PEARLAND
HERMES ATOLL, NORTHWESTERN HAWAIIAN ISLANDS: UNIQUE
CONSERVATION CHALLENGES WITHIN THE HAWAIIAN ARCHIPELAGO

BY

JEAN C. KENYON, 1 MATTHEW J. DUNEAP,i CASEY B. WIEKINSON,'
KIMBEREY N. PAGE,^ PETER S. VROOM,' and GRETA S. AEBY^

ABSTRACT

The distribution and abundance of scleractinian corals at Pearl and Hermes Atoll
(PHA), Northwestern Hawaiian Islands, were determined by georeferenced towed-diver
surveys that covered more than 85,000 m^ of benthic habitat and site-specific surveys
at 34 sites during 2000 - 2002. Three complementary methods (towed-diver surveys,
videotransects, and photoquadrats) were used to quantify percent cover of corals by
genus or species in the fore reef, back reef, lagoon, and channel habitats. Three genera
— Porites, Montipora, and Pocillopora — account for 97% of the coral cover throughout
the atoll, though their relative abundances vary considerably according to habitat and
geographic sector within habitats. Fore-reef communities are dominated by massive
and encrusting Porites, while the back reef is dominated by Montipora and the lagoon
by Porites compressa. All taxa show habitat-specific differences in colony density and
size-class distributions as assessed through colony counts within belt transects at fixed
sites. These demographic data, which provide the most thorough quantitative description
of the coral communities at PHA to date, are used to focus a discussion on risks of
reef degradation from salient contemporary hazards, including bleaching, disease,
marine debris, and Acanthaster predation. Coral communities at PHA may be the most
vulnerable in the Hawaiian Archipelago to bleaching and accumulation of marine debris,
thus warranting special management attention. These data also provide a detailed baseline
to which population parameters determined from long-term monitoring surveys can be
compared to assess the direction, pace, and drivers of change.

' Joint Institute for Marine and Atmospheric Research and NOAA Pacific Islands Fisheries Science Center,
1125B Ala Moana Blvd., Honolulu, Hawaii 96814 USA, Email: Jean.Kenyon@noaa.gov
^Hawaii Department of Land and Natural Resources, Division of Aquatic Resources, 1151 Punchbowl,

Honolulu, Hawaii 96813 USA

Manuscript received 8 December 2006; revised 5 February 2007.

2

INTRODUCTION

As a world- wide trend towards reef degradation eontinues (Gardner et al., 2003,
Hughes et al, 2003, Bellwood et al., 2004, Palumbi 2005, Pandolfi et al, 2005, Hughes
et al., 2005) and the differential responses of eorals to various stressors beeome better
known (Branham et al., 1971, Aeby 2004, Kenyon et al., 2006a, Kenyon and Brainard
2006), determining a reef’s eommunity eomposition beeomes not just a deseriptive
exereise but a useful tool for assessing its risk to the influenee of stressors (Kenyon et
al., 2006 b,e). Conventional as well as emerging approaehes to sustaining and repairing
marine eeosystems, sueh as eoral reefs, depend on knowledge of an eeosystem’s biotie
eomposition and the essential proeesses supported by key funetional groups (Hughes et
al., 2005). Hermatypie eorals play a vital role in the development and maintenanee of
eoral-reef eeosystems by providing the basie struetural framework as well as the shelter
and food requirements of numerous speeies that inhabit the reef (Grigg and Dollar 1980).

The Hawaiian Arehipelago spans 2450 kilometers aeross the north Paeifie from
the island of Hawaii in the southeast (19®N 154® W) to Kure Atoll in the northwest (29®

N 178® W) (Fig. 1). Originating over a relatively fixed point of upwelling lava (“hotspot”)
in the Paeifie Plate, the islands, banks and atolls of the Arehipelago have developed
over at least 27 million years (Dalrymple et al., 1977) through gradual erosion and
subsidenee as they slowly drift to the northwest by sea-fioor spreading (Wilson 1963,
Grigg 1982, 1997). Grigg (1983) diseerned several trends in eoral eommunity strueture
aeross the Hawaiian Arehipelago, ineluding a deerease in eoral eover tending northward
in the ehain and a varying degree of dominanee by speeies that are widely distributed
throughout the ehain. Grigg ’s surveys throughout the Arehipelago were eondueted
primarily along southwest seaward reefs at depths elose to 10 m, however, and do
not neeessarily eharaeterize eoral eommunities subjeet to different regimes of salient
environmental parameters, ineluding wave energy, temperature, light and sedimentation.
In addition, more widespread surveys eondueted by Maragos et al. (2004) throughout
the Northwestern Hawaiian Islands (NWHI, Fig. 1) indieate that the relatively uniform
speeies inventories reported by Grigg (1983) at southwest seaward sites simplify a rieher
and more spatially eomplex eoral fauna. At Pearl and Hermes Atoll, for example, 12
speeies were observed by Grigg (1983) while 32 were reported by Maragos et al. (2004).

