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



Table 114 

 Depth, m 10 25 50 100 154 



1 m 3 per litre per year) points to a very poor development of life in the inter- 

 mediate warm layer of water in the Arctic basin. 



III. FLORA AND FAUNA 

 Plankton 



Phytoplankton. P. Shirshov gives data on the distribution of phytoplankton 

 in the Chukotsk Sea (1936). In this case also a powerful stimulus to a mass 

 development of phytoplankton is given by the melting of ice in spring. This 

 outbreak of spring flowering proceeds mainly in respect of diatoms such as 

 Thalassiosira gravida, Fragrillaria islandica, Fr. oceanica, Achnanthes taeniata, 

 Amphipora hyperborea, Bacteosira fragilis, Detonula confervacea and a few 

 species of Chaetoceros socialis and Ch.furcellatus. 



Having developed a considerable biomass (18-8 to 115-1 mg of chlorophyll 

 per m 3 in alcohol extracts) and used up all the nutrient salts, phytoplankton 

 rapidly begins to decrease and, when defunct, sinks down into the lower layers 

 of water. A considerable development of zooplankton and a great scarcity of 

 phytoplankton are characteristic of the summer period of plankton life in the 

 Chukotsk Sea. The amount of chlorophyll is usually expressed in fractions of 

 a milligramme and rarely a few milligrammes (up to 5 or 6) per m 3 . In better 

 heated sea waters the predominance of the peridineans and in the colder 

 water of the Chaetoceros diatom genus are characteristic of 'summer' 

 plankton. 



Zooplankton. The Pacific Ocean forms have an influence on the Chukotsk Sea 

 zooplankton. Jashnov notes the presence here of such forms as Calanus 

 cristatus, C. tonsus, Eucalanus bungei, Acartia tumida and others, pointing out 

 the small role played by these foreign forms which are present in restricted 

 numbers. 



According to M. Virketis (1952) the Chukotsk Sea zooplankton consists of 

 93 species (not counting the larvae and the doubtful forms), the Copepoda, 

 Protozoa and Coelenterata (74 species) forming the main mass of the species. 

 The Arctic-boreal species are the most important in respect of mass (17 per 

 cent). The Arctic and boreal forms are equally represented. The following 

 forms can serve as indicators of the presence of Pacific Ocean waters : among 

 the Protozoa : Acanthostemella norvegica, Tintinnopsis japonica, T. Kofoidi, 

 Tintinnus rectus; among the jellyfish: Rathkea octopunctata ; among the 

 Cladocera : Evadne nordmanni and Podon leuckarti ; and among the Copepoda 

 Calanus cristatus, С tonsus, Eucalanus bungei, Acartia clausi, Epilabidocera 



