The impacts of flooding on the high-latitude, terrigenoclastic influenced coral reefs of Hervey Bay, Queensland, Australia

This study examines the impacts of an acute flooding event on the marginal, high-latitude, terrigenoclastic influenced coral reefs of Hervey Bay in southeast Queensland, Australia. In January 2011, the Mary River near Hervey Bay experienced its eleventh highest flood on record. The Mary River catchment has been highly modified since European colonisation, and, as a result of heavy rain and flooding, Hervey Bay was exposed to reduced salinity and elevated levels of turbidity and nutrients for approximately 14 weeks. Through the use of photograph transects and point intercept analysis, per cent cover of coral reef benthic communities was measured prior to and just after the flooding event. Sites were located between 250 m and 5 km from the mainland and from 18 to 85 km away from the mouth of the Mary River. Overall, there was a ~40 % reduction in coral cover post-flood, including significant mortality up to 89 % at four of six reefs. Mortality did not vary with distance along the coast from the Mary River, but mortality was found to be highest closer to the mainland, where turbidity and nutrients levels were also the highest. Despite the decades of input of highly turbid and nutrient laden waters from the Mary River, recovery has occurred in the past, and, given the persistence of similar conditions, would be expected to take place again. Climate change predicts increased frequency of severe storms and flooding, and this, combined with elevated sedimentation and nutrients from the highly modified catchment, may reduce these recovery periods, resulting in the deterioration of Hervey Bay reef communities.     

Coral reef mesopredators switch prey,shortening food chains,in response to habitat degradation

Diet specificity is likely to be the key predictor of a predator's vulnerability to changing habitat and prey conditions. Understanding the degree to which predatory coral reef fishes adjust or maintain prey choice, in response to declines in coral cover and changes in prey availability, is critical for predicting how they may respond to reef habitat degradation. Here, we use stable isotope analyses to characterize the trophic structure of predator–prey interactions on coral reefs of the Keppel Island Group on the southern Great Barrier Reef, Australia. These reefs, previously typified by exceptionally high coral cover, have recently lost much of their coral cover due to coral bleaching and frequent inundation by sediment‐laden, freshwater flood plumes associated with increased rainfall patterns. Long‐term monitoring of these reefs demonstrates that, as coral cover declined, there has been a decrease in prey biomass, and a shift in dominant prey species from pelagic plankton‐feeding damselfishes to territorial benthic algal‐feeding damselfishes, resulting in differences in the principal carbon pathways in the food web. Using isotopes, we tested whether this changing prey availability could be detected in the diet of a mesopredator (coral grouper, Plectropomus maculatus). The δ¹³C signature in grouper tissue in the Keppel Islands shifted from a more pelagic to a more benthic signal, demonstrating a change in carbon sources aligning with the change in prey availability due to habitat degradation. Grouper with a more benthic carbon signature were also feeding at a lower trophic level, indicating a shortening in food chains. Further, we found a decline in the coral grouper population accompanying a decrease in total available prey biomass. Thus, while the ability to adapt diets could ameliorate the short‐term impacts of habitat degradation on mesopredators, long‐term effects may negatively impact mesopredator populations and alter the trophic structure of coral reef food webs.     

Coral Luminescence Identifies the Pacific Decadal Oscillation as a Primary Driver of River Runoff Variability Impacting the Southern Great Barrier Reef

The Pacific Decadal Oscillation (PDO) is a large-scale climatic phenomenon modulating ocean-atmosphere variability on decadal time scales. While precipitation and river flow variability in the Great Barrier Reef (GBR) catchments are sensitive to PDO phases, the extent to which the PDO influences coral reefs is poorly understood. Here, six Porites coral cores were used to produce a composite record of coral luminescence variability (runoff proxy) and identify drivers of terrestrial influence on the Keppel reefs, southern GBR. We found that coral skeletal luminescence effectively captured seasonal, inter-annual and decadal variability of river discharge and rainfall from the Fitzroy River catchment. Most importantly, although the influence of El Niño-Southern Oscillation (ENSO) events was evident in the luminescence records, the variability in the coral luminescence composite record was significantly explained by the PDO. Negative luminescence anomalies (reduced runoff) were associated with El Niño years during positive PDO phases while positive luminescence anomalies (increased runoff) coincided with strong/moderate La Niña years during negative PDO phases. This study provides clear evidence that not only ENSO but also the PDO have significantly affected runoff regimes at the Keppel reefs for at least a century, and suggests that upcoming hydrological disturbances and ecological responses in the southern GBR region will be mediated by the future evolution of these sources of climate variability.     

