Boring sponges,an increasing threat for coral reefs affected by bleaching events

Coral bleaching is a stress response of corals induced by a variety of factors, but these events have become more frequent and intense in response to recent climate‐change‐related temperature anomalies. We tested the hypothesis that coral reefs affected by bleaching events are currently heavily infested by boring sponges, which are playing a significant role in the destruction of their physical structure. Seventeen reefs that cover the entire distributional range of corals along the Mexican Pacific coast were studied between 2005/2006, and later between 2009/2010. Most of these coral reefs were previously impacted by bleaching events, which resulted in coral mortalities. Sponge abundance and species richness was used as an indicator of bioerosion, and coral cover was used to describe the present condition of coral reefs. Coral reefs are currently highly invaded (46% of the samples examined) by a very high diversity of boring sponges (20 species); being the coral reef framework the substrate most invaded (56%) followed by the rubbles (45%), and the living colonies (36%). The results also indicated that boring sponges are promoting the dislodgment of live colonies and large fragments from the framework. In summary, the eastern coral reefs affected by bleaching phenomena, mainly provoked by El Niño, present a high diversity and abundance of boring sponges, which are weakening the union of the colony with the reef framework and promoting their dislodgment. These phenomena will probably become even more intense and severe, as temperatures are projected to continue to rise under the scenarios for future climate change, which could place many eastern coral reefs beyond their survival threshold.     

Monitoring of the Meager Shoal coral reef, Cahuita National Park, Costa Rica (CARICOMP site)

The coral reefs at Cahuita National Park, Caribbean coast of Costa Rica, specifically at the CARICOMP site Meager Shoal, have been monitored since 1999. Complete data sets from 2000 and 2004 have shown that live coral cover has increased less than 3 % (from 15 to 17 %), but non-coralline algae cover has increased much (63 to 74 %) and coralline algae cover has decreased (17 to 5 %) significantly. The proportion of affected colonies by diseases, injuries and bleaching decreased from 24 % in 2000 to 10 % in 2004, but the difference was not statistically significant. Densities of the urchin Diadema antillarum increased, and are probably help to maintain the macroalgae biomass low, while those of Echinometra viridis decreased significantly. The coral reef at Cahuita National Park continues to be impacted by chronic terrigenous sediments and does not show a significant recovery since the late 1970's.     

Detecting coral bleaching using high-resolution satellite data analysis and 2-dimensional thermal model simulation in the Ishigaki fringing reef,Japan

In 2007, high-temperature-induced mass coral mortality was observed in a well-developed fringing reef area on the southeastern coast of Ishigaki Island, Japan. To analyze the response of the corals to thermal stress, the coral cover was examined using Quickbird data, taken across the reef flat just before and after the bleaching event and performing a reef scale horizontal 2-dimensional thermal model simulation. The Quickbird data consisted of multispectral (MSS) imagery, which had a spatial resolution of 2.4 m, and panchromatic (PAN)-fused multispectral imagery, which had a 0.6-m spatial resolution. The observed changes in coral cover implied that the delineation of partially bleached coral was more precise with PAN + MSS. The classification accuracy achieved using PAN + MSS (93%) was superior to that obtained using MSS (88%). The in situ water temperature observations and 2-dimensional thermal model simulation results indicated that the water temperature fluctuated greatly in the inner reef area in late July 2007. Different thermal stress indices, including daily average temperature, daily maximum excess temperature, and daily accumulated temperature, were examined to define a suitable index that represented the severity of the thermal stress on coral cover. The results suggested that the daily accumulated temperature that occurred during the maximum sea surface temperature period of the bleaching season provided the best predictor of bleaching. The changes in water temperature, bathymetry, and coral patch size affected the severity of bleaching; therefore, the spatial dependence of these variables was examined using Moran’s I and Lagrange multiplier tests. An investigation of the effect of coral patch sizes on coral bleaching indicated that large coral patches were less affected than the small patches, which were more likely to suffer bleaching and coral mortality.     

