Unexpected residual habitats raise hope for the survival of the fan mussel Pinna nobilis along the Occitan coast (Northwest Mediterranean Sea)

In 2019, the status of the Mediterranean fan mussel Pinna nobilis was elevated to ‘Critically Endangered’ on the IUCN Red List, in response to the pandemic caused by the parasite Haplosporidium pinnae. Identifying refuge habitats, free from parasites, is critical to the survival of the mussel. The distribution of P. nobilis was investigated along the Occitan coast (Northwest Mediterranean Sea) because of the presence of a unique lagoonal system that may provide potential refuges. Interviews with users and managers were conducted to identify target zones where the species was sighted. In situ surveys were carried out to define the main aggregations of fan mussels and characterize the habitat. Line transects were deployed to count and measure individuals to estimate density, abundance, and size distribution. Population densities were variable, ranging from 0.6 ± 0.2 (SE) to 70.8 ± 7.6 ind. 100 m−2, representing one of the highest densities re - ported in the Mediterranean Sea. The total abundance of individuals across the coast was extra - polated to 163 000, with 87% located in Thau and Salses-Leucate, highlighting these lagoons as essential for the survival of the species. This study also revealed the diversity of habitats colonized by P. nobilis. In the context of the pandemic, only the lagoon populations remain unaffected and provide natural refuges that have disappeared from all open-water coastal areas. However, the conditions in these lagoons could become unfavorable, leading to the collapse of the last P. nobilis populations. We therefore propose that Thau and Salses-Leucate lagoons, which harbor the largest remaining populations of P. nobilis, should be declared as conservation priorities.En prens

Genetic homogeneity of the critically endangered fan mussel, Pinna nobilis, throughout lagoons of the Gulf of Lion (North‑Western Mediterranean Sea)

The fan mussel, Pinna nobilis, endemic to the Mediterranean Sea, is a critically endangered species facing mass mortality events in almost all of its populations, following the introduction of the parasite Haplosporidium pinnae. Such a unique pandemic in a marine organism, which spreads rapidly and with mortality rates reaching up to 100%, could lead to the potential extinction of the species. Only few regions, involving lagoon habitats, remain healthy throughout the entire Mediterranean Sea. This study describes the genetic structure of P. nobilis across the Gulf of Lion, including confined locations such as lagoons and ports. A total of 960 samples were collected among 16 sites distributed at 8 localities, and then genotyped using 22 microsatellite markers. Genetic diversity was high in all sites with mean allele numbers ranging between 10 and 14.6 and with observed heterozygosities (Ho) between 0.679 and 0.704. No genetic differentiation could be identified (FST ranging from 0.0018 to 0.0159) and the percentages of related individuals were low and similar among locations (from 1.6 to 6.5%). Consequently, all fan mussels, over the entire coastline surveyed, including those in the most geographically isolated areas, belong to a large genetically homogeneous population across the Gulf of Lion. Considering the ongoing mass mortality context, this result demonstrates that almost all of the genetic diversity of P. nobilis populations is still preserved even in isolated lagoons, which might represent a refuge habitat for the future of the species.En prensa2,92

Investigating population dynamics from parentage analysis in the highly endangered fan mussel Pinna nobilis

Understanding dispersal patterns is a major focus for conservation biology as it influences local survival and resilience in case of local disturbance, particularly for sessile species. Dispersal can be assessed through parentage analyses by estimating family structure and self-recruitment. This study documents the family structure of a pelagic spawner, Pinna nobilis, which is facing a major crisis that threatens its survival as most of its populations have been decimated by a parasite, Haplosporidium pinnae. In this context, we focused on a single population (Peyrefite, Banyuls-sur- mer, France) where 640 individuals were sampled in 2011, 2015, and 2018 and genotyped for 22 microsatellite markers. Genetic diversity was high and homogeneous among years, with mean allele numbers ranging between 13.6 and 14.8 and observed heterozygosities (Ho) between 0.7121 and 0.7331. Low, but significant, genetic differentiations were found between 2011–2015 and 2015–2018. A parentage analysis described 11 clusters, including one prevailing, and revealed that 46.9% of individuals were involved in half-sib relationships, even between years, suggesting that source populations were recurrent year after year. There were few individuals resampled between years (30 in 2015 and 14 in 2018), indicating a rapid turnover. Considering the large number of half-sib relationships but the low number of relations per individual, we conclude that P. nobilis exhibit homogeneous reproductive success. Self-recruitment was not detected, making this population highly vulnerable as replenishment only relies on connectivity from neighboring populations. In the context of the pandemic caused by H. pinnae, these results will have to be considered when choosing a location to reintroduce individuals in potential future rescue plans.En prensa

Development of 26 highly polymorphic microsatellite markers for the highly endangered fan mussel Pinna nobilis and cross-species amplification

