Excessive growths of phytoplankters may be costly in another 

 way; they may interfere both chemically and physically with the 

 operation of city water systems in which lakes, reservoirs, and filters 

 are involved. Copper sulphate ( Moore and Kellerman, 1905; Domo- 

 galla, 1941; Prescott, 1938), chlorine, sodium arsenite (Surber, 1929; 

 Wiebe, 1930 ) and activated carbon are required to control algae or 

 to eradicate objectionable tastes and odors produced by them. Sand 

 filters are easily clogged by some species of algae such as Melosira 

 spp. and Aphanizomeno7i flos-aquae, and must be cleaned frequently. 

 Recreational sites are ruined and open bathing pools are rendered 

 unusable when phytoplankters take advantage of optimal lim- 

 nological conditions. 



THE FOOD CHAIN 



No single phase of the great cycle of events which occur with- 

 in a water habitat is of greater importance to the main problem of 

 productivity than the one which involves physiological activities 

 carried on by the algal portion of the biota, especially the phyto- 

 plankton. This is particularly true because the phytoplankton is 

 related to the food chain of aquatic animals, especially in lakes where 

 larger aquatic vegetation is scarce. Chandler ( 1944 ) has pointed this 

 out in connection with his studies of Lake Erie. No other group of 

 organisms in a body of water, unless it be the bacteria, can produce 

 such far-reaching effects by fluctuation in quality and quantity. 



This leads to a consideration of the familiar position which phyto- 

 plankton and other forms of vegetation occupy in the food chain of 

 animals. That algae deserve the often applied term, 'pasturage of 

 the sea,' is seldom denied, and it is fairly well agreed that they hold 

 a basic position in the food cycle .of both fresh and salt water 

 animals. 



At the same time, many published studies, beginning with the 

 work of Piitter published in 1909 (see also Petersen and Petersen, 

 1911), have raised a question concerning the degree to which 

 aquatic animals are directly dependent upon phytoplankters. Hardly 

 any of these papers which have pointed out aquatic animals' inde- 

 pendence of phytoplankton made claims that all the microfauna 

 subsists on nutrients of a non-particulate nature. Some students have 

 shown, rather convincingly, that at least certain zooplankters are 

 not directly supported by plants but are able, on the other hand, 

 to take nourishment from colloidal matter, organic debris, and, to a 

 minor degree, from substances in solution. In some such studies 

 nannoplankters have been shown to be the source of food when 



[45] 