Coral bleaching: the winners and the losers

Sea surface temperatures were warmer throughout 1998 at Sesoko Island, Japan, than in the 10 preceding years. Temperatures peaked at 2.8 °C above average, resulting in extensive coral bleaching and subsequent coral mortality. Using random quadrat surveys, we quantitatively documented the coral community structure one year before and one year after the bleaching event. The 1998 bleaching event reduced coral species richness by 61% and reduced coral cover by 85%. Colony morphology affected bleaching vulnerability and subsequent coral mortality. Finely branched corals were most susceptible, while massive and encrusting colonies survived. Most heavily impacted were the branched Acropora and pocilloporid corals, some of which showed local extinction. We suggest two hypotheses whose synergistic effect may partially explain observed mortality patterns (i.e. preferential survival of thick-tissued species, and shape-dependent differences in colony mass-transfer efficiency). A community-structural shift occurred on Okinawan reefs, resulting in an increase in the relative abundance of massive and encrusting coral species.     

Bleaching Susceptibility and Recovery of Colombian Caribbean Corals in Response to Water Current Exposure and Seasonal Upwelling

Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (<10% at both sites) was observed, but corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs.     

Coral bleaching: one disturbance too many for near-shore reefs of the Great Barrier Reef

The dynamic nature of coral communities can make it difficult to judge whether a reef system is resilient to the current disturbance regime. To address this question of resilience for near-shore coral communities of the Great Barrier Reef (Australia) a data set consisting of 350 annual observations of benthic community change was compiled from existing monitoring data. These data spanned the period 1985–2007 and were derived from coral reefs within 20 km of the coast. During years without major disturbance events, cover increase of the Acroporidae was much faster than it was for other coral families; a median of 11% per annum compared to medians of less than 4% for other coral families. Conversely, Acroporidae were more severely affected by cyclones and bleaching events than most other families. A simulation model parameterised with these observations indicated that while recovery rates of hard corals were sufficient to compensate for impacts associated with cyclones and crown-of-thorns starfish, the advent of mass bleaching has lead to a significant change in the composition of the community and a rapid decline in hard coral cover. Furthermore, if bleaching events continue to occur with the same frequency and severity as in the recent past, the model predicts that the cover of Acroporidae will continue to decline. Although significant cover of live coral remains on near-shore reefs, and recovery is observed during inter-disturbance periods, it appears that this system will not be resilient to the recent disturbance regime over the long term. Conservation strategies for coral reefs should focus on both mitigating local factors that act synergistically to increase the susceptibility of Acroporidae to climate change while promoting initiatives that maximise the recovery potential from inevitable disturbances.     

Coral disease following massive bleaching in 2005 causes 60% decline in coral cover on reefs in the US Virgin Islands

In the northeast Caribbean, doldrum-like conditions combined with elevated water temperatures in the summer/fall 2005 created the most severe coral bleaching event ever documented within this region. Video monitoring of 100 randomly chosen, permanent transects at five study sites in the US Virgin Islands revealed over 90% of the scleractinian coral cover showed signs of thermal stress by paling or becoming completely white. Lower water temperatures in October allowed some re-coloring of corals; however, a subsequent unprecedented regional outbreak of coral disease affected all sites. Five known diseases or syndromes were recorded; however, most lesions showed signs similar to white plague. Nineteen scleractinian species were affected by disease, with >90% of the disease-induced lesions occurring on the genus Montastraea. The disease outbreak peaked several months after the onset of bleaching at all sites but did not occur at the same time. The mean number of disease-induced lesions increased 51-fold and the mean area of disease-associated mortality increased 13-fold when compared with pre-bleaching disease levels. In the 12 months following the onset of bleaching, coral cover declined at all sites (average loss: 51.5%, range: 42.4–61.8%) reducing the five-site average from 21.4% before bleaching to 10.3% with most mortality caused by white plague disease, not bleaching. Continued losses through October 2007 reduced the average coral cover of the five sites to 8.3% (average 2-year loss: 61.1%, range: 53.0–79.3%). Mean cover by M. annularis (complex) decreased 51%, Colpophyllia natans 78% and Agaricia agaricites 87%. Isolated disease outbreaks have been documented before in the Virgin Islands, but never as widespread or devastating as the one that occurred after the 2005 Caribbean coral-bleaching event. This study provides insight into the effects of continued seawater warming and subsequent coral bleaching events in the Caribbean and highlights the need to understand links between coral bleaching and disease.     

