Il8 BULLETIN OF THE BUREAU OF FISHERIES. 



Mussels and other animals grow more plentifully in regions of water where, with 



other conditions favorable, there is a proper gas content — abundant free oxygen and 



limited amounts of carbon dioxide. Such places are near zones of wave action in 



lakes and in rapids in streams, where the influence of green plants is felt, and where water 



circulation is good. 



VEGETATION. 



In many lakes and streams in protected locations rooted plants occur in more or 

 less abundance. If this vegetation is of open character, not producing a heavy shade, it 

 frequently harbors an extensive mussel fauna (Baker, 1916, pp. 94 and 95). This kind 

 of habitat is especially favorable to manj^ fishes," and to this fact in part may be attrib- 

 uted the presence of mussels, since the young mussels upon leaving the fish, having 

 small power of locomotion, will remain where they fall if the habitat is at all suitable. 

 Since mussels are found in abundance where there is no vegetation, as in rivers like the 

 Mississippi, and generally are conspicuously absent from dense growths, it would seem 

 that the association with rooted plants is largely incidental. There is other direct 

 evidence to indicate that mussels of such habitats are those that are parasites upon 

 species of fish that have a preference for such an environment. 



Shira's observations in Lake Pepin (unpublished manuscript) indicated a certain 

 association of juvenile mussels and vegetation, since 94 per cent of the juvenile mussels 

 taken in a survey conducted in 1914 were taken in situations where more or less vegeta- 

 tion was encountered. On the other hand, he found juveniles at as many stations 

 without vegetation as with it. As the result of many observations he concluded that a 

 dense growth of vegetation was distinctly unfavorable to the survival of young mussels, 

 and he suggests that the association of juvenile mussels with vegetation may be partly 

 due to the fact that environments marked by the presence of aquatic plants are attractive 

 to fish. He also observed that a given area of bottom supportive of mussels might 

 display a heavy growth of aquatic plants one year but be practically or entirely free 

 of them in another year. The same author has observed relatively dense growths of 

 vegetation on mussel beds in Lake Pokegama. 



It has frequently been observed in lakes that mussels live abundantly in patches of 

 Chara, a low-growing green plant usually containing a considerable proportion of 

 calcium carbonate. In the Grand River, Mich., Coker noted that mussel collecting was 

 invariably poor in the midst of abundant rooted plants. The principal species found 

 in such localities were the floaters {Anodonta grandis) , the fat mucket {Lampsilis luteola), 

 and the pink heel-splitter (Lampsilis alata). The mucket {Lampsilis ligamentina), and 

 other species were likely to be found in the vicinity of rooted aquatic plants. 



As quoted on page no, above, Wilson and Danglade (1914, p. 15) described the 

 finding of mussels beneath layers of algae and weeds in Minnesota streams. 



It must be remarked that rooted plants are not the only ones that contribute to the 

 oxygen supply and to the depletion of the carbon dioxide of the water. There are 

 thread algae and innumerable microscopic floating plants which play an important if 

 not the most important part in oxygenation of the water, and these are widely dis- 

 tributed in all zones to which sunlight penetrates. 



o "LitUe fishes and Uie greater number of mature fishes keep' more or less closely to the shelter of shores and vegetation" 

 (Needham and I,loyd, 1916. p. 23). 



