78 COMMUNITIES OF LARGE LAKES 



Other relations are, however, different. As has been stated, there 

 are no truly rooted plants in the bottom of Lake Michigan. Those 

 attached to the bottom are not rooted in the way that land plants are. 

 The things which land plants get from the soil are supplied to the aquatic 

 plants by the water itself. The same is true of the bottom animals; 

 food is floating in the water in quantities and can accordingly be secured 

 without effort, and some animals have the form of plants and simply 

 depend upon the food which may be brought within reach by accident. 



Classification of bottom formations: Bottom formations are de- 

 termined by depth (and associated phenomena) and bottom. Bottom 

 is of greatest importance in shallow water (less than 8 meters). Its 

 importance is inversely proportional to depth. 



Within the zone of wave-action conditions are somewhat different 

 than below it. Here the kind of animals is determined by (i) strength 

 of wave-action, (2) erosion and kind of material eroded, and (3) deposi- 

 tion, and animal communities may be classified as those of (i) eroding 

 rocky or stony shores, (2) depositing or sandy shores, and (3) pro- 

 tected situations. 



a) Eroding rocky shore sub-formation (80, 81, 82, 83, 84) (Stations 

 ia, 2; Table XV). There are a considerable number of rock outcrops in 

 the bottom inside the 8-meter (26 ft.) line, between Gross Point and the 

 mouth of the Calumet River at South Chicago (61). As we shall see 

 later, these are of great importance to the animals of the lake. However, 

 the communities of such situations are known to us only through the 

 study of the very shallow water in the vicinity of Glencoe. Here, attached 

 to the rocks by their silk, are caddis- worms (Hydropsyche). (Mr. W. J. 

 Saunders has given me specimens of Parnidae (Psephenus) and stone-fly 

 nymphs (Perla) taken from Lake Ontario at Kingston, Ontario.) All 

 these ordinarily live in swift streams. Under the stones and among 

 the algae attached to them are amphipods (Hyalella knickerbackeri) 

 and May-fly nymphs (Ephemeridae) , but so far as we have been able to 

 record these are the only forms common here. The animals avoid the 

 waves by creeping under stones or are attached to withstand wave- 

 action. The lake trout (Fig. 20) is known to breed on the rocks off 

 Lincoln Park. These rocks are then of considerable importance to the 

 fish. Some species of small fish may be common here, but they have 

 not been studied. 



b] Sandy depositing shore sub-formation, 0-8 meters (26 ft.), shifting 

 sand bottom (Station 3; Table XII). On the open shore inside of 1.5 

 meters (5 ft.) of water we have found nothing on the bottom. From this 



