Abstract
We investigated the phytoplankton biomass and its relationships with nutrient, suspended sediment and hydrographic characteristics, during three oceanographic cruises in May-June 2006, September 2006 and March 2007 in the Gulf of Gabes (south-eastern Mediterranean). The May-June cruise coincided with the beginning of the summer stratification, a strong stratification occurred in September and a well-mixed water column marked March cruise. Results allow characterizing the phytoplankton biomass potential limitation during hydrological transition between vertical mixing and strong stratification. The potential nutrient limitation on the phytoplankton biomass showed seasonal and spatial patterns. N-limitation was preponderant during winter mixing conditions. Potential Si and P-limitation were associated with oligotrophic signatures such as, low chlorophyll and high organic suspended solid during enhanced summer stratification. A transition period characterized by N-limitation in the coastal area and Si-limitation in the offshore area characterized the beginning of the water stratification. General opposition patterns existed between organic suspended matter and chlorophyll a vertical distributions suggesting a potential control of phytoplankton biomass by top down processes. Our observations revealed the seasonal scale variations in the physical/biological coupling in the Gulf of Gabes and the implications for nutrient, organic suspended solid and phytoplankton standing stock.