Download PATTERNS OF REEF COMMUNITY STRUCTURE, NORTH JAMAICA

BULLETIN OF MARINE SCIENCE, 40(2): 311-329,
1987
CORAL REEF PAPER
PATTERNS OF REEF COMMUNITY
NORTH JAMAICA
STRUCTURE,
W David Liddell and Sharon L. Ohlhorsl
ABSTRACT
Reefcommunities were quantitatively surveyed overthe range of 0.5 to 56 m in the vicinity
of Discovery Bay, Jamaica, at intervals spanning 1977-1982. This study provides data on
reef communities which were subsequently altered by major disturbance events (e.g., Hurricane Allen in 1980 and the mass mortality of the urchin, Diadema in 1982). Living cover
by the sessile epibiota is typically high, between 82-95%, at the census sites. Corals occupy
from 28-60% of the reef surface with no clear depth-related trends in cover. The most striking
bathymetric trends are displayed by the algae and sponges. Cover by macro- and filamentous
algae (8-32%) and fleshy sponges (2-15%) is positively correlated with increasing depth on
the fore reef while cover by coralline algae (4-37%) and boring sponges (0-32%) is negatively
correlated with increasing depth.
Coral species diversity (H', log.,) increases from 0.13 on the seaward portion of the reef
crest at 0.5 m to 2.12 at 22 m on the fore reef escarpment. This highest value at 22 m may
represent an edge effect. Despite the lowered rates of physical and biotic disturbance on the
fore reef slope (30-56 m), diversity values fluctuate between 1.49-1.76 and are similar to,
or higher than, values from the shallower (0.5-15 m) reef crest and fore reef terrace.
Q-mode cluster analyses of eight reef sites resulted in the delineation of the following five
reef zones (listed from onshore to offshore): the Rear Zone (1 m depth), Reef Crest (approximately 0.5-5 m), Lower Fore Reef Terrace (approximately 10-25 m), Upper Fore Reef Slope
(approximately 30-45 m) and Lower Fore Reef Slope (approximately 45-60+ m). Similar
zonations were produced regardless of whether the distribution of coral species or larger,
operational taxonomic units (e.g., corals, coralline algae, macro- and filamentous algae, boring
sponges and fleshy or erect sponges) were employed. Both biotic and abiotic factors contribute
to this zonation.
The well developed fringing reefs occurring along the north central coast of
Jamaica display a striking, depth-related biotic zonation which has been described
in several papers (Goreau, 1959; Goreau and Goreau, 1973; Kinzie, 1973; Lang,
1974; and others). In addition, these reefs have been the location of numerous
studies dealing with the physiology, functional morphology, and other aspects of
the biology and ecology of the reef organisms. To date, only a few studies at
Jamaica (Bonem and Stanley, 1977; Liddell and Ohlhorst, 1981; Liddell et al.,
1984a; Huston, 1985; unpubl. data) have presented data which enable the quantitative documentation of depth-related trends in species composition and diversity. In addition, such studies at Jamaica and elsewhere in the Caribbean have
been largely restricted to the shallower reefs (:5 30 m), with only a few exceptions
(Ott, 1975; Bak, 1977; Bak and Luckhurst, 1980; Liddell et al., 1984a).
The present paper presents reef census data for a north Jamaican reef from 1
m depth in the back reef to the outer edge of the fore reef at 56 m. The deep reef
differs significantly from the shallow reef in a number of important environmental
parameters, such as light and turbulence. By examining the changes which occur
in reef communities with increasing depth, the relative importance of such parameters in structuring reef communities may be evaluated. The census data is
utilized in the development of a quantitative reef zonation which may be compared
to those described for other Caribbean sites. In addition, such census data provides
much-needed base-line information which can be used to evaluate the effects of
311
312
BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2, 1981
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natural (storms, mass mortality events) and man-induced (pollution, recreational
acti vi ties) disturbance to reef systems. The latter becomes of particular importance
as coastal resources are increasingly exploited for food and energy resources and
recreation. Finally, the overall bathymetric patterns delineated by this study may
be of use to paleoecologists attempting to interpret the environments represented
by ancient reef deposits.
Two disturbance events, Hurricane Allen in 1980 (Woodley et al., 1981) and
the mass mortality of the urchin, Diadema in 1982 (Liddell and Ohlhorst, 1986),
have greatly modified the shallower «30 m) north coast communities. Although
the present tense will be used throughout this paper, the reader should be aware
that certain of the communities have changed considerably subsequent to the
censuses described herein.
STUDY LoCALITY
Discovery Bay lies on the north central coast of Jamaica at latitude, 18°30'N and longitude, 77°20'W.
The fringing reefs studied are known as "Zingorro" and "Watertower" and lie on the West Fore Reef,
approximately 0.5 km west of the Discovery Bay ship channel (Fig. 1, line A-A'). The two reeflobes
merge near the reef crest and are separated by approximately 10m of sand near the fore reef escarpment.
