Invertebrate predators of zooplankton on Georges Bank, 1977-1987

Chaetognaths, primarily Sagitta elegans, were the most abundant and widespread invertebrate predator on Georges Bank during 1977-1987 MARMAP surveys. They were present in 79% of samples collected, and their average abundance was nearly an order of magnitude greater than that of any other predator taxon. Hydrozoan and scyphozoan medusae, euphausiid shrimp, and gammarid and hyperiid amphipods were also abundant. Diversity and abundance of predators was highest in the central, well-mixed region of the bank. In this region numbers of chaetognaths and cnidaria increased following increased abundances of Calanus finmarchicus. However, on a larger scale the density of C. finmarchicus populations was inversely correlated with number of predators because this herbivore was most abundant in deeper waters surrounding Georges Bank where predators were least numerous. Chaetognaths and cnidaria were more abundant in 1978-1979 than in other years, and there was a statistically significant decline in the abundance of chaetognaths over the 10 year period. Abundance of both these groups was inversely correlated with temperature. Average numbers of chaetognaths in summer were low following a warm winter. Abundance of cnidaria in summer decreased with increasing summer temperatures. Copyright (C) 1996 Elsevier Science Ltd.