Detailed deseriptions of the eoral eommunities of individual islands, atolls
and banks in the Hawaiian Arehipelago have been limited historieally by the vast
shallow-water areas available for reef development relative to the resourees available
to eharaeterize them. More than 1,350 km^ of shallow (0-20 m) shelf area exist in the
NWHI alone (NOAA, 2003; Parrish and Boland, 2004). In 2000, Presidential Exeeutive
Order No. 13178 ( http ://hawaiireef noaa.gov ) set in motion a proeess to extend federal
management aetions to submerged areas of the NWHI not ineluded in extant state or
federal mandates and rekindled a drive to assess more eomprehensively the resourees
of the NWHI. Modern teehnologies, ineluding GPS (global positioning system), GIS
(geographie information system), digital imagery and remote sensing, have faeilitated
the development of methods by whieh benthie eommunities ean be surveyed and
eharaeterized more extensively than was possible even a deeade ago.

3

Along with Kure Atoll and Midway Atoll, Pearl and Hermes Atoll (PHA) is
one of the three most northerly atolls in the NWHI (Fig. 1). In shallow- water (0-20 m)
shelf area, PHA is seeond in size in the NWHI only to Freneh Frigate Shoals, an open
atoll farther south in the ehain (407.2 vs. 468.5 km^, respeetively) (Parrish and Boland,
2004). Thirty-two speeies of seleraetinian eorals have been reported (Maragos et al.,
2004) from the variety of habitats (e.g., fore reef, baek reef, lagoon pateh and retieulated
reefs) delineated by the atoll’s morphology. Reeent researeh suggests that while eoral
eommunities at PHA are spared from eonsiderable anthropogenie disturbanee that
frequently aeeompanies reefs elose to population eenters (e.g., pollution, dredging,
nutrient overload), they may be the most vulnerable in the entire Hawaiian Arehipelago
to more indireet stressors sueh as thermally-indueed bleaehing (Kenyon et al., 2006a;
Kenyon and Brainard 2006) and marine debris (Donohue et al., 2001, Boland and
Donohue 2003, Dameron et al., 2006). This paper deseribes the eommunity strueture
of the shallow-water (< 20 m) seleraetinian eorals at Pearl and Hermes Atoll, based on
atoll-wide surveys eondueted in 2000 - 2002 using three eomplementary methods. These
data are then diseussed in relation to other eontemporary researeh at PHA that foeuses on
faetors known to affeet the physieal eondition of eoral eommunities, ineluding bleaehing,
disease, marine debris, and Acanthaster predation. They also serve as a detailed baseline
for eomparing results from ongoing monitoring aetivities that are part of a multi-ageney
effort to enhanee long-term eonservation and proteetion.

MATERIALS AND METHODS

Benthie Surveys

Towed-diver surveys were eondueted in 2000 (25 September-5 Oetober) and
2002 (18-28 September) aeeording to the methods of Kenyon et al. (2006d). Laser-
projeeted dots used to ealibrate image size did not appear on videographie imagery
reeorded during 2002 surveys beeause of meehanieal problems. Habitat digital videotapes
were sampled at 30-see intervals (inter-frame distanee ~ 25m) and quantitatively
analyzed for eoral pereent eover using the methods of Kenyon et al. (2005), in whieh the
eoral eategories that eould be distinguished were Pocillopora, massive and enerusting
Porites (e.g., P. lobata, P. evermanni), P compressa, Montipora, Pavona, and faviids.
Average depth was ealeulated for eaeh towed-diver survey from an SBE 39 temperature/
pressure reeorder (Sea-Bird Eleetronies, Ine.) mounted on the habitat towboard and
survey distanees were ealeulated using GPS and AreView GIS 3.2.

Site-speeifie belt-transeet surveys, along with digital video reeording of benthie
eover along the transeet lines, were independently eondueted by three separate teams of
divers on 1 7-28 September 2002 aeeording to the general methods deseribed by Maragos
et al. (2004) for 2002 Rapid Eeologieal Assessments. Eoeations of site-speeihe surveys
were determined on the basis of: (1) Filing gaps in the loeations of baseline assessments
eondueted during an expedition to the NWHI in 2000; (2) depths that allowed three
dives/day/diver; (3) eonstraints imposed by other ship-supported operations; and (4) sea

4

conditions. Detailed methods for recording videographic and size class data are presented
in Kenyon et ah, 2006c.

Twelve (35 cm x 50 cm) photoquadrats were concurrently photographed with
spatial reference to the same two 25 m transect lines (i.e., 6 photoquadrats per transect) at
each site according to the methods of Preskitt et al. (2004).

Data Extraction and Analysis

Capture, sampling and analysis of frames from videotransects are described in
Kenyon et al., 2006c. The taxa that could be identified were Pocillopora meandrina,

R eydouxi, R damicornis, R. ligulata, massive and encrusting Rorites (e.g., R lobata,

R evermanni), Rorites compressa, Montipora, Ravona, Fungia and Faviidae. Detailed
methods for determining coral percent cover from photoquadrat imagery are also
presented in Kenyon et al., 2006c.

