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Coral reefs across the globe are facing threats from a variety of anthropogenic disturbances. Consequently, the proportional representation of live scleractinian corals in the benthic community has declined substantially in many regions. In contrast, parts of the reef ecosystem around Mo’orea (French Polynesia) have displayed remarkable rebound potential. Nevertheless, detailed studies of when, where, and to what extent reefs have been disturbed and subsequently recovered in the different reef habitats are lacking. Using long-term monitoring data (2004-2018), we reveal that the spatiotemporal dynamics of benthic communities differ markedly between the contiguous inner (fringing and barrier) and outer (fore) reefs. Coral communities on inner reefs vary spatially but were remarkably stable over 15 yr, exhibiting consistent levels of coral and algal cover, with no evidence for disturbance-driven regimes or community transitions. In contrast, the outer reefs showed marked declines in coral cover following consecutive acute disturbances, but coral recovered rapidly thereafter. Nevertheless, community composition changed significantly, with Pocillopora replacing Acropora as the dominant genus at several sites, indicating a more subtle but potentially critical transition into an alternative state defined by the prevalence of a single, fast-growing genus. Inner reef stability and outer reef recovery provide evidence that the effects of environmental disturbances and chronic anthropogenic stressors can manifest in fundamentally different ways, depending on prevailing conditions. Our results suggest important ecological and physical links between inner and outer reef systems that influence the observed dynamics, emphasizing that reef ecosystem management and conservation strategies need to consider all habitats.

Responses of corals to seawater acidification have been extensively studied. Sensitivity varies widely between species, highlighting the need to avoid extrapolation from one to another to get an accurate understanding of coral community responses. We tested the responses of seven coral species (Acropora cytherea, Acropora hyacinthus, Acropora pulchra, Leptastrea pruinosa, Montipora grisea, Pavona cactus, Pocillopora verrucosa) from the Mo'orea lagoon to a 48-day exposure to three pH scenarios (pH 7.95, 7.7 and 7.3). Tissue necrosis, mortality, growth rates, photophysiological performances and colour index were recorded. Few significant differences were noted between pH 7.95 and 7.7, but species-specific responses were observed at pH 7.3. While our data do not allow identification of the mechanisms behind this diversity in response between species inhabiting the same environment, it can exclude several hypotheses such as local adaptation, skeletal type, corallum morphology or calcification rate as sole factors determining coral sensitivity to pH.

Local thermal environment has a strong influence on the physiology of marine ectotherms. This is particularly relevant for tropical organisms living close to their thermal optimum, well exemplified by the increasing frequency of bleaching occurrence in shallow-water corals. Mesophotic Coral Ecosystems (MCEs) were suggested as potential oases, especially when they are submitted to internal waves inducing short-term cooling events. Indeed, probability of bleaching occurrence in scleractinians was reported to decrease with depth in Mo'orea as temperature variability increases. However, ecophysiological data are currently lacking to understand the cause of lower susceptibility/increased plasticity of deeper corals. A growing interest has been devoted the last decade to MCEs, but our understanding of the physiological performance of benthic organisms living in this environment remains relatively unexplored. To tackle that question, we first compared the metabolic responses (dark respiration, net photosynthesis and photosynthetic efficiency) of the depth-generalist scleractinian Pachyseris speciosa from two heterogeneous thermal environment (25 and 85 m depths) to acute heat stress to determine if the local thermal environment could predict coral response to warming. Then, we tested the thermal performance of two sympatric species (the scleractinian P. speciosa and the antipatharian Stichopathes sp.) to determine if there are inter-species differences in performances in species experiencing identical levels of temperature variability, at mesophotic depths (85 m). Results revealed broader thermal performances in the mesophotic P. speciosa compared to mid-depth ones, and constrained performances in the mesophotic antipatharian compared to the scleractinian species. We hypothesize that the high fluctuations in temperature due to internal waves in deeper areas contribute to the broader thermal performances of mesophotic P. speciosa. However, the constrained performances of the mesophotic antipatharian compared to P. speciosa suggests that other processes than the symbiosis with zooxanthellae also influence thermal performances of these mesophotic organisms. Our results supported that Stichopathes sp. lives close to its thermal optimum, suggesting a (relatively) cold thermal specialist strategy. In this context, composition of MCEs in the future is unlikely to shift to antipatharian-dominated landscape and will remain coral-dominated landscape.

