Nitrogen Fixing Organisms in the Sea 91 



TABLE 4 



Growth of M.\rin'e Calothrix 

 AT Different Phosphate Concentrations 



Dry wt. 

 g/L 



0.60 

 3.70 

 1.84 



0.72 

 0.44 

 0.16 

 0.06 

 Phosphate in natural seawater is 0. 003-0. 00003mM. 



It has thus been shown that nitrogen fixing microorganisms 

 occur in sea water, often in considerable numbers, and that the 

 available nutrients should permit them to grow and fix nitrogen 

 there. Isotopic studies to determine the amount of fixation actu- 

 ally taking place in the ocean now appear to be called for. 



ACKNOWLEDGMENTS 



Thanks are due to Commander, 12th Coast Guard District, 

 and the oflBcers and men of the cutters MAGNOLIA and WIL- 

 LOW for making possible collection of water samples at the San 

 Francisco Lightship and the Farallone Islands; to the Friday 

 Harbor Laboratory for hospitality; and to Dr. Joel Hedgpeth 

 and Mr. Ward Renshaw for collection of water samples off 

 Bodega Head. Dr. T. J. Starr and Mr. J. C. Murchio assisted 

 with collection and processing of the Guaymas and Friday Harbor 

 samples, and Mr. K. V. Natarajan has participated in the later 

 laboratory experiments. 



REFERENCES 



1. Ahearn, D. G.: Personal communication. 



2. Cooper, L. H. N.: The nitrogen cycle in the sea. /. Mar. Biol. Assn. 



[/.K., 22:183-204, 1937. 



3. DuGDALE, R. C: Personal Communication. 



4. Emery, K. O., Orr, W. L., and Rittenberg, S. C: Nutrient budgets 



in the ocean, pp. 299-309. in Essay in the natural sciences in honor 

 of Capt. Allan Hancock, Southern California Press, Los Angeles, 

 1955. 



