Composition and Distribution of Macrobenthic Invertebrate Fauna 



47 



NUMBER 

 MEAN PERCENTAGE 



ALL TAXA COMPOSITION 



1.513 



WEIGHT 

 BOTTOM PERCENTAGE MEAN 



TYPE COMPOSITION ALL TAXA 



610 



1,237 



2.244 



1.022 



718 



Gravel 



Till 



Shall 



Sand 



Sand-silt 



Silt-clay 



EXPLANATION 



181 



67 



223 



246 



170 



86 



□ 



CRUSTACEA 



ECMINODERMATA 



□ ° ,M " 



Figure 17 



Quantitative composition ot the total macrobenthic invertebrate fauna in 

 relation to bottom tvpe. Mean number of individuals and mean wet weight. 

 per square meter of bottom area, and percentage composition, bv density 

 and biomass, of the major taxonomic groups are shown. 



large part to occasional large animals. Those groups 

 that contributed large specimens at those depths were 

 Sipunculida, Echiura, Echinoidea, and Holothuroidea. 

 The percentage occurrence of each taxonomic group 

 in samples in each depth range class is presented in 

 Table 15. 



Relation to Bottom Sediments 



A marked disparity in the average density and biomass 

 of benthic invertebrates was found among the various 

 kinds of bottom sediments in the New England Region 



(Tables 16, 17; Fig. 17). Sand ranked far above the 

 other sediment types in density, with an average of 

 2,244 individuals/ irr. Three sediment types — gravel, 

 shell, and sand-silt — supported a moderate number of 

 animals; their average densities ranged from 1,022 to 

 1,513/m 2 . Lower densities (610 and 718/m 2 ) were found 

 in till and silt-clay sediments. 



Distribution of biomass (Tables 18, 19; Fig. 17) was 

 similar to that of density. Sand and shell supported 

 high (246 and 223 g/m L ') biomasses. Moderate quanti- 

 ties (170 and 181 g/m 2 ) occurred in gravel and sand- 

 silt. Relatively low quantities were encountered in silt- 

 clav and till sediments. 



