Funds are provided to examine the impact of sea ice on the distribution and abundance of zooplankton, and how they are partitioned among top predators. To this end, new and historical data will be used to test a series of hypotheses and answer questions relating to bottom-up and top-down control of large crustacean zooplankton and their impact on the flow of carbon and energy in the ecosystem. From the examination of these hypotheses, new mechanisms will be derived and old ones re-evaluated. Existing numerical models will be used to assess the relative importance of these mechanisms. Existing conceptual models will be tested, and new conceptual models of carbon and energy flow will be developed. Such a study of the eastern Bering Sea shelf ecosystem is timely. Some of the most direct effects of changing climate will be on sea-ice - its extent, duration, timing of retreat, and inter-annual variability. Sea ice in turn controls ocean temperature/salinity, timing of the spring phytoplankton bloom and thus the extent of export/remineralization of fixed carbon. Crustacean zooplankton can be a choke-point in the flow of carbon and energy through the food chain.

The Bering Sea ecosystem provides roughly half the commercial seafood landings in the United States, as well as significant resources for subsistence fishermen. Major fluctuations in these stocks have occurred in the past and been associated with climate variations. Improved management of these important fisheries should be enabled by the understanding derived from this project.

Project Report

The eastern Bering Sea shelf supports a productive marine ecosystem with extraordinarily valuable fishery and subsistence resources, but sub-arctic seas are predicted to be highly sensitive to ocean warming. Some of the most direct effects of changing climate will be on the extent, duration and timing of sea ice. Sea ice in turn controls water column temperature and salinity, stratification, the timing of the spring phytoplankton bloom, and provides a platform for marine mammals to haul out. Thus, one of the most urgent priorities of current research is to examine the role of changing sea-ice conditions on the chemical, physical, and biological characteristics of this ecosystem. This was a primary focus of the Bering Sea Ecosystem Study (BEST, funded by NSF) and Bering Sea Integrated Ecosystem Research Program (BSIERP, funded by NBRP). Crustacean zooplankton can be a choke-point in the flow of carbon and energy through the food chain. Species composition, standing stock and size distributions of zooplankton vary along and across the shelf, and depend on the presence of sea ice in spring, and the timing of its seasonal retreat. This BEST Synthesis project examined the interaction of sea ice with bottom-up and top-down controls of crustacean zooplankton, their standing stocks and size distributions, and explored how these controls varied among shelf domains and between extended periods of warming and cooling. In addition, we found that, on an annual basis, there was more than sufficient primary production to support euphausiid populations. Evidence of top-down control by pollock included a strong inverse relationship between pollock biomass and euphausiid biomass, the substantial percentage of euphausiid production consumed by pollock, and the modeled steep decline in euphausiid biomass between spring and fall, which may be ascribed to predation, though other possibilities could not be ruled out. Contrary evidence came from a paper by Ressler et al., 2014, Marine Ecology Progress Series, that showed water temperatures were a strong predictor of euphausiid distribution and abundance, whereas pollock biomass had little or no predictive power. Finally, comparing the relative rates of euphausiid production, pollock consumption, and other sources of euphausiid mortality, it is clear that factors other than pollock consumption are likely important in determining euphausiid standing stock. We developed a simple conceptual model of how climate variability, in particular stanzas of years with early or late ice retreat such as that observed in 2001 - 2012, might affect the likelihood of top-down or bottom-up control of euphausiids. The strong density-dependent coupling of pollock with euphausiids (and large, lipid-rich copepods), and the sensitivity of these prey to variability in climate, suggests that the eastern Bering Sea pollock stock will be vulnerable to future climate shifts. Knowledge gained from this study were disseminated through ~45 presentations at national meetings, and in ~35 journal publications. Intellectual Merit: A major goal of ecosystem research is to understand the complex interactions between the organisms comprising the ecosystem and the physical environment that governs energy flow through a system. Elucidation of the energy pathways and the controlling mechanisms requires detailed information on the physical environment, energy flow between trophic levels, and the populations, biomass and species composition of the constituent organisms over the range of environmental extremes. Data available from the BEST-BSIERP and related programs in the Bering Sea shelf include physical, process and population information for trophic levels from phytoplankton to apex predators over periods of extremely cold and warm conditions. They therefore provided a unique opportunity to identify, describe and quantify the mechanisms regulating energy flow through this system. As global warming impacts the Bering Sea shelf, this research provided a solid foundation upon which to develop and refine our conceptual and numerical models as the system evolves in response to climate change. Broader Implications: This synthesis was a multi-disciplinary (climate to predators) collaboration among academic institutions, government (NOAA), and two countries. Through two synthesis workshops and several national meetings, additional partnerships were forged with PIs from other institutions. Our synthesis products are useful to and used by commercial and subsistence users of Bering Sea resources, and federal and state agencies charged with an ecosystem approach to management. PIs on this proposal are members of the North Pacific Fisheries Management Council's Scientific and Statistical Committee (G. Hunt) and Bering Sea/Aleutian Islands Plan Team (K. Aydin). Details and results of the project will be maintained at Information and data from this project has been incorporated into a graduate course in Zooplankton Ecology at the University of Maryland and into lectures for REU students at UMCES, BIOS and other institutions. This program provided an undergraduate research assistantship at the University of Alaska, and travel funds for three graduate students to attend several workshops.

National Science Foundation (NSF)
Division of Polar Programs (PLR)
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William J. Wiseman, Jr.
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University of Washington
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