Control of phytoplankton development by nitrate availability in the Liguro-Provençal basin (western Mediterranean)

Ten years of mesoscale oceanographic studies in the Liguro-Provençal basin (Corsican area) have emphasized that phytoplankton communities distribution is characterized by a high spatial and temporal heterogeneity. The phytoplankton organization is greatly influenced by the presence of the Liguro-Provençal front whose functioning contributes significantly to increase the local productivity. The role of the front in the phytoplankton productivity enhancement is important all through the year but is much more effective from March to May. In the entire basin, a crucial moment for phytoplankton communities is encountered during summer, when surface waters are nutrient exhausted. The characteristic response of the primary producers is to sink below the surface mixed layer and to develop deep chlorophyll maxima (DCM). Their formation and maintenance are discussed. During the stratified period, all data support the view that phytoplankton distribution is primarily controlled by nitrate availability.