Phytoplankton community structure in non-stratified lakes of Pomerania (NW Poland)

Abstract

The species composition, abundance and biomass of autotrophic picoplankton and larger phytoplanktonic organisms were analysed in 17 non-stratified lakes of Pomerania. Water samples were collected in August in 1995–1999. The composition and structure of phytoplankton varied among the lakes. Two groups of lakes could be distinguished: with a low and with a high species richness. Phytoplankton abundance ranged from about 1 × 102 to 1.5 × 106 cells ml−1 and was usually dominated by green algae, cyanobacteria, chrysophytes and dinoflagellates. Phytoplankton biomass ranged from 0.04 to 16.9 mg l−1 and in half of the lakes was dominated by cyanobacteria or dinoflagellates. Biomass of the smallest size fraction i.e. autotrophic picoplankton (APP) was always small in comparison with that of larger phytoplanktonic organisms. Cyanobacterial cells were usually the main components of APP, while eukaryotic APP were rare. Colonial forms accounted for 6–93% of the total APP abundance. In terms of total phytoplankton biomass, organisms from one of the other fractions, i.e. nanoplankton or microplankton, were usually more important. As the community structure of phytoplankton showed clear differences among lakes, special attention was paid to the variation in the relative abundance and biomass of some species or groups of species.