142 



NOAA Technical Report NMFS 140 



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a a: 1400 



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u. 5 1200 



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CQ ^ 1000 



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O O NUMBER 



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tr 



LLl 



a 



800 



600 



400 — 



200 



40 



35 



30 



10 



10 25 50 100 200 500 1000 2000 4000 



WATER DEPTH IN METERS 



Figure 136 

 Density and biomass of Arthropoda in relation to water depth. 



mean density and biomass were 2.1/m 2 and 0.05 g/m 2 , 

 respectively. Density and biomass in all other sediment 

 types were significantly lower, 0.1/m 2 and <0.01 g/m 2 , 

 respectively (Tables 16, 18; Fig. 143). 



Frequency of occurrence, as might be expected, was 

 greatest in gravel (11% of samples), intermediate 

 (5%) in till, and low (1%) in the other sediment types 

 (Table 20). 



Relation to Water Temperature 



Sea spiders occurred in all temperature range classes. 

 In terms of mean density there was a wide disparity in 

 the quantities contained; the broadest temperature 

 range (20-23. 9°C) contained from 2 to 15 times more 

 individuals ( 1.5/m 2 ) than any other range class, which 

 had ranges from 0.1 to 0.7/m 2 (Table 21; Fig. 144). 



Biomass was more evenly distributed among the dif- 

 ferent temperature range classes. However, the broad- 



est temperature range did not contain the highest mean 

 biomass (only 0.01 g/m 2 ), as it did density. The highest 

 mean biomass occurred in the 4-7. 9°C range class which 

 contained 0.03 g/m 2 . Mean biomass in the other tem- 

 perature range classes was 0.01 g/m 2 or less (Table 23; 

 Fig. 144). 



Frequency of occurrence of pycnogonids in the 

 samples in the various temperature range classes was 

 rather uniformly low, ranging from 1 to 4%, with the 

 highest incidence occurring in the two range classes 

 that yielded the highest density and biomass (Table 

 25). 



Relation to Sediment Organic Carbon 



Pycnogonids were restricted to areas of low and moder- 

 ate levels of organic carbon content, being found where 

 values were between 0.01 and 1.49%. Mean density 

 decreased from 0.4 to 0.1/m 2 as organic carbon con- 



