depth (Wigley and Theroux 1981). Total biomass was domi- 

 nated by molluscs (pelecypods and gastropods) and echino- 

 derms (echinoids and ophiuroids), and density pattern was 

 dominated by amphipods, polychaetes, small bivalves, and 

 ophiuroids. According to Parsons et al. (1977), a number of 

 studies have demonstrated decreased macrofaunal numbers 

 and biomass with increased water depth. Abrupt faunal dis- 

 continuities tended to occur at 100-300 m. These changes gen- 

 erally corresponded to the vertical distribution of other envi- 

 ronmental factors, such as organic carbon, nitrogen, and total 

 particulates which decrease rapidly with increasing depth. 

 Depth-related decreases in macrobenthos are more closely 

 linked to suspended living biomass than to total particulate 

 matter (Parsons et al. 1977). 



Parsons et al. (1977) cited examples of higher mean biomass 

 in regions of higher phytoplankton production. This relation- 

 ship suggests that benthic biomass in inshore coastal areas may- 

 be strongly influenced by sedimentation of organic matter pro- 

 duced during a bloom. This process undoubtedly contributes 

 to macrobenthos at shallow depths of continental shelves. The 

 shallow depths of Georges Bank and Nantucket Shoals fit 

 these conditions. 



Data from other studies on benthic biomass with depth are 

 presented in Table 1. Mean biomass was generally highest in 

 the 50-99 m stratum. Moreover, mean biomass was higher off 

 New England than the New York Bight. Off the Scotian Shelf, 

 wet weight biomass was 24 g/m 2 at 0-90 m depth and 22. 1 g/m 2 

 at 90-180 m (Mills 1980). The inverse relationship between ben- 

 thic biomass and depth is probably more related to the geo- 

 graphic position of zones of primary productivity and sedi- 

 mentation on shelves rather than to absolute values of depth 

 per se. This relationship has been recognized for some time 

 (Rowe 1971; Sokolova 1972). 



Another aspect related to depth involves substratum stabili- 

 ty. Sediments in shallow coastal waters and the inner shelf are 

 subject to vigorous current action. Wave base to 80-85 m 

 depth is not uncommon during the winter on Georges Bank 

 (Aaron et al. 1980). Accordingly during times of high energy 

 flow, sediment stability decreases, impeding colonization by 

 many infaunal organisms. Specialized species such as haus- 

 toriid amphipods and rapidly burrowing bivalves commonly 

 dominate these sites. Nantucket Shoals represents an area of 

 high seasonal sediment instability. 



Temperature. — Although there were some quantitative rela- 

 tionships between biomass and density of various taxa and 

 bottom temperature, the presence of a cold-water cell bounded 

 by warmer watet on the north and south made it difficult to in- 



terpret distribution according to temperature (Fig. 3). In this 

 case, there was a shallow-water (0-50 m) and deep-water (80- 

 100 m) zone both containing water ranging from 7° to 12°C. 

 Although the maximum biomass of certain taxa (Ophiuroidea) 

 was associated with shallow water and deep water (Maurer and 

 Wigley footnote 6), their maximum biomass was similar ac- 

 cording to temperature (11.0 C -12.9°C). The Coelenterata, 

 another deep-water taxon, had its highest biomass in 

 11.0°-11.9 C C (Maurer and Wigley footnote 6), temperatures 

 normally associated with depths of about 40 m for this time of 

 year. Thus it is important to bear in mind the relative position 

 of the cold-water cell in relation to depth when comparing dis- 

 tribution according to temperature. 



Off Atlantic City, N.J., Boesch et al." concluded that tem- 

 perature was the principal hydrographic factor affecting 

 macrobenthic distribution. Temperatures were more variable 

 on the inner and central shelf and more constant on the outer 

 shelf. Differences in temperature regime were probably the 

 prime cause of the sharper faunal change at the outer shelf/ 

 shelf-break transition. 



Sediment End related environmental variables. — Off 



Martha's Vineyard, the pattern of biomass and number of in- 

 dividuals were relatively even throughout a range of median 

 sediment size and percent silt-clay (Fig. 6). For Georges Bank, 

 density of infauna increased significantly with percent gravel 

 (Maurer and Leathern footnote 14). In addition, there were 

 some significant relationships between the density of several 

 dominant polychaete species and sediment parameters (percent 

 silt-clay, percent silt, percent carbon, percent nitrogen, micro- 

 bial biomass, and bacterial biomass) (Maurer and Leathern 

 footnote 14). 



Off Martha's Vineyard, polychaetes were ubiquitous in re- 

 gard to sediment type and were major contributors to both 

 average density and biomass of all benthic organisms in each 

 sediment type (Maurer and Wigley footnote 6). This apparent 

 lack of correlation with a sediment type may partly be due to 

 differences in sieve size, wherein some of the smaller taxa 

 known to occur abundantly on the shelf were probably missed 

 with a 1.0 mm mesh net. In a related study off southern New 

 England, greatest amounts of polychaetes were found in shell 

 and sand-gravel (750 and 555/m 2 , respectively), somewhat lesser 

 amounts in sand, silty sand, gravel, and silt (433, 331, 289, and 

 1 18/m 2 ), and lowest (23 and 9/m 2 ) in sand-shell and clay (Wig- 



"Boesch, D., J. N. Kraeuter, and D. K. Serafy. 1977. Benthic ecological studies: 

 Megabenthos and macrobenthos. In Middle Atlantic Outer Continental Shelf En- 

 vironmental Studies, Chap. 6, 1 1 1 p. Draft Rep. to Bureau of Land Management. 



Table 1. — Comparison of wet-weight biomass (g/m 1 ) of macrobenthos (Annelida, Mol- 

 lusca, Crustacea, Echinodermata) in relation to hath> metric stratum at locations off the 

 U.S. northeastern Atlantic coast. 







Southern 



Martha's Vineyard/ 



New York Bight' 



Depth 



Georges Bank 1 



New England 2 



Nantucket Shoals 



'(1.0 mm 



(0.5 mm 



(m) 



(0.5 mm sieve) 



(1.0 mm sieve) 



(1.0 mm sieve) 



sieve) 



sieve) 



25^*9 



140.6 



308.6 



230.4 



121.0 



78.0 



50-99 



460.0 



230.1 



314.3 



156.4 



96.6 



100-199 



24.2 



60.4 



75.6 



27.2 



33.2 



'Maurer, see text footnote 16. 



! Wigley and Theroux, see text footnote 8. 



'Boesch et al., see text footnote 17. 



10 



