Sea Ice Algae, a Major Food Source for Herbivorous Plankton and Benthos in the Eastern Bering Sea

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.