The rapid decline of shallow coral reefs has increased the interest in the long-understudied mesophotic coral ecosystems (MCEs). However, MCEs are usually characterised by rather low to moderate scleractinian coral cover, with only a few descriptions of high coral cover at depth. Here, we explored eight islands across French Polynesia over a wide depth range (6 to 120 m) to identify coral cover hotspots at mesophotic depths and the co-occurrent biotic groups and abiotic factors that influence such high scleractinian cover. Using Bayesian modelling, we found that 20 out of 64 of studied deep sites exhibited a coral cover higher than expected in the mesophotic range (e.g. as high as 81.8 % at 40 m, 74.5 % at 60 m, 53 % at 90 m and 42 % at 120 m vs the average expected values based on the model of 31.2 % at 40 m, 22.8 % at 60 m, 14.6 % at 90 m and 9.8 % at 120 m). Omitting the collinear factors light-irradiance and depth, these 'hotspots' of coral cover corresponded to mesophotic sites and depths characterised by hard substrate, a steep to moderate slope, and the dominance of laminar corals. Our work unveils the presence of unexpectedly and unique high coral cover communities at mesophotic depths in French Polynesia, highlighting the importance of expanding the research on deeper depths for the potential relevance in the conservation management of tropical coral reefs.

Coral reefs are declining at an unprecedented rate as a consequence of local and global stressors. Using a 26-year monitoring database, we analyzed the loss and recovery dynamics of coral communities across seven islands and three archipelagos in French Polynesia. Reefs in the Society Islands recovered relatively quickly after disturbances, which was driven by the recovery of corals in the genus Pocillopora (84% of the total recovery). In contrast, reefs in the Tuamotu and Austral archipelagos recovered poorly or not at all. Across archipelagos, predation by crown-of-thorns starfish and destruction by cyclones outweighed the effects of heat stress events on coral mortality. Despite the apparently limited effect of temperature-mediated stressors, the homogenization of coral communities towards dominance of Pocillopora in the Society Archipelago and the failure to fully recover from disturbances in the other two archipelagos concern the resilience of Polynesian coral communities in the face of intensifying climate-driven stressors.

Antipatharians, also called black corals, are present in almost all oceans of the world, until extreme depths. In several regions, they aggregate in higher densities to form black coral beds that support diverse animal communities and create biodiversity hotspots. These recently discovered ecosystems are currently threatened by fishing activities and illegal harvesting for commercial purposes. Despite this, studies dedicated to the physiology of antipatharians are scarce and their responses to global change stressors have remained hardly explored since recently. Here, we present the first study on the physiological responses of a mesophotic antipatharian Stichopathes sp. (70-90 m) to thermal stress through a 16-d laboratory exposure (from 26 to 30.5 °C). Oxygen consumption measurements allowed identifying the physiological tipping point of Stichopathes sp. (T

International audience; Coral reefs provide a range of important services to humanity, which are underpinned by community-level ecological processes such as coral calcification. Estimating these processes relies on our knowledge of individual physiological rates and species-specific abundances in the field. For colonial animals such as reef-building corals, abundance is frequently expressed as the relative surface cover of coral colonies, a metric that does not account for demographic parameters such as coral size. This may be problematic because many physiological rates are directly related to organism size, and failure to account for linear scaling patterns may skew estimates of ecosystem functioning. In the present study, we characterize the scaling of three physiological rates — calcification, respiration, and photosynthesis — considering the colony size for six prominent, reef-building coral taxa in Mo'orea, French Polynesia. After a seven-day acclimation period in the laboratory, we quantified coral physiological rates for three hours during daylight (i.e., calcification and gross photosynthesis) and one hour during night light conditions (i.e., dark respiration). Our results indicate that area-specific calcification rates are higher for smaller colonies across all taxa. However, photosynthesis and respiration rates remain constant over the colony-size gradient. Furthermore, we revealed a correlation between the demographic dynamics of coral genera and the ratio between net primary production and calcification rates. Therefore, intraspecific scaling of reef-building coral physiology not only improves our understanding of community-level coral reef functioning but it may also explain species-specific responses to disturbances.

The resilience of coral reefs is dependent on the ability of corals to settle after disturbances. While crustose coralline algae (CCA) are considered important substrates for coral settlement, it remains unclear whether coral larvae respond to CCA metabolites and microbial cues when selecting sites for attachment and metamorphosis. This study tested the settlement preferences of an abundant coral species (Acropora cytherea) against six different CCA species from three habitats (exposed, subcryptic and cryptic), and compared these preferences with the metabolome and microbiome characterizing the CCA. While all CCA species induced settlement, only one species (Titanoderma prototypum) significantly promoted settlement on the CCA surface, rather than on nearby dead coral or plastic surfaces. This species had a very distinct bacterial community and metabolomic fingerprint. Furthermore, coral settlement rates and the CCA microbiome and metabolome were specific to the CCA preferred habitat, suggesting that microbes and/or chemicals serve as environmental indicators for coral larvae. Several amplicon sequence variants and two lipid classes—glycoglycerolipids and betaine lipids—present in T. prototypum were identified as potential omic cues influencing coral settlement. These results support that the distinct microbiome and metabolome of T. prototypum may promote the settlement and attachment of coral larvae.

