Occurrence of the putatively heat-tolerant <Emphasis Type="Italic">Symbiodinium</Emphasis> phylotype D in high-latitudinal outlying coral communities

Biogeographic investigations have suggested that coral-symbiont associations can adapt to higher temperatures by hosting a heat-tolerant Symbiodinium, phylotype D. It is hypothesized that phylotype D is absent in high latitudes due to its heat-tolerant characteristics. In this study, this hypothesis was tested by examining the symbiont diversity in a scleractinian coral, Oulastrea crispata, throughout its entire latitudinal distribution range in the West Pacific. Molecular phylotyping of the 5′-end of the nuclear large subunit of ribosomal DNA (lsu rDNA) indicated that phylotype D was the dominant Symbiodinium in O. crispata from the tropical reefs to the marginal non-reefal coral communities. Several colonies of tropical populations were associated with phylotype C, either alone or simultaneously with phylotype D. Analysis of the polymerase chain reaction products using single-strand conformation polymorphism (SSCP) detected relatively low densities of phylotype C in most of the O. crispata colonies surveyed. These results provide evidence for the occurrence of phylotype D in cold-water outlying coral communities. The dominant occurrence of phylotype C in some O. crispata colonies on tropical reefs and the relatively low densities of phylotype C identified by SSCP in subtropical and temperate populations show that the dominant symbiont type can vary in this coral species and that multiple symbionts can co-occur in the same host.     

Visibly healthy corals exhibit variable pigment concentrations and symbiont phenotypes

Understanding the natural variability of photosynthetic pigment ranges and distributions in healthy corals is central to evaluating how useful these measurements are for assessing the health and bleaching status of endosymbiotic reef-building corals. This study examined the photosynthetic pigment variability in visibly healthy Porites lobata and Porites lutea corals from Kaneohe Bay, Hawaii and explored whether pigment variability was related to the genetic identity or phenotypic characteristics of the symbionts. Concentrations of the photosynthetic pigments chlorophyll a, peridinin, chlorophyll c ₂ , diadinoxanthin, diatoxanthin, β,β-carotene and dinoxanthin were quantified using high-performance liquid chromatography (HPLC). Pigment concentrations were found to range 1.5–10 fold in colonies of each species at similar depths (0–2, 2–4, 10–15 and 19–21 m). Despite the high pigment variability, pigment ratios for each species were relatively conserved over the 0–21 m depth gradient. The genetic identity of the symbiont communities was examined for each colony using 18S nuclear ribosomal DNA (nrDNA) restriction fragment length polymorphisms. All colonies contained symbionts belonging to clade C. The density and phenotypic characteristics of the symbionts were explored using flow cytometry, and fluorescence and side scatter (cell size) properties revealed phenotypically distinct symbiont subpopulations in every colony. The symbiont subpopulations displayed pigment trends that may be driven by acclimatization to irradiance microenvironments within the host. These results highlight the biological complexity of healthy coral–symbiont associations and the need for future research on pigments and symbiont subpopulation dynamics.     

Chronic parrotfish grazing impedes coral recovery after bleaching

Coral bleaching, in which corals become visibly pale and typically lose their endosymbiotic zooxanthellae (Symbiodinium spp.), increasingly threatens coral reefs worldwide. While the proximal environmental triggers of bleaching are reasonably well understood, considerably less is known concerning physiological and ecological factors that might exacerbate coral bleaching or delay recovery. We report a bleaching event in Belize during September 2004 in which Montastraea spp. corals that had been previously grazed by corallivorous parrotfishes showed a persistent reduction in symbiont density compared to intact colonies. Additionally, grazed corals exhibited greater diversity in the genetic composition of their symbiont communities, changing from uniform ITS2 type C7 Symbiodinium prior to bleaching to mixed assemblages of Symbiodinium types post-bleaching. These results suggest that chronic predation may exacerbate the influence of environmental stressors and, by altering the coral-zooxanthellae symbiosis, such abiotic-biotic interactions may contribute to spatial variation in bleaching processes.     

