Coral identity underpins architectural complexity on Caribbean reefs

Abstract

The architectural complexity of ecosystems can greatly influence their capacity to support biodiversity and deliver ecosystem services. Understanding the components underlying this complexity can aid the development of effective strategies for ecosystem conservation. Caribbean coral reefs support and protect millions of livelihoods, but recent anthropogenic change is shifting communities toward reefs dominated by stress-resistant coral species, which are often less architecturally complex. With the regionwide decline in reef fish abundance, it is becoming increasingly important to understand changes in coral reef community structure and function. We quantify the influence of coral composition, diversity, and morpho-functional traits on the architectural complexity of reefs across 91 sites at Cozumel, Mexico. Although reef architectural complexity increases with coral cover and species richness, it is highest on sites that are low in taxonomic evenness and dominated by morpho-functionally important, reef-building coral genera, particularly Montastraea. Sites with similar coral community composition also tend to occur on reefs with very similar architectural complexity, suggesting that reef structure tends to be determined by the same key species across sites. Our findings provide support for prioritizing and protecting particular reef types, especially those dominated by key reef-building corals, in order to enhance reef complexity.

Full text

Ecological Applications, 21(6), 2011, pp. 2223 –2231
Ó2011 by the Ecological Society of America
Coral identity underpins architectural complexity on Caribbean reefs
LORENZO ALVAREZ-FILIP,
1,2,4
NICHOLAS K. DULVY,
2
ISABELLE M. Cˆ
oTE
´,
2
ANDREW R. WATKINSON,
3
AND JENNIFER A. GILL
1
1
Centre for Ecology, Evolution, and Conservation, School of Biological Sciences, University of East Anglia,
Norwich NR4 7TJ United Kingdom
2
Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University,
Burnaby, British Columbia V5A 1S6 Canada
3
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ United Kingdom
Abstract. The architectural complexity of ecosystems can greatly influence their capacity to
support biodiversity and deliver ecosystem services. Understanding the components underlying
this complexity can aid the development of effective strategies for ecosystem conservation.
Caribbean coral reefs support and protect millions of livelihoods, but recent anthropogenic
change is shifting communities toward reefs dominated by stress-resistant coral species, which are
often less architecturally complex. With the regionwide decline in reef fish abundance, it is
becoming increasingly important to understand changes in coral reef community structure and
function. We quantify the influence of coral composition, diversity, and morpho-functional traits
on the architectural complexity of reefs across 91 sites at Cozumel, Mexico. Although reef
architectural complexity increases with coral cover and species richness, it is highest on sites that
are low in taxonomic evenness and dominated by morpho-functionally important, reef-building
coral genera, particularly Montastraea. Sites withsimilar coral community composition also tend
to occur on reefs with very similar architectural complexity, suggesting that reef structure tends to
be determined by the same key species across sites. Our findings provide support for prioritizing
and protecting particular reef types, especially those dominated by key reef-building corals, in
order to enhance reef complexity.
Key words: biodiversity; coral; Cozumel, Mexico; dominance; functional groups; habitat complexity;
landscape ecology; reef.
INTRODUCTION
The architectural complexity of ecosystems often
underpins the biodiversity and ecosystem services that
they support. Architectural complexity is very often
defined or provided by foundation taxa (e.g., trees,
oysters, stony corals) that have a disproportionate
influence on ecosystem structure, function, and stability
(MacArthur 1984, Bruno and Bertness 2001, Ellison et al.
2005). However, within these broad groups of foundation
taxa, different species can contribute disproportionately
to architectural complexity. Species identity and domi-
nance have been reported as important determinants of
ecosystem functions and processes (e.g., terrestrial grass-
land, soil ecosystems; Tilman et al. 1997, McLaren and
Turkington 2010); however, studies that directly examine
the role of the type, rather than the number, of species on
habitat facilitation are rare. Understanding the influence
of different species and taxa on ecosystem structure and
function is not only of fundamental ecological interest but
can underpin the development of effective conservation
priorities and actions.