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.

International audience; Although fish is an important source of nutrients, including some of the healthiest proteins, long-chain fatty acids, and essential selenium, species at the top of the food chain frequently contain large amounts of toxic mercury (Hg). The provisional tolerable weekly intake (PTWI) of Hg from fish consumption is calculated from the total concentration of Hg and assuming that all Hg is speciated as organic methylmercury (MeHg). Using high energy-resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy, we show that blue marlin (Makaira sp.), a common top predator consumed by humans, contains high concentrations of inorganic Hg(II) complexed as 57 ± 10% Hg-tetraselenolate [Hg(Sec)4] and 43 ± 10% tiemannite (HgSe). The stable Hg–Se chemical bond likely attenuates the bioavailability of Hg and counteracts some of its health hazards to consumers. Thus, monitoring the concentration of MeHg, rather than total Hg, in top predators such as marlin would provide a more robust measure of potential Hg exposure and may be sufficient for food safety controls. The bonding of Hg atoms to four selenocysteine (Sec) residues in the Hg(Sec)4 complex severely depletes the stock of bioavailable Se, and quantification shows that blue marlin is not a chief source of dietary Se essential to selenoenzyme synthesis and activity.

The symbiosis between scleractinian corals and photosynthetic algae from the family Symbiodiniaceae underpins the health and productivity of tropical coral reef ecosystems. While this photosymbiotic association has been extensively studied in shallow waters (

In 2016, many tropical corals worldwide were exposed to anomalously high temperatures due to one of the strongest El Nino events ever recorded. Bleaching impacts were reported on 23 islands within three archipelagos of French Polynesia (Tuamotu, Society and Marquesas archipelagos). A detailed study on the effects of elevated temperatures on corals was performed on five islands (Mo'orea, Makemo, Hikueru, Marutea and Katiu) and revealed contrasting patterns of coral bleaching responses between Mo'orea (Society Archipelago) and the four islands of the Tuamotu Archipelago. While some reefs from the Tuamotu lost more than half of their coral cover, in Mo'orea, less than 1% mortality was recorded 6 months after bleaching. During the 2016 bleaching event, certain reefs at 12 m depth in the outer reef habitats were not exposed to sufficiently long high-temperature periods (heat stress not exceeding 1.1 degrees C weeks in Mo'orea) to cause large-scale bleaching-related coral mortality. In contrast, other reefs in the Tuamotu Archipelago had DHW reaching up to 9.2 degrees C weeks and experienced severe mortality (up to 71%). Our study showed how differential heat stress exposure across reefs of French Polynesia led to different impacts on corals. Until now, Mo'orea reefs have been spared abnormally high temperatures leading to mortality and should be considered an important source of larvae to help maintain reefs on the surrounding islands.

Coral reef ecosystems are declining at an alarming rate. Increasing seawater temperatures and occurrence of extreme warming events can impair sexual reproduction in reef-building corals and inhibit the ability for coral communities to replenish and persist. Here, we investigated the role of photophysiology on the reproductive ecology of Pocillopora acuta coral colonies by focusing on the impacts of bleaching susceptibility of parents on reproduction and larval performance, during an El Nino Southern Oscillation event in Mo'orea, French Polynesia. Elevated temperature conditions at that time induced bleaching phenotypic differences among P. acuta individuals: certain colonies became pale (from the loss of pigments and/or decline in symbiont cell density), while others remained pigmented (normal/high symbiont cell density). More specifically, we studied the impact of parental phenotypes on offspring's fluorescence by counting released larvae and sorting them by fluorescence types, we assessed survival to thermal stress, recruitment success and post-recruitment survival of released larvae from each fluorescent phenotype, during summer months (February to April 2016). Our results showed that red and green fluorescent larvae released by P. acuta had distinct physiological performances: red fluorescent larvae exhibited a higher survival into the pelagic phase regardless temperature conditions, with lower capacity to settle and survive post-recruitment, compared to green larvae that settle within a short period. Interestingly, pale colonies released two-to seven-fold more red fluorescent larvae than pigmented colonies did. In the light of our results, photophysiological profiles of the brooding P. acuta parental colonies may modulate the fluorescence features of released larvae, and thus influence the dispersal strategy of their offspring, the green fluorescent larval phenotypes being more performant in the benthic than pelagic phase.