Study sites on Zingorro were located at 1 m depth, immediately behind the reef crest, at 22 m on
the fore reef escarpment and at 30, 45 and 56 m on the fore reef slope and were censused during
August 1982 (Liddell et a\., 1984a; Fig. 2). The last site lies near the edge of the fore reef slope, only
1 to 2 m from the vertical escarpment of the deep fore reef (terminology after Goreau and Land,
1974).
Data from 15 m on the fore reef terrace ofWatertower Reefwere collected during May 1980 (Liddell
and Ohlhorst, 1981). Data from 0.5 and 5 m on Watertower were collected by Huston (1985; unpubl.)
during March 1977.
LIDDELL AND OHLHORST:
FORE
REEF COMMUNITY
REEF
313
STRUCTURE
REEF
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Figure 2. Generalized profile across the West Fore Reef at Discovery Bay, Jamaica along the line
A-A', Figure I (modified from Liddell et aI., I 984c). Shown are the generally recognized geomorphic
(Goreau and Land, 1974) and ecological zones (Goreau, 1959a; Goreau and Goreau, 1973; Kinzie,
1973) of the Jamaican fringing reefs and the location of the census sites described herein. Also shown,
below the profile, is a Q-mode cluster dendrogram (Euclidean Distance, UPGMA) of the reef census
sites based on relative proportions of the larger taxonomic groupings.
Although shallower reef sites were still recovering from the August 1980 Hurricane Allen and
exhibited greatly reduced coral cover at the time of our 1982 censuses, deeper sites, such as those on
the fore reef slope (2: 30 m), were less affected by the hurricane (Woodley et aI., 1981; Ohlhorst and
Liddell, 1981) and represent, at most, moderately undisturbed communities. Although the fore reef
escarpment site almost certainly suffered some hurricane damage, diversity and percent living cover
data from the site on Zingorro in 1982 (Tables I, 2) are very similar to such data from the fore reef
escarpment of the adjacent Watertower Reef collected in 1977 by Huston (1985, table 1). The largescale disturbance of shallow fore reef communities by Hurricane Allen in 1980, however, necessitated
the use of shallow reef data collected prior to 1980 (e.g., the 0.5, 5 and 15 m fore reef data).
The West Fore Reef exhibits the structural and ecological zones which characterize most Jamaican
north coast reefs (Goreau, 1959; Goreau and Goreau, 1973) and have been described by Kinzie (1973),
Goreau and Land (1974), Lang (J 974) and Moore et al. (1976). The following succession of structural/
geomorphic zones would be encountered along a transect across the West Fore Reef: reef crest, fore
reef terrace, fore reef escarpment, fore reef slope and deep fore reef. The profile (A-A', Fig. 2) presented
herein is generalized, but similar to those by others (Goreau and Wells, 1967; Kinzie, 1973; Dustan,
1975; Liddell and Ohlhorst, 1981) for sites along the West Fore Reef.
314
BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2, 1987
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LIDDELL AND OHLHORST: REEF COMMUNITY STRUCTURE
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316
BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2,
1987
The fore reef terrace (7-15 m) consists of large parallel lobes oriented perpendicular to the reef crest
and extending seaward at a moderate (15-20°) slope for approximately 200 m. These lobes are interrupted by large sand patches and channels resulting in spur and groove topography. These spurs often
rise 5 m above the surrounding sand and terminate in a steep (45+°) escarpment (15-25 m). The
landward portion of the fore reef slope, which begins at 25-30 m depth, usually consists ofa low angle
(5-20°) sand "moat" containing scattered coral heads. Coral cover increases at 30-35 m, often forming
parallel lobes and occasional pinnacles which may rise up to 10 m above the sand, At approximately
35 m the slope increases to between 45-60°. Another slope break occurring between 45 and 65 m,
typically at 55 m, marks the beginning of the deep fore reef "wall." Although corals and noncrustose
macroalgae are abundant on the upper portions of the wall, they are replaced by sclerosponges and
demosponges below 75-90 m (Lang, 1974). The steep (60-90°) escarpment ends at approximately 122
m where the more gentle (20-45°) island slope begins,
METHODS
Data from Huston were collected by a chain method (Porter, 1972); all other data were collected
by a line transect method in which to-m lines with points marked every 20 em were loosely draped
over the reef and the identity of every item beneath a transect point recorded (Iinc intercept method;
Lucas and Seber, 1977; Eberhardt, 1978). Transect lines were placed I m apart and oriented parallel
to bathymetric contours and were restricted to reef areas and did not extend into major sand channels
or grooves. From 5 to 12 lines (approximately 250-600 points) were surveyed at each site. Ninetyfive percent confidence intervals were calculated using data from each to-m transect line as discrete
entities (Table I). Fewer lines were transected at the deeper sites due to limitations of bottom time.
The line transect method was considered to be preferable to others, such as the quadrat method
(Kissling, 1965; Weinberg, 1981), in that it allows for a greater area of reef to be censused per unit of
time and, therefore, may be less subject to biasing by heterogeneous distributions of reef benthos.
Cumulative plots of coral species censused versus number of transect lines surveyed were utilized as
a test of sample adequacy (Loya, 1972), For all sites the cumulative species curves were either level
(no new species being added with increasing sample size) or at least rising at a low rate, suggesting
that the samples are nominally adequate for describing the coral community (Fig, 3).
