crayfish ( Procambarus alleni ) (Kush- 

 lan and Kushlan 1979a), the freshwa- 

 ter prawn ( Paleomonetes paludosus ) 

 (Kushlan and Kushlan 1979b), and 

 the apple snail ( Pomacea paludosa ) 

 (Kushlan 1975). Unfortunately, lit- 

 tle is known of the important and 

 pervasive aquatic and terrestrial 

 insects which form a key link in 

 the energy flow of this ecosystem 

 (Hofstetter 1973). 



The crayfish ( Procambarus 

 alleni ) is particularly common in 

 the Everglades marsh ecosystem, 

 reaching a maximum standing crop of 

 4.0 Kcal/m^ and a maximum average 

 of 1.6 Kcal/m^ in water 25 cm 

 (10 in) deep (Kushlan and Kushlan 

 1979a). The maintenance of high 

 population levels of crayfish is 

 believed to be closely tied to sea- 

 sonally oscillating water levels. 

 Extensive dry periods take their 

 toll on this facultative burrower 

 through increased desiccation of 

 ground water habitat. Extended high 

 water levels are usually accompanied 

 by increased fish production, espe- 

 cially of larger predators which 

 consequently consume greater numbers 

 of crayfish (Kushlan 1976). 



Trophically, the crayfish is a 

 grazing detritovore whose main 

 source of food is periphyton. On 

 the other side of the trophic spec- 

 trum, the crayfish comprises 75% of 

 the food of the Everglades bullfrog 

 (Ligas 1960), 32% of the food of 

 juvenile alligators (Fogarty and 

 Albury 1968), and 51% of the food of 

 white ibis (Kushlan and Kushlan 

 1975). Other predators include num- 

 erous fish, birds (American bittern, 

 pied billed grebe), and mammals 

 (raccoons, river otters). 



Population levels of the prawn 

 ( Palemonetes paludosus ) show a simi- 

 lar response to fluctuating water 

 levels. High water apparently in- 



duces increased predation through 

 changes in the fish numbers and 

 composition. Like the crayfish, 



Paleomonetes is generally adapted to 

 survive drought conditions, but not 

 by using the same adaptive mechanism 

 of burrowing. The prawn generally 

 moves into shallow ponds during 

 drought and survives low oxygen 

 stress through exploitation of high 

 concentrations of oxygen diffusing 

 across the surface water layer. 

 Reproduction appears to peak soon 

 after summer flooding of the marsh 

 (Kushlan 1976). 



6.23 FISHES 



Thirty-four species of fishes 

 are reported from the freshwater 

 Everglades (Table 25), representing 

 17 families (SFRC 1980). Dineen 

 (1974), reporting on fishes in the 

 conservation areas north of the pre- 

 sent study area, lists 43 species 

 from 18 families. Kushlan and Lodge 

 (1974) consider a total of 108 spe- 

 cies from 34 families as members of 

 the freshwater fish fauna of south 

 Florida. Of these 108, only 31 

 belong to obligatory freshwater 

 families. In this report we limit 

 our discussion to the fauna reported 

 by SFRC (1980). 



The Centrarchidae (bluegill) 

 and Cyprinodontidae (topminnow) 

 families are the more prevalent in 

 terms of genera and species. The 

 former are represented by 7 species 

 including the secretive Everglades 

 pygmy sunfish, the bluegill, the 

 blue spotted and redear sunfishes, 

 and the large mouth bass. The top- 

 minnows or killifishes include, 

 among others, the sheepshead minnow, 

 the marsh and seminole killifishes, 

 and flagfish. Another noteworthy 

 family is the Poecilidae or live 

 bearers. Three species represen- 

 tative of this family are the ubiq- 

 uitous mosquito fish, the least 



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