SECT. 2] ORGANIC REGULATION OF PHYTOPLANKTON FERTILITY 183 



(Fries, 1959), Bangia fusco-purpurea and Antithamnion sp. (Provasoli and 

 Iwasaki, unpublished), need B12 for growth. 



Folic, folinic, pantothenic and nicotinic acids were also measured in sea- 

 weeds. The content of vitamins in seaweeds varied seasonally, and in the 

 younger and older parts of the thallus (Ericson, 1953; Ericson and Carlson, 

 1953). Larsen and Haug (1959) found a correlation between salinity and the 

 nicotinic acid and biotin content of Ascophyllum nodosum and Fucus vescicu- 

 losus ; vitamin maxima occur in lower salinity and do not seem to depend on 

 pollution carried in by fresh waters. 



Whatever the origin of vitamins in seaweeds, the vitamins are bound to be 

 released in coastal waters either by excretion or decomposition of the seaweeds 

 — indirectly, more vitamins probably are produced by the bacteria decomposing 

 the immense quantities of dead seaweeds in the tidal zone. 



Phytohormones ("X" and "Z") biologically active on Avena coleoptiles were 

 found in phytoplankton samples (predominantly diatom) ; zooplankton samples 

 showed high activity, on chromatography, in the indoleacetic zone (Bentley, 

 1958, 1959). 



D. Antibiotics 



The reciprocal exchange of vitamins is one aspect of the interaction amongst 

 organisms. Another is the production of antibiotics. Co-operation and conflict 

 amongst organisms at the macroscopic level, especially for land plants, is an 

 important branch of ecology. The same phenomenon, but at the chemical levels 

 of antibiosis and growth promotion, is neglected. The possible biological and 

 ecological importance of these phenomena is discussed boldly by Burkholder 

 (1952) and Brian (1957). The high solubility of many biologically active 

 substances peculiar to the water environment permits rapid exchange of meta- 

 bolites but it also limits their effectiveness through dilution ; therefore, only 

 substances active at extreme dilutions (10~ 15 ), such as vitamins, are eligible 

 for ecological importance. The antibiotics, at least those now known, are 

 effective at much higher concentrations (10 _6 -10~ 9 ); one wonders if they can 

 play an important part in the free water environment. Their action may, how- 

 ever, be quite significant when the dilution factor is minimized, as in symbiosis, 

 cohabitation and parasitism. One example is the relationship Phaeocystis- 

 euphausids-Antarctic birds described by Sieburth (1958, 1959); a similar 

 condition may be responsible for the antibiotic effect of corals (Burkholder and 

 Burkholder, 1958a); the production of antibiotics by seaweeds (Chesters and 

 Scott, 1956) may affect the kind of epiphytic flora normally present in seaweeds. 



The sea may become a grab bag of medicinals, but the data obtained for 

 these practical motives, e.g. measurements of pathogen -active antibiotic 

 production by marine organisms, obviously lack ecological meaning. Screening 

 procedures are based generally on sensitive terrigenous bacteria followed by a 

 screening on human pathogens. To have any ecological significance, the initial 

 screening should be based on an assay with sensitive marine bacteria, and 

 later on the ecologically important bacterial species. But we cannot say now 



