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The Great Reef of Toliara, on the southwestern coast of Madagascar, has been documented as harbouring flourishing reef communities in the 1960s, but has since been affected by various threats, causing a coral decline last reported in 2008. In 2017, we examined the spatial heterogeneity in coral community structure in the region of Toliara. Coral assemblages were characterized by a marked spatial variability, with significant variation for most of the descriptors among the three major habitats and also among stations within habitats. We recorded high coral cover, with values &gt, 40% at six of the 10 stations, which was associated with high abundance of coral colonies. We also documented the return to an Acropora-dominated coral assemblage. While these positive results suggest a recent return to healthier coral assemblages, they must be tempered, as the diversity that we recorded was lower than in the 1960s. Moreover, we found a high cover of algae at several stations, suggesting that the ecosystem is likely close to the tipping point toward a phase shift. Finally, the population size-structure of major coral taxa was positively skewed, with few large colonies to ensure the replenishment of local populations. The marked spatial variation suggests that marine protected areas should integrate a sufficiently large area to capture the scale of this spatial heterogeneity.

Sea-level rise is predicted to cause major damage to tropical coastlines. While coral reefs can act as natural barriers for ocean waves, their protection hinges on the ability of scleractinian corals to produce enough calcium carbonate (CaCO3 ) to keep up with rising sea levels. As a consequence of intensifying disturbances, coral communities are changing rapidly, potentially reducing community-level CaCO3 production. By combining colony-level physiology and long-term monitoring data, we show that reefs recovering from major disturbances can produce 40% more CaCO3 than currently estimated due to the disproportionate contribution of juvenile corals. However, the buffering effect of highly productive juvenile corals is compromised by recruitment failures, which have been more frequently observed after large-scale, repeated bleaching events. While the size structure of corals can bolster a critical ecological function on reefs, climate change impacts on recruitment may undermine this buffering effect, thus further compromising the persistence of reefs and their provision of important ecosystem services.

The choice of ecological monitoring methods and descriptors determines the effectiveness of a program designed to assess the state of coral reef ecosystems. Here, we comparer the relative performance of the traditional Line Intercept Transect (LIT) method with three methods derived from underwater photogrammetry: LIT on orthomosaics, photoquadrats from orthomosaics, and surface analyses on orthomosaics. The data were acquired at Reunion Island on five outer reef slopes and two coral communities on underwater lava-flows. Coral cover was estimated in situ using the LIT method and with LITs and photoquadrats digitized on orthomosaic. Surface analyses were done on the same orthomosaics. Structural complexity of the surveyed sites was calculated from digital elevation models using three physical descriptors (fractal dimension, slope, surface complexity), and used to explore their possible influence in coral cover estimates. We also compared the methods in terms of scientific outputs, the human expertise and time required. Coral cover estimates obtained with in situ LITs were higher than those obtained with digitized LITs and photoquadrats. Surfaces analyses on orthomosaics yielded the lowest but most the precise cover estimates (i.e., lowest sample dispersion). Sites with the highest coral cover also had the highest structural complexity. Finally, when we added scientific outputs, and requirements for human expertise and time to our comparisons between methods, we found that surface analysis on the orthomosaics was the most efficient method. Photoquadrats were more time-consuming than both in situ and digitized LITs, even though they provided coral cover estimates similar to those of digitized LITs and yielded more than one descriptor. The LIT in situ method remains the least time-consuming and most effective for species-level taxonomic identifications but is the most limited method in terms of data outputs and representativeness of the ecosystem.

International audience; Structural complexity plays a key role in the functioning of coral reef ecosystems. Reef-building corals are major contributors to this complexity, providing shelter and food for numerous invertebrates and fish species. Both structural complexity and shelter capacity of reefscapes are determined by several components such as spurs and grooves, slope, caves and holes, vegetation and coral colonies. Quantifying the shelter capacity from coral col-onies to reefscapes is a fundamental step to estimating ecosystem potential to support biodiversity. Here, we applied underwater photogrammetry to quantify shelter volumes provided by individual coral colonies. Overall, 120 3D models of coral colonies from branching, massive, columnar and tabular growth forms were studied. Three reefscapes were also 3D modeled. The study encompasses three Indo-Pacific Islands: Reunion, Europa and New Caledonia. At the colony level, measurements of diameter, planar area, surface and shelter volume were computed. At the reefscape, the diameter and planar area of each colony were extracted from orthomosaics and then used to estimate shelter capacity. Linear models had high accuracy for predicting shelter volume (a 3D metric) from 2D metrics: the diameter=83.1%, R2=0.95; the planar area=87.5%, R2=0.95 and the colony surface=87.3%, R2=0.96. The surface complexity and the shelter volume of the colonies allowed inferring the size of shelters provided by coral growth forms. Quantitative descriptors (i.e. relative percentage of shelter by growth form, the abundance of coral colonies, “Shannon-Shelter Index”) revealed reefscape-scale shelter differences. Our major finding is that planar area and diameter of coral colonies are satisfactory proxies for estimating shelter volume. These new proxies allow 2D metrics to quantify 3D shelter provision, which can support sci-entists and managers in conservation actions since such metrics are widely used in monitoring programs. Future investigations on the relationships between shelter provision and reef biodiversity will improve the under-standing of these complex ecosystems

Monitoring potentially devastating coral-eating crown-of-thorns starfish (COTS) populations at scales relevant to management is a challenging task. Here, we investigated a citizen science approach to detect COTS outbreaks and prioritize management responses. Between 2014 and 2018, 38 000 COTS were recorded through 641 online observation reports submitted across New Caledonia, Vanuatu and Fiji by private stakeholders (51%), NGOs (22%), business operator (11%), research/government agencies (16%). COTS were observed in multiple areas, including in remote/inhabited reefs where they had never been reported. A three-level classification was developed to discriminate risk areas and propose operational guidelines to streamline management actions. About two-thirds of reports had low abundances (−1). Combining professional and non-professional observers increased the detection range (+27%) and the number of COTS detections (+129%). Citizen reports were eventually followed by removal campaigns organized within diverse institutional frameworks. While citizen monitoring has intrinsic limitations, we advocate that it constitutes a complementary and promising approach to support the ongoing management efforts in all countries affected by COTS.

