Meeting Abstract

11.3  Tuesday, Jan. 4  Predatory fishes’ impacts on benthic community structure in the San Juan Islands, WA TURNER, K.R.*; SEBENS, K.P.; Univ. of Washington; Univ. of Washington krturner@uw.edu

Predators can play important roles in structuring communities. In marine systems predators may act as keystone species or as the species responsible for triggering trophic cascades. In the temperate marine subtidal many of the interesting examples of community-wide impacts of predators involve predation on sea urchins. Where urchins are present in abundance, due to the absence of their predators, they are able to graze standing kelp biomass to very low levels. This can change the physical environment and reduce the structure and food sources available to other species. However, in the San Juan Islands, WA, urchin abundance does not appear to strongly influence kelp abundance, and urchin predators are naturally rare on rocky bottoms or have been locally extinct for at least a century. Therefore the region provides an opportunity to study temperate marine food webs and the effects of large predators on a benthic community that does not depend on strong urchin-kelp interactions. We are studying the effects of large carnivorous fishes (lingcod, Ophiodon elongatus, and rockfishes, Sebastes spp.) on the rocky subtidal communities of San Juan Channel. Predatory fish abundance is variable within San Juan Channel, which allows us to study community structure across a range of predator abundance. We use surveys of all trophic levels involved in this natural experiment combined with exclusion cages designed to restrict fish access from large swaths of the benthos to determine the community-wide impacts of predatory bottomfishes. We will discuss results from the first year of these surveys, and preliminary results from our fish exclusion experiment.