These observations are apparently at variance 

 with those reported by Steemann Nielsen (1952). 

 The experiment designed by Steemann Nielsen 

 (1952) is difficult to interpret because all of 

 the necessary information is not given. Never- 

 theless, it appears that Steemann Nielsen fil- 

 tered aliquots of tropical surface phytoplank- 

 ton through filters of varying porosity, the 

 coarsest having a maximum pore size slightly 

 in excess of 1 u. In these two experiments 

 no difference in retention was observed be- 

 tween the various filters and Steemann Nielsen 

 concluded that all important autotropic organ- 

 Isms in these samples were larger than 1 u. 



It would seem from the SCOPE experiments that 

 the conclusion of Steemann Nielsen cannot be ap- 

 plied universally. In two of the SCOPE experi- 

 ments only about half of the radioactive mat- 

 erial was retained on the AA filter, with pore 

 size of 0.8 u. There can be little doubt that 

 the amount of material retained on filters of 

 this porosity will vary with the population 

 composition and perhaps its physiological con- 

 dition. While the bulk of the photosynthesiz- 

 ing biomass appears to be in the size range of 

 1-30 u, if an assessment of the total activity 

 in a water sample is desired, it would seem 

 advisable to employ filters with a maximum 

 pore size somewhat less than 0.5 (!• 



BIBLIOGRAPHY" 



Steemann Nielsen, E. .^ 



The use of radio-active carbon (C ) 

 for measuring organic production in 

 the sea. 



J. du Cons., Vol. 28, No. 2, pp.ll7-ll*0, 

 1952. 



71 



