Pools, Swamps, and Marshes 



33 



often subjected to extreme variations in temperature, salinity, essen- 

 tial gases in the water, and in available water. In a South American 

 tropical swamp Carter & Beadle (1930) found that fishes survived 

 temperatures as high as 42 °C. during the middle of the day. The 

 plankton animals died when temperatures reached 42° to 43 °C. 

 and were thus often living near their limits of toleration. 



Fig. 5. A salt marsh in Colon, Panama. (Photo by R. H. Arnett, Jr 



As a small body of water evaporates, its salinity may become 

 very high. In Italy, Brighenti (1929) studied the animals in the 

 Mesola salt marshes, which reached salinities as high as 41 grams 

 per liter in summer but were nearly fresh in winter. He found a 

 varied fauna which included ciliates (Tintinnidae) and foramini- 

 ferans (Trochomorpha) . In deeper water were many amphipods, 

 isopods, clams, snails, bryozoans, anemones, and annelids. A few 

 animals ranged from fresh water to the sea — shrimps, anemones. 



