Composition and Distribution of Macrobenthic Invertebrate Fauna 



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GRAVEL TILL SHELL SAND SAND SILT- 



SILT CLAY 



BOTTOM SEDIMENTS 



Figure 72 

 Density and biomass of Annelida in relation to bottom sediments. 



(Tables 23, 24; Fig. 73). Conversely, quantities were smaller 

 (about 10 g/irr) where the temperature range was small. 

 Moderate biomasses were encountered in areas where the 

 temperature range was moderate. 



The frequency of occurrence of annelids among the 

 temperature-range classes was high and fairly uniform. 

 They occurred in 92 to 97% of the samples (Table 25). 



Relation to Sediment Organic Carbon 



Annelids of the New England region exhibited an es- 

 sentially bimodal relationship to the amount of organic 

 carbon in the sediments (Fig. 74). Greatest density 

 (504/m 2 ) occurred at low organic carbon levels (be- 

 tween 0.01 and 0.49%); another peak in density (407/ 

 irr) occurred at higher levels (between 2 and 3%); 



moderate densities prevailed at levels between these 

 two peaks, with smallest densities occurring in both 

 lowest and highest levels (0.00 and 5.00+%) of sedi- 

 ment organic carbon (Tables 26, 27). 



Annelid biomass was greatest (27 g/m 2 ) at organic 

 carbon levels between 1.5 and 2%) (Tables 28, 29; Fig. 

 74) and gradually diminished at levels both above and 

 below these values. As with density, lowest biomass was 

 found in both the lowest (0.00%) and highest (5.00+%) 

 organic carbon levels. 



Frequency of occurrence of annelids in the various 

 organic carbon content classes was uniformly high, rang- 

 ing from 80 to 100% in all classes except one, the 3-5% 

 class, in which only 50%i of the samples contained mem- 

 bers of this group (Table 30). 



