PREDATION ON CILIATES BY THE SUSPENSION-FEEDING CALANOID COPEPOD ACANTHODIAPTOMUS-DENTICORNIS

The effects of prey size, hunger, and algal presence on the predation of the suspension-feeding calanoid copepod Acanthodiaptomus denticorni s on the ciliates Tetrahymena corlisii (32 mum mean length), Parameciu m aurelia (114 mum), P. caudatum (124 mum), Loxodes sp. (greater-than- or-equal-to 130 mum), and Stentor coeruleus (greater-than-or-equal-to 280 mum) and the flagellate Astasia longa (14 mum) were evaluated in l aboratory experiments. Adult Acanthodiaptomus consumed all species, bu t not in proportion to their size. At low concentrations (prey <200 mu g C.L-1), mean clearance rates ranged from 80 mL.copepod-1.d-1 (for Pa ramecium) to 13 mL.copepod-1.d-1 (for Loxodes). Clearance rates declin ed with increasing concentration of the same prey, as expected. Prey c apture and ingestion was determined by cell width and prey escape reac tivity. Hunger significantly increased predation rates at high prey le vels. The presence of algae enhanced ciliate predation by hungry copep ods at low prey levels, but had no other significant effects. Protozoa n predation by Acanthodiaptomus generally exceeds its feeding on algae and nanoplankton. Results suggest that ciliates can be a significant part of the diet of some suspension-feeding freshwater copepods in sit u, confirming the importance of ciliates as mediators of energy transf er from the microbial loop to higher trophic levels.