Epiphytic algae and diatoms grow primarily on smooth cordgrass and supple- 

 ment its primary production. Benthic algae are relatively sparse along the 

 northern coast of the Gulf of Mexico, but they contribute measurable amounts 

 of primary production in localized areas (Day et al., 1973). 



Phytoplankton in the water column comprise the last important component 

 of primary producers in this system. The seasonality of all components should 

 be emphasized. Production of smooth cordgrass is greatest in spring. Different 

 species of epiphytes exhibit peak productions throughout the year; species of 

 phytoplankton are most abundant in the summer. Day et al. (1973) have provided 

 estimates of these annual production rates for the Barataria Bay area of 

 Louisiana. Average net productions for grasses, epiphytes, benthic algae and 

 diatoms, and phytoplankton are 1518, 26, 488, and 418 g dry wt/m^/yr, respec- 

 tively. 



All of these producers are affected by tides, sediment, and nutrients as 

 previously discussed. Salinity and heat differentially affect vegetation; 

 competition determines the dominant species and its associates for any given 

 set of conditions. The important point is that all the producers contribute 

 to the pool of detritus, the base of the food pyramid in the salt marsh systems 

 of the gulf coast (Darnell, 1961 and 1967; Teal, 1962; Day et al., 1973). 



Consumers . Day et al. (1973) have used past studies and their own data 

 to present coverage of the food chain in a gulf coast salt marsh. The fauna 

 in a salt marsh are dependent upon the vegetation for cover as well as for food. 

 The muskrat, for example, uses smooth cordgrass stems to construct its home. 

 Snails and insects are protected from predators while grazing on epiphytes and 

 plant blades, respectively. Likewise, the waterfowl, wading birds and shore- 

 birds, raccoon, and small fish use the vegetation for cover while feeding and 

 resting. 



Some species consume the marsh grasses directly. Muskrat, nutria ( Myocastor 

 coypus ), and waterfowl eat rhizomes of smooth cordgrass while insects prefer 

 blades. Oysters, meiofauna (worms, ostrocods, copepods), snails, and some fish 

 are primary consumers that feed on phytoplankton and epiphytes. Waterfowl, 

 crabs, shrimp, and some fish feed on these primary consumers. They, in turn, 

 are eaten by raccoons, wading birds, shorebirds, and large fish. 



Many of the secondary and tertiary consumers are migratory species, and 

 therefore they are present only during portions of the year. Superimposed upon 

 this regime of annual movements are the daily movements of fish, crabs, and 

 shrimp (and their predators), mediated by the tides. Consumers return materials 

 and energy to the ecosystem via feces and carcasses. 



Other important factors which may directly affect the aquatic consumers 

 include salinity, suspended sediments, pollutants, and dissolved oxygen. The 

 latter is subject to effects of heat, salinity, and content of oxidizable mate- 

 rial. All of these factors are greately influenced by anthropogenic activi- 

 ties. 



35 



