is usually considered to be. The idea 

 that herbivory is not important in marshes 

 stems partially from our qualitative 

 observations that we do not see cows, 

 deer, buffalo, and other large grazers in 

 the marsh very often. 



Smalley (1950) quantified energy flow 

 through the grasshopper (Orchel imum 

 f idici nium ) and concluded that it grazed 

 less than 10 percent of the net production 

 of its host, S_. al terni flora . Parsons 

 and de la Cruz (1980) estimated that 

 consumption by grasshoppers in a 

 Mississippi coast marsh was only about 5.4 

 g/m^/yr. Other investigators have 



identified a broad diversity of insects in 

 marshes but little is known about their 

 importance in controlling the flow of 

 organic energy. 



Common invertebrates of the Louisiana 

 coast have been enumerated (Gosselink et 

 al. 1979), but quantitative studies of 

 productivity and consumption are lacking. 

 Invertebrates other than grasshoppers may 

 ingest significant amounts of live grass 

 tissue, even though this is an accidental 

 component of their diets. For example, the 

 marsh snail (Littorina irrorata ) grazes up 

 and down S_. al terniflora stems, skimming 

 off the dead organic material and 

 epiphytes. It also scrapes off living 

 grass tissue in this process. Alexander 

 (1976) estimated that about 4 percent of 

 the marsh snail's diet is living tissue, 

 which amounts to less than 1 percent of 

 the production of that plant. In fresh 

 marshes insect herbivory is thought to be 

 more important than in salt marshes, 

 because there appear to be more insects in 

 that environment. However, no supporting 

 data are available in the delta. 



In the delta marshes larger consumers 

 such as snow geese, muskrats, and nutria 

 probably are responsible for more grass 

 consumption or destruction than insects. 

 For example. Smith (1982) reported that 

 snow geese grazing in Atlantic coast 

 marshes can reduce the plant cover by 

 two-thirds where they concentrate and 

 virtually destroy the plants by digging up 

 their roots. This results in significant 

 changes in plant composition the next 

 year. 



Similarly, O'Neil (1949) indicated 

 that dense concentrations of nutria and/or 

 muskrats can "eat out" a marsh area. 

 These mammals are attracted to stands of 

 Sci rpus olneyi , Typha spp . , _P. hemi tomon 

 and other species. They are reported to 

 eat up to one-third of their weight per 

 day (O'Neil 1949) and destroy much more 

 vegetation than they eat. 



Although grazing can be locally 

 important in marshes, most discussions of 

 marsh processes ignore it and assume that 

 over the marsh as a whole it is 

 negligible. The bulk of the organic 

 matter produced by the emergent 

 macrophytes dies and falls to the marsh 

 surface. The decomposition of this 

 material can be divided into two phases: 

 an initial rapid loss of easily soluble 

 organic compounds, followed by a longer, 

 slower decomposition rate. 



The first phase takes only about 2 

 weeks. The rapid release of easily 

 soluble metabolites from the grass tissue 

 and the continuous leaching of organic 

 compounds from the live grass (Turner 

 1978) represent a significant flow of 

 organic energy, perhaps as much as 20 - 30 

 percent of aboveground primary production 

 (Teal 1983). The fate of this material 

 has not been studied in gulf coast 

 marshes, but a number of investigations 

 were conducted in Georgia (Pomeroy and 

 Wiegert 1981). There, much of the 

 dissolved organic carbon (DOC) in the 

 water column is refractory, probably 

 released from later stages of decay of the 

 marsh detritus. It is likely that the 

 readily soluble compounds released when 

 the grass cells die are easily metabol i zed 

 by micro-organisms and disappear rapidly 

 from the water column. 



In a recent review article Ducklow 

 (1983) assembled evidence that bacterial 

 production in the ocean is not only high 

 but is also a significant food supply for 

 planktonic zooflagellates and ciliates. 

 Most of these bacteria are apparently 

 using DOC as an energy source since they 

 are not associated with particulate 

 matter. We need to know much more about 

 this pathway of energy flow in coastal 

 marshes. If Ducklow' s model for the ocean 

 and continental shelf is any guide, the 

 food chain from grass to DOC to bacteria 



57 



