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



II. Mediterranean immigrants. Mainly among the Copepoda : Acartia cluasi, 

 Paracartia latisetosa, Centropages kroyeri, Labidocera brunescens, 

 Oithona nana ; among the Tintinnoidae : Tintinnopsis minuta, T. meunieri, 

 T. tubulosa var. sub >acuta, T.relicta, Leptotintinnus pellucidus, L. botanicus; 

 among the Cladocera : Podon polyphemoides. 

 III. Fresh-water Cladocera and Rotatoria in the least saline sections (Lepto- 

 dora, Asplanchna and others). 



Calanipeda aquae dulcis, Evadne trigona, Brachionus quadridentatus, B. 

 plicatilis and Pedalion oxyuris are particularly richly developed. 



In the outer part of the Gulf of Taganrog Heterocope, Cercopagis and, in 

 the least saline parts, the fresh-water Rotatoria, Cladocera and Cyclopidae 

 are developed in large masses. 



Zooplankton biomass. Quantitative investigations of the Azov Sea plankton 

 were carried out by F. Mordukhai-Boltovskoy (1938) and A. Okul (1940), 

 by G. Pitzik and A. Novoshilova (1951) and by A. Novoshilova (1955). 



In the Sea of Azov the highest annual zooplankton biomass for the last 

 20 years was recorded in 1937 (Table 200). In recent years it has fluctuated 



Table 200 



considerably and was lowest in 1939 and 1948. Individual components of 

 plankton groups have also shown significant variations in particular years. 

 In the Gulf of Taganrog the zooplankton biomass has also fluctuated sub- 

 stantially from year to year. In 1937 it was very high (1,351-3 mg/m 3 ) and still 

 higher (up to 2,082-7 mg/m 3 ) in 1949. As has been shown by investigations 

 lasting for many years, before the flow of the river Don was controlled, the 

 total zooplankton of the Sea of Azov in early spring (March- April) consists 

 of 47 to 90 per cent Rotifera (Synchaeta). In May and June, side by side with 

 Copepoda and Rotatoria, the number of the larvae of bottom invertebrates 

 (Cirripedia, Vermes and Mollusca) increases greatly. In May 1949 and 1950 

 the biomass of the Cirripedia larvae formed 83 to 85 per cent of the total zoo- 

 plankton biomass in the northeastern part of the Sea (A. Novoshilova, 1958). 

 The number of Copepoda increases towards the beginning of the summer, 

 reaching 65 to 95 per cent of the total biomass (slightly less in the Gulf of 

 Taganrog), mostly on account of Acartia clausi and Centropages kroyeri, and 

 in the Gulf of Taganrog Calanipeda aquae dulcis and Heterocope caspia. 



