STRUCTURAL COMPOSITION OF PROTOZOOPLANKTON COMMUNITIES IN RELATION TO ENVIRONMENTAL FACTORS IN SHALLOW LAKES AND RESERVOIRS OF RÎGA, LATVIA

Protozooplankton are dominant grazers of phytoplankton and an important component of the microbial food web, as a link between pico and nanoplankton to higher trophic levels. Their fast growing rate, relative abundance, biomass and diversity are used as indicators of organic and toxic pollution. The impact of urbanisation on ecosystems and their sustainability and biodiversity have recently been much studied. We studied the protozooplankton ciliate communities during the vegetation period from April to October in two small lakes (Bâbelîtis, Gailezers) and two reservoirs (Bolderâja, Sauriesi). The largest peak of biomass (15.7 × 10^2 mg/l) was found in Gaiïezers Lake in August and of abundance (60.2 × 10^3 org/l) in Bâbelîtis Lake in July. The lowest biomass (0.006 mg/l) and abundance (0.12 × 10^3 org/l) were found in the Saurieði Reservoir station. The most abundant ciliates were from the order Oligotrichida.