THE ARAL SEA 667 



Amu-Darya delta to 6-0% at the entrance to the Sea. Most of the inlet floor is 

 occupied by a bed of Zostera nana ; in summer there are up to 3,000 stems per 

 1 m 2 . Dengina points out that Zostera 'is of great significance for the zoo- 

 benthos, since it serves as a substratum for the fixation of sessile forms 

 (Dreissena) and as a habitat for the not very mobile forms. Bacterial flora 

 developing on the stems and leaves of Zostera serves as food for cladocerans, 

 insect larvae and molluscs. Zostera is the food of almost all benthophagic 

 fish ; it offers good shelter for the young of commercial fish which float down 

 from the delta waters.' 



Among the bivalves three forms of Dreissena (D. polymorpha, D.p. var. 

 aralensis and D. caspia), Adacna vitrea var. minima and Cardium edule — and 

 among the Gastropoda Hydrobia ventrosa and Theodxus pallasi belong to the 

 highest mass forms. Ostracoda (Cyprodeis littoralis, C. torosa and Hemicy- 

 thera sicula) play an important role in the benthos. 



Among the crustaceans Dikerogammarus aralensis, and among the bryo- 

 zoans Vic tor el la bergi develop in large numbers. The larvae of insects are 

 found everywhere, sometimes in large numbers. The mean zoobenthos bio- 

 mass of the inlet has been determined by Dengina as 11-7 g/m 2 in the spring 

 and 12-2 g/m 2 in the summer. 



The data for the mean benthos biomass of the Aral Sea given by different 

 investigators range from 16 to 18 g/m 2 (Behning) to 21 g/m 2 (Kulichenko) 

 and 23 g/m 2 (V. Nikitinsky). Benthos is most abundant in the Maloe More 

 (owing to Dreissena) and in some areas of the central part of the Bol'shoe 

 More (due to chironomids). Benthos biomass is commonly 20 to 40 g/m 2 . 

 The benthos biomass of the Aral Sea undergoes considerable fluctuations 

 over a period of years (Table 282). 



Table 282. Mean benthos biomass, g/m 2 



Making a general estimate on the basis of the quantitative data of Aral Sea 

 benthos, the three above-mentioned workers do not incline to the view that 

 its benthos is very poor. On the contrary Nikitinsky and Kulichenko believe 

 that the Aral benthos with its high quality as food forms a satisfactory stock 

 of food for the present fish population. 



Thus, in contrast to the Caspian Sea and like our other seas, the Aral Sea 

 benthos biomass is greater on soft bottoms than on hard ones ; this can prob- 

 ably be explained by the peculiarities of both bodies of water and by the 

 conditions under which the different types of soil were formed in them. 



