Zooplankton Studies at Ocean Weather Station "P" in the Northeast Pacific Ocean

Abstract

Concentrations of zooplankton observed at Station "P" (50°N.L., 145°W.L.,) are less than those in the Northwest Pacific, the Bering Sea, British Columbia coastal waters and the Labrador Sea; about equal to those at Station "M" in the Norwegian Sea; and greater than those in the central Equatorial Pacific and the Sargasso Sea. Zooplankton abundance at Station "P" appears representative of that in a wide area of the central Gulf of Alaska. A vertical distribution of zooplankton characterized by maxima of concentration from 0–100 metres and from 200–500 m was observed both day and night and in all seasons. Daily means of concentration of surface zooplankton ranged from about 20 g per 1000 m3 in winter to about 150 in summer. A small autumn maximum was observed. A similar seasonal cycle of abundance occurred down to depths of about 200 m. Below 200 m the amplitude of the seasonal cycle tended to decrease with depth. Vertical hauls captured mainly copepods all year round. Horizontal surface tows revealed a marked seasonal cycle in taxonomic composition. A pronounced diurnal variation in the concentration of surface zooplankton was observed and showed the major features of typical diurnal vertical migration. Night catches of vertical hauls exceeded day catches.