204 



NOAA Technical Report NMFS 140 



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BOTTOM SEDIMENTS 



Figure 223 



Density and biomass of Ophiuroidea in relation to bottom sediments. 



where the range was greater than 16°C. Aver- 

 age density of ophinroids increased from 25 

 to 74 individuals/m 2 as the range in tempera- 

 ture increased from less than 4°C to 12°- 

 15.9°C, then dropped precipitously to less than 

 3/m 2 in the two broadest temperature range 

 classes (Table 21; Fig. 224). 



Biomass values were an order of magnitude 

 lower than those of numerical density, but 

 they revealed a general decline associated with 

 an increased range in temperature (Table 23; 

 Fig. 224). Where the temperature range was 

 less than 12°C, the average biomass was about 

 3 to 6 g/m 2 . Where the temperature range 

 was greater than 16°C, the biomass averaged 

 about 0.5 g or less/m . 



Frequency of occurrence diminished rather 

 consistently with increased range in water tem- 

 perature (Table 25). Ophiuroids occurred in 

 64% of the samples in areas where the tem- 

 perature range was less than 4°C and declined steadily 

 to 11% in areas where the range in temperature was 

 20°C or more. 



Relation to Sediment Organic Carbon 



Ophiuroids were numerically most abundant (72 to 81 

 individuals/m 2 ) where the organic carbon content was 

 between 0.50 and 1.49% (Table 26; Fig. 225). Average 



density declined in both lesser and greater amounts of 

 organic content, with the lowest density (5/m 2 ) occur- 

 ring in the highest content class they occupied (2.00- 

 2.99%). 



Biomass showed a similar trend but at considerably 

 lowered magnitude (Table 28; Fig. 225). Biomass was 

 from 5 to 6 g/m 2 in areas of organic carbon content 

 between 0.5 and 1.49% and fell off sharply to consider- 



