Preliminary studies on the role of protozoa in the food web of Donghu Lake

Abstract

Plankton from Station I of Donghu Lake, an eutrophic lake, was divided into three groups (2–32 μm, 32–112 μm and >112 μm) by filtering the water sample through 2, 32, 112 μm pores. It was supposed that the 2–32 μm Protozoa (group 1) was fed on by the 32–112 μm Protozoa and small rotifers (group 2) and >112 μm large rotifers, cladocerans and copepods (group 3). The feeding rate of zooplankton in situ was estimated by counting the protozoan individuals and also by the14C-NaHCO3 method. The P/B ratio of the small Protozoa (group 1) was 2.9 for 6 h and 1.2 for 24 h. The feeding rate of the 32–112 μm zooplankton on small Protozoa (2–32 μm) was about 2/3 the total feeding rate of zooplankton, and that of >112 μm zooplankton on the 2–32 μm Protozoa was 1/3 of the total feeding rate. The lower the density of feeders, the higher were the feeding rates. The daily production of the 2–32 μm protozoans was 1.559 mg/L, which equaled to 25% of the daily food consumption of other zooplankton. Isotope experiments showed result similar to that from the above direct counting method.