The authors are particularly grateful to Richard Farman, director ofthe Aquarium des Lagons in Noumea, for hosting our experiments. Wealso wish to express our warmest thanks to the aquarium staff for theirlogistical support, in particular Sylvain Govan and Jeff Dubosc.; International audience; Outbreaks of the coral-eating crown-of-thorns starfish Acanthaster spp. (COTS) have become to be amongst the most severe threats to coral reefs worldwide. Although most research has focused on COTS early development, it remains unclear how COTS populations will keep pace with changing ocean conditions. Since reproduction is a key process contributing to outbreaks, we investigated the reproductive success of adult COTS acclimated for 3-4 months to different treatment combinations of ambient conditions, ocean warming (+2 • C) and acidification (− 0.35 pH). Our results suggest that the optimal breeding season in New Caledonia is concentrated around the end of the calendar year, when water temperature reaches >26 • C. We found negative effects of temperature on egg metrics, fertilisation success, and GSI, conflicting with previously documented effects of temperature on echinoderm reproductive outputs. Fertilisation success dropped drastically (more than threefold) with elevated temperature during the late breeding season. In contrast, we detected no effects of near-future acidification conditions on fertilisation success nor GSI. This is the first time that COTS reproduction is compared among individuals acclimated to different conditions of warming and acidification. Our results highlight the importance of accounting for adult exposure to better understand how COTS reproduction may be impacted in the face of global change.

Este artículo contiene 10 páginas, 5 figuras., Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages—the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014–2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.

In Pacific countries, outbreaks of the crown-of-thorns starfish Acanthaster planci (COTS) raise increasing conservation concerns in areas where people heavily depend upon coral reefs for their livelihoods. Small-scale cleanups are often used in an attempt to regulate COTS densities, but their efficiency is challenged by knowledge gaps and the difficulty for the communities to frame their decisions in an ecological perspective. Here, we investigated COTS reproductive seasonality and its potential impact on removals. The spawning period of COTS was documented in two islands of the Vanuatu archipelago using the gonado-somatic index (GSI). Peak spawning occurred one month after the 28 degrees C threshold was exceeded and was delayed by 2-3 weeks with increasing latitude, theoretically allowing cleanups to be framed within the biological cycle. We demonstrated that subsampiing of two/three arms per starfish provide GSI errors 4 tons (13,000 starfish). At the end of the removals, GSI was reduced by half when compared to control areas, suggesting that traditional practices may under certain conditions trigger synchronized spawning. More effectively controlling COTS outbreaks will require teaching good ecological practices to avoid potential side-effects, a challenge in countries where a lack of knowledge on COTS does not really foster environmental concerns among local communities.

Clipperton Atoll, one of the most isolated coral reefs worldwide, is of great scientific interest due to its geomorphology and high levels of endemism. This study explored the reef fish assemblage structure of Clipperton Atoll and its relationship with live coral cover. Nine stations were sampled at three sites and three depths (6, 12 and 20 m) around the reef, measuring fish species richness and biomass and hermatypic coral cover (at genus level). We evaluated variation in species richness, biomass and diversity of fish assemblages among sites and depths, as well as the relationship between the entire fish assemblage composition and live coral cover. The results showed that species richness and biomass were similar among sites, but differed across depths, increasing with depth. In contrast, diversity differed among sites but not among depths. Multivariate analyses indicated that fish assemblage composition differed among sites and depths in relation to changes in cover of coral of the genera Pocillopora, Porites, Pavona and Leptoseris, which dominate at different depths. The results showed that fish species richness and diversity were low at Clipperton Atoll and that, in isolated coral reefs with a low habitat heterogeneity and low human disturbance, live coral cover has a significant influence on the spatial variation of the reef fish assemblages. This study highlights the importance of coral habitat structure in shaping coral reef fish assemblages. El atolón de Clipperton, uno de los arrecifes de coral más aislados del mundo, presenta un gran interés científico por su geomorfología y endemismo. Este estudio analizó la estructura de las comunidades de peces de arrecife de este atolón y su relación con la cobertura de coral vivo. Para ello se muestrearon nueve estaciones alrededor del arrecife en tres sitios a tres profundidades (6, 12, 20 m), registrando, la riqueza y biomasa de peces, así como la cobertura de coral hermatípico a nivel de género. Se evaluó la variación de la riqueza, biomasa y diversidad de peces entre sitios y profundidades, así como la relación de la composición y biomasa de peces con la cobertura de coral vivo. Los resultados mostraron que la riqueza y biomasa fueron similares entre los sitios, pero diferentes entre profundidades, ya que incrementan con la profundidad. En contraste, la diversidad difirió entre sitios pero no entre profundidades. Los análisis multidimensionales indicaron que la comunidad de peces fue diferente entre sitios y profundidades, relacionándolo con la cobertura de coral de los géneros Pocillopora, Porites, Pavona y Leptoseris, que dominan a distinta profundidad. Los resultados evidenciaron una baja riqueza y diversidad de peces arrecifales en el atolón de Clipperton. En arrecifes de coral aislados, con baja heterogeneidad de hábitats y poca perturbación humana, la cobertura de coral vivo influye en la variación espacial de las comunidades de peces arrecifales. Este estudio resalta la importancia de la estructura del hábitat de coral en la conformación de las comunidades de peces arrecifales.

Rapa (27 degrees 36S, 144 degrees 20W) is a small (similar to 40km(2)) volcanic island isolated in the Southern Austral Archipelago, where direct anthropogenic stressors are extremely limited. Here, we present the results of the first quantitative survey of coral community structure across habitats and depths around the island. Despite its geographical isolation in the depauperate South Central Pacific, its small size and unfavourable environmental conditions (competition with macroalgae, low sea surface temperatures, reduced reef accretion), the diversity of scleractinian corals at Rapa is particularly high (112 species from 32 genera, including 37 species of Acropora) in comparison to other French Polynesian islands and subtropical Pacific locations. Our results indicate that the abundance (>100 colonies per 10m(2) recorded at nine of the 17 sampling stations) and cover (>40% at four stations) of corals are relatively high for a marginal reef location. Strong spatial heterogeneity was found, with high variation in diversity, abundance, cover and community composition among stations. Variation in community composition was related to habitat types, with distinct assemblages among fringing reefs within bays, reef formations at bay entrances, and those on the submerged platform surrounding the island. On the platform, a depth gradient was detected, with generic richness, abundance and cover generally greater at deeper stations (18-20m depth) compared with medium-depth (10-12m) and shallow (1-3m) stations. A gradient was also recorded along bays, with increasing coral diversity and abundance from the bay heads to the bay entrances. The coral community at Rapa was characterized by the presence of several taxa not found in other French Polynesian archipelagos and the rarity of others that are common and abundant in the Society and the Tuamotu islands. Another distinctive feature of reef communities at Rapa is the high cover and dominance of macroalgae, particularly in the shallower parts of the surrounding platform, which probably explains the lower densities of coral colonies recorded there. These characteristics of the diversity and biogeographical composition of coral assemblages at Rapa provide considerable ecological grounds for its conservation.