Transect site locations and tracks of towed-diver surveys georeferenced with non-
differentially-corrected GPS units (Garmin® model 12) were mapped using Arc View GIS
3.2. For analytical purposes, towed-diver and site-specific surveys were grouped spatially
according to habitat (fore reef, back reef, lagoon, channel) and geographic sector (N, NE,
E, etc.).

Differences in total percent coral cover among habitats, and among sectors within
habitats, were examined using one-way ANOVA or a t-test. Kruskal- Wallis or Mann-
Whitney rank sum tests were used with percent cover data from surveys where the data
were not distributed normally, even with transformations, or showed unequal variances.
Differences in the percent cover of coral genera among habitats, and among sectors
within habitats, were examined using the chi-square test of independence among two
or more samples, aggregating all taxa other than Rorites, Pocillopora, and Montipora.
Statistical analyses were conducted using SigmaStat® software.

Maragos et al. (2004) provide two indices of the relative occurrence and
abundance of 32 coral species at PHA based on qualitative Rapid Ecological Assessment
surveys at 69 sites. Methods described in Kenyon et al., 2006c were used to compare
these indices with the relative abundance of coral species as determined by percent cover
analysis of photoquadrats in this study.

RESULTS

Towed-diver Surveys

The distance between sample frames captured at 30-sec intervals from benthic
tow videos depends on the tow speed; the average inter-frame distance ranged from
19.1 m to 35.6 m (mean = 25.5 m, w = 43 tows). The average benthic area captured
in laser-scaled frames was 4260 cm^ (SE = 80 cm^, n = 1052 frames). Towed divers
surveyed 113.9 km of benthic habitat (Table 1, Fig. 2) of which 4251 captured frames
were analyzed. Given the 3:4 aspect ratio of the captured frames and extrapolating to

5

the total number of eonseeutive, nonoverlapping still frames that eompose the benthie
imagery, this benthie analysis area (4251 frames x 0.426mVframe =1811 m^) samples a
total survey area of 85,843 m^ (Table 1). Survey effort in 2000 emphasized the fore-reef
habitat, as towed divers were able to work in eonditions of high swell or strong eurrent
that were too extreme for roving divers to survey safely. Surveying the baek-reef habitat
was emphasized in 2002 so as to doeument a novel eoral bleaehing event in progress
that was most pronouneed in this habitat. Estimates of eoral eover along the north fore
reef and east baek reef (Table 1) were derived from in situ diver observations rather than
reeorded imagery beeause of video eamera problems during those surveys. Total average
eoral eover aeross the atoll was low-to-moderate, ranging from 5.2% at the southern end
of the opening (“ehannel”) on the western side of the atoll (Fig. 2) to 19.1% in the lagoon
(Table 1, Fig. 3a). The differenees among the four habitats in their average total pereent
eoral eover were not signiheant statistieally (Kruskal- Wallis test, H= 7.24, df=3,p =
0.65). However, a signiheant differenee existed among habitats in the relative abundanee
of eoral genera present (ehi-square test, = 233.93, df = 9,p = 0.00). Considering eaeh
habitat as a whole throughout the atoll, the fore reef was dominated by massive and
enerusting Porites (e.g., P. lobata, P evermanni). Montipora eo-dominated the baek-
reef habitat, along with lesser and roughly equal proportions of Pocillopora and Porites.
Fagoon assemblages were dominated by Porites compress a (Table 1, Fig. 3 a).

The average eoral eover aeross 40,095 m^ surveyed along the fore reef was 6.8%
(Table 1). Although the differenees among the average total pereent eoral eover in the
seven video-reeorded fore-reef seetors were not signiheant statistieally (Kruskal- Wallis
test, H= 10.92, df = 6,p = 0.09), there were signiheant differenees among seetors in
the relative abundanee of eoral genera present (ehi-square test, = 249.40, df = 18,/?

= 0.00). With the exeeption of south and southwestern exposures, Porites dominated
all fore-reef seetors, usually aeeounting for more than two-thirds of the eoral eover.
Poeilloporids dominated south and southwestern exposures and were the next most
dominant member of the eoral fauna on all other fore-reef seetors. The most varied eoral
fauna was found along the southwest seetor, where P. compressa and Pavona eaeh made
a modest eontribution (7-9% of total) to eoral eover. Montipora and faviids eontributed
little to eoral eover on the fore reef (Table 1, Fig. 3a).

The average eoral eover aeross 30,900 m^ surveyed along the baek reef was 10.5%
(Table 1). Although the differenees among the average total pereent eoral eover in the
seven video-reeorded baek reef seetors were not signiheant statistieally (Kruskal-Wallis
test, H= 9.54, df = 6,p = 0.145), there were signiheant differenees among seetors in the
relative abundanee of eoral genera present (ehi-square test, = 708.42, df = 18,
p = 0.00). Patterns of eoral dominanee by geographie seetor were more variable in the
baek-reef habitat than in the fore-reef habitat. North, northeast and southwest baek-reef
exposures were dominated by Montipora; northwest and west exposures were dominated
by Porites; south and southeast exposures were dominated by Pocillopora (Table 1). The
most varied eoral fauna was found along the west seetor where P. compressa and Pavona
eaeh made a modest eontribution (10 - 14% of total) to eoral eover. Faviids eontributed
little to eoral eover on the baek reef (Table 1, Fig. 3a).

