MEPS 368:177-187 (2008)  -  DOI: https://doi.org/10.3354/meps07598

ABSTRACT: In order to avoid intense abiotic stresses at low tide, motile animals in the intertidal zone must identify and move into ‘safe’ microhabitats before the tide drops. We experimentally investigated the role of solar radiation in the microhabitat selection of the sea star Pisaster ochraceus, an ecologically important predator in the Pacific Northwest. Specifically, we tested the response of P. ochraceus to UVB radiation (290 to 315 nm), UVA radiation (315 to 400 nm), and photosynthetically active radiation (PAR; 400 to 700 nm) to determine whether specific wavelength ranges prompted specific responses. Sea stars were exposed to ambient summer light levels in shallow water in outdoor aquaria in which one-half of the tank was covered with a light-filtering material. We established 4 light filtration treatments: filter control (+UVB +UVA +PAR), no UVB (–UVB +UVA +PAR), no UVR (–UVB –UVA +PAR), and shade (–UVB –UVA –PAR), plus a no-filter control treatment (+UVB +UVA +PAR). P. ochraceus did not avoid UVB or UVA, but they did avoid PAR: individuals in tanks with shaded areas spent significantly more time under the filters than did individuals in the tanks with filters that blocked UV radiation. In field surveys, 85% of emersed P. ochraceus encountered during low tide were located in areas completely shaded from both PAR and UV radiation (by rocks or by the intertidal kelp Hedophyllum sessile). This study demonstrates that the presence of PAR in shallow water conditions prompts P. ochraceus to seek out shaded microhabitats that have more benign low-tide abiotic conditions than exposed rock benches.

KEY WORDS: Habitat selection · Pisaster ochraceus · PAR · UV radiation