Transect data were used in the determination of sessile community composition, coral species
abundance, percent living (macroscopic) cover, and in the calculation of values for coral diversity (H',
natural log, based on the number of points occurring over living tissue; Shannon and Weaver, 1948)
and evenness (1'; Pielou, 1966). Transect data were also utilized in Q-mode cluster analyses (Euclidean
Distance, UPGMA) involving relative abundances of the 15 most "common" coral species (i.e., those
comprising ~ 1.0% of the coral fauna on at least one site) or proportions oflarger, operational taxonomic
categories (e.g., corals, sponges, etc.). The groupings defined by cluster analysis were tested statistically
by using chi-square tests of frequency data to compare within and between cluster groupings.
In order to determine the amount of actual reef cover over broad expanses of the fore reefplatform,
aerial photographs and underwater maps were overlain with grids and the amounts of major sand and
reef areas counted over a 40,000 m' tract extending 100 m to the east and 100 m to the west of our
Zingorro transect sites and over a depth range of approximately 5 to 40 m.
Data were also gathered on the density of the urchin Diadema anti/larum by counting those present
in I-m-wide strips adjacent to the transect lines in 1980 at 15 m and in 1982 at the back reef I m
and fore reef22, 30,45, and 56 m sites. Diadema was also censused at 0.5 and 5 m by Huston (unpubl.
data) in 1977.
RESULTS
Patterns of Larger Taxonomic Categories. -Cover of the island shelf by reef in the
vicinity of Discovery Bay averages 74%. In our transect sites on the reef spurs,
living cover (all taxonomic categories) is typically high, between 82 to 95%, with
the highest values occurring between 30-56 m on the fore reef slope (Table I,
Fig. 4). This translates into a range of 61-70% living cover for the 40,000-m 2 fore
reef area under consideration (including sand channels as well as reef spurs). Living
cover is dominated by corals, various algae and sponges. Total living cover shows
no significant correlation with depth.
Coral cover shows no clear-cut relationship with depth and decreases from
60.0% at 5 m to 35.9% at 15 m to 27.9% at 22 m (presumably due to the unstable
nature of the steeply sloping fore reef escarpment) and then increases to 58.9%
LIDDELL AND OHLHORST:
REEF COMMUNITY
317
STRUCTURE
CUMULATIVE SPECIES PLOT
18
22 m
16
15m
104
12
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~
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..:(
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10
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NUMBER Of" UNES
-
_ BRl m
9
10
11
12
Figure 3. Cumulative species plot for corals encountered at each census site. "Lines" consist of
approximately 50 transect points each. Numbers next to curves refer to depths of sites in meters, BR
refers to back reef.
at 30 m before finally declining to 38.5% at 56 m. Coral cover in back reef areas
is highly variable. Coral cover at the back reef I m site was extremely low « 1.0%),
perhaps reflecting, in part, the fact that the site was censused after Hurricane
Allen.
The most striking depth-related trends in abundance are displayed by the algae
and sponges. Cover by both macroalgae and filamentous algae (combined 8.032.0%) and fleshy/encrusting sponges (1.7-14.5%) is positively correlated with
increasing depth (P < 0.0 I, Spearman Rank Correlation) on the fore reef, while
cover by coralline algae (36.5-3.6%; P < 0.05, SRC) and boring sponges (32.00.0%; P < 0.20, SRC-Iow significance due to small number of data points) is
negatively correlated with increasing depth on the fore reef. It should be noted
that these data show a decline in clionid abundance with increasing depth at the
reef surface; these boring sponges may, however, be abundant in cryptic habitats
(Gareau and Hartman, 1963). The urchin herbivore, Diadema antillarum, is most
abundant on the shallow fore reef terrace and decreases greatly in abundance
below 22 m (Table 1).
Coral Species Trends. -Depth-related
trends at the species level are presented
only for the corals (Table 2, Figs. 5-8) as this data is most readily comparable to
318
BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2,
Fore
lIee'
Escarpment
Slope
56 .5
30
\987
Back
lIee'
ere It
Terrace
22
15
5
O.S 1
Depth
em)
MSL
100m
Coral
Coralline
Algae
Fleshy/Filamentous
•.
Fleshy
Algae
Sponges
.....•••_~~~~~====~:>
Boring
Sponges
Figure 4. Bathymetric distributions and relative abundances of major space-occupants on a Jamaican
fringing reef. Sites (depths) upon which spindles/kites are bascd are indicated along top of profile.
Dashed lines represent an estimate as boring sponges were not included in Huston's data. If our
estimate of dionid abundance is correct, then Huston's crustose coralline algae abundance should be
reduced somewhat (to approximately 20% of reef surface).
other studies. More complete species information for the larger operational categories utilized in this paper is presented in Liddell et al. (1984c, Appendix A).