Severity of the 1998 and 2005 bleaching events in Venezuela, southern Caribbean

This study describes the severity of the 2005 bleaching event at 15 reef sites across Venezuela and compares the 1998 and 2005 bleaching events at one of them. During August and September 2005, bleached corals were first observed on oceanic reefs rather than coastal reefs, affecting 1 to 4% of coral colonies in the community (3 reef sites, n = 736 colonies). At that time, however, no bleached corals were recorded along the eastern coast of Venezuela, an area of seasonal upwelling (3 reefs, n = 181 colonies). On coastal reefs, bleaching started in October but highest levels were reached in November 2005 and January 2006, when 16% of corals were affected among a wide range of taxa (e.g. scleractinians, octocorals, Millepora and zoanthids). In the Acropora habitats of Los Roques (an oceanic reef),no bleached was recorded in 2005 (four sites,n = 643 colonies). At Cayo Sombrero, a coastal reef site, bleaching was less severe in 1998 than in 2005 (9% of the coral colonies involving 2 species vs. 26% involving 23 species, respectively). Our results indicate that bleaching was more severe in 2005 than in 1998 on Venezuelan reefs; however, no mass mortality was observed in either of these two events.     

Relocating bleached Platygyra sinensis facilitates recovery from thermal stress during a minor bleaching event

The recovery of bleached corals is crucial in ensuring the persistence of the coral reef ecosystem function. This study investigated whether relocating bleached Platygyra sinensis colonies was a viable measure to accelerate their recovery. During a mild bleaching event in 2014, eight bleached colonies of P. sinensis were relocated from an affected reef at Sultan Shoal, Singapore, to a reef at Kusu that was less impacted. Another eight colonies at Sultan Shoal were tagged as controls. After five months, 88% of relocated bleached colonies at Kusu showed full recovery whereas only 25% of the control bleached colonies at Sultan Shoal had recovered. The differential coral recovery among the two sites was most likely due to lower seawater temperatures and faster water flow at Kusu, which helped to mitigate the effects of thermal stress on the bleached corals. This relocation study demonstrated that relocating bleached P. sinensis to sites with more favourable environmental conditions is a viable approach to reduce bleaching impacts for this species.     

Predictability of coral bleaching from synoptic satellite and in situ temperature observations

Satellite and compiled in situ observations of sea surface temperatures have greatly increased the ability to detect anomalous and persistent warm water and are being widely used to predict climate change, coral bleaching and mortality. A field-based synoptic view of coral bleaching spanning eight countries and ∼35° of latitude in the western Indian Ocean tested the accuracy of synoptic temperature data derived from satellites and shipboard data to detect and predict bleaching during 2005. The ability to predict the degree of bleaching based on degree heating weeks data was moderate, but increased when past temperature anomalies and coral community susceptibility were included. It is estimated that slightly more than half of the bleaching response is due to anomalous warm water and nearly half due to taxa and community level acclimation or adaptation, where these two factors have opposing effects. Cumulative temperature anomalies do identify general areas with bleaching but both large over and underestimates of bleaching intensity were observed. Consequently, field observations are needed to confirm the synoptic satellite predictions for particular reefs, particularly where acclimation and reorganization of the coral community have occurred due to past bleaching events.     

