Composition and Distribution of Macrobenthic Invertebrate Fauna 



197 



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7 



GRAMS 



PER SQUARE METER 



ECHINOIDEA 



Figure 214 



Geographic distribution of Echinoidea: A — number of specimens per square meter of 

 bottom; B — biomass in grams per square meter of bottom. 



Echinoid density averaged 93 individuals/m 2 at mid- 

 range (Table 21; Fig. 218). From this peak the average 

 density diminished to 1.4/m 2 , where the temperature 

 range was less than 4°C, and to about 15/m where the 

 temperature change was 2()°C or more. 



The biomass of urchins was distributed in essentiallv 

 the same manner as their numerical density among the 



various temperature range groupings, with one excep- 

 tion (Table 23; Fig. 218). Large biomass (148 g/m 2 ) 

 occurred in the mid-range; moderate biomass (about 

 14 to 38 g/m ) in intermediate ranges; and small biom- 

 ass (6 g/m ) in the stable areas. The one exception was 

 a relatively large biomass (135 g/m 2 ) in the broadest 

 (20°-23.9°C) temperature range class. 



