Composition and Distribution of Macrobenthic Invertebrate Fauna 



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INDIVIDUALS 

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EXPLANATION 



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GRAMS 

 PER SQUARE METER 



GASTROPODA 



Figure 1 1 1 



Geographic distribution oi Gastropoda: A — number of specimens per square meter of 

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



In terms of biomass, the gastropods were most preva- 

 lent (3.3 g/m 2 ) in sand and gravel substates (Table 18; 

 Fig. 114). They occurred in intermediate quantities 

 (2.1 and 1.6 g/m 2 ) in shell and sand-silt. Low quantities 

 (0.2 g/m 2 ) were found in till and silt-clav sediments. 



Frequency of occurrence was high (83%) only in 

 samples from shelly sediments (Table 20). In all other 



bottom types the occurrence of gastropods was quite 

 uniform at a moderate (42 to 50%) level. 



Relation to Water Temperature 



The greatest quantities of gastropods, in terms of both 

 density and biomass, occurred where the annual range in 

 temperature exceeded 16°C (Tables 21, 23; Fig. 115). 



