Limited Hetcrotrophy of Some Photosynthetic Dinoflagellates 1 1 1 



present in seawater (0.2-20 mg C/L), if utilized by the algae, 

 might have ecological meaning. 



A few amino acids were tried as N sources. Arginine and 

 asparagine are utilized by the three Gijrodiiiitnu and the two 

 Amphidinium; glycine by the two Ampliidiniiini, G. californicum, 

 and G. splendens; glutamic acid and alanine by the two Amphi- 

 dinium, and G. splendens; the Amphidinium also utilize methi- 

 onine. Growth in amino acids is not better than in nitrate. 

 Asparagine, alanine, glycine, and glutamate, tried as C sources 

 in a medium containing nitrate, were not used by E. cassuhica, P. 

 halticum, and P. chaftoni, either alone or in combination ( 1-10 

 mg%). The three Gywdiniiim behave similarly when each amino 

 acid was added singly ( 10-50 mg% ) ; when the four amino acids 

 were added as a mixture ( 10 mg% each ) growth was increased 

 2 to 3X. A similar increase in growth above the controls was ob- 

 tained by adding soil extract. Complete amino acid mixtures, 

 peptones, yeast and other hydrolysates did not aid growth and 

 often inhibited at low levels (30-100 mg%) — a presumable indi- 

 cation of limited heterotrophic abilities. The Gijwdiniiim and 

 Amphidinium species share with most algae, utilization of 

 glycerophosphate, adenylic, guanylic and cytidylic acids as P 

 sources. 



DISCUSSION 



Even the scant nutritional data available offer some ecologi- 

 cal guide posts. These dinoflagellates, aside from their minute 

 heterotrophic need for vitamins, are, as noted, good photoauto- 

 trophs. The three Gyrodinium reach a total growth of 30-60,000 

 cells/ml in four to five weeks in mineral media enriched with 

 vitamins (ASP2); in the same medium the Amphidinium grow to 

 1-1.5 million cells/ml. That heterotrophic abilities are limited is 

 shown by these observations: 



a) Amino acids utilized as N sources do not elicit more 

 growth than nitrates. 



h) Addition of carbon sources increases growth of the 

 Gtjrodinium modestly (2 to 3 times). 



c) Peptones or various hydrolysates do not enhance growth. 



This limited hetcrotrophy and the ability of most algae to 



