Biomass and Density of Macrobenthic Invertebrates on 



the U.S. Continental Shelf off Martha's Vineyard, 

 Massachusetts, in Relation to Environmental Factors 1 



DON MAURER 2 and ROLAND L. WIGLEY 3 



ABSTRACT 



The mean density and mean biomass of macrobenthic invertebrates on the U.S. continental shelf off Martha's 

 Vineyard, Mass.. were 3,008/m ! and 245. 7 g/m\ respectively. The latter estimate was considerably higher than 

 values from the North Sea, Scotian Shelf, and Middle-Atlantic Bight. Molluscs (pelecypods and gastropods) and 

 echinoderms (echinoids and ophiuroids) greatly influenced patterns of total biomass distribution. The ocean 

 quahog, Arctica islandica, was the dominant species in terms of biomass. Total density was dominated by crusta- 

 ceans (amphipods), polychaetous annelids, molluscs (small pelecypods), and echinoderms (ophiuroids). 



Mean density of mollusca was positively associated with sediment size. Mean biomass and density of 

 Crustacea were negatively associated with depth, grain size, and bottom temperature, whereas the same param- 

 eters for the Echinodermata were positively associated with those environmental factors. 



Three fauna! assemblages emerged which were analagous to those described from earlier studies on Georges 

 Bank (sand fauna, silt-sand fauna, muddy-basin fauna). The fauna from the Mud Patch most closely resembled 

 the silty-sand fauna. 



INTRODUCTION 



Research on the northeastern U.S. continental shelf has ac- 

 celerated because of a wide variety of human activities ranging 

 from fishing and recreation to transportation, mineral 

 recovery, waste disposal, and oil and gas exploration 

 (Grosslein et al. 1979). These activities are not always com- 

 patible, and managers face important decisions attempting to 

 reconcile diverse uses of this valuable resource — the continen- 

 tal shelf. Before decisions can be made, the resource must be 

 assessed in a variety of ways. 



Any assessment of the shelf should involve benthic in- 

 vertebrates, an important component of the shelf ecosystem 

 (Mills and Fournier 1979). The benthos are important in their 

 own right and as a measure of the health of the ecosystem, and 

 play a critical role in trophic relationships providing a major 

 source of energy to economically and ecologically important 

 groundfish (Cohen et al. 4 ). In addition, the benthos play a sup- 

 porting role in nutrient exchange, providing a mechanism for 

 flux of nutrients initially trapped in sediments to the water col- 

 umn (Zeitzschel 1980). The purpose of this account is to report 

 on the distribution of biomass and density of macrobenthic in- 

 vertebrates off Martha's Vineyard. 



Georges Bank off southern New England has been the scene 

 of intensive fishing activity for over 300 yr (Wigley 1961). The 

 Georges Bank area is bounded on the southwest by Martha's 



Vineyard and Nantucket Island. Directly south of Martha's 

 Vineyard is an area about 80-100 m deep termed the Mud 

 Patch, consisting of fine-grain sediment. This sediment type is 

 relatively rare on the northeastern shelf which normally con- 

 sists of sand. The origin of the Mud Patch is uncertain, but it 

 may be an active site of deposition (Milliman et al. 5 )- If so, 

 then processes controlling deposition of fine-grain sediment 

 must be considered in assessing their effect on benthic biota. 

 Presumably, benthos living in the Mud Patch would be 

 exposed to relatively higher levels of particulate contaminants 

 (trace metals, hydrocarbons) than benthos living on the sur- 

 rounding, relatively dynamic, sand bottoms. Assuming this 

 relationship, bioaccumulation of contaminants by the benthos 

 might provide opportunity for biomagnification through food 

 webs. The trophic relationship between demersal fish and ben- 

 thos is well documented for Georges Bank (Wigley 1965). 



In the early 1960's benthic research was conducted on the 

 shelf south of Martha's Vineyard and Nantucket I. Some of 

 these data were reported (Wigley 1963; Wigley and Mclntyre 

 1964; Wigley and Stinton 1973), but the largest portion was 

 placed in a data file report pending further analysis and syn- 

 thesis (Maurer and Wigley 6 ). The report contains maps of 

 biomass and density distribution. With the advent of gas and 

 oil exploration, together with other diverse activities on 

 Georges Bank, documentation of the benthos in and around 

 the Mud Patch would seem to be of special interest to man- 



'Contribution No. 13 from the Southern California Ocean Studies Consortium. 



'Southern California Ocean Studies Consortium, California State University, 

 Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840. 



'35 Wilson Road, Woods Hole, MA 02543. 



'Cohen, E. B., M. D. Grosslein, M. P. Sissenwine, and F. Steimle. 1979. An 

 energy budget of Georges Bank. Workshop on Multispecies Approaches to Fish- 

 eries Management, St. John's, Newfoundland, 26-30 November 1979, p. 1-37. Na- 

 tional Marine Fisheries Service Woods Hole Lab., Woods Hole, Mass. 



'Milliman, J. D., M. H. Bothner, and C. M. Parmenter. 1980. Seston in New 

 England Shelf and Slope Waters, 1976-1977. In J. M. Aaron (editor). Environ- 

 mental geological studies in the Georges Bank area, United States northeastern 

 Atlantic Outer Continental Shelf, 1975-1977, p. 1-1 to 1-73. Final Report submit- 

 ted to the Bureau of Land Management. U.S.G.S., Woods Hole, Mass. 



'Maurer, D., and R. L. Wigley. 1981. Distribution of biomass and density of 

 macrobenthic invertebrates on the U.S. Continental Shelf off Martha's Vineyard. 

 Lab. Ref. Doc. 81-15 (unpubl.), 97 p. Northeast Fisheries Center, NMFS, NOAA, 

 Woods Hole, Mass. 