Coral diversity (H'; Shannon and Weaver, 1948) at the back reef l-m site is
1.05. Coral diversity increases from the reef crest (0.5 m, H' = 0.13) to the fore
reef escarpment (22 m, HI = 2.12) and then decreases on the upper fore reef slope
(30 m, H' = 1.54) with the lowest value occurring at the boundary between the
lower fore reef slope and the deep fore reef (56 m, H' = 1.49). S (species richness)
closely tracks the depth pattern for H', with the exception of the back reef l-m
site, while l' (evenness; Pielou, 1966) closely follows the HI pattern, with the
exception of the fore reef slope 56-m site (Fig. 5). If the back reef I-m site is
excluded, coral diversity (HI) is negatively correlated (P < 0.05, SRC) with percent
coral cover (Fig. 6) and the same relationship is shown to hold when H' is plotted
against total living cover. Although the 0.5- and 5-m sites were censused by a
chain method and all other sites were censused by a linear point intercept method,
values obtained by the two methods from the same (15 m) site are essentially
LIDDELL AND OHLHORST:
REEF COMMUNITY
319
STRUCTURE
CORAL DIVERSITY
2.~
2~
2
20
1.~
1~
S
10
O.~
Legend
o
BRI
0.5
5
15
22
DEPTH M
30
45
55
o
•
H'
•
A
J'
S
Figure 5. Plot of H' (diversity, natural log; Shannon and Weaver, 1948), l' (evenness; Pielou, 1966)
and S (species number) versus depth for corals on a Jamaican fringing reef
identical (H' = 1.87 for line transect, Table 2, herein; H' = 1.83 for chain, Huston,
1985, Table 1).
It should be noted that some confusion exists concerning the taxonomic status
of the deeper-water, plate-shaped Agaricia species, which are extremely polymorphic. Zlatarski and Estalella (1982) have gone so far as to combine all of the
Agaricia species into one species, A. agaricites, with various morphological form
designations. The three plate-shaped species we recognized on the deeper fore
reef slope, tentatively assigned to A. fragilis, A lamarcki, A. undata, possessed
differing morphologies which could be recognized while conducting censuses.
Whether or not they represent varieties ofa single species (we feel this is unlikely)
or should be even further subdivided, will require a major effort by coral taxonomists. Considering that 82% of the corals at the 56-m site are Agaricia species
and that their taxonomic status is in doubt, H' values from the deeper fore reef
slope must be regarded with caution.
Of the 48 "hermatypic" (zooxanthellae bearing) coral species described from
Jamaica by Goreau and Wells (1967),27 were encountered in our censuses (Table
2); of these only 15 may be considered to be common-that
is, accounting for
1.0% or more of the coral fauna at at least one reef site. Although certain of the
common species (e.g., Agaricia agaricites) show a very broad bathymetric distribution with little depth-related changes in abundance, many others achieve their
highest relative abundances over fairly narrow depth limits (e.g.,Acropora palmata
or Madracis mirabilis) (Fig. 7). The corals clearly show species replacement along
the depth gradient with Acropora palmata dominating the coral fauna at 0.5 and
5 m on the fore reef (97.8 and 78.2%, respectively, of corals, Table 2), Acropora
cervicornis (45.3%) dominating at 15 m, Madracis mirabilis (27.2%) and Agaricia
320
BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2, 1987
CORAL DIVERSITY VS. PERCENT COVER
2.5
& 22m
2
&15m
&45m
& 56m
1.5
& 30m
&BRlm
&5m
0.5
&.5m
O..L-_-~--,,----.----'----'-------'r-------'r-------'r---20
30
40
SO
60
70
o
10
PERCENT COVER
Figure 6. Plot of coral diversity (H', natural log) versus coral percent cover. Numbers next to symbols
rcfcr to depths of sites in meters, BR refers to back reef.
agaricites (28.7%) dominating at 22 m, Montastrea annularis (54.2%) dominating
at 30 m and various species of Agaricia (54.6-82.1 %) dominating at 45-56 m.
Although a pre-hurricane 10-m site was not censused, M. annularis is relatively
abundant at this depth (pers. obs.; Dustan, 1975; Huston, 1985).
A Quantitative Reef Zonation. - The census data (Tables 1 and 2) were utilized
in Q-mode cluster analyses to better delineate the reef zonation. Based on the
proportions of the common, large, operational taxonomic units (e.g., macro- and
filamentous algae, crustose coralline algae, corals, boring sponges and fleshy
sponges), the interval from the back reef at 1 m to the outer edge of the fore reef
at 56 m may be divided into 5 zones (Fig. 2). The crest (0.5 and 5 m) sites are
tightly clustered together and, along with the back reef l-m site, form the most
distinct clusters. The 15-m and 22-m sites form a lower terrace-escarpment cluster.
The fore reef slope sites are separated from all shallow sites and can also be
subdivided into upper (30 m) and lower (45 and 56 m) clusters. All clusters (e.g.,
rear zone, crest, lower terrace-escarpment, upper slope, lower slope) were significantly different (x2, P < 0.01). Within each cluster there were no significant
differences at the P < 0.05 level, with the exception of the two sites (15 m and
22 m) comprising the lower terrace-escarpment cluster which were significantly
different at 0.05 < P < 0.0 1.
