Figure 2. --Distribution of the plankton at the time of the second 

 survey (September 7-23). Notations the same as for figure 1. 

 (Isotherms are for the period September 7-23) 



The northern temperature boundary of the 

 subtropical fauna can be considered the 18°C. 

 surface isotherm in July, and 22°C. for the 

 tropical fauna. 



Thus, judging by the changes in the 

 composition of the plankton and the quantity of 

 its separate components, and also by the size 

 of the biomasa, in the area investigated it is 

 possible to distinguish the following zoogeo- 

 graphical zones or areas of the plankton. 



I. Zone with Calanus tonsus . 



This zone with the highest biomass is 

 regarded by us as the southern boundary of the 

 highly productive North Pacific region. Large 

 volumes of plankton determined by settling are 

 characteristic for this zone as well as its red 

 color caused by the large number pf individuals 

 of Calanus tonsus which have a great deal of 

 fatty substances containing red pigment. 



II. The transitional zone with great 

 quantities of Calanus pacificus . 



This zone lies farther south than the first 

 one and is characterized by the blue color of 

 the plankton sedinnent caused by the presence 

 in the sannples of individuals of the above-named 



species. The content of fatty substance in these 

 crustaceans is significantly less than in Calanus 

 tonsus; the blue color of the sediment depends 

 on general coloration of the body and appendages 

 of the crustacean. 



III. The tropical zone lying south of the 

 transitional zone is characterized by small 

 colorless plankton sediments consisting of a 

 large number of small species of copepods with 

 an abundance of siphonophores, salps, chaeto- 

 gnath worms, and so forth. 



In enumerating the zones of the plankton it 

 is not by chance that we pay attention to the 

 color of the plankton sediments; it very obvious- 

 ly (at the time of collection of the plankton) 

 shows the change from one type of plankton to 

 another. If we were to present a picture of the 

 changes in the plankton encountered as a vessel 

 moves from the Kuriles to the open sea, i.e., 

 roughly from north to south, we would get the 

 following succession of changes in color of the 

 sediments. At the Kurile Islands, very large 

 (in volume) samples of a dark green color 

 ("bloom"). After that, with the same volume, 

 they would become red ( Calanus tonsus ), and 

 with a decrease in the volume a beautiful blue 

 color (Calanus pacificus ), and finally with a 

 sharp decrease in volume of the samples the 



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