The Role of Non-Consumptive Effects in Structuring West Coast Rocky Intertidal Communities

Recent research suggests that the non-consumptive effects of predators (effects a predator has on other organisms due to its simple presence) may be as important as consumptive effects (consumption), but few studies have examined the impact of non-consumptive effects on west coast rocky intertidal communities. In our research, we examined the non-consumptive effects of sea stars (Pisaster ochraceus), a keystone predator in intertidal communities, on the behavior, morphology (growth and shape), and feeding patterns of whelks (or sea snails, Nucella emarginata), a secondary predator in the communities. Both of these predators preferentially consume competitively-dominant mussels (Mytilus sp.), meaning changes in consumption may have an impact and result in community-level consequences. Snail growth, shape, behavior, and feeding patterns (consumption rate and size preference) were measured and analyzed in both the presence and absence of two densities of sea stars. We attempted to mimic natural communities by supplying whelks with mussels of various sizes that had formed clumps similar to natural variation in communities. We hypothesized that in the presence of sea stars, sea snails would grow less, choose smaller prey, and display more avoidance behaviors.