When the 15 common coral species are utilized in a cluster analysis, a pattern
LIDDELL AND OHLHORST:
REEF COMMUNITY
Fore
Reef
Bock
E HO rpment
Cm)
56 '5
Reef
Crest
Terrace
Slope
Depth
321
STRUCTURE
30
22
15
5
0.5
1
MSl
100 m
•••
-----~
Acropora
cervicornis
Acropora
pa Imata
Agaricia
agaricites
Agaricia
species
Madracis
mirabifis
Montastrea
annularis
Montastrea
cavernosa
Porites
astreoides
Figure 7. Bathymetric distributions and relative abundances of selected coral species on a Jamaican
fringing reef. Sites (depths) upon which spindles/kites are based are indicated along top of profile.
Note that at 10 m M. annularis would comprise approximately 17% of the corals (data from Huston,
1985).
similar to that above emerges (Fig. 8). The placement of the boundary between
the upper and lower fore reef slope zones differs (between 45 and 56 m versus
between 30 and 45 m) and the back reef l-m site joined with the upper fore reef
slope site and, therefore, was excluded from the final analysis. Although corals
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0.5 M
Shallow
5M
TERRACE
15 M
Deep
22 M
30M
Shallow
45 M
SLOPE
Deep
56 M
0.0
100.7
EUCLIDEAN
Figure 8. Q-mode cluster dendrogram (Euclidean Distance, UPGMA) of the reef census sites based
on relative proportions of the 15 most abundant coral species (i.e., those comprising"" 1.0% of the
coral fauna at one site). Refer to Figure 2 for location of sites along reef profile.
are very rare at the back reef site, accounting for < 1.0% of the bottom cover,
those that are present are often abundant at deeper reef sites.
DISCUSSION
Reef Zonation at Jamaica. - Wells (1954) defined a reef zone as "an area where
local ecological differences are reflected in the species association and signalized
by one or more dominant species." Although Goreau's (1959) reef zones were
originally described from the Ocho Rios area (some 40 km to the east of Discovery
Bay), they have been applied to the Discovery Bay reefs by Goreau and Goreau
(1973), Kinzie (1973) and others (Fig. 2).
The five ecological zones delineated by our cluster analyses are the following:
REARZONE.This shallow (1 m) back reef area located immediately behind the
reef crest is dominated by filamentous and macroalgae (both calcareous and fleshy
forms).
CREST.This zone extends from approximately 0.5 to 5 m and is dominated by
the coral Acropora palmata, crustose coralline algae and clionid sponges. This
would encompass the Upper Palmata (or Breaker) and Lower Palmata (or Barren)
Zones of Gareau (1959) and Gareau and Gareau (1973).
LOWERFOREREEFTERRACE-EsCARPMENT.
This zone includes the outer edge of
the fore reef terrace at approximately 15 m and the 45° fore reef escarpment which
extends from approximately 15 to 25 m. This zone is dominated by the corals
Acropora cervicornis, Agaricia agaricites and Madracis mirabilis, as well as crustose coralline algae, clionid sponges and, to a lesser degree, filamentous and macroalgae. Although these organisms overlap considerably within this zone, A. cervicornis is most abundant on the terrace, while M. mirabilis increases in abundance
at the terrace edge and on the escarpment and filamentous and macroalgae increase
in abundance on the escarpment, particularly its deeper portions. Kinzie (1973)
has divided Gareau and Goreau's (1973) Annularis-Cervicornis Zone into an upper
Mixed Zone (approximately 3-10 m depth), which is characterized by abundant
Montastrea annularis and A. cervicornis as well as other corals, and a lower
Cervicornis zone (approximately 10-25 m). This subdivision appears to be accepted by most reef workers at Jamaica. Ifa 10-m pre-Hurricane Allen site were
included in our cluster analyses, it would most likely be included in the lower
fore reef terrace-escarpment grouping based on the composition of the total reef
LIDDELL
AND
OHLHORST:
REEF COMMUNITY
STRUCTURE
323
community (larger taxonomic units), but may well have formed a distinct group
based on coral species only.
UPPERFOREREEFSLOPE.This zone extends from the beginning of reef growth
on the fore reef slope at approximately 30 m to approximately 35 to 40 m (a
deeper boundary for this zone, approximately 50 m, occurs when defined solely
on the basis of coral species). Corals are, by far, the dominant category of organisms, although filamentous and macro algae occur in numbers equivalent to that
on the fore reef escarpment. The dominant corals are Montastrea annularis and,
to a lesser degree, Agaricia agaricites. This corresponds to the Upper Fore Reef
Slope Structural Region (no biotic zone defined) of Goreau and Goreau (1973).
LOWERFORE REEF SLOPE.This zone extends from approximately 35-40 m
down to the end of the fore reef slope at approximately 56 m (our deepest census
site) and even beyond to a depth of 60-65 m on the nearly vertical wall of the
deep fore reef(personal observations from a submersible made during the summer
of 1984). Dominant corals are various plate-shaped Agaricia species (82% of
corals). In addition to the corals, demosponges and macroalgae are important
components of this reef zone, which corresponds to the Agaricia Zone of Goreau
and Goreau (1973).
