Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


The macrobenthic invertebrates of the North Carolina continental shelf in the vicinity of Cape Hatteras were sampled during four seasonal cruises, June 1977 to January 1978. Macrobenthos-sediment relationships were investigated in the area surrounding Diamond Shoals. Four benthic assemblages were recognized, each representative of specific sediment regimes. The results of multivariate analyses were interpreted as indicating that the percentages of very fine sand and silt and clay were of greatest biological significance. It is suggested that the importance of finer particles is due to their influence on sediment permeability and organic content. The degree of particle sorting was also important in accounting for some faunal differences with fossorial species predominating in the most well-sorted sediments. Thermal factors were found to be the dominating factor in species distributions on the shelf north of Cape Hatteras, an area occupied by a sharp thermal front between Gulf Stream and Virginia Shelf Water. The benthic community exposed to the greatest thermal variability within the front was more speciose than the benthos of more thermally stable areas, but otherwise demonstrated no unique characteristics. For several species the front represented a zoogeographic barrier. at mid-shelf depths the Cape Hatteras region was far more effective in limiting the northward distribution of southern species than in limiting the southward distribution of northern species. Biogeographic affinities, extent of geographic range, and ability to traverse the Cape Hatteras area were compared among the four most speciose groups, the Polychaeta, Amphipoda, Bivalvia and Gastropoda. The polychaetes and amphipods exhibited the broadest geographic distributions while the molluscs, particularly the gastropods, were the most narrowly distributed. These differences are related to the dispersal capabilities and comparative degree of eurytopy among the four macrofaunal groups considered. The present-day distributions and biogeographic affinities of the North Carolina macrofauna are also a function of the geologic history of the northwestern Atlantic and the evolutionary origin of the fauna.



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