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Coral reefs are rich in biodiversity, in large part because their highly complex architecture provides shelter and resources for a wide range of organisms. Recent rapid declines in hard coral cover have occurred across the Caribbean region, but the concomitant consequences for reef architecture have not been quantified on a large scale to date. We provide, to our knowledge, the first region-wide analysis of changes in reef architectural complexity, using nearly 500 surveys across 200 reefs, between 1969 and 2008. The architectural complexity of Caribbean reefs has declined nonlinearly with the near disappearance of the most complex reefs over the last 40 years. The flattening of Caribbean reefs was apparent by the early 1980s, followed by a period of stasis between 1985 and 1998 and then a resumption of the decline in complexity to the present. Rates of loss are similar on shallow (<6 m), mid-water (6-20 m) and deep (>20 m) reefs and are consistent across all five subregions. The temporal pattern of declining architecture coincides with key events in recent Caribbean ecological history: the loss of structurally complex Acropora corals, the mass mortality of the grazing urchin Diadema antillarum and the 1998 El Nino Southern Oscillation-induced worldwide coral bleaching event. The consistently low estimates of current architectural complexity suggest regional-scale degradation and homogenization of reef structure. The widespread loss of architectural complexity is likely to have serious consequences for reef biodiversity, ecosystem functioning and associated environmental services.
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Flattening of Caribbean coral reefs:
region-wide declines in architectural
Lorenzo Alvarez-Filip1,*, Nicholas K. Dulvy3, Jennifer A. Gill1,4,
Isabelle M. Co
´3and Andrew R. Watkinson2
Centre for Ecology, Evolution and Conservation, School of Biological Sciences, and
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
Tyndall Centre for Climate Change Research, Norwich NR4 7TJ, UK
Coral reefs are rich in biodiversity, in large part because their highly complex architecture provides shelter and
resources for a wide range of organisms. Recent rapid declines in hard coral cover have occurred across the
Caribbean region, but the concomitant consequences for reef architecturehave notbeen quantified on a large
scale to date. We provide, to our knowledge, the first region-wide analysis of changes in reef architectural
complexity, using nearly 500 surveys across 200 reefs, between 1969 and 2008. The architectural complexity
of Caribbean reefs has declined nonlinearly with the near disappearance of the most complex reefs over the
last 40 years. The flattening of Caribbean reefs was apparent by the early 1980s, followed by a period of stasis
between 1985 and 1998 and then a resumption of the decline in complexity to the present. Rates of loss are
similar on shallow (,6 m), mid-water (6–20 m) and deep (.20 m) reefs and are consistent across all five
subregions. The temporal pattern of declining architecture coincides with key events in recent Caribbean
ecological history: the loss of structurally complex Acropora corals, the mass mortality of the grazing
urchin Diadema antillarum and the 1998 El Nino Southern Oscillation-induced worldwide coral bleaching
event. The consistently low estimates of current architectural complexity suggest regional-scale degradation
and homogenization of reef structure. The widespread loss of architectural complexity is likely to have serious
consequences for reef biodiversity, ecosystem functioning and associated environmental services.
Keywords: climate change; ecosystem degradation; ecosystem services; foundation species;
habitat complexity; vulnerability
The physical structure of a habitat profoundly influences
its associated biodiversity and ecosystem functioning
(MacArthur & MacArthur 1961), with more complex
habitats facilitating species coexistence through niche par-
titioning and the provision of refuges from predators and
environmental stressors (Bruno & Bertness 2001;Willis
et al. 2005). In tropical shallow waters, the calcium
carbonate skeletons of stony corals contribute to reef
frameworks that sustain the most diverse ecosystem in
our seas (Spalding et al. 2001). However, coral reefs
have been heavily impacted worldwide by a combination
of local and global stressors, including overfishing,
climate change-induced coral bleaching, eutrophication
and disease (Hughes et al. 2003). The marked declines
in live hard coral cover documented over recent decades
throughout the Caribbean and the Indo-Pacific regions
(Gardner et al. 2003;Bruno & Selig 2007) exceed those
reported for many other foundation species in terrestrial
or marine ecosystems (Balmford et al. 2003). However,
in contrast to other ecosystems where degradation usually
indicates reductions in habitat area (e.g. deforestation),
decreases in live coral cover on coral reefs do not immedi-
ately result in loss of available habitat because the reef
framework can persist long after the death of corals.
In the Caribbean, declines in live coral cover began in
the late 1970s, when substantial loss of the major reef-
forming corals Acropora palmata and Acropora cervicor nis
occurred as a result of white-band disease (Aronson &
Precht 2001). Coral mortality, in combination with
the mass mortality of the black sea urchin (Diadema
antillarum), which was a major remover of algae, and
the long-term depletion of herbivorous fishes through
overfishing, facilitated phase shifts to macro-algal dominance
on many reefs (Carpenter 1988;Precht & Aronson 2006).
In the Caribbean and elsewhere, reef-building corals now
face new threats from climate change, particularly in the
form of thermally induced coral bleaching and mortality,
which are becoming increasingly frequent and extensive
as thermal anomalies intensify and lengthen (Hughes
et al. 2003;McWilliams et al. 2005).
A potential consequence of the widespread reduction
in Caribbean coral cover is a reversal of the historic net
accretion of calcium carbonate, resulting in a decrease
in calcification and erosion of the reef framework. At
local scales, hard coral mortality is associated with the
loss of architectural complexity and ‘reef flattening’ after
direct impacts such as hurricanes through the breakage
of coral skeletons (e.g. Rogers et al. 1982). Reefs may
*Author for correspondence (
Electronic supplementary material is available at
1098/rspb.2009.0339 or via
Proc. R. Soc. B (2009) 276, 3019–3025
Published online 10 June 2009
Received 26 February 2009
Accepted 13 May 2009 3019 This journal is q2009 The Royal Society
on 14 July 2009rspb.royalsocietypublishing.orgDownloaded from
also erode gradually owing to the natural activity of host
organisms, such as herbivorous fishes and sea urchins,
and by physical abrasion or geochemical shifts. However,
widespread mortality of hard corals, for example, after
severe bleaching events, moves the balance towards net
reef erosion (Sheppard et al. 2002). These impacts
could be exacerbated in the future by ocean acidification,
which is expected to enhance calcium carbonate dissol-
ution with negative consequences, initially for coral
growth and eventually for the entire reef framework
(Hoegh-Guldberg et al. 2007).
The ecological and socio-economic consequences of
declining architectural complexity are likely to be sub-
stantial (Pratchett et al. 2008). For many reef organisms,
risk of predation is influenced by access to refuges, and
the densities of herbivores and grazing rates typically
increase with architectural complexity (Beukers & Jones
1997;McClanahan 1999;Almany 2004;Lee 2006).