Parameters Affecting Reef Zonation At Jamaica. - While the principal, geomorphic/structural features of the north Jamaican reefs can be attributed to features
of the underlying Pleistocene basement (Goreau and Land, 1974; Liddell and
Ohlhorst, 1981) and, perhaps, wave regime (Roberts et aI., 1975), the depthrelated biotic zonation shown by these reefs is the result of the complex interplay
between a variety of physical/chemical parameters as well as biotic interactions.
Light, sedimentation and wave regime are highly correlated with depth and, as
such, are parameters likely to exert a strong influence on the biotic zonation of
the reefs. It is of interest to note that nearly identical clusters (Figs. 2, 8) are
produced regardless of whether the relative abundances of coral species or the
entire sessile community (larger taxonomic units) are utilized.
Depth-related shifts in the relative abundances of coral species (Table 2, Fig.
7) occurring below usual wave base (approximately 20-30 m) are likely to be
attributable to changing light conditions (Geister, 1977). In this context, Roger's
(1979) study of the effects of shading on coral community structure is of interest
as it showed A. cervicornis to be most susceptible to shading while corals, such
as M. cavernosa, which are important components of deeper coral communities
(Table 2; Fig. 7), were less affected.
Dodge et al. (1974) report a reduction in coral growth rates and a paucity of
suspension feeders in lagoon areas within Discovery Bay which they attribute to
high rates of resuspension of fine-grained sediment. Ohlhorst (1980), however,
found no correlation at eight fore reef sites and a site within the bay (Columbus
Park) between size or shape of coral colonies and sedimentation rates. Although
quantities of resuspended sediment were inversely correlated with increasing depth
(P < 0.05, SRC), sedimentation rates did not correlate with living cover or coral
abundance (P < 0.05, SRC) and were positively correlated with coral diversity
at these sites (P < 0.05, SRC). It appears that sediment, in amounts found resuspended over most Jamaican reef sites, does not negatively influence the reef
community and may, in fact, act in the manner of a low level disturbance (Paine,
1966; Harper, 1969) to increase species diversity. The difference between the
results of these two studies may be related to differences in sediment grain size
with finer-grained sediments predominating at the back reef sites of Dodge et al.
(1974).
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Reef organisms are responsive to the direction and magnitude of waves. At
Jamaica the northeasterly tradewinds generate waves which typically approach
the reefs from the northeast to southwest and are responsible for substantial
bidirectional surge currents in the shallow, fore reef zones. In addition to wave
surge, there is also a westward trending unidirectional current on the shallow fore
reef, but this is usually slight. Within the back reef, the tradewinds generate a
slow, clockwise surface current and may also produce waves capable of stirringup bottom sediments and, thus, restricting coral growth.
In areas located above wave-base (approximately 20-30 m), depth-related shifts
in reef community composition are most likely influenced by environmental
turbulence (Geister, 1977). Light levels will probably not limit coral species diversity on the shallower «30 m) reefs (Loya, 1976). Acropora cervicornis, for
example, is not well adapted to the highly turbulent conditions on the shallow
fore reef terrace (Tunnic1iffe, 1982), while A. palmata (Shinn, 1963; Graus et aI.,
1977) and more massive corals, such as Montastrea annularis, apparently are. In
addition, corals possessing certain growth forms (e.g., densely branched species,
such as Porites porites or Madracis mirabilis) may be excluded from deeper, quieter
waters (Table 2, Fig. 7) as they require greater turbulence for feeding and cleansing
of the colonies (Chamberlain and Graus, 1975). The common occurrence of Madracis at breaks in slope (e.g., the fore reef escarpment; Table 2; Liddell et al.,
1984c, appendix A, Pear Tree Bottom site) where turbulence may be concentrated,
further supports the requirement of sufficient water movement for corals with
such branching morphologies.
Another, more subtle, effect of turbulence on reef community composition may
be the generation of hard substrata by the toppling and fragmentation of coral
colonies in shallow water. Such hard substrata is rapidly colonized by coralline
algae and boring sponges (Ohlhorst and Liddell, 1981; Liddell et al., 1984b),
which are important components of shallow reef communities (Table 1, Fig. 4).
The inverse correlation of these groups with depth suggests that the lack of turbulence-generated hard substrata may account for their much reduced abundance
on the deeper reef (Table 1, Fig. 4). The fact that both groups are known from
much deeper (> 200 m) waters (Lang, 1974; Littler et al., 1985) suggests that they
are not being excluded by reduced light levels on the fore reef slope. An additional
contributing factor to the reduced abundance of coralline algae and boring sponges
on the deeper reef may be the plate-like growth morphology of deeper reef corals,
which provide little exposed skeleton on their upper surfaces (Goreau and Hartman, 1963). Boring sponges may occur on the undersurfaces of coral plates, but
would not be recorded by our transects.