Ocean acidification has emerged as a major concern in the last fifteen years and studies on the impacts of seawater acidification on marine organisms have multiplied accordingly. This review aimed at synthesizing the literature on the effects of seawater acidification on tropical scleractinians under laboratory-controlled conditions. We identified 141 articles (published between 1999 and 2021) and separated endpoints into 22 biological categories to identify global trends for mitigation and gaps in knowledge and research priorities for future investigators. The relative number of affected endpoints increased with pH intensity (particularly for endpoints associated to calcification and reproduction). When exposed to pH 7.6-7.8 (compared to higher pH), 49% of endpoints were affected. The diversity in experimental designs prevented deciphering the modulating role of coral life stages, genera or duration of exposure. Finally, important bias in research efforts included most experiments on adult corals (68.5%), in 27 out of 150 (18%) coral ecoregions and exclusively from shallow-waters.

Environmental pollution, particularly oil pollution, has been a long-standing problem in marine areas. With the aim to assess the pollution status in the Persian Gulf, Iran, herein surface sediments were collected from Kharg and Lark coral reefs, in summer (dry season) and winter (wet season), to evaluate the spatio-temporal variations of n-alkanes and PAHs. The mean total organic carbon (TOC) contents of sediments showed a significantly dramatic variation (p 0.76) was observed between ∑25n-alkanes and ∑30PAHs at Kharg and Lark sediments with TOC content, especially for the sites with high total pollutant concentrations. Based on the potential impact and ecological risk of n-alkanes and PAHs in surface sediments, it is, therefore, necessary in future studies to focus on their effects on corals and other marine organisms within this ecosystem.

International audience; French Polynesia exhibit a wide diversity of islands and coral-reef habitats, from urbanized high islands to remote atolls. Here, we present a geographically extensive baseline survey that examine the levels of nine metals (Ag, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) and one metalloid (As) in superficial sediments from 28 sites spread over three islands of French Polynesia. We used Principal Component Analysis, Pearson's correlation, hierarchical cluster analysis and generalized linear mixed-effect models on Pollution Load Index to investigate site contamination and metal(loid) associations. At most sites, metal(loid) levels below commonly applied sediment quality guidelines. However, a few sites located near farming activities, river discharges and urbanized areas showed contamination levels above these guidelines. This study provides critical baseline values for metal(loid) contaminants in this region and in coral-reef areas in general, and spur decreased discharge of metal(loid) contaminants in the anthropogenised areas of French Polynesia.

Development of nickel mining activities along the New Caledonia coasts threatens the biodiversity of coral reefs. Although the validation of tropical marine organisms as bioindicators of metal mining contamination has received much attention in the literature over the last decade, few studies have examined the potential of corals, the fundamental organisms of coral reefs, to monitor nickel (Ni) contamination in tropical marine ecosystems. In an effort to bridge this gap, the present work investigated the bioaccumulation of (63)Ni in the scleractinian coral Stylophora pistillata and in its isolated zooxanthellae Symbiodinium, using radiotracer techniques. Results highlight the high capacities of coral tissues (zooxanthellae and host tissues) to efficiently bioconcentrate (63)Ni compared to skeleton (Concentration Factors CF at 14 days of exposure are 3 orders of magnitude higher in tissues than in skeleton). When non-contaminated conditions were restored, (63)Ni was more efficiently retained in skeleton than in coral tissues, with biological half-lives (Tb½) of 44.3 and 6.5 days, respectively. In addition, our work showed that Symbiodinium bioconcentrated (63)Ni exponentially, with a vol/vol concentration factor at steady state (VCFSS) reaching 14,056. However, compilation of our results highlighted that despite efficient bioconcentration of (63)Ni in Symbiodinium, their contribution to the whole (63)Ni accumulation in coral nubbins represents less than 7%, suggesting that other biologically controlled processes occur in coral host allowing such efficient bioconcentration in coral tissues.

International audience; Previous molecular studies have shown that many corals host a dynamic consortium of dominant and background populations of Symbiodiniaceae genotypes with putatively distinct physiological traits. In the present study, we developed a quantitative PCR assay combined with high-resolution melting analysis (qPCR–HRM) to distinguish which Symbiodiniaceae clades are present in a sample. Because the qPCR–HRM used in isolation yielded identical melt profiles for both clades A and C, this analysis was then coupled with further specific qPCR assays to enable the absolute quantification of all Symbiodiniaceae clades and host cells. When the assays were applied to in hospite samples, they had an absolute quantification level corresponding to one coral embryo of two cells and 1000 symbiont cells. The assays were successful on coral fragments from twelve species (eight families). We then used the qPCR–HRM assay in an ecological survey of Acropora pulchra at different spatial scales (within colony, between colonies and between sites). Differences in abundance and composition of Symbiodiniaceae clades in A. pulchra were observed at all spatial scales, suggesting that various environmental factors drove changes in Symbiodiniaceae assemblages among and within coral colonies. The qPCR–HRM assay developed in this study is a relatively simple, cost-effective and reproducible tool that can be used to accurately differentiate and quantify endosymbiont Symbiodiniaceae clades in coral in the field. This will provide new insights into coral-symbiont shuffling mechanisms and the resilience of coral colonies to environmental stressors.

