Ecology of Algae, Protozoa, Fungi and Viruses 33 



deal of work has yet to be done before we can assess the theories 

 on tliis subject. Smayda's reference to the importance in biological 

 succession of rhythms and physical and chemical factors is timely, 

 but I do not think we know enough about any of them to place 

 them in order of importance. It may well be that some external 

 metabolites are effective in the heterotrophic growth of phy- 

 toplankton below the photic zone, and we have seen in the 

 various papers of this session some of the ways in which this 

 could happen. And remember that persistence in a relatively 

 unfavorable environment is a powerful weapon to an organism 

 struggling to maintain its position in a succession. 



In theory, a dearth of inorganic nitrogen compounds should 

 encourage the growth of nitrogen-fixing species, and may well 

 account for the massive blooms of Trichodesmium in the tropics 

 and of the Nostocaceae recorded by Bernard. But we have no 

 information regarding the nitrogen content of these waters due 

 to the reluctance of hydrologists to analyse for anything other 

 than nitrates and nitrites. As many phytoplankton organisms grow 

 better when amino acids are present in addition to inorganic 

 nitrogen sources, it is probable that such amino-acids are exten- 

 sively utilized. Do "red tides" of Trichodesmium become mono- 

 specific by monopolizing available food, by deterrent exocrines 

 or by spatial crowding? Speculation cannot avail us here. Obser- 

 vation and experimentation are required to solve this problem, 

 the answer to which may have extensive application. 



Inhibition of growth by metallic ions may be controlled by 

 the ability of certain microorganisms to chelate these substances, 

 e.g., the chelation of iron in the pectinoid sheatlis of diatoms as 

 observed by Baas Becking and Mackay (1). 



SORPTION 



Smayda and Wood, Chapter 27, 24, botli referred to sorption 

 phenomena in somewhat different connections. It is not always 

 possible to demonstrate the surface phenomena associated with 

 adsorption when two organisms or an organism and a particle ad- 

 here to each other. At the same time, there is evidence that ad- 

 sorption is an important phenomenon in the oceans, and that, 

 when the smaller phytoplankton elements adhere to particles. 