Coral reefs are among the most rapidly changing and
valuable ecosystems in the world. It is estimated that
nearly 70%of the world’s coral reefs are threatened by
anthropogenic activities (Wilkinson 2008) and are expe-
riencing unprecedented rates of degradation (Veron
2008). In the Caribbean, for instance, the architectural
complexity ofreefs has declined substantially over the past
40 years with the loss of ;80%of the most complex reefs
(Alvarez-Filip et al. 2009a). Because of the importance of
reef-building corals as foundation species within the
diverse reef ecosystem, patterns of degradation and
ecological resilience on coral reefs are typically measured
through changes in overall coral cover (e.g., Gardner et al.
2003, Bruno and Selig 2007, Mumby et al. 2007).
However, changes in coral cover often do not capture
the changes in reef architectural complexity (Alvarez-Filip
et al., in press) that can underpin a suite of important
ecosystem services, such as the dissipation of wave energy;
nutrient recycling; and the abundance, diversity, and
trophic structure of coral reef fishes (Szmant 1997, Lugo-
Fernandez et al. 1998, Sheppard et al. 2005, Wilson et al.
2007, 2010).
There is considerable potential for taxon identity and
the composition of reef-building corals to influence the
architectural complexity of reefs because hard sclerac-
Manuscript received 8 August 2010; revised 26 January 2011;
accepted 22 February 2011. Corresponding Editor: T. E.
Essington.
4
Present address: Department of Biological Sciences,
Simon Fraser University, 8888 University Drive, Burnaby,
British Columbia V5A 1S6 Canada.
E-mail: lorenzoaf@gmail.com
2223

tinian corals are a taxonomically and morphologically
diverse group (Veron and Stafford-Smith 2002, Dullo
2005). While qualitative differences in the relative
contribution of different coral species to reef complexity
are readily apparent, the contribution of coral identity
and community composition to architectural complexity
has yet to be quantified at the larger reef scales.
Quantifying the relative contribution of different coral
species to the architectural complexity of the reefscape is
therefore particularly important in order to understand
the trajectory of coral reefs under changing environ-
mental conditions.
Disturbances commonly favor a few species that are
able to competitively dominate the landscape (Tilman
and Lehman 2001, Seabloom et al. 2003). Although the
Caribbean underwent rapid losses of the structurally
important Acroporid corals in the late 1970s, many reefs
remained dominated by healthy populations of the other
major reef-building coral Montastraea (e.g., McClana-
han and Muthiga 1998), suggesting that reef complexity
could be maintained to some degree in reefs across the
region. Since then, the spread of several recently
emerged diseases, combined with recent bleaching events
and other biotic disturbances, are fostering high rates of
mortality of Montastraea and other coral species
previously thought to be more resistant to disturbance
(Weil 2004, Bruckner and Bruckner 2006 ). Throughout
the Caribbean, the loss of these main reef-building coral
species (Acropora and Montastraea) has been accompa-
nied by an increase in the relative abundance (often
leading to eventual dominance) of stress-tolerant, early-
colonizing corals that form smaller and less architectur-
ally complex colonies, such as Porites and Agaricia
(Jackson 2001, Aronson et al. 2002, Green et al. 2008,
Lirman and Manzello 2009). This shift toward weedy
coral species may constrain reefs to a state of lower
potential architectural complexity (Steneck et al. 2009),
even if overall coral cover remains stable.
Here we explore the contribution of coral community
composition to reef architectural complexity across a
broad range of sites in Cozumel, Mexico. First, we
quantify whether sites with similar coral community
composition also tend to be similar in terms of
architectural complexity. Second, we test whether greater
coral species diversity is related to greater architectural
complexity. Finally, we explore how the taxonomic and
functional attributes of coral dominance influence the
relationship between coral cover and architectural
complexity.
MATERIALS AND METHODS
Study area
Cozumel is a continental island 18 km off the
northeastern coast of the Mexican Peninsula of
Yucatan. The island is surrounded by coral reefs. The
most developed formations are in the western shelf,
where three terraces can be found between 5 m below sea
level and the shelf edge (;20 m). Unlike many other
Caribbean reefs that originally comprised Acroporid
species, in Cozumel the reefs close to the shore have been
built mainly by Montastraea (Muckelbauer 1990). The
southwestern coast of Cozumel has been under official
protection since 1980 (Alvarez-Filip et al. 2009b; Fig. 1),
and while visitation and tourist activities are permitted,
fishing is banned on the western coast of the marine
reserve.
