Persistent spatial and temporal abundance patterns for late-stage copepodites of Centropages hamatus (Copepoda: Calanoida) in the U.S. northeast continental shelf ecosystem

The annual cycle of abundance and the monthly distribu­ tions of the copepod Cenfropages hamatus are described for U.S. north­ east continental shelf waters from plankton samples collected approxi­ mately bimonthly from 1977 to 1987. The copepod was found distributed throughout the study area with a strong onshore-offshore abundance gradient. After its annual low, C. hamatuswas found to increase in abun­ dance slowly along the coast and to ex­ pand offshore following the northward progression of spring conditions. The highest monthly mean abundance es­ timates of C. hamatus were found on Georges Bank during the month ofJuly. Distribution begins to constrict inshore following peak abundance periods. Examination of environmental vari­ ables revealed that in general Cenfro­ pages hamatus was prevalent when surface temperatures ranged from 12 to 17°C, when water-column chloro­ phyll levels were high, and where sa­ linity was low on the shelf. The popu­ lation in the MiddleAtlantic Bight sub­ area declines sharply as water tem­ peratures rise in summer and does not begin to recover until temperatures decline in the fall. In contrast, popula­ tions in the more northern regions de­ crease slowly from peak abundance and do not increase from their annual low until water temperatures rise in early spring. The pelagic population that sur­ vives through low abundance periods is concentrated in shoal or inshore (or both) waters where temperature is low and phytoplankton biomass high. There was no evidence from survey data that predation by ctenophores, chaetognaths. or the copepod Centropages typicus has a majoreffect on C. hamafusabundance.