Dietary shift in juvenile coral trout (<Emphasis Type="Italic">Plectropomus maculatus</Emphasis>) following coral reef degradation from a flood plume disturbance

Acute environmental disturbances impact on habitat quality and resource availability, which can reverberate through trophic levels and become apparent in species’ dietary composition. In this study, we observed a distinct dietary shift of newly settled and juvenile coral trout (Plectropomus maculatus) following severe coral reef habitat degradation after a river flood plume affected the Keppel Islands, Australia. Hard coral cover declined by ~28 % in the 2 yr following the 2010–2011 floods, as did the abundance of young coral trout. Gut contents analysis revealed that diets had shifted from largely crustacean-based to non-preferred prey fishes following the disturbances. These results suggest that newly settled and juvenile coral trout modify their diet and foraging strategy in response to coral habitat degradation. This bottom-up effect of habitat degradation on the diet of a top coral reef predator may incur a metabolic cost, with subsequent effects on growth and survival.     

Habitat dynamics,marine reserve status,and the decline and recovery of coral reef fish communities

Severe climatic disturbance events often have major impacts on coral reef communities, generating cycles of decline and recovery, and in some extreme cases, community‐level phase shifts from coral‐ to algal‐dominated states. Benthic habitat changes directly affect reef fish communities, with low coral cover usually associated with low fish diversity and abundance. No‐take marine reserves (NTRs) are widely advocated for conserving biodiversity and enhancing the sustainability of exploited fish populations. Numerous studies have documented positive ecological and socio‐economic benefits of NTRs; however, the ability of NTRs to ameliorate the effects of acute disturbances on coral reefs has seldom been investigated. Here, we test these factors by tracking the dynamics of benthic and fish communities, including the important fishery species, coral trout (Plectropomus spp.), over 8 years in both NTRs and fished areas in the Keppel Island group, Great Barrier Reef, Australia. Two major disturbances impacted the reefs during the monitoring period, a coral bleaching event in 2006 and a freshwater flood plume in 2011. Both disturbances generated significant declines in coral cover and habitat complexity, with subsequent declines in fish abundance and diversity, and pronounced shifts in fish assemblage structure. Coral trout density also declined in response to the loss of live coral, however, the approximately 2:1 density ratio between NTRs and fished zones was maintained over time. The only post‐disturbance refuges for coral trout spawning stocks were within the NTRs that escaped the worst effects of the disturbances. Although NTRs had little discernible effect on the temporal dynamics of benthic or fish communities, it was evident that the post‐disturbance refuges for coral trout spawning stocks within some NTRs may be critically important to regional‐scale population persistence and recovery.     

Building resilience into practical conservation: identifying local management responses to global climate change in the southern Great Barrier Reef

Climate change is now considered the greatest long-term threat to coral reefs, with some future change inevitable despite mitigation efforts. Managers must therefore focus on supporting the natural resilience of reefs, requiring that resilient reefs and reef regions be identified. We develop a framework for assessing resilience and trial it by applying the framework to target management responses to climate change on the southern Great Barrier Reef. The framework generates a resilience score for a site based on the evaluation of 19 differentially weighted indicators known or thought to confer resilience to coral reefs. Scores are summed, and sites within a region are ranked in terms of (1) their resilience relative to the other sites being assessed, and (2) the extent to which managers can influence their resilience. The framework was applied to 31 sites in Keppel Bay of the southern Great Barrier Reef, which has a long history of disturbance and recovery. Resilience and ‘management influence potential’ were both found to vary widely in Keppel Bay, informing site selection for the staged implementation of resilience-based management strategies. The assessment framework represents a step towards making the concept of resilience operational to reef managers and conservationists. Also, it is customisable, easy to teach and implement and effective in building support among local communities and stakeholders for management responses to climate change.     

