Discussion 



Dr. Sweeney: Dr. Ryther has made clear in his presentation, an 

 understanding of the nutritional requirements of the dinoflagellates is 

 prerequisite to any explanation of the occurrence of "red tides." 

 These organisms have been found to require for growth, substances 

 not present in aged autoclaved sea water and usually supplied by the 

 addition to the culture medium of small amounts of soil extract. In 

 our laboratory, an analysis of the activity of soil extract with respect 

 to the growth of bacteria-free Gymnodinium splendens has shown that 

 soil extract may be replaced by vitamin B12, the optimum concentra- 

 tion being at 0.01 microgram vitamin B12 per liter. Provasoli has 

 shown that the dinoflagellate Gyrodinium sp. also requires vitamin 

 B12. The organic requirements of Prorocentrum micans and Gonyau- 

 lax polyedra appear to be more complex and cannot be met by 

 vitamin B12 alone. 



Gonyaulax polyedra may be grown successfully in mineral-enriched 

 aged sea water with soil extract. Maximum populations reached are of 

 the order of 40,000 cells per milliliter and the generation time is 40 

 to 60 hours. This organism is bioluminescent in culture. (Prorocen- 

 trum micans, Gymnodinium splendens, and Gyrodinium in our cultures 

 are not luminescent.) Because it is both luminescent and photosyn- 

 thetic, Gonyaulax provides interesting material for the study of biolu- 

 minescence. 



4J4 



