The Effect of Bleaching on the Terpene Chemistry of Plexaurella fusifera: Evidence that Zooxanthellae Are Not Responsible for Sesquiterpene Production

The close association between marine invertebrates, zooxanthellae, and numerous bacteria gives rise to the question of the identity of the actual producer of secondary metabolites. In fall of 2005, a widespread bleaching event occurred throughout the Caribbean Sea in which some colonies of the gorgonian coral Plexaurella fusifera bleached. This study investigated whether zooxanthellae play a key role in the biosynthesis of secondary metabolite terpenes from P. fusifera. The extent of bleaching was examined by chlorophyll A analysis and also by zooxanthellae isolation and cell counting. The bleached and unbleached colonies were found to contain similar concentrations of eremophilene as the major terpene, and both exhibited similar biosynthetic capability as evaluated by the transformation of [C(1)-(3)H]-farnesyl diphosphate to the sesquiterpenes. Differences in bacterial communities between the bleached and unbleached colonies were analyzed using molecular techniques, and preliminary indications are that unbleached and bleached corals are dominated by low G + C firmicutes and gammaproteobacteria, respectively. It therefore appears that terpene biosynthesis can proceed independently of the zooxanthellae in P. fusifera, suggesting that the coral or a bacterium is the biosynthetic source.     

Impacts of bleaching on the soft coral Lobophytum compactum. I. Fecundity, fertilization and offspring viability

We document long-term effects of a simulated bleaching event on the reproductive output and offspring viability of the soft coral Lobophytum compactum. Corals were subjected to temperature and solar radiation treatments to produce both moderately (48–60%) and heavily (90–95%) bleached colonies. Although bleached colonies recovered their zooxanthellae within 10 to 18 weeks, impacts on reproductive output were significant for at least two annual spawning seasons. In the first year, both polyp fecundity and mean oocyte diameter were reduced and inversely correlated with the degree of bleaching, with complete failure of fertilization in the group of heavily bleached colonies. For moderately bleached soft corals, survival and growth of sexual offspring did not differ significantly from those of unbleached colonies. Although no further reductions in zooxanthellae densities in experimental soft corals were recorded throughout the subsequent second year, egg size and fecundity of the heavily bleached soft corals were still significantly reduced 20 months later. Severe bleaching clearly has long-term sub-lethal impacts, reducing overall reproductive output for at least two spawning seasons. Accepted: 1 June 2000     

Spring “bleaching” among <Emphasis Type="Italic">Pocillopora</Emphasis> in the Sea of Cortez,Eastern Pacific

A mild bleaching event was observed among Pocillopora spp. in the southern Gulf of California in the spring of 2006. Uniform bleaching occurred in numerous colonies on the upper portions of their branches. Most (∼90%) colonies that exhibited bleaching contained a species of endosymbiotic dinoflagellate, Symbiodinium C1b-c, which differed from the Symbiodinium D1 found inhabiting most unbleached colonies. Analysis of chlorophyll fluorescence, indicated a decline in photosystem II photochemical activity, especially among colonies populated with C1b-c. By early August, most affected colonies had recovered their normal pigmentation and fluorescence values were once again high for all colonies. No mortality was observed among tagged bleached colonies nor did symbiont species composition change during recovery. This unusual episode of bleaching did not appear to be a response to thermal stress, but may have been triggered by high levels of solar radiation during a period of unseasonally high water clarity in the early spring.     

Endolithic algae: an alternative source of photoassimilates during coral bleaching

Recent reports of worldwide coral bleaching events leading to devastating coral mortality have caused alarm among scientists and resource managers. Differential survival of coral species through bleaching events has been widely documented. We suggest that among the possible factors contributing to survival of coral species during such events are endolithic algae harboured in their skeleton, providing an alternative source of energy. We studied the dynamics of photosynthetic pigment concentrations and biomass of endoliths in the skeleton of the encrusting coral Oculina patagonica throughout a bleaching event. During repeated summer bleaching events these endolithic algae receive increased photosynthetically active radiation, increase markedly in biomass, and produce increasing amounts of photoassimilates, which are translocated to the coral. Chlorophyll concentrations and biomass of endoliths were 4.6 +/- 1.57 and 1570 +/- 427 microg cm(-2) respectively, in skeletons of relatively healthy colonies (0-40% bleaching) but up to 14.8 +/- 2.5 and 4036 +/- 764 microg cm(-2) endolith chlorophyll and biomass respectively, in skeletons of bleached colonies (greater than 40% bleaching). The translocation dynamics of (14)C-labelled photoassimilates from the endoliths to bleached coral tissue showed significantly higher 14C activity of the endoliths harboured within the skeletons of bleached corals than that of the endoliths in non-bleached corals. This alternative source of energy may be vital for the survivorship of O. patagonica, allowing gradual recruitment of zooxanthellae and subsequent recovery during the following winter.     