Consequently, the species richness, abundance and
biomass of coral reef fishes and invertebrates are all
influenced by architectural complexity (e.g. Gratwicke &
Speight 2005;Idjadi & Edmunds 2006;Wilson et al.
2007). The loss of architectural complexity may therefore
drive declines in diversity, particularly of habitat special-
ists, and compromise fisheries productivity through
elevated post-settlement mortality (Beukers & Jones
1997;Graham et al. 2007). Reef architectural complexity
also plays a key role in providing important environmental
services to humans, including enhancing coastal protec-
tion through the dissipation of wave energy transmitted
over reefs (Lugo-Fernandez et al. 1998).
While recent regional-scale analyses have revealed
declines in hard coral cover (Gardner et al.2003;Bruno &
Selig 2007), the consequences for reef habitat complexity
on a similar large scale have not been quantified. The
capacity of reefs to continue to perform key functions of
refuge provision and coastal protection will depend on
whether reef architecture persists for a substantial period
of time following the loss of live coral. Here we collate
published and unpublished estimates of reef complexity
spanning four decades from reefs across the Caribbean,
a region with clear evidence of recent declines in coral
cover. We explore the rate and timing of changes in reef
architecture in relation to region-wide events such as the
demise of Acropora corals and grazing urchins. As the
drivers of reef degradation are apparent throughout the
Caribbean, we also examine whether the patterns are
consistent throughout the entire region.
(a)Estimating architectural complexity
Habitat complexity on coral reefs has been measured using a
variety of methods that differ in the attributes measured, the
scale of measurement and the degree of subjectivity (with
attendant variation in inter-observer comparability). The
rugosity index is by far the most widely used method for
measuring reef architectural complexity (see electronic sup-
plementary material for further details) and is generally
highly correlated with other methods (Wilson et al. 2007).
Studies reporting the rugosity index were therefore chosen
to quantify spatial and temporal variation in the architectural
complexity of reefs across the Caribbean.
The rugosity index is expressed as the ratio between the
total length of a chain and the length of the same chain
when moulded to a reef surface. A perfectly flat surface
would have a rugosity index of 1, with larger numbers indicat-
ing a greater degree of architectural complexity (figure 1). The
index tends towards infinity with increasing architectural com-
plexity; however, rugosity estimates greater than 3 are very rare.
(b)Data search
A database of quantitative surveys that measured reef rugos-
ity within the wider Caribbean was compiled. We searched
online ISI Web of Science, Google Scholar and other relevant
Figure 1. Examples of three different values of rugosity index
of architectural complexity on Caribbean reefs. The values of
theindexare(a)1.2,(b)1.5and(c) 2.5. Source for photos:
L. Alvarez-Filip, M. Uyarra and W. Henry Marine Photobank.
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databases (e.g. Reefbase) for peer-reviewed and grey litera-
ture using several search terms (see electronic supplementary
material for examples). We also searched for papers that used
the rugosity index in all issues of the journals Coral Reefs,
Bulletin of Marine Science,Atoll Research Bulletin,Caribbean
Journal of Science and in all Proceedings of the International
Coral Reef Symposium. Additionally, we directly contacted
coral reef scientists, site managers and those responsible for
reef monitoring programmes throughout the Caribbean,
asking for any available data pertaining to their study sites.
A total of 464 records from 200 reefs surveyed between
1969 and 2008 across the Caribbean were obtained
(figure 2a,b). The database includes reefs that were surveyed
only once (n¼214) and reefs where repeated measures of
rugosity were collected over more than 1 year (n¼250).
Both datasets provide highly consistent results (table S2,
electronic supplementary material). We therefore present
findings only from the whole dataset, because they offer a
wider spatial and temporal representation.
To assess the temporal pattern of change in region-wide
architectural complexity, we calculated annual estimates of
rugosity averaged across all available sites for each year
from 1969 to 2008. We fitted a range of linear and nonlinear
models to represent increasing degrees of complexity in the
rate of change in rugosity over time and used the
small-sample adjusted Akaike information criterion (AIC
to evaluate the models (Burnham & Anderson 2002).
Linear models were fitted using both simple regressions
and robust regression, to reduce the influence of outliers.
We contrasted these linear models, which represent a hypoth-
esis of constant change in rugosity over the whole time
period, against segmented models that assumed piecewise
linear relationships (i.e. two or more straight lines connected
by breakpoints) and a general additive model (GAM) of an
unspecified nonlinear (spline) function, which assumed that
the rate of change in rugosity varied over time (Venables &
Ripley 2002;Muggeo 2003). In addition, because the
number of sites contributing to each annual rugosity estimate
varied, with more sites available towards the end of the time
period, we ran all models with annual estimates unweighted
and weighted by sample size. Weighted models consistently
provided a significantly better fit (lower AIC and higher var-
iance explained) than unweighted models. All analyses were
implemented in R (R 2008).
We used randomization techniques to evaluate whether
the pattern and rate of change were sensitive to the inclusion
of any particular site or year. For the best-supported model
identified in the AIC
analysis, we tested whether the rate
of decline in rugosity was biased by the inclusion of any
particular year, using a jackknife method to calculate the
distribution of annual decline rates while sequentially
removing each individual year. To evaluate any potential
site selection bias, we used a bootstrap method to compare
the annual decline rate with the range of possible decline
rates for 10 000 random combinations of year, rugosity and
To explore whether the trends of changing architectural
complexity varied with depth and within the region, we
aggregated the data by decade to maximize the signal relative
to interannual variation while retaining sufficient power. To
evaluate the change in rugosity at different depths, we
divided the data into three zones: (i) ,6 m, which represents
the optimal range of A. palmata (and therefore Acropora
reefs); (ii) 6 20 m, to include the range of other reef-
building scleractinian corals, including A. cervicornis; and
(iii) .20 m, to reflect sites where hard corals are present
but do not necessarily form complex three-dimensional
structures. We also aggregated the data within five subregions
to explore spatial variation in changes in rugosity within the
Caribbean region (figure 2a).
A key question is whether the regional change in reef
structure has produced more structurally homogeneous habi-
tats throughout the Caribbean. We classified each reef into
one of five rugosity index categories (1.01.49, 1.5–1.99,
2.02.49, 2.5– 2.99 and greater than 3.0) to explore the
change in the region-wide representation of complex (rugos-
ity greater than 2.0) and flatter (rugosity less than or equal to
1.5) reefs for the four different decades.
