SUMMARY 



1. Determinations of bacterial increases and 

 C-^Og fixation in surface samples of tropical 

 Pacific sea water contained in cleaned as well 

 as in cleaned and autoclaved 250-ml. reagent 

 bottles incubated in the light indicated that 

 both the bacterial populations and the C-^ up- 

 take were slightly lower in the autoclaved 

 bottles during the first few hours of incuba- 

 tion. The rate of increase of both the bac- 

 terial populations and the Cl^ uptake was 

 greater in the autoclaved bottles after the 

 first few hours and by the end of the l8-hour 

 incubation period their values were higher. 

 However, complete sterilization of the bottles 

 is not considered necessary for determinations 

 of productivity during the eight-hour period 

 generally employed, since the differences were 

 not great . 



2. Dark-bottle fixation of C 1 ^ varied be- 

 tween 15.5 and 21. 6% of light-bottle fixa- 

 tion during test periods up to eight hours 

 and up to almost 50*/o by 37-5 hours, indicat- 

 ing that such controls are necessary for 

 estimating productivity. 



3. Bacterial C fixation was calculated as 

 varying between 3 and 13°/o of the total dark 

 fixation during the first eight hours of in- 

 cubation. The importance of bacteria would, 

 of course, be proportionally les6 in the 

 light. 



h. The bacterial counts as determined by 

 the pour-plate technique were essentially the 

 same in both the light and dark bottles, and 

 there was no indication that either light or 

 antibiotics produced by the phytoplankton were 

 acting adversely on the bacterial populations. 



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