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



function to the previous nitrifying ones and are usually found in all the 

 samples. The nitrogen fixer, the anaerobic Clostridium pasterianum, which 

 sometimes goes down 80 cm into the sea-bed, performs the function of 

 nitrogen accumulation. 



Anaerobic bacteria of methane and hydrogen fermentation of cellular 

 tissue, stimulating the process of carbohydrate decomposition, are of great 

 significance in the decomposition of organic residues in the soil. Large amounts 

 of methane and hydrogen are contained in the mud bottoms of the Caspian 

 shallows. At times these gases bubble up to the surface. A kind of 'boiling' 

 has at times been observed on the dump wrack lying off the Volga estuary, 

 formed by the mass of gas bubbles rising from the bottom. This process is 

 neutralized by micro-organisms which live in the uppermost layer of the 

 bottom ; they require a certain quantity of oxygen for their development and 

 have an oxidizing effect on the compounds of sulphur (sulphur micro- 

 organisms), methane (methane micro-organisms) and hydrogen (hydrogen 

 micro-organisms) formed at greater depths. The column of water is protected 

 from the entry of hydrogen, methane and hydrogen sulphide by the presence 

 of these three groups of micro-organisms in the uppermost layer of the bottom 

 soil. This film, as previously noted, can be destroyed by violent disturbances 

 of the water caused by wind, and the harmful gases may then enter the water 

 and poison it. The slight disturbances common in these shallows bring to the 

 surface of the floor the oxygen required for the development of thioneine, 

 methane and hydrogen micro-organisms, which, besides protecting the water 

 from poisonous gases, give a brown colour to the upper layer of the floor. 

 Deeper down, there usually lie thick layers of black, stinking mud. 



This protective film in its turn serves, according to Voroshilova and 

 Dianova, as a substratum for the development of huge amounts of unicellular 

 algae, which synthesize organic matter. In Butkevitch's opinion life would 

 have completely disappeared from Caspian waters if this bacterial film, with 

 its reducing effect on hydrogen sulphide, methane and hydrogen, had been 

 removed. 



The presence of a huge number of micro-organisms in the Northern Cas- 

 pian (100,000 to 400,000 and up to 17,000,000 specimens per one millilitre 

 of water) had already been recorded by V. Butkevitch (1938). The number of 

 micro-organisms is, as usual, related to the total amount of plant and animal 

 life, or to the amount of decaying organic remains (batkaks). Kriss points 

 out that the amount of micro-organisms in the waters of the middle parts of 

 the Northern, Central and Southern Caspian varies generally between 100,000 

 to 300,000 specimens per 1 ml of water. Below 100 m the amount of bacteria 

 drops to a few thousands (Figs. 274 and 275). According to V. Butkevitch's 

 calculations the biomass of the Northern Caspian micro-organisms is 50 to 

 250 mg/m 3 , and even 1 g/m 3 off the Volga. Kriss, however, says that these 

 values are about twice too high. In the central and southern parts of the 

 Caspian Sea, according to Kriss, if the average biomass of micro-organisms 

 is taken as 36 mg/m 3 (or 7-2 mg/m 3 dry weight) within the layer of active 

 photosynthesis (0 to 50 m), the coefficient of its daily increase is 0-35. The 

 amount of decomposed organic matter will be 11-2 mg/m 3 . In Kriss's opinion 