Chronic nutrient enrichment increases prevalence and severity of coral disease and bleaching

Nutrient loading is one of the strongest drivers of marine habitat degradation. Yet, the link between nutrients and disease epizootics in marine organisms is often tenuous and supported only by correlative data. Here, we present experimental evidence that chronic nutrient exposure leads to increases in both disease prevalence and severity and coral bleaching in scleractinian corals, the major habitat‐forming organisms in tropical reefs. Over 3 years, from June 2009 to June 2012, we continuously exposed areas of a coral reef to elevated levels of nitrogen and phosphorus. At the termination of the enrichment, we surveyed over 1200 scleractinian corals for signs of disease or bleaching. Siderastrea siderea corals within enrichment plots had a twofold increase in both the prevalence and severity of disease compared with corals in unenriched control plots. In addition, elevated nutrient loading increased coral bleaching; Agaricia spp. of corals exposed to nutrients suffered a 3.5‐fold increase in bleaching frequency relative to control corals, providing empirical support for a hypothesized link between nutrient loading and bleaching‐induced coral declines. However, 1 year later, after nutrient enrichment had been terminated for 10 months, there were no differences in coral disease or coral bleaching prevalence between the previously enriched and control treatments. Given that our experimental enrichments were well within the ranges of ambient nutrient concentrations found on many degraded reefs worldwide, these data provide strong empirical support to the idea that coastal nutrient loading is one of the major factors contributing to the increasing levels of both coral disease and coral bleaching. Yet, these data also suggest that simple improvements to water quality may be an effective way to mitigate some coral disease epizootics and the corresponding loss of coral cover in the future.     

Turbid reefs moderate coral bleaching under climate‐related temperature stress

Thermal‐stress events that cause coral bleaching and mortality have recently increased in frequency and severity. Yet few studies have explored conditions that moderate coral bleaching. Given that high light and high ocean temperature together cause coral bleaching, we explore whether corals at turbid localities, with reduced light, are less likely to bleach during thermal‐stress events than corals at other localities. We analyzed coral bleaching, temperature, and turbidity data from 3,694 sites worldwide with a Bayesian model and found that K_d490, a measurement positively related to turbidity, between 0.080 and 0.127 reduced coral bleaching during thermal‐stress events. Approximately 12% of the world's reefs exist within this “moderating turbidity” range, and 30% of reefs that have moderating turbidity are in the Coral Triangle. We suggest that these turbid nearshore environments may provide some refuge through climate change, but these reefs will need high conservation status to sustain them close to dense human populations.     

Strong relationship between coral bleaching and growth anomalies in massive Porites

Reports of coral diseases are increasing and may result from human land use and climate change conditions such as increased water temperature, coral bleaching, runoff from land, and changes in the ecology of heavily fished reefs. We examined a stable coral syndrome or a growth anomaly [ Porite growth anomaly (PGA)] (skeletal tissue anomaly, hyperplasia, or 'tumor') that was present in 0–15% of massive Porites colonies in 12 Kenyan reef lagoons. At the level of the calice morphology, this growth anomaly showed larger calices with less distance between calices and some calices with higher than normal numbers of septa, which indicate the influence of microboring organisms. Scanning electron micrographs of affected corals revealed a high abundance of fungal hyphae, a potential microboring pathogenic agent. To test the hypothesis that the PGA covaries with environmental variables, we evaluated its prevalence in relationship to 16 parameters of water quality, temperature, intensity of bleaching, benthic composition, and management at the end of the 2005 warm season. Stepwise regression models found eight environmental variables significantly associated with the frequency of the PGA, and the site's bleaching intensity was the most strongly associated variable. When bleaching intensity was removed from the dataset, the concentration of phosphorus was the one significant and positively associated variable, which suggest that the other significant environmental variables were associated with bleaching and not the growth anomalies. Our hypothetical model of causation is that the patchy loss of symbionts, often associated with bleaching, reduces calcification, increases susceptibility to pathogens, and allows endolithic fungi to perforate the skeleton creating a porous and anomalous growth of the skeleton. Consequently, we suggest that the frequency of skeletal growth anomalies is expected to increase with the frequency of coral bleaching.     

