THE SEA OF AZOV 



511 



currents. In this way the combination of currents and soils favourable to the 

 development of the large numbers of larvae carried in by the currents, i.e. 

 soils found red on their journey which either are slightly populated or have 

 been altogether deprived of organisms, creates conditions for the develop- 

 ment of the populations of uniform age which are so characteristic of the 

 benthos of the Sea of Azov. The theory of soil-currents is expounded by 

 the English investigator F. Davis (1924) for the North Sea and is more applic- 

 able to the Sea of Azov than to any other. The distribution of some patches 



Fig. 240. Benthos biomass of the Sea of Azov in a cross section (meridional direction 



from Arbat Banks to Achuev shoal head, which crosses the deep central part of the 



Sea (data of Vorobieff and Mordukhai-Boltovskoy). 



along a circular current in the Sea of Azov seems to confirm this point of 

 view. These patches will move from year to year according to the life-span of 

 the molluscs in the direction of the currents, depending on the distribution 

 of soils and the bottom topography, and then after an interval they will 

 occur again in their old places. Larvae will not be able to develop in places 

 occupied already by a powerful population of some other organism ; they 

 will perish there in masses. Such patches of molluscs will exist for 3 to 4 years 

 if the population neither dies nor is eaten by fish in a shorter time — which 

 may be almost an annual occurrence in the deeper parts of the Sea of Azov. 



General assessment of zoobenthos productivity. A quantitative investigation of 

 benthos and its productivity carried out by Vorobieff and Mordukhai- 

 Boltovskoy enabled the former to calculate the indices of biomass and pro- 

 ductivity of the Sea of Azov benthos with the greatest accuracy possible at that 

 time, both in its total and for the different biocoenoses discussed above and 

 their variants for 1933-35 {Table 214). 



A comparison of the biomass indices of the Sea of Azov with those of other 

 seas shows that the Sea of Azov is in a class by itself. The average benthos 

 biomass of the Sea of Azov was 418 g/m 2 in the autumn, while the average for 

 the years 1934 and 1935 was 313 g/m 2 . 



