The flux of detritus to the open sea can be determined indirectly by 

 correlating changes in concentration of sestonic detritus with changes in 

 the standing biomass of plant materials on the marsh during the year. In 

 a tidal system such as a marsh-estuary, the conditions in the surrounding 

 waters are influenced by biological processes going on in the marsh. The 

 disappearance of dead plants (source of detritus) from the marsh, beginning 

 in winter (the period during which the dead biomass was highest because of 

 frost-kill) and extended through fall, was inversely related to increase 

 in detritus content of estuarine waters (de la Cruz 1973). 



The transport of particulate detritus can also be estimated by measuring 

 the net output of a tidal creek draining a known area of marsh watershed. 

 This output has been determined to be 3.4 tons per hectare per year for 

 a Georgia salt marsh and 3.6 tons per hectare per year for a Florida mangrove 

 estuary. Subsequent studies have confirmed this movement of suspended 

 detrital materials from the marsh to the aqueous system, although other 

 investigations have indicated that the import of organic materials into tidal 

 marshes also occur. Variations in transport direction have been attributed 

 to hydrological characteristics such as tidal regime, to the proximity of 

 the freshwater input, and to the geomorphic orientation of the marsh drainage 

 system (Hackney and de la Cruz 1977). Our current investigations indicate 

 that exports of particulate detritus are irregular in some coastal areas 

 (e.g., Mississippi Gulf Coast) and that the marsh serves as a holding 

 area for riverborne materials. The marshes not only export detritus to 

 offshore waters but also regulate the overall release of organic detritus 

 from estuaries. 



The ultimate ecological value of the high primary production of a marsh 

 occurs when suspended detritus of marsh plant origin enters the food web of 

 the estuarine and coastal marine systems. Particulate detritus, suspended 

 in the water and deposited on the sediment surface, is a high-quality food 

 source for consumers because of its high energy content and nutritional 

 value. A number of studies involving stomach analyses and experimental feed- 

 ing using radioactive tracers have shown that many species of fish and 

 invertebrates feed wholly or partially on particulate detritus. 



The availability of different sizes of detritus relative to the degree 

 of decomposition is also significant because the detritus provides energy to 

 various feeding niches (Figure 1). Most filter feeders are presumably size- 

 selective with regard to their food and are unable to differentiate between 

 detritus particles and similar size plankton material. Detritus eaters, 

 or detritivores, are important in that they form the base of the food web 

 in the estuarine-marine environment. Detritivores are the critical link 

 between detritus production and the production of higher consumers. 



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