266 Marine Microbiology 



sorbed organics generally provide convenient microscosms for 

 bacterial activity. It is not to be inferred, however, tliat only 

 adsorbed organic matter can be degraded. There is evidence that 

 variable pelagic bacterial communities exist ( 56 ) . Although dead 

 phytoplankters are readily decomposed by bacteria (56), in- 

 creased acti\ ity of natural phytoplankton communities is likewise 

 accompanied by a heightened bacterial response (56, 34). In- 

 deed, Pratt and Berkson suggest that this increased bacterial 

 activity may facilitate further phytoplankton growth through nu- 

 trient regeneration. These data, coupled with the remarkable 

 facility of marine bacteria to degrade a vast spectrum of organic 

 types (56), suggest that the susceptibility of metabolites to bac- 

 terial degradation may severely attenuate their inherent biologi- 

 cal potency. It is difficult to forebear the conclusion that a me- 

 tabolite must also be markedly bacteriostatic ( although the bac- 

 teria are capable of altering metabolites and producing new ones ) 

 beyond that nonnally attributed to sea water and algal metab- 

 olites in order to exert a major influence in succession. 



NATURE OF METABOLITES AND ROLE IN SUCCESSION 



Algal metabolites may be biologically inert, or active as 

 nutrients (36) or more subtle growth regulators (45), being 

 either phyto-toxic or phyto-stimulatory in the latter instance. As 

 growth regulators, they are also auto- or hetero-regulatory. But 

 regardless of their biological influence their ultimate effect is 

 regulation of cell division. 



It must be remembered that the production of active metab- 

 olites is ecologically significant to both the producer and its 

 competitors. Assume a species produces a metabolite which 

 "chemically" affects only its competitors. It is apparent that this 

 species may be ecologically auto-inhibited or auto-stimulated, de- 

 pending on the physical environmental conditions, in that its 

 abundance and duration of occurrence may be curtailed or pro- 

 moted. The nature and regularity of succession suggest, then, that 

 if ectocrine substances are important in this phenomenon they 

 must be intimately related to the temperature, light and nutrient 

 regimes enabling a consistent, predictable ecological response of 

 the producers and reactants alike. Otherwise, an irregular, non- 



