The Prodiictivily of Pish Food in Oiicida Lake loi 



poiiance of investigations of this kind at different seasons of 

 the year is thus shown. 



There is an increase in number of species from boulder to 

 sand bottom. Thus the boulder bottom contained 13 species 

 of mollusks and 30 associated animals, the gravel bottom 25 

 species of mollusks and 26 associated animals, and the sand 

 bottom 33 species of mollusks and 61 associated animals. It 

 is noteworthy that the greatest number of species occur where 

 there is a heavy growth of filamentous algae, principally 

 (Edogonium and Cladophora, and where these plants are absent 

 little life is found. Thus in Habitat No. 35, where the alga 

 CKdogonium occurred in masses, .302 mollusks were found, but 

 in Habitat No. 122, where no algae was collected, only three 

 mollusks were found. The influence of this plant is at once 

 apparent when fresh 'material from a unit area is examined. 

 Upwards of seven species of filamentous algae were collected 

 from the sand bottom, together with a number of the gelatinous 

 blue-green species. A study of the table will bring out many 

 other points which cannot be dwelt upon at length. 



Life on the Clay Bottcm. The unit areas examined on the 

 clay bottoms were the same as on sand bottoms, 16 s(|uare 

 inches. The clay bottom is comi)osed of two types of soil, 

 ty])ical clay and a clay more or less mixed with sand of varying 

 degrees of fineness. From the ty[)ical clay bottom, material 

 was collected from 88 units (liable No. 19). The molluscan 

 life totalled 629 and the associated animal life 1,397 individ- 

 uals, the mollusks forming less than a third of the total animal 

 life of 2,026 individuals. Per unit area, the mollusks average 

 7.14 and the associated animals 15.87, a total of 23.02 indi- 

 viduals per unit area. As there are 87 acres of clay bottom, 

 the total animal population is calculated to be 785,222,404, of 

 which mollusks are 243,766,159 and associated animals 

 541,456,245.* (See figures 31-33 for illustrations of animal 

 life of the clay units.) 



* The computations for ihc clay bottom are as follows: 43,560 X 

 144:^=6,272,640 square inches in one acre; X 87 = 545,719,680 square 

 inches in 87 acres; -^16 = 34,107,480 unit areas in 87 acres; X 7.14 

 mollusks per unit area = 243,766,159 mollusks. 34,107,480 X 15.87 asso- 

 ciated animals per unit area ^ 541,456,245 -j- 243,766,159 = 785,222,404 

 total animal population. 



