Zooplankton abundance trends on Georges Bank, 1977-2004

Abstract

Interannual trends in Georges Bank zooplankton abundance are described and related to variations in environmental variables for the period 1977-2004. Total zooplankton counts increased to above average levels in 1989 and stayed over or close to average through 2004. This analysis identi.ed a group of taxa including Centropages typicus, Metridia lucens, and Temora longicornis that had similar interannual patterns of abundance. All these taxa increased sharply in the early 1990s and remained high through 2001. Some taxa declined sharply in 2002, others have continued elevated through 2004. Total zooplankton counts in the past two years were also boosted by a substantial increase in the abundance of the copepod Calanus.nmarchicus. Evidence is presented that these changes may be related to variations in Scotian Shelf in.ow, which freshened water on the Northeast US continental shelf, perhaps increasing both primary production and the in.ux of zooplankton into the region. There was a positive correlation between the biomass of pelagic predators and the abundance of several zooplankton taxa, suggesting that bottom-up processes and advective supply are the key factors that regulate the Georges Bank foodweb. © 2007 International Council for the Exploration of the Sea.