THE WHITE SEA 201 



If we set side by side the poverty of the Barents Sea fauna, against its transit 

 into the White Sea, and the analogous impoverishment in the Baltic Sea, the 

 coincidence, quantitatively, is most graphic ; and in the flood-tides which lead 

 into the Baltic Sea, the hydrological factor is absent by which Derjugin ex- 

 plains the poverty of the fauna of the White Sea. 



With the passage from the North Sea at flood-tide, and with a fall in 

 salinity from 35 to 27 or even 23% , there occurs a sharp decrease in fauna from 

 1,500 species to nearly 1,000. Thus 'negative features' in the fauna of the 

 central part of the Skagerrak are defined as approximately 500 animal 

 species. A fall of salinity even to 32% causes a loss of 350 forms. It is likewise 

 possible that the qualitative impoverishment of the fauna, with the transit 

 from the open coasts of the ocean into a system of inlets and sounds jutting 

 deeply into the land has, besides the loss of salinity and the powerful circu- 

 latory currents, yet other causes which have not yet been taken into account. 

 It is known, for instance, that there is a general qualitative impoverishment of 

 flora and fauna in seas that are smaller in dimensions. 



In any case, it is impossible to explain this complicated phenomenon simply 

 by the unfavourable hydrological conditions in the Gorlo. This is one of many 

 causes, and very likely the least important. 



Vertical displacement of zones. Likewise far from being fully understood by 

 us are the phenomena of the vertical displacement ('the displacement of zones' 

 in the earlier terminology) of groups and of individual forms, which are so 

 pronounced in the fauna of the White Sea. On the one hand it is as if a general 

 tendency to rise to lesser depths occurs, which may be conditioned in the first 

 place by the low temperature of the depths and the lower transparency of the 

 water ; and on the other hand a series of littoral forms moves into the sub- 

 littoral and some forms from upper layers of the sublittoral into lower layers. 

 The only explanation so far for these displacements is seen in the unfavourable 

 influence of the piling up of ice on the shore in the course of a long harsh 

 winter. For a series of forms, a part is probably also played by the consider- 

 able warming up of the surface waters at the shores in summer, which drives 

 the cold-loving forms down into the depths. 



Very significant data were produced by M. Gostilovskaya (1957) in a com- 

 parative study of the vertical distribution of bryozoans in the Barents and 

 White Seas {Table 86). 



Population of the supralittoral. Everywhere in the supralittoral of the White 

 Sea, especially where there are accumulations of sea-weed cast up by the 

 breakers, an abundant supralittoral fauna is found. 



On the supralittoral, partly moving into the littoral, and even mingling with 

 certain typically marine forms (Balanus balanoides, Littorina rudis and others), 

 usually on the more sloping shores that are not subject to considerable surf, 

 there settle in large numbers the flowering plants, Plantago maritima, Triglochin 

 maritimus, Aster trifolium and Salicornia herbacea, which descend lowest of 

 all on the littoral and mingle there with the fucoids. 



