U.S. GLOBEC: Recruitment Variability and Advective Processes on Georges Bank--Diet of Early Stage Copepods

Dian J. Gifford
University of Rhode Island
Michael E. Sieracki
Bigelow Laboratory for Ocean Science

The specific focus of the research is to describe quantitatively the contribution of nano- and micro- plankton prey fields to recruitment of target copepod populations on the Bank. We hypothesize that early stage copepods advected onto the Bank from the Gulf of Maine and the Great South Channel experience an enriched food environment on-Bank relative to source regions. We will measure consumption of nano- and microplankton organisms (i.e. plant and animal prey 2-200 microns in size) by naupliar stages N3-N6 of the calanoid copepods Calanus finmarchicus and Pseudocalanus spp. in (1) source areas in the Great South Channel and the Gulf of Maine where the advective regime contributes water (and presumably copepods) to Georges Bank; (2) on-Bank regions receiving these inputs, including the region of enhanced production on the Northeast Peak, and (3) areas on either side of the tidal front separating the Bank crest from deeper waters on the Southern Flank. We focus on Calanus and Pseudocalanus because these species dominate the zooplankton biomass of Georges Bank during the January- June period that is the focus of the U.S. GLOBEC Georges Bank program. We propose to study nauplii because these are the stages at which copepods recruit to the population. We emphasize source areas in the Great South Channel and southern Gulf of Maine because these are sites for advective inputs of water and zooplankton onto the Bank. We focus on the Northeast Peak as an on-Bank site because it is an area of enhanced production of both plankton and benthos relative to the rest of the Bank. And we compare zooplankton on the Bank crest versus flank because U.S. GLOBEC studies conducted during 1994-1995 indicate that, although nauplii of Calanus and Pseudocalanus are advected onto the Bank crest early in the season, strong cohorts do not subsequently develop, possibly as a result of intense predation pressure in this area. Ingestion rates of nauplii will be measured directly in shipboard experiments using natural prey assemblages. The proximate influence of omnivorous feeding will be interpreted in the context of the in situ prey field and physical regime. Ultimately, the influence of plant versus animal prey in consumer diet will be addressed collaboratively in the context of measurements made by other investigators of consumer distribution, condition, life history parameters and production. In addition to their specific importance in the Georges Bank ecosystem, copepod nauplii have not been extensively studied overall, and the proposed research provides a valuable opportunity to acquire fundamentally important information on their physiological ecology.