EN
In the studies on phytoplankton done within the framework of the biological monitoring of the Baltic Sea in 1979-1993 significant changes were found in the dominance structure though not the species composition.The previously dominant phyla Chrysophyta and Cyanophyta have been replacement by Pyrrophyta and Flagellata.No long-term trends in abundance and biomass of phytoplankton or in chlorophyll a concentration could be detected.