216 



NOAA Technical Report NMFS 140 



Frequency of Occurrence 



Among the four dominant taxa, 

 Annelida was the most ubiquitous 

 in distribution, occurring in 96% of 

 all stations sampled (Table 5). Next 

 in order were members of Mollusca, 

 which occurred in 88% of all 

 samples, followed by Crustacea in 

 85% of the samples; echinoderms 

 ranked fourth with a 72% occur- 

 rence rate. 



For comparative purposes, some 

 nondominant taxa showed inter- 

 mediate frequencies; among these 

 were Coelenterata, which occurred 

 in 42% of the samples, and Nemer- 

 tea and Sipunculida with frequen- 

 cies of 34% and 23%, respectively. 

 Ascidiacea, Bryozoa, Aschelmin- 

 thes, Porifera, Brachiopoda, Pogo- 

 nophora, Turbellaria, and Hemi- 

 chordata were encountered with 

 diminishing frequencies ranging 

 from 17% to<l%. 



Percentage Composition 



The four dominant macrobenthic components collec- 

 tively contributed more than 90% of the total number 

 of individuals, and 90%) of the accumulated wet weight 

 of the macrobenthos sampled within the New England 

 region. The relative contribution and ranking of the 

 four, however, differed markedly between the two mea- 

 sures of abundance (Fig. 243). 



Crustacea, with Amphipoda providing the single larg- 

 est amount of individuals, was the highest ranking taxo- 

 nomic component in terms of density, accounting for 

 nearly one half (48%) of all individuals within the 

 region. Annelida ranked second, providing slightly more 

 than 28% of the total number of individuals encoun- 

 tered; Mollusca and Echinodermata followed, contrib- 

 uting somewhat more than 12% and 5% of the total 

 number of individuals, respectively. 



The biomass ranking was nearly the reverse of that 

 for density. Mollusca, with Bivalvia predominating, 

 ranked first in biomass versus third in density, contrib- 

 uting 46% of the total weight. Echinodermata ranked 

 second versus fourth; Annelida ranked third versus sec- 

 ond; and Crustacea, first in density, ranked fourth in 

 biomass. 



The differences in rank order between the two mea- 

 sures of abundance are attributable to size differences 

 within the various taxonomic groups. 



NUMBER 



WEIGHT 



Figure 243 



Percentage composition of the dominant components of the macrobenthic 

 invertebrate fauna expressed in terms of number of individuals and wet 

 weight of the total fauna. 



Geographic Distribution 



The geographic distribution of density and biomass of 

 each of the four dominant components of the 

 macrobenthos of the New England region is depicted 

 in Figures 69, 99, 146, and 202. Within the subareas of 

 the region, the rank order of the four dominant taxa 

 varied in terms of density and biomass (Figs. 13B, 14B; 

 Tables 6, 8). In the Nova Scotia subarea, Annelida 

 ranked first in density (648/m 2 ) but third in biomass 

 (19 g/m 2 ); Crustacea was second in density (329/m'-) 

 but fourth in biomass (17 g/m 2 ); Mollusca, third in 

 density (77/m 2 ), was first in biomass (54 g/m 2 ); while 

 Echinodermata fourth in density (24/m L ), was second 

 in terms of biomass (39 g/m 2 ). 



In the Gulf of Maine, mollusks (306/m 2 ) replaced 

 annelids (29/m 2 ) as the dominant taxon in terms of 

 density, the latter occupying second place, whereas 

 mollusks were second (32 g/m 2 ) and annelids third 

 (16g/m 2 ), in biomass. Crustaceans (150/m 2 ) and echi- 

 noderms (43/m 2 ) ranked third and fourth, respectively, 

 in density but were fourth (2 g/m 2 ) and first (56 g/m 2 ), 

 respectively, in biomass. 



On Georges Bank, the crustaceans (1052/m )were 

 nearly twice as "abundant as the annelids (546/m 2 ), 

 almost nine times denser than echinoderms (121/m 2 ), 

 and 22 times denser than mollusks (47/m 2 ). In terms 

 of biomass, however, the echinoderms ( 120 g/m - ) out- 

 weighed mollusks (80 g/m 2 ) by 1.5 times, and crusta- 

 ceans (10 g/m 2 ) and annelids (8 g/m 2 ) by 12 and 15 

 times, respectively. 



