Specific phytoplankton signatures and their relationship to hydrographic conditions in the coastal northwestern Mediterranean Sea

a n intensive sampllng p r q g a m was carried out at a coastal station in the Northwestern Mediterranean Sea to study the relations9:p between phytoplankton distributions, as evaluated by taxonomic pigments, and the hydrographx structures of the water column. The study period covered the range of hydrographlc conditions whlct prevail in the Mediterranean Sea. The 0 to 75 m integrated chlorophyll a concent]-ation averaged 23 3 m g m 2 , with the highest values (above 45 mg m-') restricted to semi-mixed penods. The major ph floplankton signature and water column structure r e l a t ~o n s h ~p s were: (1) phytoplankton~c prokaryotes (ryanobacteria and prochlorophytes] appear sensitive to water column mixing with prochlorophylc~ being the most sensitive group a s strong stratification is associated with the highest biomass found mainly in deeper waters;