Biologie des Organismes et Écosystèmes Aquatiques

Climate change is expected to significantly affect insurers’ liabilities through an increase in claims associated with more frequent and intense meteorological hazards. These include both extreme events such as tropical cyclones and storms, and more recurrent phenomena such as floods and droughts. In this context, the mutual insurance group Covéa conducts climate-impact studies in collaboration with the specialized climate-risk Hydroclimat company.The study focuses on the projected evolution of coastal flooding risk in France by 2050. According to the HANZE database (Paprotny D., 2024), between 1950 and 2020, approximately one-third of flood events in France involved a coastal flooding component. Major historical events, such as Storm Xynthia in 2010 and the October 1987 storm, resulted in insured losses of €660 million and €1.5 billion (CCR, 2023), highlighting the significant financial exposure associated with coastal hazards.To anticipate future impacts, Hydroclimat produced coastal flood-extent maps based on CMIP6 climate projections, integrating existing coastal protection systems within a hydro-geomorphological modelling framework. Exposure and vulnerability analyses were conducted using Covéa’s national residential building database. These results provide an initial assessment of the projected increase in the number of exposed residential buildings and the associated insured losses by mid-century.This work contributes to a better understanding of future coastal flood risk under climate change and supports insurers in adapting risk assessment and portfolio management strategies to evolving coastal hazards.ReferencesPaprotny, D. (2024) - HANZE catalogue of modelled and historical floods in Europe, 1950–2020 (v1.2) https://doi.org/10.5281/zenodo.12635205Caisse Centrale de Réassurance (2023) – Risque de submersion sur la côte atlantique : l’analyse CCR – https://www.ccr.fr/submersion-marine-cote-atlantique-scenario-ccr/ [last access : 2025/12/15]

Beneath the Earth's surface lies a network of interconnected caves, voids, and systems of fissures forming in rocks of sedimentary, igneous, or metamorphic origin. Although largely inaccessible to humans, this hidden realm supports and regulates services critical to ecological health and human well-being. Subterranean ecosystems are integral to major biogeochemical cycles, sustain diverse surface habitats, and serve as the primary source of irrigation and drinking water. They also offer non-material benefits, including scientific discovery, education, and cultural practices. Yet, these contributions often go unrecognised, partly due to the lack of a unified synthesis of ecosystem services across terrestrial, freshwater, and marine subterranean compartments. This gap limits effective communication of their value to scientists, practitioners, and the public. Through a systematic expert-based review, we show that subterranean ecosystems contribute to up to 75% of classified ecosystem services. Notably, many of these contributions are described only qualitatively, lacking numerical or economic quantification. Next, we list examples of the main ecosystem services provided by subterranean systems to offer a global overview of their multifaceted value and vulnerability to environmental change. We believe this synthesis provides researchers and practitioners with concrete examples to communicate more effectively the importance of subterranean ecosystems to diverse audiences.

Aquitanian pike, Esox aquitanicus , is a new esocid species described in 2014 and endemic to Southwestern France. The four main goals of the present study were to (i) obtain the first morphological data on the early life stages, (ii) test the effects of temperature on their survival and development, (iii) compare the results with the Northern pike, and (iv) produce a few individuals to exhibit them at the Aquarium of Limoges. Eggs are yellowish, demersal, and sticky. The mean diameter was 2.73 ± 0.08 mm ( n = 174). The larval size at hatching was 9.09 ± 0.24 mm ( n = 14). The morphological development of 15 larvae was followed during 11 weeks as well as the snout growth in relation to eye size. It appeared that already after three weeks, slight differences between the two species were apparent, and after nine weeks, this snout/eye ratio was twice greater for Northern pike than Aquitanian pike. At the end of the yolk-feeding period, which lasted from 12 days at 18 °C to 36 days at 6 °C, the overall survival rate was over 85% and larvae were of similar size, except at 6 °C. After three months, the best results in term of survival were obtained at 12 °C (60%) and for growth at 15 °C (34.11 mm), followed at 12 °C (27.85 mm). Based on these results, we were able to rear Aquitanian pike for more than 2 years in the Aquarium of Limoges in order to promote the conservation of the species to the public.

Area-based conservation is a popular strategy to address biodiversity decline. However, despite the identification of enabling conditions, many initiatives still fail at delivering positive outcomes for nature and people. This study examines how enabling conditions are operationalized and their influence on conservation effectiveness using social-ecological approaches. Guided by the central question of whether the way enabling conditions are put into practice affects conservation outcomes, the study pursues three objectives: (1) to document the processes through which enabling conditions are operationalized, (2) to distinguish the different forms of operationalization, and (3) to assess how these processes influence conservation outcomes, in order to extract lessons that may serve as best practices for future initiatives. By comparing the establishment of two coral reef conservation initiatives in the same region, we identified diverse ways in which enabling conditions are put into practice, providing examples for conservation practitioners. Discourse analysis of stakeholders’ perception highlighted that enabling conditions being in place alone does not guarantee success. Instead, the way they are implemented—through specific action-situations, their interactions, and the stakeholders involved—plays a crucial role in delivering conservation outcomes. Operationalization can have both direct and indirect effects, influencing outcomes at one stage of establishment or at later stages. Sequencing and timing also emerged as critical factors affecting perceptions of benefits, compliance with regulations, and the sustainability of conservation measures. These findings offer practical guidance for decision-makers and managers by illustrating how enabling conditions can be operationalized to support more effective and context-sensitive conservation efforts.

