The Productivity of Fish Food in Oneida Lake 151 



study of fresh-water animals. Writing of the comparison of 

 the animals of Danish marine waters with those of other 

 localities he says: " It would indeed have been difficult to do 

 so with the old method of investigation, based as it was upon 

 dredging, and with separate treatment of each group of ani- 

 mals, which furnished no comprehensive view, but merely a 

 series of long lists of the different groups. We know now, 

 however, that it is only by investigation of the communities 

 themselves that it is possible to arrive at a true comparison 

 which furnishes a proper idea of the respective conditions. 

 One might easily imagine two waters exhibiting approximately 

 the same list of species, but yet differing in a very high degree; 

 the frequency with which individuals of the various species 

 occur forms a factor which cannot be disregarded." 



This statement is not only true for comparative localities 

 but holds good for different depths of the same locality ; thus, 

 we find listed the name of Amnicola oneida from two depths, 

 4 and 15 feet, but in the shallow water, its more usual habitat, 

 89 individuals occur in a unit area, while in the deeper water 

 habitat only one was found. Many examples could be cited 

 illustrating this fact showing that a mere list does not give a 

 correct idea of the relations of the animals of the community. 



Among the striking results obtained by the field study of 

 Lower South Bay are the relation of the mollusks to the 

 physical and general biological features of the area. 



I. Relation to Algae. One of the surprising things 

 revealed by the detailed examination of the bay was the vast 

 amount of filamentous algse covering the greater part of the 

 bottom and also the higher plants, from shore to deeper water. 

 Among these are 10 species of QLdogoniiim, two of Ulothrix, 

 two of Spirogyra, and a Cladophora. The' plankton forms 

 were also abundant. In this filamentous alg^e the mollusks 

 live in great numbers finding here unlimited quantities of food. 

 A small cjuantity of Cladophora or CEdogoniiim would fre- 

 quently form a tangled mass of mollusks, worms, insect larvae, 

 and crustaceans, the whole affording a tempting diet for bot- 

 tom-feeding fish. The abundance of this algal food caused all 

 of the mollusks, worms, and chironomid larvae living in it to 



