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



Centropages hamatus and Temora longicornis, and some species of diatom of 

 the genus Chaetoceros {Ch. danicum, common in the Baltic Sea, Ch. curvisetum, 

 Ch. constriction, Ch. scolopendra). 



Negative characteristics of the plankton of the White Sea. On the other hand 

 more than 50 Barents Sea phytoplankton forms and about 50 zooplankton 

 forms are absent from the White Sea. As M. Virketis has shown (1926), a 

 series of boreal forms of copepods, Rhinocalanus nasutus, for instance, and 

 Metridia lucens, Oithona plumifera and Acartia clausi, and equally typical 

 Arctic forms Ptychogastria polaris, Tiara conifera, Calanus hyperboreus, 

 Euchaeta norvegica, Krohnia hamata, Oikopleura Jabradoriensis, common in 

 the Barents Sea, are absent from the White Sea. No less interesting also is the 

 fact that ' certain species, common with Barents Sea species, exist in the White 

 Sea in entirely different conditions'. 



Quantitative distribution of zooplankton. As V. Jashnov has shown (1940), in 

 the White Sea zooplankton Calanus finmarchicus, Metridia longa and Pseu- 

 docalanus elongatus are predominant in the spring, and, in contrast with the 

 Barents Sea, only 38 per cent of the total biomass of zooplankton falls to the 

 share of Calanus finmarchicus, to Metridia longa 23 per cent, to Chaetognatha 

 13 per cent, and to Euphausiaceae 1-1 per cent. At the same time Calanus 

 finmarchicus (49-2 per cent) is dominant in the surface layer (down to 25 m), 

 and Metridia longa (42-2 m) in the depths. 



Nevertheless in the more thoroughly warmed areas of the Sea, in the Gulf of 

 Onega, for example (L. Epstein, 1957), the main representatives of zooplank- 

 ton are species of the genus Acartia with an admixture in time of warmth 

 of Centropages hamatus, Temora longicornis, Cladocera and others, and in 

 time of cold of Calanus finmarchicus and Metridia longa. 



The greatest average density of zooplankton in the 25 m surface layer is 

 200 mg/m 3 (Fig. 86a). At a depth of 200 to 300 m the zooplankton biomass 

 amounts to 50 mg/m 3 . The mean spring biomass for the whole Sea is 100 

 mg/m 3 . Jashnov (1940) suggests that the maximum zooplankton biomass of 

 the White Sea must be approximately equal to the biomass of the southwestern 

 part of the Barents Sea, and notices likewise a very great poverty in numbers 

 of plankton in the Gulf of Onega and the Gorlo of the White Sea. V. Jashnov 

 (1940) takes the maximum total zooplankton biomass of the White Sea as 

 equal to 1^ to 2 million tons. 



But L. Epstein (1957), for the more productive Gulf of Onega, points for 

 1951 to a mean plankton biomass in the open part of the Gulf of 157 mg/m 3 

 in the summer period and 37 mg/m 3 in the autumn ; and, in the gubas of the 

 White Sea coastline, to 210 mg/m 3 in summer and 11 mg/m 3 in winter. 

 Epstein's data and certain other material give reason for suggesting that the 

 biomass indicated by Jashnov is somewhat overestimated. Moreover, in the 

 White Sea the phytoplankton sometimes gives a very great density (V. 

 Khmisnikova, 1947) which in some areas is as high as 10 mg/m 3 . The quanti- 

 tative distribution of phyto- and zoo-plankton in August 1932 is shown in 

 Fig. 86, a and в. 



