Detecting habitats considering the mesozooplankton size structure and environmental conditions in the Gulf of Lion, NW Mediterranean Sea.

International audienceThe Gulf of Lion in northwestern Mediterranean Sea is characterized by a large continental shelf reaching up 40 miles width. Several hydroclimatic processes such as river discharges, strong winds and permanent current induce a complex hydrodynamics resulting in several habitats for plankton communities. The whole French continental shelf of the Gulf of Lion was sampled with a LOPC at two periods (May 2010 and January 2011). Zooplankton community’s characteristics and environmental parameters were investigated to describe biophysical interactions. Statistical tests allowed us to define 3 coherent ecoregions representing different types of habitat: (1) the coastal area, (2) the Rhône plume influence and (3) the continental shelf area. The zooplankton size distribution was investigated within the three areas using the normalized biomass size spectrum (NBSS). The size structure of zooplankton community differs following the areas and their environmental conditions. The coastal area was characterized by the steepest NBSS and highest chla concentrations, the upwelling and the formation of deep water participated to keep the water mixed. The Rhône plume showed the lowest NBSS slopes associated with strong water stratification. These waters were rich in nutrient promoted high chlorophyll a concentrations in the surface water layer and carried on the continental shelf a lot of organic matter. The continental shelf showed the lowest abundances and was hit by the Northern Current depending on the season.Defining habitats provides a firm basis to develop efficient sampling strategies for studying zooplankton dynamics, to validate zooplankton distribution models and to improve coastal management programs