Pelagic ciliated protozoa in a shallow eutrophic lake: community structure and seasonal dynamics

Seasonal population dynamics and community composition of planktonic ciliates of shallow eutrophic Lake Vortsjarv were studied from January 1995 to December 1996. The abundances (1995 mean = 39.0 x 10(3) cells/l, 1996 mean = 60.1 x 10(3) cells/l) and biomasses (1995 mean = 0.68 mg/l, 1996 mean = 2.91 mg/l) were high and showed an increasing trend with the decrease in water level. Ciliate abundances peaked in spring (May) and in late summer (July, August) reaching values up to 191.1 x 10(3) cells/l. The biomass maxima did not coincide with maximum abundances and were tied with the mass occurrences of large-sized carnivorous species. Ciliates accounted for 50 to 64% of the zooplankton biomass (in 1995 and 1996, respectively). Oligotrichs, haptorids, scuticociliates and prostomatids dominated the community of ciliates.