Collaborative Proposal: Cross-Shelf Transport and Post-Bloom New Production Near the Pribilof Islands

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The proposed study will test the hypothesis that on-shelf flow of nutrient- and zooplankton-rich slope water influences post-spring-bloom new production and zooplankton populations in the vicinity of the Pribilof Islands, thereby enhancing the region's ability to support juvenile fish and planktivorous seabirds. The project will investigate on-shelf transport of slope water, which supplies nutrients that sustain new primary production in summer, a season when the availability of new production on the shelf is limited by stratification. A second hypothesis is that this new production will be dominated by diatoms rather than by flagellates, and a diatom-based food web will result in meso-zooplankton with a greater energy content than meso-zooplankton in a flagellate-based food web. These energy-rich zooplankton are expected to be of greater value to juvenile fish and planktivorous seabirds than those that have fed upon less lipid-rich phytoplankton. The project will also test these hypotheses during July/August cruises in 2004 to 2007. During these cruises, the PIs will compare production and its fate in an area on the middle shelf where summer-time cross-shelf advection is weak (Mooring 2), on the middle shelf in an area of episodic advection but little vertical mixing (Mooring 4) and at the Pribilof Islands where there is both on-shelf transport and tidal mixing of nutrients into the upper mixed layer. The project will measure along- and across-shelf flows (Stabeno, PMEL), nutrient concentrations (Mordy, UW/PMEL), standing stocks of phytoplankton (Zeeman, U. New England), new, regenerated and total production (Zeeman, Sambrotto, Lamont-Doherty), the grazing rates of micro-zooplankton in relation to phytoplankton standing stocks and production (Strom, Western Washington University), zooplankton biomass and composition (Coyle, U. Alaska, Fairbanks), lipid content, fatty-acid composition, and stable isotope signatures of zooplankton, juvenile fish and seabirds (Napp, NMFS), and the foraging distributions and food habits of marine birds (Hunt, U. California, Irvine). In addition, the project will use satellite-tracked drifters and moorings to measure currents. This proposal is the first in the Bering Sea to address the effect of on-shelf fluxes of nutrient-rich slope water on post-spring-bloom new production, and in turn, how this new production affects the abundance and quality of prey for juvenile fish (i.e., age-0 walleye pollock) and planktivorous seabirds. Post-bloom new production may be particularly important for providing high quality prey at a time when juvenile fish are developing the reserves to carry them through the winter and seabirds are feeding growing young. The work focuses on a region of great economic and societal importance, and examines the ecological processes that affect the productivity of Pribilof Islands' waters and their ability to support juvenile fish, and the seabirds and marine mammals that depend on them. The most abundant fish in the area are juvenile walleye pollock, the target of the world's largest single-species fishery. The information generated by the proposed research will be of value in assessing the mechanisms whereby global climate change can affect the amount of post- spring bloom new production and the nutritional quality of prey available to upper trophic levels. The project will include undergraduate, graduate and post-doctoral students in the field and in the laboratory for the analysis and workup of the data and will strive to develop outreach programs with the school systems on St Paul and St. George Islands. The work will be disseminated in the refereed literature and through web sites.