Figure 5. Population dlatxibution of individual species of plankton during the spring-summer 

 period of 1951. 1. Themisto libellula; 2. Oithona slmilis ; 3. Pseudocalanus 

 elongatus; 4. Aglantha digitale; 5. Oikopleura labradoriensls . 



A small group of organisms which are found in very large quantities during the summer 

 must be mentioned. To this group belong the marine Cladocera (Evadne nordmanni.Podon leuckarti ), 

 Cyclopidae ( Oithona similis) , Calanidae ( Centropages hamatus , C. tipicus , Paracalanus parvus , 

 Acartia clausi, A. longiremis ) and others . In the literature these are described as neritic species 

 (8). However, according to the data available to us, these organisms are found in large quantities 

 in the open part of the sea (central areas of the Norwegian Sea) far from any coast, in areas with 

 varying hydrological conditions . They therefore withstand the various fluctuations in salinity and 

 temperature. They live exclusively in the surface water layers 0-50 m., and mainly in the 0-25 m. 

 layer . They can therefore be regarded as surface species . 



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