196 NOAA Technical Report NMFS 140 



Fig. 21(1). At depths greater than 100 m, their density 

 was drastically reduced (2.0 or fewer individuals/m 2 ) . 



The pattern of biomass distribution was quite similar 

 to that for density. Average biomass was exceptionally 

 high (154 g/m L> ) near mid-shelf depths (25 to 49 m) 

 and decreased in both shallower and deeper regions 

 (Table 13; Fig. 216). The decrease was only moderate 

 in the shallower depth class but was severe (0 to 1.8 g/ 

 m 2 ) in depths greater than 500 in. 



Occurrence of echinoids in the samples was moder- 

 ate to low in all depth classes and followed the same 

 trend as densitv and biomass. They were present in 57% 

 of the samples near the mid-shelf depths and decreased 

 in samples from both shallower and deeper bathymet- 

 ri< c lasses (Table 15). 



sity averaged 67 individuals/m in sand but only 3.4 or 

 less per square meter in other sediments. 



Precisely the same pattern was revealed for biomass. 

 The average biomass in sand sediments was 81 g/irr; in 

 all other sediments the biomass of echinoids averaged 

 7.3gorless/m 2 (Table 18; Fig. 217). The proportion of 

 the total benthic biomass that was formed by echinoids 

 in the sand sediments was 33%, which is an exception- 

 ally large contribution for one taxon (Table 19). 



The occurrence of echinoids in the samples was mod- 

 erate to low in all sediment types (Table 20). As 

 expected, it was highest (47%) in sand substrates. Some- 

 what unexpectedly, the incidence rate was lowest 

 (S'V ) in sand-silt sediments and relatively high (32%) 

 in till. 



Relation to Sediments 



The correlation of echinoids with sand substrates was 

 exceedingly high (Table 16; Fig. 217). Although they 

 were present in all other types of sediments, their den- 



Relation to Water Temperature 



Ki hinoids were most abundant in terms of both density 

 and biomass in areas where the annual range in bottom 

 water temperature was moderate, 12° to 15.9°C. 



