in many locations and report that they can be as pro- 

 ductive as saU marshes. An estimate of net primary 

 production for fresh marshes in Louisiana, based on 

 the measured productivity of selected plants is re- 

 ported in table 4.13. The estimate of 2,200 g/m^/yr 

 must be considered tentative. It is similar to the esti- 

 mate for salt marsh and slightly less than the esti- 

 mates for brackish and intermediate marshes. 



In fresh and intermediate marshes, succulent 

 broad-leaved plants like buUtongue dominate some 

 areas. The leaves of these plants are shortlived; they 

 die and decompose rapidly. These habitats are usually 

 devoid of vegetation throughout the winter with little 

 accumulation of organic detritus. 



Table 4.13. Estimated net primary production per 

 square meter for the fresh marsh habi- 

 tat. Total net primary production is 

 calculated as the 2, (percent coverage 

 times net primary production) for 

 n species. 



Chabreck 1972 



Gosselinket il. 1977 



"Boyd 1969 



Productivity assumed to be equal to the average for other 

 species in the habitat. 



Epiphytic and epibenthic algae also occur in the 

 fresh marsh habitat, but no information about their 

 importance in the Chenier Plain marshes is available. 

 Many of the same species, especially the large fila- 

 mentous forms, are common in adjacent open waters 

 (part 4.9). 



4.5.2 CONSUMERS 



Salt stress is reduced in the fresh marsh habitat 

 and amphibian and reptilian species richness is greater 

 than that for more saUne habitats (appendix 6.3). 

 Most reptiles Uve on elevated areas, including levees 

 and spoil banks, rather than in the marsh proper. Bird 

 species diversity is high and is generally comparable 

 to that for other marsh habitats. The same species of 



mammals that use the intemiediate and brackish 

 marsh habitats are found in fresh marsh habitat. The 

 nutria is the most abundant large herbivore in fresh 

 marsh areas. 



Insects are important functional components of 

 freshwater wetlands, assuming many of the roles 

 played by crustaceans in more saUne environments. 

 In a buUtongue community in southeastern Louisiana, 

 Louton and Bouchard (1976) identified 40 insect 

 taxa. The grazing pressure that these invertebrates 

 put on marsh vegetation is not known, but studies by 

 Hine (1904, 1906) indicated that insects caused con- 

 siderable damage to marsh grasses in the Cameron 

 area of southwestern Louisiana. 



Amphipods and isopods are thought to be major 

 consumers among the aquatic arthropods, which 

 shred and ingest detritus fragments (appendix 6.3). As 

 in other wetlands, bacteria and fungi are responsible 

 for metabolic conversion of most of this detritus. 

 Hood and Meyers (1976) isolated more bacterial types 

 from fresh marshes than from more saUne ones. 



Practically nothing is known about either her- 

 bivorous or carnivorous (or parasitic) insects in 

 marshes, although the density of biting flies and 

 mosquitoes in some marsh areas makes them very 

 important to man. Dragonflies and robberfhes prey 

 on all flying insects, including bees and wasps (Wright 

 1946). Their impact on the fly, mosquito, and gnat 

 population is significant. Wright (1946) showed cor- 

 relations between dragonfly populations and the 

 swarming of mosquitoes and dog flies along the 

 Florida coast. However, he further concluded that no 

 effective control of these pest insects is accomphshed 

 due to their large numbers and the short Hfe-cycle of 

 the dragonfly (Wright 1946). Parasitism of Tabanid 

 (horsefly) eggs by parasitic wasps, which reaches 

 levels greater than 50% in the early summer, is also 

 another factor which controls the number of fhes in 

 southern Louisiana (Jackson and Wilson 1966). 



Aquatic predaceous insects are also significant in 

 controUing mosquitoes and gnats. Beetles (Dytiscidae) 

 have been singled out by several workers to have the 

 best potential as aquatic insect predators (Bay 1974). 

 When concentrated in small pools, dytiscid and hy- 

 drophilid larvae are important in killing mosquito 

 larvae (Bay 1967). Hemiptera, the true bugs, are also 

 effective in controlling mosquitos. Bay (1967) studied 

 backswimmers (Notonecta unfasciata) that com- 

 pletely prevented emergence of mosquitos in field- 

 situated tubs. Water scorpions (Nepidae) and giant 

 waterbugs (Belostomatidae) will attack tadpoles, 

 fishes, crayfishes, and salamanders. All of these insect 

 groups are found in the fresh marshes and ponds of 

 the Chenier Plain. Those predatory insects which are 

 functionally most important, however, are the species 

 which help to maintain a check on such grazing species 

 as weevils and grasshoppers. 



4.6 SWAMP FOREST HABITAT 



A swamp is classically defined as a woody com- 

 munity where the soil is saturated or covered with 



183 



