THE WHITE SEA 217 



the upper sublittoral, the determining factors are the very long, severe winter, 

 the short vegetation period of the plant organisms and the ice conditions of 

 the off-shore zone which are adverse for this latter. Life has no time to attain 

 any great density during the four or five summer months, while the severe 

 winter destroys a large number of organisms. In the lower sublittoral and the 

 pseudo-abyssal the low temperature and the gas content constitute adverse 

 factors for full development of life. Deep-sea layers and especially the true 

 deep-floor layer have not yet been sufficiently studied, and the possibility 

 of the periodical occurrence of shortage of oxygen cannot be denied. On the 

 other hand, the wide distribution of brown muds in the White Sea depression, 

 as in other bodies of water, may be an indication of unfavourable conditions 

 of the vertical circulation, and probably of a considerable periodical con- 

 centration of carbon dioxide in the presence, apparently, of sufficient amounts 

 of oxygen. Brown mud with its very poor life, always characteristic of depres- 

 sions and hollows, and undoubtedly very badly aerated (for instance the deep 

 depression of the Polar basin), still remains an enigma. Brown mud is un- 

 doubtedly unsuitable for the development of life owing either to some specific 

 mechanical (considerable softness ; porosity) or chemical (presence of carbon 

 dioxide ; abundance of ferric or manganic oxides) properties. The productivity 

 of the flora and fauna is limited by the seven months of winter and the heavy 

 ice cover. The sharp summer stratification, restricting vertical circulation, is 

 also of great importance, since it causes the weak development of bottom 

 life frequently from a depth of 15 to 25 m. Low temperature, characteristic 

 of the whole depth of the White Sea, except for its thin uppermost layer, 

 has a considerable effect on the growth of living forms. M. Kamshilov (1957), 

 however, confirms V. Jashnov's (1940) opinion, by some data obtained much 

 later, that as regards the plankton biomass the White Sea could rank side by 

 sidewith the southwestern part of the Barents Sea {Table 95). 



Table 95. Mean annual zooplankton biomass of the Barents and White Sea 

 (M. Kamshilov, 1957) 



Biomass 

 Sea Regions investigated mg/m 2 



Barents Sea Coastal regions (B. Manteufel) 44-2 

 The regions of the Murman Biological Station in- 

 vestigation in 1952 61 -8 

 Open Sea (V. Jashnov's and B. Manteufel's data) 1000 



White Sea Gulf of Kandalaksha (Murman Biological Station 



survey in 1952) 198-8 



Food correlations 



The diet of White Sea fish has not been properly studied. Only the feeding 

 of herring has been comprehensively studied by L. Chayanova. Although in 

 the White Sea Calanus finmarchicus is the most common component of the 

 herring's food, its diet is most varied, however, consisting of Copepoda, 