We report here an interannual survey (2006-2012) of coral cover in the northwestern lagoon of New Caledonia, to assess the impact of an important dredging operation (August 2008-February 2010) associated with the construction of the largest nickel mining site in the Pacific. A BACI (Before-After Control-Impact) analysis failed to detect any significant interaction between period (before, during, and after dredging) and the category of the stations (impact vs. control). Among the 31 stations surveyed, only seven showed decreasing coral cover during the study period, mainly due to a decline in Acroporidae. However, the relationship between the dredging and this decrease was highly plausible only for one station, situated 0.9 km from the dredging site. High hydrodynamism in the study area, the abundance of resistant corals and efficient protective measures during the dredging operation might explain these localised and limited impacts.

International audience

International audience; Previous observations suggested that microbial communities contribute to coral health and the ecological resilience of coral reefs. However, most studies of coral microbiology focused on prokaryotes and the endosymbiotic algae Symbiodinium. In contrast, knowledge concerning diversity of other protists is still lacking, possibly due to methodological constraints. As most eukaryotic DNA in coral samples was derived from hosts, protist diversity was missed in metagenome analyses. To tackle this issue, we designed blocking primers for Scleractinia sequences amplified with two primer sets that targeted variable loops of the 18S rRNA gene (18SV1V2 and 18SV4). These blocking primers were used on environmental colonies of Pocillopora damicornis sensu lato from two regions with contrasting thermal regimes (Djibouti and New Caledonia). In addition to Symbiodinium clades A/C/D, Licnophora and unidentified coccidia genera were found in many samples. In particular, coccidian sequences formed a robust monophyletic clade with other protists identified in Agaricia, Favia, Montastraea, Mycetophyllia, Porites, and Siderastrea coral colonies. Moreover, Licnophora and coccidians had different distributions between the two geographic regions. A similar pattern was observed between Symbiodinium clades C and A/D. Although we were unable to identify factors responsible for this pattern, nor were we able to confirm that these taxa were closely associated with corals, we believe that these primer sets and the associated blocking primers offer new possibilities to describe the hidden diversity of protists within different coral species.

Populations of marine organisms on coral reef islands (CRI) are connected in space and time by seawater that transports propagules of plants, animals, and algae. Yet, despite this reality, it is often assumed that routine replenishment of populations of marine organisms on CRI is supported by locally-sourced propagules (hereafter, larvae). Following large disturbances, however, distantly-sourced larvae from less disturbed CRI within a regional meta-population are likely to be important for local population recovery, but evaluating the roles of locally- vs. distantly-sourced larvae remains difficult. While larval sources are relatively well-known for some fishes, they remain virtually unknown for most taxa, particularly those associated with the benthos, as exemplified by scleractinian corals. This review focuses on reef recovery and larval connectivity. Using corals as examples, we argue that CRI can serve as natural laboratories in which studies of these issues can enhance understanding of coral reef community dynamics under future disturbance regimes. Rather than focusing on synthesizing empirical data, we focus on the capacity for CRI to realize their potential in this research area, concluding that progress is impeded by the limited breadth, detail, and spatio-temporal concordance of existing research. Using long-term observational programs of coral reefs in Mo'orea (French Polynesia), Okinawa (Japan), and St. John (US Virgin Islands) as examples of the data currently available, we make the case that new modes of multidisciplinary and collaborative research will be required to exploit the value of CRI in understanding the role of connectivity in mediating ecosystem resilience in a future affected by anthropogenic disturbances.

A single ecosystem can exhibit great biogeographic and environmental variability. While a given ecological driver might have a strong impact in one region, it does not necessarily hold that its importance will extend elsewhere. Coral reefs provide a striking example in that coral communities have low resilience in the Atlantic and remarkable resilience in parts of the species-rich Pacific. Recent experimental evidence from the Atlantic finds that fishing of large herbivorous fish can be a strong driver of coral resilience. Here, we repeat the Atlantic experiment in the highly resilient forereef of Moorea (French Polynesia), which has repeatedly recovered from disturbances. A combination of cages, fish deterrents (FDs), and controls allowed us to simulate the consequences of fishing large herbivores on algal assemblages, coral recruitment, and the demographic rates of coral juveniles. We find that the impacts of removing large herbivorous reef fish vary with early coral ontogeny. Reduced herbivore access led to a modest macroalgal bloom and reduction in coral recruitment. However, larger juvenile corals (> 1 cm diameter) survived better and grew faster under these conditions because of a reduction in corallivory. To determine the net impact of losing larger herbivorous fish, we combined experimental results with estimated demographic parameters in an individual-based model. Simulating coral recovery trajectories for five years, we find that protecting larger reef fish led to better recovery in 66–99% of simulations, depending on underlying assumptions (with the more credible assumptions being associated with greater likelihood of net positive impacts). While we find that fishing effects are detrimental to corals in both the Atlantic and Pacific systems studied, the nature of the interactions varied markedly. In the identical previously-published study in the Atlantic, macroalgae exhibited a rapid bloom and caused a sufficiently large reduction in coral recruitment to force a predicted ecosystem shift to an alternative attractor. The commensurate macroalgal bloom in Moorea was weak yet the corals were two orders of magnitude more sensitive to its presence. We do not suggest that a reduction in recruitment in Moorea will lead to alternative attractors but the long-term risks of a reduction in recovery rate are cause for concern as rates of coral mortality are projected to increase. The emerging picture is that Pacific reefs are less likely to experience macroalgal blooms but are surprisingly sensitive to such blooms if they occur.

Outbreaks of the predator crown-of-thorns seastar (COTS) Acanthaster planci cause widespread coral mortality across the Indo-Pacific. Like many marine invertebrates, COTS is a nocturnal species whose cryptic behaviour during the day can affect its detectability, particularly in structurally complex reef habitats that provide many refuges for benthic creatures. We performed extensive day and night surveys of COTS populations in coral reef habitats showing differing levels of structural complexity and COTS abundance. We tested whether estimations of COTS density varied between day and night observations, and if the differences were related to changes in COTS abundance, reef structural complexity and the spatial scale of observation. Estimations of COTS density were on average 27% higher at night than during the day. Differences in COTS detection varied with changing seastar abundance but not reef structural complexity or scale of observation. Underestimation of COTS abundance in daytime was significant for a broad seastar density range, thus potentially affecting most outbreak events. Our study suggests that portions of COTS populations can be undetected during conventional surveys and control campaigns, which are exclusively conducted by day, and significantly affect the trajectory of coral reefs. Accounting for bias in COTS detection can strengthen coral reef management broadly.

