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



marginatus, Chaetoceros gracile and Ch. Wighami, Caloneis brevis, Navicula 

 sp., Dinophysus arctica, Peridinium breve, P. pellucidum and others. 



Qualitative composition of zooplankton 



Virketis gives the composition (species and forms) for the zooplankton of the 



same part of the Sea in the form shown in Table 110. 



Table 110 



Tintinnoidea 5 Rotatoria 27 



Scyphomedusae 1 Cladocera 5 



Ctenophora 1 Copepoda 10 



Total 49 



Seasonal phenomena in plankton development 



Bogorov who collected plankton in the western part of the Laptev Sea in 

 1934 during the period of plankton 'spring' found in the surface layer (0 to 

 10 m) some algae in bloom (average 3,400 mg/m 3 ) ; the zooplankton, however, 

 had not yet reached its maximum (the average biomass was 1 10 mg/m 3 ). On 

 the other hand in the eastern part of the Sea the plankton development had 

 already reached its summer phase — phytoplankton decreased (average 500 

 mg/m 3 ) while the amount of zooplankton had risen to 313 mg/m 3 . At places 

 of maximum bloom the phytoplankton biomass had in the western part of the 

 Sea reached 14,132 mg/m 3 . 



Quantitative distribution of zooplankton 



In his quantitative analysis of the plankton of the Laptev and East Siberian 

 Seas, V. Jashnov (1940) compares the data for: (7) the middle part of the 

 Laptev Sea (depth 50 to 80 m) ; (2) a number of stations to the north and 

 northeast of Novosibirsk Islands, and (3) the cross section from Kotelni 

 Island to the Gulf of Tiksi (Table 111). 



In some cases Appendicularia, mollusc and polychaete larvae and the ptero- 

 poda molluscs are of importance in the plankton. 



It is evident from Table 111 that Copepoda form not less than a third of the 

 total plankton, frequently reaching 98 to 99 per cent of the whole biomass in 

 the surface layer. Here the plankton still retains its Kara Sea character, chang- 

 ing its composition sharply as one moves eastward: Calanus finmarchicus 

 practically disappears and is replaced first by Pseudocalanus elongatus and 

 then by the inhabitants of brackish waters — Pseudocalanus major, Limno- 

 calanus grimaldi, and Drepanopus bungei. 



'Thus', says Jashnov, 'three concentric zones running along the Siberian 

 coast may be distinguished. The first zone, situated in close proximity to the 

 shore, is inhabited by a typical brackish- water fauna ; the second, farther away 

 from the shore, is characterized by the presence of marine, mainly euryhaline, 

 species which penetrate here through the lower water layers ; the third zone is 

 a transitional one between the second and the true marine one. The width 