Field surveys
In total, 91 sites along the southwestern coast of
Cozumel, all separated by at least 200 m (Fig. 1), were
surveyed between October 2007 and February 2008. At
each site, one 30-m transect was haphazardly located on
the top of the reef crest (between 10 and 15 m depth) and
parallel to the coast. Reef attributes such as coral cover
or reef architecture were not used to determine the
position of transects. To evaluate coral abundance, we
used the point intercept method to record the occurrence
of corals every 25 cm along each transect (120 counts per
transect). This method is widely used in the Caribbean
and elsewhere to describe reef benthic composition, and
it has been shown to provide comparable information to
measuring benthic composition along the entire length
of transects (Hill and Wilkinson 2004). All corals were
identified in the field at species level according to Veron
and Stafford-Smith (2002).
Reef architectural complexity was quantified using the
rugosity index (Risk 1972), which was obtained by
fitting a fine, 3-m chain (0.7 cm link length) to the reef.
While laying the chain, care was taken to follow the
detailed contour of corals and other reef attributes (rock
crevices, sponges) by lining up individual branches and
fitting the chain between coral ramets. To calculate the
index, the contoured distance was divided by the linear
distance between its start and end point. A perfectly flat
surface has a rugosity index of one, with larger numbers
indicating more complex surfaces. Rugosity measures
were taken in five equally spaced points along the same
30-m transect, which were then averaged to give
transect-level rugosity.
Data analyses
To examine whether transects with similar coral
community composition also tended to have similar
architectural complexity, we constructed matrices of site
community composition and site rugosity for all pairs of
sites. The similarity matrix for coral community
composition was constructed using all coral species
and their relative cover in each site and computed using
the Bray-Curtis similarity coefficient. The architectural
complexity matrix was constructed by calculating the
relative percentage similarity in rugosity between each
pair of sites using the following formula:
% similarity ¼ðjRiRjj=MDÞ3100
where jR
i
R
j
jis the absolute difference between the
values of rugosity in site
i
and site
j
for each pair of sites,
LORENZO ALVAREZ-FILIP ET AL.2224 Ecological Applications
Vol. 21, No. 6

and MD is the maximum observed difference between
all the pairwise comparisons. We evaluated whether
architectural complexity among sites is a function of
coral community composition among sites using a
Mantel test (Mantel 1967 ). This test measures the
correlation between two matrices and assesses the
significance of the correlation by randomizing one of
the matrices and calculating a null distribution of values
from the randomly generated associations. In this study,
the Mantel test was calculated using the package Vegan
in R (R Development Core Team 2009), with 10 000
random matrix permutations used to assess significance
levels.
To test whether greater coral species diversity is
related to greater architectural complexity, we quantified
coral diversity using three univariate dimensions of
diversity: coral species richness (number of species
recorded at each site), evenness in species abundance
(the Pielou index of percentage areal cover of each
species), and taxonomic diversity. For the last dimen-
sion, we calculated the average taxonomic distinctness
(D
þ
) and the variation in taxonomic distinctness (K
þ
)
with a widely used and accepted coral taxonomy (Veron
and Stafford-Smith 2002). Average taxonomic distinct-
ness measures average evolutionary relatedness as the
mean path (or branch) length of the local community,
and the variation in taxonomic distinctness is the
variance in path (or branch) lengths of the local
community (Clarke and Warwick 2001). We also
calculated richness and evenness of the morpho-func-
tional groups. We then used linear regressions to explore
the strength and nature of the associations between each
of these measures of coral diversity and reef architec-
tural complexity.
To explore the influence of species identity and
morpho-functional attributes on reef structure, we
grouped coral species by genus and by morphology.
Morpho-functional groups were constructed from the
maximum size and colony shape of each coral species
(Table 1). Following Reyes-Bonilla (2004 ), three shape
categories (massive or nodular; branching, ramose, or
phaceloid; platy, foliaceous, or encrusting) and three size
categories (small, ,10 cm; medium, 10–30 cm; large,
.30 cm) were used. Combining shape and size
categories resulted in seven different morpho-functional
groups (Table 1).
