External metabolites in the sea I47 



be great reserves of nutrient in the bottom deposits but, as the Haskins Laboratories 

 have demonstrated, many algae can tolerate only quite dilute nutrient solutions, and 

 can thrive on them, so long as the necessary free metabolites are present. Perhaps 

 particularly in some " barren " fresh waters, it may be that certain types of ecological 

 development are blocked, just as in some laboratory experiments, by the natural 

 absence of a specific metabolite essential to the life of an essential organism in fish 

 management. 



Such possibilities as these various lines of work indicate may make this field an 

 attractive one to fisheries worker and biologist alike. Certainly, considerable develop- 

 ment can be expected during the next few years. A number of those working in the 

 various fields, however, may possibly have missed something of the community of 

 interest they share with many others. With a few striking exceptions, what now seem 

 to be very relevant cross references are frequently missing from bibliographies. 

 Perhaps this paper may serve to emphasize, where necessary, some of the fundamental 

 features thought to be common to the various investigations. 



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