Acanthaster planci is a major cause of coral mortality in Indonesia

The corallivorous crown-of-thorns starfish (COTS), Acanthaster planci, is recognised as a major cause of coral reef degradation throughout much of the Pacific Ocean. However, the effects of COTS on the high diversity reefs in Indonesia have been largely overlooked. In 2007, high densities of COTS were observed in two regions of Indonesia: Aceh and Halmahera. Densities of COTS ranged from 0 to 52 starfish 2,000 m² across 24 sites in Aceh and from 0 to 18 starfish 2,000 m² at 10 sites in Halmahera. Mortality rates of Acropora spp. were very high at affected sites: over 50 % of colonies had been killed at seven of the 16 affected sites. A review of historical sources going back to 1969 suggests that COTS have damaged many reefs throughout Indonesia, including much activity within the Indonesian section of the Coral Triangle. Furthermore, the data suggest that COTS activity has increased rapidly since 2000. Very little of this activity has been reported in the primary literature, and there is a general lack of awareness in Indonesia of COTS as a potential cause of reef degradation. This lack of awareness, combined with limited monitoring efforts, means that damage caused by COTS is often attributed to other causes, such as destructive fishing, bleaching or tsunami. COTS are clearly a major source of coral mortality in Indonesia of which scientists and government need to be more cognizant.     

Legacy effects of anthropogenic disturbances modulate dynamics in the world's coral reefs

Rapidly changing conditions alter disturbance patterns, highlighting the need to better understand how the transition from pulse disturbances to more persistent stress will impact ecosystem dynamics. We conducted a global analysis of the impacts of 11 types of disturbances on reef integrity using the rate of change of coral cover as a measure of damage. Then, we evaluated how the magnitude of the damage due to thermal stress, cyclones, and diseases varied among tropical Atlantic and Indo-Pacific reefs and whether the cumulative impact of thermal stress and cyclones was able to modulate the responses of reefs to future events. We found that reef damage largely depends on the condition of a reef before a disturbance, disturbance intensity, and biogeographic region, regardless of the type of disturbance. Changes in coral cover after thermal stress events were largely influenced by the cumulative stress of past disturbances and did not depend on disturbance intensity or initial coral cover, which suggests that an ecological memory is present within coral communities. In contrast, the effect of cyclones (and likely other physical impacts) was primarily modulated by the initial reef condition and did not appear to be influenced by previous impacts. Our findings also underscore that coral reefs can recover if stressful conditions decrease, yet the lack of action to reduce anthropogenic impacts and greenhouse gas emissions continues to trigger reef degradation. We uphold that evidence-based strategies can guide managers to make better decisions to prepare for future disturbances.     

Coral and sandstone reef-habitats in north-western Sri Lanka: patterns in the distribution of coral communities

Coral and sandstone reefs cover a significant part ofSri Lanka‘s continental shelf and contain incomparison unique reef structures. Despite this, reefsin this region of the northern Indian Ocean havereceived little research attention. In an attempt tobetter understand these ecosystems and their innatecharacter, this study describes the variety of reeftypes and habitats that are found in this area. Thestudy concentrated on four major reef areas: the BarReef Marine Sanctuary (BRMS), Kandakuliya Reefs,Talawila Reef, and Mampuri Reef. These reefs showedapparent differences in habitat structure in terms ofthe proportion coral cover, coral species compositionand structural complexity. Two reef types were presentwithin the continental shelf of BRMS: coral andsandstone patch-reefs. Acropora was the mostdominant coral genera however in total 118madreporarian species and 50 coral genera wererecorded in the sanctuary. Distinct habitats wereidentified within reef types including shallow reefflat, shallow patch reef, deep reef flat and Porites dome habitats for the coral-reef patcheswhile the sandstone-reef patches were divided intostructured and flat sandstone reef habitats.Kandakuliya Reef south of BRMS was by large dominatedby coral rubble. Talawila Reef and Mampuri Reef showedunique structures with the former being dominated bymassive corals and the latter mainly containingsandstone structures. In addition to factors such asbio-erosion, sedimentation, hydrodynamics, andrecruitment or colonisation processes, some reefs wereclearly under significant direct human impact whichappeared to play a dominant role in habitatstructuring. However, type and degree of humandisturbance varied among the reefs. Habitat alterationat Kandakuliya Reef was the result of intense fishingusing destructive fishing methods. Talawila Reef andMampuri Reef was also influenced by fishing activitiesthough reef structure seemed less affected. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coral reefs in the Southern Barents Sea: habitat description and the effects of bottom fishing

