The Productivity of Fish Food in Oneida Lake 95 



mollusks represent about a third of the entire population in 

 individuals while on gravel bottoms they are relatively more 

 abundant, the numbers of mollusks and associated animals 

 being about e\cn. "fhis greater abundance of animals on 

 gravel bottoms is prol)ably due to a greater variety of physical 

 conditions in this habitat, permitting such animals as the small 

 bivalves to obtain a foothold, the gravel areas containing 8 

 species of Sphaeriidie which cannot thrive on the pure boulder 

 habitats. The boulder bottom area is on the whole much 

 poorer in species as well as individuals than is the grave) 

 bottom, the respective number of molluscan species being 13 

 and 25, or a difference of nearly 50 per cent. It is noteworthy 

 that the same species are dominant in both areas, w^hich really 

 provide the same kind of a habitat, a stony substratum upon 

 which the mollusks may cling. Goniobasis livescens, Galba 

 cafascopiuJii, and Fhysa zvarreniana are the dominant species 

 on the boulder bottoms, and Sphcrrium vermontanum, Atnni- 

 cola oneida, Galba catascopium, Fhysa warreniana, and Flan- 

 orbis parvus are dominant species on the gravel bottoms. The 

 other species present, which are mostly attendant forms, are 

 not conspicuous by their abundance in individuals. 



Among the associated animals, the oligochsete family 

 Naididse, the spiral caddis-fiy larva Helicopsyche, and the 

 amphipod Hyalella are the dominant forms as regards number 

 of individuals on the boulder bottom; while Naididse, Heli- 

 copsyche, Hyalella, and chironomid larvae are the dominant 

 forms on the gravel bottom. Much of the sameness of these 

 two habitats, especially as regards the associated animals, is 

 due to the presence of filamentous algae, principally Spirogyra, 

 Qidoyonlum, and Cladophora, which provide a uniform habitat 

 on both boulder and gravel bottoms. The oligochaete worms, 

 chironomid larvae, Cladocera, and Amphipoda, all inhabit this 

 vegetation as do also Amnicola, some Flanorbis, and young 

 Galba catascopium. The decrease in the number of dominant 

 species, Goniobasis and Galba, in the gravel area, and the 

 increase in Amnicola and Flanorbis is to be especially noted. 

 Corresponding differences in the complexion of the two areas 

 as regards the associated animals will also be noted in the 

 tables. 



