GLOBEC 2000: Spatial and Temporal Variability of Microplankton in the Gulf of Alaska

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The focus of this project is to describe quantitatively the abundance, biomass and size-structure of the microplankton (phytoplankton and microzooplankton 200 um) prey fields as part of the Gulf of Alaska GLOBEC program. A central objective of the mesoscale studies is to determine how physical forcing affects the availability and production of zooplankton prey for juvenile pink salmon. Juvenile salmon prey (copepods, euphausiids, pteropods, amphipods) depend directly or indirectly on diverse mircroplanktonic prey, including microzooplankton (flagellates and ciliates) which have recently been recognized to be a significant dietary component of zooplankton. The size-structure, taxonomic composition and growth dynamics of the lower trophic food web are expected to be highly responsive to physical forcing and, in turn, exert strong influences on zooplankton growth, fecundity, community composition and nutritional state. Group-specific phytoplankton growth and microzooplankton grazing rates will also be measured to identify trophic pathways and responses to changing physical regimes. This study will provide critical mechanistic insight and validation for coupled biological-physical models of the Gulf of Alaska shelf ecosystem.