Composition and Distribution of Macrobenthic Invertebrate Fauna 



191 



Frequency of occurrence was moderate to low in all 

 sediment types, and the relationship of holothurians 

 with various sediments was similar to that described for 

 numerical density (Table 20). Occurrence was highest 

 (50%) in till, lowest (8%) in sand, and intermediate 

 (16 to 36%) in the other sediment types. 



Relation to Water Temperature 



The relation of holothurian numerical density to the 

 range in water temperature was the opposite of that 

 exhibited by their biomass. Density generally decreased 

 as the temperature range increased (Table 21; Fig. 

 212). The average density of holothurians was about 6 

 individuals/m where the temperature range was less 

 than 4°C and decreased to about 2 individuals/m 2 where 

 the temperature variation was 16° to 19°C. 



Conversely, the biomass of holothurians increased as 

 water temperature ranges increased (Table 23; Fig. 212). 

 Their biomass was relatively small (3 g/m') where the 



temperature range was small (<4°C). With increased 

 annual temperature range, the biomass of holothuri- 

 ans increased substantially to an average of 128 g/m 2 

 where the range was greatest (20°-23.9°C). 



Size disparity of specimens in the various tempera- 

 ture range classes was the principal cause of the re- 

 versed trends. The size of specimens increased mark- 

 edly in waters having a broad temperature range, 

 whereas the numerical density diminished slightly. 



Holothurians contributed a moderately large pro- 

 portion (4—9%) of the total biomass in five of the six 

 temperature range classes. In the other class, where the 

 temperature variation was high (>20°C), they contrib- 

 uted an extraordinarily large share (>30%) of the bio- 

 mass (Table 24). 



Frequency of occurrence was quite uniform at a mod- 

 erate level (14-25%) in all temperature range classes 

 except one (16°"19.9°C), in which holothurians con- 

 tributed only 8% of the samples (Table 25). 



