214 



NOAA Technical Report NMFS 140 



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BOTTOM SEDIMENTS 



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SILT CLAY 



Figure 240 

 Density and biomass of Ascidiacea in relation to bottom sediments. 



Relation to Sediment Organic Carbon 



A general trend of diminishing density and biomass 

 with increasing sediment organic carbon content was 

 exhibited by New England region ascidians (Tables 26, 

 28; Fig. 242) , and they were restricted to the low to mid- 

 range carbon content classes between 0.01 and 2.99%. 

 Mean density ranged from 21 to 4.4 individuals/m 2 , 

 and mean biomass from 4.4 to 0.2 g/m 2 . 



Frequency of occurrence in samples was low and 

 paralleled the trend of density and biomass, ranging from 

 23% to 8% as carbon content increased (Table 30). 



Dominant Components of the 

 Macrobenthos 



This section identifies and defines the dominant fauna! 

 constituents of the New England region macrobenthos 

 and their relationship to each of the abiotic parameters 

 considered in the treatment of each taxonomic group in 

 the preceding sections. "Dominance," as used in this re- 



port, refers to the taxonomic group that mathematically 

 contributed the highest number of individuals or greatest 

 total accumulated wet weight. Results are expressed in 

 both measures of abundance because of the marked dif- 

 ferences that existed between them. 



In spite of individual disparity in rank order within 

 each measure of abundance, members of four taxo- 

 nomic groups, collectively, made up the bulk of the 

 macrobenthic invertebrate fauna of the New England 

 region. The four major taxonomic components are 1) 

 Annelida; 2) Mollusca, comprising Bivalvia, the chief com- 

 ponent, as well as Gastropoda, Scaphopoda, Poly- 

 placophora, and Cephalopoda; 3) Crustacea, with 

 Amphipoda the chief component of this group, followed 

 by Cumacea, Isopoda. Decapoda, Cirripedia, Mysidacea, 

 Tanaidacea, Ostracoda, and Copepoda in progressively 

 smaller proportions; and 4) Echinodermata composed of 

 Ophiuroidea, Echinoidea, Holothuroidea, Asteroidea, and 

 Crinoidea in diminishing proportions. Table 3 lists the 

 contributions of each of the above taxa to the total density 

 and biomass of the New England macrobenthic fauna. 



