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Abstract

Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverThe sea star Pisaster ochraceus is a dominant intertidal predator in the northeast Pacific Ocean, and holds the distinction of being the original "keystone" species* used in framing the concept that the stability of a biological community can be disproportionately influenced by a single species-usually a predator. P. ochraceus feeds on a variety of sessile invertebrates, and controls local diversity by preying preferentially on competitively dominant mussels. It is abundant on rocky intertidal shores from Alaska to the Baja Peninsula in Mexico.Over most of this range, several color morphs are present, including orange and a variety intergrading purples and browns. Although multiple color morphs are present at most sites throughout the range (the animals shown on the cover were photographed in Pacific Grove, California), P. ochraceus populations in the protected waters of northern Puget Sound (Washington) and the southern Strait of Georgia (British Columbia) are almost entirely bright purple. The underlying causes of the P. ochraceus color polymorphism, and the regional variation in the frequency of color morphs, remain a mystery.As reported by Harley et al. on page 248 of this issue, genetic structure in P. ochraceus from Alaska to southern California, including the inland waters of Washington and British Columbia, is very low. This suggests that variation in color frequencies is not a vestige of population isolation during the last ice age. Color frequencies are also unrelated to adult size and the frequency of injury. There are, however, suggestive relationships between color morph frequency and diet and local salinity. The authors propose that the polymorphism may well have an underlying genetic component, but that the regional-scale patterns in color are under ecological control.Credits: Photo, Chris Harley (University of British Columbia); cover layout, Beth Liles (Marine Biological Laboratory).*Paine, R. T. 1969. A note on trophic complexity and community stability. Am Nat. 103:91-93. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 211, Number 3December 2006 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv211n3cover Views: 173Total views on this site © 2006 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.