Lateral diffusion of rhodopsin in photoreceptor cells measured by fluorescence photobleaching and recovery.

Frog rod outer segments were labeled with the sulfhydryl-reactive label iodoacetamido tetramethylrhodamine. The bulk of the label reacted with the major disk membrane protein, rhodopsin. Fluorescence photobleaching and recovery (FPR) experiments on labeled rods showed that the labeled proteins diffused rapidly in the disk membranes. In these FPR experiments we observed both the recovery of fluorescence in the bleached spot and the loss of fluorescence from nearby, unbleached regions of the photoreceptor. These and previous experiments show that the redistribution of the fluorescent labeled proteins after bleaching was due to diffusion. The diffusion constant, D, was (3.0 +/- 10(-9) cm2 s-1 if estimated from the rate of recovery of fluorescence in the bleached spot, and (5.3 +/- 2.4) x 10(-9) cm2 s-1 if estimated from the rate of depletion of fluorescence from nearby regions. The temperature coefficient, Q10, for diffusion was 1.7 +/- 0.5 over the range 10 degrees--29 degrees C. These values obtained by FPR are in good agreement with those previously obtained by photobleaching rhodopsin in fresh, unlabeled rods. This agreement indicates that the labeling and bleaching procedures required by the FPR method did not significantly alter the diffusion rate of rhodopsin. Moreover, the magnitude of the diffusion constant for rhodopsin is that to be expected for an object of its diameter diffusing in a bilayer with the viscosity of the disk membrane. In contrast to the case of rhodopsin, FPR methods applied to other membrane proteins have yielded much smaller diffusion constants. The present results help indicate that these smaller diffusion constants are not artifacts of the method but may instead be due to interactions the diffusing proteins have with other components of the membrane in addition to the viscous drag imposed by the lipid bilayer.     

Coscinaraea marshae corals that have survived prolonged bleaching exhibit signs of increased heterotrophic feeding

Colonies of Coscinaraea marshae corals from Rottnest Island, Western Australia have survived for more than 11 months in various bleached states following a severe heating event in the austral summer of 2011. These colonies are situated in a high-latitude, mesophotic environment, which has made their long-term survival of particular interest as such environments typically suffer from minimal thermal pressures. We have investigated corals that remain unbleached, moderately bleached, or severely bleached to better understand potential survival mechanisms utilised in response to thermal stress. Specifically, Symbiodinium (algal symbiont) density and genotype, chlorophyll-a concentrations, and δ¹³C and δ¹⁵N levels were compared between colonies in the three bleaching categories. Severely bleached colonies housed significantly fewer Symbiodinium cells (p < 0.05) and significantly reduced chlorophyll-a concentrations (p < 0.05), compared with unbleached colonies. Novel Symbiodinium clade associations were observed for this coral in both severely and moderately bleached colonies, with clade C and a mixed clade population detected. In unbleached colonies, only clade B was observed. Levels of δ¹⁵N indicate that severely bleached colonies are utilising heterotrophic feeding mechanisms to aid survival whilst bleached. Collectively, these results suggest that these C. marshae colonies can survive with low symbiont and chlorophyll densities, in response to prolonged thermal stress and extended bleaching, and increase heterotrophic feeding levels sufficiently to meet energy demands, thus enabling some colonies to survive and recover over long time frames. This is significant as it suggests that corals in mesophotic and high-latitude environments may possess considerable plasticity and an ability to tolerate and adapt to large environmental fluctuations, thereby improving their chances of survival as climate change impacts coral ecosystems worldwide.     

Continuation of sexual reproduction in <Emphasis Type="Italic">Montipora capitata</Emphasis> following bleaching

Bleaching is generally expected to produce detrimental impacts on coral reproduction. This study compared the fecundity of bleached and unbleached colonies of the Hawaiian coral Montipora capitata. It was hypothesized that bleaching would have no effect on reproduction because previous studies have shown that Montipora capitata can increase heterotrophic feeding following bleaching. Reproductive parameters, total reproductive output (bundles released ml⁻¹ coral colony), number of eggs bundle⁻¹, and egg size, measured in the summer of 2005 did not differ between colonies that bleached or did not bleach during 2004. These data were collected following a single bleaching event and cannot be used to predict the outcome should bleaching episodes become more frequent or severe.     

