On the foraging and feeding ability of Oithona davisae (Crustacea, Copepoda)

Abstract

The foraging behavior and feeding ability of the cyclopoid copepod Oithona davisae, using the flagellate Tetraselmis tetrathele as prey organism, were observed microscopically and three dimensionally in a flow-cell. The distance between O. davisae and prey was estimated, and prey in front of the antennules or close to the mandible or mouthparts was ingested. Before attacking, O. davisae either sank or jumped. Both these motions are typical of foraging behavior. The instantaneous perceptive sphere was measured from the ingested prey position, while the encounter rate was estimated from the volume of the perceptive sphere, sinking speed, jump frequency plus swimming speed of prey. The calculated encounter rate was in good agreement with previously reported ingestion rates at low prey concentrations. From encounter rate and natural prey density, we conclude that O. davisae is capable of locating sufficient prey for its demands. Under natural conditions, where prey organisms may not be encountered regularly, the voracious O. davisae will ingest prey frequently when available. Our experimental methodology, devised to quantify the feeding abilities of O. davisae, is applicable to studying the foraging behavior of other copepod species.