The spawning of Calanus usually coincides with the mass-development of the alga Phaeo - 

 cystis . 



In most regions, the mass-spawning of Calanus flnmarchicus is accomplished in a short 

 period. Immediately following reproduction, the large sexually mature Calanus specimens perish. 

 Only their microscopic eggs and nauplii remain in the plankton. Due to this, the biomass of plank- 

 ton is reduced to 80-100 mg/m3. 



The intensive "green blooming" (Phaeocystis) is seldom lengthy. In most cases it is over 

 in 7 to 10 days . 



Development of Phaeocystis begins along the shores of Norway in the latter part of March. 

 "Green blooming" can be observed in April on the Lofoten Banks and in the region of the Norwegian 

 shelf. In May, the zone of "blooming" shifts to the central deep-water regions and to the western 

 regions of the Norwegian Sea. Towards June, the biological spring reaches the boundaries of the 

 Norwegian and Greenland Seas. In July, Phaeocystis is already developing in the north, at the 

 boundaries of the polar waters (Figure 4). 



Diatom development foUows that of Phaeocystis. The former produce the brown "blooming" . 

 The "diatom blooming" lasts longer than the "green blooming". It is longest in mixed waters, in 

 shallows and on shoals . Favorable conditions for the development of phytoplankton are observed 

 where the waters of the Norwegian current touch upon the waters of the East Icelandic and of the 

 East Greenland currents. For the polar waters bring to these places of contact a large quantity of 

 nutritive substances of i^osphorous up to 25-30 mg/mS.-!^ 



In keeping with the exhaustion of the reserves of nutritive substances and the changes in the 

 thermal conditions, some species of algae are replaced by others. In March-April, the "diatom 

 blooming" in coast waters is caused by the mass development of Thallassiosira gravida and Th. 

 Nordenskioldi . After they have died off, there begins the development of Chaetoceras atlanticus , 

 Ch. decipiens, and Ch. borealis. Rhizosolenia styliformis is well -represented in the Atlantic 

 waters in June-July, whereas Chaetoceras concavicornis and Ch. convolutus are represented in the 

 Greenland Sea . 



The 'Tjlooming" of Rhizosolenia and of Chaetoceras always coincides with the development 

 of the roseate or pink and red young of Calanus ( Calanus flnmarchicus of the I-II-III and IV -V 

 copepod stages) . 



The diatoms form a layer of 3 to 5 m. at the surface. Somewhat deeper (down to 25 m.) are 

 the young of Calanus that decrease in quantity with depth . 



The dying-off of diatoms usually coincides with the beginning of the mass development of 

 the medusa or jellyfish Aglantha digitalis in the Norwegian Sea and of the Ctenophora Be roe cucumis 

 and of Bolina infundibulum in the north . About this time, the quantity of plankton in the upper layers 

 of the water Is sharply decreasing, because a considerable part of the crustaceans is being destroy- 

 ed by plankton -feeding fish. Those specimens of Calanus flnmarchicus that survive, namely, those 

 of the in-IV-V copepod stages descend to a depth of more than 100 m. 



Tiny Copepoda, Cladocera develop near the surface, there appear peridinean algae (Perl- 

 dinea) . 



In the southern regions of the Norwegian Sea, it is possible in warm years to encounter also 

 \_l The hydrochemlcal material was received from M. A. Istoshlna. It refers to April, 1954. 



112 



