1. Mesozooplankton-microbial food web interactions in a climatically changing sea ice environment Evelyn & Barry Sherr, Oregon State University Carin Ashjian, Woods Hole Oceanographic Institution Robert Campbell, University of Rhode Island Role of sea ice algae versus phytoplankton as a food resource for grazers

2. Major objective: Field study of impact of changing sea ice conditions on planktonic food web structure, focusing on microzooplankton and mesozooplankton trophic linkages and the fate of phytoplankton blooms in the Bering Sea during spring Specific goals: at process stations analysis of - Biomass, composition, and size structure of initial phytoplankton, microzooplankton and mesozooplankton Phytoplankton and microzooplankton growth rates and mesozooplankton reproduction rates Grazing rates and prey preferences of heterotrophic protists and dominant species of mesozooplankton, ice algae as potential food resource Thin layers of plankton/particles in association with hydrographic features

3. Specific Hypotheses: H-a. Grazing impact of the microzooplankton on phytoplankton growth rate will be positively related to microzooplankton standing stock biomass and to proportion of phytoplankton biomass < 20 μm in size. H-b. Grazing impacts of the mesozooplankton on phytoplankton wo;; vary according to the species/size composition and abundance of grazers and phytoplankton present. H-c. Mesozooplankton grazing on microzooplankton will exert significant top-down control on microzooplankton stocks, limiting potential for microzooplankton grazing on phytoplankton. H-d. Mesozooplankton community reproductive success (animal physiological state/condition and egg production rate) will be positively related to stocks of available phytoplankton and microzooplankton (type, size) and to water temperature. Both of these variables may change with the changing sea ice environment.