To explore how the taxonomic and functional
attributes of coral dominance influence the relationship
between coral cover and architectural complexity, we
compared the slopes of these relationships among (a) the
three most abundant genera (Agaricia,Porites, and
Montastraea) and (b) the three most abundant morpho-
functional groups (Fig. 2B). The 91 transects were
categorized depending on the single most-dominant
(highest relative abundance on the site) genus and
morpho-functional group. Differences between each
pair of linear models were explored by dividing the
difference between both regression coefficients by the
square root of the sum of the squared standard errors.
Assuming normally distributed residuals, this estimate
follows a tdistribution with n2 degrees of freedom
(Zar 1999).
FIG. 1. Map of Cozumel Island, Mexico, and (inset) the location within the Caribbean Sea. The continuous line delimits the
polygon of the Marine Protected Area (Parque Nacional Arrecifes de Cozumel), and the bold dotted line represents the area
surveyed in this study.
September 2011 2225CORAL IDENTITY UNDERPINS REEF COMPLEXITY

RESULTS
A total of 33 species of reef-building corals were
recorded in Cozumel during this study (Table 1). The
dominant genera included Agaricia,Montastraea, and
Porites (primarily P. astreoides), and hence corals with
large, massive, and foliaceous colonies were the most
abundant morpho-functional groups (Fig. 2A, B). Both
coral cover and reef architectural complexity varied
greatly across the study area, from flat sites with low
coral cover to highly complex areas of reef. Coral cover
for the 91 sites was 16%61.32%(mean 6SE; range: 0%
to 52%), while rugosity averaged 1.49 60.04 (range 1.02
to 2.77).
Pairs of sites with similar coral community composi-
tion tended also to have similar levels of architectural
complexity (Mantel test r
m
¼0.18; P,0.001). Very high
similarity in coral community composition (.70%)
occurred only in reefs with similar architectural com-
plexity (.50%similarity in rugosity) regardless of
whether the sites were similarly complex or similarly
flat (Fig. 3).
Architectural complexity was positively associated
with the number of coral species; sites with fewer than
five coral species tended to be relatively flat, while more
diverse sites, with between eight and 13 species, had the
greatest complexity (Fig. 4A). However, the evenness in
coral cover among coral species declined with increasing
coral species richness (r¼0.40; P,0.001), and
consequently sites with greater architectural complexity
tended to be species rich but dominated by one or a few
coralspecies(Fig.4B).Theflatreefsprimarily
comprised bare rock and/or algae rather than mono-
typic patches of relatively flat corals (e.g., Millepora or
Siderastrea), as indicated by the lack of any sites with
high coral cover and low rugosity (Fig. 4A). The
relationship between taxonomic distinctness among
coral species and architectural complexity was highly
nonlinear (R
2
¼0.01; P¼0.22), with a small number of
flat reefs tending to be either particularly distinct or
particularly related (Fig. 3C). The variation in taxo-
nomic distinctness was not significantly related to
architectural complexity (Fig. 4D). From the morpho-
logical and functional perspective, the greatest complex-
ity was found on reefs with higher morpho-functional
diversity (Fig. 4E) but dominated by relatively few
morpho-functional types (Fig. 4F).
Reefs with greater coral cover tended to have greater
architectural complexity, but the variance in architec-
TABLE 1. Cover and morphological information of the coral species recorded in the 91 sites surveyed on Cozumel Island, Mexico.
Genus Species Mean cover (%)Colony shapeàColony size§ Morphological group}
Acropora A. cervicornis 0.03 (0.03) B L BL
A. palmata 0.16 (0.1) B L BL
Madracis M. decactis 0.16 (0.04) M M MM
M. formosa 0.02 (0.01) B M BM
Stephanocoenia S. intersepta 0.24 (0.05) M M MM
Eusmilia E. fastigiata 0.39 (0.07) B M BM
Colpophyllia C. natans 0.06 (0.04) M L ML
Diploria D. clivosa 0.03 (0.02) M L ML
D. labyrinthiformis 0.05 (0.02) M M MM
D. strigosa 0.07 (0.04) M M MM
Montastraea M. annularis 1.43 (0.39) M L ML
M. cavernosa 0.97 (0.12) M L ML
M. faveolata 1.68 (0.26 ) M L ML
M. franksi 0.09 (0.03) M M MM
Favia F. fragum 0.02 (0.01) M S MS
Dendrogyra D. cylindrus 0.01 (0.01) M L ML
Dichocoenia D. stokesii 0.04 (0.02) M M MM
Meandrina M. meandrites 0.13 (0.04) M M MM
Isophyllastrea I. rigida 0.02 (0.01) M M MM
Mycetophyllia M. lamarckiana 0.15 (0.04) P M PM
Agaricia A. agaricites 4.56 (0.41) P L PL
A. humilis 0.03 (0.02) M L ML
A. lamarcki 0.02 (0.01) P L PL
A. tenuifolia 0.43 (0.13) P L PL
Siderastrea S. radians 0.02 (0.01) M S MS
S. siderea 1.45 (0.16) M L ML
Porites P. astreoides 2.45 (0.3) M M MM
P. colonensis 0.03 (0.02) P M PM
P. divaricata 0.02 (0.01) B L BL
P. furcata 0.10 (0.04) B L BL
P. porites 0.82 (0.13) B L BL
Millepora M. alcicornis 0.27 (0.06) B M BM
M. complanta 0.06 (0.02) P L PL
SE in parentheses.
