SHOWALTER, Ann M*; BURNAFORD, Jennifer L; University of Puget Sound; University of Puget Sound: Habitat selection and predation pressure of the seastar Leptasterias hexactis

In complex communities, predation from top trophic levels can determine the distribution patters of lower-level organisms. Microhabitat selection by predators could affect prey distribution in a patchy manner, if predation is restricted to some microhabitats. The seastar Leptasterias hexactis is a common intertidal predator in the Pacific Northwest, but the effect of this seastar on the distribution of its prey items is not well known. The perennial kelp Hedophyllum sessile provides physiological refugia during low tide for marine invertebrates including Leptasterias, which could increase contact between the seastar and its prey. We examined diet and microhabitat selection of Leptasterias at three sites on San Juan Island, Washington. These sites differed in the availability of microhabitats and in the relative abundance of invertebrate prey species. In field studies, we compared predator diets with prey availability in different microhabitats to examine whether seastar diet varied between microhabitats and between sites. We also used laboratory experiments with common prey species to determine whether predator diet composition in the field was determined by predator choice or availability of prey items. Through field experiments we determined that Leptasterias predation is more intense under the Hedophyllum canopy than in nearby non-canopy areas. Our results suggest that Leptasterias diet composition is determined both by predator prey selection and microhabitat availability, and that the seastar�s effect on its prey varies on small spatial scales.