Using a Diver-operated Suction Dredge to Evaluate the Effects of a Top- predator on Subtidal Soft-sediment Infaunal Bivalve Communities

In many unconsolidated substrate ecosystems, the majority of biomass available to top predators such as the sea otter (Enhydra lutris), exists as infaunal bivalves. While the effects of sea otter predation in hard-substrate systems are well documented, their effects in softsediment environments are less studied. Here we describe a method to sample subtidal clams in Glacier Bay, Alaska. The patchy nature of infaunal communities in soft-sediment systems makes them difficult to sample with traditional line transect methodology, where sampling may extend well beyond the edge of a clam bed, leading to induced error and exaggerated variance in the sample. In order to compensate for the spatially heterogeneous distribution of clam beds we used a suction-dredge method and developed a “spoked wagon-wheel” sampling design, where radiating transects begin at a focal point within the estimated center of a clam bed. We utilized the uneven spatiotemporal pattern of sea otter colonization within Glacier Bay to document changes to subtidal clam communities in areas with and without sea otters, both before and after colonization. This design provided a rigorous methodology to sample infaunal species that are of social, commercial, and ecological significance.