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Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera, Pocillopora and Acropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, but Acropora bleached more severely than Pocillopora overall. Acropora bleached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching in Pocillopora corals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10–29 cm) or small colonies (5–9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality. [ABSTRACT FROM AUTHOR]

Aim: The symbioses between corals and endosymbiotic dinoflagellates have been described as a flexible relationship whose dynamics could serve as a source of resilience for coral reef ecosystems. However, the factors that drive the establishment and maintenance of this co‐evolutionary relationship remain unclear. We examined the environmental and geographical factors structuring dinoflagellate communities in a wide‐ranging Indo‐Pacific coral to begin to address this gap. Location: Djibouti, Oman, Taiwan and French Polynesia. Taxon: Cauliflower corals (Pocillopora spp.), dinoflagellates (family Symbiodiniaceae). Methods: We analysed publicly available amplicon sequence data from the nuclear ribosomal DNA internal transcribed spacer 2, originating from Pocillopora spp. We also compiled environmental data such as sea surface temperature (SST) and time since the last local mass bleaching event. We ran generalized least squares models, PERMANOVAs and indicator species analyses, to understand how thermal regimes and geographical distances impacted Pocillopora spp.'s Symbiodiniaceae community composition. Results: Sea surface temperature was the most important factor driving Symbiodiniaceae community differences, with the largest effect size of the statistically significant factors. When focusing on individual Symbiodiniaceae genera, SST was likewise the most important factor. Our indicator species analyses revealed that specimens that had recently bleached were characterized by roughly equal proportions of Cladocopium spp. and Durusdinium spp., while specimens that had not recently bleached had a similar proportion of Durusdinium spp. as those that had recently bleached, but also showed a reduction in Cladocopium spp., with this deficiency made up by the presence of Symbiodinium spp. Main Conclusions: We provide further support for the hypothesis that coral's Symbiodiniaceae communities could facilitate host resilience to thermal stress. Our work is in direct conversation with a larger body of biogeography literature that highlights how local environmental regimes can impact contemporary population structure, even in marine taxa with widespread distributions. [ABSTRACT FROM AUTHOR]

Artificial reefs and, more recently, ecoengineering are frequently advocated as possible tools to counteract the loss of tropical coral reefs worldwide. Despite increasing availability of novel materials, there is limited understanding of how different materials and their physical and chemical properties can influence coral recruitment success and early benthic community development. This study investigated the efficacy of several innovative materials as recruitment substrates for corals and other sessile benthic communities. Stacks of vertically oriented tiles made of eight innovative materials and two common (control) materials were deployed for 6 months during major coral spawning events on the forereef of Mo'orea, French Polynesia. Tiles were separated from their neighbors by 15 mm to mimic cryptic habitats that are sheltered from predation and typically favored by coral recruits. Six innovative materials, including 3D printed concrete, polyvinyl chloride (PVC) with chitosan coating, fiberglass polymer, and flax‐based polylactic acid, produced similar coral recruitment to control materials (Portland concrete and PVC). Two materials (porous concrete and ceramic foam) produced lower recruitment. Porous concrete was characterized by a high abundance of non‐coralline encrusting red algae, which negatively correlated with coral recruitment, while ceramic foam was prone to erosion. The results suggest the structural micro‐complexity and durability of an artificial material and the composition of the benthic communities colonizing it can strongly influence coral recruitment. This study highlights several innovative materials as suitable recruitment substrates for coral restoration and provides a better understanding of the properties of artificial materials that are critical for coral recruitment success. [ABSTRACT FROM AUTHOR]

Variation among functionally similar species in their response to environmental stress buffers ecosystems from changing states. Functionally similar species may often be cryptic species representing evolutionarily distinct genetic lineages that are morphologically indistinguishable. However, the extent to which cryptic species differ in their response to stress, and could therefore provide a source of response diversity, remains unclear because they are often not identified or are assumed to be ecologically equivalent. Here, we uncover differences in the bleaching response between sympatric cryptic species of the common Indo‐Pacific coral, Pocillopora. In April 2019, prolonged ocean heating occurred at Moorea, French Polynesia. 72% of pocilloporid colonies bleached after 22 d of severe heating (>8oC‐days) at 10 m depth on the north shore fore reef. Colony mortality ranged from 11% to 42% around the island four months after heating subsided. The majority (86%) of pocilloporids that died from bleaching belonged to a single haplotype, despite twelve haplotypes, representing at least five species, being sampled. Mitochondrial (open reading frame) sequence variation was greater between the haplotypes that experienced mortality versus haplotypes that all survived than it was between nominal species that all survived. Colonies > 30 cm in diameter were identified as the haplotype experiencing the most mortality, and in 1125 colonies that were not genetically identified, bleaching and mortality increased with colony size. Mortality did not increase with colony size within the haplotype suffering the highest mortality, suggesting that size‐dependent bleaching and mortality at the genus level was caused instead by differences among cryptic species. The relative abundance of haplotypes shifted between February and August, driven by declines in the same common haplotype for which mortality was estimated directly, at sites where heat accumulation was greatest, and where larger colony sizes occurred. The identification of morphologically indistinguishable species that differ in their response to thermal stress, but share a similar ecological function in terms of maintaining a coral‐dominated state, has important consequences for uncovering response diversity that drives resilience, especially in systems with low or declining functional diversity. [ABSTRACT FROM AUTHOR]