Bleaching and mortality of reef organisms during a warming event in 1995 on the Caribbean coast of Costa Rica

Coral reefs at the Caribbean coast of Costa Rica were affected during a bleaching event associated with the 1995 warming of the Western Caribbean. During doldrum weather in late August 1995, reef organisms at Parque Nacional Cahuita were 62% and 7.4% bleached and dead respectively, whilst 67.6% bleached and 8.2% died in the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo. However, Cahuita had the highest mean number of bleached (257 +/- 51.1) and dead (30.5 +/- 5.6) colonies in the surveyed transects, and bleaching was observed down to a depth of 20 m. The most affected species (>10% of dead colonies) were the hydrocoral Millepora complanata and the scleractinian corals Montastraea spp. at Cahuita, and Porites furcata, Porites porites and M. complanata at Gandoca-Manzanillo. Mean seawater temperature was between 30.5 and 31.1 degrees C (0-18 m depth) during four days of observation at the end of August 1995. Coral reefs of the Costa Rican Caribbean coast have shown a rapid decline during the last 20 years due to natural and anthropogenic disturbances. The effect of the 1995 warming added more pressure to the already deteriorated reefs.     

High spatial variability in coral bleaching around Moorea (French Polynesia): patterns across locations and water depths

Mass coral bleaching events are one of the main threats to coral reefs. A severe bleaching event impacted Moorea, French Polynesia, between March and July 2002, causing 55+/-14% of colonies to suffer bleaching around the island. However, bleaching varied significantly across coral genera, locations, and as a function of water depth, with a bleaching level as high as 72% at some stations. Corals in deeper water bleached at a higher rate than those in shallow water, and the north coast was more impacted than the west coast. The relatively small scale of variability in bleaching responses probably resulted from the interaction between extrinsic factors, including hydrodynamic condition, and intrinsic factors, such as differential adaptation of the coral/algal association.     

Differential scanning calorimetry of bovine rhodopsin in rod-outer-segment disk membranes.

Rhodopsin-containing retinal rod disk membranes from cattle have been examined by differential scanning calorimetry. Under conditions of 67 mM phosphate pH 7.0, unbleached rod outer segment disk membranes gave a single major endotherm with a temperature of denaturation (Tm) of 71.9 +/- 0.4 degrees C and a thermal unfolding calorimetric enthalpy change (delta Hcal) of 700 +/- 17 kJ/mol rhodopsin. Bleached rod outer segment disk membranes (membranes that had lost their absorbance at 498 nm after exposure to orange light) gave a single major endotherm with a Tm of 55.9 +/- 0.3 degrees C and a delta Hcal of 520 +/- 17 kJ/mol opsin. Neither bleached nor unbleached rod outer segment disk membranes gave endotherms upon thermal rescans. When thermal stability is examined over the pH range of 4-9, the major endotherms of both bleached and unbleached rod outer segment disk membranes were found to show maximum stability at pH 6.1. The observed delta Hcal values for bleached and unbleached rod outer segment disk membranes exhibit membrane concentration dependences which plateau at protein concentrations beyond 1.5 mg/mL. For partially bleached samples of rod outer segment disk membranes, the calorimetric enthalpy change for opsin appears to be somewhat dependent on the degree of bleaching, indicating intramembrane nearest neighbor interactions which affect the unfolding of opsin. Delta Hcal and Tm are particularly useful for assessing stability and testing for completeness of regeneration of rhodopsin from opsin. Other factors such as sample preparation and the presence of low concentrations of ethanol also affect the delta Hcal values while the Tm values remain fairly constant. This shows that the delta Hcal is a sensitive parameter for monitoring environmental changes of rhodopsin and opsin.     