Fifteen Lophelia reefs from offshore to coastal areas off northern Norway were studied using video. Health status of the coral habitat (degree of physical impact, % cover of living tissue, colony size), occurrence of trawl marks and lost fishing gear, height of coral colonies and associated fauna were analysed from 44 video-lines. Fishing impact was more frequent on the offshore reefs (36.5% of the observed areas) than those in the coastal reefs (0.6%). The most visible effects of fishing were broken and displaced coral colonies. At some sites only small scattered fragments of live corals were observed, indicating recent impact. The mean colony height of Lophelia and gorgonian corals at impacted sites was around half the size of those at non-impacted sites. Both species richness and abundance was higher at non-impacted coral habitats compared to impacted. The actinarian Protanthea simplex and unidentified brittlestars were the only taxa with higher abundance on impacted compared with non-impacted habitats. The reefs at the offshore location were protected against bottom trawling in 2009 through the establishment of a marine protected area (MPA), but a general ban against trawling on known coral reefs had already been implemented in 1999. In the MPA, signs of regrowth were observed. Most of the observed damage probably occurred over 10 years earlier. Results show that live and non-impacted cold water coral reefs have an important ecological function by enhancing the local biodiversity and fish abundance. Preventing further damage to impacted reefs may lead to full recovery within a few decades.     

Coral and sea urchin assemblage structure and interrelationships in Kenyan reef lagoons

Patterns of hard coral and sea urchin assemblage structure (species richness, diversity, and abundance) were studied in Kenyan coral reef lagoons which experienced different types of human resource use. Two protected reefs (Malindi and Watamu Marine National Parks) were protected from fishing and coral collection, but exposed to heavy tourist use. One reef (Mombasa MNP) received protection from fishermen for one year and was exploited for fish and corals prior to protection and was defined as a transitional reef. Three reefs (Vipingo, Kanamai, and Diani) were unprotected and experienced heavy fishing and some coral collection. Protected and unprotected reefs were distinct in terms of their assemblage structure with the transitional reef grouping with unprotected reefs based on relative and absolute abundance of coral genera. Protected reefs had slightly higher (p<0.01) coral cover (23.6 ± 8.3 % ± S.D.) than unprotected reefs (16.7 ± 8.5), but the transitional reef had the highest coral cover (30.8 ± 6.4) which increased by 250% since measured in 1987: largely attributable to a large increase inPorites nigrescens cover. Protected reefs had higher coral species richness and diversity and a greater relative abundance ofAcropora, Montipora andGalaxea than unprotected reefs. The transitional reef had high species richness, but lower diversity due to the high dominance ofPorites. Sea urchins showed the opposite pattern with highest diversity in most unprotected reefs. Coral cover, species richness, and diversity were negatively associated with sea urchin abundance, but the relative abundance ofPorites increased with sea urchin abundance to the point wherePorites composed >90% of the coral cover at sites with the highest sea urchin abundance. Effects of coral overcollection was only likely for the genusAcropora (staghorn corals). A combination of direct and indirect effects of human resource use may reduce diversity, species richness, and abundance of corals while increasing the absolute abundance of sea urchins and the relative cover ofPorites.     

