CARLSON, R.L.*; SHULMAN, M.J.; ELLIS, J.C.; Univ. of California, Davis; Cornell University; Brown University: Distribution patterns of the common periwinkle Littorina littorea (L.) in the southern Gulf of Maine

The common periwinkle Littorina littorea is a ubiquitous inhabitant of rocky shores in the North Atlantic. Although the snail exhibits a relatively consistent pattern of vertical distribution (ranging from the mid-intertidal to the shallow subtidal) throughout the North Atlantic, its horizontal distribution and abundance are highly variable. In this study, we investigated the snail�s distribution patterns in the intertidal and shallow subtidal on Appledore Island, ME. We asked whether wave exposure, surface complexity, predator (e.g. Carcinus maenas and Cancer borealis) density, or the percent of the substrate covered by bare rock, Ascophyllum nodosum, Chrondrus crispus, Polysiphonia spp., or ephemeral green algae (e.g. Ulva, Cladophora, and Enteromorpha) was correlated with L. littorea density in two regions of the intertidal at nine study sites. In the intertidal, surface complexity was positively correlated with L. littorea density, whereas the percent of the substrate covered by C. crispus and ephemeral green algae were negatively correlated with snail density. In the shallow subtidal, only one factor, C. maenas density, was positively correlated with L. littorea density. These results indicate that a combination of biotic and abiotic factors explains the distribution of the common periwinkle on Appledore Island.