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^Area surveyed is based on average area of laser-calibrated frames captured at 30-sec intervals.
Proportions are graphically presented by habitat in Figure 3a .

Estimates are from in situ diver observations

7

The average eoral eover aeross 12,888 surveyed in the lagoon habitat was
19.1% (Table 1). Although the differenees between the average total pereent eoral eover
in the east and west lagoon seetors were not signifieant (Mann- Whitney rank sum test,

T= 1.00, p = 0.29), there were signifieant differenees in the relative abundanee of eoral
taxa (ehi-square test, = 187.35, df=2,p = 0.00). Nearly all (99.7%) of the eoral eover
in the eastern lagoon was Porites compressa, whereas both Pocillopora and massive and
enerusting Porites eomprised most of the sparse eoral eover in the western lagoon (Table
1, Fig. 2).

Coral eover along the single tow survey eondueted in the opening (“ehannel”) on
the western side of the atoll (Fig. 2) was low (5.2%), and eonsisted mainly of Pocillopora
(Table 1).

Site-specific surveys
A Fore Reef

□ Back Reef

O Lagoon
Towed-diver surveys

0 3 6 Km

Fore Reef
Back Reef
Lagoon
Channel

Figure 2. Location of towed-diver and site-specific surveys at Pearl and Hermes Atoll, NWHI, using
IKONOS satellite imagery as a basemap.

8

(a) Towed-diver surveys

^ Porites
E3 Pocillopora
B P. compressa

□ Montipora
@ Pavona

□ Faviidae

Fore Reef Back Reef Lagoon Channel Habitat
6.8% 10.5% 19.1% 2.6% % cover

(b) Videotransects

Fore Reef Back Reef Lagoon
8.8% 15.1% 19.5%

^ Porites
ESI Pocillopora
g P. compressa

□ Montipora
S Pavona

□ Faviidae

Habitat
% cover

100%

80 %

60 %

40 %

20%

0%

Fore Reef Back Reef Lagoon
6.4% 10.1% 14.4%

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□ Faviidae

Habitat
% cover

Figure 3. a- c. Relative abundance of primary coral taxa by habitat at Pearl and Hermes Atoll, NWHI,
derived from three different methods. Values below habitat labels are total coral percent cover within each
habitat. Porites = massive and encrusting Porites.

9

Site-specific Surveys: Video Transects

A total of 800 at 25 sites (32 mVsite) was quantitatively assessed from transect
videotapes. Overall coral cover was lowest on the fore reef (8.8%) with progressively
greater cover on the back reef (15.9%) and lagoon (19.5%) (Table 2, Fig. 3b). The
differences among the three habitats in their average total percent coral cover were not
statistically significant (one-way ANOVA, F= 1.07; df = 2, 22; p = 0.36).

Nine scleractinian taxa were seen in PHA video transects (Pocillopora meandrina,
R eydoujci, R ligulata, R damicornis, massive and encrusting Rorites, R compressa,
Montipora, Leptastrea, Pavona duerdeni). A significant difference existed among the
three habitats in the relative abundance of coral taxa present (chi-square test, JV =

360.22, df = 6,p = 0.00). The fore-reef habitat was co-dominated by pocilloporids and
by poritiids with massive and encrusting growth forms (Table 2, Fig. 3b). Of the four
distinguishable species of Pocillopora present in video transects, P. meandrina comprised
92.3% of the total pocilloporid cover throughout the atoll. The back-reef habitat was
dominated by Montipora. Similar to results from towed-diver surveys, the lagoon was
dominated by Porites compressa (Table 2, Fig. 3b) and faviids contributed little to coral
cover in all habitats (Table 2, Fig. 3b). Pavona was most abundant on the fore-reef
habitat.

Site-specific Surveys: Photoquadrats

Video transects and photoquadrats were recorded concurrently at 25 sites with
an additional nine sites surveyed for percent cover by photoquadrats alone. Of the 25
sites where both methods were applied, the maximum difference in total coral cover
calculated with the two methods was 14.7%; the average of the absolute values of the
difference between video transect and photoquadrat total coral cover was 4.9%. Overall
coral cover was lowest on the fore reef (6.4%) with progressively greater cover on the
back reef (10.1%) and the lagoon (14.4%) (Table 2, Fig. 3c). The differences among the
three habitats in their average total percent coral cover were not significant statistically
(Kruskal- Wallis test, H= 0.967, df = 2,p = 0.62).

