Spatio-temporal dynamics and habitats of zooplankton communities: characterization of the ecological state of French pelagic ecosystems

Plankton is an essential component of the pelagic domain. It includes all plant (phytoplankton) and animal (zooplankton) organisms living in the water column, which have a relative passivity towards water mass movements. Planktonic organisms are thus particularly sensitive to changes in environmental conditions (hydrodynamic, hydrological, physico-chemical, biological) which can affect both their structure (e.g. composition, size spectrum, diversity) and their distribution (e.g. horizontal, vertical). These spatio-temporal variations in communities can condition the functioning of the food web (e.g. phytoplankton-herbivore food chain; remineralization) and the balance of biogeochemical cycles. Plankton is therefore a good component for studying and monitoring the evolution of marine ecosystems. In this context, the objective of my thesis is to analyse the spatio-temporal variations of zooplankton communities from marine and coastal ecosystems of the French coastline, to characterise the forcing factors influencing these dynamics at different scales, and to assess the ecological status of these pelagic habitats. This work will be at the interface between research and management, since the aim will be to: 1) Characterise zooplankton assemblages along the English Channel, Atlantic and Mediterranean coasts in order to identify sites/periods at stake (e.g. hotspot of abundance, biomass, diversity) in the ecosystems studied ;  2) Analyse the variations of these assemblages in response to physical, hydrological, hydrographical and climatic forcing, at different spatial and temporal scales while considering different levels of ecological integration (species, communities, functional groups, stocks) ;  3) Develop and/or adapt indicators to detect changes and quantify variations in zooplankton communities (structure, functional types, diversity, etc.) in support of public policies (in particular in the context of the Marine Strategy Framework Directive) ;  4) Assess the ecological status of the pelagic habitats of the French coastline (Descriptor 1 - Biodiversity of the MSFD) and consider management support measures in the case of degraded status.