a. Productivity . 



(1) Primary Production (Energy] . Tidal marskes can be ex- 

 tremely productive. Primary production is carried out by two groups 

 of plants, the mar^ grasses (or other vascular plants) and the algae 

 on living and dead plants and on the surface of the marsh mud. Cooper 

 (1969) summarized data on productivity and energy flow in low marsh 

 of smooth cordgrass typical of the Georgia coast . This is the most 

 complete study of salt marsh available and these marshes are some of 

 the most productive. Along creek banks where growth is greatest, an- 

 nual net production of the grass was as high as 22,000 kilograms of 

 biomass per hectare, equaling or exceeding the highest yielding food 

 and forage crops of the world. Net production of the short grass in 

 higher marshes away from the creeks was much lower, about 6,000 kilo- 

 grams per hectare. Net production from algae added about 500 kilograms 

 per hectare. Average net production for the marsh as a whole, consid- 

 ering the relative areas in the different types, was about 16,000 

 kilograms per hectare. These amounts are typical of the more produc- 

 tive east coast low marshes but stunted forms of the same species 

 elsewhere may have net production of 2,000 kilograms per hectare or 

 less, only 10 percent of that of the most productive marshes. Also, 

 along the Atlantic coast, production by smooth cordgrass decreases 

 from south to north. This is not true of all marsh species (Reimold 

 and Linthurst, 1977). 



(2) Utilization . Little of the biomass of salt marsh, about 

 5 percent, is consumed while the plant material is still living (Fig. 

 4). Grasshoppers and planthoppers graze on the grass and are, in turn, 

 eaten by spiders and birds. Direct consumption of rhizomes and culms 

 of marsh grasses by wild fowl may be significant locally near winter- 

 ing grounds. Periwinkles graze on algae growing on the grass. The 

 majority of the energy is believed to move through the detrital food 

 chain. Dead grass is broken down by bacteria in the surrounding 

 waters and on the surface of the marsh. This process greatly decreases 

 the total energy but increases the concentration of protein, thereby 

 increasing the food value. Some detrital particles and mud algae are 

 eaten by a variety of detritus feeders such as fiddler crabs, snails, 

 and mussels; these organisms are, in turn, eaten by mud crabs, rails, 

 and raccoons. The remaining detritus, augmented by the dead matter 

 from the primary and secondary consumers, is washed from the marsh by 

 tidal action as new export. This exported detritus, with material 

 from submergent aquatic plants and the plankton, feeds the myriads of 

 larvae and mature fish and shellfish which use estuaries, bays, and 

 adjoining shallow waters. Marsh grasses may account for most of the 

 primary production of the system in waters where high turbidity re- 

 duces light penetration, thereby reducing phytoplankton and submergent 

 aquatic production. 



