4.3.2 CONSUMERS 



Less than 10% of the emergent vegetation of sah 

 marshes is directly grazed (Smalley 1959). As in all 

 wetlands, most consumers are detritus eaters. A list 

 of the dominant species is included in appendix 6.3. 

 Homopterans (leafhoppers), Orthopterans (grasshop- 

 pers), Dipterans (flies), and some Hemiptera (true 

 bugs) are the major grazing insects of the salt marsh 

 habitat. In one of the few studies of grazing insects in 

 salt marshes, Smalley (1959, 1960) concluded that 

 leaflioppers. assimilated more than 6% of the annual 

 primary production of smooth cordgrass in a Georgia 

 salt marsh, while grasshoppers assimilated less than 

 1%. 



Of the remaining primary consumers, most ingest 

 a combination of detritus and epiphytic or benthic 

 algae. Marsh snails (Littorina irrorata) are important 

 detritivores that may ingest as much as 12% of the 

 annual net production of smooth cordgrass, mostly 

 as detritus, and are undoubtedly important animals 

 at this trophic level (Alexander 1977). 



Bacterial populations in salt marshes vary sea- 

 sonally around lO'' ceUs/g (2.83 x 10* cells/oz) of 

 sediment. Hood and Meyers (1976) found that the 

 bacteria are concentrated at the interface between the 

 marsh and adjacent streams. These workers isolated 

 30 forms of bacteria from salt marshes, a low diversity 

 compared to freshwater habitats. Of all the hetero- 

 trophic types isolated, 19% were found to be pro- 

 teolytic, 1% cellulose degraders, and 1 0% chitinoclas- 

 tic. Predominant genera were Bacillus, Vibrio, Pseud- 

 omonas, and Achromobacter. 



Meiofauna and small macrobenthic forms are also 

 important primary consumers in sah marsh sediments. 

 These include such groups as copepods, amphipods, 

 polychaetes, mites, insect larvae, and nematodes (ap- 

 pendix 6.3). Feeding habits of the latter group are 

 not clear, since some nematodes feed on protozoa 

 and some are strictly detritivores. The total amount 

 of organic material ingested by nematodes is un- 

 doubtedly significant, since these minute animals com- 

 monly occur in six-figure densities in one square meter 

 (10.8 ft ) of marsh surface. The complex trophic rela- 

 tionships of the benthic community are discussed 

 more completely in part 4.8, Aquatic Habitats. 



The saline conditions of the salt marsh are hostile 

 to many organisms which inhabit other marsh habi- 

 tats. Nevertheless, most of the predatory species which 

 use the salt marsh as a feeding ground include the same 

 general forms and the same species that are found in 

 intermediate and brackish marsh habitats. Spiders, 

 insects, birds, and mammals are included in this cate- 

 gory. Amphibians, with their highly permeable skin, 

 seem to have no mechanisms for combating the dry- 

 ing effect of salt, and are not represented. Only four 

 species of reptiles, including the American alligator, 

 Mobile cooler, diamondback terrapin, and the Gulf 

 salt marsh snake are found in this habitat (appendix 

 6.3). 



Aquatic species such as the Gulf menhaden, 

 shrimp, and blue crab use salt marsh extensively during 



high water periods, as do many small fishes such as 

 killifish that have no direct economic importance. Or- 

 ganic materials transferred from marshes to the open 

 Gulf by these latter species may be significant. 



Spiders are reported to be the principal carnivores 

 in smooth cordgrass communities (Marples and Odum 

 1964), outnumbering carnivorous insects (Barnes 

 1953; Davis and Gray 1966). Many parasitic insect 

 pests inhabit the salt marsh habitat. Early discussions 

 by Hine (1904, 1906) indicate that biting or sucking 

 flies were abundant in Louisiana salt marshes at the 

 turn of the century, causing damage to livestock. Wil- 

 son and Richardson (1969) mention that horseflies 

 and deerflies are among the most damaging groups of 

 insects that attack livestock in estuarine and alluvial 

 areas of the state. Besides being irritants to livestock, 

 they are known vectors of anaplasmosis, an infectious 

 disease of cattle. Cattle, horses, deer, and rabbits are 

 the only major hosts attacked by them. Birds, reptiles, 

 and smaller mammals are apparently not essential 

 hosts. Mosquitoes and other pests feed mostly on cat- 

 tle, rabbits, and horses; other mammals, birds, and 

 amphibians are rarely attacked (Schaefer and Steel- 

 man 1969). 



Marsh alterations influence the populations of 

 these invertebrates. Dukes etal.( 1974a) found tabanid 

 larvae in North Carolina salt marshes most abundant 

 where living plants maintain uniform moisture condi- 

 tions. Bailey (1948) observed that Massachusetts salt 

 marshes that were ditched to control mosquitoes had 

 greater expanses of suitable larvae habitats than nat- 

 ural marshes which were subject to drying and flood- 

 ing. Additional studies of tabanid larvae (Duke et al. 

 1974b) in North Carolina indicate that as mixed veg- 

 etation increases, and smooth cordgrass decreases, the 

 numbers of larvae decline. Thus, uniform stands of 

 smooth cordgrass contain the greatest numbers of 

 tabanidae. No comparative study in Louisiana's 

 marshes has been made. 



Species richness of birds in the salt marsh may 

 not be as high as indicated (appendix 6.3), since most 

 seabirds and wading birds primarily utilize areas pe- 

 ripheral to salt marshes. Population densities of water- 

 fowl species are also genersdly low in this habitat (part 

 5). 



Predation by mammals in the salt marsh is exem- 

 plified by the raccoon which feeds on practically any- 

 thing, including fiddler crabs, snails, rail eggs, and 

 plant material. Other mammalian consumers include 

 the Virginia opossum, nine-banded armadillo, swamp 

 rabbit, marsh rice rat, muskrat, and Nearctic river 

 otter. 



4.4 BRACKISH AND INTERMEDIATE 

 MARSH HABITATS 



Brackish and intermediate marsh habitats in the 

 Chenier Plain probably serve the same function as salt 

 marsh habitat in other coastal regions. This is because 

 the area of salt marsh in the Chenier Plain is small rela- 

 tive to the areas of brackish and intermediate marshes. 

 The estuarine water bodies along this coast are usually 

 edged by brackish to fresh marshes; and at least in 



175 



