PROTOZOA IN THE DIETS OF NEOCALANUS SPP IN THE OCEANIC SUB-ARCTIC PACIFIC-OCEAN

Copepod species of the genus Neocalanus dominate the zooplankton bioma ss of the oceanic subarctic Pacific Ocean. Neocalanus spp. populations in the subarctic Pacific environment are successful: they feed, accum ulate lipid, and persist from year to year. Prior experimental observa tions derived from a variey of methods indicated that, although their functional morphology is such that they clear the small phytoplankton cells characteristic of the oceanic subarctic Pacific environment effi ciently, Neocalanus spp. do not consume sufficient phytoplankton to me et even basic metabolic requirements in that environment. Hence, their success in the subarctic Pacific must depend on their ability to obta in nutrition from other sources. As part of the SUPER (SUbarctic Pacif ic Ecosystem Research) program, experiments were performed to test the hypothesis that N. plumchrus and N. cristatus obtain a significant po rtion of their nutrition from planktonic Protozoa. The experiments dem onstrate that Protozoa alone do not provide sufficient nutrition for N . cristatus to meet its basic metabolic needs. Protozoa constitute the major dietery component of N. plumchrus however, in agreement with th e predictions of FROST'S (1987) model of the subarctic Pacific ecosyst em. At a minimum this diet permits N. plumchrus to meet basic metaboli c requirements. Copepod grazing activities appear to be sufficient to control protozoan stocks in the oceanic subarctic Pacific during late spring and early summer when Neocalanus spp. inhabit the upper water c olumn.