Randy LATCHY

Implication of recruitment variability of diadromous species in the stability and functioning of insular freshwater aquatic environments

Species demography is mediated by ecological processes subject to selective pressures, which contribute to maximizing the individuals’ performances depending to environmental constraints. Among these processes, the migration can, for instance, contribute to optimizing the successive exploitation of two contrasting environments depending on the phases of life history. In aquatic organisms, the “diadromy” is a complex behavioral trait describing migrations between freshwater and marine water environments, which occurs at a specific life stage. These species can thus contribute substantially to the functioning of both ecosystems, by supporting demographic flows and materials involved in food webs. This project aims to describe the contributions of diadromous species to the functioning of freshwater environments in a tropical island system (Reunion Island). Firstly, the (a)biotic factors likely to influence the recruitment abundance of different species will be identified and prioritized, based on time series analysis, in order to characterize the influence of recruitment variability on functional diversity and stability of river communities. Secondly, the contribution of recruits to the trophic functioning of rivers will be analyzed using stable isotopic ratios of nitrogen and carbon. This approach will make it possible to highlight the propagation of organic matter with marine origin throughout the freshwater food web. Finally, the implication of heterogeneity in marine dispersal routes on recruitment abundances will be investigated to test the assumption that a larger larval portfolio can promote abundance and stability of recruitment, i.e. portfolio effect, by analyzing the chemical composition of otoliths.