Effets de l'eutrophie et de la dessalure sur les populations phytoplanctoniques

A study undertaken in the surface waters of the Gulf of Fos (France), revealed very low salinities, high nutrient concentrations, and very rich phytoplanktonic populations (maximum 7.5·10⁵ cells/l). Very often the phytoplanktonic populations attain abundances 2 to 15 times higher than maximum population densities found in the Mediterranean Sea. Such high cellular concentrations seem to suppress more or less the rates of relative photosynthesis if the concentration of chlorophyll a per 1 million cells is considered. Furthermore, the analysis of particular carbon yields high values. This phenomenon can be explained by the fact that, in addition to organic carbon, other organic forms of carbon were measured, especially some carbonates which are abundant in fresh waters. The C/N ratios found seem to support this explanation.