Cyclone effects on coral reef habitats in New Caledonia (South Pacific)

The impacts of the unusually strong Cyclone Erica (March 2003) on coral reef habitats at a site located on the northwest coast of New Caledonia (South Pacific) were assessed using a 6-year data set (2002–2007). We examined the interannual variations of key variables describing reef habitats (live hard and soft corals, dead corals in place, coral debris, algae and relative proportion of mechanically vulnerable and resistant live hard corals). The cyclone-induced disturbances of habitats differed according to three reef types: patch reefs, barrier reefs far from passes (more than 3 km from the nearest pass) and barrier reefs near passes (less than 3 km from the nearest pass). Short-term mechanical damage was detected on the three-dimensional structure of reef habitats with a notable shift from a community dominated by mechanically vulnerable corals to one dominated by resistant corals on barrier reefs far from passes. The history of habitats and their pre-disturbance characteristics, in link with local hydrodynamics, was found to influence their short-term susceptibility to extreme events such as cyclones. However, the most significant effects appeared in the midterm (within 2 years after the cyclone) as the cover of live hard corals significantly decreased by approximately 45% between 2002 and 2004 on all reef types. The short- and midterm disturbances of coral reef habitats are discussed with regard to published temporal variations in reef fish assemblages, underlining the delayed effects of this cyclonic event on fish as well as benthic habitats. Coral reef habitats and live corals had shown significant patterns of recovery 4 years after the cyclone, followed by similar recovery in fish community, suggesting good resilience in a face of this major natural disturbance in an area under moderate anthropogenic pressure.     

Coral Reef Community Composition in the Context of Disturbance History on the Great Barrier Reef,Australia

Much research on coral reefs has documented differential declines in coral and associated organisms. In order to contextualise this general degradation, research on community composition is necessary in the context of varied disturbance histories and the biological processes and physical features thought to retard or promote recovery. We conducted a spatial assessment of coral reef communities across five reefs of the central Great Barrier Reef, Australia, with known disturbance histories, and assessed patterns of coral cover and community composition related to a range of other variables thought to be important for reef dynamics. Two of the reefs had not been extensively disturbed for at least 15 years prior to the surveys. Three of the reefs had been severely impacted by crown-of-thorns starfish outbreaks and coral bleaching approximately a decade before the surveys, from which only one of them was showing signs of recovery based on independent surveys. We incorporated wave exposure (sheltered and exposed) and reef zone (slope, crest and flat) into our design, providing a comprehensive assessment of the spatial patterns in community composition on these reefs. Categorising corals into life history groupings, we document major coral community differences in the unrecovered reefs, compared to the composition and covers found on the undisturbed reefs. The recovered reef, despite having similar coral cover, had a different community composition from the undisturbed reefs, which may indicate slow successional processes, or a different natural community dominance pattern due to hydrology and other oceanographic factors. The variables that best correlated with patterns in the coral community among sites included the density of juvenile corals, herbivore fish biomass, fish species richness and the cover of macroalgae. Given increasing impacts to the Great Barrier Reef, efforts to mitigate local stressors will be imperative to encouraging coral communities to persist into the future.     

Marine Reserves Enhance the Recovery of Corals on Caribbean Reefs

The fisheries and biodiversity benefits of marine reserves are widely recognised but there is mounting interest in exploiting the importance of herbivorous fishes as a tool to help ecosystems recover from climate change impacts. This approach might be particularly suitable for coral reefs, which are acutely threatened by climate change, yet the trophic cascades generated by reserves are strong enough that they might theoretically enhance the rate of coral recovery after disturbance. However, evidence for reserves facilitating coral recovery has been lacking. Here we investigate whether reductions in macroalgal cover, caused by recovery of herbivorous parrotfishes within a reserve, have resulted in a faster rate of coral recovery than in areas subject to fishing. Surveys of ten sites inside and outside a Bahamian marine reserve over a 2.5-year period demonstrated that increases in coral cover, including adjustments for the initial size-distribution of corals, were significantly higher at reserve sites than those in non-reserve sites. Furthermore, macroalgal cover was significantly negatively correlated with the change in total coral cover over time. Recovery rates of individual species were generally consistent with small-scale manipulations on coral-macroalgal interactions, but also revealed differences that demonstrate the difficulties of translating experiments across spatial scales. Size-frequency data indicated that species which were particularly affected by high abundances of macroalgae outside the reserve had a population bottleneck restricting the supply of smaller corals to larger size classes. Importantly, because coral cover increased from a heavily degraded state, and recovery from such states has not previously been described, similar or better outcomes should be expected for many reefs in the region. Reducing herbivore exploitation as part of an ecosystem-based management strategy for coral reefs appears to be justified.     

