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Copyright of Environnement, Risques & Santé is the property of John Libbey Eurotext Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nitrogen pollution increases the susceptibility of corals to heat-induced bleaching. However, different forms of nitrogen (nitrate vs. ammonium/urea) may have different impacts on thermal tolerance of corals. We used an 18-month field experiment on the oligotrophic fore reef of Moorea, French Polynesia, to test how different forms of nitrogen (nitrate vs. urea) impacted coral bleaching. The experiment spanned two moderate thermal stress events in 2016 and 2017. Nitrate increased bleaching prevalence in Acropora by up to 100% and in Pocillopora by up to 60% compared to control corals. Urea exposure often had intermediate effects on bleaching (not different from either control or nitrate-exposed corals) in both taxa. Importantly, nitrate prolonged bleaching in both Acropora and Pocillopora as nitrate-exposed corals remained bleached even after thermal stress ended, while control and urea-exposed corals had mostly recovered. Nitrate exposure also increased the prevalence of partial mortality in Pocillopora colonies and more than tripled the number of colonies that completely died. Our data are the first to show contrasting effects of different forms of nitrogen on coral bleaching and mortality in a natural reef environment, linking previous patterns from large-scale correlative studies with results from more mechanistic laboratory experiments. Most importantly, we showed that corals exposed to nitrate exhibited more frequent bleaching, bleached for longer duration, and were more likely to die than corals in low nitrogen conditions. Exposure to excess nitrogen, particularly anthropogenic nitrogen, may lower the temperature threshold at which corals bleach, triggering bleaching events on polluted reefs even when typical thermal stress thresholds have not been crossed. [ABSTRACT FROM AUTHOR]

Reef-building corals can harbour high abundances of diverse invertebrate epifauna. Coral characteristics and environmental conditions are important drivers of community structure of coral-associated invertebrates; however, our current understanding of drivers of epifaunal distributions is still unclear. This study tests the relative importance of the physical environment (current flow speed) and host quality (e.g., colony height, surface area, distance between branches, penetration depth among branches, and background partial mortality) in structuring epifaunal communities living within branching Pocillopora colonies on a back reef in Moorea, French Polynesia. A total of 470 individuals belonging to four phyla, 16 families and 39 genera were extracted from 36 Pocillopora spp. colonies. Decapods were the most abundant epifaunal organisms (accounting for 84% of individuals) found living in Pocillopora spp. While coral host characteristics and flow regime are very important, these parameters were not correlated with epifaunal assemblages at the time of the study. Epifaunal assemblages associated with Pocillopora spp. were consistent and minimally affected by differences in host characteristics and flow regime. The consistency in abundance and taxon richness among colonies (regardless of habitat characteristics) highlighted the importance of total habitat availability. With escalating effects of climate change and other localized disturbances, it is critical to preserve branching corals to support epifaunal communities. [ABSTRACT FROM AUTHOR]

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

Trends in mean and extreme annual and seasonal temperature and precipitation over the 1951–2015 period were calculated for 57 stations in 20 western Pacific Ocean island countries and territories. The extremes indices are those of the World Meteorological Organization Expert Team on Sector-Specific Climate Indices. The purpose of the expert team and indices is to promote the use of globally consistent climate indices to highlight variability and trends in climate extremes that are of particular interest to socioeconomic sectors and to help to characterize the climate sensitivity of various sectors. Prior to the calculation of the monthly means and indices, the data underwent quality control and homogeneity assessment. A rise in mean temperature occurred at most stations, in all seasons, and in both halves of the study period. The temperature indices also showed strong warming, which for the majority was strongest in December–February and weakest in June–August. The absolute and percentile-based indices show the greatest warming at the upper end of the distribution. While changes in precipitation were less consistent and trends were generally weak at most locations, declines in both total and extreme precipitation were found in southwestern French Polynesia and the southern subtropics. There was a decrease in moderate- to high-intensity precipitation events, especially those experienced over multiple days, in southwestern French Polynesia from December to February. Strong drying trends have also been identified in the low- to moderate-extreme indices in the June–August and September–November periods. These negative trends contributed to an increase in the magnitude of meteorological drought in both subregions. [ABSTRACT FROM AUTHOR]

