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The implications of ocean acidification are acute for calcifying organisms, notably tropical reef corals, for which accretion generally is depressed and dissolution enhanced at reduced seawater pH. We describe year‐long experiments in which back reef and fore reef (17‐m depth) communities from Moorea, French Polynesia, were incubated outdoors under pCO2 regimes reflecting endpoints of representative concentration pathways (RCPs) expected by the end the century. Incubations were completed in three to four flumes (5.0 × 0.3 m, 500 L) in which seawater was refreshed and circulated at 0.1 m s−1, and the response of the communities was evaluated monthly by measurements of net community calcification (NCC) and net community productivity (NCP). For both communities, NCC (but not NCP) was affected by treatments and time, with NCC declining with increasing pCO2, and for the fore reef, becoming negative (i.e., dissolution was occurring) at the highest pCO2 (1067–1433 μatm, RCP8.5). There was scant evidence of community adjustment to reduce the negative effects of ocean acidification, and inhibition of NCC intensified in the back reef as the abundance of massive Porites spp. declined. These results highlight the risks of dissolution under ocean acidification for coral reefs and suggest these effects will be most acute in fore reef habitats. Without signs of amelioration of the negative effects of ocean acidification during year‐long experiments, it is reasonable to expect that the future of coral reefs in acidic seas can be predicted from their current known susceptibility to ocean acidification. [ABSTRACT FROM AUTHOR]

Measurements of coral recruitment can improve understanding of coral population dynamics, but in short duration studies high variance impedes interpretation of this vital rate. Here, coral recruitment in Moorea, French Polynesia, was measured over 13 yr and tested for associations with environmental conditions. Recruitment of spawning pocilloporid corals was recorded using settlement tiles immersed for ~ 6 months at 10 m and 17 m depth, biannually, and the environment was quantified through seawater clarity (Kd490), surface and bottom flow speeds, coral cover, and temperature. Using GAMs, most of the variation (63–74%) in recruitment was explained using depth and three predictors. Recruitment was high in January/February following a year of low seawater clarity (high Kd490), and in August/September following a year of high clarity. Recruitment in January/February was elevated by high coral cover, and by high surface flow during larval dispersal; recruitment was low in August/September following high temperature during gametogenesis. These effects reveal the extent to which early life stages of corals are exposed to annually variable environmental conditions that have differential consequences depending on the phenology of reproduction and recruitment. The temporal mosaic defining interactions between reproduction, recruitment, and environmental conditions create opportunities for acclimatization to affect where and when coral recruitment is successful. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is negatively affecting calcification in a wide variety of marine organisms. These effects are acute for many tropical scleractinian corals under short-term experimental conditions, but it is unclear how these effects interact with ecological processes, such as competition for space, to impact coral communities over multiple years. This study sought to test the use of individual-based models (IBMs) as a tool to scale up the effects of OA recorded in short-term studies to community-scale impacts, combining data from field surveys and mesocosm experiments to parameterize an IBM of coral community recovery on the fore reef of Moorea, French Polynesia. Focusing on the dominant coral genera from the fore reef, Pocillopora, Acropora, Montipora and Porites, model efficacy first was evaluated through the comparison of simulated and empirical dynamics from 2010–2016, when the reef was recovering from sequential acute disturbances (a crown-of-thorns seastar outbreak followed by a cyclone) that reduced coral cover to ~0% by 2010. The model then was used to evaluate how the effects of OA (1,100–1,200 μatm pCO2) on coral growth and competition among corals affected recovery rates (as assessed by changes in % cover y−1) of each coral population between 2010–2016. The model indicated that recovery rates for the fore reef community was halved by OA over 7 years, with cover increasing at 11% y−1 under ambient conditions and 4.8% y−1 under OA conditions. However, when OA was implemented to affect coral growth and not competition among corals, coral community recovery increased to 7.2% y−1, highlighting mechanisms other than growth suppression (i.e., competition), through which OA can impact recovery. Our study reveals the potential for IBMs to assess the impacts of OA on coral communities at temporal and spatial scales beyond the capabilities of experimental studies, but this potential will not be realized unless empirical analyses address a wider variety of response variables representing ecological, physiological and functional domains. [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]

