THE FOOD OF WALRUS AND DUCKS: BIVALVE ECOLOGY DURING RECENT SEA ICE SHIFTS IN THE N BERING AND CHUKCHI SEAS

The Alaskan Arctic ecosystem supports large populations of marine mammals and birds that depend on sea ice for rest and mating and on the densely productive seafloor communities for food. Bivalve communities of the Bering and Chukchi Seas are the main food source for both spectacled eider ducks (Somatera fuscgeri) and walrus (Odobenus rosmarus). The Arctic bivalve community and their predators have been monitored consistently since the 1970s and have been responding to the decreasing persistence of seasonal sea-ice in the Bering and Chukchi Seas. However, the effects of human induced climate change started before monitoring began. I have reconstructed a 150-year history of benthic community change in the N Bering and Chukchi Seas using historic museum collections to understand the relationship between seasonal sea ice and the seafloor ecosystem and what large ecologic shifts might mean for higher-trophic level animals. Semi-quantitative periodic benthic surveys began in 1865 and are archived in museums, libraries, and online databases. The past geographic distributions of these bivalves can now can be compared to the “ecologic baseline” of the 1970s. From 1865 to 1900, taxa that are most dominant today in Subarctic and Arctic waters were concentrated in the Chukchi Sea, with very few occurrences south of the Bering Strait. This northern offset includes Nuculanidae, the favorite food of spectacled eider ducks. The food of walrus (Myidae, Cardiidae) are found throughout the region until 1960, after which these bivalves are only found as far south as the Bering Strait. Historic observations on bivalve family distributions thus indicate that the 1970s-based ecologic baseline is the result of a benthic community reorganization in the 1960s, which coincided with a sudden increase in the variability of sea ice concentration across the region and the onset of sea ice retreat related to secular warming and climate change. Spectacled Eiders and Walrus in this region are thus losing sea ice habitat at the same time as their bivalve prey community reorganized at the sea floor. These historic observations will help highlight how these coupled biologic and physical changes affect the populations of benthivores in the Arctic and how they might react to future changes.