192 NOAA Technical Report NMFS 140 



Relation to Sediment Organic Carbon 



Holothuroidea was one of only a very few taxonomic 

 groups for which definite, consistent trends were clearly 

 demonstrated in relation to the amount of organic 

 carbon in the sediments. 



The trend was the reverse of that pertaining to water 

 temperature. The organic carbon-density relationship 

 was in general negatively correlated, whereas the or- 

 ganic carbon-biomass relationship was essentially posi- 

 tively correlated. Seven of the eight carbon content 

 classes were occupied; the one exception was the high- 

 est class (5.0+%). 



Holothurian average density was highest (18 indi- 

 viduals/m ) where no measurable organic carbon was 

 found (Table 26; Fig. 213). Much lower average densi- 

 ties (ranging from 8 to 2/m' J ) prevailed in the other 

 carbon content classes with a general tendency oi de- 

 creasing with increasing organic carbon content. 



Average biomass, on the other hand, showed a trend 



that was the reverse of the one for density (Table 28; Fig. 



!13). Average biomass was lowest (6 g/m ) in the 0% 



carbon content class and steadily increased with in- 

 creasing organic carbon content, culminating in excep- 

 tionally large biomasses in the two highest classes occu- 

 pied. There was nearly a threefold increase between 

 the 1.50 and 1.99% class and the 2.00 and 2.99% class 

 (41 vs. 104 g/m 2 ) and a fivefold increase from the latter 

 class to the 3.00-4.99% class (562 g/m 2 ). 



Frequency of occurrence was quite uniform at a mod- 

 erate level (15 to 40%) in all organic carbon content 

 classes (Table 30). 



Echinoidea — Sea urchins are the second largest (after 

 bivalves) contributors to the New England benthic bio- 

 mass, providing 20% of the total (Table 3). This large 

 contribution was made by a group with low taxonomic 

 diversity. Fewer than six species contributed over 95% 

 of the specimens. The major contributors were sea 

 urchins, heart urchins, and sand dollars. 



The feeding habits of echinoids are varied. Most are 

 bottom feeders (carnivores, herbivores, or omnivores) , 

 but some common species are plankton feeders, and 