The Moorea Coral Reef Long Term Ecological Research program affords a unique opportunity to study the implications of ocean acidification (OA) for coral reefs, as ongoing ecological and physical monitoring there provides a context in which the patterns of community change attributed to OA can be detected. We used mesocosms to study the impacts of OA on corals and calcified algae, and conducted experiments to compare multiple species and evaluate how they are affected by changing concentrations of the different forms of dissolved inorganic carbon. Our results reveal taxonomic variation in the response to OA, with some corals and algae showing signs of resistance to OA conditions. This discovery is informing an urgent debate over the form in which coral reefs will survive (if at all) in the future. [ABSTRACT FROM AUTHOR]

The Moorea Coral Reef Long Term Ecological Research project funded by the US National Science Foundation includes multidisciplinary studies of physical processes driving ecological dynamics across the fringing reef, back reef, and fore reef habitats of Moorea, French Polynesia. A network of oceanographic moorings and a variety of other approaches have been used to investigate the biological and biogeochemical aspects of water transport and retention processes in this system. There is evidence to support the hypothesis that a low-frequency counterclockwise flow around the island is superimposed on the relatively strong alongshore currents on each side of the island. Despite the rapid flow and flushing of the back reef, waters over the reef display chemical and biological characteristics distinct from those offshore. The patterns include higher nutrient and lower dissolved organic carbon concentrations, distinct microbial community compositions among habitats, and reef assemblages of zooplankton that exhibit migration behavior, suggesting multigenerational residence on the reef. Zooplankton consumption by planktivorous fish on the reef reflects both retention of reef-associated taxa and capture by the reef community of resources originating offshore. Coral recruitment and population genetics of reef fishes point to retention of larvae within the system and high recruitment levels from local adult populations. The combined results suggest that a broad suite of physical and biological processes contribute to high retention of externally derived and locally produced organic materials within this island coral reef system. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that the response of corals to temperature and pCO2 is consistent between taxa. Juvenile massive Porites spp. and branches of P. rus from the back reef of Moorea were incubated for 1 month under combinations of temperature (29.3 °C and 25.6 °C) and pCO2 (41.6 Pa and 81.5 Pa) at an irradiance of 599 μmol quanta m−2 s−1. Using microcosms and CO2 gas mixing technology, treatments were created in a partly nested design (tanks) with two between-plot factors (temperature and pCO2), and one within-plot factor (taxon); calcification was used as a dependent variable. pCO2 and temperature independently affected calcification, but the response differed between taxa. Massive Porites spp. was largely unaffected by the treatments, but P. rus grew 50% faster at 29.3 °C compared with 25.6 °C, and 28% slower at 81.5 Pa vs. 41.6 Pa CO2. A compilation of studies placed the present results in a broader context and tested the hypothesis that calcification for individual coral genera is independent of pH, [HCO3 −], and [CO3 2−]. Unlike recent reviews, this analysis was restricted to studies reporting calcification in units that could be converted to nmol CaCO3 cm−2 h−1. The compilation revealed a high degree of variation in calcification as a function of pH, [HCO3 −], and [CO3 2−], and supported three conclusions: (1) studies of the effects of ocean acidification on corals need to pay closer attention to reducing variance in experimental outcomes to achieve stronger synthetic capacity, (2) coral genera respond in dissimilar ways to pH, [HCO3 −], and [CO3 2−], and (3) calcification of massive Porites spp. is relatively resistant to short exposures of increased pCO2, similar to that expected within 100 y. [ABSTRACT FROM AUTHOR]

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/Fm' effective photochemical efficiency) for massive Porites spp.; ΔF/Fm' 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/Fm' to flow and temperature was explored to evaluate the functional significance of colony shape in small corals. ΔF/Fm' 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/Fm' on downstream surfaces was unresponsive to flow. ΔF/Fm' 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. [ABSTRACT FROM AUTHOR]

The article details a study which described the spatio-temporal variation in coral recruitment in the back reef of Moorea, French Polynesia. The study also examined the association between spatio-temporal variation in coral recruitment and community structure, seawater temperature and wave regimes. The coral recruitment was assessed using settlement tiles that were deployed at 10 sites on the north, southeast and southwest shores from 2005 to 2007. They include acroporids, poritids and pocilloporids. Study authors hypothesized that coral recruitment in the back reef of Moorea is influenced by the interaction of seasonal variation in wave exposure, family-level differences in coral reproductive timing, and spatial distribution of adult corals.

Focuses on free-living colonies of porites in Moorea, French Polynesia. Greater abundance of unattached colonies than attached colonies in some locations; Abundance and size of free-living colonies; Likely modes of transformation of the colonies.