316 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



The region of the typical Baltic mesomixed and oligomixed communities 

 only begins, however, east of the Darss ridge (Fig. 151). This ridge may in fact 

 be called a distinct quantitative-biocoenotic boundary (I. Valikangas, 1933). 

 The quantitative researches of the Swedish investigator G. Thulin (1922), and 

 of the Polish workers under K. Demel (1935, 1951, 1954), covered the Arcona 

 and Bornholm depressions, and in addition Demel's investigations covered all 



mo 



102-5 



31-11 



3-03 2 384 



U 



] 9 

 10 

 11 

 12 



Fig. 150. Composition of typical bottom communities of the 

 Baltic Sea. Numerals above circles denote mean biomass in g/m 2 

 (Zenkevitch). 1 Cyprina islandica; 2 Macoma calcarea; 3 M. 

 baltica; 4 Astarte borealis; 5 Cardium edule; 6 Polychaeta; 7 

 Mesidothea; 8 Mytilus edulis; 9 My a arenaria; 10 Crustacean, 

 1 1 Pontoporeia affinis ; 1 2 Others. / Cryprina- Astarte of Kiel Bay ; 

 // Macoma calcarea of Bornholm depression; /// Macoma- 

 Cardium on Oderbank (to the north of Pommern); IV Macoma 

 baltica community of southern half of Gulf of Bothnia ; V Deep- 

 water community of the same part (Pontoporeia-Mesidothea) ; 

 VI Community of northern part of the Gulf of Bothnia (Macoma- 

 Pontoporeia-Mesidothea). 



the southern part of the Sea. A. Hagmeier (1923-30) surveyed the same areas 

 in part, and also the southern Baltic. Farther to the north and as far as 

 the end of the Gulf of Bothnia lies the area investigated by the Swedish scien- 

 tist Chr. Hessle (1924). Along the Finnish shores of the Gulf of Finland the 

 Finnish investigator S. Sagerstrale conducted research (1933). A. Schurin has 

 described the distribution of benthos in the Bay of Riga (1957). The researches 

 of these investigators make it possible to give a quantitative biocoenotic 

 estimate of the Baltic Sea benthos. 



On the whole it can be assumed that to the east of the Darss ridge there is a 

 single bottom biocoenosis, Macoma baltica; this form, however, develops 