Coral recruitment and recovery after the 2004 Tsunami around the Phi Phi Islands (Krabi Province) and Phuket, Andaman Sea, Thailand

The 2004 tsunami left a discontinuous pattern of destruction in the reefs along Andaman Sea coast of Thailand. Here, a comparative assessment of coral recruitment was carried out to assess differences in recovery between damaged and undamaged sites in near-shore fringing reefs 1 and 3 years after the tsunami. Settlement plates showed high frequencies of coral spat after 4 months (<17 spat tile⁻¹) in both, damaged and undamaged locations. Field surveys carried out 3 years after the tsunami on natural substrate confirmed that tsunami damage did not suppress recruitment in damaged sites relative to no impacted controls. New and stable settlement space along with unabated larval supply supported post-tsunami recruit densities up to 7.2 m⁻² year⁻¹. Mean recruit densities were found at the level of post-storm situations with rapid recovery success, suggesting that the duration of disturbance, degree of sorting and, hence, stability of coral rubble is a key determinant of recruitment success. Low regeneration success of some species e.g. branching acroporids and rebounding tourism industry at sites like Patong and partly around the Phi Phi Islands (dense carpets of filamentous algae) led to the assumption of selectivity and eventually to an alternation of the coral community even though live coral cover might be recovered soon.     

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.     

Effects of herbivory,nutrients, and reef protection on algal proliferation and coral growth on a tropical reef

Maintaining coral reef resilience against increasing anthropogenic disturbance is critical for effective reef management. Resilience is partially determined by how processes, such as herbivory and nutrient supply, affect coral recovery versus macroalgal proliferation following disturbances. However, the relative effects of herbivory versus nutrient enrichment on algal proliferation remain debated. Here, we manipulated herbivory and nutrients on a coral-dominated reef protected from fishing, and on an adjacent macroalgal-dominated reef subject to fishing and riverine discharge, over 152 days. On both reefs, herbivore exclusion increased total and upright macroalgal cover by 9-46 times, upright macroalgal biomass by 23-84 times, and cyanobacteria cover by 0-27 times, but decreased cover of encrusting coralline algae by 46-100% and short turf algae by 14-39%. In contrast, nutrient enrichment had no effect on algal proliferation, but suppressed cover of total macroalgae (by 33-42%) and cyanobacteria (by 71% on the protected reef) when herbivores were excluded. Herbivore exclusion, but not nutrient enrichment, also increased sediment accumulation, suggesting a strong link between herbivory, macroalgal growth, and sediment retention. Growth rates of the corals Porites cylindrica and Acropora millepora were 30-35% greater on the protected versus fished reef, but nutrient and herbivore manipulations within a site did not affect coral growth. Cumulatively, these data suggest that herbivory rather than eutrophication plays the dominant role in mediating macroalgal proliferation, that macroalgae trap sediments that may further suppress herbivory and enhance macroalgal dominance, and that corals are relatively resistant to damage from some macroalgae but are significantly impacted by ambient reef condition.     

High macroalgal cover and low coral recruitment undermines the potential resilience of the world's southernmost coral reef assemblages

