THE BLACK SEA 431 



Table 176 



The macrophyte biomass of the littoral zone of the Black Sea (without the 

 Phyllophora Sea vegetation) is only 0-5 million tons; moreover, the second 

 place after Phyllophora is occupied by the brown alga Cystoseira barbata. 

 The Cystoseira association produces at depths of 0-5 to 23-28 m a biomass of 

 an average of 3 kg/m 2 (at times up to 6 or 7 kg/m 2 ). 



If 90 per cent of the total mass of the Black Sea macrophytes consists of 

 Phyllophora, then about 9 per cent of it is Cystoseira, whereas all the other 

 macrophytes form not more than about 0-7 per cent. Thus only two species of 

 benthos bottom-living algae are markedly predominant in the Black Sea. 



Whereas the littoral zone of the Black Sea is not as rich in macrophytes as 

 the northern part of the Atlantic, its annual productivity is very near to that 

 of the latter, and is even somewhat higher. 



According to N. Morozova-Wodjanitzkaja (1941) the highest annual macro- 

 phyte productivity is observed in bays, inlets and lagoons (up to 17 kg/m 2 , 

 and 7 to 8 kg/m 2 in the open sea) {Table 177). 



The qualitative composition of zoobenthos and fish fauna. The Black Sea fauna 

 is on the average four or five times poorer than that of the Mediterranean ; 

 moreover, different groups vary in the degree of their impoverishment. Some 

 groups could not penetrate into the Black Sea at all : such were Siphonophora, 

 Gephyrea, Brachipoda, Scaphopoda and Cephalopoda, Enteropneusta and 

 Salpae. Other groups became much poorer in the Black Sea, as for example 

 Ctenophorae, corals, Amphineura, Echinodermata and Tunicata {Table 178). 



The number of species of macrophytes and animals decreases greatly from 

 the Black Sea to the Sea of Azov ; this can be seen by the example of the poly- 

 chaetes (according to V. Vorobieff, 1932) {Table 179). Evidently in the case 

 of polychaetes the number of genera decreases more rapidly than that of the 

 families, and that of the species more rapidly than that of the genera. 



Lowered salinity (to 19% ) and the compal-atively narrow habitable upper 

 layer were the main factors preventing the Mediterranean fauna from settling 

 in the Black Sea. V. Wodjanitzky (1936) has brought out this last factor as 

 affecting the life of fish when writing 'that members of the Mediterranean 

 ichthyofauna could settle in the Black Sea only when in all stages of their 

 development they kept to the upper layers of water (or off the shores) '. In 



