Factors influencing zooplankton communities in 108 mountain lakes from the Western Alps (Italy and France).

Travail mené en 2022 par Rocco Tiberti (GreenRes) dans le cadre du PITEM Biodiv'Alp sur un grand nombre de lac dont les 24 lacs suivis par le réseau

Résumé

The present report provides a description of the zooplankton communities (planktonic rotifers, crustaceans, and insects) occurring in 108 mountain lakes and ponds of the Western Alps (Italy and France). In total, 585 samples (1-44 samples per lake collected between 2006 and 2021) were analysed for zooplankton density (Individuals m-3). The list of taxonomic units encompasses a total of 55 species and higher taxa (5.51 ± 2.05 taxa per sample; range: 0-14), which were grouped according to their feeding mode, their thermal tolerance (cold stenothermal taxa vs. eurythermal taxa), and habitat preference (littoral vs. pelagic taxa). Generalized linear mixed models (GLMM) were used to explore which factors influence zooplankton diversity, and the densities of the most common taxa and families (frequency of occurrence > 10%), of each functional feeding group, thermal-tolerance group, and habitat preference group. Investigated factors include seasonality, year of sampling, elevation (as a proxy of climatic conditions), maximum depth (as a proxy of lakes size), some catchment characteristics including the percentage of glacial cover, and some local impacts (presence of introduced fish and hydroelectric infrastructures). The main results indicate that most zooplankton taxa and groups are affected by a strong seasonality as well as by some lake and catchment characteristics. Interestingly, glaciers have a strong impoverishment effect on the zooplankton communities and stenothermal taxa diminished along the study period, which suggest that mountain zooplankton is already affected by the effects of climate change (warming and glacial retreat). Introduced fish also exert a deep impact on some zooplankton taxa and on entire functional groups; their impact depends on the composition of introduced fish communities. On the other hand, lake damming seems to have little influence on zooplankton communities. However, it should be highlighted that all dammed lakes are also affected by fish introduction which ultimately questions their possible conservation value. The present report provides a reference database and some preliminary results to describe the ecological preferences, long-term dynamics, and conservation state of zooplankton taxa and communities in a representative number of mountain lakes from the Western Alps.