àB, branching, ramose, or phaceloid; M, massive or nodular; P, platy, foliaceous, or encrusting.
§ S, small (,10 cm); M, medium (10–30 cm); L, large (.30cm).
}Morphological group is the combination of shape and size.
LORENZO ALVAREZ-FILIP ET AL.2226 Ecological Applications
Vol. 21, No. 6

tural complexity also increased with coral cover (Fig.
5A). Much of the variance in architectural complexity at
high levels of coral cover was the result of dominance by
a particular coral genus. Sites dominated by species from
the genus Montastraea had greater architectural com-
plexity for a given coral cover, followed by Agaricia,
then Porites (Fig. 5B). On Montastraea-dominated sites,
architectural complexity increased more rapidly with
increasing coral cover than on Porites-dominated sites
(T
24
¼2.23; P¼0.03). However, the slopes of
relationships between coral cover and architectural
complexity for Agaricia and each of the other two
genera did not differ significantly (Agaricia vs.
Montastraea T
49
¼1.65, P¼0.10; Agaricia vs. Porites
T
47
¼1.23, P¼0.22).
The differences in architectural complexity for given
levels of coral cover are also strongly related to the
morpho-functional attributes of the dominant species.
Sites dominated by massive and large coral species have
greater architectural complexity for a given coral cover,
followed by sites dominated by large platy, foliaceous,
or encrusting (PL) and then medium-sized massive
corals (Fig. 5C ). Architectural complexity on sites
dominated by massive and large (ML) coral species also
increased significantly more rapidly with increasing
coral cover than on reefs dominated by medium-sized
massive corals (T
34
¼2.72, P¼0.01). However, the
slope of the relationship between architectural complex-
ity and coral cover on large platy, foliaceous, or
encrusting-dominated reefs did not differ significantly
from the other two morphological groups (PL vs. ML
T
54
¼1.56, P¼0.13; PL vs. MM [massive medium-sized]
T
30
¼0.81, P¼0.43).
DISCUSSION
Our findings suggest that the type and dominance of
foundation species can be just as important as their
overall abundance in providing architectural complexity
to their ecosystems. Reef complexity increases with
increasing coral cover, but the rate of increase in
complexity depends on coral community composition
and, in particular, the identity of the dominant species
and their associated morphological and functional traits.
The most architecturally complex sites are dominated by
few coral species (and morpho-functional groups), and
the identity of these corals largely explains the differ-
ences in the architecture of these sites. These findings
underscore the importance of considering coral species
composition and shifts in coral dominance on Caribbean
reefs in order to understand the implications of changes
in these ecosystems on the associated biodiversity and
ecosystem services.
Generally, species diversity is considered a fundamen-
tal feature of ecosystem structure and function (Loreau
et al. 2001, Hooper et al. 2005), and in coral reefs, greater
species diversity might be expected to increase reef
complexity simply because of the large variety of coral
FIG. 2. Cover (mean þSE) of hard corals on Cozumel reefs,
grouped by (A) genus and (B) morphology (see Table 1 for
definitions of morpho-functional groups). For panel (B) the
total number of species included in each morpho-functional
group is given in parentheses.
