Abstract
Clearance rate of the planktonic cyclopoid copepod Mesocyclops dissimilis on the planktonic calanoid copepod Eodiaptomus japonicus was measured in laboratory experiments. Ontogenetic changes were investigated using several combinations of different developmental stages of the two species. To minimize the side effects of laboratory experiments, predation was examined for a short duration using field-captured animals at natural prey densities and temperatures. Individual predators showed a large variation in the clearance rate even within replicates of the same experiment. The clearance rates of adult female predators on late naupliar prey were similar (about 0.15 L ind.−1 d−1) within a range of prey density 12–31 ind. L−1. Ontogenetic tendencies in clearance rate, though seldom significant, translated to an increase with development of the predators and a decrease with that of the prey. Present clearance rates and the natural densities of predators and prey suggest that M. dissimilis was sometimes an influential predator of E. japonicus in the field.
