258 Marine Microbiology 



Asteromphalus heptactis, at Sta. 4 did not show any indication of 

 light saturation at 8000 lux. The photosynthesis of this population 

 seemed to require much higher intensity of light. This was also 

 true of the mixed population with a boreal oceanic species, 

 Thalassiothrix longissima and a neritic species, Fragilaria striatula, 

 at Sta. 6, of the mixed population with Thalassiothrix longissima 

 and a neritic species Nitzschia seriata at Sta. 7, and of the mixed 

 population with Fragilaria striatula and an oceanic cold water 

 species, Chaetoceros convohitus, at Sta. 10. The photos\Tithesis 

 of the population mainly composed of a neritic species, Nitzschia 

 seriata, at Sta. 13, of the population almost exclusively composed 

 of a cosmopolitic species, Coscinodisciis suhtilis, at Sta. 14, and 

 of the mixed population with Fragilaria siriatuJa and a wide- 

 spread species, Coscinodisciis lineatus, at Sta. 15, did not show 

 any retardation under increasing intensity of light up to 8000 

 lux. 



From the obsen ations made in the course of this study the 

 conclusion can be drawn that under the environments in the 

 northern North Pacific, Chaetoceros dehilis would be light satur- 

 ated in its photosynthesis at about 5000 lux. Tailing (8) pro- 

 posed to use the value, Ik which is equivalent to the light intensity 

 at which in a photosynthesis-light intensity curve, the extrapola- 

 tion of the initial linear region and the light saturated region 

 intersect (7). Ik oi Chaetoceros debilis in the present case corre- 

 sponds to about 3800 lux. The photosynthesis of Fragilaria stria- 

 tula and Denticula marina would be saturated with light at 

 about 8000 lux, while Nitzschia seriata and Coscinodiscus suhtilis 

 require much more intensive light than 8000 lux to attain the 

 maximum activity of photosynthesis. 



REFERENCES 



1. Data Record of Oceanographic Observations and Exploratory Fishing: 



Faculty of Fisheries, Hokkaido University, 5:392 pages, 1961. 



2. Doty, M. S. and Oguri, M.: Selected features of the isotopic carbon 



primary productivity technique. Rapp. et Proc, Verb., 144:47-55, 

 1958. 



3. IcHiMURA, S.: Photosynthesis pattern of natinal phytoplankton relating 



to light intensity. Bat. Mag. Tokyo, 73:869-870, 458-467, 1960. 



