THE BLACK SEA 423 



Table 169. Role of inedible forms of zooplankton in the Black Sea, 

 according to 1948-49 data (A. Kusmorskaya) 



amount of zooplankton and its separate components may undergo consider- 

 able annual and seasonal fluctuations, like those mentioned above for phyto- 

 plankton, as is evident from a comparison of Figs. 199 and 201. In the north- 

 western part of the Sea, in bays and inlets, the amount of plankton is always 

 greater than in the open sea ; in all these fluctuations, however, it is on a fairly 

 high level in the open sea too, as compared with other seas. An increased 

 amount of plankton is always observed in the western part of the Sea, which 

 is due to the proximity of the highly productive, northwestern, shallow 

 area and to an abundant river-discharge. A second highly productive Sea 

 area lies off the southeastern coast of the Crimea, this peculiarity being due to 

 the outflow of highly productive waters from the Sea of Azov. Generally 

 speaking the fluctuations in Black Sea plankton productivity display a 

 definite dependence (Fig. 204) on the variations of river-discharge (A. Kus- 

 morskaya, 1955). The mean biomass of food plankton in the Black Sea varies 

 between the limits 175 and 930 mg/m 3 (A. Kusmorskaya, 1955) {Table 170). 

 Pseudocalanus elongatus and Acartia clausi are the main zooplankton forms 

 of the shallows of the northwestern area of the Black Sea (0 to 10 m). Calanus 

 helgolandicus becomes a mass form in the deeper part. There is a considerable 

 admixture of Penilla, Evadne and Podon in the shallows in summer (Fig. 205). 



The nature of the zooplankton biomass distribution in the lower level of 

 the inhabited zone is different, where it corresponds well with the general 

 character of the circulation of the Black Sea water masses (Fig. 206). 



The changes in the biomass and composition of the summer food-zoo- 

 plankton of the northwestern area shallows are given in Table 171. 



Similar data are obtained from a comparison of the Black and Caspian 

 Seas zooplankton biomass (A. Kusmorskaya, 1950) (Table 172). 



However, substantial additions should be made to this table. The predatory 

 plankton forms (Medusa, Ctenophora, Sagittae, Flagellata, Noctiluca miliaris), 

 which probably devour zooplankton like the Ctenophora of the Barents Sea 

 and thus decrease its significance as nutrient for fish, are absent from the 

 Caspian Sea. 



The shallow northwestern part of the Black Sea, distinguished by its high 

 indices of plankton and benthos biomass, serves in summer as feeding ground 

 for many fish and their young. In some years, however, the picture is quite 