In 2002, bleaching was reported throughout many Indo-Pacific coral-reef regions, including French Polynesia. Bleaching occurred again in French Polynesia in 2003, providing an opportunity to compare the effects of successive bleaching events on coral susceptibility. During 2002 and 2003, underwater video surveys were completed in stations at four depths (lagoon: 0–2, 2–4m; outer reef slope: 6–8, 12–14m) at two locations on the northern and north-western coast of Moorea (Society Archipelago) to compare the cover of healthy-appearing, the cover of partially bleached and the cover of fully bleached coral. Bleaching patterns were genus specific and differences in susceptibility among major genera were generally consistent between 2002 and 2003, with Acropora showing the greatest susceptibility. Some genera exhibited substantial spatial variability in bleaching susceptibility between years (e.g. Pocillopora, Montipora); however, this variability was significant only for fully bleached and partially bleached Acropora. Multivariate analyses showed that spatial patterns in the proportion of healthy-appearing coral were similar over time within the assemblages, whereas the cover of partially bleached and the cover of fully bleached coral were more variable among depths and locations. This variability has important implications for assessing changes to coral community structure over time and for estimating coral-reef resistance and resilience to future bleaching disturbance.

Patterns and processes affecting juvenile scleractinian corals have received very little attention due to difficulties associated with detecting small corals on natural substrata. However, processes occurring during juvenile life stages are likely to play a strong role in population ecology. In particular, spatial differences in juvenile demographic rates may result in prominent differences in population and community structure for corals. In the present study, we compared the density, taxonomic composition, size structure, growth and mortality rates of juvenile corals (≤50 mm) and the cover and composition of adult coral assemblages among sites on Trunk Reef (central Great Barrier Reef) and Moorea (French Polynesia). There was significant regional variation in the taxonomic composition of coral assemblages within both adult and juvenile assemblages, with Pocillopora being the predominant coral genus in Moorea and Acropora at Trunk Reef. However, there were no differences in the density, growth or mortality rates of juvenile corals between Moorea and Trunk Reef. Most of the variation in these variables was evident at the small (within-reef) scale, with exposed sites having lower densities and higher rates of mortality of juvenile corals than sheltered sites at both locations. The lack of geographic variation in the density, growth and mortality rates of juvenile corals is interesting given that the cover of adult coral was 3-fold higher on Moorea (31.1%) than Trunk Reef (10.8%), suggesting that adult coral assemblages are structured more by differential adult mortality, larval settlement or very early post-settlement mortality (before colonies can be observed in situ), rather than demographic rates of juvenile growth or mortality.

Mass bleaching events resulting in coral mortality are among the greatest threats to coral reefs, and are projected to increase in frequency and intensity with global warming. Achieving a better understanding of the consistency of the response of coral assemblages to thermal stress, both spatially and temporally, is essential to determine which reefs are more able to tolerate climate change. We compared variations in spatial and taxonomic patterns between two bleaching events at the scale of an island (Moorea Island, French Polynesia). Despite similar thermal stress and light conditions, bleaching intensity was significantly lower in 2007 (approximately 37 % of colonies showed signs of bleaching) than in 2002, when 55 % of the colonies bleached. Variations in the spatial patterns of bleaching intensity were consistent between the two events. Among nine sampling stations at three locations and three depths, the stations at which the bleaching response was lowest in 2002 were those that showed the lowest levels of bleaching in 2007. The taxonomic patterns of susceptibility to bleaching were also consistent between the two events. These findings have important implications for conservation because they indicate that corals are capable of acclimatization and/or adaptation and that, even at small spatial scales, some areas are consistently more susceptible to bleaching than others.

In this study, we describe spatio-temporal variation in coral recruitment in the back reef of Moorea, French Polynesia, and explore the extent to which it is associated with community struc- ture, seawater temperature, and wave regimes. Recruitment was assessed with settlement tiles deployed at 10 sites on the north, southeast, and southwest shores and sampled every 5 to 7 mo from 2005 to 2007. Temperature and waves were measured using thermistors and pressure sensors, and community structure was assessed using in situ surveys. Mean recruitment varied from 0 to 6 recruits tile -1 (510 cm 2 ) and was generally greater in the second compared to the first year of the study. Recruitment varied among sites, and this variation was similar between years but differed among sampling periods: acroporids were common on the southwest shore between January and September, but rare from September to January; poritids were common on the north shore between September and January, but rare on the southwest shore from January to September; and pocillo- porids were found all year, but at slightly elevated densities between January and September. The mean daily seawater temperature, and the daily range, varied among sites, but neither was closely related to coral recruitment, and both were of biologically small magnitudes. The coral community structure also varied among sites, but likewise, was not associated with coral recruitment. In contrast, outer reef wave energy exposure, which likely played an important role in driving cross-reef trans- port of seawater into the lagoon, differed between shores and seasons in a pattern consistent with the variation in coral recruitment in the back reef. We hypothesize that coral recruitment in the back reef of Moorea is influenced by the interaction of seasonal variation in wave exposure, family-level differ- ences in coral reproductive timing, and the spatial distribution of adult corals.

International audience; We report variation in the size-structure of three coral taxa in the Society Islands (French Polynesia)using a hierarchical sampling design that integrates the regional (among three islands: Moorea, Raiatea,Tahiti), island (among three locations around each island), and local levels (among three depths: 6, 12,18 m, at each location). All coral taxa exhibited strong heterogeneity in their size-structure, with markedvariation among depths, locations, and islands. Porites spp. and Acropora globiceps populations at 6 mdepth were dominated by smaller size classes compared to other depths. Regional-scale variation wasparticularly evident for Pocillopora meandrina and A. globiceps, with a higher proportion of smaller coloniesfound at Raiatea, probably as a result of recent cyclones followed by higher recruitment rates.Porites spp. populations were characterized by a preponderance of larger colonies, and greater sizeranges compared to the other two taxa

Little information is available on reproductive processes among corals in isolated central Pacific reef regions, including French Polynesia. This study examined the timing and mode of sexual reproduction for Acropora reef corals at Moorea. Spawning was observed and/or inferred in 110 Acropora colonies, representing 12 species, following full moon periods in September through November 2002. Gamete release was observed and inferred in four species of Acropora between 9 and 13 nights after the full moon (nAFM) in September 2002. Twelve Acropora spp. spawned gametes between 5 and 10 nAFM in October 2002, with six species spawning 7 nAFM and four species spawning 9 nAFM. In November 2002, spawning of egg and sperm bundles was observed and inferred in 27 colonies of Acropora austera, 6 nAFM. These are the first detailed records of spawning by Acropora corals in French Polynesia.

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 of Pocillopora 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.

