THE BALTIC SEA 



319 



Astarte borealis extends through the Arcona depression and the Slypsk 

 trough and farther to the east; the Bornholm depression is inhabited by 

 Macome calcarea (Fig. 1 54). In the Slypsk trough Terebellides stromi appears 

 in great masses, and Demel thinks it possible to distinguish in this area an 

 Astarte-Terebellides biocoenosis. 



At lesser depths in the southern part of the Baltic Sea Mytilus edulis is 

 numerically a markedly preponderant form (Fig. 155), accompanied by 

 Cardium edule, My a arenaria, Macoma baltica and others. 



PONTOPOREIA FEMORATA 



* ж. ■ on the a' 



Fig. 153. Total biomass of Pontoporeia femorata (20,460 tons) and of Pontoporeia 

 affinis (29,533 tons) (Demel). 



The mass forms of the fauna at times provide a great density of population 

 as regards number of specimens {Table 128). 



In comparison with the middle and northern parts of the Baltic Sea, the 

 large number of Mytilus, Astarte and Macoma calcarea is conspicuous. 

 K. Demel and Z. Mulicki (1954) have also drawn a chart of the distribution 

 of the benthos biomass in the southern part of the Baltic Sea (Fig. 1 56) and 

 its contents by separate components {Table 129). 



Thus 90 per cent of the total biomass of bottom fauna consists of bivalves. 



Some visual outlines of the distribution of bottom fauna are also given by 

 Demel and Mulicki; the meridional cross section through the Bornholm 

 depression is given in Fig. 157. 



The same picture, as for all the southern part of the Sea, is repeated on a 



