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Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverThe sea star Pisaster ochraceus is a dominant rocky intertidal predator that lives along the west coast of North America. It plays a large role in determining local patterns of biodiversity via its interactions with mussels in the genus Mytilus. The cover image depicts juvenile P. ochraceus (the maroon, purple, and ochre sea stars) foraging among Mytilus trossulus (the bluish-black mussels) on a floating dock at the Hakai Beach Institute on Calvert Island, British Columbia. Several empty mussel shells are evidence of recent sea star predation events. The Pisaster-Mytilus interaction is famous for providing the inspiration for the “keystone predator” concept, and is now widely featured in textbooks.As a well-studied predator-prey pair, Pisaster and Mytilus make an ideal model system for addressing ecological and behavioral theory relating to the effects of body size. Body size of both predator and prey are key attributes of trophic interactions, as differences in body size can determine ease of prey capture, time required to handle and consume the prey, and number of prey required to meet energetic demands. On pages 192–200 of this issue, Gooding and Harley explore the ways in which variation in body size can affect the relationship between the predator P. ochraceus and its preferred prey in wave-protected waters, Mytilus trossulus.Gooding and Harley found that predation rates, expressed as mussels consumed per unit time, increased with increasing sea star size and decreased with increasing mussel size. Larger sea stars preferred to consume larger mussels. For juvenile sea stars, in which size relationships could be worked out in the greatest detail, prey-size preference corresponded with mussel size classes that allowed Pisaster to consume the most tissue in the least amount of time. Overall, the study found that even small changes in predator or prey body size could play a large role in predator energetics (tissue consumed per unit time) and prey population dynamics (individuals consumed per unit time). Because sea star and mussel growth rates and body size frequency distributions are affected by temperature and ocean acidification, changes in body size and the accompanying shifts in predation rates may be one important pathway through which global change alters community structure.Credits: Photo, Christopher D.G. Harley, University of British Columbia; cover design, Beth Liles, Marine Biological Laboratory. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 228, Number 3June 2015 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv228n3cover © 2015 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.