102 



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



25' 30° 35° 40° 45' 



25° 30° 35° 40° 45' 



Fig. 37. Sequence of occurrence of 'red Calanus' zones in 

 Barents Sea (Manteufel). Months of occurrence are shown 

 in Roman numerals and days of life in Arabic numerals. 



Sea. A second generation appears only in the extreme southwestern part of 

 the Sea brought in from the west. The so-called 'red Calanus' (fourth to fifth 

 Copepoda stages) which acquires the red tint as a consequence of colouring 

 by some oil drops, has the highest nutritional value. In summer, as reported 

 by B. Manteufel (1941), a kind of wave of the red Calanus passes from the 

 west to the east and north. Calanus reaches sexual maturity in the western 

 part of the Sea in April (Fig. 37) and in the eastern part in August. Moreover 

 the life span of red Calanus decreases from 65 to 75 days in the west to 15 to 30 

 days in the east and its numbers also decrease from west. The herring's most 

 abundant Calanus feeding ground is in the to 25 m layer in the south- 

 western part of the Sea. 



In some years even with a slight rise of temperature and some decrease in 

 salinity of the upper layers of the southwestern part of the Barents Sea 

 Ctenophora, Bolinopsis infundibulum and some medusae (Cyanea, Aurelia, 

 Staurophora) develop in large numbers in July, August and September. If 

 their period of mass development coincides with that of the red Calanus it is 

 devoured in large numbers by Ctenophora and medusa, and its amount may 

 be decreased so much that the herring would not find enough food in such 

 feeding grounds. Coelenterata devour not only Copepoda and other plankton, 

 but they clear masses of water of all living matter. In some years (for instance 

 in 1938) the number of Ctenophora was so great that it is actually possible to 

 assume that all the water of the layer inhabited by the Ctenophora was 

 cleared of the main mass of zooplankton by them. The quantitative ratio of 

 Ctenophora and Calanus in various regions of the sea in 1938 is shown in 

 Table 37. Table 37 



Regions 



1 



Bolinopsis infundibulum None Small number Large number Masses 



Calanus finmarchicus Many Fair amount Small number Very few 



