Within the framework of INSU–CNRS program MERMEx–MISTRALS, the Ph.D. project is focused on the study of the structure of pelagic communities in relation to the biogeochemical cycles of major elements (C, N, P and Si) in Mediterranean waters. As part of SPEciMed project (Structure of Planktonic Ecosystems in the North-western Mediterranean), it combines modern approaches in biological analyses (microscopy/image analysis/FlowCam for species identification, counting, and associated biomass contribution) as well as in biogeochemical analyses (chemical measurements of C, N, P and Si stocks) to describe and compare the seasonal evolutions of pelagic communities in the Gulf of Lions and the pelagic ecosystems of North Tunisia (Bay of Bizerte and Gulf of Tunis). The data obtained will be compared with measurements performed using an in situ sensor for the determination of biovolume and biomass by size classes (LISST) to assess the operational benefits of this new instrument in defining a sampling strategy in the context of long-term monitoring of pelagic environments. The Ph.D. project addresses the following questions :
What is the current diversity of the individual compartments (bacteria, flagellates, microphytoplanton, microzooplankton, mesozooplankton) of the pelagic assemblages in the Gulf of Lions?
What are the characteristic structures of food webs across the Gulf of Lions and for different seasons? How are they spatially distributed during the different seasons between the coastal zone and the continental slope?
What is the range of the annual variability in these food web structures?