Diadema grazing has been shown to markedly influence the macroalgal community structure of coral reefs, and also affects sessile epibenthic invertebrates
(Sammarco et al., 1974; Carpenter, 1981). The increase in macroalgal abundance
on the fore reef slope «30 m) (Table 1, Fig. 4) is most likely due to the decrease
in Diadema abundance below this depth (Table 1), and therefore, may reflect a
release from grazing pressure, The reasons for Diadema's depth limitation are
unknown.
ReejCommunity Patterns- Comparisons with other Studies. - Several papers document depth-related coral zonations from Caribbean and south Florida sites which
are similar to Goreau's (1959) zonation model for Jamaica (see summary in
Scatterday, 1974), although component species may fluctuate from site to site and
the geomorphologies of the reefs may differ. Additionally, species lists appear to
be roughly comparable (see summary in Bak, 1977). Only a small number of the
LIDDELL AND OHLHORST:
REEF COMMUNITY
STRUCTURE
325
studies dealing with Caribbean reefs provide quantitative data on reef community
composition (Kissling, 1965; Lewis, 1970; Goldberg, 1973; Ott, 1975; Van den
Hoek et al., 1975; Dana, 1976; Goodwin et al., 1976; Loya, 1976; Bak, 1977; Bak
and Luckhurst, 1980; Huston, 1985). Of these, most consider mainly cnidarians
(the papers by Ott, 1975; Van den Hoek, et aI., 1975; Bak, 1977; Bak and Luckhurst, 1980; and Huston, 1985 are exceptions), cover a small portion of the
bathymetric range occupied by reef communities, or present their data in such a
way (e.g., phytosociologic abundance rankings) to make direct comparisons with
the present study difficult.
Quantitative diversity (H', J') patterns for corals from south Florida and Caribbean sites are presented by Porter (1972, 1974), Goldberg (1973), Loya (1976),
and Huston (1985 - his shallow diversity data is incorporated into the present
paper). At Panama, Porter (1972, fig. 2) found coral diversity (H', based on amount
ofliving tissue encountered beneath transect lines, Porter's log2values transformed
herein to log" for comparison with this and other studies) to increase from the
surface to 2.2 at 5 m and then to fluctuate between approximately 1.0-2.4 over
the range of 5-25 m and then abruptly decline to 0 at 30 m. The abrupt drop in
diversity at 30 m at Panama is most likely attributable to a lack of suitable hard
substrata and the change from the rocky reef slope to a gently sloping sandy
bottom (pers. obs.). Porter also documents an "edge effect" with the highest
diversities occurring at breaks in the reef slope or profile. In contrast to the present
study, Porter found a significant positive correlation between diversity and percent
coral cover. Porter's H' values of 1.0-2.4 (log,,) are similar to those found at
Jamaica and elsewhere in the Caribbean (Goldberg, 1973; Loya, 1976; herein),
but the attainment of nearly maximum values at the relatively shallow depth of
only 5 m is unusual. At Jamaica, diversity continues to increase down to 22 m
(H' = 2.12) and remains relatively high below 22 m without a precipitous drop
at 30 m (Fig. 5). The maximum diversity of 2.12 at 22 m on the fore reef
escarpment at Jamaica may be related to an edge effect as found by Porter.
At Florida Goldberg (1973, fig.3) found coral diversity (H', unclear as to whether
based on number of colonies or area occupied) to vary between approximately
1.0-2.4 over the range of 9-30 m with a general decrease in diversity with increasing depth and an abrupt decline in diversity below 30 m. The abrupt decline
in diversity below 30 m is due to a lack of suitable substrata types; below 30 m
the Florida reefs described by Goldberg consist largely of rubble. Goldberg does
not provide coral cover data (percent of bottom occupied by living coral tissue),
therefore, the relationship between coral diversity and coral cover cannot be
examined for his sites.
At Puerto Rico, Loya (1976, table 3) found coral diversity (H', based on amount
ofliving tissue encountered beneath transect lines) values of between 1.8-2.2 over
the range of 6-20 m and relates lowered diversity to increased sedimentation.
The low coral diversity (H' 1.05) in the back reef site at Jamaica may also be due
to increased sedimentation (Dodge et al., 1974). When coral cover is plotted
against coral diversity for the four sites studied by Loya no significant correlation,
either positive or negative, is found.
Ott (1975, fig. 7) provides diversity data for the range of9-50 m on a submerged
barrier reef at Barbados. Diversity values (H', based on number of colonies encountered along transects, log used not specified) are based on all zoobenthos
(corals, sponges, zoanthids, etc.). As such, these values cannot be directly compared with those cited above; however the general patterns exhibited are of interest. Over the range of 9-30 m H' values were typically on the order of 2.5.
Below 30 m H' values declined to a low of 1.5 by 50 m. The reef did not extend
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1987
below this depth due to a decrease in slope angle and a lack of suitable hard
substrata. Finally, diversity was significantly (P < 0.05) and positively correlated
with percent living cover on the outer and inner slopes of the barrier reef. No
significant correlation between diversity and living cover was found on the top
of the barrier.