Taxonomic patterns of bleaching within a South African coral assemblage

In 1998, the Indian Ocean coral reefs suffered a severe and extensive mass bleaching event. The thermal tolerances of corals were exceeded and their photosynthetic symbionts (zooxanthellae) lost. Mortalities of up to 90% were recorded on the reefs of Seychelles, Maldives, Kenya and Tanzania. South African coral reefs were among the few that largely escaped the 1998 mass bleaching event, but may be threatened in the future if global warming increases. This study assessed the extent of coral bleaching and partial recovery at Sodwana Bay, South Africa during 2000 and 2001. Bleaching levels in this study varied over the course of a year, which suggested that seasonally varying parameters such as sea temperature were the most likely cause of bleaching. Bleaching levels were highest at the shallowest site. However, these bleaching levels were very low in comparison with those of reefs elsewhere in the Indian Ocean. The greater volume of water over the relatively deeper reefs of Sodwana Bay may have protected the reefs from severe bleaching. Field measurements on the three reefs indicated that, although the reefs at Sodwana Bay are still healthy, bleaching increased from <1% in 1998 to 5–10% in 2002. Bleaching occurred in 26 coral genera. The Alcyonacea were highly susceptible to bleaching, especially Sarcophyton sp. Among the hard corals, Montipora spp. were the species most susceptible to bleaching. The sensitivity of these genera to early and slight increases in temperature suggests that they can forewarn of a possible greater bleaching event. In contrast, the coral genera Turbinaria and Stylophora were most resistant to bleaching.     

Effects of the 1991-92 El Niño on scleractinian corals of the Costa Rican central Pacific coast

Coral communities on the central Pacific coast of Costa Rica were affected during the 1991-92 El Ni?o warming event. More than 57% of all observed colonies at three localities (Parque Nacional Manuel Antonio, Punta Cambutal, and Parque Marino Ballena) were bleached. Mortality during this El Ni?o was much lower (approximately 9%) than in previous events. Psammocora spp. accounted for approximately 66% of dead corals, while massive (Porites lobota, Pavona spp.) and branching (Pocillopora spp.) for approximately 34%. Our results suggest that the observed bleaching in P. lobata was related to zooxanthellar densities and not to changes in pigment concentrations: only chlorophyll a varied between normally pigmented and bleached colonies at one locality (Ballena). Site differences in zooxanthellar densities or their pigment concentrations, may not be the result of the bleaching event itself, because a percentage of dead corals and zooxanthellar densities of bleached colonies seems to follow a trend with the exposure to tidal regimes and currents at each site. Local oceanographic conditions can be influencing the zooxanthellar densities and their response to the warming, together with intrinsic differences between colonies as well. The impact of this event can be considered serious given the short period of time that elapsed between El Ni?o related mortalities and the slow reefs recovery, the mode of reproduction of reef building species, and the anthropogenic-originated disturbances which affect the coral communities and reefs of the Costa Rican central Pacific coast.     

The cumulative impact of annual coral bleaching can turn some coral species winners into losers

