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Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverThe cover image shows a large Antarctic isopod (Glyptonotus antarcticus) crawling on an ice-encrusted sponge (Homaxinella balfourensis) in the shallow water adjacent to McMurdo Station in the Ross Sea, Antarctica. Sea ice typically forms at the ocean's surface, but given a source of exceptionally cold water, an unusual form of ice—anchor ice—can grow on benthic objects such as this sponge. For several decades, ecologists have considered anchor ice to be an important agent of disturbance in the shallow-water benthic communities in McMurdo Sound and potentially elsewhere in polar seas. The presence of anchor ice coincides with reduced abundance of sponges, which provide habitat for a diverse assemblage of benthic organisms. However, the mechanism of the presumed preferential disturbance of sponges by anchor ice has not been explored.At a typical salinity of 33 psu, it is thermodynamically favorable for seawater at its freezing point (–1.81 °C) to transition from its liquid phase to ice, its solid phase. However, just because it is thermodynamically favorable for seawater to freeze does not ensure that the transition from seawater to ice takes place spontaneously. Under circumstances that occur periodically in McMurdo Sound, water can be cooled below its freezing point (supercooled), priming it to solidify as anchor ice on the first organism it encounters.In this issue, Denny et al. (pages 155 to 163) report differences in how various species of Antarctic benthic organisms form and propagate anchor ice. The sponges H. balfourensis and Suberites caminatus are more likely than urchins and sea stars to form ice crystals, and the spread of the crystals occurs more quickly. These differences may explain the disturbance patterns observed in shallow polar benthic communities. Interspecific differences in ice formation raise questions about how surface tissue characteristics such as surface area, rugosity, and mucus coating affect ice formation on invertebrates.Credits: Cover photo: Stephen Wing, University of Otago, Department of Marine Science; cover design, Beth Liles, Marine Biological Laboratory. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 221, Number 2October 2011 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv221n2cover © 2011 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.