some areas (e.g., Galveston Bay, Texas, Parker 1965; 

 Lake Pontchartrain, Louisiana, Hinchee 1977), 

 these marshes are known to act as nurseries for migra- 

 tory fishes and shellfishes. Figure 4-21 shows the dis- 

 tribution of brackish and intemiediate marshes. They 

 are the dominant wetlands in every basin except the 

 Mennentau, which is nearly all fresh marsh habitat. 



Unlike the fresh and salt marshes which are fairly 

 distinct, the intermediate and brackish vegetation 

 types overlap and boundaries are often diffuse transi- 

 tion zones. For this reason, and because the two 

 habitats are similar, they are discussed together. 



A broad band of brackish marsh habitat crosses 

 the entire state of Louisiana. This marsh zone is the 

 most extensive and productive of all wetland types. 

 It also seems to be the most vulnerable to loss since 

 the brackish marsh habitat is eroding and becoming 

 open water at an alamiing rate statewide (Craig and 

 Day 1977). 



The brackish marsh habitat has lower aver- 

 age salinities than salt marsh (5.1%o compared to 

 12.4%o), but salinity varies widely and may reach 

 13°/oo (Chabreck 1972). Tidal water level fluctuation 

 is attenuated but present, and storm surges periodically 

 raise water levels and increase salinities. However, 

 sustained winds are probably the most important 

 factor in marsh flooding (part 3.3). During periods of 

 heavy rainfall, these marshes are flushed with fresh 

 water. These conditions seem to favor the production 

 of large amounts of organic matter, much of which is 

 deposited in sediments to form peat. 



The intermediate marsli habitat supports a transi- 

 tional community of organisms which includes both 

 marine and freshwater fomis. Salinities average 

 2.2''/oo, but sometimes reach 60/00 (Chabreck 1972). 

 Flushing frequency in the intermediate marsh habitat 

 is reduced compared to that in salt marsh habitat, 

 while peat production probably reaches a maximum 

 in this environment. 



4.4.1 PRODUCERS 



The most common plant in the brackish and 

 intermediate marshes is saltmeadow cordgrass. Vegeta- 

 tion in the intermediate marsh habitat is more diverse 

 than that in the brackish marsh habitat (tables 4.8 

 and 4.9), probably because of the presence of a 

 number of fresh marsh species such as bulltongue and 

 common reed that can survive occasional flooding 

 with brackish water. There is much open area in both 

 marsh types with as much as 20 to 40% of the area 

 being unvegetated. 



Almost nothing is known about the primary pro- 

 ductivity in brackish and intermediate marshes. No 

 production studies of tiiesc marsh types include the 

 Chenier Plain region. Annual production of saltmea- 

 dow cordgrass is the higliest reported for any vascular 

 plant in this country (GosseUnk et al. 1977). Using 

 production figures from a number of studies and the 



percent occurrence of each species, production in 

 intermediate and brackish marshes was estimated to 

 be about 2,800 g/m^/yr (tables 4.10 and 4.1 1). 



Because winters are mild, growth occurs actively 

 throughout the year and dramatic seasonal changes in 

 standing crop do not result. Similarly, mortality 

 occurs throughout the year, providing detrital con- 

 sumers, waterfowl, and furbearers a ready food 

 supply. 



Large mats of dead grass accumulate in marshes 

 dominated by saltmeadow cordgrass. These mats tend 

 to smother other plant species and increase the domi- 

 nance of saltmeadow cordgrass, which is not used ex- 

 tensively by waterfowl and furbearers. Management 

 techniques such as marsh burning and water level con- 

 trol have been developed to maximize production of 

 desirable plants for wildlife such as widgeongrass and 

 Olney's three-comer grass. These techniques are dis- 

 cussed in part 4.7, Management of Chenier Plain 

 Coastal Wetlands. 



4.4.2 CONSUMERS 



The brackish marsh habitat is the most saline 

 area in which amphibians occur in appreciable 

 numbers. Reptiles are represented by 16 species, fewer 

 than in fresh marsh habitat, but four times more than 

 in salt marsh areas. Some 79 bird species have been 

 identified in the brackish marsh habitat, mostly mi- 

 grants; but 16 species are year-round residents. The 

 1 1 species of mammals include several important 

 furbearers and the endangered red wolf. 



Intermediate marsh habitat has a vertebrate 

 species richness abnost identical to that for the 

 brackish marsh. This similarity is, at least in part, be- 

 cause vertebrate species apparendy do not distinguish 

 between these two habitats. Among amphibians, the 

 dwarf salamander probably reaches its gulfward Hmit 

 within the intemiediate marsh zone. The diamond- 

 back terrapin and Gulf salt marsh snake occur in the 

 brackish marshes, while the stinkpot, Graham's water 

 snake, and the garter snake are found in intermediate 

 marshes. Among birds found in brackish marshes, the 

 reddish egret, clapper rail, and great-tailed grackle 

 rarely, if ever, inhabit intemiediate marsh. The hooded 

 merganser, common yellowthroat, and swamp spar- 

 row, on tlie other hand, are found in intermediate 

 marsh but seldom in brackish areas. Appendix 6.3 

 contains a list of representative vertebrates of the in- 

 termediate and brackish marsh habitats. 



Herbivores and Detritivores. The size of the 

 microbial population may be larger in brackish and 

 intemiediate marshes than in salt marshes. Benthic 

 species richness (the majority of detritivores), how- 

 ever, is lowest in the brackish marsh habitat. Nema- 

 todes are abundant in sediments across the coast and 

 may make up about 60% of the total number of ani- 

 mals found at the edges of brackish marshes. Poly- 

 chaetes (segmented womis) are also abundant and 

 represent a major food item for many predaceous fin- 

 fishes and other carnivores. Ostracods and amphipods 

 are also abundant (Farlow 1976, Thomas 1976). 



176 