Mass coral bleaching events caused by elevated seawater temperatures result in extensive coral loss throughout the tropics, and are projected to increase in frequency and severity. If bleaching becomes an annual event later in this century, more than 90% of coral reefs worldwide may be at risk of long‐term degradation. While corals can recover from single isolated bleaching and can acclimate to recurring bleaching events that are separated by multiple years, it is currently unknown if and how they will survive and possibly acclimatize to annual coral bleaching. Here, we demonstrate for the first time that annual coral bleaching can dramatically alter thermal tolerance in Caribbean corals. We found that high coral energy reserves and changes in the dominant algal endosymbiont type (Symbiodinium spp.) facilitated rapid acclimation in Porites divaricata, whereas low energy reserves and a lack of algal phenotypic plasticity significantly increased susceptibility in Porites astreoides to bleaching the following year. Phenotypic plasticity in the dominant endosymbiont type of Orbicella faveolata did not prevent repeat bleaching, but may have facilitated rapid recovery. Thus, coral holobiont response to an isolated single bleaching event is not an accurate predictor of its response to bleaching the following year. Rather, the cumulative impact of annual coral bleaching can turn some coral species ‘winners’ into ‘losers’, and can also facilitate acclimation and turn some coral species ‘losers’ into ‘winners’. Overall, these findings indicate that cumulative impact of annual coral bleaching could result in some species becoming increasingly susceptible to bleaching and face a long‐term decline, while phenotypically plastic coral species will acclimatize and persist. Thus, annual coral bleaching and recovery could contribute to the selective loss of coral diversity as well as the overall decline of coral reefs in the Caribbean.     

Variance of coral anti-pathogen defense in response to transplantation between coral- and macroalgal-dominated reefs

Coral Reefs - Coral reefs are undergoing precipitous decline due to coral bleaching and disease following warming events, with impacted reefs often shifting from coral to macroalgal dominance. We...     

Unprecedented Mass Bleaching and Loss of Coral across 12° of Latitude in Western Australia in 2010–11

Background

Globally, coral bleaching has been responsible for a significant decline in both coral cover and diversity over the past two decades. During the summer of 2010–11, anomalous large-scale ocean warming induced unprecedented levels of coral bleaching accompanied by substantial storminess across more than 12° of latitude and 1200 kilometers of coastline in Western Australia (WA).

Methodology/Principal Findings

Extreme La-Niña conditions caused extensive warming of waters and drove considerable storminess and cyclonic activity across WA from October 2010 to May 2011. Satellite-derived sea surface temperature measurements recorded anomalies of up to 5°C above long-term averages. Benthic surveys quantified the extent of bleaching at 10 locations across four regions from tropical to temperate waters. Bleaching was recorded in all locations across regions and ranged between 17% (±5.5) in the temperate Perth region, to 95% (±3.5) in the Exmouth Gulf of the tropical Ningaloo region. Coincident with high levels of bleaching, three cyclones passed in close proximity to study locations around the time of peak temperatures. Follow-up surveys revealed spatial heterogeneity in coral cover change with four of ten locations recording significant loss of coral cover. Relative decreases ranged between 22%–83.9% of total coral cover, with the greatest losses in the Exmouth Gulf.

Conclusions/Significance

The anomalous thermal stress of 2010–11 induced mass bleaching of corals along central and southern WA coral reefs. Significant coral bleaching was observed at multiple locations across the tropical-temperate divide spanning more than 1200 km of coastline. Resultant spatially patchy loss of coral cover under widespread and high levels of bleaching and cyclonic activity, suggests a degree of resilience for WA coral communities. However, the spatial extent of bleaching casts some doubt over hypotheses suggesting that future impacts to coral reefs under forecast warming regimes may in part be mitigated by southern thermal refugia.     

How much time can herbivore protection buy for coral reefs under realistic regimes of hurricanes and coral bleaching?

Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 °C over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral‐reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual‐based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral‐reef resources and maximizing resource management investments.     

Interspecific comparison of the symbiotic relationship in corals with high and low rates of bleaching-induced mortality

Some coral species are more resistant than others to environmental factors that cause bleaching and bleaching-related mortality. This study compared aspects of the coral/zooxanthellae symbiosis in species and genera that suffered either high or low mortality during a bleaching event. These characteristics were assessed in Okinawa between March and June 1999, 5-10 months after the bleaching event there in August-September 1998. Species with low mortality rates generally had higher densities of zooxanthellae per square centimeter and a very low rate of release of degraded zooxanthellae. Low-mortality species also had more total coral tissue per square centimeter of coral surface area. The size of zooxanthellae varied little among species. The differences in these characteristics among coral species suggest that the symbiotic relationship operates very differently among coral species.