BENTHIC COMMUNITY STRUCTURE ON THE US SOUTH-ATLANTIC SLOPE OFF THE CAROLINAS - SPATIAL HETEROGENEITY IN A CURRENT-DOMINATED SYSTEM

Faunal communities of the continental slope and rise seaward of North and South Carolina (U.S.A.) are strongly influenced by the Gulf Stream , the Western Boundary Undercurrent, and an increasingly steep declina tion of the slope toward Cape Hatteras. Sixteen stations in depths of 600-3500 m were sampled to characterize the sediment and benthic macro fauna. Box cores were taken along four transects: Cape Hatteras, Cape Lookout, Cape Fear and Charleston. On the Cape Hatteras transect infau nal densities at the 600-m station were as high as those typical of sh allower waters, and the dominant organisms were species that are more characteristic of continental shelf depths. There is high, nearly cont inuous sedimentation of terrigenous fine sandy sediments that are funn eled over the Cape Hatteras slope by southerly-flowing, long-shelf cur rents. We postulate that organic material is transported rapidly over the site and that the high depositional rates are enhanced by scavengi ng activities of filter-feeding organisms. Large, deep-burrowing depos it feeders serve to carry organic material deep into the sediments. Th e shallow stations on the Charleston transect were dominated by sand w aves generated by the Gulf Stream, while deeper stations were enriched by macroalgae transported downslope. Transects off Cape Lookout and C ape Fear were more typical of those found elsewhere in the western Nor th Atlantic. Macrofaunal analysis yielded 1202 species, 520 of which w ere new to science. Annelids were the dominant taxa in terms of densit y and numbers of species. A partial zoogeographic barrier was identifi ed between Cape Lookout and Cape Fear. Species diversity was high at m ost stations, with the highest at an 800-m site off Charleston where 4 36 species were taken from nine box cores (0.81 m(2)). Diversity data from off the Carolinas support previously stated views that the deep s ea is a resource of high species richness and biodiversity. Densities of macrofauna from all depths were generally higher than in previously published accounts. The faunal assemblage at each station was consist ent over 2 years in that samples from one station were always more sim ilar to one another than to any other station. Stations grouped into u pper slope, middle slope, lower slope and continental rise assemblages ; the upper slope stations were the most variable, both in density and community composition. Transect differences in types of sediment and macrofaunal communities along and across isobaths, indicated considera ble regional heterogeneity.