Anticipated environmental changes and increased anthropogenic pressures on coastal area could affect the functionning of ecosystems through changes in the structure and species composition of benthic communities. My Ph.D. project aims to describe the natural variability of communities dominated by macroalgae (Fucus sp.) and eelgrass (Zostera marina), and their responses following multiple disturbances. I work on benthic communities of the intertidal zone of the St. Lawrence estuary. I am looking at how grazers (top-down), resources (bottom-up) and key species are shaping these communities. To do that, I do in situ experiments that manipulate grazers, nutrients, light and density of structuring species. I measure simple and multiple effects of the factors on biodiversity variables. I am also interested by community resilience, that is to say their ability to return to a reference state after a temporary disturbance. This ability to recover is very important in the actual context of increasing anthropogenic pressures on ecosystems.