THE SEASONAL OCCURRENCE OF MYTfLUS EDULIS ON THE CAROLINA COAST AS A RESULT OF TRANSPORT AROUND CAPE HATTERAS 1 HARRY W. WELLS AND I. E. GRAY Department of Zoology, Duke University, Durham, North Carolina The edible mussel, Mytilus e dulls L., attaches to rocks, pilings, and other firm substrates, being particularly abundant in the lower intertidal zone, where it is a dominant organism in the community (Newcombe, 1935; Dexter, 1947). A temperate and boreal species, it is found on both American and European coasts of the North Atlantic as well as Asian and American coasts of the North Pacific Ocean. Its distribution has aroused the interest of ecologists as an example of the effects of temperature on determining the geographical limits of species. Hutchins (1947) has suggested that the southern limit of M. e dulls occurs where the mean sea surface temperature during the warmest month is approximately 80 F. (26.6 C). In the western Atlantic, M. e dulls reaches its southern limit in the Carolinas. Although Hutchins showed the 80 summer isotherm intersecting the coast in the vicinity of Cape Hatteras, the edible mussel has been reported as far south as Charleston, South Carolina, three hundred miles below Cape Hatteras. This apparent contradiction of Hutchins' temperature limitation of M. c dulls is discussed and related to the biology of the species. Its occurrence on the North Carolina coast is analyzed in relation to coastal water masses, their temperature and move-ment, and meteorological conditions. The authors wish to express their grateful appreciation to the Cape Hatteras National Seashore of the National Park Service for its aid and support; to Mrs. Mary Jane Wells, who drew the figures and assisted this research in many other ways ; and to Alex Marsh, Bruce Welch, Jack Taylor, and Steve Bishop for their assistance in collecting. OBSERVATIONS Mytilus edulis has been collected in the course of study of littoral organisms in the Beaufort and Cape Hatteras areas (Fig. 1). In the latter region, this study has centered on fauna attached to a group of eight wrecks near the outer beach. All but one wreck ordinarily extend above the water surface ; all are metal and provide a firm substrate for many sessile organisms. Mytilus edulis occurs all year long on wrecks north of Cape Hatteras (stations 1-6: Kitty Hawk, Overlook, Pea Island, Rodanthe, Waves, and Salvo), where it is the dominant organism in the lower part of the intertidal zone and extends into deeper water on subtidal surfaces. 1 This study was supported by a grant (G-S838) from the National Science Foundation. 550
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