112 Marine Microbiology 



utilize some organic P compounds shows that complete minerali- 

 zation is not necessarily needed for their nutrition. Even incom- 

 plete mineralization permits a more rapid cycling of the N and P 

 sources; this is particularly important for phosphorus which is 

 often limiting, or close to limiting. 



Because of the need for media permitting isolation and culti- 

 vation of the greatest variety possible of marine algae, emphasis 

 has been to find metabolites and concentrations good for all. The 

 successes so far may encourage the conclusion that algae have 

 much the same requirements. This is only partly true. The ability 

 of all to utilize some organic N and P compounds and to require 

 only three vitamins should be viewed only as a widening of the 

 number of metabolites (i.e., ecological factors) for which the 

 algae compete. 



Species do bloom and succeed one another — an obvious sign 

 of diversity in requirements and tolerances for various physical 

 and chemical factors. Biotic and antibiotic interactions as well 

 as the nutritional factors may here be important. Competition 

 experiments in common media or differential enrichments of 

 natural waters containing their living flora are needed. Thomas 

 (18) obtained in the same sample of water early growth of 

 diatoms followed by late growth of a Cymnodinium when he 

 added a complete enrichment (N, P, Si, trace elements, soil 

 extract); the diatoms failed to grow when Si or the trace metals 

 were omitted, but Gymnodinimn grew. Jolmston (7) enriched 

 many samples of seawater with N, P, Si, and chelated trace 

 metals; this enrichment favored the growth of spring diatoms in 

 all samples while the dinoflagellates, even when abundant in 

 the natural inoculum, failed to grow. Is this to be interpreted only 

 as an antibiotic effect? Silica favors the growth of diatoms; do 

 the diatoms then excrete substances inhibiting the dinoflagellates? 

 Although the most evident factor may be an antibiosis, the dia- 

 toms may be favored, besides silica, by a differential tolerance and 

 need for the other constituents of the enrichment. Needed now 

 are detailed comparisons of the requirements and tolerances of 

 the organisms. 



REFERENCES 



1. BiECHELER, B.: Recherches siir les Peridiiiiens. Bttll. Biol. Fiance et de 

 Belgique. Suppl. 36: pp. 1-149, 1952. 