Coral reefs in French Polynesia, just like many others throughout the world, have been subjected to several natural disturbances including 15 cyclones, seven major bleaching events, and several Acanthaster planci outbreaks since the 1980s. In order to document the effects of these perturbations on coral assemblages, we initiated a long-term monitoring program that extended over both local and regional scales. Coral cover was quantified at 20 sites situated on the outer reef slope of 13 islands. The results from the first decade (1992-2002) are analyzed and the adequacy of our approach is discussed in the context of identifying potential indicators of coral reef health. Among 13 islands in French Polynesia, only two were unaffected by natural disturbances. We found important local and regional variation in the impacts of coral bleaching and cyclones, and three major temporal trends were distinguished: 1) 10 sites where coral cover decreased in relation to the occurrence of major disturbances; 2) nine sites where coral cover increased, despite the occurrence of disturbances affecting seven of them; and 3) a site where no significant variation in coral cover was found. The responses to perturbations were different among coral genera: Acropora species were particularly susceptible to bleaching events, whereas physical damages induced by cyclones concerned mainly branching species of Acropora and Pocillopora. Thus, monitoring surveys could be improved by selecting different and complementary indicators (one on the variation in diversity, one estimating changes in the abundance/cover, and one estimating the potential for recovery), by integrating several spatial scales, and by including at least the most informative species. High frequency recordings of environmental parameters (e.g. sea surface temperature) may be also a complementary tools for identifying causal relationships between changes in coral reef community structure and the factors causing the changes.

Coral reef fishes often exhibit a high degree of structure in their distribution and abundance, but the factors that influence their spatial arrangement are poorly understood. This study sought to explain the spatial structure of coral reef fish communities in the Ryukyu Archipelago. southern Japan. Visual surveys of coral reef fishes were conducted at multiple stations across the fringing reef (from the inner reef flat to the outer slope) at each of three different islands; Aka, Ishigaki and Sesoko. Spatial variation in fish communities (within and among reefs) was then compared to changes in environmental variables (water depth, distance from the shoreline, reef zone, coral abundance and coral richness). Despite being small islands, the total species richness of coral reef fishes in the Ryukyu Islands was very high (>87 species per reef). Mean abundance of reef fishes was also very high (x = 2.26 +/- 0.20 S.E. fishes per m(2)), but more than 80% of all fishes were from the family Pomacentridae. The structure of fish communities was very consistent among reefs, but varied greatly among zones within each reef. On the reef flat, the fish community was dominated by the pomacentrid Chrysiptera cyanea and the acanthurid Acanthurus nigrofuscus. In contrast, the reef slope community was characterised by high densities of the pomacentrids Pomacentrus lepidogenys and P. richardsoni, as well as high densities of the acanthurid Ctenochaetus striatus. Canonical correspondence analysis showed that the structure of the coral reef fish communities varied in relation to reef zone, water depth, and distance from the shoreline, but these changes were not related to spatial variation in either coral abundance or coral richness., Les poissons des récifs coralliens ont souvent une forte structuration spatio-temporelle de leur distribution et de leur abondance, mais les facteurs qui l’influencent sont encore peu connus. Cette étude a pour but d’analyser la distribution spatiale des communautés de poissons coralliens dans l’archipel des Ryukyus (sud du Japon). Des comptages visuels de poissons sont réalisés sur trois îles coralliennes (Aka, Ishigaki et Sesoko) avec différentes stations d’échantillonnage réparties du récif frangeant à la pente externe. La distribution spatiale obtenue à l’échelle intra- et inter-îles, est ensuite corrélée à différents facteurs environnementaux (profondeur de chaque station, distance des stations à la côte, unité géomorphologique sur laquelle la station est présente – lagon ou pente externe, abondance et richesse spécifique des coraux). Malgré le fait d'être des îles de petites tailles, la richesse spécifique des poissons aux Ryukyus est très élevée (>87 espèces par île). L’abondance moyenne des poissons est aussi trés forte (x = 2,26 ± 0,20 ES poissons par m2), mais plus de 80 % de cette abondance provient de la famille des Pomacentridae. Enfin, la structure des communautés des poissons est identique entre les îles, mais varie fortement à l’échelle insulaire avec la différenciation de deux communautés, une lagonaire et une de la pente externe. La communauté lagonaire est dominée par le Pomacentridae Chrysiptera cyanea et l’Acanthuridae Acanthurus nigrofuscus alors que la communauté de la pente externe est caractérisée par une forte densité de Pomacentridae, Pomacentrus lepidogenys et P. richardsoni, et d’Acanthuridae, Ctenochaetus striatus. L’analyse des correspondances canoniques démontre que la différenciation des deux communautés est corrélée à la localisation géomorphologique, à la profondeur et à la distance à la côte des stations, et non à l’abondance et à la richesse spécifique des coraux.

We analysed the interannual variability of the major reef communities (algae, corals and fishes) on the outer slope of the Tiahura sector on Moorea Island between 1991 and 1997, and exam- ined the impacts of natural disturbances on these communities. Patterns of temporal variation and the response to natural perturbations were clearly different among the taxa examined. A sharp decrease in the percent cover of branching corals (Pocillopora and Acropora) followed cyclonic and bleaching events that occurred in 1991. After 1993, a slight increase in coral cover values was recorded, and can be interpreted as a sign of recovery. Despite a similar proportion of bleached colonies at the begin- ning of bleaching events in 1991 and 1994, the bleaching in 1994 had no significant impact on coral cover. This result demonstrates the importance of understanding the ecological history of reefs (i.e. the chronology of disturbances) in interpreting the specific impacts of a particular disturbance. The decline in coral cover was accompanied by an increase in the percent cover of turf algae, but sur- prisingly, the percent cover of macroalgae did not show any significant temporal variation during the 7 yr period. Thus, the decrease in the percent cover of corals, which opens up new substrate, does not always result in an increase in macroalgal cover. The temporal variation of the fish community was mainly characterized by (1) the high variability in the recruitment of juveniles, with a peak in 1991; (2) the slight increase in the density of adult species; and (3) the decrease in the density of coralli- vorous chaetodontid fishes from 1991 to 1994. Since corals were the only taxon directly affected by natural disturbances, they were consequently the cause of the indirect effects of these disturbances (i.e. increase in turf algae and decrease in chaetodontid fishes), and can therefore be regarded as the 'key component' of the outer slope reef communities in Moorea.

© 2014 Edmunds et al. The reduction in coral cover on many contemporary tropical reefs suggests a different set of coral community assemblages will dominate future reefs. To evaluate the capacity of reef corals to persist over various time scales, we examined coral community dynamics in contemporary, fossil, and simulated future coral reef ecosystems. Based on studies between 1987 and 2012 at two locations in the Caribbean, and between 1981 and 2013 at five locations in the Indo-Pacific, we show that many coral genera declined in abundance, some showed no change in abundance, and a few coral genera increased in abundance. Whether the abundance of a genus declined, increased, or was conserved, was independent of coral family. An analysis of fossil-reef communities in the Caribbean revealed changes in numerical dominance and relative abundances of coral genera, and demonstrated that neither dominance nor taxon was associated with persistence. As coral family was a poor predictor of performance on contemporary reefs, a trait-based, dynamic, multi-patch model was developed to explore the phenotypic basis of ecological performance in a warmer future. Sensitivity analyses revealed that upon exposure to thermal stress, thermal tolerance, growth rate, and longevity were the most important predictors of coral persistence. Together, our results underscore the high variation in the rates and direction of change in coral abundances on contemporary and fossil reefs. Given this variation, it remains possible that coral reefs will be populated by a subset of the present coral fauna in a future that is warmer than the recent past.