Suitable Environmental Ranges for Potential Coral Reef Habitats in the Tropical Ocean

Coral reefs are found within a limited range of environmental conditions or tolerance limits. Estimating these limits is a critical prerequisite for understanding the impacts of climate change on the biogeography of coral reefs. Here we used the diagnostic model ReefHab to determine the current environmental tolerance limits for coral reefs and the global distribution of potential coral reef habitats as a function of six factors: temperature, salinity, nitrate, phosphate, aragonite saturation state, and light. To determine these tolerance limits, we extracted maximum and minimum values of all environmental variables in corresponding locations where coral reefs are present. We found that the global, annually averaged tolerance limits for coral reefs are 21.7—29.6 °C for temperature, 28.7—40.4 psu for salinity, 4.51 μmol L^-1 for nitrate, 0.63 μmol L^-1 for phosphate, and 2.82 for aragonite saturation state. The averaged minimum light intensity in coral reefs is 450 μmol photons m^-2 s^-1. The global area of potential reef habitats calculated by the model is 330.5 × 10³ km². Compared with previous studies, the tolerance limits for temperature, salinity, and nutrients have not changed much, whereas the minimum value of aragonite saturation in coral reef waters has decreased from 3.28 to 2.82. The potential reef habitat area calculated with ReefHab is about 121×10³ km² larger than the area estimated from the charted reefs, suggesting that the growth potential of coral reefs is higher than currently observed.     

Ecological impact of a fresh-water “reef kill” in Kaneohe Bay,Oahu, Hawaii

Storm floods on the night of December 31, 1987 reduced salinity to 15 in the surface waters of Kaneohe Bay, resulting in massive mortality of coral reef organisms in shallow water. A spectacular phytoplankton bloom occurred in the following weeks. Phytoplankton growth was stimulated by high concentrations of plant nutrients derived partially from dissolved material transported into the bay by flood runoff and partially by decomposition of marine organisms killed by the flood. Within two weeks of the storm, chlorophyll a concentrations reached 40 mg m^-3, one of the highest values ever reported. The extremely rapid growth rate of phytoplankton depleted dissolved plant nutrients, leading to a dramatic decline or crash of the phytoplankton population. Water quality parameters returned to values approaching the long-term average within 2 to 3 months. Corals, echinoderms, crustaceans and other creatures suffered extremely high rates of mortality in shallow water. Virtually all coral was killed to depths of 1–2m in the western and southern portions of the bay. Elimination of coral species intolerant to lowered salinity during these rare flood events leads to dominance by the coral Porites compressa. After a reef kill, this species can eventually regenerate new colonies from undifferentiated tissues within the dead perforate skeleton. Catastrophic flood disturbances in Kaneohe Bay are infrequent, probably occurring once every 20 to 50 years, but play an important role in determination of coral community structure. The last major fresh water reef kill occurred in 1965 when sewage was being discharged into Kaneohe Bay. Coral communities did not recover until after sewage abatement in 1979. Comparison between recovery rate after the two flood events suggests that coral reefs can recover quickly from natural disturbances, but not under polluted conditions.     

Branching coral as a macroalgal refuge in a marginal coral reef system

Marginal coral reef systems may provide valuable insights into the nature of ecosystem processes in systems on the trajectory towards a phase shift to an alternate ecosystem state. This study investigates the process of herbivory in a marginal coral reef system in the Keppel Islands at the southern end of the Great Barrier Reef. Branching Acropora coral and the brown macroalga Lobophora variegata occupied up to 95% of the reef crest substratum at the three surveyed reefs. Feeding rates of herbivorous fishes and removal rates of Lobophora were directly quantified within areas of branching Acropora and on planar surfaces. Feeding rates by herbivorous fishes were habitat dependent with the highest bite rates being found in planar habitats for both Lobophora and the epilithic algal matrix (EAM) by 1–2 orders of magnitude, respectively. Feeding rates on Lobophora were, however, much lower than rates on the EAM. The low rates of Lobophora removal and significantly lower rates of herbivory in branching habitats were consistent with the high biomass of this brown alga throughout the Keppel Islands and with its distribution on reef crests, where Lobophora biomass was 20 times greater in branching than in planar habitats. This lack of feeding by herbivorous fishes within branching coral habitats in the Keppel Islands contrasts with the typical role of coral and topographic complexity on herbivores on coral reefs and highlights the potential for complex interactions between algae, corals and fishes on coral reefs. On marginal systems, herbivory may modify algal distributions but may be unable to contain the proliferation of algae such as Lobophora.     