There has been a marked decline in the architectural
complexity of Caribbean reefs over the past four decades
(figure 3). The best-supported model of change in rugos-
ity over time was a weighted segmented model (table 1),
90°0'0'' W
0 500 1000
10°0'0'' N 20°0'0'' N 30°0'0'' N
80°0'0'' W 70°0'0'' W 60°0'0'' W
1965 1980 1995 2010
number of studies
Figure 2. (a) Regional distribution of locations from which
rugosity values were obtained. Grey circles, Central America;
white circles, South America; black circles, lesser Antilles;
circles with vertical lines, greater Antilles; circles with
crosses, southwest North Atlantic. (b) Number of studies
from which rugosity data were collated per year, from 1969
to 2008.
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which suggests that the decline in rugosity has three
distinct phases of change (figure 3). Architectural
complexity declined steeply early in the time series
(19691985), from reefs with indices of approximately
2.5 to much flatter reefs with indices of approximately 1.5.
This period of decline ended in 1985 (+2.4 years s.e.),
and architectural complexity throughout the region then
remained relatively stable until the late 1990s. However,
since 1998 (+2.8 years s.e.), the declining trend has
resumed, with rugosity indices after the mid-2000s reach-
ing the lowest levels recorded in the time series (approx.
1.2; see example in figure 1). The pattern of change is
robust to the inclusion or exclusion of individual years
(jackknife) and individual sites (bootstrap) (figure S1,
electronic supplementary material).
The decline in architectural complexity is widespread.
The temporal pattern of change was consistent across all
three depth intervals (figure 4a) and across the three sub-
regions for which the available data spanned the whole
time period, and the two regions with patchier data
(Central America and southwest North Atlantic; figure 4b).
Caribbean reefs are becoming both flatter and
more structurally homogeneous across the region. The
proportion of complex reefs (rugosity greater than 2) has
declined from approximately 45 per cent of sites to
approximately 2 per cent in the past four decades (figure 5).
The architectural complexity of coral reefs has declined
drastically over the last 40 years throughout the
Caribbean. Structurally complex reefs with a rugosity of
greater than 2 have been virtually lost from the entire
region. Today, the flattest reefs (rugosity less than 1.5)
comprise approximately 75 per cent of the total compared
with approximately 20 per cent in the 1970s, with most of
the increase in the proportion of flattest reefs occurring in
the 2000s. The high proportion of complex reefs in the
1960s and 1970s is unlikely to result from researchers
tending to visit just the most pristine reefs at this time,
because less architecturally-complex categories were also
well represented during this period. The loss of architec-
tural complexity is nonlinear and has occurred over three
distinct phases that coincide closely with large-scale
events that have affected Caribbean reef ecosystems.
The rate of decline was steepest prior to 1985. The
sample sizes are small and variance high during the
1960s and 1970s, hence it is unclear whether the decline
began prior to the early 1980s, when widespread loss of
acroporid corals began (Precht & Aronson 2006). After
this period, average architectural complexity changed
little until the late 1990s, when a new episode of decline
began. The pattern of decline is consistent across depth
zones and subregions. The widespread occurrence of
flatter reefs could have serious implications for reef-
associated biodiversity and reef-based environmental
The nonlinearity in the loss of architectural complexity
suggests that different drivers operating at different times
have influenced components of the reef community. Dis-
turbances on reefs range in scale and intensity, from local
tropical storms that can break and displace coral skel-
etons, to widespread events such as climate-induced
bleaching and diseases that kill coral tissue without
immediately compromising the reef structure (Pratchett
et al. 2008). In the late 1970s, one key event is likely to
have had a major role in the early, steep decline in
Caribbean reef architecture. White-band disease killed
approximately 90 per cent of the shallow-water, structu-
rally dominant acroporid corals, exposing their fragile
branching skeletons to erosion and hurricanes that prob-
ably led to their collapse in subsequent years (Aronson &
Precht 2001). However, declines also occurred at depths
greater than those at which acroporids were dominant,
suggesting that the systematic loss of Caribbean reef
corals was more widespread than previously thought
during the 1970s and early 1980s.
After 1985, the main driver(s) of declining architec-
tural complexity appear to cease; by this time, acroporids
had disappeared almost entirely from the Caribbean, and
the sea urchin D. antillarum had experienced a region-
wide disease-induced mass mortality in 1983 1984
(Carpenter 1988). The loss of this important source of
bioerosion may have slowed the decline following the
first phase of reef flattening. This intermediate stable
period of architectural complexity in the region persisted
in the face of several disturbance events, including the
first large-scale bleaching events and several major
hurricanes (Gardner et al. 2005;McWilliams et al. 2005).
Around 1998, Caribbean reefs were tipped into a new
phase of structural decline, following the most
intense and widespread coral bleaching event to date
(McWilliams et al. 2005). The coral mortality and
reductions in growth rates that typically follow such
bleaching events are likely to have precipitated the
resumption of loss of architectural complexity. The low
levels of coral cover, and presumably reef accretion, at
this time (Gardner et al. 2003) may also have increased
rates of erosion of underlying geological structures that
were no longer shielded by actively growing hard corals.
Since 1998, further mass bleaching events have occurred
1965 1980 1995 2010
Figure 3. Changes in reef rugosity on reefs across the
Caribbean from 1969 to 2008. Black line represents
the best fitting model—a segmented regression weighted by
the number of sites contributing to each annual rugosity
estimate (mean +95% confidence intervals). Black dots at
the top of the figure indicate the significant breakpoint in
1985 and 1998 (+1 s.e.) for the segmented regression.
Model slopes: 19691984, 20.054; 19851997, 0.008;
19982008, 20.038.
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regularly (McWilliams et al. 2005), probably contributing
to the continued decline in reef complexity.
All of the major events that are likely to have impacted
reef complexity have occurred against a backdrop of
changes not only in coral abundance but also in commu-
nity composition. Following the disappearance of
acroporids, massive species with slower growth rates,
such as Montastrea spp., remained as the primary reef
framework builders, and weedy corals, such as Porites
spp. and Agaricia spp., that form rapidly growing, small
colonies that are short-lived and quickly replaced, started
to increase in abundance (Green et al. 2008). The shift
from major reef-building species to weedy species that
contribute less to maintenance of the reef framework,
combined with increases in macro-algae (Co
´et al.
2006) that compete for space with coral recruits
(Mumby et al. 2007), probably reduced the rates of
coral accretion on Caribbean reefs.