Seasonal and local spatial patterns in the upper thermal limits of corals on the inshore Central Great Barrier Reef

 Experimental studies of the upper thermal limits of corals from Orpheus Island, an inshore reef in the central Great Barrier Reef, show that Acropora formosa has a 5-day 50%-bleaching threshold of between 31 and 32 °C in summer, only 2 to 3 °C higher than local mean summer temperatures (29 °C). Summer bleaching thresholds for Pocillopora damicornis and A. elseyi were 1 °C higher (between 32 and 33 °C). The winter bleaching threshold of Pocillopora damicornis was 1 °C lower than its summer threshold, indicating that seasonal acclimatisation may take place. This seasonal difference raises the possibility that at least some corals may be capable of short-term thermal acclimatisation. Neither P. damicornis nor A. elseyi showed habitat-specific (reef flat versus reef slope) differences in bleaching thresholds. Further, colonies of P. damicornis collected from sites 3 km apart also showed no difference in bleaching threshold despite populations of this species responding differently at these two sites during a natural bleaching event. The bleaching thresholds determined in this study are best considered as the maximum tolerable temperatures for local populations of these species because they were determined in the absence of additional stressors (e.g. high light) which often co-occur during natural bleaching events. We consider the 5-day 50% bleaching thresholds determined in these experiments to be fair indicators of upper thermal limits, because >50% of a sample population died when allowed to recover in situ. We found a delay of up to a month in the bleaching response of corals following thermal stress, a result that has implications for identifying the timing of stressful conditions in natural bleaching events. Accepted: 26 May 1999     

Symbiotic crabs maintain coral health by clearing sediments

Stony corals are the foundation of coral reef ecosystems and form associations with other reef species. Many of these associations may be ecologically important and play a role in maintaining the health and diversity of reef systems, rendering it critical to understand the influence of symbiotic organisms in mediating responses to perturbation. This study demonstrates the importance of an association with trapeziid crabs in reducing adverse effects of sediments deposited on corals. In a field experiment, mortality rates of two species of branching corals were significantly lowered by the presence of crabs. All outplanted corals with crabs survived whereas 45–80% of corals without crabs died within a month. For surviving corals that lacked crabs, growth was slower and tissue bleaching and sediment load were higher. Laboratory experiments revealed that corals with crabs shed substantially more of the sediments deposited on coral surfaces, but also that crabs were most effective at removing grain sizes that were most damaging to coral tissues. The mechanism underlying this symbiotic relationship has not been recognized previously, and its role in maintaining coral health is likely to become even more critical as reefs worldwide experience increasing sedimentation.     

Highly stable symbioses among western Atlantic brooding corals

The reproductive mode of corals largely determines how zooxanthellae (Symbiodinium spp.) are acquired. Typically, broadcast spawning corals obtain symbionts from the surrounding environment, whereas most brooders transfer symbionts from maternal parent to offspring. Brooding corals are therefore predicted to harbor stable communities of Symbiodinium. This study documents the associations between Symbiodinium spp. and brooding corals in response to seasonal environmental fluctuations. Between March 2002 and December 2005, endosymbiont identity was determined seasonally from replicate colonies (n = 6) of three brooding species, Agaricia agaricites, Porites astreoides and Siderastrea radians, from shallow environments (1–4 m) of the Florida Keys and Bahamas. Symbionts were identified via denaturing gradient gel electrophoresis (DGGE) of the internal transcribed spacer 2 (ITS2) region. No change was detected in the Symbiodinium communities harbored within these brooding colonies. Additionally, no change in symbiosis was observed through a moderate bleaching event, thereby demonstrating that some bleached corals recover without changing symbionts.     

Understanding diversity in coral-algal symbiosis: a cluster-based approach to interpreting fine-scale genetic variation in the genus <Emphasis Type="Italic">Symbiodinium</Emphasis>

