forms another link In 



Ca(HC03)2 + O2 = H2O + CaCOa + CO2 + O2 



a complex chain of chemical-biological events . 



A still unexplained aspect of algal blooms Is 

 the phenomenon of dominance and succession of 

 species. (An arbitrary index of 33-1/3 per cent of 

 the flora can be used to define dominance) . When 

 a bloom develops, invariably a single species is 

 involved. Aphanizomenon flos-aquae , for example, 

 is never in abundance, or scarcely present at all, 

 when Microcystis aeruginosa is in peak production, 

 and vice versa. Anabaena Lemmermannii com- 

 pletely takes over in some lakes early in the sum- 

 mer and after a week or two, disappears as Gloeo- 

 trichia echinulata assumes a bloom condition . 

 Algal species , like other organisms have their own 

 metabolic rate, time of development and maturation, 

 and then have a decline. No doubt some of the 

 sequences commonly observed of algal species in 

 lakes are related to natural life histories. Also, 

 dominance is related to specific rates of cell di- 

 vision. The fission method used by blue-green 

 algae gives them an 'edge' over more slowly repro- 

 ducing Chlorophyta . 



But at the same time, there are incompati- 

 bilities between species which must be explained 

 other than by differences in life histories. For ex- 

 ample, two lakes within less t.han a hundred feet 

 of one another may at the same time support in one 

 a bloom of Microcystis , in the other a bloom of 

 Anabaena . Or, as in the Yahara River system in 

 Wisconsin, Lake Waubesa in the chain often has a 

 pure'e of Aphanizomenon (as many as 16 , 000 ,000 

 filaments per L.), whereas Lake Kegonsa, about 

 three miles below in the chain, supports a dense 

 bloom of Microcystis . The masses of Aphanizo- 

 menon carried into the lower lake are completely 

 eliminated, and one might say annihilated as de- 

 termined by plankton sample counts from Lake 

 Kegonsa . 



Ideas are expanding in respect to the causes 

 of and explanations for such incompatibilities and 

 successions of species and dominance. Many 

 points are difficult of clarification because of the 

 highly refined chemical analyses that are called 

 for. The best explanation of these phenomena is 

 that there are extracellular by-products produced 

 by one species which inhibit the growth of another, 

 or of others . These by-products well may be 

 classed as antibiotics and, indeed, there is ample 

 evidence to indicate that they are . The sudden 

 'crash' of a dense population of a single species 

 is due to its inability to tolerate its own growth- 

 inhibiting substances . After a growth period when 

 extracellular products have accumulated, it is 

 thought that these act as deterrents and that the 

 plant, in a sense, manufactures its own algacide . 

 The extracellular substances (possibly of a toxic 



nature) have prevented the growth of selected or 

 certain other species, and thereby the plant which 

 begins its development first in a body of water 

 quickly assumes a dominance (depending upon its 

 inherent rate of cell division) . With autodestruc- 

 tion comes a reduction in the inhibitor, thus per- 

 mitting another species or group of species to de- 

 velop. We say "selected" species because when 

 one plant, such as Microcystis aeruginosa , for 

 example, is in dominance, a combination of a few 

 other phytoplankters, relatively sparse in numbers, 

 occurs along with the bloom. The accompanying 

 phytoplankters are mostly species in other phyla of 

 algae, and the species which apparently are elimi- 

 nated are members of the phylum to which the in- 

 hibiting alga belongs. Akehurst (1931) long ago 

 pointed out the succession of oil-producing and 

 carbohydrate-producing algae. The brown-pig- 

 mented algae undergo self-destruction by their own 

 toxins and/or antibiotics, which In turn serve as 

 stimulators to Chlorophyta . Although there is some 

 variability from lake to lake, or region to region 

 (as ecological factors vary) , it has been noted that 

 the same combination of associated species occurs 

 and recurs along with the dominant. Species which 

 are usually associated with Microcystis aeruginosa 

 when this plant is in a bloom condition, are: 

 Anabaena circinalis; Coelosphaerium Kuetzingia - 

 num; Stephanodiscus Niagarae ; Asterionella gracil - 

 lima ; Tabellaria fenestrata ; Ceratium hirundinella . 

 With Aphanizomenon flos-aquae are usually found 

 Anabaena Lemmermannii ; Go mpho s pha eri a aponina; 

 Lyngbya Birgei ; Stephanosphaera Niagarae ; Cosci - 

 nodiscus spp.; Melosira granulata ; Pediastrum 

 spp. 



As mentioned elsewhere, we do not know 

 wherein antibiotics of algae differ from exotoxins, 

 if indeed they are different. From the many studies 

 which have been made , we know that extracellular 

 substances occur in the dissolved organic matter of 

 lakes. In Wisconsin, for example, dissolved or- 

 ganic substances vary from 2.9 to 39.6 ppm . , 

 whereas as much as 300 ppm. have been measured. 

 Secreted nitrogenous and carbohydrate materials 

 from algae have been detected (Bishop eta^, 1954; 

 Fogg, 1951). Some are liberated by autolysis 

 (Aleyev, 1934). Complex proteins , peptides, leu- 

 cine , aspartic acid, tyrosine, and many other sub- 

 stances have been found in the medium of the algae 

 and in bottom deposits (Petersen et al, 1925; 

 Wangersky, 1952). It is among these organic sub- 

 stances that we must search for specific antibiotics 

 and toxins; growth stimulators and growth inhibi- 

 tors, sometimes both, depending upon the concen- 

 tration . 



Laboratory experiments (Pratt, Akehurst, 

 Proctor and others) have demonstrated incompati- 

 bility of two algal species and the inhibition of 

 growth of one plant in the presence of another. 

 Chlorellin from Chlorella vulgaris is a well-known 



25 



