The world population of Spectacled Eiders winters in pack ice in the Bering Sea, diving 40 to 70 m to feed on bivalves. These eiders are listed as Threatened under the U.S Endangered Species Act, which requires delineation of critical habitat. By integrating studies of the dispersion of eiders and benthic prey, dive costs and intake rates of captive ducks, biomechanics of deep-diving birds, and remote sensing of sea ice patterns, we developed computer models of prey densities needed for profitable foraging. However, maps of prey densities and ice cover over 3 decades showed that both prey dispersion and access through ice varied greatly among years, so that much larger protected areas were needed to ensure adequate prey availability under all conditions. Projecting effects of climate change on the long-term trajectory of key habitats required better understanding of ecosystem processes that determine the abundance and dispersion of prey. In this talk I will review our efforts to link the ecology of a mobile top predator to processes throughout the food web, including factors governing bacterial production which fuels this deposit-feeding community.