Reef corals associate with an extraordinary diversity of dinoflagellate endosymbionts (genus Symbiodinium), and this diversity has become critical to understanding how corals respond to environmental changes. A popular molecular marker for Symbiodinium diversity, the Internal Transcribed Spacer-2 (ITS-2) region of ribosomal DNA, has revealed hundreds of distinct variants that are generally interpreted as representing different species, even though many have not been systematically tested for functional or ecological differentiation. Many of these variants are only minimally divergent from one another (1 bp or less), and others occupy basal nodes of traditional species phylogenies (“living ancestors”), indicating that some Symbiodinium ITS-2 diversity may represent intraspecific sequence variation. This hypothesis was tested for Symbiodinium clades A–D (the dominant symbionts of reef corals) through the construction of statistical parsimony networks of ITS-2 sequence diversity, and identification of clusters of closely related sequences within these networks. Initial assessments indicated that ecological differentiation exists between, but not within, these clusters. This approach, although imperfect in its ability to identify species boundaries in all cases, nevertheless dramatically reduces “species” diversity in Symbiodinium (from ~175 to 35). This testable alternative hypothesis indicates that, in Symbiodinium, “species” consist of clusters of closely related ITS-2 sequences diverging from ancestral variants that are typically ecologically dominant. A cluster-based view of Symbiodinium ITS-2 diversity improves our ability to: (1) construct well-supported symbiont phylogenies; (2) establish functional niches for symbiont species; and (3) understand flexibility and specificity within coral-algal symbioses. This cluster-based approach can ultimately be integrated with emerging population-level datasets (microsatellites and microsatellite flanking regions) to improve understanding of species diversity in Symbiodinium. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Communicated by Biology Editor Dr Ruth Gates     

Change in algal symbiont communities after bleaching,not prior heat exposure,increases heat tolerance of reef corals

Mutualistic organisms can be particularly susceptible to climate change stress, as their survivorship is often limited by the most vulnerable partner. However, symbiotic plasticity can also help organisms in changing environments by expanding their realized niche space. Coral–algal (Symbiodinium spp.) symbiosis exemplifies this dichotomy: the partnership is highly susceptible to ‘bleaching’ (stress‐induced symbiosis breakdown), but stress‐tolerant symbionts can also sometimes mitigate bleaching. Here, we investigate the role of diverse and mutable symbiotic partnerships in increasing corals' ability to thrive in high temperature conditions. We conducted repeat bleaching and recovery experiments on the coral Montastraea cavernosa, and used quantitative PCR and chlorophyll fluorometry to assess the structure and function of Symbiodinium communities within coral hosts. During an initial heat exposure (32 °C for 10 days), corals hosting only stress‐sensitive symbionts (Symbiodinium C3) bleached, but recovered (at either 24 °C or 29 °C) with predominantly (>90%) stress‐tolerant symbionts (Symbiodinium D1a), which were not detected before bleaching (either due to absence or extreme low abundance). When a second heat stress (also 32 °C for 10 days) was applied 3 months later, corals that previously bleached and were now dominated by D1a Symbiodinium experienced less photodamage and symbiont loss compared to control corals that had not been previously bleached, and were therefore still dominated by Symbiodinium C3. Additional corals that were initially bleached without heat by a herbicide (DCMU, at 24 °C) also recovered predominantly with D1a symbionts, and similarly lost fewer symbionts during subsequent thermal stress. Increased thermotolerance was also not observed in C3‐dominated corals that were acclimated for 3 months to warmer temperatures (29 °C) before heat stress. These findings indicate that increased thermotolerance post‐bleaching resulted from symbiont community composition changes, not prior heat exposure. Moreover, initially undetectable D1a symbionts became dominant only after bleaching, and were critical to corals' resilience after stress and resistance to future stress.     

Symbiont diversity in scleractinian corals from tropical reefs and subtropical non-reef communities in Taiwan

We examined zooxanthellae diversity in scleractinian corals from southern Taiwan and the Penghu Archipelago, a tropical coral reef and a subtropical non-reefal community, respectively. Zooxanthellae diversity was investigated in 52 species of scleractinian corals from 26 genera and 13 families, using restriction fragment length polymorphism (RFLP), and phylogenetic analyses of the nuclear small-subunit ribosomal DNA (nssrDNA) and large-subunit ribosomal DNA (nlsrDNA). RFLP and phylogenetic analyses of nuclear-encoded ribosomal RNA genes showed that Symbiodinium clade C was the dominant zooxanthellae in scleractinian corals in the seas around Taiwan; Symbiodinium clade D was also found in some species. Both Symbiodinium clade C and D were found in colonies of seven species of scleractinian corals. Symbiodinium clade D was associated with corals that inhabit either shallow water or the reef edge in deep water, supporting the hypothesis that Symbiodinium clade D is a relatively stress-tolerant zooxanthellae found in marginal habitats.Communicated by Biological Editor H.R. Lasker     