The loss of reef architecture is likely to have profound
ecological, social and economic impacts. A growing body
of evidence indicates severe repercussions for biodiversity
of the loss of architectural complexity. On Indo-Pacific
reefs, major changes in fish community composition
have resulted from the long-term loss of structure
following coral bleaching events (Pratchett et al.2008and
references therein). The effects of bleaching are first manifest
in obligate coral-dwelling species, followed by impacts on
other small-bodied fishes (both small adults and juveniles
of larger species) when the physical matrix of the reef col-
lapses (Pratchett et al.2008). In the Caribbean, the greatest
impacts on biodiversity are expected to occur only with the
breakdown of the reef matrix because no fish species feed
1970s 1980s 1990s 2000s
Figure 4. Change in Caribbean reef rugosity in four different
decades (a) at three depth intervals (filled circle, 06 m;
open diamond, 6 –20 m; filled triangle, 20 m) and (b)in
five subregions (filled square, southwest North Atlantic;
grey circle, greater Antilles; open diamond, lesser Antilles;
filled triangle, South America; open circle, Central America)
(mean index value +95% confidence intervals).
1970s 1980s 1990s 2000s
proportion of reefs
Figure 5. Proportion of reefs in five rugosity index categories
across the Caribbean between 1969 and 2008. Number of
studies for each decade: 1970s: n¼32; 1980s: n¼52;
1990s: n¼136 and 2000s: n¼167. Black, .3; dark grey,
2.5– 3; mid grey, 2– 2.5; pale grey, 1.5 2; white, 1– 1.5.
Table 1. Model structure and the temporal pattern of change in Caribbean architectural complexity. Summary of AIC
analysis of linear and nonlinear models of change in yearly mean rugosity (derived from all 464 estimates), ordered by
decreasing weight. (Models in which annual rugosity estimates have been weighted by sample size are indicated (wt). df,
degrees of freedom of the model (for GAM, we use the estimated degrees of freedom). AIC
is the Akaike information
criterion corrected for small sample size; Dis the difference in AIC
between a given model and the best-supported model
(indicated in bold); and Wis the Akaike weight, which represents the probability that a given model is the best of those
models considered. The asterisks indicate the average slope of the different model segments.)
model R
slope df AIC
segmented model (wt) 0.64 20.028*26 225.8 0 0.8695
linear model (wt) 0.53 20.019 30 217.1 8.7 0.0112
robust linear model (wt) 20.018 30 216.9 8.8 0.0107
segmented model 0.65 20.038*26 22.9 22.9 0.0000
generalized additive model (wt) 0.99 20.033*3.6 0.1 25.8 0.0000
linear model 0.49 20.026 30 9.4 35.2 0.0000
robust linear model 20.021 30 11.2 37 0.0000
generalized additive model 0.59 20.044*3.3 22.8 48.6 0.0000
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exclusively on live coral, although many reef-associated
species depend highly on rugose substrata to feed, recruit
and hide (Gratwicke & Speight 2005). In this context, declin-
ing reef complexity may explain the onset of a decline in
Caribbean reef fishes that has occurred since approximately
1996 (Paddack et al.2009). Given that the loss of reef archi-
tecture began much earlier, our analysis supports the notion
of a degradation debt for Caribbean reef fishes. Reduced
recruitment resulting from a lack of settlement sites and
refuges for species with commercial importance, such as lob-
sters and large fishes (Graham et al.2007;Wynne & Co
2007), may compromise the long-term sustainability of fish-
eries and fishing communities. Collapsing reef structures
may also lead to the loss of important environmental services
such as coastal protection. Simulation models predict that a
reduction in reef surface roughness of approximately 50 per
cent could produce a doubling of the wave energy reaching
the shores behind those reefs (Sheppard et al.2005). The vul-
nerability of coastal human communities in the Caribbean to
projected increases in the intensity of Atlantic Ocean hurri-
canes and sea levels (Hopkinson et al.2008) will therefore
probably be compounded by the reduced wave dissipation
function of architecturally simpler reefs.
Reversing declines in reef architecture will be a major
challenge for scientists and policy-makers concerned
with maintaining reef ecosystems and the security and
wellbeing of Caribbean coastal communities. Although
recent evidence suggests increases in coral cover on
some Caribbean reefs (e.g. Cho & Woodley 2000;Idjadi
et al. 2006), the effect of coral recovery on architectural
complexity is unknown. If weedy corals dominate this
recovery in the long term, future reef complexity is unli-
kely to mirror any improvement in coral condition. To
regain the levels of architectural complexity that were
prevalent prior to 1980, the recovery of large branching
corals (i.e. Acropora spp.) and the maintenance of healthy
populations of massive robust species (e.g. Montastrea
spp.) are essential within the region. Not meeting these
challenges will most probably result in a continued flat-
tening of reefs throughout the region and seriously
compromised biodiversity and environmental services.
We are grateful to Peter Edmunds, Michelle Paddack, Philip
Molloy, Renata Goodridge and Hazel Oxenford
(CARICOMP Barbados), Francisco Geraldes (Centro de
Investigaciones de Biologı
´a Marina de la Universidad
´noma de Santo Domingo and CARICOMP) and
Simon Pittman and the NOAA Biogeography Branch for
contributing unpublished data. L.A.-F. was supported by a
scholarship from the CONACYT (171864) Mexico. I.M.C.
and N.K.D. are supported by Discovery grants from the
Natural Sciences and Engineering Research Council of
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... Removal of large, complex, three-dimensional animal forests may have far reaching implications for reef-associated taxa (Alvarez-Filip et al., 2009;Rossi, 2013;Maldonado et al., 2017). The ecosystem functions that invertebrates provide sustain reef-associated fauna. ...
... Recovery experiments in the Caribbean examining the survival of coral fragments and recruits after an anchoring event reported low survival and limited recovery attributed to the instability of the broken substratum (Rogers and Garrison, 2001). There is evidence of widespread loss of reef complexity on tropical Caribbean reefs (Alvarez-Filip et al., 2009), and there is building evidence, albeit anecdotal, of the break-down of rocky reef substrata in both tropical settings and temperate reefs (see supporting material in Broad et al., 2020). ...
... We provide evidence that anchor scour dramatically reduces the relative abundance and diversity of almost all of the erect animal taxa examined (6/7 morphotypes). Drastic reductions of sessile biota are likely to have long lasting impacts on reefs owing to the life-history traits of these habitat forming taxa, as well as the loss of three-dimensional biogenic habitat for associated taxa (Alvarez-Filip et al., 2009;Rossi, 2013). Failure to manage the impacts stemming from anchoring activities will result in a reduction of biodiversity, ecosystem services and compromise valuable fisheries resources. ...