The use of satellite images for environmental monitoring has shown a great potential to monitor large areas at relatively low costs. Classically, domain experts identify natural habitats in small areas, and construct habitat distribution maps over larger areas using a supervised classification. Since each pixel may correspond to several habitats, we are in a multi-target classification framework. Instances are pixels. Each pixel is associated with several target variables (i.e. habitats) simultaneously. Each variable is a set of category labels, i.e. a set of intervals (bins) representing habitat proportions. In such context, training data often comes from field data acquired by domain experts. However, location of these data may be approximate (e.g. due to accuracy of handheld GPS). This spatial inaccuracy is particularly problematic when these data are used to train a classifier on very high resolution (VHR) satellite images. Indeed, in some cases, spatial accuracy of field data may be much lower than the one of images. In this paper, we propose a preprocessing approach to correct this spatial inaccuracy of field data w.r.t. VHR satellite images. First, our process extracts candidate sequences of pixels related to a given field inventory. Then, it extracts the corresponding sequence of habitats in the field data and compare its similarity with the corresponding candidate sequence of pixels. Finally, it ranks candidate sequences of pixels and select the best one as training data. Two similarity measures are studied in this work. To validate our approach, we compare the performances of 46 multi-target supervised classification algorithms on a dataset dealing with coral reef monitoring. We study accuracy of classifiers with and without our preprocessing approach. We also compare performances of the two proposed similarity measures. Results show that the percentage of pixels whose labels were accurately predicted is much higher with our preprocessed data than the one with raw data.

Understanding the relationship between coral reef condition and recruitment potential is vital for the development of effective management strategies that maintain coral cover and biodiversity. Coral larvae (planulae) have been shown to use certain sensory cues to orient towards settlement habitats (e.g. the odour of live crustose coralline algae - CCA). However, the influence of auditory cues on coral recruitment, and any effect of anthropogenic noise on this process, remain largely unknown. Here, we determined the effect of protected reef (MPA), exploited reef (non-MPA) soundscapes, and a source of anthropogenic noise (boat) on the habitat preference for live CCA over dead CCA in the planula of two common Indo-Pacific coral species (Pocillopora damicornis and Acropora cytherea). Soundscapes from protected reefs significantly increased the phonotaxis of planulae of both species towards live CCA, especially when compared to boat noise. Boat noise playback prevented this preferential selection of live CCA as a settlement substrate. These results suggest that sources of anthropogenic noise such as motor boat can disrupt the settlement behaviours of coral planulae. Acoustic cues should be accounted for when developing management strategies aimed at maximizing larval recruitment to coral reefs.

The clam Gafrarium pectinatum was investigated to assess its usefulness as a bioindicator species of metal mining contamination in the New Caledonia lagoon. The uptake and depuration kinetics of Ag, Cd, Co, Cr, and Zn were determined following exposures via seawater, sediment, and food using highly sensitive radiotracer techniques (Ag-110m, Cd-109, Cr-51, Co-57, and Zn-65). When the clams were exposed to dissolved metals, Co, Zn, and Ag were readily incorporated in their tissues (concentration factors (CF) ranging from 181 to 4982 after 28 days of exposure) and all metals were strongly retained (biological half-lives always > 2 months). The estimated transfer factor (TF) in clam tissues after a 35-day sediment exposure was 1 to 4 orders of magnitude lower than the estimated CF, indicating a lower bioavailability of sediment-bound metals than dissolved ones. Once incorporated, metals taken up from sediment and seawater were retained longer than metals ingested with food, indicating that the uptake pathway influences the storage processes of metals in clam tissues. Compilation of our data into a global bioaccumulation model indicated that, except for Ag that essentially originated from food (92%), sediment was the main source of metal bioaccumulation in the clam (more than 80%). These results highlight that bioaccumulation processes strongly depend from one metal to the other. The overall efficient bioaccumulation and retention capacities of the clam G. pectinatum confirm its usefulness as a bioindicator species that can provide time-integrated information about ambient contamination levels in the tropical marine coastal environment.

Rising temperature can adversely affect specific functions of corals. Coral gametes and planulae of Acropora pulchra were evaluated to determine their temperature resistances, and the potential of developmental thermal acclimation was examined on gametes. Results highlight that fertilization success displays a relatively high thermal resistance at ET50 (median effective temperature) 31.5 ± 0.5 °C after 4 h and 30 min. Additionally, probability of larval survival is halved at LT50 (median lethal temperature) 28.4 ± 0.42 °C after 14 days. The pre-exposure of oocytes to 30 °C and 32 °C for 1 h increases the cell development pace during fertilization at ambient temperature. Pre-exposure of gametes, separately at 32 °C for 1 h, increases fertilization success rate by 63% at 32°C, conversely, pre-exposure to 30 °C induces more variable results. These results evidenced the occurrence of developmental thermal acclimation as a result of thermal pre-exposure of oocytes.