Fourteen scleractinian taxa were seen in PHA photoquadrats (Table 3). A
significant difference existed among the three habitats in the relative abundance of coral
taxa present (chi-square test, JV = 284.77, df=6,p = 0.00). Relative abundances of
coral taxa derived from photoquadrat methods in back-reef and lagoon habitats were
highly similar to those derived from videotransect methods (Table 2, Fig. 3b,c). The
fore-reef habitat was co-dominated by poritiids with massive and encrusting growth
forms and by pocilloporids (Table 2, Fig. 3c). Of the four species of Pocillopora present
in photoquadrats, P. meandrina comprised 83.1% of the total pocilloporid cover and P.
ligulata comprised 12.0% of the cover throughout the atoll using this method. Pavona
and faviids contributed relatively little to coral cover in all habitats but were best
represented on the fore reef (Table 2, Fig. 3c).

10

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11

Site-specific Belt-transect Surveys: Colony Density and Size Classes

A total of 4188 colonies were counted and classified by size class within belt
transects covering 1950 m^at 31 sites. Porites was the most numerically abundant
(i.e., highest density) taxon across the atoll system followed by Pocillopora, Faviidae,
Montipora and Pavona (Fig. 4, All Habitats). Only 40 colonies of Fungia and
Psammocora (<1% of total) were not in these taxa. Relative densities of coral taxa
followed a similar pattern within the fore-reef and lagoon habitat as across the atoll
system (Fig. 4); i.e., in both habitats, Porites, followed by Pocillopora and faviids, was
the most numerically abundant taxon. In the back-reef habitat, however, Porites was the
least abundant taxon with substantially fewer colonies than Montipora or Pocillopora.
Highest overall colony density occurred on the fore reef (3.7 colonies/m^) and lowest on
the back reef (0.5 colonies/m^).

Figure 4. Colony density (n/m^) of five coral taxa at Pearl and Hermes Atoll, NWHI, in the lagoon, back
reef, fore reef, and the three habitats combined. Number of colonies (n) were determined from belt transect
surveys; area (m^) surveyed in each habitat is shown next to habitat label. Values to the right of bars are the
number of colonies of each taxon.

Coral communities at PHA are primarily composed of small colonies; nearly three-
quarters (72.7%) of all colonies measured < 20 cm maximum diameter. Although most
taxa had distinctive size-class distributions in different habitats (Figs. 5, 6, 7), only
Montipora in the back-reef habitat had more than 50% of colonies measuring > 20 cm
maximum diameter (Fig. 6b).

12

(c) Lagoon, Porites

60

50

240

o

(d) Fore Reef, Pocillopora

n =926

“T 1

0-5 5-10 10-20 20-40 40-80 80-160 >160

Figure 5. Size class (cm) distributions, by habitat, of scleractinian corals at Pearl and Hermes Atoll, NWHI.
a- c Porites, d-f Pocillopora.

13

(d) Fore Reef, Faviidae

70

60

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(e) Back Reef, Faviidae

0-5 5-t] n-20 20-40 40-80 80-160 >160

(c) Lagoon, Montipora

(f) Lagoon, Faviidae

Figure 6. Size class (cm) distributions, by habitat, of scleractinian corals at Pearl and Hermes Atoll, NWHI.
a- c Montipora, d-f Faviidae.

14

Porites' size-class distributions on the fore reef and back reef are highly similar (Fig. 5a,
b) despite the taxon’s disparate representation in the two habitats both in coral
cover (Fig. 3) and density (Fig. 4). In the lagoon, this genus is largely represented by P.
compressa (Fig. 3), whose tendency to form large thickets by clonal propagation (Hunter
1993) accounts for the increased proportions in larger-size classes (Fig. 5c).

Pocilloporids are more dense (Fig. 4) and make a greater contribution to
coral cover (Fig. 3) on the fore reef than on the back reef or in the lagoon. Their density is
lowest on the back reef, but a greater proportion of larger (> 20 cm maximum diameter)
colonies is found here compared to other habitats (Fig. 5d-f).

Montiporids dominate the back reef both in terms of density (Fig. 4) and
contribution to coral cover (Fig. 3) but are rare on the fore reef and lagoon (Fig. 3, 4). On
the back reef, as noted above, the proportion of Montipora colonies in larger size classes
(> 20 cm maximum diameter) exceeds that of other taxa throughout the atoll.

More than 75% of faviids in all habitats measure < 20 cm maximum diameter
(Fig. 6d-f); their small size and low densities (Fig. 4) account for their small contribution
to total coral cover.

At belt-transect survey sites, Pavona (primarily P duerdeni) was only common
enough on the fore reef to construct a size-class distribution (Fig. 7). There, the taxon
ranked second only to back reef Montipora in the proportion of colonies measuring > 20
cm diameter (43.3% vs. 62.1%, respectively).

Figure 7. Size class (cm) distribution of Pavona in the fore-reef habitat at Pearl and Hermes Atoll, NWHI.
Too few colonies were found in other habitats to construct distributions.

15

DISCUSSION

Comparison with Previous Surveys

The three survey methods used in the present study produeed highly eongruent
patterns in the atoll-wide distribution and abundanee of eoral taxa. The ehief
diserepaney among the methods in eoral eover was found in the baek-reef habitat where
videotranseets and photoquadrats yielded similar results but overestimated Montipora
eompared to towed-diver surveys (Tables 1, 2, Fig. 3). The dominanee of Porites with
massive and enerusting growth forms on the fore reef (Tables 1, 2, Fig. 3) is eonsistent
with the top ranking of Porites lobata by Maragos et al. (2004) and by Grigg (1983)
along the southwest fore reef (Table 3), but in the present study baek-reef and lagoon
habitats were dominated by Montipora and Porites compressa, respeetively.