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Anchor scour from shipping is increasingly recognised as a global threat to benthic marine biodiversity, yet no replicated ecological assessment exists for any seabed community. Without quantification of impacts to biota, there is substantial uncertainty for maritime stakeholders and managers of the marine estate on how these impacts can be managed or minimised. Our study focuses on a region in SE Australia with a high proportion of mesophotic reef (>30 m), where ships anchor while waiting to enter nearby ports. Temperate mesophotic rocky reefs are unique, providing a platform for a diversity of biota, including sponges, ahermatypic corals and other sessile invertebrates. They are rich in biodiversity, provide essential food resources, habitat refugia and ecosystem services for a range of economically, as well as ecologically important taxa. We examined seven representative taxa from four phyla (porifera, cnidaria, bryozoan, hydrozoa) across anchored and ‘anchor-free’ sites to determine which biota and which of their morphologies were most at risk. Using stereo-imagery, we assessed the richness of animal forest biota, morphology, size, and relative abundance. Our analysis revealed striking impacts to animal forests exposed to anchoring with between three and four-fold declines in morphotype richness and relative abundance. Marked compositional shifts, relative to those reefs that were anchor-free, were also apparent. Six of the seven taxonomic groups, most notably sponge morphotypes, exhibited strong negative responses to anchoring, while one morphotype, soft bryozoans, showed no difference between treatments. Our findings confirm that anchoring on reefs leads to the substantial removal of biota, with marked reductions of biodiversity and requires urgent management. The exclusion of areas of high biological value from anchorages is an important first step towards ameliorating impacts and promoting the recovery of biodiversity.
... For the structure to be maintained, the carbonate budget must be positive (i.e., the rate of growth must exceed that of erosion) ). If the system switches to a net negative state however (as is caused by large scale coral mortality for example), net erosion can ensue, resulting in deterioration of the reef structure over time , flattening of the reef (Alvarez-Filip et al., 2009) and a reduction in the structureś ability to attenuate wave energy . ...
... Approximately 75% of Caribbean reefs fall into this category, with reefs exhibiting an index higher than 2 (complex reefs) being extremely rare. (Alvarez-Filip et al., 2009). ...
... While structural complexity increases with coral cover and species richness, massive growth forms (e.g., Orbicella spp) and fast growers (e. g., Acropora spp.) are thought to contribute the most to the structure Kuffner and Toth, 2016) and hence to wave dissipation. A significant decline in coral cover and hence structural complexity results in crumbling of the reef and a change from a more varied topographical surface to a flatter surface, with less ability to reduce wave heights (Alvarez-Filip et al., 2009;Osorio-Cano et al., 2019). ...
La protection côtière est un service écosystémique (SE) des récifs coralliens extrêmement important, en particulier avec les impacts négatifs imminents et croissants du changement climatique mondial (GCC). Le SE de protection côtière n'a cependant pas retenu la même attention que celle portée à des SE plus « évidents » peut-être parce que les avantages du SE ne sont visibles que sur terre (pas en mer) et sont couplés à des défis dans son évaluation tels que la détermination précise du rôle du corail vivant dans la fourniture du service. Malgré ces défis, la contribution des récifs à la prestation des SE a été scientifiquement prouvée. Les récifs coralliens sont en déclin à l'échelle mondiale à cause des impacts locaux et mondiaux, exacerbés par un financement inadéquat et non durable de leur protection et gestion. Il est impératif que nous déterminions les méthodes les plus adaptées pour améliorer la santé des récifs, dans un monde où la situation est à la fois désastreuse et sensible au temps ; avec un délai estimé à moins de 50 ans pour agir. Un élément essentiel de toute solution est de savoir comment payer pour ces améliorations, à un moment où les méthodes de financement traditionnelles semblent insuffisantes et où un financement inadéquat est identifié comme un obstacle majeur au succès de la conservation. L'objectif de cette thèse est d'étudier des solutions à la fois écologiques et financières pour améliorer la santé des récifs coralliens et son SE de protection des côtes. Nous concentrons l'analyse sur la viabilité et le financement de récifs artificiels “gris-verts” avec des solutions de restauration des récifs coralliens visant à protéger les plages de l'érosion. Le chapitre 2. Du paper pose le « décor » des chapitres suivants. Les interventions écologiques et financières interviennent dans le cadre d'une Aire Marine Protégée (AMP). Le document a analysé les données de 2 nations insulaires et via des analyses coûts-avantages a fourni des preuves de l'attractivité de l'investissement dans les AMP pour protéger les SE. Le chapitre prochaine passe en revue ce que l'on sait de la protection côtière des récifs coralliens et détermine sa faisabilité pour un système de paiement pour les services écosystémiques (PSE). Au cours du processus, le rôle du corail vivant a été analysé et les actions de gestion identifiées qui pourraient améliorer la santé des récifs pour la prestation de services ont été identifiées. Ce document identifie la restauration des coraux comme une intervention clé pour la protection côtière et fournit la justification du chapitre 5. Le chapitre 5 explore plus en détail les moyens non publics de financement de la conservation marine via des investissements à impact et des financements mixtes. Ayant identifié qu'il est logique d'investir dans les AMP au chapitre 1, nous identifions le type de financement et proposons un mécanisme de financement pour l'investissement. Les sorties sont utilisées dans le chapitre 5Le chapitre 6 utilise les résultats des chapitres 4 et 5 et développe des solutions écologiques et financières pour la protection côtière. Dans cet article, nous démontrons l'impact positif de la restauration des récifs, proposons des options pour le faire et montrons l'additionnalité obtenue en utilisant de telles solutions basées sur la nature par rapport aux infrastructures grises traditionnelles pour atténuer l'érosion côtière. Le chapitre 7 synthétise les résultats des chapitres précédents et conclut que si la restauration n'est pas une solution « parfaite », c'est peut-être notre meilleure chance d'améliorer la santé des récifs pour la protection côtière. Le fardeau du financement de telles solutions - dont le coût varie considérablement - ne devrait pas incomber uniquement aux gouvernements et devrait être partagé avec le secteur privé, en particulier ceux qui bénéficient directement de la protection côtière.
... Since the 1970s, coral cover in many areas decreased with >80% (Gardner et al., 2003;Jackson et al., 2014). Without the three dimensional structure of the corals, shelter availability (Alvarez-Filip et al., 2009), biodiversity (Newman et al., 2015) and productivity (Rogers et al., 2018) of Caribbean reefs has decreased significantly. Artificial reefs, structures mimicking one or more functions of a natural reef (Baine, 2001), are often deployed as alternative fish habitat for the purpose of creating a dive site, to restore ecosystems or to (temporarily) sustain fish catches (Lima et al., 2019;Hylkema et al., 2021). ...
