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



of the biocoenosis, the following are the most common : Nassa neritea, Venus, 

 Angulus, Paramysis kroyeri, Cumopsis, Pseudocwna longicornis pontica, 

 Gastrosaccus, Pontogammarus maeoticus, Nerine, Aricidea, Spio filicornis 

 and others. Apart from macrobenthos the author gives the first comprehen- 

 sive description of the microbenthos of the Black Sea. One cubic centimetre 

 of sand was found to contain 250 to 900 Foraminifera, 50 to 120 nematodes, 

 1 to 9 Harpacticidae (mainly Canuella perplexa and Ectinosoma elongatum) 

 and 11 other species (0-5 to 2-5 polychaetes, 0-5 to 1 higher crustaceans and 

 1 to 4 specimens of the young fry of Corbulomya). 



V. Nikitin has given a very detailed description of an oyster bank near 

 Gudaut (1934), lying at a depth of 10 to 30 m among sand and mussel-mud and 

 occupying an area of about four square miles (Fig. 212). It can be seen from 

 the figure that the oyster bank lies on a slanting, slightly muddy slope. De- 

 pending on the nature of the sea-floor and the swell, the oyster ground lies 

 lower or higher. Among the large number of forms found on the oyster bank 

 Nikitin distinguishes four dominant forms of molluscs: Ostrea taurica, 

 Mytilus galloprovineialis \ax.frequens, Pecten ponticus and Modiola adriatica, 

 and a number of growths which accompany them. The stock of oysters in the 

 Gudaut bank was found (V. Nikitin) to be, in 1930-32, 14 millions with a total 

 weigh of flesh of 300 centners. The Gudaut oyster bank remained up to 1949 

 in practically the same state as, according to Nikitin's data (1934), it had been 

 in 1930-32, but during the last ten years the bank has been attacked by the 

 mollusc Rapana, which exterminates large bivalves such as oysters and sea 

 mussels. At present 'the oyster industry ... is not at all profitable. ... If 

 the stay of Rapana on the Gudaut bank is only temporary, its stock of oysters 

 may be restored' (I. Stark, 1950). 



Rapana bezoar (Muricidae family) was first found in the Black Sea off 

 Novorossiysk in 1947 (E. Drapkin, 1947); it probably appeared in the Black 

 Sea in the early forties. This mollusc, common in the Yellow Sea and the Sea of 

 Japan and in Peter the Great Gulf, was brought from the Far East. The mol- 

 lusc probably travelled this long distance in the form of egg masses in growths 

 on a ship's bottom. It is usually found when ships are cleaned. 



On the lower horizon the oyster bank may be displaced by mussel-shell 

 gravel as a result of the floor becoming too muddy for oysters ; and somewhat 

 deeper, on still more mud, the community of mussel bed — the strongest benthic 

 group of the Black Sea, except for the still deeper-lying grouping of the 

 phaseolin ooze — comes into force. As has been pointed out by Zernov, the 

 fauna of the mussel-ooze 'is really, in most cases, the shell gravel fauna, except 

 for oysters and other forms which cannot tolerate the ooze, so that mussels 

 have taken up the dominant position'. Farther up, at the tops of the bays and 

 inlets, the upper boundary of the mussel-ooze community rises to 9 to 1 1 m 

 below the surface (off Odessa even to 1 m below the surface), while in the 

 open sea it occupies a zone 55 to 78 m deep. For the mussel-ooze besides the 

 dominant form — mussel — the following are most characteristic : among the 

 molluscs; Cardium simile, Meretrix rudis and Tapes; the huge colonies of 

 hydroids, Aglaophenia pluma and Serture/la polyzonias ; the tunicates : 

 Ascidiella aspersa, Ciona intestinalis, Botryllus schlosseri, Eugyra adriatica; 