Table 3. Relative Abundanee of Coral Speeies at Pearl and Hermes Atoll Ranked by
Photoquadrats in This Study, in Maragos et al. (2004), and in Grigg (1983)

Rank

This Study

Maragos et al. (2004)

Grigg (1983)

1

Porites lobata

Porites lobata

Porites lobata

2

Porites compressa

Pocillopora damicornis

Porites compressa

3

Montipora capitata

Porites compressa

Pavona duerdeni

4

Pocillopora meandrina

Leptastrea purpurea

Pocillopora meandrina

5

Montipora flabellata

Pocillopora ligulata

Montipora verrucosa ^

6

Leptastrea purpurea

Pocillopora meandrina

Leptastrea purpurea

7

Pocillopora ligulata

Cyphastrea ocellina

NA."

8

Pavona duerdeni

Montipora capitata

NA.*”

9

Pocillopora damicornis

Psammocora stellata

NA.*”

10

Pocillopora eydouxi

Fungia scutaria

NA.*”

11

Pavona varians

Porites evermanni

NA.*”

12

Fungia scutaria

Montipora flabellata

NA.*”

13

Psammocora stellata

Montipora turgescens

NA.*”

14

Cyphastrea ocellina

Pavona varians

NA.*”

^RQYiSQd dis Montipora capitata (Maragos 1995).

^Not available; data only provided for 6 speeies by Grigg (1983).

Grigg (1983) reported a mean eoral eover of 19% from two 50-m seaward
transeets off the southwest seetor of PHA. This value is eonsistent with eoral eover
obtained from videotranseets and photoquadrats at one southwest fore-reef site in our
study (21.9% and 17.1%, respeetively). However, Grigg’s value is high relative to the
average eoral eover (7.5%) obtained from analysis of 9.3 km surveyed by towed-divers
along the southwest fore reef (Table 1, Fig. 2) as well as eoral eover obtained from
photoquadrats at a seeond southwest fore-reef site (6.3%). These eomparisons highlight
the need for broad survey eoverage in eharaeterizing a habitat.

16

Galtsoff (1933), working primarily in the lagoon with samples eolleeted by free-
divers and observing from the surfaee through a glass-bottom box, reeorded nine eoral
speeies: Porites lobata, R compress a, Pocillopora ligulata P damicornis, P meandrina,
Montipora verrucosa, M. verrilli, Pavona varians, and Cyphastrea ocellina. Grigg
(1983) reported 12 speeies from southwest seaward reefs (Table 3). Maragos et al. (2004)
reported 32 speeies from 69 survey sites but provided no demographie data pertaining to
their distribution aeross the atoll. In the present study, 14 speeies were distinguished in
photoquadrats (Table 3). Of these 14 speeies, 11 are ineluded among the top 14 speeies
ranked with the use of oeeurrenee and abundanee indiees developed by Maragos et al.
(2004) (Table 3). All six speeies reeorded by Grigg (1983) on southwest seaward reefs
were observed in photoquadrats in the present study.

In eomparing eoral abundanee throughout the Hawaiian Arehipelago, Grigg
(1983) noted that “the most signiheant differenee in eommunity strueture between
islands in the arehipelago as represented by stations off southwest exposures is the degree
of dominanee by individual speeies”. The present study, along with analyses of eoral
eommunity strueture at Freneh Frigate Shoals (FFS) reported by Kenyon et al. (2006e),
supports Grigg’s statement and extends it to additional exposures and habitats. With the
exeeption of Acropora, whieh had not been observed at PHA (Grigg 1981, Maragos et al.,
2004, this study) until 2006 (Kenyon et al., unpublished data), the same suite of speeies
are the major eontributors to eoral eommunity strueture, but their relative abundanees
as assessed through pereent eover and density vary between these two atolls. At both
atolls, massive and enerusting Porites along with Pocillopora dominate or eo-dominate
all seetors of the fore reef Montipora, rare at FFS, dominates several baek-reef seetors at
PHA. Lagoon reefs at PHA are largely made up of Porites compressa, whieh is mueh less
prevalent on FFS lagoon reefs than massive and enerusting Porites.

Unique Challenges

Jokiel and Rodgers (2005) used hve, equally weighted metries of eoral-reef
biologieal “health” or “value” (reef-hsh biomass, reef-hsh endemism, eoral eover,
endangered monk seal [Monachus schauinslandi\ population, and numbers of female
green sea turtles [Chelonia my das] nesting annually) to rank the eondition of 18 islands/
atolls throughout the Hawaiian Arehipelago. PHA along with Lisianski (Fig. 1) ranked
seeond to FFS in this integrated index of reef eondition. Mueh of PHA’s eomposite seore
derived from its top seores in the reef-hsh biomass and endemism eategories, whereas it
ranked 12th in the eoral-eover eategory. While this ranking implies that PHA is presently
among the least disturbed reef systems in the Hawaiian Arehipelago, due in part to
distanee from population eenters, reeent researeh suggests its eoral eommunities are
the most vulnerable in the Arehipelago to stressors, ineluding mass eoral bleaehing and
marine debris aeeumulation, whose reaehes extend well beyond populated areas.

