BIOLOGICAL DISTURBANCES RESULTING FROM ALGAL POPULATIONS 

 IN STANDING WATERS 



G. W. Prescott 

 Michigan State University 



Nowhere can there be found more striking ex- 

 amples of interactions between, and interdepend- 

 ence of organisms in nature than in the ramifying 

 effects produced by algal populations . The roles 

 which these plants play in aquatic biology and in 

 limnology are clearly recognized but often incom- 

 pletely understood. Whereas the place of algae in 

 nature may involve some benefits to man and to 

 other organisms , some of the effects produced are 

 radically and offensively disturbing, sometimes 

 costly and even lethal. The putrefying masses of 

 algae in recreational lakes and in water supply 

 reservoirs are aesthetically disturbing and econom- 

 ically aggravating . But of greater importance are 

 the indirect and far-reaching effects algae have on 

 other aquatic organisms, including their ability to 

 kill. 



It is from populations of algae in standing 

 water, of course, that effects are most obvious 

 and most disturbing because concentration of num- 

 bers of individuals is possible. To be sure, some 

 of the same disturbances occur in slowly flowing 

 waters which have ecological conditions condu- 

 cive to bloom- forming algae. We are not primar- 

 ily concerned with marine waters here, but it is 

 appropriate to recall that some of the same effects 

 are produced by algae in the sea (Red Tides; fish 

 poisoning) . 



It is well-known that of the countless 

 species of fresh-water algae, only a few produce 

 disturbances which attract our attention. These 

 belong almost entirely to three phyla, the Cyano- 

 phyta, Chrysophyta, and Pyrrhophyta . The 

 species with which the present subject mostly 

 deals are listed for reference. It will be recog- 

 nized immediately that these are mostly so-called 

 "bloom "-producing species. 



Ill . Pyrrhophyta 



Gymnodinium brevis 

 G . veneficum 



Ceratium 



hirundinella 



I. Cyanophyta 

 Microcystis 



aeruginosa 

 M . toxica II . 



Coelosphaerium 



Kuetzinqianum 

 Oscillatoria 



rubescens 

 O. lacustris 

 Anabaena circinalis 

 A . flos - aguae 

 A . Lemmermannii 

 Anabaenopsis 



Elenkinii 

 Nodularia spumigena 



Aphanizomenon flos - 

 aguae 



Chrysophyta 

 Dlnobryon sertularia 

 D . sociale 

 Svnura uvella 

 Fraqilaria spp. 

 Tabellaria fenestrata 

 Asterionella gracillima 

 Coscinodiscus spp . 

 Melosira aranulata 

 Stephanodiscus 

 Niaqarae 



When the algae guilty of causing disturb- 

 ances are examined and their ecology analyzed, a 

 few generalities appear: 



1 . Disturbances occur in waters which are 

 enriched with phosphates and nitrates; usually the 

 algae occur in bloom condition, and the disturb- 

 ances arise in relatively shallow lakes where it is 

 possible for nitrates and phosphates to be recircu- 

 lated from bottom decomposition. 



2. Excessive and troublesome growths can 

 occur only in lakes which are amply supplied with 

 CO2 or with bicarbonates from which carbon di- 

 oxide necessary for photosynthesis can be ex- 

 tracted . Hence, hard water lakes support blooms, 

 whereas soft water or acid lakes are spared. 



3 . Most of the adverse effects of algal 

 blooms occur when one species dominates in a 

 standing body of water . A population density in- 

 volving one species is often followed by succes- 

 sions of other dominants in a repeating sequence. 



4. The most drastic and often lethal effects 

 of algal blooms appear in a curious distribution in 

 both the Eastern and the Western Hemispheres. 



5 . The disturbing effects of algae are both 

 directly and indirectly produced . 



6 . Effects are mostly related to algal physi- 

 ology, but in some instances the simple morphology 

 of algae is involved. 



ECOLOGICAL CONDITIONS 



Some of these generalities can now be con- 

 sidered in limited detail to illustrate the inter- 

 actions of those factors which are responsible for 

 algal disturbances. 



First to be considered are the conditions of 

 the environment which are responsible for super- 

 abundant algal populations . Of all the nutritive 

 elements and dissolved substances known to be 

 used by algae, those which are most often control- 

 ling or critical are phosphorus and nitrogen. Phos- 

 phates and nitrates are essential nutrients for all 

 chlorophyll-bearing organisms; but when these are 

 present in unusual quantities, a lake can support 

 tremendous populations of algae which recur year 

 after year. Those who are familiar with the lakes 

 in north mid-America know the relationship between 

 polluted lakes and algal blooms . This relationship. 



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