Climate change has an ever-increasing impact on island territories. Whether it is due to rising sea levels or the increase in recurrence and intensity of extreme events, island territories are increasingly vulnerable. These impacts are expected to affect marine and terrestrial biodiversity, human occupation (infrastructure) and other activities such as agriculture and tourism, the two economic pillars of French Polynesia. While the current and future impacts of climate change on island territories are generally accepted, data acquisition, modeling, and projections of climate change are more complex to obtain and limitedly cover the island territories of the Pacific region. This article aims to develop methodologies for the acquisition and exploitation of data on current and future climate risks and their impacts in French Polynesia. This work of acquisition and valorization is part of a research project for the development of an observatory of resilience to climate risks in the perspective of building a spatial decision support system. [ABSTRACT FROM AUTHOR]

Le Cozannet, G., Garcin, M., Petitjean, L., Cazenave, A., Becker, M., Meyssignac, B., Walker, P., Devilliers, C., Le Brun, O., , Lecacheux, S., Baills, A., Bulteau, T. Yates, M., and Wöppelmann, G., 2013. Exploring the relation between sea level rise and shoreline erosion using sea level reconstructions: an example in French Polynesia. The climate component of sea level variation displays significant spatial variability, and it is now possible to reconstruct how sea level varied globally and regionally over the past half century. The fact that sea level rose faster than the global mean since 1950 in the central Pacific stimulated a study of decadal shoreline changes in this region. Here, the study of Yates et al. (2013) was extended to two additional atolls (17 islets): Tetiaroa and Tupai in the Society islands. Both atolls remain stable on the whole from 1955 to 2001/02, however with significant differences in shoreline changes among their islets and within the period. A modeling of waves generated by historical cyclonic events in French Polynesia since 1970 reveals consistency between major shoreline changes and cyclonic and seasonal waves. As in previous studies, this suggests that waves' actions are a dominant cause of shoreline dynamics on relatively undeveloped atolls, even if affected by higher sea level rise rates. In such regions, numerous joint analyses of shoreline changes and their potential causes may help to explain the relation between erosion and sea level rise. [ABSTRACT FROM AUTHOR]

Three sediment cores, from one upland and two lowland sites on Nuku Hiva, Marquesas Islands, provide a c. 750-year record of palaeo-environmental change on the island. Accelerator mass spectrometry (AMS) dating of pollen concentrates from the base of each core indicates that the three widely separated marshes developed c. AD 1200 and 1350, after the known period of human colonisation and establishment. Detailed analyses (pollen, sediments, and charcoal) and additional dating of the upland core from Tōvi’i Plateau (810 m) allow for identification of four chronozones. The core sediment data and age-depth curve suggest an alternation of wet-dry-wet conditions over the c. 750-year period. The pollen spectra, in contrast, are fairly stable, with ferns dominating but arborescent species also present. The micro-charcoal evidence points to regional burning and long-distance transport until c. AD 1640, after which localised burning may be indicated. Among the more notable changes is a major increase in pollen and spore deposition after c. AD 1640, a trend most evident in the pollen concentration diagram. Overall, the data suggest rapid sedimentation in the fourteenth century AD, followed by drier and/or more settled conditions until the mid-seventeenth century, and finally wetter conditions after c. AD 1640. The latter in particular is consistent with emerging regional evidence for warm-wet conditions in the central eastern Pacific during the seventeenth century, the height of the Northern Hemisphere ‘Little Ice Age’. The charcoal record also provides insights into human activities on the island, suggesting burning in the lowlands from the fourteenth century AD, probably in conjunction with forest clearance preparatory to tree and root crop cultivation. [ABSTRACT FROM AUTHOR]

Ciguatera poisoning (CP) results from the consumption of seafood contaminated with ciguatoxins (CTXs). This disease is highly prevalent in French Polynesia with several well-identified hotspots. Rapa Island, the southernmost inhabited island in the country, was reportedly free of CP until 2007. This study describes the integrated approach used to investigate the etiology of a fatal mass-poisoning outbreak that occurred in Rapa in 2009. Symptoms reported in patients were evocative of ciguatera. Several Gambierdiscus field samples collected from benthic assemblages tested positive by the receptor binding assay (RBA). Additionally, the toxicity screening of ≈250 fish by RBA indicated ≈78% of fish could contain CTXs. The presence of CTXs in fish was confirmed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The potential link between climate change and this range expansion of ciguatera to a subtropical locale of French Polynesia was also examined based on the analysis of temperature time-series data. Results are indicative of a global warming trend in Rapa area. A five-fold reduction in incidence rates was observed between 2009 and 2012, which was due in part to self-regulating behavior among individuals (avoidance of particular fish species and areas). Such observations underscore the prominent role played by community outreach in ciguatera risk management. [ABSTRACT FROM AUTHOR]