Coral reefs are under increasing pressure from anthropogenic and climate-induced stressors. The ability of reefs to reassemble and regenerate after disturbances (i.e., resilience) is largely dependent on the capacity of herbivores to prevent macroalgal expansion, and the replenishment of coral populations through larval recruitment. Currently there is a paucity of this information for higher latitude, subtropical reefs. To assess the potential resilience of the benthic reef assemblages of Lord Howe Island (31°32'S, 159°04'E), the worlds' southernmost coral reef, we quantified the benthic composition, densities of juvenile corals (as a proxy for coral recruitment), and herbivorous fish communities. Despite some variation among habitats and sites, benthic communities were dominated by live scleractinian corals (mean cover 37.4%) and fleshy macroalgae (20.9%). Live coral cover was higher than in most other subtropical reefs and directly comparable to lower latitude tropical reefs. Juvenile coral densities (0.8 ind.m(-2)), however, were 5-200 times lower than those reported for tropical reefs. Overall, macroalgal cover was negatively related to the cover of live coral and the density of juvenile corals, but displayed no relationship with herbivorous fish biomass. The biomass of herbivorous fishes was relatively low (204 kg.ha(-1)), and in marked contrast to tropical reefs was dominated by macroalgal browsing species (84.1%) with relatively few grazing species. Despite their extremely low biomass, grazing fishes were positively related to both the density of juvenile corals and the cover of bare substrata, suggesting that they may enhance the recruitment of corals through the provision of suitable settlement sites. Although Lord Howe Islands' reefs are currently coral-dominated, the high macroalgal cover, coupled with limited coral recruitment and low coral growth rates suggest these reefs may be extremely susceptible to future disturbances.     

Life histories predict coral community disassembly under multiple stressors

Climate change is reshaping biological communities against a background of existing human pressure. Evaluating the impacts of multiple stressors on community dynamics can be particularly challenging in species‐rich ecosystems, such as coral reefs. Here, we investigate whether life‐history strategies and cotolerance to different stressors can predict community responses to fishing and temperature‐driven bleaching using a 20‐year time series of coral assemblages in Kenya. We found that the initial life‐history composition of coral taxa largely determined the impacts of bleaching and coral loss. Prior to the 1998 bleaching event, coral assemblages within no‐take marine reserves were composed of three distinct life histories – competitive, stress‐tolerant and weedy– and exhibited strong declines following bleaching with limited subsequent recovery. In contrast, fished reefs had lower coral cover, fewer genera and were composed of stress‐tolerant and weedy corals that were less affected by bleaching over the long term. Despite these general patterns, we found limited evidence for cotolerance as coral genera and life histories were variable in their sensitivities to fishing and bleaching. Overall, fishing and bleaching have reduced coral diversity and led to altered coral communities of ‘survivor’ species with stress‐tolerant and weedy life histories. Our findings are consistent with expectations that climate change interacting with existing human pressure will result in the loss of coral diversity and critical reef habitat.     

Human impact on atolls leads to coral loss and community homogenisation: a modeling study

We explore impacts on pristine atolls subjected to anthropogenic near-field (human habitation) and far-field (climate and environmental change) pressure. Using literature data of human impacts on reefs, we parameterize forecast models to evaluate trajectories in coral cover under impact scenarios that primarily act via recruitment and increased mortality of larger corals. From surveys across the Chagos, we investigate the regeneration dynamics of coral populations distant from human habitation after natural disturbances. Using a size-based mathematical model based on a time-series of coral community and population data from 1999-2006, we provide hind- and forecast data for coral population dynamics within lagoons and on ocean-facing reefs verified against monitoring from 1979-2009. Environmental data (currents, temperatures) were used for calibration. The coral community was simplified into growth typologies: branching and encrusting, arboresent and massive corals. Community patterns observed in the field were influenced by bleaching-related mortality, most notably in 1998. Survival had been highest in deep lagoonal settings, which suggests a refuge. Recruitment levels were higher in lagoons than on ocean-facing reefs. When adding stress by direct human pressure, climate and environmental change as increased disturbance frequency and modified recruitment and mortality levels (due to eutrophication, overfishing, pollution, heat, acidification, etc), models suggest steep declines in coral populations and loss of community diversification among habitats. We found it likely that degradation of lagoonal coral populations would impact regeneration potential of all coral populations, also on ocean-facing reefs, thus decreasing reef resilience on the entire atoll.     

