Processes Controlling Abundance of Dominant Copepod Species on Georges Bank: Local Dynamics and Large-Scale Forcing

Cabell Davis (WHOI), Robert Beardsley (WHOI), Changsheng Chen (UMassD), Rubao Ji (WHOI), Ted Durbin (URI), David Townsend (UMaine), Jeffrey Runge (UNH), Charles Flagg (SUNY-SB) (SUNY)

A fundametal goal of Biological Oceanography is to understand how underlying biological- physical interactions determine abundance of marine organisms. For animal populations, it is well known that factors controlling survival during early life stages (i.e., recruitment) are strong determinants of adult population size, but understanding these processes has been difficult due to model and data limitations. Recent advances in numerical modeling, together with new 3D data sets, provide a unique opportunity to study in detail biological-physical processes controlling zooplankton population size. We propose to use an existing state-of-the-art biological/physical numerical model (FVCOM) together with the recently processed large 3D data set from the Georges Bank GLOBEC program to conduct idealized and realistic numerical experiments that explore the detailed mechanisms controlling seasonal evolution of spatial patterns in dominant zooplankton species on Georges Bank. We will examine a series of hypotheses that address how dominant copepod species populations are maintained on the bank, including local dynamics and large-scale forcing. Specifically we will determine whether the observed characteristic seasonal spatial pattern of each species (long-term and inter-annual) is predictable from the interaction between its characteristic life-history traits and physical transport. The extent to which the copepod populations are controlled by food-availability (bottom-up) or predation (top-down) processes will be examined, including the influence of Warm Slope Water versus Labrador Slope Water (NAO-dependent) on nutrient influx through the Northeast Channel and subsequent upwelling and biological enhancement on the bank.

Self-sustainability of each species population on the bank itself and in the Gulf of Maine will be studied by controlling immigration from specific source regions. Large-scale forcing including NAO and catastrophic global warming (e.g. complete polar ice melt) will be examined explicitly by forcing the model at the boundaries, using scenarios based on basin-scale data and from concurrent basin-scale modeling efforts.

Intellectual Merits:/ The proposed modeling study will provide new insights into the role of local and large-scale processes controlling zooplankton abundance in the ocean. The dominant copepod species to be studied include small species that are the dominant prey for larval cod and haddock in this region, thus providing critical information for concurrent larval fish modeling studies. This detailed, process-oriented, regional-scale modeling with boundary forcing will lay the groundwork for integration with models of the entire ocean basin. The resulting model will be a legacy of the GLOBEC Georges Bank program by providing a powerful new tool for understanding how local and large-scale forcing interact to control plankton production in the sea. Broader Impacts: Results of the proposed work will be broadly disseminated to the general oceanographic community, the fishing industry, K-12 institutions, and to the population at large, through web-based servers using existing infrastructure at the proposers' institutions. Web-based users will be able to access model results and run the model using chosen parameter settings to obtain predictions of currents, hydrography, and plankton abundance patterns given selected climate forcing scenarios. Collaboration with the WHOI/UMASS COSEE program will foster communication with K12 students and the public both nationally and internationally.