International audience; Clonality and genetic structure of the coral Pocillopora damicornis sensu lato were assessed using five microsatellites in 12 populations from four islands of the Society Archipelago (French Polynesia) sampled in June 2008. The 427 analysed specimens fell into 132 multilocus genotypes (MLGs), suggesting that asexual reproduction plays an important role in the maintenance of these populations. A haploweb analysis of ITS2 sequences of each MLG was consistent with all of them being conspecific. Genetic differentiation was detected both between and within islands, but when a single sample per MLG was included in the analyses, the populations turned out to be nearly panmictic. These observations provide further evidence of the marked variability in reproductive strategies and genetic structure of P. damicornis throughout its geographic range; comparison with results previously obtained for the congeneric species Pocillopora meandrina underlines the importance of life history traits in shaping the genetic structure of coral populations.

Epibenthic macrofauna communities (corals, molluscs, echinoderms, and macroalgae) were investigated at Hikueru Atoll, Tuamotu Archipelago. The very low diversity and abundance that we observed (1 coral genus, and 2 mollusc, 1 echinoderm, and 17 macroalgal species) is likely to be the result of a mass mortality event that occurred 18 months earlier. Hydrological surveys suggest that this high mortality was the result of a major dystrophic crisis. Other atoll lagoons in the Tuamotu Archipelago have also been affected by high mortalities in the past, but Hikueru appears to have been the most frequently and intensely affected. The present study confirms that mass mortalities associated with phytoplankton blooms may be one of the major disturbances affecting coral reef ecosystems.

Zonation of macrobenthic communities (corals, algae, molluscs, sponges and echinoderms) on fringing reefs was investigated in two bays in a coral reef ecosystem (Moorea, French Polynesia). Species richness, abundance and coral cover, and species richness of macroalgae increased from the bayhead to the bay entrance. For molluscs and sponges, no general trend was observed. Species richness and abundance of echinoderms increased from the head to the entrance of Opunohu Bay, but this trend was less pronounced in Cook Bay. The gradients observed for corals, macroalgae and echinoderms were correlated with one or several of the following abiotic factors: salinity, turbidity, concentration of silicates in surface waters, and concentrations of organic carbon, carbohydrates and amino acids in the sediments. These factors are associated with terrestrial run-off via river discharge that occurs at the bayheads, where the major river is located. The high degree of confinement in the bayheads allowed the establishment of only a few tolerant macrobenthic species. Although the low diversity and abundance of corals and echinoderms seem to be a characteristic of Polynesian bays, a high diversity of corals can be found in the vicinity of the bayheads in coral reefs of the western Pacific.

Nine atolls were characterized in order to understand how physical factors control the species composition, diversity, and abundance of macrobenthic (coral, mollusc, echinoderm, and algal) communities inside the lagoons. Only one region, the central part of Tuamotu Archipelago, French Polynesia, was considered, in order to minimise the variation due to regional factors between regions. The lagoons investigated showed a gradient of physical factors, providing various landscape configurations. The physical factors were surface area, abundance of pinnacles, degree of hydrodynamic aperture, and relative importance of passes in this degree of aperture. Macrobenthic communities were characterized by low diversity and strong dominance of a few mollusc or echinoderm species that generally occurred in lagoons without passes. Correlation analyses indicated that species richness increases with the surface area of the lagoon. Species richness of corals, echinoderms, and macroalgae was also higher in lagoons having numerous pinnacles. Canonical correspondence analyses revealed that the distribution and the relative abundance of coral, echinoderm, and macroalgae species were correlated to the relative importance of passes, whereas degree of aperture of the lagoon was also relevant for corals and molluscs. The physical factors that control the processes of water exchange between ocean and lagoon, including passes, submerged reef flats, and spillways, influence the identity and the abundance of most macrobenthic species inside the lagoons.

The spatial patterns of butterflyfish assemblages (Chaetodontidae) were examined within and between five islands of the Ryukyu Archipelago, southern Japan. Despite being the northernmost reef communities in the world and despite the severe natural and human-induced disturbances that have affected them since the 1970s, the coral reefs of the Ryukyu Islands have one of the most diversified assemblages of chaetodontids in the world. A total of 30 species were identified, and species richness per island ranged from 20 to 25 species. On each of the 45 stations prospected, between four and 17 species were recorded, and between 0.75 and 21.75 ind 250 m−2 were counted. Variation in species composition, species richness and abundance between islands was less pronounced than the variation within islands, where assemblages of the major reef environments (i.e. the reef flat, the reef edge, and the reef slope) were distinguished. The highest species richness and abundance were found on the reef slope and the reef edge. Canonical correspondence analysis revealed that depth, substrate complexity, and live coral cover influenced the distribution of chaetodontid fishes. These factors accounted for 20% of the variation in the species data matrix.

This paper analyses the spatial patterns of fish communities on a narrow fringing reef of Mauritius and identifies some controlling factors. Canonical Correspondence Analysis revealed that the location in the reef ecosystem, the living coral coverage, and the proximity to a dredged area were the major factors controlling the distribution and abundance of fish species. Two distinct communities were observed across the fringing reef, representing a land-ocean gradient. The low diversity of fish species, and also of invertebrates such as corals, molluscs, and echinoderms is probably a consequence of the narrowness of the fringing reef and of anthropogenic impacts, notably the high pollution by nutrients.

The 9 km2 uplifted lagoon of Taiaro Atoll (15i45@S, 144i38@W) is hypersaline due to its isolation from the ocean, yet it contains a high diversity of fish. The question unifying our expedition was to discover whether these assemblages could be self-sustaining des- pite very limited contact with the ocean. Although we were constrained by time, collections of fish larvae showed that some species can complete their life-cycle within the lagoon, while others di⁄ered genetically bet- ween the lagoon and the ocean, consistent with re- stricted gene flow. The lagoon contained few oceanic species of zooplankton, confirming its general isolation, but nevertheless some fish species may depend upon infrequent colonisation from the ocean (when large waves drive water over the normally dry reef crest). Isotopic signatures in fish otoliths suggest the basis for a more definitive and inclusive test of the sources of the lagoonal assemblage.