Environmental conditions can influence the physiology of marine organisms and have important implications for their reproductive performance and capacity to supply new recruits. This study examined the seasonal reproductive patterns of the coral Montipora capitata in habitats exposed to different sedimentation regimes. Although M. capitata is a main reef-building coral in the Hawaiian Archipelago, little is known about the gametogenic cycle and reproductive ecology of this important species. Our results indicate that gamete production in M. capitata is a resilient process; no differences in gamete development or fecundity were observed among sites with very different sedimentation regimes. The gametogenic cycle of M. capitata lasts between 10 and 11 months, with spawning occurring over 3-5 months during warmer months (May-September). Oocytes were found throughout the year, but spermatocysts were only found April-August. The largest increases in oocyte size occurred during February to May, the months when solar radiation increased rapidly. The largest variation in oocyte sizes was found during July and August; during this period individual colonies contained mature oocytes for immediate spawning and new oocytes being formed for spawning the next year. The capacity of M. capitata to reproduce in areas with high sedimentation is an interesting finding highlighting the potential of the species for acclimatization, adaptation, or both. Despite this optimistic finding, the management of terrestrial runoff and the restoration of habitat quality for corals remains a top priority to ensure the renewal and maintenance of coral populations.

International audience; Metal pollutants in marine systems are broadly acknowledged as deleterious: however, very little data exist for tropical scleractinian corals. We address this gap by investigating how life-history stage, season and thermal stress influence the toxicity of copper (Cu) and lead (Pb) in the coral Pocillopora damicornis. Our results show that under ambient temperature, adults and larvae appear to tolerate exposure to unusually high levels of copper (96 h-LC50 ranging from 167 to 251 μg Cu L−1) and lead (from 477 to 742 μg Pb L−1). Our work also highlights that warmer conditions (seasonal and experimentally manipulated) reduce the tolerance of adults and larvae to Cu toxicity. Despite a similar trend observed for the response of larvae to Pb toxicity to experimentally induced increase in temperature, surprisingly adults were more resistant in warmer condition to Pb toxicity. In the summer adults were less resistant to Cu toxicity (96 h-LC50 = 175 μg L−1) than in the winter (251 μg L−1). An opposite trend was observed for the Pb toxicity on adults between summer and winter (96 h-LC50 of 742 vs 471 μg L−1, respectively). Larvae displayed a slightly higher sensitivity to Cu and Pb than adults. An experimentally induced 3 °C increase in temperature above ambient decreased larval resistance to Cu and Pb toxicity by 23–30% (96 h-LC50 of 167 vs 129 μg Cu L−1 and 681 vs 462 μg Pb L−1).Our data support the paradigm that upward excursions in temperature influence physiological processes in corals that play key roles in regulating metal toxicity. These influences are more pronounced in larva versus adult corals. These findings are important when contextualized climate change-driven warming in the oceans and highlight that predictions of ecological outcomes to metal pollutants will be improved by considering environmental context and the life stages of organism under study.

Parental effects have been largely unexplored in marine organisms and may play a significant role in dictating the phenotypic range of traits in coral offspring, influencing their ability to survive environmental challenges. This study explored parental effects and life-stage differences in the Hawaiian reef-building coral Montipora capitata from different environments by examining the biochemical composition of mature coral colonies and their eggs. Our results indicate that there are large biochemical differences between adults and eggs, with the latter containing higher concentration of lipids (mostly wax esters), ubiquitinated proteins (which may indicate high turnover rate of proteins) and antioxidants (e.g., manganese superoxide dismutase). Adults displayed high phenotypic plasticity, with corals from a high-light environment having more wax esters, lighter tissue δ13C signatures and higher Symbiodinium densities than adults from the low-light environment who had higher content of accessory pigments. A green-algal pigment (α-carotene) and powerful antioxidant was present in eggs; it is unclear whether this pigment is acquired from heterotrophic food sources or from endolithic green algae living in the adult coral skeletons. Despite the broad phenotypic plasticity displayed by adults, parental investment in the context of provisioning of energy reserves and antioxidant defense was the same in eggs from the different sites. Such equality in investment maximizes the capacity of all embryos and larvae to cope with challenging conditions associated with floating at the surface and to disperse successfully until an appropriate habitat for settlement is found.

