Composition and Distribution of Macrobenthic Invertebrate Fauna 



181 



Incidence of occurrence was highest (50%) 

 in shell, moderately high in till and gravel, and 

 low (10% or less) in the fine-grain sediments 

 (Table 20). 



Relation to Watei Temperature 

 Although bryozoans were rather severely lim- 

 ited in distribution by specific substrate require- 

 ments, water temperature range appeared to 

 play a lesser role in inhibiting abundance. Mem- 

 bers of this phvlum occurred in all tempera- 

 ture range classes but revealed a pronounced 

 trend of increasing densitv with a broadening 

 of the temperature range (Table 21; Fig. 194). 

 The density of bryozoans averaged only 3 colo- 

 nies/m 2 where the temperature range was less 

 than 4°C. Their density increased to an average 

 of 66 colonies/m 2 where the temperature range 

 was greater than 20°C. 



Biomass values also exhibited a general up- 

 ward trend (0.28-2.45 g/m 2 ) as the tempera- 

 ture range broadened. This increase, however, 

 was less consistent than that exhibited by nu- 

 merical density (Table 23; Fig. 194). 



The occurrence of bryozoans in the samples 

 ranged from 8 to 21%. Generally, incidence of 

 occurrence was low where the temperature 

 range was narrow, and high where the tem- 

 perature range was broad (Table 25). 



Relation to Sediment Organic Carbon 

 The relationship of bryozoans to sediment or- 

 ganic carbon was not nearly as well defined as 

 that in other parameters because no orderly 

 trend or pattern was discernible. Relativelv high 

 average densities, between 21 and 35 individual 

 colonies/ m'-, occurred in widely separated or- 

 ganic carbon content classes in the low. middle, 

 and higher regions of the content spectrum 

 (Table 26; Fig. 195). Significantly lower aver- 

 age densities, ranging between and 8/ni'-', 

 occurred in adjacent carbon content classes, 

 effectively separating and isolating the higher 

 values. 



Average biomass was distributed in a manner 

 similar to that for density but was not as pro- 

 nounced. Highest bryozoan biomasses (1.95 and 

 1.21 g/m 2 ) occurred in the low and upper middle 

 carbon content range, interspersed with significantly 

 lower values (Table 28; Fig. 195). 



The percentage of samples containing bryozoans 

 ranged from to 25% (Table 30). Incidence of occur- 

 rence showed a general trend of decreasing (20 to 0%) 

 as organic carbon content increased from to 2.99%, 

 but it shot up to 25% in the 3.00-4.99%, class. 



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GEOGRAPHIC AREA 



Figure 191 



Density and biomass of Bryozoa in each of the six geographic areas. 



Brachiopoda 



Brachiopods, commonly known as lamp shells, are sessile 

 organisms normally found attached to rocks and other 

 firm substrata at continental shelf depths, usually in 

 cold water. These requirements limited the scope of 

 their distribution to the northeastern sectors where 

 suitable habitats were more prevalent than elsewhere in 



