Original paper

Protozoan grazing in shallow macrophyte- and plankton lakes

Zingel, Priit; Nõ ges, Tiina


The aim of the present study was to describe the role of ciliates and heterotrophic nanoflagellates in macrophyte and phytoplankton dominated shallow lakes and to compare the grazing on pico- and nano-sized particles by these protozoans. We sampled three shallow lakes, seasonally, one dominated by macrophytes, one by phytoplankton, and one with both conditions (two basins of this lake were sampled separately). The role of ciliates as consumers of bacteria and small algae was important in both lake types. In plankton dominated lakes the grazing rate of ciliates on bacteria was higher than in macrophyte dominated ones. But when ciliates were grazing on small algae, the highest rates were found in macrophyte lakes. Our results suggest that the microbial loop is weaker in macrophyte dominated lakes and grows stronger, when a lake becomes more turbid. The dominance of herbivorous ciliates in macrophyte lakes in summer and their high grazing rates on phytoplankton may have contributed to the decrease in phytoplankton abundance in these lakes. Heterotrophic nanoflagellates were relatively less abundant and, due to their low specific filtering rates, grazed only a minor fraction of the bacterioplankton.


ciliatesheterotrophic nanoflagellateshnfgrazingbacterioplankton grazing