COMMUNITIES IN STANDING WATERS 



329 



all, this habitat forms the center of life for both adult and larval 

 insects, 16 which find nourishment and resting places, as well as scaf- 

 folds for climbing in order to obtain air at the surface of the water; 

 in winter the oxygen liberated by plant assimilation gathers in large 

 bubbles under the ice and can be utilized by air-breathing insects with 

 open tracheal systems. Contrary to a condition frequently found in 

 terrestrial insects, the aquatic insects are seldom limited to definite 

 plants; only Stratiotes aloides has its own fauna (the caterpillar of 

 Paraponyx stratiotata, several chironomid larvae, the caddis fly, 

 Agrypnia pagetana, the larvae of the dragonfly, Aeschna viridis) . On 

 the reeds, on stones, tree stems, etc., grow fresh-water sponges and 

 occasionally many kinds of Bryozoa. 



a 





Fig. 95. — Littoral mud-inhabiting copepods: a, Iliocryptus sordidus; b, Rhyn- 

 chotalona jalcata, digging in the mud with its rostrum. X 25. a, after Fric 

 and Vavra, b, after Herr. 



A large number of fishes find rich nourishment in the region of 

 plant growth, and especially a favorable spawning place; for this 

 reason young fishes are plentifully represented in this region. Thus it 

 happens that the degree of development of littoral plant growth may 

 have a marked effect on the fish fauna of a lake. The Konigssee (in 

 Bavaria) without a littoral region, produces annually 1 kg. of fish 

 per hectare; Lake Constance, the fertility of whose littoral region 

 suffers from rather large variations in water level, produces 8 kg.; 

 the Chiemsee (in Bavaria), whose shallow and wide littoral region 

 is well covered with plants, produces about 20-25 kg. of fish 17 per 

 hectare. It is unsafe, however, to generalize too confidently at this 

 point. 



The animal life of wave-beaten shores, where no plants are found, 

 has a faunal composition much like that of swift water in streams. 18 

 A close observer always finds teeming life. Fresh-water sponges grow 

 on the stones in flat, slab-like crusts, while in quiet bays they develop 



