Distribution spatio-temporelle des communautés benthiques en environnement marin profond

The deep marine environment is home to a mosaic of complex ecosystems. Understanding the spatial and temporal distribution of the associated biological communities is a central question in ecology. It requires the identification of patterns of heterogeneity, the underlying sources of variation and the factors responsible. My research on the spatial structuring of benthic communities associated with hydrothermal ecosystems highlights the intertwined roles of local and regional factors. The distribution area of species is strongly linked to the geodynamics of ridges, through the creation of barriers to gene flow, but are also driven by species life-history traits and habitat availability, which control the structure of local communities and population effective sizes. At local scale, the development of innovative approaches helped identify the role of physico-chemical conditions, substrate, topography and benthic currents on biodiversity patterns, and their associated scales of heterogeneity. But these structuring factors vary over time. Using deep-sea observatories to study the dynamics of ecosystems from hours to decades, we highlighted, in an environment thought to be acyclic, the presence of periodicities in the behaviour, physiology and biology of species, as well as in communities’ composition. We show the predominant role of tides and storms in all the ecosystems studied, and seasons on the continental margin. Results point to the multi-annual stability of vent communities, where populations and communities appear to have reached the climax stage of ecological succession for more than 25 years, suggesting low ecosystem resilience. These results have major implications in terms of biodiversity conservation, particularly in the context of potential mining activities, but also in terms of climate change in the deep sea, and underlines the need to consider biologically relevant scales of heterogeneity in environmental management plans.