Résumé
Predicting and acting against infectious diseases that are increasingly emerging and spreading, as well as halting biodiversity loss, are intertwined challenges that are crucial to ensure global health. Several links were already established between biodiversity levels and the circulation of pathogens at global scales. On one hand, a high diversity of potential hosts can lead to a high diversity of pathogens present in ecosystems, with a greater risk of host hopping and possibly the emergence of infectious diseases. On the other hand, biodiversity can also drastically influence (either positively or negatively) the circulation of a given pathogen species through several biotic interactions and ecological processes. This is particularly true for trematodes that display complex life cycles hence involving several hosts and several, sometimes free-living, life stages. We here investigate how biodiversity at the ecosystem scale influences the composition of trematodes communities and their circulation in Mediterranean coastal wetlands (Bagnas Nature Reserve). We first assess the theoretical parasitic (trematode) pressure exerted by the fluctuating diversity of definitive hosts (particularly birds) on the Bagnas aquatic ecosystems and the potential risks of local circulation of trematodes based on the reconstructed communities of aquatic snails, the first obligatory intermediate host for all trematodes species. We next investigate the seasonal dynamics of local snail diversity and abundance, to study their effects on the circulation of the most prevalent trematodes species identified locally. This empirical study shed lights on the ecological mechanisms linking biodiversity and the circulation of trematodes.