Concern about the potential impact of climate change on the eastern Bering Sea ecosystem prompted a study of the species composition, abundance and biomass of the mesozooplankton populations forming the ecosystem and estimation of population trends as part of the Bering Sea Ecosystem Study (BEST). The PIs have been previously funded to collect and process approximately 260 zooplankton samples from the eastern Bering Sea during each of two cruises per year for the three BEST field seasons, to analyze the data, and to publish the results in peer-reviewed journals. However, during field collection, the need for additional information was identified in order to ensure robust results. In response to these needs, an additional 200 samples per year were collected during the BEST cruises. This award funds the processing of those samples.
The entire rational of the BEST ecosystem study is based on the fundamental hypothesis that the eastern Bering Sea ecosystem is changing under the influence of climate. The goal of the BEST research effort is to identify and quantify mechanistic links between climate and the ecosystem response. An ecosystem responds to changes in climate forcing by altering the abundance, biomass and species composition of its constituent populations. Therefore, a central requirement of the research is to collect and process a sufficient number of samples to determine robustly the state of the system during the study, estimate the direction or magnitude of change, if any, to validate or refute hypotheses concerning change, and to adequately validate or parameterize the lower trophic level models generated by other program participants. Processing of the 200 extra samples per year will substantially improve our ability to detect statistically significant changes in zooplankton populations during the BEST program, thus helping to address the above requirements.
The primary task of this project was to assess the amount of zooplankton on the Bering Sea continental shelf. Zooplankton are large and small animals, mostly invertebrates, which drift in the water. Information on zooplankton abundance is being used by the Bering Sea Ecosystem Project (BEST) to assess the health of the Bering Sea ecosystem and to aid in understanding the potential effects of global climate change on Bering Sea fisheries. Since the Bering Sea sustains large commercial fisheries and subsistence resources for native communities, understanding the potential effects of climate change on zooplankton and their associated fish populations will aid policy makers in planning for and mitigating climate-related impacts on the fishing and indigenous communities along the Bering Sea coast. The project resulted in 675 zoopalnkton samples collected and processed. The samples will be stored at University of Alaska for at least 20 years and made available upon request to future researchers. The data on zooplankton composition and surrounding environment, which were simultaneously collected with automated sensors during the tows, were uploaded into the BEST interdisciplinary database (www.eol.ucar.edu/projects/best/) to make them available for other researches and general public for current and/or retrospective analyses and interpretations. Ecosystem studies over the last decade revealed substantial declines in populations of large zooplankton during the warm period of 2002 – 2006. These declines were accompanied by declines in the survival of juvenile pollock, a major commercial fish on the Bering Sea shelf. Since large zooplankton are an important food for young pollock, the declines in large zooplankton are a potential reason for observed declines in survival of young pollock. In addition, large zooplankton are an important food for salmon, herring, capelin and other large fish species. In the absence of large zooplankton, other large fish were consuming juvenile pollock, thus lowering pollock survival and stock size. As fish stalks decline, the supply of fish to the fishery also declines, resulting in lower incomes and employment in the fishing communities. Colder temperatures in 2007-2010 were accompanied by a recovery of large zooplankton populations as assessed by the BEST project. Increases in abundance of large zooplankton during the recent cold period are further evidence that declines in zooplankton during the warm period were temperature-related. In addition to increases in populations of large zooplankton during the cold period of 2007 – 2010, large Arctic zooplankton species occurred in the samples. These arctic species had not been observed in the southern Bering Sea since the 1970s. Arctic species can be an important food source for seabirds and commercial fish, so their reappearance on the Bering Sea shelf is an indication that climate change can impact the Bering Sea ecosystem by changing the species composition of the constituent populations in addition to changing population size. The species composition and abundance of plant and animal populations in ecosystems are continuously changing in response to climate. Since climate warming is predicted to occur more rapidly in arctic and subarctic environment, these changes in species composition and abundance are likely to accelerate and increase in amplitude. Nevertheless, ecosystems are extremely complex and can change in unpredictable ways. Therefore, sound resource management in a changing world requires continuous assessment of the plant and animal populations to allow resource managers to modify management policies in a timely manner, to minimize the potential impacts of unexpected changes in fish and wildlife populations on the coastal communities which depend on these resources for subsistence and commercial harvests.