The vent crab, Xenograpsus testudinatus (xtcrab), is adapted to inhabit shallow-water, high sulfide and hypoxic hydrothermal vent. Our previous study revealed sulfide tolerance of vent xtcrabs which sulfide: quinone oxidoreductase (xtSQR) paralogs aid in sulfide detoxification. However, the mechanisms of how xtcrab adapts to high sulfide-hypoxic conditions in the vent area remain to be explored. In the present study, we tested the tolerance of xtcrab to sulfide-induced hypoxia, and investigated their aerobic and anaerobic responses in situ and in the laboratory. Comparisons were made to a non-vent, intertidal species, Thranita danae (tdcrab). We analyzed the several factors related to aerobic metabolism (SQR, cytochrome c [CYTC], complex IV [COXIV]), the product of anaerobic metabolism (hemolymph lactate levels) and glucose levels. Our results showed a higher survival tolerance to hypoxia of xtcrabs than tdcrabs. Hemolymph lactate levels increased more rapidly in xtcrabs than tdcrabs exposed to experimental hypoxia, revealing a rapid induction of anaerobic metabolism in hypoxic xtcrabs. Lactate measurement in xtcrabs returned from aquaria to original capture sites (vent habitats), further assessed the remarkable ability of xtcrabs to rapidly switch on and off their anaerobic metabolism. To assess aerobic metabolism, long-term exposure of xtcrabs to hydrothermal vent habitat increased gill xtCYTC transcripts and protein levels together with steadily enzymatic activity of COXIV. This revealed ability of xtcrabs to maintain functional capacity of aerobic respiration in hypoxia. Phylogenetic analysis showed that xtSQR paralogs in xtcrabs were more distant compared to tdSQR paralogs in tdcrabs. The increase of transcripts and enzymatic activity of gill xtSQR, and co-localization of xtSQR and xtCYTC also contribute to maintain aerobic metabolism by preventing sulfide toxicity on mitochondrial respiratory function. Overall, our study suggests that multiple strategies including detoxification of sulfide by gill xtSQR, and a quick/dynamic switch between aerobic and anaerobic metabolisms may play important roles in the metabolic adaptations of xtcrabs to extreme hydrothermal vent environment.The online version contains supplementary material available at 10.1038/s41598-025-31968-1.

Pelagic Sargassum, denoting the two species S. natans and S. fluitans, has become a focal point of both scientific and public interest due to recent superbloom events. As a result, investigation into the dynamics of Sargassum-associated microbiota, which was previously quite limited, has regained momentum in the past five years. This review collates the current state of knowledge relating to the Sargassum microbiome as well as synthesizes relevant biogeochemical findings which may aid future efforts in this field. We explore microbiome composition and functional roles within this holobiont, specifically in terms of taxonomic diversity, macronutrient cycling, and the fate of Sargassum-derived organic matter. Despite progress, significant gaps remain in our understanding of the dynamic interactions within these microbial communities and their broader ecological significance. Future research directions are identified alongside recommendations for standardized protocols, emphasizing the need for more in-depth studies utilizing advanced molecular and biogeochemical techniques to unravel the full complexity of the Sargassum microbiome.

Understanding ecological succession is essential for managing complex ecosystems like coral reefs. This study investigates the successional dynamics of sessile cryptobenthic communities (SCC), a key component of coral reef biodiversity and functioning, focusing on deterministic and stochastic ecological processes. To assess changes in SCC richness and composition, we deployed five triplicates of Autonomous Reef Monitoring Structures (ARMS) at a coral reef slope site in Reunion Island (South-West Indian Ocean) during both hot and cool seasons, and recovered them after 6 months, 1 year, and 2 years. ARMS photo-analysis revealed that pioneer communities consisted of biofilms, hydrozoans, crustose coralline algae, and foraminifers, while sponges, macroalgae, and bivalves emerged as late colonisers. Seasonal effects were strongest in early succession but diminished over time. Mean morphospecies richness increased from 24.8 ± 1.9 at 6 months to 33.3 ± 5.8 at 2 years, with taxa turnover driving β-diversity. Null model analyses indicated that stochastic processes shaped community membership, while deterministic processes regulated taxa abundances throughout succession. SCC required more than 2 years to reach maturity, raising reef productivity and diversity concerns as extreme events like coral bleaching become more frequent. These findings, supported by metabarcoding, provide insights for reef monitoring and conservation amid increasing disturbances.