FIG. 3. Similarities in coral community composition (Bray-
Curtis similarity coefficient) and reef architecture (similarity in
rugosity indices) for 4095 different pairs of sites from 91 sites in
Cozumel. Circle shading indicates pairs of sites that both have
rugosity values .1.5 (black), both ,1.5 (gray), or one from
each category (white).
September 2011 2227CORAL IDENTITY UNDERPINS REEF COMPLEXITY

forms and shapes (e.g., Chabanet et al. 1997, Bruno and
Bertness 2001). However, positive relationships between
the number of coral species and architectural complexity
may, in fact, be a consequence of the positive relationship
between coral cover and architectural complexity, as
species diversity can also be positively associated with the
extent of coral cover (this study, r¼0.83, P,0.001)
(Bell and Galzin 1984). Moreover, taxonomic related-
ness indices showed that most sites shared a very similar
species composition and that there was no clear effect of
increasing taxonomic composition on reef architectural
complexity. By contrast, the distribution of species
relative abundances (percent cover) clearly showed that
predominance by one or few species increased the
complexity of the reef structure. Historically, Carib-
bean reefs have comprised small numbers of abundant
species rather than a high diversity of coral species
(Johnson et al. 2008), supporting the importance of coral
FIG. 4. The relationships between reef architectural complexity on 91 sites in Cozumel and (A) total number of coral species ( y
¼1.06 þ0.08x,R
2
¼0.34; P,0.001); (B) Pielou index of coral species evenness (y¼3.99 2.79x,R
2
¼0.30; P,0.001); (C)
average taxonomic distinctness of coral species; (D) variation in taxonomic distinctness of coral species; (E) total number of coral
morpho-functional groups (y¼0.79 þ0.19x,R
2
¼0.33; P,0.001); and (F) Pielou index of morpho-functional groups evenness ( y
¼4.08 2.90x,R
2
¼0.32; P,0.001).
LORENZO ALVAREZ-FILIP ET AL.2228 Ecological Applications
Vol. 21, No. 6

dominance in their structure. In addition, Caribbean
corals have relatively low diversity and redundancy in
comparison with other regions of the world. For
example, there are 120 massive coral species in
Australia’s Great Barrier Reef, while the Caribbean
harbors ,25 (Bellwood et al. 2004). This lack of
functional diversity might explain why Caribbean reef
architectural complexity relies more on the presence and
identity of dominant species than on the combined
structural attributes of a wider range of species.
We found that the strength of the positive effect of
foundation species in providing structure to the habitat
largely depends on the identity of the dominant taxa. At
the reefscape scale, architectural complexity increased
faster in sites dominated by large, massive species, such
as Montastraea, than in sites dominated by short-lived
and stress-resistant species. Branching corals are rela-
tively uncommon in Cozumel; for example, branching
species of the genus Porites (P. porites) occur at much
lower relative abundance than the sister massive species
(P. astreoides; Table 1), and the main differences in reef
complexity found in this study are therefore primarily a
consequence of the largeandmassivenatureof
Montastraea corals. Among Caribbean reef-building
corals, Montastraea spp. play critical roles in reef
construction and community ecology (Harborne et al.
2008, Harborne 2009). The relative abundance of such
massive species is declining in the Caribbean (Edmunds
and Elahi 2007). For example, Cozumel reefs were
largely dominated by Montastraea spp. in the 1980s
(Muckelbauer 1990) but more recently they are increas-
ingly dominated by Agaricia and Porites (Alvarez-Filip
et al. 2009b; Fig. 2). Cozumel reefs may therefore no
longer be providing the structural benefits that they were
in recent decades. Similar shifts from assemblages
dominated by physically large and long-lived coral
species toward assemblages dominated by weedy corals
are being recorded throughout the Caribbean (Jackson
2001, Aronson et al. 2002, Green et al. 2008, Lirman and
Manzello 2009, Steneck et al. 2009), highlighting the
large-scale consequences that these changes in coral
community composition may have for the architectural
complexity of Caribbean reefs.
On sites with relatively low coral cover (20 %),
architectural complexity varies little, even across sites
dominated by different coral species and types (Fig. 5B,
C), probably because dominant species are not abun-
dant enough (high evenness; Fig. 5A) to contribute
significantly to the reef framework. Assuming that this
also applies elsewhere in the Caribbean, our findings
may help to explain the rapid structural homogenization
toward relatively flat reefs reported in recent decades
(Alvarez-Filip et al. 2009a). Most Caribbean reefs have
been near or below 20%coral cover since the early 2000s
(Gardner et al. 2003, Bruno et al. 2009, Schutte et al.
