Funds are provided to study the role of sea ice algae in the food web of the eastern Bering Sea shelf ecosystem. The scarce observations available from the Bering Sea indicate that ice algal production may be as high as 30% of the phytoplankton production; during times of ice cover, ice algal biomass can be nearly as high as integrated pelagic algal biomass. The overarching hypothesis of this proposal is that sea ice algae are the major food source for pelagic and benthic herbivores in spring, specifically during periods of ice melt. In addressing this hypothesis, this proposal aims at providing information on the spatial and temporal patterns of abundance, biomass, community composition and productivity of sea ice algae and phytoplankton just below the ice in relation to the physical and chemical environment. Environmental measurements will include salinity, temperature, and nutrient concentrations in ice cores and under-ice water, as well as ice thickness, snow cover and light regime. Sedimenting material, stable isotope ratios (d13C, d15N) and algal community composition will be used as three lines of evidence to follow the fate of ice algal production through the pelagic and into the benthic food web of the Bering Sea. Field work conducted during different ice cover regimes will be augmented with experimental work on pelagic and benthic herbivores, producing the first-ever stable isotope turnover rate measurements for any Bering Sea invertebrates. The combined data set will allow for a refined interpretation of the relevance of the sea ice produced organic matter for the food web structure in the Bering Sea.
This project is part of a larger program designed to develop understanding of the integrated ecosystem of the eastern Bering Sea shelf, a highly productive region of US coastal waters. This ecosystem is home to a major portion of the commercial fisheries of the US and also provides significant resources to subsistence hunters and fisherman of Alaska. Understanding role of sea ice algae in this system is essential to being able to predict how and why the system may respond to changes in sea ice conditions, such as have been observed in recent years.
About 35 million km2 of the surface of the oceans are seasonally or permanently covered with a thin crust of frozen sea water called sea ice. Research in various parts of the Arctic and Antarctica over the last 100 years has shown that sea ice harbors a unique assemblage of small animals and plants called sympagic biota. The total abundances within the ice can be very high exceeding for example over 100000 little worms in Arctic sea ice m-2 of sea ice. The biota growing within the ice contribute to the total biological activity, harbor partially endemic flora and fauna, and provide food for organisms living at the sea floor or in the water column, specifically when the sea ice melts. In many Arctic and sub-Arctic areas sea ice primary production can contribute 5% to 50% of the overall yearly primary production. Although sea ice occurs every year in the Bering Sea, its biological properties were poorly studied. Given the lack of information, our research therefore focused on some very basic biological questions: - what kind of organisms live within the Bering Sea ice? - how active are they, and in which abundances do they occur? - what happens when the ice melts and the biota is released into the ocean, will it sink to the bottom or start to grow in the water (a process we call seeding). In scientific terms, the overarching hypothesis of this project was that sea ice algae are a major food source for pelagic and benthic herbivores in spring, specifically during periods of ice melt. In addressing this hypothesis, this project aimed at providing information on the spatial and temporal patterns of abundance, biomass, community composition and productivity of sea ice algae and phytoplankton just below the ice in relation to the physical and chemical environment. In order to address the questions, we participated in field expeditions in 2008 to 2010 and conducted experimental work on benthic herbivores, producing the first-ever stable isotope turnover rate measurements for any Bering Sea invertebrates. The combined data set allows for a refined interpretation of the relevance of the sea ice produced organic matter for the food web structure in the Bering Sea. Here a short summary of our major results: An astonishing diverse and high abundance community occurred within the ice. We estimated that about 80 different species of algae grow within the ice, about double the number of species compared to those found in the water column at the same time. Abundances are among the highest ever reported from Arctic sea ice with over 10 000 000 algal cells in one liter of melted sea ice. We also estimated that the sea ice algae contribute about 5 to 10% to the total annual plant growth production of the Bering Sea marine environment for areas where ice cover occurs. We found that most of this biota is released from the ice over a short time span as soon as the ice starts to melt in late spring – our data indicate that some species will sink to the sea floor, while others will indeed seed the water column and contribute to the spring phytoplankton bloom. Our work looking at food web markers demonstrated that important herbivores living in the water column like euphausiids and copepods (different kind of crustaceans) do feed on the organic matter coming from the ice, which does support observations by other colleagues. We also learned that many biological processes in the Bering Sea later winter-early spring are so slow that they are hard to measure (like stable isotope turn over experiments), while others were surprisingly fast and active. One important side aspect of our study was the success of our students. Two female graduate students have successfully completed their theses, one female student is close to finish, and the material collected stimulated the research for a new male PhD graduate student. The scientific results were published in peer-reviewed journals, and we developed an educational web site for teachers that can be used in classroom environments with lesson plans and additional material. All in all, this project did deliver a benchmark evaluation of the status of the Bering Sea ice biota in the years 2008 to 2010. It was the first ever status report for this region and it will be important as one of the many references needed to assess the impacts of climate change on the Bering Sea ecosystem. The data were also important as context information for colleagues working on other parts of the Bering Sea marine food web. In addition they will be very important contributions to look at the total functioning of the Arctic Ocean, comparing the different seas and look at their connections.