Geomorphology and community structure of Middle Reef, central Great Barrier Reef, Australia: an inner-shelf turbid zone reef subject to episodic mortality events

Middle Reef is an inshore turbid zone reef located 4 km offshore from Townsville, Queensland, Australia. The reef consists of four current-aligned, interconnected reef patches that have reached sea level and formed reef flats. It is regularly exposed to high turbidity (up to 50 mg l⁻¹) generated by wave-driven sediment resuspension or by episodic flood plumes. Middle Reef has a high mean hard coral cover (>39%), relatively low mean macro-algal cover (<15%) and a coral community comprising at least 81 hard coral species. Cluster analysis differentiated six benthic communities which were mapped onto the geomorphological structure of the reef to reveal a spatially patchy community mosaic that reflects hydrodynamic and sediment redistribution processes. Coral cover data collected annually from windward slope transects since 1993 show that coral cover has increased over the last ~15 years despite a history of episodic mortality events. Although episodic mortality may be interpreted as an indication of marginality, over decadal timescales, Middle Reef has recovered rapidly following mortality events and is clearly a resilient coral reef.     

Linking Demographic Processes of Juvenile Corals to Benthic Recovery Trajectories in Two Common Reef Habitats

Tropical reefs are dynamic ecosystems that host diverse coral assemblages with different life-history strategies. Here, we quantified how juvenile (<50 mm) coral demographics influenced benthic coral structure in reef flat and reef slope habitats on the southern Great Barrier Reef, Australia. Permanent plots and settlement tiles were monitored every six months for three years in each habitat. These environments exhibited profound differences: the reef slope was characterised by 95% less macroalgal cover, and twice the amount of available settlement substrata and rates of coral settlement than the reef flat. Consequently, post-settlement coral survival in the reef slope was substantially higher than that of the reef flat, and resulted in a rapid increase in coral cover from 7 to 31% in 2.5 years. In contrast, coral cover on the reef flat remained low (~10%), whereas macroalgal cover increased from 23 to 45%. A positive stock-recruitment relationship was found in brooding corals in both habitats; however, brooding corals were not directly responsible for the observed changes in coral cover. Rather, the rapid increase on the reef slope resulted from high abundances of broadcast spawning Acropora recruits. Incorporating our results into transition matrix models demonstrated that most corals escape mortality once they exceed 50 mm, but for smaller corals mortality in brooders was double those of spawners (i.e. acroporids and massive corals). For corals on the reef flat, sensitivity analysis demonstrated that growth and mortality of larger juveniles (21–50 mm) highly influenced population dynamics; whereas the recruitment, growth and mortality of smaller corals (<20 mm) had the highest influence on reef slope population dynamics. Our results provide insight into the population dynamics and recovery trajectories in disparate reef habitats, and highlight the importance of acroporid recruitment in driving rapid increases in coral cover following large-scale perturbation in reef slope environments.     

Seascape-scale trophic links for fish on inshore coral reefs

It is increasingly accepted that coastal habitats such as inshore coral reefs do not function in isolation but rather as part of a larger habitat network. In the Caribbean, trophic subsidies from habitats adjacent to coral reefs support the diet of reef fishes, but it is not known whether similar trophic links occur on reefs in the Indo-Pacific. Here, we test whether reef fishes in inshore coral, mangrove, and seagrass habitats are supported by trophic links. We used carbon stable isotopes and mathematical mixing models to determine the minimum proportion of resources from mangrove or seagrass habitats in the diet of five fish species from coral reefs at varying distances (0–2,200 m) from these habitats in Moreton Bay, Queensland, eastern Australia. Of the fish species that are more abundant on reefs near to mangroves, Lutjanus russelli and Acanthopagrus australis showed no minimum use of diet sources from mangrove habitat. Siganus fuscescens utilized a minimum of 25–44 % mangrove sources and this contribution increased with the proximity of reefs to mangroves (R ² = 0.91). Seagrass or reef flat sources contributed a minimum of 14–78 % to the diet of Diagramma labiosum, a species found in higher abundance on reefs near seagrass beds, but variation in diet among reefs was unrelated to seascape structure. Seagrass or reef flat sources also contributed a minimum of 8–55 % to a fish species found only on reefs (Pseudolabrus guentheri), indicating that detrital subsidies from these habitats may subsidize fish diet on reefs. These results suggest that carbon sources from multiple habitats contribute to the functioning of inshore coral reef ecosystems and that trophic connectivity between reefs and mangroves may enhance production of a functionally important herbivore.     

