118 



NOAA Technical Report NMFS 140 



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0-39 4-79 8-119 12-159 16-199 20-239 



ANNUAL RANGE IN BOTTOM WATER TEMPERATURE 



IN DEGREES CELSIUS 



Figure 103 



Density and biomass of Mollusca in relation to the annual range of 

 bottom water temperature. 



most numerous, namely till, gravel, and sand-silt (Table 

 20). Their occurrence rate was low (3 to 9% of the 

 samples) in sand and silt-clay. 



Relation to Water Temperature 



Polyplacophorans were found to inhabit a rather broad 

 span of annual ranges in water temperature, from 0- 

 3.9° to 16-19.9°C, inclusive (Table 21, Fig. 109). They 

 were numerous; average density was 7.3/m 2 , where the 

 water temperature range was greatest. Lower densities 

 (0.8 to 1.4/m ) were found in the middle and low 

 temperature range groupings. 



Biomass values in relation to water temperature range 

 rather closely paralleled the trends described above for 

 density (Table 23; Fig. 109). At the greater temperature 

 range, 16° to 19.9°C, the biomass averaged 1.3 g/m 2 , 

 whereas in the middle and lower range groupings, the 

 biomass averaged 0.12 g/m 2 or less. 



Frequency of occurrence was low in all temperature 

 ranges but was relatively higher (10%) where the fluctua- 

 tion in temperature was less than 8°C (Table 25). Occur- 

 rence rate was relatively moderate (5 to 7%) where the 

 temperature range was moderate. No chitons were taken 

 where the temperature range was greater than 20°C. 



Relation to Sediment Organic Carbon 



Polvplacophorans were rather restricted in their distri- 

 bution in relation to the quantity of organic carbon in 

 the sediments, occurring only where the carbon con- 

 tent ranged from 0.01 to 1.99% (Table 26; Fig. 110). 

 Average density was highest (2.5 /m ) in the lowest 

 carbon content class (0.01-0.49%), lower still (1/m 2 ) 

 in the 1 to 1.5% content class; and significantly lower in 

 the other two classes they occupied. 



Average biomass decreased markedly from its high- 

 est point (0.25 g/m 2 ) in the lowest content class (0.01- 



