antibiotic to some other species of algae, and It 

 has been found further (Pratt and Fong , 1942; Rice, 

 1954) that two species may be mutually antagonis- 

 tic. Rice used varying concentrations of Nitzschia 

 and Chlorella and by evaluating growth rates he de- 

 termined that there were varying degrees of mutual 

 inhibition. His findings, when applied to condi- 

 tions in nature, could explain seasonal fluctua- 

 tions. Sampaio (1946) discovered that Closterium 

 acerosum produced an antibiotic to species of bac- 

 teria, especially Bacillus subtilis . Pandorine from 

 Pandorina morum produces marked effects and ab- 

 normal shapes in Scenedesmus ; whereas scenedes- 

 mine III inhibits completely the development of 

 Pediastrum Boryanum . Not exactly pertinent, but 

 of interest, is the fact that Elodea and Potamoqeton 

 foliosus in Wisconsin were found to produce anti- 

 biotics which inhibited populations of phytoplank- 

 ton and rotifers . 



Laboratory experiments by Proctor, and by 

 Lefevre and his co-workers have clearly demon- 

 strated antibiotic effects of algae. In Proctor's 

 work (1957) two closely related species of green 

 algae were employed — one inhibiting the growth of 

 the other. His supposition is that antibiotics are 

 located in unsaturated fatty acids liberated from the 

 algae. The hypothesis is advanced that antibiotics 

 interfere with oxidation of nutritive substances, 

 and that they interfere with chlorophyll behavior . 



Both Microcystis and Chlorella secrete sub- 

 stances active against Staphylococcus and Clostri - 

 dium , and it is thought highly possible that many 

 other species of algae have the same capacity. 



Antibiotics may even have Inhibitory effects 

 on fish . In Europe it was found that the fish Gor- 

 donus rutilus was stunted in habitats dominated by 

 Aphanizomenon . 



If one allows a plankton collection domi- 

 nated by Aphanizomenon to stand in the laboratory 

 for a time , Ankistrodesmus , Pediastrum and Oocys - 

 tis will flourish after the dominant has died . As 

 long as the Aphanizomenon is alive, it completely 

 inhibits development of the other plankters . 



The idea has been advanced that by-products 

 of one species, or the substances characteristi- 

 cally produced by one phylum of the algae, actually 

 serve as stimulators to another species or to a 

 group of species belonging to another phylum. Thus, 

 the death and destruction of one protoplasmic mass 

 frees substances that are veritable fertilizers for 

 other algae. In the research on this facet, the sur- 

 face film over a great sea of ignorance has been 

 punctured only in a few places . Most of the 

 studies on stimulators has been done with marine 

 organisms and their ecology, but some investiga- 

 tions have been carried out using fresh-water algae. 

 In any case, results and implications are appli- 

 cable to fresh-water algae and their ecology, and 

 to the determination of blooms . 



The present state of our knowledge concern- 



ing growth stimulators has been derived largely 

 from culture studies which, because of their arti- 

 ficiality, introduce an element of questionability 

 when laboratory-derived concepts are applied to 

 situations in nature. Possibly Pringsheim (1921) 

 was the first to recognize and to publish on growth 

 stimulators in the form of acetate-peptone and 

 acetate-ammonium present in his soil-extract cul- 

 tures of Polytoma spp. and other unicellular forms. 



Since then Hutner and his co-workers in- 

 cluding Provasoli, Lwoff and co-workers, Lewin, 

 Starr and others have determined the existence of 

 growth stimulators and have used microorganisms 

 for their assay. These workers have found that 

 6^2 is an essential requirement, especially for 

 Dinoflagellata . In fact, the seeming universality 

 of the demand for B12 by algae has led Provasoli to 

 postulate that this factor alone might be a deter- 

 miner of algal blooms . Inferential but strong evi- 

 dence for this is to be found in the appearance of 

 marine blooms in coastal waters periodically fol- 

 lowing rainy seasons and floods which wash large 

 amounts of B]^2 i^^^ other growth promoters) into 

 the sea. Thus the death-dealing red tide may be 

 related to B,, increment because these blooms seem 

 to follow periods of flooding . 



Measurements have shown that B12 occurs in 

 marine waters such as Vinyard Sound (0.03 to 2.0 

 iig/L). near Nova Scotia (O.Ol^ag/L), at Millport 

 Marine Station (0.005 to O-Oljag/L). These 

 amounts are apparently normally present (and well 

 they should be if they are as critical as observa- 

 tions indicate; otherwise there would be no coastal 

 phytoplankton) . Robbins , Hervey and Stebbins dis- 

 covered that in one fresh-water habitat the 8^2 

 varied greatly seasonally from 0.1 to 2.0^g/L. 

 Hence in lakes receiving pollution or where B12 

 analogues can be formed by bacteria, it is possible 

 for blooms to develop. This would be especially 

 true for species whose requirements for growth pro- 

 moters are not highly selective. They would have, 

 therefore, an advantage over competing organisms, 

 the requirements for which are highly specialized . 



It has been shown that there is a specificity 

 for various analogues of B12 which are produced by 

 bacteria. Thus the activity of these microorganisms 

 is caught up in the complex cycle of exchange of 

 metabolites. Provasoli, for example, reports Am- 

 phora spp . , Skeletonema sp . (diatoms) , and Phorm- 

 idium (a blue-green genus) to use all cobalorains, 

 including factor B (one of the fractions of 8^2) ■ Two 

 dinoflagellates were found to require factors A, H, 



Bj2/ arUficial B^2 ^"^^ ^12"^^^' ^^^ ^^"^^ "°^ '"^~ 

 sponsive to pseudovitamin 822- 



What such specificity means in respect to 

 our present consideration is that the appearance 

 and disappearance of algal populations and bloom- 

 producers are related to growth promoters and vita- 

 mins . Thus, both the regular sequence of peak 

 populations of different groups of algae, and also 



26 



