Composition and Distribution of Macrobenthic Invertebrate Fauna 



77 



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10 IS 2 3.0 



PERCENT ORGANIC CARBON 



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Figure 38 

 Densitv and biomass of Hydrozoa in relation to sediment organic carbon. 



Alcyonarians were relatively more abundant in both 

 the narrow (less than 4°C) temperature range class and 

 where temperatures were moderately broad (12° to 

 15.9°C) than in areas of intermediate range. The densi- 

 ties averaged between 1.1 and 1.7/m in the narrow 

 and relatively broad range classes and between 0.2 and 

 1.2/m in the intermediate range classes. Biomass aver- 

 aged 0.31 to 0.42 g/m 2 in the narrow and relatively 

 broad range classes and only 0.11 g/m 2 or less in the 

 intermediate classes. 



Frequency of occurrence of alcyonarians in samples 

 ranged from 1 1 to 8% where the temperature was narrow 

 and relatively broad, and only 2 to 5% in areas where the 

 temperature range was intermediate (Table 25). 



Relation to Sediment Organic Carbon 



Alcyonarians occurred only in sediments with low (from 

 0.01 to 1.5%) organic carbon content; they were absent 

 in areas with no measurable organic carbon, as well as 

 in areas with carbon contents exceeding 1.5% (Fig. 44). 



The 0.50-0.99% carbon content class contained the 

 highest average density (Tables 26, 27) as well as highest 

 average biomass (Tables 28, 29). The only other carbon 

 content classes in which alcyonarians occurred, 0.01-0.49% 

 and 1.00-1.49%, had reduced measures of abundance. 



Frequency of occurrence in samples showed a trend 

 similar to density and biomass (Table 30), highest in 

 the 0.50-0.99% carbon content class and significantly 

 lower in the two adjacent classes. 



Zoantharia — Four morphologically diverse orders of 

 Zoantharia were represented in our samples from the 

 New England region: 1) Actiniaria — sea anemones; 2) 

 Ceriantharia — burrowing anemones; 3) Madreporaria — 

 stony corals; and 4) Zoanthidea — colonial anemones. 

 Altogether they contributed 1.5% of the number of 

 animals and 3.5% of the biomass in the total macrofauna 

 (Table 3). 



Our samples contained specimens ranging in size from 

 small (1 cm or slightly less) Edwardsia and other burrow- 

 ing anemones to large Cerianthw over 30 cm in length. 



