The Trophic Role of Euphausiids in the Eastern Bering Sea: Ecosystem Responses to Changing Sea-ice Conditions

The principal investigators' primary hypothesis is that seasonal and interannual variation in the timing and coverage of sea-ice and associated food resources will lead to differences in age structure, diet history and nutritional condition for euphausids, which ultimately translate into differences in production rates and availability as prey to higher trophic levels. Funds are provided to quantify the age structure and diet history of important euphausids together with detailed information on their consumption and growth and to link field collections and analysis with laboratory rearing for age calibrations and shipboard feeding experiments to test the validation and retention of trophic lipid markers as well as the quality and quantity of food resources.

The investigators' objectives include:

1. To determine the potential impact of climate driven changes in sea-ice conditions on lipid content and lipid classes in major euphausid species and thus nutritional condition and reproductive potential over seasonal and interannual time scales.

2. To understand the feeding history, feeding rates and grazing strategies of euphausids under changing spatial (i.e. ice-covered, ice-edge, and open water zones) and temporal (i.e. seasonal and interannual) prey fields. Multiple approaches (i.e. feeding experiments, gut content analysis) will be used for validation and determination of retention of specific lipid dietary markers.

3. To apply recent advances in biochemical approaches to determine the age structure in field populations of euphausids and the potential effects of climate change on maintenance or disruption of cohort populations seasonally and interannually. Laboratory rearing conducted in parallel by Alaskan colleagues will allow calibrating precise ages in cohorts.

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. Euphausids are believed to be a critical link in the food web connecting plankton to fish resources in the region. Understanding the ecology of these organisms is critical to understanding how the commercial and subsistence fisheries may respond to a changing environment.