Ratiometric imaging of gastrodermal lipid bodies in coral–dinoflagellate endosymbiosis

Cnidaria–dinoflagellate endosymbiosis is the phenomenon of autotrophic symbionts living inside the gastrodermal cells of their animal hosts. The molecular mechanism that regulates this association remains unclear. Using quantitative microscopy, we now provide evidence that the dynamic lipid changes in gastrodermal “lipid bodies” (LBs) reflect the symbiotic status of the host cell and its symbiont in the hermatypic coral Euphyllia glabrescens. By dual-emission ratiometric imaging with a solvatochromic fluorescent probe, Nile red (9-diethylamino-5H-benzo[α]phenoxazine-5-one), we showed that the in situ distribution of polar versus neutral lipids in LBs in living gastrodermal cells and symbionts can be analyzed. The ratio of Nile red fluorescence at red (R) versus green (G) wavelength region (i.e., R/G ratio) correlated with the relative molar ratio of polar (P) versus neutral (NP) lipids (i.e., P/NP ratio). The R/G ratio in host LBs increased after bleaching, indicating a decrease in neutral lipid accumulation in gastrodermal cells. On the other hand, neutral lipid accumulation inside the symbiont LBs resulted in gradual decreases of the R/G ratio as a result of bleaching. In comparison with the bleaching event, there was no relative lipid concentration change in host LBs under continual light or dark treatments as shown by insignificant R/G ratio shift. Patterns of R/G ratio shift in symbiont LBs were also different between corals undergoing bleaching and continual light/dark treatment. In the latter, there was little lipid accumulation in symbionts, with no resulting R/G ratio decrease. These results, demonstrating that the symbiotic status positively correlated with morphological and compositional changes of lipid bodies, not only highlight the pivotal role of LBs, but also implicate an involvement of lipid trafficking in regulating the endosymbiosis.     

The effect of sub-lethal increases in temperature on the growth and population trajectories of three scleractinian corals on the southern Great Barrier Reef

To date, coral death has been the most conspicuous outcome of warming tropical seas, but as temperatures stabilize at higher values, the consequences for the corals remaining will be mediated by their demographic responses to the sub-lethal effects of temperature. To gain insight into the nature of these responses, here I develop a model to test the effect of increased temperature on populations of three pocilloporid corals at One Tree Island, near the southern extreme of the Great Barrier Reef (GBR). Using Seriatopora hystrix, S. caliendrum and Pocillopora damicornis as study species, the effects of temperature on growth were determined empirically, and the dynamics of their populations determined under natural temperatures over a 6-month period between 1999 and 2000 [defined as the study year (SY)]. The two data sets were combined in a demographic test of the possibility that the thermal regime projected for the southern GBR in the next 55–83 years—warmer by 3°C than the study year (the SY+3 regime), which is equivalent to 1.4°C warmer than the recent warm year of 1998—would alter coral population trajectories through the effects on coral growth alone; the analyses first were completed by species, then by family after pooling among species. Laboratory experiments showed that growth rates (i.e., calcification) varied significantly among species and temperatures, and displayed curvilinear thermal responses with growth maxima at ∼27.1°C. Based on these temperature-growth responses, the SY+3 regime is projected to: (1) increase annualized growth rates of all taxa by 24–39%, and defer the timing of peak growth from the summer to the autumn and spring, (2) alter the intrinsic rate of population growth (λ) for S. hystrix (λ decreases 26%) and S. caliendrum (λ increases 5%), but not for P. damicornis, and (3) have a minor effect on λ (a 0.3% increase) for the Pocilloporidae, largely because λ varies more among species than it does between temperatures. Ten-year population projections suggest that the effects of a sub-lethal increase in temperature (i.e., the SY+3 regime) are relatively small compared to the interspecific differences in population dynamics, but nevertheless will alter the population size and increase the relative abundance of large colonies at the expense of smaller colonies for all three species, as well as the Pocilloporidae. These effects may play an important role in determining the nuances of coral population structure as seawater warms, and their significance may intensity if the coral species pool is depleted of thermally sensitive species by bleaching.     

