Composition and Distribution of Macrobenthic Invertebrate Fauna 179 



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 PERCENT ORGANIC CARBON 



Figure 189 

 Density and biomass of Decapoda in relation to sediment organic carbon. 



Geographic distribution 



Bryozoans were distributed in somewhat scattered tracts 

 in nearly all sections of the study area (Fig. 190). They 

 occurred most commonly in coastal areas and on off- 

 shore banks. Specimens were noticeably scarce in the 

 central part of the Gulf of Maine, over large portions of 

 the eastern Nova Scotian Shelf, from offshore parts of 

 the Southern New England Shelf, and on the continen- 

 tal slope and rise. Dense assemblages of over one 

 hundred colonies per square meter were present in 

 small areas dispersed throughout the banks and coastal 

 areas. 



In the six standard geographic areas, bryozoans were 

 most prevalent, on the average, on Georges Bank (28 

 colonies/m 2 ) and on the Southern New England Shelf 

 (22 colonies/m 2 ) (Table 6; Fig. 191). They were mod- 

 erately common in the Nova Scotia and Gulf of Maine 

 areas and scarce or absent in the two slope areas. 



The largest average biomass, 6.3 g/m 2 , occurred in 

 the Nova Scotia area (Table 8; Fig. 191). Georges Bank 

 ranked second with 2.6 g/m 2 , and all other areas con- 

 tained less than 1 g/m 2 . 



Incidence of occurrence in the four continental shelf 

 areas generally diminished from a high of 19% in the 

 northeast to a low of 1 1 % in the southwest. Their occur- 

 rence was even lower. 6 and 0%, in the two slope areas 

 (Table 10). 



Bathymetric Distribution 



Bryozoans were taken at water depths ranging from 8 to 

 3,820 m. There was a very pronounced decrease in the 

 density as water depth increased (Table 11; Fig. 192). 

 The average number of colonies in the shallowest (0- 

 24 m) depth zone was 39/m 2 and decreased steadily to 

 an average of 4.3/m 2 on the upper continental slope at 

 a depth of 500 m. Below 500 m they were absent or 

 present in very low (0.5 colony/m 2 ) quantities. 



The average biomass of bryozoans was higher in shal- 

 low water than in deep water. This relationship 

 was similar to that described above for density, except 

 for an unusually large average biomass of 2.9 g/m 2 

 at depths between 50 and 99 m. This was the largest 

 average biomass from any one depth class (Table 13; 

 Fig. 192). 



