THE WHITE SEA 215 



Cardium ciliatum, the echinoderms Stegophiura nodosa and Ophiura robusta, 

 many polychaetes and a considerable number of amphipoda. The Arctic 

 forms are predominant at this depth of the Bab'e Sea. Mysis oculata typica is 

 abundant throughout. The deepest part of the Sea (below 25 m) is almost 

 free of animal forms. 



This impoverishment of fauna, common in such cases, and the rise of the 

 boundaries of the vertical zones observed when passing from the Barents Sea 

 to the White Sea is even more accentuated as one moves from the White Sea 

 to the more or less isolated gubas, lagoons and pools. We have here a case of 

 the changes repeating the zonalities characteristic for the whole of the White 

 Sea as if in miniature. 



Some original bottom communities of the Gulf of Dvinak may also be 

 noted. Thus, for instance, large colonies of Mesidothea entomon and Macoma 

 baltica, with a biomass of 18 g/m 2 , consisting mostly (86 per cent) of Mesido- 

 thea, live at fairly high temperature in the fresh or almost fresh waters off the 

 Northern Dvina estuary, on sandy bottoms at a depth of 5 to 10 m. A little 

 farther down the Sea lives a community poor in numbers (about 5 g/m 2 ), 

 but characterized by one of its constituents — Portlandia arctica. In some 

 places the Sea is abundantly populated by Mytilus colonies. Portlandia arctica, 

 a relict of the coldest phases of the post-glacial period, is characteristic of the 

 coldest parts of the Arctic basin. It lives in large numbers in the central depres- 

 sion of the White Sea, in the Novaya Zemlya trench, in Sturfjord in eastern 

 Spitsbergen, in the Kara Sea, etc. Special races of this mollusc, which can 

 stand considerable water-dilution and, probably, periodically, a rise of tem- 

 perature, inhabit the estuaries of the rivers flowing into the Arctic basin, such 

 as the Dvina, Pechora, Ob, Yenisey and others. 



It is remarkable that a deep-floor fauna like that of the White Sea, and in 

 particular Portlandia arctica, has remained till this day in comparatively 

 shallow, stagnant gubas along the White Sea shores, and in the never-warmed 

 deep parts. One of these gubas — the Glubokaya Guba of the Great Solovest- 

 kiy Island — served as the object of N. Livanov's fundamental study (1912). 

 Derjugin thinks that the bathymetric fauna must have remained in these gubas 

 since the severe climate period, and that the cold-water fauna, which has now 

 migrated to the depths, at that time populated the whole sea. 'Glubokaya 

 Guba', says Derjugin, 'represents in miniature those properties which, on a 

 larger scale, are found throughout the White Sea, as the relicts of a vast 

 ancient basin. ' 



Productivity 



The great poverty of White Sea bottom fauna is clearly shown by the quanti- 

 tative data given above. This quantitative impoverishment increases 

 gradually with depth, and in the lower sublittoral and the pseudo-abyssal 

 zone the benthos biomass becomes 5-10-15 times smaller than that of the 

 Barents Sea. The average benthos biomass of the White Sea is probably about 

 20 g/m 2 , whereas in the Barents Sea it is 100 g/m 2 . This quantitative impover- 

 ishment affects, as has been mentioned above, not only animal and vegetable 

 organisms, not only the biomass as a bulk, but also the average weight and 