Maintenance of fish diversity on disturbed coral reefs

Habitat perturbations play a major role in shaping community structure; however, the elements of disturbance-related habitat change that affect diversity are not always apparent. This study examined the effects of habitat disturbances on species richness of coral reef fish assemblages using annual surveys of habitat and 210 fish species from 10 reefs on the Great Barrier Reef (GBR). Over a period of 11 years, major disturbances, including localised outbreaks of crown-of-thorns sea star (Acanthaster planci), severe storms or coral bleaching, resulted in coral decline of 46–96% in all the 10 reefs. Despite declines in coral cover, structural complexity of the reef framework was retained on five and species richness of coral reef fishes maintained on nine of the disturbed reefs. Extensive loss of coral resulted in localised declines of highly specialised coral-dependent species, but this loss of diversity was more than compensated for by increases in the number of species that feed on the epilithic algal matrix (EAM). A unimodal relationship between areal coral cover and species richness indicated species richness was greatest at approximately 20% coral cover declining by 3–4 species (6–8% of average richness) at higher and lower coral cover. Results revealed that declines in coral cover on reefs may have limited short-term impact on the diversity of coral reef fishes, though there may be fundamental changes in the community structure of fishes.     

Skeletal isotope microprofiles of growth perturbations in<Emphasis Type="Italic"> Porites</Emphasis> corals during the 1997–1998 mass bleaching event

Severe coral bleaching occurred throughout the tropics in 1997/98. We report high-resolution skeletal oxygen isotope (¹⁸O) and carbon isotope (¹³C) microprofiles for bleached corals from Pandora Reef, Great Barrier Reef, and Ishigaki Island, Japan, in order to examine the ability of Porites corals to record clear signals of bleaching. Analysis of the annual cycle in ¹⁸O revealed abrupt reductions in skeletal extension immediately after the 1997–98 summer temperature maximum, indicating that bleaching inhibits coral calcification. Skeletal ¹³C in the Ishigaki corals showed lower values during bleaching, indicating depressed coral metabolism associated with a reduction in calcification. In contrast, microprofiles of skeletal ¹³C from the shaded sides of Pandora Reef corals exhibited little change, possibly because algal photosynthesis was already slow prior to bleaching, thus subduing the ¹³C-response to bleaching. Comparison of ¹⁸O microprofiles from bleached corals with instrumental temperature records showed that Porites corals can recover following 5 months with little skeletogenesis. The results indicate that isotopic microprofiling may be the key to identifying gaps in coral growth that are diagnostic of past bleaching events. We have tested this hypothesis using blue UV fluorescent bands to guide us to coral skeleton where isotope microprofiling identifies bleaching events in 1986, 1989, and 1990. These events, detected by proxy, suggest that coral bleaching may have occurred more commonly on Ishigaki Island than previously recorded.     

Population dynamics of zooxanthellae during a bacterial bleaching event

Each summer 80–90% of the colonies of Oculina patagonica undergo bleaching off the Mediterranean coast of Israel. To investigate fluctuations through a yearly bleaching cycle, monthly measurements of zooxanthella density, mitotic index and chlorophyll-a concentration were conducted. Results showed (1) a significant negative correlation between sea surface temperature (SST) and zooxanthella density; (2) both significantly lower zooxanthella mitotic index and higher chlorophyll-a per zooxanthella content during the bleaching season compared with the non-bleaching period; (3) prior to bleaching, a lag between the peak of zooxanthella density and chlorophyll-a concentration followed by a similar lag during recovery. Zooxanthella density declined significantly between March and May while chlorophyll-a concentration peaked in April, and then declined. Zooxanthella density increased significantly in November while chlorophyll-a concentration increased significantly in January. We conclude that during bacterial bleaching events, zooxanthellae are severely damaged. However, by the time of the following bleaching event the coral tissues regain their “normal” (pre-bleaching) zooxanthella population density.     

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.     

