Assemblage Structure in Shoal and Flat-Bottom Habitats on the Inner Continental Shelf of the Middle Atlantic Bight, USA

Sand shoals provide both a potentially unique habitat resource for marine organisms and a source of sand for the replenishment of eroded beaches. Sand removal may negatively influence marine communities, so understanding how marine fauna utilize habitats at and around shoals would provide much-needed guidance in selecting sites for sand harvest. A 2-year study was conducted on the inner continental shelf of the Middle Atlantic Bight, U.S.A., to compare finfish and invertebrate assemblages at sand shoal and nearby flat-bottom habitats. Multiple sampling modalities were used to sample organisms across a range of sizes, living habits, and life history stages. There was a trend toward greater abundance, species richness, and species diversity in flat-bottom habitats than in shoal habitats, and all of these community measures were generally lower during winter than in spring, summer, or fall. Moreover, species groups, including pelagic finfish, pelagic invertebrates, benthic finfish, and benthic invertebrates, were all more abundant in the flat-bottom habitats. Particular species characterized each type of habitat and these associations varied with season. Sampling with a large commercial trawl indicated that shoal finfish assemblages were characterized by striped bass Morone saxatilis and little skate Leucoraja erinacea in the fall, by scup Stenostomus chrysops in the spring, and by American sand lance Ammodytes americanus, scup, and clearnose skate Raja eglanteria in the summer. Experimental trawl sampling, which targeted primarily smaller organisms, found that communities on shoals were characterized by gastropods in the winter, squid (class Cephalopoda), and right-handed hermit crabs (family Paguridae) in the spring, and right-handed hermit crabs and scup in the summer. Winter was the period of lowest finfish and invertebrate use of shoal habitat and thus would be the best time of year for dredging sand to minimize acute impacts.