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean

Two naturally occurring colonies of Millepora alcicornis were monitored during 1997 and 1998, both years in which this species bleached in the Mexican Caribbean. One colony (HL) was naturally exposed to a high light environment and another nearby colony (LL) was exposed to 5.9 times lower light levels due to shadowing by a pier. For 10 days in August 1997, seawater temperatures in the surrounding reef lagoon rose up to 1.5 degrees C above the 6-year August average. The HL colony bleached to white during this period, whereas, the LL colony remained dark-brown colored. The HL colony recovered its normal dark-brown coloration (reversible bleaching) within several weeks, during which time the seawater temperatures returned to average. The following year, for 10 days, seawater temperatures rose up to 3 degrees C above the 7-year August average and both colonies bleached to white and neither colony recovered (irreversible bleaching). Both colonies were rapidly overgrown by algae and hydroids and, as of June 2003, no recovery has taken place. Prior to the 1997 bleaching, experiments using solar radiation showed that the quantum yield of photosystem II charge separation of branches from HL and LL colonies were affected for several hours by exposure to ultraviolet radiation (UVR, 280 to 400 nm), but recovered by the same evening, suggesting that UVR does not have long-term effects on photochemistry in M. alcicornis. In situ effective quantum yield of photosystem II charge separation (deltaF/Fm') measurements before the 1998 bleaching event indicate that both colonies were healthy in terms of the physiological status of their endosymbionts. During and after the 1998 bleaching event, both colonies showed a reduction in deltaF/Fm' and consequently an increase in excitation pressure on photosystem II. The data suggest that temperature is not the only factor that causes bleaching and that solar radiation may play an important role in coral bleaching.     

Cellular processes of bleaching in the Mediterranean coral Oculina patagonica

Annual bleaching of Oculina patagonica on the Israeli Mediterranean coastline has been reported since 1993, although the cellular mechanisms underlying the bleaching have not yet been investigated. This survey examined 48 coral colonies of O. patagonica (bleached and unbleached) from various sites along the Israeli coast. Histopathological investigations of bleached lesions revealed a loss of endosymbionts, and an apparent in situ degradation of the endosymbionts. In situ end labelling of bleaching lesions did not provide evidence of apoptotic cell death. Electron microscopy of bleaching lesions also demonstrated an apparent in situ degradation and no evidence of apoptotic cell death of the host.     

Caribbean massive corals not recovering from repeated thermal stress events during 2005–2013

Massive coral bleaching events associated with high sea surface temperatures are forecast to become more frequent and severe in the future due to climate change. Monitoring colony recovery from bleaching disturbances over multiyear time frames is important for improving predictions of future coral community changes. However, there are currently few multiyear studies describing long‐term outcomes for coral colonies following acute bleaching events. We recorded colony pigmentation and size for bleached and unbleached groups of co‐located conspecifics of three major reef‐building scleractinian corals (Orbicella franksi, Siderastrea siderea, and Stephanocoenia michelini; n = 198 total) in Bocas del Toro, Panama, during the major 2005 bleaching event and then monitored pigmentation status and changes live tissue colony size for 8 years (2005–2013). Corals that were bleached in 2005 demonstrated markedly different response trajectories compared to unbleached colony groups, with extensive live tissue loss for bleached corals of all species following bleaching, with mean live tissue losses per colony 9 months postbleaching of 26.2% (±5.4 SE) for O. franksi, 35.7% (±4.7 SE) for S. michelini, and 11.2% (±3.9 SE) for S. siderea. Two species, O. franksi and S. michelini, later recovered to net positive growth, which continued until a second thermal stress event in 2010. Following this event, all species again lost tissue, with previously unbleached colony species groups experiencing greater declines than conspecific sample groups, which were previously bleached, indicating a possible positive acclimative response. However, despite this beneficial effect for previously bleached corals, all groups experienced substantial net tissue loss between 2005 and 2013, indicating that many important Caribbean reef‐building corals will likely suffer continued tissue loss and may be unable to maintain current benthic coverage when faced with future thermal stress forecast for the region, even with potential benefits from bleaching‐related acclimation.     

Slow bleach-induced cooperative fluorescence changes in bovine photoreceptor disk membranes

The increase of protein fluorescence in suspensions of bovine photoreceptor disk membrane fragments was investigated under various conditions. The increment of fluorescence on bleaching was dependent on temperature, being about 10% at 10°C and 50% at 40°C. The time course of fluorescence increase also depended on temperature, and the activation energy was estimated to be about 14 kcal/mole. The relationship between the extent of fluorescence increase and the degree of bleaching was not stoichiometric. It was concluded that the environment of tryptophan residues of unbleached rhodopsin molecule(s) located near a bleached rhodopsin molecule is cooperatively modified upon bleaching (to a more hydrophobic environment).     

