Grazing on autotrophic and heterotrophic picoplankton by ciliates isolated from Lake Kinneret, Israel

The rates of ingestion of three ciliates (Colpoda steinii, Cyclidium sp. and Srylonichia sp.) on fluorescently labeled heterotrophic bacteria, picocyanobacteria (Synechococcus P, CN) and a picoeukaryote isolated from Lake Kinneret were measured. Uptake values were 930, 35 and 1210 bacteria ciliate (cil)−1 h−1 for Colpoda, Cyclidium and Sylonichia, respectively, depending on prey concentrations. An increase in prey concentration resulted in a decrease in clearance rates from 405 to 32 nl cil−1 h−1. Clearance rates of Colpoda fed on Synechococcus (P. CN) and on picoeukaryotes ranged from 27 to 62 and from 3 to 7 nl cil−1 h−1, respectively. Cyclidium, which is classified as a picoplankton feeder, showed lower clearance rates when fed on Synechococcus P and bacteria. Specific clearance (body volume cell−1 h−1 for the three ciliates studied decreased when prey supply increased, for all three food sources. Relating to body volume, Colpoda could manage successfully on bacteria as its sole food source. It appears from our measurements that bacteria in Lake Kinneret are abundant enough to sustain the carbon requirements of Colpoda.