306 AQUATIC CLIMAX COMMUNITIES 



Ontario, etc. (Rawson 1928, 1930), Lake Baikal, Leman, and others 

 of comparatively large size.^ These lakes have sufficient circulation to 

 pi'event chemical stagnation and to maintain a bottom primarily of 

 silt (terrigenous), as well as sufficient depth and area to support num- 

 bers of fishes of the types described as river dominants and for a large 

 pelagic assemblage. 



The Great Lakes have been too little studied quantitatively to 

 make possible any adequate description of their bottom communities. 

 Lake Erie, however (Shelford and Boesel, 1939) , offers somewhat of an 

 exception, also the pelagic life has not been described from a com- 

 munity standpoint. In the plankton studies of Eddy (1927), the 

 pelagic animals belonging properly with the plankton were not con- 

 sidered along with it. 



The smaller lakes of Wisconsin (Muttkowski, 1918), Michigan 

 (Eggleton, 1931, 1935), Germany (Lundbeck, 1926), Ontario (Raw- 

 son, 1928, 1930), etc., and most small lakes studied in Europe and 

 America are early stages of land seres. 



Dominants. These are all bottom feeders (Forbes and Richardson, 

 1909; Clemens, Dymond, et al., 1923). 



Acipenser fulvescens Raf. Lake sturgeon 



Aplodinotus grunniens Raf. Sheepshead 



Haustor lacustris (Walb.) Catfish 



Carpiodes thompsoni kg. Lake carp 



Corcgonus dupcijormis (Mitch.) White fish 



Bottom Subdominants. Bottoms off sand-deposition shores, which 

 characterize the south end of Lake Michigan, have an extremely lim- 

 ited fauna in 0-8 meters' depth, and communities hardly exist. Bot- 

 tom conditions are very unstable, as the sand is constantly shifting. 

 1\\ water of 8 to about 35 meters' depth in Lakes Erie, Michigan, and 

 Ontario, a community dominated by snails and sphaerid bivalves oc- 

 curs on a stable bottom composed of fine sand and mud and some 

 organic detritus. In Lake Michigan, abundant individuals of two to 

 four species of Amnicola, two or more of Valvata, and five to ten of 

 Sphaeridae occur together, some of the latter extending down to about 

 100 meters or below. Leeches and worms of the genus Limnodrilus 

 are associated with Mollusca but extend more deeply, and crayfishes 

 are of common occurrence (Shelford, 1913, a; Adamstone, 1924). 

 Midge larvae occur in mucli shallower water and also extend to con- 

 siderable depths. This community gradually thins out toward the 



1 There is much literature on some of the large lakes, but verj' little con- 

 cerned with communities. 



