Succession of Phytoplankton 265 



Vishniac and Riley (55) mention the potential non-biological 

 destruction of thiamine induced by pH and temperature. The 

 photo-oxidation of unsaturated fatty acids present in inert 

 Chlorella extracts leading to antibacterial activity is a notable 

 example of environmentally induced alteration of organic sub- 

 stances (50). 



The discovery that many soil antibiotics are highly unstable 

 under the prevailing pH conditions (22) is undoubtedly repre- 

 sentative of the marine environment as well. Fatty acids appear 

 to be the toxic principles involved in unequivocal cases of algal 

 and bacterial antibiosis (50, 35, 46). These investigators have 

 shown that the toxicity is very pH dependent, short-chained fatty 

 acids becoming highly active at low pH, while alkaline conditions 

 spurred the activity of others. The toxicity of these compounds 

 is markedly reduced near neutrality. Consequently, the high 

 buffering capacity of sea water, which needs no elaboration here, 

 probably represents a most formidable environmental constraint 

 upon the potential activity of this group of compounds. 



Adsorption 



There are numerous substances in natural waters which 

 function as adsorbents, including gels, colloids, tenigenous parti- 

 cles and organisms (43, 16). Admittedly, sorption reactions are 

 dependent upon numerous environmental factors (6) and prob- 

 ably vary in importance throughout a growth cycle. ZoBell (56) 

 has shown that inert solids adsorb measurable quantities, 2 to 

 27 per cent, of organic matter in sea water. Adsorption, which 

 may be considered analogous to an activated charcoal ( self-purif i- 

 cation) process, not only reduces the soluble concentration of 

 organic substances, but increases the likelihood of bacteriological 

 degradation. 



Biological Degradation 



It is well established that marine bacteria require a suitable 

 substrate for development, and that the concentration of organic 

 matter is a principal factor affecting heterotrophic bacterial 

 growth (56). Although adsorbed organic material in clay lattice 

 may be somewhat resistant to biological decomposition (16), ad- 