The importance of zooplankton to the daily metabolic carbon requirements of healthy and bleached corals at two depths

Bleached and non-bleached fragments of three species of Hawaiian corals were exposed to enhanced and ambient concentrations of zooplankton at 1 and 6 m depth to determine the contribution of zooplankton to the coral's daily carbon budget. The size and taxonomic grouping were recorded for every zooplankton captured and the relative input of zooplankton of different size classes was determined. The contribution of heterotrophy to animal respiration (CHAR) was calculated using an improved method that included the proportionate contribution of zooplankton from all size classes. Results show that the proportionate effects of species, depth and bleaching treatments on coral feeding rates were not significantly different between ambient and enhanced zooplankton concentrations. Corals captured the same size and assemblage of zooplankton under all evaluated conditions, and preferentially captured plankters smaller than 400 µm. Feeding rates of Porites lobata increased with depth regardless of bleaching status. Feeding rates of Porites compressa increased with depth in non-bleached corals, but not in bleached corals. Within depth, feeding rates of bleached Montipora capitata increased, P. compressa decreased and P. lobata remained unchanged relative to non-bleached fragments. Therefore, the feeding response of corals to the same disturbance may vary considerably. Calculated CHAR values show that heterotrophic carbon from zooplankton plays a much larger role in the daily carbon budget of corals than previously estimated, accounting for 46% of some coral species' daily metabolic carbon requirements when healthy and 147% when bleached. Thus, heterotrophically acquired carbon made an important contribution to the daily carbon budget of corals under all experimental conditions. These results suggest that the relative importance of autotrophic and heterotrophic carbon to a coral's energetic needs is mediated by a coral's bleaching status and environment, and should be considered on a continuum, from 100% photoautotrophy to 100% heterotrophy.     

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     

In situ measured seasonal variations in F v/F m of two common Red Sea corals

Pulse amplitude modulated (PAM) fluorometry has been suggested as a tool for estimating environmental stresses on corals. However, information regarding natural changes in maximal quantum yields (F _v/F _m) of corals during “normal” (i.e. non-bleaching) years has been limited. In this study, seasonal variations in F _v/F _m for Stylophora pistillata and Favia favus, measured in situ, correlated with seasonal changes in solar irradiance but not in sea temperature. Interactions between sea temperature and irradiance were further studied by growing these corals and Pocillopora damicornis under controlled conditions. Exposure to high light with normal or high temperatures resulted in lower F _v/F _m values than exposure to low light at both temperatures. Thus, high irradiances may cause decreased F _v/F _m values in corals at least as much as, if not more than, high temperatures. Such seasonal variations should be taken into account when using PAM fluorometry as a diagnostic tool for predicting coral bleaching.     

Recovery without resilience: persistent disturbance and long-term shifts in the structure of fish and coral communities at Tiahura Reef, Moorea

Disturbances have a critical effect on the structure of natural communities. In this study long-term changes were examined in the reef community at Tiahura Reef, on the northern coast of Moorea, which had been subject to many and varied disturbances over the last 25 years. Tiahura Reef was subject to an outbreak of crown-of-thorns starfish (Acanthaster planci) in 1980–1981, causing significant declines in the abundance of scleractinian corals and butterflyfishes. By 2003, the abundance of corals and butterflyfishes had returned to former levels, but despite this apparent recovery, the species composition of coral communities and butterflyfish assemblages was very different from those recorded in 1979. Ongoing disturbances (including further outbreaks of crown-of-thorns starfish, cyclones, and coral bleaching events) appear to have prevented recovery of many important coral species (notably, Acropora spp.), which has had subsequent effects on the community structure of coral-feeding butterflyfishes. This study shows that recurrent disturbances may have persistent effects on the structure and dynamics of natural communities.     

Bleached Porites compressa and Montipora capitata corals catabolize ��13C-enriched lipids

Corals rely on stored energy reserves (i.e., lipids, carbohydrates, and protein) to survive bleaching events. To better understand the physiological implications of coral bleaching on lipid catabolism and/or synthesis, we measured the δ¹³C of coral total lipids (δ¹³C_TL) in experimentally bleached (treatment) and non-bleached (control) Porites compressa and Montipora capitata corals immediately after bleaching and after 1.5 and 4 months of recovery on the reef. Overall δ¹³C_TL values in treatment corals were significantly lower than in control corals because of a 1.9 and 3.4‰ decrease in δ¹³C_TL immediately after bleaching in P. compressa and M. capitata, respectively. The decrease in δ¹³C_TL coincided with decreases in total lipid concentration, indicating that corals catabolized δ¹³C-enriched lipids. Since storage lipids are primarily depleted during bleaching, we hypothesize that they are isotopically enriched relative to other lipid classes. This work further helps clarify our understanding of changes to coral metabolism and biogeochemistry when bleached and helps elucidate how lipid classes may influence recovery from bleaching and ultimately coral survival.