Optical spectra and pigmentation of Caribbean reef corals and macroalgae

 Coastal reef degradation and widespread bleaching of corals, i.e. loss of pigments and/or symbiotic zooxanthellae, is increasing globally. Remote sensing from boats, aircraft or satellites has great potential for assessing the extent of reef change, but will require ground-verified spectral algorithims characteristic of healthy and degraded reef populations. We collected seven species of Caribbean reef corals and also representative macroalgae from reefs near Lee Stocking Island, Bahamas and quantified their pigments using high performance liquid chromatography. We also measured the fluorescence and reflectance spectra of corals and macroalgae using an in situ benthic spectrofluorometer. In visibly pigmented (unbleached) coral from 4 to 5 m depth, the mean (±SD) surface density of pigments (3.0±1.3 μg chlorophyll-a cm^-2 and 2.1±0.7 μg peridinin cm^-2) was similar between colonies of the same species, but differed among species. The mean quantity of pigment per zooxanthella (1.8±0.9 pg chl-a cell^-1 and 1.4±0.7 pg peridinin cell^-1) also differed among species and sometimes between colonies of the same species. Chl-a and peridinin densities per surface area of coral were positively correlated. When excited with blue light (480 nm), macroalgae and corals had typical chlorophyll fluorescence with a peak at 680 nm and a smaller shoulder peak at 730 to 740 nm. Most corals, unlike macroalgae, also had distinct fluorescence peaks between 500 and 530 nm. In visibly bleached corals 680 nm fluorescence was greatly reduced in amplitude. Pigmented coral, under natural lighting conditions, had a reflected light peak at about 570 nm. Reflectance increased over all wavelengths in bleached corals, with the greatest increase at the wavelengths where chlorophyll and accessory pigments absorb light, i.e. 670 and 450 to 550 nm. Both fluorescence and reflectance spectra appear promising to remotely differentiate between pigmented and bleached coral and between coral and macroalgae. Accepted: 15 March 1999     

Choosing the appropriate spatial resolution for monitoring coral bleaching events using remote sensing

Bleached corals provide a strong optical signal that suggests that remote sensing investigations of major bleaching events are feasible using airborne or satellite sensors. However, patchy coral cover, varying intensities of bleaching, and water depths are likely to limit the application of remote sensing techniques in monitoring and mapping coral bleaching. Today, satellite multispectral sensors routinely provide images of reefs from 4 m (Ikonos) to 30 m resolution (Landsat); however, the adequacy of these sensors for monitoring and mapping bleaching events remains unclear. To clarify these issues, scanned aerial photographs acquired during the 1998 bleaching event over the Great Barrier Reef (Australia) were analyzed at various spatial resolutions, from 10 cm to 5 m. We found that the accuracy of mapping bleaching is highly sensitive to spatial resolution. Highest accuracy was obtained at 10 cm resolution for detection of totally bleached colonies. At 1 m resolution, as much as 50% of the 10-cm resolution signal is lost, though the spatial patterns remain correctly described. Partially bleached (pale) corals are difficult to detect even in aerial surveys, leading to an underestimation of overall bleaching levels (total and partial bleaching) in aerial photos compared to in-situ surveys. If data volume and processing time are limiting factors, local variance analysis suggests that the optimal resolution necessary to capture spatial patterns of bleaching is in the range 40-80 cm.     

Microscopic observations of recovery in the reef-building scleractinian coral,Montastrea annularis,after bleaching on a Cayman reef

Living tissues of a single massive colony of the reef-building scleractinian coral, M. annularis, were sampled at one month intervals following the observation that areas of marked discoloration (bleaching) had developed by the beginning of the summer of 1988. Histological analysis of replicate plugs of tissue from bleached and unbleached regions of that colony allowed comparison of time-matched samples as well as zone-matched samples over a period of six months. During that interval, the entire colony was restored to a uniform and normal degree of pigmentation. Histology of the bleached zones documents the gradual accumulation of zooxanthellae and the thickening of the gastrodermal epithelium of the coral. Once reconstituted, the previously bleached gastrodermis, repopulated with algal symbionts, is indistinguishable from unbleached tissue in the coral colony.     

