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RESEARCH PRODUCT

Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna

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1. Groundwater ecosystems represent the greatest proportion of unfrozen freshwa- ter on Earth and harbour high numbers of rare taxa with restricted distributions. Stygofaunal abundance, species richness, and ecology play essential roles in groundwater ecosystem services and functioning, as well as providing an impor- tant contribution to global biodiversity. However, as global depletion and contam- ination of groundwater pose serious and often irreversible threats to stygofauna, more information is urgently needed about the ecology of rare groundwater spe- cies to guide effective strategies for their conservation or restoration. 2. In this study, analyses of carbon and nitrogen stable isotopes were used to com- pare and evaluate trophic niches and diets of a vulnerable stygobiont isopod, Gallasellus heilyi living in sympatry in French groundwater ecosystems with the isopod Caecosphaeroma burgundum and the amphipod Niphargus ladmiraulti. 3. Stable isotope results showed trophic niche partitioning among the three sty- gobiont species and indicated that G. heilyi and C. burgundum occupy the role of primary consumers and N. ladmiraulti that of predator. Moreover, although G. heilyi and C. burgundum were shown to rely on the same food sources, indicat- ing similar diets, and their trophic niches did not overlap, suggesting trophic specialization. 4. The results suggest that detritus (i.e. decaying organic material) is an important food source for G. heilyi, and its availability could determine the survival of this endangered species. As a practical conservation measure for G. heilyi and the whole stygofauna community, we suggest reconnecting surface and subterranean ecosystems, as they probably were before natural sinks and many wells were filled up or closed. Funding information: Agence de l’Eau Adour-Garonne; Centre National de la Recherche Scientifique; DREAL Nouvelle-Aquitaine; Estonian Ministry of Education and Research, Grant/Award Number: IUT 21-2; Estonian Research Council, Mobilitas Pluss, Grant/Award Number: MOBJD29; Foundation LISEA Biodiversité; Regional Council of Nouvelle-Aquitaine; University of Poitiers. Funding information: Agence de l’Eau Adour-Garonne; Centre National de la Recherche Scientifique; DREAL Nouvelle-Aquitaine; Estonian Ministry of Education and Research, Grant/Award Number: IUT 21-2; Estonian Research Council, Mobilitas Pluss, Grant/Award Number: MOBJD29; Foundation LISEA Biodiversité; Regional Council of Nouvelle-Aquitaine; University of Poitiers.