Composition and Distribution of Macrobenthic Invertebrate Fauna 



139 



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SAND 

 SILT 



SILT- 

 CLAY 



BOTTOM SEDIMENTS 



Figure 132 



Density and biomass of Cephalopoda in relation to bottom sediments. 



Relation to Sediment Organic Carbon 



Cephalopods occurred only where organic carbon con- 

 tent ranged between 0.01 and 0.99%. Highest density (2.1 

 individuals/m 2 ) and biomass (0.03 g/m 2 ) occurred in 

 sediments with between 0.5 and 0.99% organic carbon; 

 significantly lower quantities of both measures occurred 

 at levels between 0.01 and 0.49% (Tables 26, 28; Fig. 134). 

 Frequency of occurrence of cephalopods in the 

 samples was only 1% in each of the content classes into 

 which they were grouped (Table 30). 



Arthropoda 



Representatives of the phylum Arthropoda in the New 

 England region, members of the classes Arachnida, 

 Pycnogonida, and Crustacea, contribute significantly to 



both measures of abundance. Among the nine orders 

 of Crustacea inhabiting the region (see Table 4), 

 Amphipoda is the overall dominant taxon in terms of 

 density, contributing slightly over 43% of the total num- 

 ber of specimens; this is the same as their ranking in the 

 Middle Atlantic Bight (Wigley and Theroux, 1981). 

 The classes Arachnida and Pycnogonida and the nine 

 orders of class Crustacea will be discussed separately 

 below. In keeping with the phylogenetic order of treat- 

 ment, the figures relating to Arthropoda (Figs. 135- 

 139) are presented here, but the detailed discussion of 

 the phylum, represented almost wholly by the class 

 Crustacea, will be presented in the section "Dominant 

 Components of the Macrobenthos" below. 



Pycnogonida — The class Pycnogonida, a relatively small 

 group of marine arthropods containing about 600 