International audienc

Assessment of the impact of coral bleaching and marine protection measures through passive acoustic monitoring

peer reviewe

Resilience dynamics of marine protected areas to coral bleaching extremes in the South Pacific Ocean: insights from passive acoustic monitoring

editorial reviewed14. Life below wate

Listening to global warming: assessment of the impact of coral bleaching and marine protection measures in Polynesia through passive acoustic monitoring

peer reviewedAmong the different disturbances affecting coral reefs, climate change is expected to become the major cause of their degradation towards this century. In coral reefs, anomalously high sea temperatures are linked to coral bleaching events. Mass bleaching events alter the ecological process of coral reefs while marine protected areas (MPAs) can increase the resilience of coral reef communities to natural disturbances, playing a role in sheltering biodiversity from climate-related impacts and in the recovery of corals from massive bleaching events. In Moorea Island (French Polynesia), two bleaching events occurred between 2015 and 2021. The aims of this study are to compare the soundscape of the external slope of Moorea Island within and outside MPAs in 2021 to access the presence or the absence of a protection effect on acoustic data and to compare them to data sampled in 2015 to access both temporal and protection effects, in relation with the benthic cover and the fish species present. MPAs have a greater fish species richness and coral cover than surrounding areas (contrary to what was observed in 2015, showing a possible reserve effect) while their low-frequency power spectral density was lower. Between 2015 and 2021, coral cover decreased by 10%. When comparing 2015 and 2021 soundscapes, nocturnal high-frequency biophony were louder on the sites from the east coast, i.e. the only sites with an increase of coral cover between 2015 and 2021. This link between high power spectral density values and coral cover between 2015 and 2021 confirm the efficacity of passive acoustic for long term monitoring.14. Life below wate

Passive acoustic monitoring to assess the impact of marine protection measures and bleaching events on coral reefs

editorial reviewedMass bleaching events alter the ecological process of coral reefs while marine protected areas (MPAs) can increase the resilience of coral reef communities to natural disturbances, playing a role in sheltering biodiversity from climate-related impacts and in the recovery of corals from massive bleaching events. In Moorea Island (French Polynesia), two bleaching events occurred between 2015 and 2021. The aims of this study are to compare the soundscape of the external slope of Moorea Island within and outside MPAs in 2021 to access the presence or the absence of a protection effect on acoustic data and to compare them to data sampled in 2015 to access both temporal and protection effects, in relation with the benthic cover and the fish species present. MPAs have a greater fish species richness and coral cover than surrounding areas (contrary to what was observed in 2015, showing a possible reserve effect) while their low-frequency power spectral density was lower. Between 2015 and 2021, coral cover decreased by 10%. When comparing 2015 and 2021 soundscapes, nocturnal high-frequency biophony were louder on the sites from the east coast, i.e. the only sites with an increase of coral cover between 2015 and 2021. This link between high power spectral density values and coral cover between 2015 and 2021 confirm the efficacity of passive acoustic for long term monitoring.14. Life below wate

Status of coral reefs of Upolu (Independent State of Samoa) in the South West Pacific and recommendations to promote resilience and recovery of coastal ecosystems

International audienceCoral reef ecosystems worldwide are immediately threatened by the impacts of climate change. Here we report on the condition of coral reefs over 83 km of coastline at the island of Upolu, Samoa in the remote South West Pacific in 2016 during the Tara Pacific Expedition. Despite the distance to large urban centers, coral cover was extremely low (<1%) at approximately half of the sites and below 10% at 78% of sites. Two reef fish species, Acanthurus triostegus and Zanclus cornutus, were 10% smaller at Upolu than at neighboring islands. Importantly, coral cover was higher within marine protected areas, indicating that local management action remains a useful tool to support the resilience of local reef ecosystems to anthropogenic impacts. This study may be interpreted as cautionary sign for reef ecosystem health in remote locations on this planet, reinforcing the need to immediately reduce anthropogenic impacts on a global scale

Pervasive tandem duplications and convergent evolution shape coral genomes

Background: Over the last decade, several coral genomes have been sequenced allowing a better understanding of these symbiotic organisms threatened by climate change. Scleractinian corals are reef builders and are central to coral reef ecosystems, providing habitat to a great diversity of species. Results: In the frame of the Tara Pacific expedition, we assemble two coral genomes, Porites lobata and Pocillopora cf. effusa, with vastly improved contiguity that allows us to study the functional organization of these genomes. We annotate their gene catalog and report a relatively higher gene number than that found in other public coral genome sequences, 43,000 and 32,000 genes, respectively. This finding is explained by a high number of tandemly duplicated genes, accounting for almost a third of the predicted genes. We show that these duplicated genes originate from multiple and distinct duplication events throughout the coral lineage. They contribute to the amplification of gene families, mostly related to the immune system and disease resistance, which we suggest to be functionally linked to coral host resilience. Conclusions: At large, we show the importance of duplicated genes to inform the biology of reef-building corals and provide novel avenues to understand and screen for differences in stress resilience.ISSN:1474-760