The Contribution of Ciliated Protozoa to Plankton and Benthos Biomass in a European Ricefield

The densities and biomass of ciliates inhabiting the water-sediment interface and the water column of an experimental ricefield were investigated throughout four annual cycles. Ciliate abundance and biomass were higher at the water-sediment interface than in the water column. In both sites, large ciliates (> 10⁵μm³) contributed the higher biomass values, but the highest densities were found in the intermediate size class (10⁴-10⁵μm³). The prorodontid Coleps hirtus dominated the ciliate assemblage and usually comprised > 50% of total ciliate density. Blooms of C. hirtus , occurred in June in the water column and in July at the sediment surface. During the four cycles of rice cultivation, the average daily values for production of the entire ciliate community was 69.6 mgC/m²/d, and the net production efficiency (K₂) was 72.0%. The estimated production values in the present study are high if compared to production measured for ciliates in other freshwater ecosystems.