Using Stable Isotopes to Investigate the Dietary Ecology of the Sea Star Pisaster ochraceus

Laura Strong, University of Puget Sound


The sea star Pisaster ochraceus plays an important role in intertidal communities as a keystone species, however many aspects of its life history remain unknown. Pisaster exhibits three major color morphs, ranging from purple, to brown, to bright orange. Previous studies have found that Pisaster on the open coast of Washington tend to be 65%-90% brown and with 6%-28% orange individuals; in the more protected waters of Puget Sound, 90% are purple, some are brown, and few are orange (Harley et al. 2006). The sea stars also tend to be larger on average in Puget Sound than on the outer coast. Although patterns in the variation in size and color of Pisaster have been well documented, little is known about the underlying causes of these patterns. Stable isotope analysis has proven to be a useful technique in studying trophic interactions in marine ecosystems. I used stable isotope analysis to investigate the effects of diet on Pisaster color and size, which varies among geographic regions.