Pacific walrus: Benthic bioturbator of Beringia

The dependency of walruses on sea ice as habitat, the extent of their feeding, their benthic bioturbation and consequent nutrient flux suggest that walruses play a major ecological role in Beringia. This suggestion is supported by several lines of evidence, accumulated during more than three decades of enquiry and leading to the hypothesis that positive feedbacks of walrus feeding strongly influence productivity and ecological function via benthic bioturbation and nutrient flux. Walruses annually consume an estimated 3 million metric tons of benthic biomass. Walrus prey species inhabit patches across the shelf according to sediment type and structure. Side-scan sonar and our calculations indicate that the area affected by walrus feeding is in the order of thousands of square kilometers per year. Annual to long-term walrus bioturbation results in significant, large-scale changes in sediment and biological-community structure, and magnifies nutrient flux from sediment pore water to the water column by about two orders of magnitude over wide areas. The combined effects of walrus feeding must be placed in the context of long-term, regional climate changes and responses. Should sea ice continue to move northward as a result of climate change, the walrus' ecological role could be diminished or lost, the benthic ecosystem could be fundamentally altered and native subsistence hunters would be deprived of important resources.