Response of the coral reef benthos and herbivory to fishery closure management and the 1998 ENSO disturbance

The hypothesis that herbivory is higher in areas without fishing and will increase the rate at which hard coral communities return to pre-disturbance conditions was tested in and out of the marine protected areas (MPA) of Kenya after the 1998 El Niño Southern Oscillation (ENSO). Herbivory was estimated by assay and biomass methods, and both methods indicated higher herbivory in fishery closures. Despite higher herbivory, the effect of the ENSO disturbance was larger within these closures, with reefs undergoing a temporary transition from dominance by hard and soft coral to a temporary dominance of turf and erect algae that ended in the dominance of calcifying algae, massive Porites, Pocillopora and a few faviids six years after the disturbance. The fished reefs changed the least but had a greater cover of turf and erect algae and sponge shortly after the disturbance. Higher herbivory in the fishery closures reduced the abundance and persistence of herbivore-susceptible erect algae and created space and appropriate substratum for recruiting corals. Nonetheless, other post-settlement processes may have had strong influences such that annual rates of coral recovery were low (～2%) and not different between the management regimes. Recovery, as defined as and measured by the return to pre-disturbance coral cover and the dominant taxa, was slower in fishery closures than unmanaged reefs.     

Reef-scale failure of coral settlement following typhoon disturbance and macroalgal bloom in Palau,Western Pacific

Factors affecting coral recruitment are critical in influencing the scope and rate of reef recovery after disturbance. In December 2012, super-typhoon Bopha caused immense damage to the eastern reefs of Palau, resulting in near complete loss of coral cover. Within weeks following the typhoon, an ephemeral monospecific bloom of the foliose red macroalga Liagora (up to 40 % cover in February 2013) was recorded at impacted reefs with moderate wave exposure. Conversely, impacted and un-impacted reefs in areas of low wave exposure remained Liagora free. To quantify the effect of this ephemeral macroalgal bloom on coral recruitment, we installed settlement tiles during the major spawning period (March–April 2013) at forereefs with and without Liagora. Reefs (n = 3) with Liagora (13–24 % cover in April) experienced an almost complete failure of settlement, with only two individual corals recorded on settlement tiles (n = 90). This settlement failure was unexpected, as tiles were situated adjacent to, and not within Liagora canopies. In contrast, settlement was significantly higher on reefs that lacked macroalgae (n = 3), ranging from an average of 0.5–2.5 and 2.7–18.9 individuals 25 cm^?2 per top- and under-sided tile, respectively. Reefs with and without Liagora were in close proximity (≤8 km), and hydrodynamic models predicted that larval supply did not limit coral settlement among sites. While some differences in the community composition on the tiles were observed among sites, settlement substrate availability also did not limit coral settlement. Generalised linear mixed effects models indicated that while no settlement substrate explained more than 10 % of the variability in coral settlement, coral cover positively accounted for 26 %, and the cover of Liagora on reefs negatively accounted for more than 50 % of the observed variation. Combined, our results indicate that the typhoon induced ephemeral macroalgal bloom resulted in a reef-scale failure of coral settlement.     

Context-dependent corallivory by parrotfishes in a Caribbean reef ecosystem

This study assesses the patterns of corallivory by parrotfishes across reefs of the Florida Keys, USA. These reefs represent a relatively unique combination within the wider Caribbean of low coral cover and high parrotfish abundance suggesting that predation pressure could be intense. Surveys across eight shallow forereefs documented the abundance of corals, corallivorous parrotfishes, and predation scars on corals. The corals Porites porites and Porites astreoides were preyed on most frequently with the rates of predation an order of magnitude greater than has been documented for other areas of the Caribbean. In fact, parrotfish bite density on these preferred corals was up to 34 times greater than reported for corals on other reefs worldwide. On reefs where coral cover was low and corals such as Montastraea faveolata, often preferred prey for parrotfishes, were rare, predation rates on P. porites and P. astreoides, and other less common corals, intensified further. The intensity of parrotfish predation increased significantly as coral cover decreased. However, parrotfish abundance showed only a marginal positive relationship with predation pressure on corals, likely because corallivorous parrotfish were abundant across all reefs. Parrotfishes often have significant positive impacts on coral cover by facilitating coral recruitment, survival, and growth via their grazing of algae. However, abundant corallivorous parrotfishes combined with low coral cover may result in higher predation on corals and intensify the negative impact that parrotfishes have on remaining corals.     