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Fish assemblages of different types of artificial reefs can differ greatly in abundance, biomass and composition, with some reef types harboring over five times more herbivores than others. It is assumed that higher herbivorous fish abundance results in a higher grazing intensity, affecting the benthic community by means of enhanced coral recruitment, survival and growth. Territorial fish species might affect this process by chasing away other fish, especially herbivores. In this study we compared the fish assemblage, territorial behavior and grazing intensity by fish on two artificial reef types: reef balls and layered cakes, differing greatly in their fish assemblage during early colonization. In addition, the effect of artificial reef type on benthic development and coral recruitment, survival and growth, was investigated. Although layered cakes initially harbored higher herbivorous fish biomass, this effect was lost during consecutive monitoring events. This seems to be the result of the higher territorial fish abundance around the layered cakes where almost four times more chasing behavior was recorded compared to the reef balls. This resulted in a more than five times lower fish grazing intensity compared to the reef-ball plots. Although macroalgae were effectively controlled at both reefs, the grazing intensity did not differ enough to cause large enough structural changes in benthic cover for higher coral recruitment, survival or growth. The high turf algae cover, combined with increasing crustose coralline algae and sponge cover likely explained reduced coral development. We recommend further research on how to achieve higher grazing rates for improved coral development on artificial reefs, for example by facilitating invertebrate herbivores.
... It is well known that reef fish abundance is higher at reefs with a high reef bottom rugosity (Coker et al., 2014;Graham & Nash, 2013). Furthermore, reef bottom complexity is positively associated to coral cover, and areas with a high alive hermatypic coral cover also have higher rugosities (Álvarez-Filip et al., 2009(Álvarez-Filip et al., , 2011(Álvarez-Filip et al., , 2013. During our surveys we also determined the cover of hermatypic corals and crustose coralline algae, the main reef-builders in the VRSNP (Horta-Puga et al., 2020). ...
Reef fish species richness of the Veracruz Reef System National Park (VRSNP) in the SW Gulf of Mexico is well known. However, the knowledge of the assemblage structure and its spatial variability in the reef ecosystem is quite limited. For that purpose, 5 field surveys (2012-2015) were performed, using the stationary visual census method, at 10 selected reefs. The most important findings were: 116 reef species were recorded. Average total reef fish density (2.31 Ind/m2) is similar to the records for the Caribbean reefs in the 20th century. The top 5 most abundant species were: Chromis multilineata, Ocyurus chrysurus, Abudefduf saxatilis, Stegastes leucostictus, and Elacatinus jarocho. We found evidence of a spatial distribution pattern with 3 well-defined groups of reefs: (1) those near the city of Veracruz, (2) those near the outlet of the Jamapa River, and (3) those farther from the city. Higher fish densities are associated to both high hermatypic coral and low crustose coralline algae bottom covers. The assemblage structure of reef fishes is different at distinct geomorphological reef zones. As expected, with some differences in the species abundance order, the assemblage structure of reef fishes is similar at all coral reefs in the Gulf of Mexico.
... -The stressors impacting coral reefs have progressively increased in magnitude since the 1980s. Over the past four decades, coral cover has decreased, while macroalgal cover has increased (Jackson et al., 2014) and structural complexity has been reduced (Alvarez-Filip et al., 2009). At reef sites with recovered D. antillarum populations, macroalgae have been reduced, stimulating coral recruitment, growth and survival (Edmunds and Carpenter, 2001;Carpenter and Edmunds, 2006;Myhre and Acevedo-Gutieŕrez, 2007;Idjadi et al., 2010). ...
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The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effects on Caribbean coral reefs. Without the grazing activities of this key herbivore, turf and macroalgae became the dominant benthic group, inhibiting coral recruitment and compromising coral reef recovery from other disturbances. In the decades that followed, recovery of D. antillarum populations was slow to non-existent. In late January 2022, a new mass mortality of D. antillarum was first observed in the U.S. Virgin Islands. We documented the spread and extent of this new die-off using an online survey. Infected individuals were closely monitored in the lab to record signs of illness, while a large population on Saba, Dutch Caribbean, was surveyed weekly before and during mortality to determine the lethality of this event. Within four months the die-off was distributed over 1,300 km from north to south and 2,500 km east to west. Whereas the 1983-1984 die-off advanced mostly with the currents, the 2022 event has appeared far more quickly in geographically distant areas. First die-off observations in each jurisdiction were often close to harbor areas, which, together with their rapid appearance, suggests that anthropogenic factors may have contributed to the spread of the causative agent. The signs of illness in sick D. antillarum were very similar to those recorded during the 1983-1984 die-off: lack of tube feet control, slow spine reaction followed by their loss, and necrosis of the epidermis were observed in both lab and wild urchins. Affected populations succumbed fast; within a month of the first signs of illness, a closely monitored population at Saba, Dutch Caribbean, had decreased from 4.05 individuals per m 2 to 0.05 individuals per m 2. Lethality can therefore be as high as 99%. The full extent of the 2022 D. antillarum die-off Frontiers in Marine Science event is not currently known. The slower spread in the summer of 2022 might indicate that the die-off is coming to a (temporary) standstill. If this is the case, some populations will remain unaffected and potentially supply larvae to downstream areas and augment natural recovery processes. In addition, several D. antillarum rehabilitation approaches have been developed in the past decade and some are ready for large scale implementation. However, active conservation and restoration should not distract from the primary goal of identifying a cause and, if possible, implementing actions to decrease the likelihood of future D. antillarum die-off events.
... configuration) of the underlying seascape and the diversity and extent of the associated benthic habitats (Hart, 1993;Chapman and Kramer, 1999;McClanahan and Arthur, 2001;Grober-Dunsmore et al., 2007;Gullström et al., 2008;Grüss et al., 2011). Especially in coral reefs with their highly complex architecture habitat structure has been proven to be an important determinant for species abundances, diversity, and biomass (Gratwicke and Speight, 2005a;Gratwicke and Speight, 2005b;Wilson et al., 2006;Alvarez-Filip et al., 2009) and is thus recommended to be explicitly considered when investigating fish-habitat relationships (Harborne et al., 2012). ...
