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



regions of the most active mixing of waters coincide with the coolest parts of 

 the sea, an erroneous idea of an inverse dependence between the benthos bio- 

 mass and temperature might be formed, since the line of the polar front 

 coincides with a bottom temperature of from 0° to 1 °. The cause of the fall 

 of biomass towards the west should be sought in the more and more 

 difficult upwelling and in the shortage of food, rather than in the rise of 

 temperature. 



As has been noted above, the areas of abundant biomass lie on the lines of 

 the polar front. This is confirmed by a comparison of the charts of currents 

 and of the biomass. The main areas of low biomass (the western and northern 

 parts of the Sea and its central depression) are situated within the centre of the 

 three great zones of cyclonic rotation, but at the meeting place of the alien 

 warm waters and the local cold ones the biomass increases sharply. However, 

 some other interlinking factors are active here. The horizontal circulation is 

 conditioned by the bottom contour ; halistatic areas are formed over the de- 

 pressions and soft mud sediments are deposited there. Poor development of 

 life is the result of somewhat impeded upwelling, an accumulation of carbon 

 dioxide in the bottom layer and of the chemical and mechanical properties of 

 the bed. 



An interesting analysis of the quantitative distribution of the bottom fauna 

 on the Spitsbergen bank has been given by M. Idelson (1930). On the middle 

 parts of the bank, where the bed is washed clean, the fauna is very scarce, 

 most frequently only 1 to 4 g/m 2 . At the edges of the shallow, however, the 

 biomass increases sharply to 1 to 3 kg/m 2 , from 95 to 99 per cent of it epi- 

 fauna. Farther on at the very slope of the bank the benthos biomass is again 

 reduced to 150 to 350 g/m 2 , and then on the mud beds encircling the bank it 

 rises again to 500 to 1,500 g/m 2 . The main factor conditioning this biomass 

 range is the distribution of foodstuffs, mainly organic detritus. The high bio- 

 mass at the edges of the shallow, consisting mostly of epifauna, is conditioned 

 by the presence of rich detritus washed out from the central parts of the bank 

 and brought by water as a solid suspension. Farther on the reduction of the bio- 

 mass is due to conditions unfavourable for the development of the epifauna 

 and infauna. The last increase of the biomass is not due to the infauna, which 

 receives here, in a comparatively calm zone, an abundant amount of sedi- 

 mentary detritus. 



The sum total of the benthos biomass of the whole Sea must be no less than 

 150 million tons of wet weight, i.e. on average 100 g/m 2 . The richest infauna 

 grows on the sandy silts and the silty-sand floors. Epifauna is numerous on 

 hard floors in regions of strong currents. Areas rich in infauna are usually poor 

 in epifauna and vice versa. On the one hand this is explained by the properties 

 of the floor since infauna cannot develop on rocky or cliff floors. On the other 

 hand, in some areas the floor could have given refuge to infauna, but the 

 abundant epifauna has taken all the food supplies ; the bottom may contain 

 large amounts of Porifera spicules and owing to mechanical factors may be- 

 come unfit for benthos habitation. This occurs on the Kildin bank, where finely 

 cartilaginous and sufficiently silted floors give refuge to a rich epifauna, and 

 are almost devoid of infauna. The same picture is observed in the wide belt 