The goal of this study was to assess the contamination of Honolua Bay using an ecotoxicological approach. First, the concentrations of 9 contaminants (metals and metalloid) were assessed in sediments and tropical marine organisms (alga Halimeda kanaloana, goatfish Parupeneus multifasciatus and urchin Tripneustes gratilla) sampled from Honolua and surrounding Bays. Then, the ecological parameters characterizing coral health (e.g. coral cover) were evaluated in Honolua Bay in the context of these contaminants. High concentrations of Co, Cr, Mn, Ni, and V in sediments from Honolua and Honokohau Bay were measured, but these concentrations were not mirrored in the organisms examined, except for Mn, suggesting that the metals are generally bound in chemically inert forms in these sediments. Moreover, few anthropogenic activities impact these bays and so the elevated Co, Cr, Mn, Ni and V concentrations in sediments appear to stem from their high natural background in Honolua and Honokohau watersheds. An analysis of the relationship between the ecological parameters and metal concentrations in Honolua Bay revealed a significant correlation between coral cover and Co, Cr, Mn, Ni, V, Zn concentrations in sediments, with coral cover decreasing with increasing metal concentration. Collectively, however, the data suggest that a complex mixture of land-based stressors (e.g. sediment, metals, nutrients) affect the coral health in Honolua Bay, rather than metal stress alone.

International audience; The bioaccumulation and depuration kinetics of selected metals (Ag, Co, Hg, Mn and Zn) were determined in the European variegated scallop Chlamys varia following exposures via seawater and food, using highly sensitive radiotracer techniques (110mAg, 57Co, 203Hg, 54Mn and 65Zn). Body distribution of Ag, Co, Mn and Zn was similar for both waterborne and dietary metals. Ag was mainly present in the digestive gland (> 80%); Co and Mn were generally localized in similar proportions in the digestive gland and kidneys, whereas Zn was mainly found in the kidneys (> 40%). In contrast, Hg was mainly present in gills during seawater exposure whereas it was mainly distributed in the digestive gland after food exposure. The results from all the experiments have been integrated into a bioaccumulation model in order to delineate the relative contribution of each metal uptake route in C. varia. Computation indicated that food is the main uptake route of Ag, Co, Mn, and Zn in scallop, whereas waterborne and dietary pathways were shown to contribute similarly in the global bioaccumulation of Hg in C. varia. Except for Hg, dietary transfer was investigated using two different phytoplankton species (Isochrysis galbana and Skeletonema costatum). For Mn and Zn, the dietary contribution was not influenced by the phytoplankton species used. In contrast, food quality played a major role for Ag and Co intake, (e.g., dietary pathway contributed for 97% of global Ag bioaccumulation when S. costatum was used as food vs. 58% for Ag ingested with I. galbana).

Uptake and depuration kinetics of Cd, Co, Cr, Mn, Ni and Zn were determined in the brown alga Lobophora variegata exposed to realistic concentrations of these metals, using highly sensitive radiotracer techniques. The experiments were designed to assess the possible influence of varying dissolved metal concentrations on the capacity of metal bioconcentration and retention in the alga. Results indicate that the alga takes up Cd, Co, Cr, Ni, and Zn in direct proportion to their ambient dissolved concentrations over the entire range of concentrations tested (three orders of magnitude). In contrast, Mn was taken up in proportion to its dissolved concentration only over a concentration range of 2 orders of magnitude (up to 250 ng Mn L − 1 , i.e. 4.55 nM), then at higher concentrations its accumulation efficiency slightly decreased. Overall, L. variegata appears to be a reliable bioindicator species that shows a rapid response time in metal uptake (uptake rate constants ranging from 60 to 1,023 d − 1 ) and has a suitable potential to furnish valuable information on the bioavailable contamination levels occurring in New Caledonian areas affected by land-based mining activities. Furthermore, due to its wide geographical distribution, L. variegata could be considered as a useful bioindicator species for surveying metal contamination in many other tropical areas.

Uptake of waterborne Cd, Co, Mn and Zn was determined in laboratory experiments using radiotracer techniques (Cd-109, Co-57, Mn-54 and Zn-65). Labelled Zn was mainly accumulated in the digestive gland (65%) and Co in kidneys (81%); Cd and Mn were similarly distributed in digestive gland and gills. In a complementary field study, Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, and Zn were analysed in scallops collected at two stations showing different contamination levels. Digestive gland and kidneys displayed the highest concentrations. Ag, As, Cd, and Fe differed in soft tissues from the two stations, suggesting that Comptopallium radula could be a valuable local biomonitor species for these elements. Low Mn and Zn concentrations found in kidneys suggest that their content in calcium-phosphate concretions differs from the other pectinids. Preliminary risk considerations suggest that As would be the only element potentially leading to exposure of concern for seafood consumers. (c) 2007 Elsevier Ltd. All rights reserved.