Climate change is increasing the frequency and magnitude of temperature anomalies that cause coral bleaching, leading to widespread mortality of stony corals that can fundamentally alter reef structure and function. However, bleaching often is spatially variable for a given heat stress event, and drivers of this heterogeneity are not well resolved. While small-scale experiments have shown that excess nitrogen can increase the susceptibility of a coral colony to bleaching, we lack evidence that heterogeneity in nitrogen pollution can shape spatial patterns of coral bleaching across a seascape. Using island-wide surveys of coral bleaching and nitrogen availability within a Bayesian hierarchical modeling framework, we tested the hypothesis that excess nitrogen interacts with temperature anomalies to alter coral bleaching for the two dominant genera of branching corals in Moorea, French Polynesia. For both coral genera, Pocillopora and Acropora, heat stress primarily drove bleaching prevalence (i.e., the proportion of colonies on a reef that bleached). In contrast, the severity of bleaching (i.e., the proportion of an individual colony that bleached) was positively associated with both heat stress and nitrogen availability for both genera. Importantly, nitrogen interacted with heat stress to increase bleaching severity up to twofold when nitrogen was high and heat stress was relatively low. Our finding that excess nitrogen can trigger severe bleaching even under relatively low heat stress implies that mitigating nutrient pollution may enhance the resilience of coral communities in the face of mounting stresses from global climate change. [ABSTRACT FROM AUTHOR]

The article presents a study which explores the role of Stegastes nigricans and Stegastes lividus territorial damselfishes in facilitating the survivability of corals at Moorea, Society Islands, French Polynesia and Guam, Mariana Islands. The researchers assessed the S. nigricans inhabiting in the fringing reef slope of Maharepa, Moorea and S. lividus at the inner reef slope of Guam, Mariana Islands, via laying transect lines in the study sites. Coral Transplant experiment was also conducted to determine the effect of damselfishes among corals. The result of the study shows that greater diversity of corals were found within territory of damselfishes. It adds that damselfishes enable to establish associational defense with corals against predators.

Dispersal may be a critical factor in the ability of reef-building corals to recover after major disturbances. We studied patterns of geographical structure using four microsatellite markers in seven South Pacific populations ofPocillopora meandrina,a major coral species from Polynesia. Variation within populations showed evidence of heterozygote deficiency. Genetic differentiation between populations was detected at a large scale (2000 km) between the Tonga and the Society Islands. Within the Society Islands, four of the five studied populations from Bora Bora, Moorea and Tahiti were not significantly different from each other. Unexpectedly, one of the three populations surveyed in Moorea was genetically different from the other two populations of this island (that were 5 and 10 km apart), and from the populations of the other two surveyed islands in this archipelago. We cannot rule out the possibility that this pattern is an equilibrium state, whereby short-range dispersal is locally more differentiating than long-range dispersal, as has been suggested by similar patterns reported in other studies. An alternative explanation that is globally consistent with all observations is that this is the signature of a large-scale destruction event, as for instance a bleaching event, followed by the recent restoration of populations by new colonists. [ABSTRACT FROM AUTHOR]

Coral reefs are declining at an unprecedented rate as a consequence of local and global stressors. Using a 26-year monitoring database, we analyzed the loss and recovery dynamics of coral communities across seven islands and three archipelagos in French Polynesia. Reefs in the Society Islands recovered relatively quickly after disturbances, which was driven by the recovery of corals in the genus Pocillopora (84% of the total recovery). In contrast, reefs in the Tuamotu and Austral archipelagos recovered poorly or not at all. Across archipelagos, predation by crown-of-thorns starfish and destruction by cyclones outweighed the effects of heat stress events on coral mortality. Despite the apparently limited effect of temperature-mediated stressors, the homogenization of coral communities towards dominance of Pocillopora in the Society Archipelago and the failure to fully recover from disturbances in the other two archipelagos concern the resilience of Polynesian coral communities in the face of intensifying climate-driven stressors. • Long-term monitoring allows tracking coral communities through space and time • Crown-of-thorns outbreaks and cyclones heavily impacted corals in French Polynesia • Recovery dynamics in cover and compositional changes vary among archipelagos • Homogenization of genus Pocillopora may compromise the future resilience of reefs [ABSTRACT FROM AUTHOR]