Estimated annual net production by 

 emergent nacrophytes in the study area has 

 been reported at 980 gC/mVyr, when pro- 

 rated for the entire marsh estuarine sys- 

 tem (Pomeroy and Wiegert 1980). This num- 

 ber does not include leachate, however, 

 making it a conservative estimate. 



It should be noted that some contro- 

 versy exists regarding the paradigm that 

 emergent macrophytes are the primary 

 source of particulate carbon in coastal 

 ecosystems in the South Atlantic Bight. 

 Arguments have been advanced (Haines 1976, 

 1977) that perhaps production by phyto- 

 plankton is more significant than that of 

 emergent macrophytes. Counterarguments 

 and hypotheses by Peterson et al. (1980) 

 provide alternative interpretations of 

 Haines' (1976, 1977) studies. Until more 

 definitive research resolves this contro- 

 versy, the paradigm is still viable. 



Phytoplankton 



The major phytoplanktonic producers 

 in a "typical" estuary in Georgia were 

 listed (Pomeroy and Wiegert 1980) as pela- 

 gic diatoms (and occasional benthic pen- 

 nate diatoms swept up from the bottom into 

 the water column), dinoflagellates and 

 green flagellates. Their combined produc- 

 tion rate was estimated as 125 gC/m-^/yr 

 (Pomeroy and Wiegert 1980) when prorated 

 for the entire marsh water surface (water 

 comprises about one-third of this area). 



Benthic Algae and Epiphytes 



The principal primary producers in 

 the marsh sediments are benthic pennate 

 diatoms. These organisms migrate verti- 

 cally in the sediment, depending on the 

 tidal stage and light conditions. They 

 are often clearly visible on exposed creek 

 banks as a golden sheen on the brown mud. 

 Pomeroy and Wiegert (1980) reported that 

 benthic algae account for about 11% of 

 total net primary production in a marsh 

 estuarine system in the study area, or 

 134 gC/m^/yr, prorated for total estuarine 

 area. 



Another group of primary producers in 

 the marsh-estuarine ecosystem is the com- 

 munity of epiphytic algae that inhabits 

 the culms or stalks of marsh grass. This 

 diverse community is not readily apparent 



but attracts grazers, especially the gas- 

 tropod Littorina irrorata . In terms of 

 production rates, the epiphytic community 

 is relatively unimportant compared to 

 Spartina alterniflora (Pomeroy and Wiegert 

 1980). 



Mixotrophic 



Chemosynthetic Bacteria: 

 and Photolithotrophic 



Two groups of anaerobic microbial 

 organisms inhabiting sediments within the 

 salt marsh-estuarine system are the mixo- 

 trophic sulfate-reducing bacteria and the 

 photolithotrophic bacteria, which have re- 

 cently received scientific attention. The 

 abundance of sulfate in salt marsh sedi- 

 ments makes this ion the obvious substi- 

 tute for oxygen as the electron acceptor 

 in the anaerobic respiration of many mi- 

 crobes. These organisms use dissolved 

 organic matter as an energy source. Sul- 

 fate reduction is now recognized as an 

 extremely important process in the salt 

 marsh estuary (Fenchel and Riedl 1970; 

 Howarth and Teal 1979). As sulfate is 

 reduced (primarily by a bacterial group 

 known as Desulfovibrio ), the resulting 

 sulfide diffuses upward. Its reducing 

 "power" is subsequently used along with 

 light as the energy source to fix atmos- 

 pheric carbon dioxide by anaerobic bacte- 

 ria. The release of the resulting organic 

 matter from salt marsh sediments is prob- 

 ably augmented by tidal flushing and may 

 be quite significant along creek banks. 



A major implication of this overall 

 process is that the initial carbon source 

 for the sulfate reducers is leachate from 

 the roots of macrophytes. Thus, the wet- 

 land macrophyte production is ultimately 

 the source of this (unknown) amount of 

 extra organic carbon that goes into the 

 ecosystem. 



1.4 ESTUARINE CONSUMERS 



The following description of the con- 

 sumers of the salt marsh estuarine ecosys- 

 tem in the study area is necessarily in- 

 complete because it describes only those 

 groups of organisms that are considered 

 dominant, functionally significant, or 

 that directly affect the oyster reef com- 

 munity. These are bacteria, benthic in- 

 fauna, zooplankton, nekton, and terres- 

 trial consumers. 



10 