The New Caledonian lagoon is submitted to intense heavy metal input from land-based Ni mining. Therefore, the use of sentinel species is strongly recommended in order to develop and implement coastal zone management programmes of the metal contamination. The tropical oysters Isognomon isognomon and Malleus regula and the clam Gafrarium tumidum were previously proposed as such possible sentinel organisms and were thus investigated in this context. The three species were exposed to Ni via seawater or food using radiotracer techniques. Results indicate that uptake and retention efficiencies of Ni are independent of the dissolved Ni concentrations in the surrounding seawater. Hence, for the three species, body concentrations of Ni taken up from the dissolved phase are directly proportional to the ambient dissolved concentrations. Biokinetic patterns indicated that the major part of Ni was rapidly lost from bivalves during the first days of depuration, whereas 7 to 47% of 63 Ni were retained in tissues with a biological half-life not significantly different from infinity. Finally, feeding experiments showed that Ni ingested with food (phytoplankton) was assimilated more efficiently in clams (assimilation efficiency, AE = 61%) than in oysters (AE = 17%), and was strongly retained (Tb1/2 P 35 d) in the tissues of both bivalves. It is concluded that the investigated species examined are efficient bioaccumulators of Ni from both the surrounding seawater and the food, and that they would be useful bioindicators for monitoring the status of Ni contamination in tropical coastal waters. � 2006 Elsevier Ltd. All rights reserved.

Bioaccumulation of (134)Cs was determined in 5 tropical marine species: three bivalves (the oysters Isognomon isognomum and Malleus regula, and the clam Gafrarium pectinatum), one decapod (shrimp Penaeus stylirostris) and one alga (Lobophora variegata). Marine organisms were exposed to the radionuclides via different pathways: seawater (all of them), food (shrimp and bivalves) and sediment (bivalves). Our results indicate that the studied tropical species accumulate Cs similarly than species from temperate regions whereas retention capacities seems to be greater in the tropical species. Bioaccumulation capacities of the two oysters were similar for all the exposure pathways. The alga, and to a lesser extent the shrimp, concentrated dissolved Cs more efficiently than the bivalves (approx. 14 and 7 times higher, respectively). Assimilation efficiencies of Cs in bivalves and shrimp after a single feeding with radiolabelled food were comprised between 7.0 ± 0.4 and 40.7 ± 4.3%, with a variable retention time (half-life -Tb1/2- ranging from 16 ± 3 to 89 ± 55 d). Although the clam lives buried in the sediment, this exposure pathway resulted in low bioaccumulation efficiency for sediment-bound Cs (mean transfer factor: 0.020 ± 0.001) that was lower than the two oyster species, which are not used to live in this media (0.084 ± 0.003 and 0.080 ± 0.005). Nonetheless, Cs accumulated from sediment was similarly absorbed (61.6 ± 9.7 to 79.2 ± 2.3%) and retained (Tb1/2: 37 ± 2 to 58 ± 25 d) for the three bivalves species. Despite the poor transfer efficiency of Cs from food, the use of a global bioaccumulation model indicated that the trophic pathways was the main uptake route of Cs in the bivalves and shrimp. In shelled organisms, shells played a non-negligible role in Cs uptake, and their composition and structure might play a major role in this process. Indeed, most of the Cs taken up from seawater and sediment was principally located on the hard parts of the bivalves and shrimp, with the exception of G. pectinatum, where Cs was mainly distributed in the soft-parts.

The life cycle of coral is affected by natural and anthropogenic perturbations occurring in the marine environment. In the context of global changes, it is likely that rainfall events will be more intense and that coastal reefs will be exposed to sudden drops in salinity. Therefore, a better understanding of how corals—especially during the pelagic life stages—are able to deal with declines in salinity is crucial. To fill this knowledge gap, this work investigated how gametes and larva stages of two species of Acropora (Acropora cytherea and Acropora pulchra) from French Polynesia cope with drops in salinity. An analysis of collected results highlights that both Acropora coral gametes displayed the same resistance to salinity changes, with 4h30-ES50 (effective salinity that decrease by 50% the fertilization success after 4h30 exposure) of 26.6 ± 0.1 and 27.5 ± 0.3‰ for A. cytherea and A. pulchra, respectively. This study also revealed that coral gametes were more sensitive to decreases in salinity than larvae, for which significant changes are only observed at 26‰ for A. cytherea after 14 d of exposure. Although rising seawater temperatures and ocean acidification are often perceived as the main threat for the survival of coral reefs, our work indicates that 70% of the gametes could be killed during a single night of spawning by a rainfall event that decreases salinity to 26‰. This suggests that changes in the frequency and intensity of rainfall events associated with climate changes should be taken seriously in efforts to both preserve coral gametes and ensure the persistence and renewal of coral populations.