Mass eoral bleaehing oeeurred on reefs throughout the NWHl in 2002 and 2004;
in both years, the ineidenee of bleaehing was highest at PHA (Kenyon et al., 2006a,
Kenyon and Brainard 2006). Bleaehing was most pronouneed in the baek-reef habitat
where 97% of Montipora and Pocillopora eolonies examined during 2002 surveys {n =

17

340) at PHA showed bleached tissue, as did 71% of colonies in these genera examined
during 2004 surveys {n = 121). Both mass bleaching episodes coincided with periods of
prolonged, elevated sea-surface temperatures (SST) detected by satellite remote sensing
and in situ temperature recorders (Hoeke et al., 2006a,b; Kenyon and Brainard 2006).
Analyses of historical SST datasets show a warming trend in the Hawaiian Archipelago
(Jokiel and Brown 2004, Barton and Casey 2005) that is most pronounced at the northern
end of the chain, suggesting the frequency and severity of thermally induced bleaching
events may increase in the Hawaii region (Jokiel and Brown 2004) with shallow back
reef corals at PHA potentially the most vulnerable. Quantihcation of coral mortality from
the 2002 bleaching event, as assessed through photoquadrat analysis of sites surveyed
in both 2002 and 2004, indicated a decrease of live Montipora cover by as much as 20%
at some PHA back-reef sites (P. Vroom and J. Kenyon, unpublished data). The size class
distribution of Montipora from back-reef sites surveyed in 2004 (w = 350 colonies) is also
more right-skewed (J. Kenyon, unpublished data) than the 2002 distribution {n = 153,

Fig. 6c), as partial mortality effectively fissions a genet into multiple ramets, which in
following years become counted as separate, smaller colonies.

Elevated temperatures and associated bleaching have been shown to increase
the incidence of numerous opportunistic coral diseases (Harvell et al., 1999, Kuta and
Richardson 2002, Rosenberg and Ben-Haim 2002), which can contribute significantly to
coral-reef degradation (Santavy et al., 2005). Six disease syndromes affecting Porites,
Pocillopora, or Montipora have been documented at PHA (Aeby 2006). During surveys
conducted throughout the NWHl in 2005, ~ 4% of colonies examined at PHA showed
signs of disease with the highest prevalence of diseased colonies (~ 7%) at Maro Reef
(Fig. 1). These levels are low compared to the main Hawaiian Islands (Aeby et al., 2006)
and may represent baseline levels of coral disease normally found in an undisturbed
system. Populations weakened by further stressors, such as additional bleaching events,
could experience increased disease levels with deleterious consequences to the ecosystem
as has occurred in the Caribbean and Florida Keys over the past two decades (Santavy et
al., 2005).

Derelict fishing gear causes substantial damage to reefs throughout the NWHl
(Donohue et al., 2001). Debris originating from North Pacific fisheries may accumulate
in the region of the NWHl because of their location in a convergence zone associated
with the North Pacific subtropical high (Kubota 1994, Brainard et al., 2000). Driven
over northeast-facing reefs in the NWHl by prevailing winds, the debris begins a cycle
of destruction, snagging on reefs, breaking off coral through wind-driven water motion,
snagging and damaging additional coral, and so on. Most reef-hung derelict fishing
gear occurs in shallow (< 10 m) water (Donohue et al., 2001). Based on quantified
removal efforts at PHA and Fisianski (Fig. 1) in 1999, Donohue et al. (2001) suggested
the oceanic convergence zone associated with the North Pacific subtropical high may
intersect PHA more frequently than Fisianski, resulting in more debris accumulation at
PHA. Re-survey of areas at Kure Atoll, PHA and Fisianski in 2001 that were cleaned
of marine debris in 2000 indicated the highest accumulation rate (number of items/kmV
year) occurred at Kure Atoll (Boland and Donohue 2003) followed in order by PHA and
Fisianski. Both studies focused on small areas (< 1.3 km^) at each location frequently

18

used by endangered Hawaiian monk seals (Monachus schauinslandi) and did not purport
to quantify aeeumulation rates on larger seales or in habitats eharaeterized by different
regimes of bathymetry, rugosity, or wave energy.

