BIODIVERSITY AND ABUNDANCE OF THE ZOOPLANKTON OF THE NORTHEAST SHELF ECOSYSTEM

Since 1961, the Northeast Fisheries Science Center of the National Mar ine Fisheries Service has been conducting a study of the zooplankton o f the US Northeast Shelf ecosystem. One of the objectives is to invest igate ecological patterns of the system for any evidence of regime shi fts and their effects on biodiversity and abundance of zooplankton and fish stocks. Two sampling strategies have been used: collections with Continuous Plankton Recorders beginning in 1961; and collections with bongo nets during the decade of MARMAP surveys (1977-1987), augmented by a time series of collections made during the autumn and spring gro undfish surveys (1977-1993). The climate regime of the region leads to distinct and recurring seasonal pulses in zooplankton biomass and spe cies succession in each of the four subareas of the shelf ecosystem di stinguished. Evidence was detected in the analyses of inter-annual var iability in species abundance and zooplankton biomass. However, no evi dence of a large-scale regime shift of the magnitude described recentl y for other areas was detected From our analyses. Species shifts in ab undance and the inter-annual and decadal variability observed in zoopl ankton biomass levels have allowed for sufficient residual sustainabil ity in zooplankton biodiversity and abundance to support the recovery of depleted pelagic fish stocks.