2010), which may suggest that the abundance of
previously dominant corals in most reefs is now too
low to contribute significantly to reef architectural
FIG. 5. (A) The relationship between coral cover and
architectural complexity indices across 91 sites in Cozumel
(R
2
¼0.61, slope ¼0.024; P,0.001) for sites dominated by
Montastraea (black), Agaricia (dark gray), Porites (pale gray),
or no dominant species (white). Increasing symbol size
represents increasing evenness (Pielou index) of coral commu-
nity composition. (B) The linear regression and 95%confidence
intervals for sites dominated by the three most common coral
genera: Montastraea (y¼1.02 þ0.04x,R
2
¼0.61; P,0.001),
Agaricia (y¼1.12 þ0.02x,R
2
¼0.55; P,0.001), and Porites (y
¼1.05 þ0.02x,R
2
¼0.84; P,0.001). (C) The linear regression
and 95%confidence intervals for coral morphological groups:
massive-large (y¼1.05 þ0.03x,R
2
¼0.62; P,0.001), platy-
large (y¼1.16 þ0.02x,R
2
¼0.50; P,0.001), and massive-
medium (y¼1.02 þ0.02x,R
2
¼0.93; P,0.001). See Table 1
for details of morphological groups.
September 2011 2229CORAL IDENTITY UNDERPINS REEF COMPLEXITY

complexity. It is likely that the high frequency of
disturbances or chronic mortality that Caribbean reefs
face may prevent some structurally important species
from dominating (Hughes and Connell 1999), and these
reefs are therefore likely to remain in the current state of
low complexity and high evenness.
More complex reefs tend to have greater numbers of
individuals, biomass, or richness of reef-associated fishes
and invertebrates (Dulvy et al. 2002, Idjadi and
Edmunds 2006, Wilson et al. 2007). Consequently, our
findings suggest that assemblages with dominant reef-
building species such as Montastraea spp. would be
expected to facilitate more biodiverse and functionally
important coral reefs in the Caribbean. Montastraea
historically ranked high in importance along with
Acropora palmata and A. cervicornis in overall contri-
bution to Western Atlantic reef structure. Acroporids
have now almost vanished from Caribbean reefs, and
the unique structural role (i.e., large-branching colonies)
of these corals is likely no longer filled by any other
species (Bruckner 2003, Aronson and Precht 2006 ). In
the Caribbean, therefore, it is likely that halting rates of
architectural complexity loss will require a major
emphasis on facilitating the maintenance and endurance
of healthy populations of Montastraea corals and
promoting the recovery of Acroporids, rather than just
focusing efforts on restoring the overall abundance of
scleractinian corals. This seems to be particularly
important for those reefs that have relatively high coral
cover (.20%), where the presence of healthy popula-
tions of these key coral species may considerably
increase the reef architectural complexity. Important
regional differences in the species richness and function-
al composition of reef systems (Bellwood et al. 2004)
also highlight the need to explore the generality of these
findings. Assessing whether similar patterns occur in
regions with considerably higher diversity of coral forms
and functional redundancy, such as in the Indo-West
Pacific, would enrich our understanding of the role of
coral species composition in the provision of ecological
and ecosystem services.
ACKNOWLEDGMENTS
This study was carried out with the permission and support
of the Parque Nacional Arrecifes de Cozumel and the Comisio
´n
Nacional de A
´reas Naturales Protegidas of Mexico. We thank
M. Millet-Encalada, R. Hernandez-Landa, A. Brito-Bermudez,
and the staff of the PNAC for their invaluable help during the
surveys. This research was funded by the Mexican scholarships
from the CONACYT (171864) and SEP to Lorenzo Alvarez-
Filip. Nicholas K. Dulvy and Isabelle M. C ˆ
ote
´were supported
by Discovery grants from the Natural Sciences and Engineering
Research Council, Canada, and Jennifer A. Gill was supported
by the Natural Environment Research Council, United
Kingdom. Our manuscript was significantly improved by
insightful comments of two anonymous referees.
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