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Introduction Space use patterns in fish result from the interactions between individual movement behaviour and characteristics of the environment. Herbivorous parrotfishes, for instance, are constrained by the availability of resources and different predation risks. The resulting spatial distribution of the fish population can strongly influence community composition and ecosystem resilience. Methods In a novel approach, we combine individual-based modelling (IBM) with an artificial potential field algorithm to realistically represent fish movements and the decision-making process. Potential field algorithms, which are popular methods in mobile robot path planning, efficiently generate the best paths for an entity to navigate through vector fields of repellent and attracting forces. In our model the repellent and attracting forces are predation risk and food availability, both implemented as separate grid-based vector fields. The coupling of individual fish bioenergetics with a navigation capacity provides a mechanistic basis to analyse how the habitat structure influences population dynamics and space utilization. Results Model results indicate that movement patterns and the resulting spatial distributions strongly depend on habitat fragmentation with the bioenergetic capacity to spawn and reproduce being particularly susceptible processes at the individual level. The resulting spatial distributions of the population are more irregularly distributed among coral reef patches the more the coral reef habitat becomes fragmented and reduced. Discussion This heterogeneity can have strong implications for the delivered ecosystem functioning, e.g., by concentrating or diluting the grazing effort. Our results also highlight the importance of incorporating individual foraging-path patterns and the spatial exploitation of microhabitats into marine spatial planning by considering the effects of fragmentation. The integration of potential fields into IBMs represents a promising strategy to advance our understanding of complex decision-making in animals by implementing a more realistic and dynamic decision-making process, in which each fish weighs different rewards and risks of the environment. This information may help to identify core areas and essential habitat patches and assist in effective marine spatial management.
... Structural complexity denotes the amount of structural features, their sizes, and distribution. In coral reefs, biodiversity and structural complexity are clearly linked [15][16][17]. Therefore, although resilience was traditionally studied through metrics of community composition (species richness and diversity), structural complexity is a suitable proxy for reef-state in phase-shift studies. ...
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Extreme weather events are increasing in frequency and magnitude. Consequently, it is important to understand their effects and remediation. We studied the impact of a powerful storm on coral reef structural complexity using novel computational tools and detailed 3D reconstructions captured at seven sites in three time-points over three years. We employed six geometrical metrics, two of which are new algorithms for calculating fractal-dimension of reefs in full 3D. Three metrics showed a significant difference between time-points, i.e., decline and subsequent recovery in structural complexity. We also explored the changes in fractal dimension per size category and found a similar trend. A multivariate analysis helped us to reveal which sites were affected the most and their relative recovery. The full picture suggests that the reef has not gone through a phase-shift and is returning to its prior state w.r.t. structural complexity.
... This collapse was caused by rapid human population growth and likely agricultural impacts (Cramer et al. 2020b), white-band disease (Aronson & Precht 2001, Knowlton 2001, Jackson 2008) and bleaching (Aronson et al. 2000). It has caused a 'flattening of the Caribbean reefs', or a decrease in reef complexity, leading to further biodiversity loss and altering ecosystem function (Alvarez-Filip et al. 2009, O'Dea et al. 2020. Similar human-induced collapse of Acropora, the dominant reef builder for the last 1.8 Myrs, is known regionally and globally , Cybulski et al. 2020. ...
... This collapse was caused by rapid human population growth and likely agricultural impacts (Cramer et al. 2020b), white-band disease (Aronson & Precht 2001, Knowlton 2001, Jackson 2008) and bleaching (Aronson et al. 2000). It has caused a 'flattening of the Caribbean reefs', or a decrease in reef complexity, leading to further biodiversity loss and altering ecosystem function (Alvarez-Filip et al. 2009, O'Dea et al. 2020. Similar human-induced collapse of Acropora, the dominant reef builder for the last 1.8 Myrs, is known regionally and globally , Cybulski et al. 2020. ...
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Hotspots of tropical marine biodiversity are areas that harbour disproportionately large numbers of species compared to surrounding regions. The richness and location of these hotspots have changed throughout the Cenozoic. Here, we review the global dynamics of Cenozoic tropical marine biodiversity hotspots, including the four major hotspots of the Indo-Australian Archipelago (IAA), western Tethys (present Mediterranean), Arabian Sea and Caribbean Sea. Our review supports the ‘Hopping Hotspots’ model, which proposes that the locations of peak biodiversity are related to Tethyan faunal elements and track broadscale shallow-marine habitats and high coastal complexity created by the collision of tectonic plates. A null hypothesis is the ‘Whack-A-Mole’ model, which proposes that hotspots occur in habitats suitable for high diversity regardless of taxonomic identity or faunal elements. Earlier ‘Centre-of’ theories (e.g. centres of origin with diversity decreasing with distance from supposed areas of exceptionally high rates of speciation, for which easy connection to adjacent regions to the east and west is important) were based on the analysis of recent biotas with no palaeontological foundation, and may better explain diversity dynamics within a hotspot rather than those between hotspots. More recently, however, human disturbance is massively disrupting these natural patterns.
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Understanding the drivers of net coral reef calcium carbonate production is increasingly important as ocean warming, acidification, and other anthropogenic stressors threaten the maintenance of coral reef structures and the services these ecosystems provide. Despite intense research effort on coral reef calcium carbonate production, the inclusion of a key reef forming/accreting calcifying group, the crustose coralline algae (CCA), remains challenging both from a theoretical and practical standpoint. While corals are typically the primary reef builders of today, ongoing declines in coral cover due to a range of environmental perturbations will likely increase the relative importance of CCA and other non-scleractinian calcifying taxa to coral reef carbonate production. Here, we demonstrate that CCA are important carbonate producers that, under certain conditions, can match or even exceed the contribution of corals to coral reef carbonate production. Despite their importance, CCA are often inaccurately recorded in benthic surveys or even entirely missing from coral reef carbonate budgets. We outline several recommendations to improve the inclusion of CCA into such carbonate budgets under the ongoing climate crisis.
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In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region. Paleontological data suggest that the regional Acropora kill is without precedent in the late Holocene. In Belize, A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon until the mid-1980s. After constructing reef framework for thousands of years, A. cervicornis was virtually eliminated from the area over a ten-year period. Evidence from other parts of the Caribbean supports the hypothesis of continuous Holocene accumulation and recent mass mortality of Acropora spp. Prospects are poor for the rapid recovery of A. cervicornis, because its reproductive strategy emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than A. cervicornis If the Acropora spp. do not recover, macroalgae will continue to dominate Caribbean reefs, accompanied by increased abundances of brooding corals, particularly Agaricia spp. and Porites spp. The outbreak of white-band disease has been coincident with increased human activity, and the possibility of a causal connection should be further investigated.
