Although this much energy is made 

 available by the oxidation of sulfide, it 

 is not very efficiently captured by the 

 marsh microbes. Only recently has it been 

 shown that Beggiatoa , a common marsh 

 microbe that oxidizes sulfide (Figure 24), 

 can capture any significant part of the 

 available energy (Nelson and Jannasch 

 1983). 



Most of the sulfide oxidizers are 

 bacteria; however, these may live within 

 higher organisms. The bacteria oxidize 

 sulfide as a source of energy and fix 

 carbon, making organic matter from carbon 

 dioxide. The host animals provide the 

 bacteria a place to live and, in return, 

 derive food from them. This symbiotic 

 association has been found in mud-flat 



worms in North Carolina (Ott et al. 1983) 

 and clams living in Massachusetts eel 

 grass beds (Cavenaugh 1983), and has 

 recently been discovered to be the basis 

 for life occurring around the deep-sea 

 vents (Cavanaugh et al . 1981). It is 

 reasonable to expect that further 

 investigations will reveal the same 

 symbiosis in some organisms, such as worms 

 and clams, living in marsh sediments. 



5.3.4. Carbon 



carbon cycle is discussed 

 in sections 5.1 (Productivity) 



The 

 primari ly 



and 5.2 (Decomposition). Two further 

 points connected with the sulfur cycle 

 shed light on processes involving carbon 

 within the marsh. 



Figure 24. Beggiatoa growing at the low edge of the salt marsh. This microbe is 

 visible as tiny white threads on the marsh surface. The color is due to grains of 

 sulfur that result from the microbe's oxidation of sulfide. Photo by J.M. Teal, Woods 

 Hole Oceanographic Institution. 



41 



