al aliquots were used at once for pigment determinations following 

 Strickland and Parsons (I965) and another set preserved with 

 glutaraldehyde for later examination. After incubation, particulate 

 materials were recovered on Millipore filters, washed with Millipore- 

 filtered sea water, dried and counted within 2 days on a Widebeta II 

 planchet system. 



RESULTS 



The mean photosynthetic index was 5.8 mg carbon/hr/mg chlorophyll a. 

 Mean values for acetylene reduction from each of the plankton samples 

 were 8.7, 19- 5? 1^.0 and U8.5 n moles ethylene/hr/mg protein, taking 

 the ratio of cell protein/ chlorophyll a as 30 • 



CONCLUSIONS 



The values obtained average 22.7 n moles ethylene/hr/mg protein and 

 compare with the results obtained with material collected in the Florida 

 Current (Bunt et al. I97O) . Stewart, Fitzgerald and Burris (1968) 

 reported figures between 24 and 282 n moles ethylene/hr/mg protein based 

 on pure cultures of heterocystous blue-green algae. The current data 

 approach this range and exceed rates obtained by Bunt _et al. (1970) 

 with a marine Nostoc sp. Especially when considered in relation to the 

 very low values obtained at the same time with benthic algae, the 

 current results demand attention and call for renewed efforts at achiev- 

 ing laboratory culture of Trichodesmium . 



REFERENCES 



Bunt, J. S., Cooksey, K. E., Heeb, M. A., Lee, C.C. and Taylor, 



B. F. 1970. Assay of algal nitrogen fixation in the marine subtropics 



by acetylene reduction. Nature, 227 , Il63-ll64. 



Dugdale, R. C, Menzel, D. W. and Ryther, J. H. I96I. Nitrogen 

 fixation in the Sargasso Sea. Deep-Sea Research, 7? 297-300. 



Stewart, W. D. P., Fitzgerald, G. P. and Burris, R. H. I967. In situ 

 studies on N2 fixation using the acetylene reduction technique. Proc. 

 Natl. Acad. Sci., 58, 207I-2078. 



Stewart, W.D.P., Fitzgerald, G. P. and Burris, R. H. I968. Acetylene 

 reduction by blue-green algae. Arch. Mikrobiol., 62, 336-3^8. 



IN SITU MEASUREMENTS OF CARBON FIXATION AND TURNOVER IN 



SEVERAL REEF CORALS 



OBJECTIVES 



The relatively few attempted measurements of reef productivity (see 

 review by Stoddart, I969) indicate high rates of carbon fixation 



VI-249 