Destruction of corals and other reef animals by coral spawn slicks on Ningaloo Reef,Western Australia

In March 1989, most of the corals near Coral Bay, off the north-western coastline of Australia, spawned several nights earlier than usual. Flood, rather than ebb, tides at the time of spawning combined with light north-west winds and low swell conditions to restrict the dispersal of coral propagules and, as a result, large amounts of coral spawn were trapped in the bay, forming extensive slicks. Fish and other animals began to die almost immediately, and over the next few days, over 1 million fish, representing at least 80 species, were washed ashore. A survey of the benthic communities revealed extensive mortality of corals and other reef animals over an area of about 3 km². Live coral cover in this area decreased from 42.9% to 9.4% and several large coral colonies up to 10 m in diameter were killed. The observed mortality was presumably the result of hypoxia (oxygen depletion) created initially by the respiratory demand of the coral spawn and maintained by the biological oxygen demand of the decomposing spawn slicks and dead animals. Anecdotal reports of corals and other reef animals dying in the vicinity of coral spawn slicks on other reefs in Western Australia suggest that this phenomenon may be a relatively common event on shallow coral reefs where coral mass spawning occurs. These records and observations document, for the first time, a new source of natural disturbance that has a significant influence on the community structure of some coral reefs.     

Coral diversity across a disturbance gradient in the Pulau Seribu reef complex off Jakarta, Indonesia

Very few coral reefs are located close enough to metropolitan cities to study the influence of large urban populations on reef communities. Here, we compare the impact of a large-scale disturbance gradient with local-scale disturbance on coral richness, cover, and composition in the Jakarta Bay and Pulau Seribu reef complex off Jakarta, Indonesia. We found no effect of local land-use type of coral reef islands on richness, composition or cover, nor did taxon richness differ among zones at the large-scale. There was, however, a pronounced difference in composition and coral cover among zones. Cover was very low and composition differed markedly in the near-shore zone 1 (Jakarta Bay) where human-induced disturbance is most intense. Cover was highest in the outlying reefs of zone 3. The highly perturbed zone 1 reefs were, furthermore, distinguished by the virtual absence of otherwise abundant coral taxa such as Acropora hyacinthus and Porites rus and the prevalence of taxa such as Oulastrea crispata and Favia maxima. Almost 60% of the spatial variation in composition was related to variation in shelf depth and island size. The importance of shelf depth was related to the prevalence of a strong environmental gradient in reef depth, pollution, and mechanical reef disturbance and salinity from Jakarta Bay to the outlying reefs. Although there was a significant univariate relationship between spatial variation in composition and distance, this did not enter into the multivariate model, except when presence–absence data was used, indicating that environmental processes are the primary structuring forces in determining local coral assemblage composition across the Pulau Seribu complex.     

Holocene coral reef accretion in Hawaii: a function of wave exposure and sea level history

 In the high Hawaiian Islands, significant accretion due to coral reef growth is limited by wave exposure and sea level. Holocene coral growth and reef accretion was measured at four stations off Oahu, Hawaii, chosen along a gradient in wave energy from minimum to maximum exposures. The results show that coral growth of living colonies (linear extension) at optimal depths is comparable at all stations (7.7–10.1 mm/y), but significant reef accretion occurs only at wave sheltered stations. At wave sheltered stations in Hanauma Bay and Kaneohe Bay, rates of long term reef accretion are about 2.0 mm/y. At wave exposed stations, off Mamala Bay and Sunset Beach, reef accretion rates are virtually zero in both shallow (1 m) and deeper (optimal) depths (12 m). At wave sheltered stations, such as Kaneohe Bay and Hanauma Bay, Holocene reef accretion is on the order of 10–15 m thick. At wave exposed stations, Holocene accretion is represented by only a thin veneer of living corals resting on antecedent Pleistocene limestone foundations. Modern coral communities in wave exposed environments undergo constant turnover associated with mortality and recruitment or re-growth of fragmented colonies and are rarely thicker than a single living colony. Breakage, scour, and abrasion of living corals during high wave events appears to be the major source of mortality and ultimately limits accretion to wave sheltered environments. Depth is particularly important as a modulator of wave energy. The lack of coral reef accretion along shallow open ocean coastlines may explain the absence of mature barrier reefs in the high Hawaiian Islands. Accepted: 14 May 1998     

亚龙湾珊瑚礁大型礁栖生物的群落结构及生态警示

鱼类和大型底栖生物等礁栖生物是珊瑚礁生态系统的重要组成部分,其群落信息是全面评价珊瑚礁生态系统健康状况的必要基础数据.基于录像样带法,分析了2018年12月底海南省三亚市亚龙湾珊瑚礁区17个站位礁栖鱼类和大型底栖生物的群落结构、数量分布及相似性,揭示了其中的生态警示,并提出相应的监管建议,旨在保护和恢复亚龙湾的珊瑚礁....     

