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



Caspian Sea by the daily changes in oxygen content and pH in the sea itself, 

 that is by the difference between the afternoon maximum and the night 

 minimum of oxygen content. The average hourly consumption of oxygen was 

 determined by the difference between oxygen content after sunset and before 

 sunrise divided by the number of hours between the two determinations. 



Brujevitch recorded the greatest phytoplankton production in the Mertvyi 

 Kultuk inlet in August 1934 (3-65 to 3-25 mg of glucose per litre). In the 

 Central Caspian the average phytoplankton production in August and 

 September 1934 was about 0-68 mg of glucose per litre, in the Southern part 

 about 0-75 mg/1. of glucose. Taking the plankton biomass for the Southern 

 Caspian as approximately 02 g/m 3 of glucose, Brujevitch determines its daily 

 P/B ratio as 3-7, and for Mertvyi Kultuk as 2-8. If the distribution of 

 plankton in the upper 25 m column is more or less uniform, then the daily 

 plankton production is 17 to 19 g under 1 m 2 , or 170 to 190 kg of glucose 

 under 1 hectare. 



Qualitative composition of zooplankton. We do not as yet possess sufficient 

 data on the Caspian Sea zooplankton similar to those on its phytoplankton. 

 According to V. Arnoldi and N. Tchougounov 92 species of zooplankton were 

 recorded for the whole of the Northern Caspian in the proportions shown in 

 Table 244. The fresh-water forms consist mainly of Rotatoria and Cladocera. 



Table 244 



Fresh-water forms 56-5% Rotatoria 45-2% 



Brackish-water forms 7-5% Cladocera 28-6% 



Marine 33-8% Copepoda 21-7% 



Indifferent 2-2% Others 4-5% 



According to these investigators 1 1 5 zooplankton forms have been dis- 

 tinguished in the Azov, Caspian and Aral Seas ; of these 60 per cent are fresh- 

 water and 40 per cent marine and brackish-water forms. The Northern Cas- 

 pian has the greatest similarity with the Aral Sea (25 per cent common 

 forms). 



A. Kusmorskaya made a detailed study of the Northern Caspian zoo- 

 plankton in 1938 (Fig. 282). According to her data the qualitative composition 

 of Northern Caspian zooplankton does not differ from the characteristics 

 given in Table 244. Among the Protozoa, Tintinnoidea are the most numer- 

 ous and most widely distributed; they are represented by three species: 

 Tintinnus mitra, Codortella relicta and Tintinnopsis spp. ; moreover, the first 

 of them is not found in Mertvyi Kultuk and Kaidak, where C. relicta and 

 Tintinnopsis spp. reach their highest development. The Coelenterata are 

 represented by the medusa Caspionema pallasi, by its hydroid and by a hydroid 

 of a new form not yet described. The most numerous Rotifera are Asplanchna 

 priodonta, three species of Brachionus {B. bakeri, B. pala, and B. mulleri) and 

 a few species of Synchaeta and Ceratella aculeata var. tropica. The distribution 

 of many fresh-water species is limited to the estuarian zones of the rivers ; 



