Chapter 26 



Light Assimilation Curves of Surface 

 Phytoplankton in the North Pacific 



42° N — 61° N* 



SiGERU MoTODA and TIeruvoshi Kavvamura 



-Txlthough the activity of phytoplankton may be studied for 

 a single species by placing its pure culture under various arti- 

 ficial conditions, observations on the activity of a natural popu- 

 lation are also useful, because a species in pure culture might 

 act differently from that existing in natural environments in the 

 sea. Moreover, in experiments using pure cultures, the density 

 of population is often far greater than in nature. Observations 

 on natural populations when composed almost exclusively of one 

 species would be most helpful. 



During the Trans-Pacific cruise through the Bering Sea by 

 the training ship, Oslioro Maru of Hokkaido University from 

 June to August, 1960, the present writers had opportunity to 

 make experiments on photosynthetic activity of phytoplankton at 

 fifteen stations which were scattered in the area ranging from 

 42°N to 61°N and from 151°E to 168°W (Fig. 1). The tem- 

 perature of the surface water varied with stations Sta's 1-11, from 

 5.5 C to 7.7 C on the eastbound course, and stations Sta's 12 and 

 13, from 13.4 C to 16.4 C on the westbound course. At these 

 stations, standing crops of phytoplankton in the surface water 

 were studied by counting the number of cells separately by 

 species, and also by measuring photometrically their chlorophyll 

 content. Diatoms comprised the major part of the phytoplankton 

 population in the samples. Microplants other than the diatoms 

 were almost non-existent. 



* This work was supported by the financial assistance provided on Contract 

 AT (04-3) -15 with the U. S. Atomic Energy Commission through Dr. Maxwell 

 S. Doty of the University of Hawaii, and also by funds from the Japanese 

 National Commission for UNESCO. 



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