When coral diversity (H') is plotted against percent coral cover (or percent total
living cover) for our fore reef sites at Jamaica, a significant inverse correlation is
found (Fig. 6; P < 0.05, SRC). This matches the pattern for Pacific sites (Grigg
and Maragos, 1974; Porter, 1974). It, therefore, remains to be determined whether
or not Caribbean coral communities are organized differently from Pacific communities. Further studies from more numerous localities are needed to test this
hypothesis.
Patterns of Coral Species Diversity- Possible Controls. - The intensity of certain
physical and biotic factors, such as turbulence, light, bioerosion and grazing!
predation, vary with depth and may, thus, influence depth-related patterns of
coral diversity and are discussed below. An interesting model for interpreting the
effects of these factors on diversity is the intermediate disturbance nonequilibrium
model as applied to coral reefs by Connell (I978). Depending upon the intensity
ofa particular factor, the effect may be to lower or increase diversity. For example,
at intermediate levels turbulence may act as an agent of disturbance, toppling
weakened corals and opening areas of free space within the community. High
levels of turbulence, however, as at the reef crest, will exclude most species due
to biomechanical constraints and, thereby, lower diversity. Extremely low levels
of turbulence will have little or no physical effect on the benthos. Thus, the trend
ofIowest coral diversity on the very shallow fore reef with diversity then increasing
out to 22 m depth may reflect the transition from turbulence acting as a limiting
factor to merely one of physical disturbance. An additional contributing factor to
the maximum diversity found at 22 m at Jamaica (H' = 2.12) may be the steep
slope (approximately 45°) of the fore reef escarpment. This perhaps enhances the
effects of turbulence by allowing toppled colonies to slide down-slope and off the
reef.
At intermediate levels of grazing by urchins overall reef diversity has been
shown to increase by Birkeland (1977), Sammarco (1980), and others. In as much
as Diadema is one of the most important grazers on the Jamaican reefs, the drastic
decline in urchin abundance below IS m at Jamaica (Table I) results in sharply
lowered levels of grazing activity below this depth and, therefore, potentially
reduced levels of biological disturbance. Other grazers such as the polychaete
Hermodice and the gastropod Coralliophila also appear to be most abundant on
the shallower « 15 m) reefs as documented at Barbados by Ott and Lewis (1972).
To summarize, although the shallow Jamaican reefs may sustain moderate to
severe disturbances, the deeper reefs (2::30 m) appear to experience reduced physical and, perhaps, biotic disturbance. This is supported by the studies of Bak and
Luckhurst (1980) and Hughes and Jackson (1985), which document a greater
degree of spatial rearrangement of substratum components over time at shallow
rather than at deep reef sites at Curac;ao and Jamaica.
What is perhaps incongruous, with respect to the predictions of the intermediate
disturbance nonequilibrium model, is the relatively high coral diversity at 30 m
and 45 m, considering the regime of lowered disturbance (compare H' values of
1.54 and 1.76 at 30 and 45 m to values of 0.80-1.87 from over the range of 5IS m, Table 2). Furthermore, if the diversity of the larger community (corals,
sponges and algae) is considered, an increase occurs from 25 species at 15 m to
LIDDELL AND OHLHORST:
REEF COMMUNITY
STRUCTURE
327
35 species at both 30 and 39 m (species data from Liddell et al., 1984c, appendix
I). Perhaps these seemingly anomalous diversity trends can be explained by considering the effect of decreasing resource levels on growth rates. Decreasing resource levels, to a point, might be expected to increase diversity by lowering
growth rates and reducing competitive displacement (Huston, 1979; 1980; 1985).
In as much as light decreases in intensity with increasing depth, the similarity of
coral species diversity at 15 and 45 m (H' = 1.87 and 1.76, respectively) may
reflect a balance between the effects of intermediate disturbance and lowered
resource (light) levels. The low diversity at 56 m (H' = 1.49) may reflect the point
at which the light resource level is approaching a limiting value and few species
are capable of adapting to it. Alternatively, the diversities of these deeper (:2: 30
m ) reef sites may be due simply to the fact that they are stable (low disturbance)
environments (the stability hypothesis, Slobodkin and Sanders, 1964).
We should point out that the data discussed in this paper are from a single reef
area at Jamaica and caution should be exercised in extrapolating these results to
other sites. Despite the existence of a tremendous body of descriptive literature
on Caribbean reefs, additional quantitative studies are needed for many areas
prior to the construction of a more encompassing model for Caribbean reef communities.
ACKNOWLEDGMENTS
We wish to dedicate this paper to the memory of Steven A. Kohut who participated in much of
the reef censusing upon which this paper is based. We also wish to extend our appreciation to S. K.
Boss for his assistance in the collection of reef census data, to M. Huston for providing us with
unpublished census data and a draft of his manuscript on reef diversity patterns and to two anonymous
reviewers for their thoughtful comments on the manuscript. This paper represents contribution No.
365 from The Discovery Bay Marine Laboratory of the University of the West Indies.
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DATE ACCEPTED:
August
13, 1986.
(W.D.L.) Department of Geology and Ecology Center, Utah State University, Logan,
Utah 84322-0705; (S.L.O.) Department of Fisheries and Wildlife and Ecology Center, Utah State
University, Logan, Utah 84322-5210.
ADDRESSES: