Abundance and composition of picoplankton in the mid Adriatic Sea

The abundance and structure of the picoplankton community were studied at two stations, one in coastal waters and one in offshore waters, of the middle Adriatic from December 1996 to June 1998. The abundance of prokaryotic Synechococcus cells, eukaryotic autotrophic picoplankton, and heterotrophic nanoflagellates (HNF) was determined, as were the chlorophyll a, physical and chemical factors, and nutrients of the water. Synechococcus dominated the picoplankton abundance by 96%. In offshore waters, the abundance of Synechococcus was influenced by nutrient availability and HNF abundance more than by temperature. In coastal waters, where nutrients were not a limiting factor, temperature had greater influence. Picophytoplankton contributed more to the total phytoplankton biomass in offshore (31%) than in coastal (9%) waters.