Energy Flow in Euphausia pacifica

Abstract

To understand relationships within food webs in the sea, with an eye to predicting and perhaps ultimately improving the efficiency of the production of commercially important species, we must understand the energetics of the lower elements of the food web. Energy flow more accurately represents the significance of a species in a community than either the numbers or the biomass of the species¹. Euphausiids (class Crustacea) are pelagic filter-feeders of world-wide distribution which serve as forage for a wide variety of marine animals, including whales² and salmon³. Euphausia pacifica Hansen, the principal species in the North Pacific, often represents the largest biomass of the macroplankton in the subarctic and transitional water masses⁴. The species is a vertical migrant, inhabiting depths of roughly 100–500 m during the day and ascending to surface waters at night⁴. It is exposed to water temperatures of about 5°–15° C off Oregon (depending upon season and depth of migration); 10° C is the approximate average⁵. Day length varies off Oregon from about 8 h in winter to 16 h in summer, so that the time spent in waters of different temperature varies seasonally⁶.