Epibenthic macrofauna communities (species composition and densities of the dominant species) were investigated at Taiaro Atoll, Tuamotu Archipelago, 22 years after a previous survey. This small atoll is completely closed, has no permanent functional hoa, and is not affected by direct anthropogenic disturbances since it is a Biosphere Reserve. Ten species were identified in 1994 (5molluscs, 4 corals, and 1 echinoderm). With the 14 species identified in 1972 (12 molluscs, 1 coral, and 1 echinoderm), a total of 17 species (12 molluscs, 4 corals, and 1 echinoderm) has been recorded for the lagoon. There has been a shift in dominance away from the bivalve Crassostrea cucullata (in 1972) to Pinctada maculata (in 1994). A high mortality of the epibenthic macrofauna affected the central part of the lagoon shortly before1972 and reached the inner reef flat afterwards. The distance of Taiaro from sources of colonizers, its small size, and the isolation of its lagoonal waters posing a physical barrier to colonization by organisms and leading to harsh environmental conditions (e.g. very high salinities: 42.5–43 psu), are likely to be the major causes of the exceptionally low diversity observed.

This study provides a baseline describing natural small scale variability ofSymbiodiniumdensity in the sentinel coralAcropora globicepsduring the summer, under non-bleaching conditions. Spatial scales investigated range from the colony scale (1–10 cm, i.e. among branches of the same colony) to the reef scale (1–10 km, i.e. among stations distributed over several locations and depths), at Moorea Island, French Polynesia. The coral–Symbiodiniumsymbiosis is a key process in scleractinian coral physiology, andSymbiodiniumdensity provides an easy-to-measure and inexpensive biomarker of this symbiosis health. Spatial variability of three major environmental factors: light intensity, sedimentation and water motion was also assessed to evaluate their potential link withSymbiodiniumdensity. Density ofSymbiodiniumdid not significantly differ within colonies or among colonies within a station. However, a marked depth gradient was observed, showing increasing density with increasing depth and decreasing light intensity. These observations provide an interesting reference for forthcoming comparisons with disturbed conditions, such as bleaching events.

International audience; We compared relationships among distribution patterns of recruits, juveniles and adults of 3 different coral families with distinct life history traits at multiple spatial scales in an insular, fragmented reef system characterized by recurrent disturbances to better understand recruitment and maintenance processes of reef corals. The goal of our study was to detect at what scale most abundance variation occurred, and if this was consistent among life cycle stages and life histories. Results demonstrate a very high spatial variability of recruitment rates at the regional, insular and local hierarchical levels, with some locations displaying much higher recruitment rates than others, in 2 successive seasons. Juvenile and adult abundances were less variable, and most of the variation occurred at a local level for these life cycle stages. Recruit assemblage composition differed from juvenile and adult ones, which were much more similar. Moreover, abundance variation of recruits was unrelated to variation of juveniles and adults, but juvenile abundance was significantly correlated with adult abundance across all levels. These results have important implications for conservation planning, showing that some locations have better recovery abilities, and revealing the paramount importance of events occurring during the first weeks and months after settlement on the distribution of adults at regional, island and local levels, thus confirming the significance of local processes in shaping coral assemblages distribution and maintenance.

No-take marine reserves are one of the oldest and most versatile tools used across the Pacific for the conservation of reef resources, in particular for invertebrates traditionally targeted by local fishers. Assessing their actual efficiency is still a challenge in complex ecosystems such as coral reefs, where reserve effects are likely to be obscured by high levels of environmental variability. The goal of this study was to investigate the potential interference of small-scale habitat structure on the efficiency of reserves. The spatial distribution of widely harvested macroinvertebrates was surveyed in a large set of protected vs. unprotected stations from eleven reefs located in New Caledonia. Abundance, density and individual size data were collected along random, small-scale (20×1 m) transects. Fine habitat typology was derived with a quantitative photographic method using 17 local habitat variables. Marine reserves substantially augmented the local density, size structure and biomass of the target species. Density of Trochus niloticus and Tridacna maxima doubled globally inside the reserve network; average size was greater by 10 to 20% for T. niloticus. We demonstrated that the apparent success of protection could be obscured by marked variations in population structure occurring over short distances, resulting from small-scale heterogeneity in the reef habitat. The efficiency of reserves appeared to be modulated by the availability of suitable habitats at the decimetric scale ("microhabitats") for the considered sessile/low-mobile macroinvertebrate species. Incorporating microhabitat distribution could significantly enhance the efficiency of habitat surrogacy, a valuable approach in the case of conservation targets focusing on endangered or emblematic macroinvertebrate or relatively sedentary fish species.

International audience; Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea's appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems.

Coral reefs in Tonga have been confronted by multiple threats of various origins, including large-scale disturbances and human-induced stressors. These reef communities have been poorly studied, and efficient conservation actions are urgently needed. The aim of this study was to: (1) examine the spatial distribution of coral assemblages in the lagoon of Tongatapu; (2) determine the degree to which spatial heterogeneity of adult corals is influenced by recruitment processes; and (3) examine the implications of these results in terms of conservation actions. We recorded a total of 37 adult and 28 juvenile coral genera, a mean density of 11.6 adult and 5.5 juvenile colonies m(-2), and a dominance of Montipora, Acropora, and Porites. For seven of the 10 dominant genera, spatial patterns of adults were linked to the short-term recruitment pattern history. Despite a reduced diversity and abundance of adult corals in some areas, the lagoon of Tongatapu retains the potential for replenishment through recruitment of young corals. Consequently, we suggest that conservation actions should focus on reducing factors causing coral mortality and maintain suitable conditions for the establishment and growth of juvenile corals, thus increasing the probability that they will reach maturity and participate to the maintenance of local populations. Rather than establishing a large marine protected area, which will almost certainly suffer from a lack of control and poor enforcement, alternative conservation measures could be successfully implemented through the establishment of several small village-based marine reserves, as has been undertaken in other South Pacific islands with promising results.

