SINKING PARTICLES AS A POSSIBLE SOURCE OF NUTRITION FOR THE LARGE CALANOID COPEPOD NEOCALANUS-CRISTATUS IN THE SUB-ARCTIC PACIFIC-OCEAN

Shipboard incubations of Neocalanus cristatus CV in natural seawater from the subarctic Pacific Ocean near Ocean Station ''P'' (50-degrees-N, 145-degrees-W) indicate that ingestion of uniformly suspended phytoplankton averages 6.3 mugC cop-1 day-1 and ingestion of protozoan microzooplankton is 3.0-4.6 mugC cop-1 day-1. Metazoan microzooplankton may contribute an additional 2.1-4.3 mugC cop-1 day-1. Total ingestion from these sources is considerably less than the 34-92 mugC cop-1 day-1 required for a growth rate of only 2% body C day-1. Levels of gut chlorophyll and pheopigments indicate ingestion rates of pigment containing materials were approximately four times greater than determined by in vitro incubations. Microscopic examination of gut contents suggests that aggregated particulate material was being ingested, and the morphology. behavior and vertical distribution of N. cristatus CV further suggest that sinking aggregates may be a significant source of nutrition: (a) N. cristatus CV has a large perceptive volume. It is a large copepod, 7-9 mm long from the apex of the head to the apex of the caudal rami, and its first antennae are disproportionately long relative to its body size. In addition, it has elaborate plumose setulation at the end of its antennae and its caudal furcae; (b) N. cristatus CV is a stationary suspension feeder. It hangs motionless in the water column for long periods and uses a feeding current to bring particles within the working range of its mouthparts. It is not an efficient carnivore; (c) N. cristatus CV is concentrated below the surface mixed layer (upper 30-50 m), in the depth stratum of maximum particulate flux. Measured levels of gut pigment in N. cristatus CV could be obtained by ingestion of the particulate flux from only a few cm2 day-t. This would provide sufficient nutrition to maintain a growth rate consistent with known rates in this region.