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We tested for depth-dependent vertical zonation in coral reef community structure with surveys conducted in 2013 at 10 m and 27 m depth off the islands of Moorea, Tahiti, Maiao, and Tetiaroa, which are distributed over ~3500 km2 of the tropical south Pacific. Benthic communities were censused using photoquadrats to obtain percentage cover, first by functional groups (scleractinians, macroalgae, and crustose coralline algae, algal turf, and bare space combined [CTB]), and second by genus for scleractinians and Millepora. Virtually every aspect of community structure differed between the two depths, but the effects were dependent on spatial scale of investigation. Interactive effects of islands and depths determined the abundance of functional groups, as well as seven of eight common coral genera. On the two islands at which two sites were censused, the abundance of functional groups also differed between sites, and was affected by depth × site interactions. The spatially variable effects of depth on community structure underscores the importance of context-specific synergy between biotic and abiotic factors in driving these patterns. Spatial scale-dependent vertical zonation also shows the potential for these effects to be modulated by the changes that have affected coral community structure on contemporary reefs over the last few decades. [ABSTRACT FROM AUTHOR]

Body size profoundly affects organism fitness and ecosystem dynamics through the scaling of physiological traits. This study tested for variation in metabolic scaling and its potential drivers among corals differing in life history strategies and taxonomic identity. Data were compiled from published sources and augmented with empirical measurements of corals in Moorea, French Polynesia. The data compilation revealed metabolic isometry in broadcasted larvae, but size-independent metabolism in brooded larvae; empirical measurements of Pocillopora acuta larvae also supported size-independent metabolism in brooded coral larvae. In contrast, for juvenile colonies (i.e. 1-4 cm diameter), metabolic scaling was isometric for Pocillopora spp., and negatively allometric for Porites spp. The scaling of biomass with surface area was isometric for Pocillopora spp., but positively allometric for Porites spp., suggesting the surface area to biomass ratio mediates metabolic scaling in these corals. The scaling of tissue biomass and metabolism were not affected by light treatment (i.e. either natural photoperiods or constant darkness) in either juvenile taxa. However, biomass was reduced by 9-15% in the juvenile corals from the light treatments and this coincided with higher metabolic scaling exponents, thus supporting the causal role of biomass in driving variation in scaling. This study shows that metabolic scaling is plastic in early life stages of corals, with intrinsic differences between life history strategy (i.e. brooded and broadcasted larvae) and taxa (i.e. Pocillopora spp. and Porites spp.), and acquired differences attributed to changes in area-normalized biomass., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Understanding population dynamics is a long-standing objective of ecology, but the need for progress in this area has become urgent. For coral reefs, achieving this objective is impeded by a lack of information on settlement versus post-settlement events in determining recruitment and population size. Declines in coral abundance are often inferred to be associated with reduced densities of recruits, which could arise from mechanisms occurring at larval settlement, or throughout post-settlement stages. This study uses annual measurements from 2008 to 2021 of coral cover, the density of coral settlers (S), the density of small corals (SC), and environmental conditions, to evaluate the roles of settlement versus post-settlement events in determining rates of coral recruitment and changes in coral cover at Moorea, French Polynesia. Coral cover, S, SC, and the SC:S ratio (a proxy for post-settlement success), and environmental conditions, were used in generalized additive models (GAMs) to show that: (a) coral cover was more strongly related to SC and SC:S than S, and (b) SC:S was highest when preceded by cool seawater, low concentrations of Chlorophyll a, and low flow speeds, and S showed evidence of declining with elevated temperature. Together, these results suggest that changes in coral cover in Moorea are more strongly influenced by post-settlement events than settlement. The key to understanding coral community resilience may lie in elucidating the factors attenuating the bottleneck between settlers and small corals., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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 (>8 o C-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., (© 2021 The Authors. Ecology published by Wiley Periodicals LLC on behalf of Ecological Society of America.)

One response to the coral reef crisis has been human intervention to enhance selection on the fittest corals through cultivation. This requires genotypes to be identified for intervention, with a primary basis for this choice being growth: corals that quickly grow on contemporary reefs might be future winners. To test for temporal stability of growth as a predictor of future performance, genotypes of the coral Porites spp. were grown in common gardens in Mo'orea, French Polynesia. Growth was measured every two to four months throughout 2018, and each period was used as a predictor of growth over the subsequent period. Area-normalized growth explained less than 29% of the variance in subsequent growth, but for biomass-normalized growth this increased to 45-60%, and was highest when summer growth was used to predict autumn growth. The capacity of initial growth to predict future performance is dependent on the units of measurement and the time of year in which it is measured. The final choice of traits to quantify performance must be informed through consideration of the species and the normalization that best capture the information inherent in the biological processes mediating variation in traits values.