International audience; Outbreaks of predatory crown-of-thorns seastars (COTS) can devastate coral reef ecosystems, yet some corals possess mutualistic guardian crabs that defend against COTS attacks. However, guarded corals do not always survive COTS outbreaks, with the ecological mechanisms sealing the fate of these corals during COTS infestations remaining unknown. In August 2008 in Moorea (17.539° S, 149.830° W), French Polynesia, an unusually dense multi-species aggregation of predators was observed feeding upon guarded corals following widespread coral decline due to COTS predation. Concurrent assaults from these amplified, mixed-species predator guilds likely overwhelm mutualistic crab defense, ultimately leading to the fall of guarded corals. Our observations indicate that guarded corals can sustain devastating COTS attacks for an extended duration, but eventually concede to intensifying assaults from diverse predators that aggregate in high numbers as alternative prey decays. The fall of guarded corals is therefore suggested to be ultimately driven by an indirect trophic cascade that leads to amplified attacks from diverse starving predators following prey decline, rather than COTS assaults alone

SUMMARY As the effects of climate change have become increasingly visible over the past three decades, coral reefs have suffered from a number of natural and anthropogenic disturbances that have caused a critical decline in coral populations. Among these disturbances are coral diseases, which have appeared with increasing frequency and severity, often in correlation with increases in water temperature. Although the crucial role played by Vibrio species in coral disease has been widely documented, the scientific community does not yet fully understand the infection process of Vibrio or its impact on coral physiology and immunology. Here, we investigated the physiological and transcriptomic responses of a major reef-building coral, Pocillopora damicornis, when exposed to a specific pathogen (Vibrio coralliilyticus) under virulent (increasing water temperature) and non-virulent (constant low temperature) conditions. The infection process was examined by electron microscopy and quantitative reverse-transcription PCR, and coral health was monitored by visual observations and measurements of zooxanthellar density. The results obtained suggest that coral tissue invasion occurs upon increasing water temperature only. Transcriptomic variations were investigated using a suppression–subtractive–hybridization approach, and the expression levels of six candidate immune-related genes were examined during bacterial exposure. These genes correspond to three lectin-like molecules putatively involved in the recognition of pathogens, two metal-binding proteins putatively involved in antibacterial response and one cystein protease inhibitor. The transcription patterns of these selected genes provide new insights into the responses of coral colonies to virulent versus non-virulent bacteria.

SUMMARY Expert opinion was canvassed to identify crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes. Scientists that had published three or more papers on the effects of climate and environmental factors on reef fishes were invited to submit five questions that, if addressed, would improve our understanding of climate change effects on coral reef fishes. Thirty-three scientists provided 155 questions, and 32 scientists scored these questions in terms of: (i) identifying a knowledge gap, (ii) achievability, (iii) applicability to a broad spectrum of species and reef habitats, and (iv) priority. Forty-two per cent of the questions related to habitat associations and community dynamics of fish, reflecting the established effects and immediate concern relating to climate-induced coral loss and habitat degradation. However, there were also questions on fish demographics, physiology, behaviour and management, all of which could be potentially affected by climate change. Irrespective of their individual expertise and background, scientists scored questions from different topics similarly, suggesting limited bias and recognition of a need for greater interdisciplinary and collaborative research. Presented here are the 53 highest-scoring unique questions. These questions should act as a guide for future research, providing a basis for better assessment and management of climate change impacts on coral reefs and associated fish communities.

International audience; We investigated the spatial distribution of adult and juvenile coral assemblages in the southwestern lagoon of New Caledonia, from disturbed fringing reefs within bays, to oceanic barrier reefs. Generic richness, abundance, and percent cover were highly variable at this scale, but no clear cross-shelf gradient was found. Rather, community composition was more related to reef biotopes. Correlations and canonical correspondence analyses revealed that composition and abundance of coral assemblages were related to substrate types (cover of turf algae and cover of encrusting coralline algae), but not to water quality or metal concentrations in sediments. We found a strong relationship between juvenile and adult distribution for all dominant genera, which suggests that recruitment processes are also a major factor structuring these populations. The densities of juveniles and their proportion in the coral assemblages were relatively low, which implies that replenishment capacities and potential for recovery are probably limited for these reefs.

International audience; Coral bleaching is often characterized by high spatial variation across reef systems. Using a field survey and manipulative experiment, we tested whether the physical structure of coral reefs modifies environmental conditions that, in turn, influence spatial variation in bleaching in 3 scleractinian corals, Pocillopora verrucosa, Acropora elseyi, and Porites rus. Corals inhabit mainly the hard-bottom seafloor, or dead or partially dead coral heads (‘bommies'). Bommies (0.10 to 3.0 m tall) position corals at different water depths and expose them to differences in light, temperature, hydrodynamics, and sedimentation, factors that can influence patterns of bleaching. We conducted our study in association with a 14 d warming event that caused bleaching in lagoons of Moorea, French Polynesia. Bleaching in naturally occurring colonies of Pocillopora spp. and Acopora spp. was greater on the seafloor (0 m tall) than on short (0.35 to 0.40 m tall) and tall bommies (1.0 to 1.2 m tall). Bleaching in P. verrucosa and A. elseyi transplanted to reef structures in the experiment generally decreased with increasing reef height (seafloor > short bommies > tall bommies). P. rus did not bleach under any conditions observed. Regression analyses revealed that reef structure controlled current speed and sedimentation at the microhabitat scale (from centimeters to meters), and that these factors regulated bleaching and mortality in P. verrucosa and A. elseyi. Our results imply that the physical structure of shallow water reef habitat influences the performance of coral colonies by modifying environmental stress, and that accounting for this structure is important in managing coral reef systems.

influence de la localisation et de la profondeur. Les evenements de blanchissement corallien sont parmi les perturbations les plus frequentes et les plus devastatrices que subissent les recifs coralliens. A Moorea (Polynesie francaise), entre mars et juillet 2002, une moyenne de 55 ± 14% des colonies a blanchi. L'intensite du blanchissement variait fortement en fonction des genres consideres, de la localisation et de la profondeur, atteignant 72% en certaines stations. Les coraux ont davantage blanchi au niveau des stations profondes qu'aux faibles profondeurs, et plus sur la cote nord que sur la cote ouest. Cette forte variabilite a petite echelle spatiale est probablement le resultat d'interactions entre des facteurs extrinseques, comme l'hydrodynamisme, et intrinseques, comme des adaptations differentielles des associations algues/corail a l'augmentation de la temperature.

The size structure of coral populations is influenced by biotic and physical factors, as well as species-specific demographic rates (recruitment, colony growth, mortality). Coral reefs surrounding Moorea Island are characterized by strong environmental gradients at small spatial scales, and therefore, we expected that the size structure of coral populations would vary greatly at this scale. This study aimed at determining the degree of spatial heterogeneity in the population size structure of two coral taxa, Pocillopora meandrina and massive Porites spp., among depths (6, 12, and 18 m) and among locations (Vaipahu, Tiahura and Haapiti) representing different exposure to hydrodynamic forces. Our results clearly underlined the strong heterogeneity in the size structure of both P. meandrina and massive Porites spp., with marked variation among depths and among locations. However, the lack of any consistent and regular trends in the size structure along depths or among locations, and the lack of correlation between size structure and mean recruitment rates may suggest that other factors (e.g., stochastic life history processes, biotic interactions, and disturbances) further modify the structure of coral populations. We found that the size structure of P. meandrina was fundamentally different to that of massive Porites spp., reflecting the importance of life history characteristics in population dynamics.