Grazing of Marine Copepod Developmental Stages on Naturally Occurring Particles

Abstract

Grazing experiments were performed with copepodids (stages CI–IV) of Pseudocalanus minutus feeding on naturally occurring particulate matter. Variations in the feeding rate of copepodids were associated with seasonal changes in the standing stock of particulate matter. Copepodids adapted to seasonal variations within the particle spectrum. Particle sizes < 22 μm contributed most of the standing stock of particles during the period studied. Maximum consumption was recorded when copepodids fed on small-size particles. The importance of fine particles is illustrated in comparative feeding experiments performed with adults and copepodids fed simultaneously on the same particles. The differences between the mean consumption of copepodids and adults are highly significant in the particle size ranges below 22 μm. The fact that copepodids obtain more food than adults on particles < 10 μm is probably related to the smaller mesh size and to the higher frequency of vibration of their mouth appendages. Although all copepod stages are opportunistic feeders, such a mechanism allows copepodids to reduce feeding competition with adults and allows them to fulfil their higher requirements for energy from food particles that have a high productive potential and a high nutritive value. This provides the evidence that feeding niches are partially separated between young and adult copepods. Key words: calanoid copepods, copepodids, Pseudocalanus minutus, grazing, competition, naturally occurring particles