VASQUEZ, M. S.*; BURNAFORD, J. L.; University of Puget Sound; University of Puget Sound: The role of UV radiation in microhabitat selection by the seastar, Pisaster ochraceus

Ultraviolet radiation (UVR, 280-400nm) has been found to cause cellular damage in a wide variety of organisms from many phylogenetic groups. UVR can penetrate into surface waters, and examples of invertebrates that actively avoid UVR have been found in both freshwater and marine habitats. Because the organisms that inhabit the intertidal zone are emersed during low tides, they are potentially exposed to higher levels of UVR than subtidal species. In this study, we examined the role of UVR in low-tide microhabitat selection of the sea star Pisaster ochraceus, an important invertebrate predator in Pacific Northwest intertidal areas. In field surveys conducted on San Juan Island, Washington, during low tides from June-August, we found that Pisaster were located more frequently in shaded microhabitats than in sun-exposed areas. These shaded microhabitats had approximately 25% of the incident UVR in open microhabitats. We hypothesized that adult Pisaster select shaded areas such as algal canopies or rock crevices to avoid exposure to UVR during summertime midday low tides. To determine if Pisaster actively avoid UVR, we conducted experiments in outdoor aquaria exposed to ambient summertime light levels. We tested 110 Pisaster individuals in four-hour experimental trials (10am � 2pm). We used UV-filtering plastics to examine the effects of UVA, UVB, visible light, and full-spectrum (vis + UV) light on Pisaster movement. Adult Pisaster did not avoid UVR, but they did actively avoid visible light. We concluded that by avoiding visible light, adult Pisaster also functionally avoid the incident UVR levels of open microhabitats at low tide.