Pelagic biocenosis in the oligo-mesotrophic lake of Pomerania (Poland): study of communities of microbial loop and phytoplankton
This study presents results of investigations on abundance and biomass of the main communities of the microbial loop (heterotrophic bacteria, autotrophic picoplankton, heterotrophic flagellates, ciliated protozoa) as well as nano- and microalgae in the large (525 ha) and deep (48 m) oligo-mesotrophic lake Bobifcigskie Wielkie located in West Pomerania, Poland. Samples were taken from the pelagial zone in 1996. Within organisms of picoplankton size the heterotrophic bacteria were the most abundant trophic group. Their biomass, together with the much lower abundant autotrophic picoplankton (3.5 to 5.4 μg·C L-1), constituted 15% to 22% of the total microbial biomass. The sum of biomasses of heterotrophic flagellates and ciliated protozoa was similar at all depth (3.0-3.8 μg·C·L-1), ranging between 8-24% of total biomass. Phytoplankton organisms larger than 2.0 μm represented the biggest part of the total microbial biomass, i.e. from 50% to 78% (8.4-27.5 μg·C·L-1). The microplankton constitutes the largest part of the phytoplanktonic biomass. Whereas the diatoms and cryptomonads were the most abundant in the upper layers of the lake. The filamentous cyanobacteria of the genus Planktothrix dominated in the deeper waters.