The demography of Calanus finmarchicus (Copepoda: Calanoida) in the Middle Atlantic Bight, USA, 1977-2001

Abstract

The spatial distribution and annual cycle of abundance for the late-stage copepodites of the calanoid copepod Calanus finmarchicus are described for the shelf and slope waters of the Middle Atlantic Bight (MAB), a subregion of the US Northeast large marine ecosystem. Samples were collected with bongo nets from 1977 to 2001 on broad-scale surveys of the region and from a continuous plankton recorder (CPR) towed at 10-m depth along a route that traversed the area. The copepod's abundance in shelf waters increased rapidly in early spring and reached maximum levels in May-June. It declined slowly thereafter, until a minor secondary pulse occurred in late autumn, which was followed by the annual winter low. Slope water abundance of C. finmarchicus peaked in April and was virtually absent there at 10-m depth from July through the following February. The two samplers, both portrayed similar high interannual abundance variability with no long-term trend evident for the 25-year period. Cluster analysis pinpointed three shelf areas with similar abundance patterns, one of which was a region of high density located in the northeastern offshore waters. Evidence is presented that indicates the source of this high abundance is likely from the populations that overwinter in deep water basins of the Gulf of Maine (GOM). The copepod's interannual abundance variability was found to be negatively correlated with water temperature and unrelated to fluctuations of the North Atlantic oscillation (NAO) index.