COMMUNITIES IN OTHER INLAND WATERS 369 



without outlet to the sea become salt by concentration though their 

 affluents may be normal fresh-water streams. The numerous salt- 

 water lakes in steppes, the salt swamps of Lorraine, the Dead Sea, the 

 Great Salt Lake in Utah, and many others arise in one or both of 

 these ways. Salt lagoons may also originate by the separation of salt 

 seas from the ocean by narrow dams. These receive their salt water 

 from the ocean, as the salt estuaries of Odessa or the salt lakes near 

 the mouth of the Rhone. The Caspian Sea must at some time have 

 been connected with the ocean. Because of the origin of their salt 

 content, the pools formed by the spray dashing over cliffs also belong 

 to this group. These fill basin-like hollows in the cliffs along the shore 

 and are supplied with salt water whenever the sea is rough. 



The fauna in these salt waters varies according to their origin. 

 Inland waters fed by salt springs are inhabited by animals related to 

 those of fresh waters; marine forms are not definitely known from 

 any of these. In salt ponds of marine origin, on the other hand, a large 

 part of the inhabitants have their origin in the ocean ; but with these 

 are a number of forms which came from fresh waters, such as tur- 

 bellarians and especially the insects. 



The salt content of such waters varies greatly. Thus the amount 

 reported for Lake Aral is 10.7%o, for the Caspian Sea 13%o, for the salt 

 ponds of Salzburg (Siebenburgen) 88%o to 203% , for Great Salt Lake 

 (Utah) 222.4% , for the Dead Sea 231.3%o, and for the Gi'isgundag 

 (Ararat) even 368% . Usually, however, the salt content varies even 

 in similar water basins, according to the weather or the season, or even 

 in longer cycles. In the spray pools along rocky coasts, quiet weather 

 brings about an increase in concentration; storm and rain cause a de- 

 crease. In the salt lakes of the steppe, the rainy season lessens the 

 salt content, the period of drought raises it. The water level of Lake 

 Aral has been constantly rising since 1880, and as a consequence the 

 salt content has decreased from 12%« to 10.7%o. Such fluctuations may 

 influence the composition of the fauna also. During the period of high 

 salt content (222.4% ) only a few small crustaceans live in Lake 

 Urmia (north Persia), but during the wet season it is abundantly 

 inhabited by fishes which enter from its tributaries. 



The influence of salt water on the animals depends on the one hand 

 on the abundance of dissolved salts, and on the other hand on their 

 composition. Daphnia can adapt themselves to sea water with a 

 10.8% o salt content, of which 8% is NaCl. But in pure solutions of 

 NaCl, Daphnia can tolerate a concentration of only 4% . The addition 

 of other salts, therefore, lessens the effect of NaCl, and in such bal- 

 anced salt solutions an animal may tolerate a higher total concentra- 



