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



In the glacial period, as Derjugin suggests, the fauna of the White Sea 

 must have been destroyed, since the basin of the sea was blocked with glacier 

 ice. From the latest post-glacial phase to the present time a large number of 

 high Arctic forms have been preserved in the White Sea, the most typical of 

 them being the mollusc Portlandia arctica. Many of these forms possess a 

 definitely relict character ; they are not encountered in the adjacent parts of the 

 Barents Sea, and are common in the Kara Sea and farther east. Such, for 

 instance, besides P. arctica, are the polychaetes Harmothoe badia, Melaenis 

 loveni, the holothurian Cucumaria calcigera, the crustaceans Paroediceros 

 intermedins and Aeanthostepheia malmgreni, the molluscs Cylichna densistriata 

 and Bela novaja-zemljensis, the ascidians Eugyra pedunculata and Rhizomilguta 

 globidaris, the fishes Lycodes agnostus and Liparis major and others. At the 

 same time, possibly there was also a link with the Baltic Sea. 



In the warm Littorina stage the Arctic elements were shifted far to the 

 eastward and remained in the shape of relicts in the coldest corners of the 

 White Sea. A mass of thermophilic forms settled in the White Sea. Most 

 probably in the period of this same post-glacial rise of temperature there also 

 penetrated into the White Sea some Pacific Ocean forms such as the herring, 

 the lamprey and others. 



The colder temperature of modern times destroyed some of these forms, and 

 some it transformed in the White Sea into thermophilic relicts. Examples of 

 these forms we have already adduced. The period which has passed since the 

 Ice Age has been shown to be sufficient for the creation of a whole series of 

 endemic forms chiefly variants and sub-species and, only to a small extent, of 

 new species. 



Negative features in the fauna of the White Sea. Derjugin likewise subjected to 

 analysis another interesting phenomenon in the fauna of the White Sea, which 

 he called the negative features of the White Sea fauna. A whole series of forms 

 which are most common in the Barents Sea are absent from the White Sea, 

 as has been pointed out above in the description of the plankton. Of these 

 common forms of benthos alone there may be reckoned no fewer than 125, 

 which includes 45 molluscs, more than 25 crustaceans, 8 echinoderms, 7 poly- 

 chaetes, 6 coelenterates, 5 poriferae and only 3 species of fish. 



Derjugin explains this phenomenon by the entirely unfavourable hydrolo- 

 gical conditions of the Voronka and the Gorlo. The turbulent mixing of the 

 whole mass of water which takes place at flood-tide and ebb-tide, the consider- 

 able warming of the water in summer and its severe chilling in winter, the 

 absence of soft sea-bed — all this makes extremely hard the transfer of tender 

 pelagic forms and stages of development through the 200 to 300 km of the 

 Voronka and Gorlo. In addition, the whole base mass of water in the Voronka 

 and Gorlo is shifted by the tide alternately in one direction and then in the 

 other, and the forward motion of permanent currents here is relatively feeble. 

 Derjugin calls the conditions of the Gorlo 'a biological plug'. One cannot help 

 agreeing with the correctness of this explanation for certain forms ; but for the 

 majority it is more probable to conjecture the destructive influence of a con- 

 siderable fall in salinity — to 7 to 8% — within a comparatively short distance. 



