(introduced from Japan) and Cer ithidea 

 calif ornica (native species), at three 

 central California salt marshes. Diatoms 

 accounted for most of the gut contents of 

 both snails, and comparisons of 

 chlorophyllose pigments in gut and fecal 

 samples indicated that the diatoms were 

 being digested. 



4.3 CONCEPTUAL MODELS OF ENERGY FLOW 



In the brackish marshes of Georgia, 

 Teal (1962) described energy as moving 

 predominantly through a vascular 

 plant-decomposer-detritivore pathway. The 

 highly productive Spartina alterniflora is 

 little used by grazers (Smalley 1959). 

 Most are first broken down by fungi and 

 bacteria, which make the material more 

 digestible and improve the nutritional 

 quality of the detritus by adding organic 

 nitrogen. Consumers feed on the resulting 

 mixture of microbes and vascular plant 

 fragments (Lopez et al. 1977). 



Tremendous effort is required to 

 quantify energy flow in marsh ecosystems 

 and, unfortunately, work comparable to 

 that reported in Teal (1962) has not been 

 done in southern California. The concept 

 which follows (Figure 36) is speculative, 

 but is consistent with the observations of 

 vascular plant and algal productivity and 

 the relative values of the foods produced. 



Vascular plants of southern 

 California marshes are probably utilized 

 by detritivores, as in Georgia marshes. 

 But since algae are more productive, both 

 on an absolute and relative scale, the 

 grazer pathway may be more important in 

 channeling primary productivity to higher 

 trophic levels. Energy is lost to 

 respiration at every feeding level and, 

 because decomposers attack the vascular 

 plants prior to their consumption by 

 higher trophic levels, a large portion of 

 the energy fixed by this group of 

 producers is used up by fungi and 

 bacteria. This leaves a smaller amount of 

 energy for consumption by detritivores. 

 Hence, a given amount of vascular plant 

 energy would support a smaller biomass of 



top carnivores than the same amount of 

 energy fixed by algae and used directly by 

 grazers (cf. Figure 36). 



n.n FLUX OF ORGANIC CARBON AND THE 

 FUNCTION OF MARSH PLANTS AS NUTRIENT 

 TRAPS 



Tidally flushed wetlands are open 

 systems; they exchange materials, both 

 living and dead, with adjacent upland and 

 ocean ecosystems. In southern California, 

 where there is usually little input of 

 freshwater, tidal waters provide the major 

 route of exchange with the ocean. 

 Measurements of the concentrations of 

 organic matter and nutrients on incoming 

 and outgoing tides allow net fluxes to be 

 determined. When followed over the year, 

 it becomes possible to determine if a 

 system functions as a net exporter or 

 importer of various substances. 



For many years coastal marshes were 

 viewed as accumulators of nutrients and 

 exporters of organic matter, with the 

 highly productive cordgrass being moved 

 into bays and providing food for fish and 

 shellfish (e.g. Odum 1971). However, this 

 model of estuarine functioning has 

 recently been challenged by Haines (1979), 

 and Nixon (1980) has critically reviewed 

 evidence which concerns these functions of 

 coastal wetlands. An alternative model of 

 wetland-coastal interactions has emerged, 

 which itself must stand the test of future 

 investigations before being accepted as 

 fact. As summarized by Haines (1979), 

 East Coast wetlands have four major 

 features: (1) Marsh soils and estuarine 

 sediments function as dominant sites for 

 accumulation, consumption and 

 remineralization of particulate organic 

 carbon (POO. Dissolved organic carbon 

 (DOC) and nutrients move into the 

 estuarine waters. (2) Salt marsh 

 productivity is utilized by fish, shrimp, 

 crabs, and other consumers which move into 

 the marsh to feed. The marsh thus serves 

 both as a food source and feeding habitat. 

 (3) Phytoplankton are important producers 

 in estuarine waters; their productivity is 

 responsible for much of the bay's fish and 



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