The effect of prolonged “bleaching” on skeletal banding and stable isotopic composition in Montastrea annularis

X-radiography and carbon and oxygen stable isotope analysis have been used to examine the effects of prolonged bleaching on the growth rate and chemical composition of the skeleton of the massive reef coral, Montastrea annularis. The post-bleaching linear growth of one colony that remained bleached for 10 to 12 months following the 1987 Caribbean-wide bleaching event was only 37% of mean annual growth from pre-bleaching years, and was manifest as a loss of the following year's low density band. Two colonies that did not bleach (normal) and two that bleached and regained their coloration (recovered) had linear growth rates over the same period that were 81 to 98% of mean pre-bleaching annual growth. Linear growth by a third recovered coral was 66% of pre-bleaching growth. No sub-annual stress bands were associated with the bleaching. The skeleton of the bleached colony had carbon and oxygen isotopic compositions that were reduced in range and enriched (increased) in both ¹³C and ¹⁸O in the post-bleaching year. The skeletons of two of the nine colonies, one bleached and one recovered, had depleted (reduced) ¹⁸O values (-5.3 and -4.8%., respectively) during the bleaching episode that agree with the suggestion that positive temperature anomalies occurred during, and may have caused, the bleaching event. The range and values for all other normal and recovered corals, however, were not different between the post-bleaching year and previous years. Our data suggest that stress bands and isotopic analysis of coral skeletons may not always be reliable tools for examining the occurrence, cause or effects of certain discrete stress events that may interrupt skeletal growth.     

The effects of prolonged “bleaching” on the tissue biomass and reproduction of the reef coral Montastrea annularis

Colonies of Montastrea annularis from Carysfort Reef, Florida, that remained bleached seven months after the 1987 Caribbean bleaching event were studied to determine the long term effects of bleaching on coral physiology. Two types of bleached colonies were found: colonies with low numbers of zooxanthellae with normal pigment content, and a colony with high densities of lowpigment zooxanthellae. In both types, the zooxanthellae had an abnormal distribution within polyp tissues: highest densities were observed in basal endoderm and in mesenteries where zooxanthellae are not normally found. Bleached corals had 30% less tissue carbon and 44% less tissue nitrogen biomass per skeletal surface area, but the same tissue C:N ratio as other colonies that either did not bleach (normal) or that bleached and regained their zooxanthellae (recovered). Bleached corals were not able to complete gametogenesis during the reproductive season following the bleaching, while recovered corals were able to follow a normal gametogenic cycle. It appears that bleached corals were able to survive the prolonged period without nutritional contribution from their zooxanthellae by consuming their own structural materials for maintenance, but then, did not have the resources necessary for reproduction. The recovered corals, on the other hand, must have regained their zooxanthellae soon after the bleaching event since neither their tissue biomass nor their ability to reproduce were impaired.     

Coral microbiome diversity reflects mass coral bleaching susceptibility during the 2016 El Niño heat wave

Repeat marine heat wave‐induced mass coral bleaching has decimated reefs in Seychelles for 35 years, but how coral‐associated microbial diversity (microalgal endosymbionts of the family Symbiodiniaceae and bacterial communities) potentially underpins broad‐scale bleaching dynamics remains unknown. We assessed microbiome composition during the 2016 heat wave peak at two contrasting reef sites (clear vs. turbid) in Seychelles, for key coral species considered bleaching sensitive (Acropora muricata, Acropora gemmifera) or tolerant (Porites lutea, Coelastrea aspera). For all species and sites, we sampled bleached versus unbleached colonies to examine how microbiomes align with heat stress susceptibility. Over 30% of all corals bleached in 2016, half of which were from Acropora sp. and Pocillopora sp. mass bleaching that largely transitioned to mortality by 2017. Symbiodiniaceae ITS2‐sequencing revealed that the two Acropora sp. and P. lutea generally associated with C3z/C3 and C15 types, respectively, whereas C. aspera exhibited a plastic association with multiple D types and two C3z types. 16S rRNA gene sequencing revealed that bacterial communities were coral host‐specific, largely through differences in the most abundant families, Hahellaceae (comprising Endozoicomonas), Rhodospirillaceae, and Rhodobacteraceae. Both Acropora sp. exhibited lower bacterial diversity, species richness, and community evenness compared to more bleaching‐resistant P. lutea and C. aspera. Different bleaching susceptibility among coral species was thus consistent with distinct microbiome community profiles. These profiles were conserved across bleached and unbleached colonies of all coral species. As this pattern could also reflect a parallel response of the microbiome to environmental changes, the detailed functional associations will need to be determined in future studies. Further understanding such microbiome‐environmental interactions is likely critical to target more effective management within oceanically isolated reefs of Seychelles.