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Sets of artificial reefs were replicated in 5 bays off Tortola in the British Virgin Islands to investigate the effects of habitat complexity on fish assemblages. Increasing percentage hard substrate and the number of small reef holes increased fish abundance on reefs. The observed number of species (S-obs) occurring on each reef increased with increasing rugosity, variety of growth forms, percentage hard substrate, and variety of refuge hole sizes. A rarefied or abundance -corrected species richness measure (S,a,e) was calculated to take the varying fish abundances into account. After this correction, rugosity was the only variable that significantly increased fish species-richness. Experimental reefs of different height (20 and 60 cm) did not have significantly different fish abundance or species richness. The presence of long-spined sea urchins Diadema antillarum increased Sob, and total fish abundance on artificial rock-reefs and in seagrass beds, but the effect was most pronounced in seagrass beds where shelter was a strongly limiting factor. These results indicate that complex habitats or animals such as D. antillarum that provide shelter to fish are essential for maintaining fish biodiversity at local scales. The most important aspects of complexity are rugosity, hard substrate and small refuge holes. Artificial reefs may be used to mitigate habitat damage in impacted areas, and if management objectives are to increase local fish abundance and species richness, the reefs should provide a stable substrate where this is unavailable, have a rugose surface with many small refuge holes, and have a variety of growth forms.
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Coral bleaching is a stress-related response that can be triggered by elevated sea surface temperatures (SST). Recent increases in the frequency of coral bleaching have led to concerns that increases in marine temperatures may threaten entire coral reef regions. We report exponential increases in the geographical extent and intensity of coral bleaching in the Caribbean with increasing SST anomalies. A rise in regional SST of 0.1°C results in 35% and 42% increases in the geographic extent and intensity of coral bleaching, respectively. Maximum bleaching extent and intensity are predicted to occur at regional SST anomalies of less than + 1°C, which coincides with the most conservative projections for warming in the Caribbean by the end of the 21 st century. Coral bleaching is therefore likely to become a chronic source of stress for Caribbean reefs in the near future.
Coral reefs are the 'rain forests' of the ocean, containing the highest diversity of marine organisms and facing the greatest threats from humans. As shallow-water coastal habitats, they support a wide range of economically and culturally important activities, from fishing to tourism. Their accessibility makes reefs vulnerable to local threats that include over-fishing, pollution and physical damage. Reefs also face global problems, such as climate change, which may be responsible for recent widespread coral mortality and increased frequency of hurricane damage. This book, first published in 2006, summarises the state of knowledge about the status of reefs, the problems they face, and potential solutions. The topics considered range from concerns about extinction of coral reef species to economic and social issues affecting the well-being of people who depend on reefs. The result is a multi-disciplinary perspective on problems and solutions to the coral reef crisis.
A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods. The emphasis is on presenting practical problems and full analyses of real data sets.
The decline of corals on tropical reefs is usually ascribed to a combination of natural and anthropogenic factors, but the relative importance of these causes remains unclear. In this paper, we attempt to quantify the contribution of hurricanes to Caribbean coral cover decline over the past two decades using meta-analyses. Our study included published and unpublished data from 286 coral reef sites monitored for variable lengths of time between 1980 and 2001. Of these, 177 sites had experienced hurricane impacts during their period of survey. Across the Caribbean, coral cover is reduced by ;17%, on average, in the year following a hurricane impact. The magnitude of this immediate loss increases with hurricane intensity and with the time elapsed since the last impact. In the following year, no further loss is discernible, but the decline in cover then resumes on impacted sites at a rate similar to the regional background rate of decline for nonimpacted sites. There is no evidence of recovery to a pre-storm state for at least eight years after impact. Overall, coral cover at sites impacted by a hurricane has declined at a significantly faster rate (6% per annum) than nonimpacted sites (2% per annum), due almost exclusively to higher rates of loss in the year after impact in the 1980s. While hurricanes, through their immediate impacts, appear to have contributed to changing coral cover on many Caribbean reefs in the 1980s, the similar decline in coral cover at impacted and nonimpacted sites in the 1990s suggests that other stressors are now relatively more important in driving the overall pattern of change in coral cover in this region. The overall lack of post-hurricane recovery points to a general impairment of the regeneration potential of Caribbean coral reefs.
There is increasing evidence that facilitative effects of various organisms can play important roles in community organization. However, on tropical coral reefs, where scleractinian corals have long been recognized as important foundation species creating habitat and resources that are utilized by a diversity of taxa, such relationships have rarely been studied and never within the contemporary theoretical context of facilitation. In the present study, we surveyed coral reefs on the south coast of St. John, US Virgin Islands, with the goal of quantifying the relationship between 'coral traits' (3 distinctive characteristics of scleractinian communities) and the abundance and diversity of benthic invertebrates associated with the reefs. We defined coral traits as coral diversity, percentage cover of live coral, and the topographic complexity created by coral skeletons, and statistically evaluated their roles in accounting for the abundance and diversity of conspicuous invertebrates at 25 sites. The analysis yielded contrasting results in terms of the putative facilitative roles of scleractinian corals. Coral traits were significantly and positively related to the diversity of reef-associated invertebrates, but were not related to invertebrate abundance. Topographic complexity (but not coral cover) had relatively strong explanatory ability in accounting for the variation in invertebrate diversity, although a substantial fraction of the variance in invertebrate diversity (45%) remained unexplained. While these results are correlative, they demonstrate that a statistical majority of the variation in the diversity of conspicuous invertebrates on Caribbean reefs can be explained by the role of coral skeletons in creating topographic relief with diverse morphologies, although processes independent of coral traits also play important roles. In an era of globally declining coral cover, these findings suggest that the progressive loss of coral skeletons from tropical reefs will lead to substantial losses of invertebrate diversity that might initially be obscured by conserved abundances.
Wave measurements during three experiments at Tague Reef, St. Croix (U.S.V.I.) in April 1987 showed a net energy decrease across the reef profile of 65-71% between the forereef and crest, wave propagation to the backreef increased energy reduction to 78-88%. Tidally induced water depth changes (range of 0.3 m) increased wave energy dissipation by 15% between forereef and crest and 20% between forereef and backreef. Significant wave heights throughout the experiment were low (< 0.5 m) and exhibited a tidal modulation in the backreef or lagoon. Wave transmission over the reef averaged 0.46 and modulated by the tide (0.32 at low tide vs 0.62 at high tide). The spectral time-delay model applied to analyzed wave transformations across the reef produced attenuation coefficients that averaged 0.62 between 0.05 and 0.1 cps (20-10 s) and afterwards oscillate between 0.22 and 0.35. For waves between the forereef and backreef, the attenuation coefficients from the time-delay model decay exponentially between 0.05 and 0.1 cps, afterwards they oscillate between 0.13 and 0.2. The steady wave-energy model with bottom friction, essentially form drag, and wave breaking dissipation yield wave heights modulated by the tides and errors of < 19% in the crest and > 20% at the backreef. The model revealed that while frictional and wave-breaking dissipation are equally important, frictional dissipation is greater.