Insects are usually considered major consumers 

 in all wetland habitats. No study has been made to 

 verify this in the Chenier Plain region, but Farlow 

 (1976) included data on insect diversity and density 

 in Cameron Parish. Major herbivore-detritivore species 

 that were collected included water scavenger beetles 

 {Hydrophilidae) and \NeQ\]l%{Curculionidae). 



Brackish and intemiediate marsh habitats are im- 

 portant nursery areas for shrimp and Gulf menhaden. 

 Herbivorous waterfowl, including the dabbling ducks 

 that are prized by hunters, prefer intermediate 

 marshes for feeding grounds, but also use brackish 

 and fresh marshes extensively. Diving ducks are also 

 found in brackish marshes and represent the most 

 numerous group of waterfowl that over winters in the 

 Chenier Plain. 



Muskrats are herbivores that prefer brackish 

 marshes to other habitat types (part 5). They are an 

 important node in the food web of the marsh system, 

 being preyed upon by the alligator, various snakes, 

 hawks, and the mink. 



Carnivores. Marsh birds in brackish and inter- 

 mediate marsh habitats become extremely numerous 

 during spring and summer. Wading birds seem to have 

 a prominent role among the predators, obtaining their 

 food from water bodies within the marsh. This group 

 includes various egrets, herons, bitterns, and ibises. 

 Some of these birds have an extremely varied diet and 

 will eat practically any small animal. Dabbling ducks, 

 which are primarily herbivorous, reach their greatest 

 densities in the intermediate marsh habitat (part 5). 



At least ten species of predaceous water beetles 

 (Dytisicidae) are found in the intermediate marshes 

 of the Chenier Plain. Of these, Hygrotus spp. and 

 Cybister fimbriolatus are the most common (Farlow 

 1976). Dragonflies are highly predaceous, and several 

 species prefer the intennediate marshes (Bick 1957), 

 but their numbers decrease in the more saline areas. 

 The most common insect collected by Fariow(1976) 

 in intermediate marshes was the biting midge 

 (Heleidae). 



4.5 FRESH MARSH HABITAT 



The broad band of fresh marsii extending across 

 the Chenier Plain (fig. 4-22) is one of the major water- 

 fowl habitats of the Gulf coast. The region's high 

 rainfall and abundant freshwater flow from upstream, 

 coupled with the continuous beach ridge barrier 

 against saltwater encroachment, combine to make 

 this broad expanse of freshwater wetlands. 



Water levels in Louisiana freshwater marshes are 

 controlled more by upstream flows, rainfall, and the 

 direction of prevailing winds than by tidal effects. 

 The total annual inundation time does not vary much 

 across different marsh habitats, but the frequency of 

 inundation (a measure of marsh flushing) is lowest in 

 the freshwater areas. As a consequence much of the 

 organic production of the emergent plants accumu- 

 lates in place. This often gives rise to floating marshes, 

 called "flotants." Flotants consist of a diverse mat of 



vegetation supported by organic detritus several feet 

 thick held together by a matrix of living roots. This 

 floating marsh is indistinguishable from other wetlands 

 until trod upon. It often extends the true shoreline 

 out into shallow adjacent lakes, forming a new shore- 

 line and shrinking the lake. This kind of growth does 

 not occur extensively in more energetic hydrologic 

 regimes. 



Because freshwater marsh sediments are water- 

 logged and poorly flushed, anoxic conditions are 

 probably more severe in this habitat than in others. 

 In more saline marshes, sulfate from seawater is re- 

 duced to sulfide, donating its oxygen for biological 

 respiration. In fresh marshes sulfate availability is 

 much lower. In the absence of sulfates, carbonates 

 and carbon dioxide act as oxygen donors, with result- 

 ing methane formation. 



4.5.1 PRODUCERS 



The richness of the emergent flora increases 

 dramatically in fresh marsh habitat (table 4.12), 

 compared to more saline areas (Chabreck 1972). 

 Maidencane is the dominant true fresh marsh plant 

 species and it is seldom found in other wetland 

 habitats. The ubiquitous saltmeadow cordgrass also 

 flourishes here. Bulltongue and alligatorweed are 

 common in this habitat, as well as in the intermediate 

 marsh habitat. 



Alligatorweed is an introduced species that has 

 reached pest proportions. It grows in shallow marsh 

 ponds and on the edges of bayous and sheltered lakes, 

 as well as on the wetland surface. Recently, the 

 alligatorweed flea beetle (Agasicles hygrophila) was 

 introduced as a means of biologically controlling 

 alligatorweed; it has apparently succeeded in hold- 

 ing this plant in check in certain areas (Don Lee, 

 Louisiana Department of Wildlife and Fisheries, 

 unpublished data). 



One common plant association in the fresh marsh 

 habitat is the maidencane association, which typically 

 includes water hyacinth, duckweed, water lettuce, 

 smartweed, bulltongue, soft-stem bulrush, and cat- 

 tail as minor components. The number of such asso- 

 ciations is greatest in the fresh marsh (Gosselink et al. 

 1976). This increased plant diversity is due, in part, 

 to the presence of annuals. Brackish and salt marsh 

 habitats are dominated by perennials, which form 

 stable communities that change relatively little from 

 year to year. In contrast, fresh marshes support a 

 large number of annual grasses. The seed of some of 

 these gemiinate in the spring and others in the fall. 

 Most require a bare moist soil for germination. The 

 dominant annual at a single location, therefore, often 

 changes from season to season and from year to year, 

 depending on the degree of competition from 

 perennials and on marsh water levels during germina- 

 tion periods. 



Little is known about the productivity of fresh 

 marsh emergent plants. Whigham et al. (1978) have 

 cataloged production from freshwater tidal wetlands 



180 



