EVALUATION OF BACTERIVORY OF ROTIFERA BASED ON MEASUREMENTS OF IN-SITU INGESTION OF FLUORESCENT PARTICLES, INCLUDING SOME COMPARISONS WITH CLADOCERA

Bacterivory of pelagic rotifers and cladocerans in eutrophic Lake Loos drecht (The Netherlands) was determined by microscopic observation of in situ tracer particle uptake. Ingestion rates of rotifer species usi ng 0.51 mu m microspheres or fluorescently labelled bacteria as tracer s differed, with one exception. The ingestion rates depended on both t he species and the tracer type. For cladocerans, fluorescently labelle d bacteria seemed to underestimate grazing, presumably due to rapid di gestion of tracer cells. Comparing results obtained with 0.51 mu m mic rospheres, rotifers were much more important grazers on bacteria than cladocerans in the study period (April-September). Based on microspher es, the rotifer populations with the highest uptake of bacteria were F ilinia longiseta (May-July) and Anuraeopsis fissa (June-September). Ac cording to the uptake of fluorescently labelled bacteria, Conochilus u nicornis had the highest uptake in June and A. fissa in July.