Marine debris removal efforts undertaken by NOAA’s Coral Reef Eeosystem
Division over more extensive areas ineluding a greater diversity of habitats in the NWHl
from 1999-to-2006 have removed 560 metrie tons of hshing debris whieh ineludes
295 metrie tons from PHA (R. Brainard, unpublished data). Weight analysis of debris
removed in 2005 from shallow areas (< 4.5 m) that were eleaned of marine debris in
2004 at PHA and Kure Atoll indieates the mean aeeumulation density (kg/km^) in areas
of retieulated lagoon reef is ~ 2.5 times greater than aeeumulation in areas with a deeper,
more homogeneous reef strueture that are eloser to a barrier reef (Dameron et al., 2006).
When aeeumulation rates in these two types of “net habitat” are eoupled to the area of
eaeh habitat in the NWHl, PHA emerges as the loeation with the greatest predieted future
aeeumulation (kg/yr) of dereliet hshing gear. PHA’s predisposition to high aeeumulation
densities derives both from the large area oeeupied by the labyrinth of shallow retieulated
reefs in the eastern lagoon and the broad expanse of barrier reef exposed to prevailing
northeast winds. Moreover, visual assessment of net density helds at PHA generated
from plots of net loeations reveals that nets tend to aeeumulate along the northeast and
southwest baek reef as well as a linear expanse of retieulated lagoon reefs extending from
northwest to southeast aeross the atoll (Dameron et al., 2006). Examination of submerged
debris during removal aetivities at PHA in 2002 and 2003 showed that live eoral had
reeruited on or grown within the mesh of 32% of debris items {n = 4434) (Asher and
Timmers 2004). Consistent with eoral abundanee data in the present study, Montipora
and Pocillopora were the primary genera found on dereliet gear from the baek reef, and
Porites and Pocillopora were prevalent on debris reeovered from retieulated lagoon reefs.

The eorallivorous sea-star Acanthaster planci oeeurs naturally at low densities
on Hawaiian reefs (Chess et al., 1997) and only a single large-seale aggregation has
been reported from Hawaii (Branham et al., 1971). While faetors regulating population
levels remain eontroversial, outbreaks have oeeurred in areas far from agrieultural,
industrial and urban development and ean have signiheant eeosystem effeets (Birkeland
1982, 1989). In situ observations of non-eryptie Acanthaster during towed-diver surveys
eondueted throughout the NWHl between the years 2000 and 2003 indieated their highest
frequeney of oeeurrenee was at PHA relative to other atolls (1.9/tow) (Timmers et al.,
2004). When different habitats within atolls were eompared, frequeney of sightings was
highest on the fore reef, with the highest fore-reef frequeney at PHA and Midway Atoll
(3.8/tow). In the main Hawaiian Islands, Montipora and Pocillopora were reported
as preferred prey by Branham et al. (1971) and Chess et al. (1997), respeetively, even
when more abundant Porites was present. Keenan et al. (2004) report more than 500
Acanthaster sightings during tows eondueted in seareh of marine debris in the lagoon and
baek reef at PHA in 2003 and that the sea stars were eommonly feeding on Porites. PHA
might therefore be at greatest risk in the NWHl for sustaining future outbreaks given the
extant highest frequeney of Acanthaster at this loeation and the abundanee, in different
habitats, of all three genera reported as preferred Acanthaster prey in Hawaii.

The shallow-reef systems diseussed in the present study politieally eome within

19

overlapping jurisdictions of the state of Hawaii and the U.S. Fish and Wildlife Service’s
National Wildlife Refuge system. Submerged lands seaward of state and other federal
authority in the NWHl were given additional federal oversight through the creation of the
NWHl Marine National Monument by presidential proclamation in 2006 (http://www.
whitehouse.gov/news/releases/2006/06/200606 15- 18.html). Renewed political interest in
the NWHl has accelerated the pace of scientific investigation in this remote region and
helped generate the means by which long-term assessment and monitoring of biological
resources and environmental parameters are being conducted. Demographic coral data
shown in the present study and interpreted within the context of known risks to habitat
integrity suggest that shallow-water (< 20 m) coral communities at PHA are especially
vulnerable to stressors that have led to reef degradation in other regions and may
therefore warrant special management attention. Our data serve as a detailed baseline to
which population parameters along specific tow tracks and at 1 5 long-term monitoring
sites established in 2003 can be compared in future years to better understand the
direction, pace, and drivers of change.

ACKNOWLEDGEMENTS

This work is part of an interdisciplinary effort by the NOAA Pacific Islands
Fisheries Science Center Coral Reef Ecosystem Division to assess and monitor coral-
reef ecosystems in the U.S. Pacific. We thank the officers and crew of the NOAA
ship Townsend Cromwell and the charter vessel Rapture for logistic support and field
assistance. Rusty Brainard and Joe Chojnacki assisted in collection of towed-diver
survey data; Kimberly Peyton, J. Kanekoa Kukea- Schultz, Karla McDermid and Brooke
Stuercke assisted in collection of photoquadrat data; D. Potts assisted in collection of
coral size class data. Permission to work in the NWHl was granted by the Pacific Remote
Islands Wildlife Refuge Complex, U.S. Fish and Wildlife Service, Department of the
Interior and the State of Hawaii Department of Land and Natural Resources. Funding
from NOAA’s Coral Reef Conservation Program and the NWHl Coral Reef Ecosystem
Reserve supported this work, with facilitation by Tom Hourigan and Robert Smith,
respectively.

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