Annual cycle in abundance, distribution, and size in relation to hydrography of important copepod species in the western Arctic Ocean

A yearlong study of the zooplankton biomass and the abundance, vertical distribution, life stage proportions, and body size and condition for five target copepod species (Calanus glacialis, C. hyperboreus, Metridia longa, Microcalanus pygnuteus.. Oithona similis) was conducted from October 1997 to October 1998 in the Western Arctic Ocean. The research was staged from Ice Station SHEBA that drifted from Canadian Basin over the Northwind Ridge and Chukchi Plateau and back over the Basin during this period. Four hydrographic regimes were surveyed during the period of the study. Zooplankton biomass was least over the basin during the fall and winter and greatest over the Chukchi Plateau during summer, with most biomass in the 200-1500 m depth interval except during summer when greatest biomass was present in the upper 200 m. The five copepod species followed two general life history strategies: (1) sustained reproduction with all life stages present throughout the year and constant depth distribution (M. longa, M. pygmaeus, O. similis) and (2) pulsed reproduction with overlapping cohorts present and ontogenetic redistribution of preferred depths through the year (C. glacialis, C hyperboreus). Body size and condition did not demonstrate consistent temporal or regional patterns. Based on population age structure, both C. hyperboreus and C glacialis were reproducing in the Arctic Ocean. However, extremely low abundances of C. glacialis suggested that this species may not be self-sustaining in the Arctic Ocean. Plankton biomass was consistent with that observed in recent studies and supported an emerging paradigm of a more productive Arctic Ocean than traditionally believed. (C) 2003 Elsevier Ltd. All rights reserved.