THE BLACK SEA 445 



and frequently large numbers of the nemerteans Cerebratulus kowalevskyi ; 

 the ooze-polychaetes Melinna palmata and Terebellides stromii; and the 

 brittle star Amphiura florifera. Among the crustaceans the most typical is 

 Crangon crangon. Among the plants Phyllophora is very characteristic. The 

 most interesting feature of this group is the huge mass development of a 

 typical littoral form — the sea mussel at depths of 27 to 65 m. In many places 

 thesea mussel goes down in ocean and seas with tides to depths unusual to it 

 as a littoral form ; this occurs either in tideless seas with no littoral (the Baltic 

 and the Mediterranean Seas), or owing to unfavourable conditions prevailing 

 on the littoral (Cheskaya Guba). However, nowhere does the sea mussel accu- 

 mulate in such huge masses at such low levels as in the Black Sea. In the Medi- 

 terranean (in the vicinity of Naples) the sea mussel does not go lower than 

 10 m. The cause of this mass development of sea mussel at a considerable 

 depth must be sought in biocoenotic relationships. Apparently at higher levels 

 sea mussel encounters some restricting rivals, which are absent at depths 

 where the mussel bed occurs. The main species of mussel which inhabits the bed 

 evolved an independent variety — Mytilus galloprovincialis var. frequens; 

 this is also of interest. 



The biocoenosis of the Phyllophora field. On some sectors of mussel bed, in 

 quiet depths, huge accumulations of live (Phyllophora) or dead (Zostera) 

 plants are formed and carried away by the currents. We have already men- 

 tioned the existence of a colossal accumulation of Phyllophora in the middle of 

 the Sevastopol-Danube-Odessa area at depths of 27 to 55 m (mostly at 

 35-45 m). 'The Phyllophora fauna is very poor', writes Zernov, 'almost all 

 the organisms living on Phyllophora are coloured brown-red — in full harmony 

 with the colour of Phyllophora itself. 



' The crustaceans such as Amphipoda, Isopoda are the most numerous here ; 

 there are some crabs (Portunus arcuatus), a few polychaetes, molluscs and 

 small fish. Apparently the huge beds of Phyllophora prevent any considerable 

 development of animal life.' 



The biocoenosis populating the dead plants on the sea-bottom is specially 

 well developed at depths of 35 to 45 m in Karkinitsk Bay, where Zostera, 

 brought out from inside the bay, which is entirely overgrown by this sea-weed, 

 is gathered in large masses. It is abundant also in the Bay of Taman and other 

 places on the Black Sea coast. Masses of Amphipoda, Mysidae, Decapoda, 

 molluscs, Turbellaria, and some small fish live in the accumulations of dead 

 plants. 



The phaseolin-ooze biocoenosis. This is even more original than that of the 

 mussel. It is the deepest zone of benthic life in the Black Sea. Usually found 

 first at 55 to 65 m (at times at 40 to 45 m ; in some places at 80 m) with a sharp 

 transition from the mussel-mud, the phaseolin ooze reaches on the average a 

 depth of 1 80 to 1 85 m. Modiola phaseolina is the main component of this group. 

 Modiola phaseolina is an interesting example of the ecological aspect of 

 many representatives of the Mediterranean fauna in the Black Sea. Outside the 

 Black Sea M. phaseolina is widely distributed in the Atlantic Ocean, as far as 