Coral abundance continues to decline on tropical reefs around the world, and this trend suggests that coral reefs may not persist beyond the current century. In contrast, this study describes the near-complete mortality of corals on the outer reef (10 m and 17 m depth) of the north shore of Mo'orea, French Polynesia, from 2005 to 2010, followed by unprecedented recovery from 2011 to 2017. Intense corallivory and a cyclone drove coral cover from 33-48% to <3% by 2010, but over the following seven years, recovery occurred through rapid population growth (up to 12% cover y -1 ) to 25-74% cover by 2017. The thirteen-year, U-shape trajectory of coral cover over time created by the loss and replacement of millions of corals through sexual reproduction underscores the potential for beneficial genetic responses to environmental conditions for at least one genus, Pocillopora. The high ecological resilience of this coral community appears to have been enhanced by variation among genera in the susceptibility to declining cover, and the capacity for population growth (i.e., response diversity). These results suggest that the outer coral communities of Mo'orea may be poised for genetic changes that could affect their capacity to persistence.

Tropical reefs often undergo acute disturbances that result in landscape-scale loss of coral. Due to increasing threats to coral reefs from climate change and anthropogenic perturbations, it is critical to understand mechanisms that drive recovery of these ecosystems. We explored this issue on the fore reef of Moorea, French Polynesia, following a crown-of-thorns seastar outbreak and cyclone that dramatically reduced cover of coral. During the five-years following the disturbances, the rate of re-establishment of coral cover differed systematically around the triangular-shaped island; coral cover returned most rapidly at sites where the least amount of live coral remained after the disturbances. Although sites differed greatly in the rate of return of coral, all showed at least some evidence of re-assembly to their pre-disturbance community structure in terms of relative abundance of coral taxa and other benthic space holders. The primary driver of spatial variation in recovery was recruitment of sexually-produced corals; subsequent growth and survivorship were less important in shaping the spatial pattern. Our findings suggest that, although the coral community has been resilient, some areas are unlikely to attain the coral cover and taxonomic structure they had prior to the most recent disturbances before the advent of another landscape-scale perturbation.

Juvenile colonies of massive Porites spp. were exposed to manipulated pH and bicarbonate ([HCO3-]) in situ to test the hypothesis that ocean acidification (OA) does not affect respiration and calcification. Incubations lasted 28 h and exposed corals to ambient temperature and light with ecologically relevant water motion. Three treatments were applied: (1) ambient conditions of pH 8.04 and 1751 μmol HCO3- kg(-1) (Treatment 1), (2) pCO2-induced ocean acidification of pH 7.73 and 2011 μmol HCO3- kg(-1) (Treatment 2), and (3) pCO2 and HCO3--enriched seawater of pH 7.69 and 2730 μmol HCO3- kg(-1) (Treatment 3). The third treatment providing elevated [HCO3-] was used to test for stimulatory effects of dissolved inorganic carbon on calcification under low pH and low saturation of aragonite (Ωarag), but it does not reflect conditions expected to occur under CO2-driven OA. Calcification of juvenile massive Porites spp. was affected by treatments, with an 81% elevation in Treatment 3 versus Treatment 1, but no difference between Treatments 1 and 2; respiration and the metabolic expenditure concurrent with calcification remained unaffected. These findings indicate that juvenile massive Porites spp. are resistant to short exposures to OA in situ, and separately, that they can increase calcification at low pH and low Ωarag if [HCO3-] is elevated. Juvenile Porites spp. may therefore be limited by dissolved inorganic carbon under ambient pCO2 conditions.

To test for threshold effects in the response of coral physiology to increasing seawater flow, field and laboratory experiments were conducted in Moorea. First, the growth of juvenile massive Porites spp. and branching P. irregularis was compared among habitats differing in water motion. Growth of massive Porites spp. responded to flow in a pattern consistent with a threshold effect, whereas growth of P. irregularis increased linearly with flow. Second, a recirculating flume was used to test the effect of flow on photophysiology (ΔF/F(m)', effective photochemical efficiency) for massive Porites spp.; ΔF/F(m)' displayed a threshold response at 23 cm s(-1) and 28 °C, but not at 31 °C. Finally, intra-colony variation in the response of ΔF/F(m)' to flow and temperature was explored to evaluate the functional significance of colony shape in small corals. ΔF/F(m)' on the top and upstream surfaces of massive Porites spp. responded with a threshold effect of flow at 28 °C (but not 31 °C), but ΔF/F(m)' on downstream surfaces was unresponsive to flow. ΔF/F(m)' for P. irregularis was less responsive to flow than for massive Porites spp., suggesting that the photophysiological response of corals to varying flow speeds may differ between species and morphologies. Together, these results emphasize that flow can have diverse effects on the physiology of corals, with the outcome depending on flow speed, temperature, location on the colony, and perhaps morphology.