feeding , the vernal flourishing of the development of plankton. 



*i>ny» 



4 5 6 



Plankton composition 



Figure 6. 



A. Biomass of plankton in mg/in3. B. Winter. C. Spring. D. Summer. 



E . Autumn . F . Main plankton complexes . 



Change in the average biomass of plankton when the biological seasons change 

 (material of 1948-1954). 1. "wintering stock" of plankton on the bottom; 2. 

 pre -spawning concentrations of Calanus at the surface (start of the feeding of 

 large herring); 3. "green blooming" of Phaeocystis (the large herring move to 

 the north); 4. "diatom blooming" and the pink fry of Calanus (feeding of the 

 small fry of herring); 5. red Calanus at the surface (feeding of the young fry 

 of herring); 6 . red Calanus descends into the deep (end of the feeding of £ill 

 herring); 7 . development of tiny crustaceans and jellyfish (end of the feeding 

 of all herring) . 



In this connection it must be said that the Atlantic herring is a very plastic organism and 

 easily endures the changes that occur in the environment . 



For instance, when there is a change in the hydro-meteorological conditions, one can often 

 observe considerable deviations in the time of plankton development and a corresponding change in 

 the speed with which herring move from one region to another . 



2. The simultaneous development- -in their areas- -of several different biological seasons 

 is characteristic of the Norwegian and the Greenland Seas as well as of the other northern seas. 

 All the vernal biological processes begin in March- April in the coast and southern regions of the 

 Norwegian Sea, After that, they begin in the waters of the Atlantic current. 



A delay in the vernal development of plankton is characteristic of the regions of eddyings 

 or vortexes between the individual streams of the warm current and of the boundaries of the cold 

 East Icelandic current . TTie delay in the development of plankton in the mixed and polar waters of 

 the Greenland Sea is still greater. 



118 