Coral recruitment and juvenile mortality as structuring factors for reef benthic communities in Biscayne National Park, USA

Coral communities of Biscayne National Park (BNP) on offshore linear bank-barrier reefs are depauperate of reef corals and have little topographic relief, while those on lagoonal patch reefs have greater coral cover and species richness despite presumably more stressful environmental regimes closer to shore. We hypothesized that differences in rates of coral recruitment and/or of coral survivorship were responsible for these differences in community structure. These processes were investigated by measuring: (1) juvenile and adult coral densities, and (2) size-frequency distributions of smaller coral size classes, at three pairs of bank- and patch-reefs distributed along the north-south range of coral reefs within the Park. In addition, small quadrats (0.25 m²) were censused for colonies <2 cm in size on three reefs (one offshore and one patch reef in the central park, and one intermediate reef at the southern end), and re-surveyed after 1 year. Density and size frequency data confirmed that large coral colonies were virtually absent from the offshore reefs, but showed that juvenile corals were common and had similar densities to those of adjacent bank and patch reefs. Large coral colonies were more common on inshore patch reefs, suggesting lower survivorship (higher mortality) of small and intermediate sized colonies on the offshore reefs. The more limited small-quadrat data showed similar survivorship rates and initial and final juvenile densities at all three sites, but a higher influx of new recruits to the patch reef site during the single annual study period. We consider the size-frequency data to be a better indicator of juvenile coral dynamics, since it is a more time-integrated measurement and was replicated at more sites. We conclude that lack of recruitment does not appear to explain the impoverished coral communities on offshore bank reefs in BNP. Instead, higher juvenile coral mortality appears to be a dominant factor structuring these communities. Accepted: 9 September 1999     

Marine reserves help coastal ecosystems cope with extreme weather

Natural ecosystems have experienced widespread degradation due to human activities. Consequently, enhancing resilience has become a primary objective for conservation. Nature reserves are a favored management tool, but we need clearer empirical tests of whether they can impart resilience. Catastrophic flooding in early 2011 impacted coastal ecosystems across eastern Australia. We demonstrate that marine reserves enhanced the capacity of coral reefs to withstand flood impacts. Reserve reefs resisted the impact of perturbation, whilst fished reefs did not. Changes on fished reefs were correlated with the magnitude of flood impact, whereas variation on reserve reefs was related to ecological variables. Herbivory and coral recruitment are critical ecological processes that underpin reef resilience, and were greater in reserves and further enhanced on reserve reefs near mangroves. The capacity of reserves to mitigate external disturbances and promote ecological resilience will be critical to resisting an increased frequency of climate‐related disturbance.     

Detriments to post-bleaching recovery of corals

Predicting the response of coral reefs to large-scale mortality induced by climate change will depend greatly on the factors that influence recovery after bleaching events. We experimentally transplanted hard corals from a shallow reef with highly variable seawater temperature (23–36°C) to three unfished marine parks and three fished reefs with variable coral predator abundance and benthic cover. The transplanted corals were fragmented colonies collected from a reef that was relatively undisturbed by the 1997–1998 warm-water temperature anomaly, one of the most extreme thermal events of the past century, and it was assumed that they would represent corals likely to succeed in the future temperature environment. We examined the effects of four taxa, two fragment sizes, an acclimation period, benthic cover components, predators and tourists on the survival of the coral fragments. We found the lowest survival of transplants occurred in the unfished marine parks and this could be attributed to predation and not tourist damage. The density of small coral recruits approximately 6 months after the spawning season was generally moderate (~40–60/m²), and not different on fished and unfished reefs. Coral recovery between 1998 and 2002 was variable (0–25%), low (mean of 6.5%), and not different between fished and unfished reefs. There was high variability in coral mortality among the three unfished areas despite low variation in estimates of predator biomass, with the highest predation occurring in the Malindi MNP, a site with high coralline algal cover. Stepwise multiple regression analysis with 14 variables of coral predators and substratum showed that coralline algae was positively, and turf algae negatively associated with mortality of the transplants, with all other variables being statistically insignificant. This suggests that alternate food resources and predator choices are more important than predator biomass in determining coral survival. Nonetheless, large predatory fish in areas dominated by coralline algae may considerably retard recovery of eurythermal corals. This will not necessarily retard total hard coral recovery, as other more predator-tolerant taxa can recover. Based on the results, global climate change will not necessarily favor eurythermal over stenothermal coral taxa in remote or unfished reefs, where predation is a major cause of coral mortality.     

Flattening of Caribbean coral reefs: region-wide declines in architectural complexity

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.