The relative importance of protozoans, rotifers, and crustaceans in a freshwater zooplankton community1

A complete analysis of the macro‐ and microzooplankton of a monomictic lake indicates that Protozoa dominate the community numerically. During winter mixis, ciliates are found at densities of 1–8 × 10 3 ·liter −1 and constitute up to 32% of the zooplankton community biomass. With summer stratification crustaceans decline, while both the relative and absolute abundance of protozoans and rotifers increase. Densities of protozoans are highest (1–2 × 10 5 ·liter −1 ) in the metalimnion where scuticociliates bloom in zones of intense bacterial activity. During the period of these blooms (July–October), Protozoa account for 15–62% of the zooplankton biomass. This suggests that Protozoa make a significant contribution to rates of grazing, nutrient regeneration, and secondary productivity and should not be overlooked in zooplankton community studies.