Resilience of coral communities on an isolated system of reefs following catastrophic mass-bleaching

As a result of climate change, sea-water temperatures around the world are expected to increase, potentially causing more frequent and severe episodes of coral bleaching. In this study, the impact of elevated water temperatures at an isolated system of reefs was assessed by quantifying the changes in benthic communities over almost 10 years. Mass-coral bleaching in 1998 dramatically altered the community structure of the reefs, including a >80% relative decrease in the cover of hard and soft corals and a twofold increase in the cover of algae, but which did not include macroalgae. The magnitude of the impact varied among the different sites according to their initial cover and community structure, largely due to the differing susceptibilities of the dominant groups of hard corals. Subsequent increase in the cover of these groups varied according to their life history traits, such as modes of reproduction and rates of growth. Additionally, the increase in cover was strongly correlated with the magnitude of the impact at the different sites, suggesting that recovery was driven by processes acting over local scales. Six years after the bleaching, the hard corals had returned to approximately 40% of their pre-bleaching cover, but there was little change in the cover of soft corals, and the structure of most hard coral communities remained very different to that prior to the bleaching. These data provides insights into the degree to which coral communities are resilient to catastrophic disturbances, when they are isolated from other reef systems but not exposed to some of the chronic stressors affecting many reefs around the world.     

Hurricanes and coral reefs: The intermediate disturbance hypothesis revisited

A review of research on the effects of hurricanes on coral reefs suggests that the intermediate disturbance hypothesis may be applicable to shallow reef zones dominated by branching or foliaceous coral species that are especially susceptible to mechanical damage from storms. Diversity (H') increases because of an increase in evenness following destruction or removal of the species that was monopolizing the space. The intermediate disturbance hypothesis as presented by Connell focuses on changes in number of species, but should be expanded to include diversity (H') and evenness. It should also be modified to incorporate changes in living cover and the time elapsed since disturbances of varying intensities. This hypothesis predicts that when cover is high, diversity will be low. However, research on coral reefs does not consistently demonstrate an inverse correlation of coral diversity, and coral cover. An increase in cover and decrease in diversity with depth would also be expected because deeper reef zones generally experience less disturbance. However, higher diversity (both H' and species richness) is often associated with deeper zones. The effects of hurricanes on coral reefs will depend on the temporal and spatial scales under consideration, the life history characteristics and morphology of the dominant species, the depth of the reef zone, the ecological history of the site, and the influence of any additional natural or human stresses.     

Biogeographic variation in coral species diversity on coral reefs in three regions of Indonesia

Abstract . This paper assesses variation in coral species diversity within the Indonesian archipelago, and the influence of regional species pools, geomorphology and anthropogenic pollution on coral species diversity and occurrence. We obtained transects from 33 sites on 14 reefs in three regions of Indonesia: Ambon (Moluccas), South Sulawesi and the Java Sea. We determined the within‐site species richness by using species‐sampling curves. Cluster analysis and multi‐dimensional scaling showed that land‐based pollution was the primary determinant of coral species diversity and species occurrence on reefs. Relatively unaffected reference sites in eastern Indonesia were approximately 20% more diverse than Java Sea reference sites. Rare species formed a higher proportion of the coral fauna on eastern Indonesian sites, and eastern Indonesian apparent endemic species contributed approximately 25% of the total species pool sampled. Between‐site variation in species occurrence was lower on Java Sea reefs than on eastern Indonesian reefs. A larger species pool in eastern Indonesia than in the Java Sea probably accounted for most of the difference in within‐site species diversity between eastern Indonesian and Java Sea reference sites. High fishing intensity in the Java Sea, including destructive fishing practices, may have also contributed to reduced within‐site species diversity on Java Sea reference reefs. Despite the fact that the Java Sea was exposed during Pleistocene lowstands, and was recolonized by marine organisms only within the last 10 000 years, coral species diversity and assemblage composition on the Java Sea reefs was largely similar to open ocean reefs in eastern Indonesia.