relative to the other primary producers. 

 The chemosynthetic organisms do not 

 contribute to overall marsh production if 

 they are oxidizing reduced substances 

 produced in the marsh (see Section 

 5.5.4.). 



Measurements of benthic microalgal 

 production along the Atlantic coast (Table 

 4) indicate that algal production in the 

 grassy parts of the Massachusetts marsh is 

 limited by low light during the darker 

 parts of the year (Van Raalte et al . 

 1976). There is little indication of 

 inhibition by high light intensity in any 

 studies (see Pomeroy and Wiegert 1981). 

 Competition for available nutrients by 

 grasses during their growing season also 

 limits algal production. 



Microscopic algae make a significant 

 contribution to total salt marsh 

 production because they contain low 

 amounts of refactory structural compounds 

 and, thus, are better food than higher 

 plants. The lignins and celluloses of 

 higher plants are all relatively resistant 

 to digestion by animals. We usually speak 

 of them as "resistant to degradation," 

 implying that they are attacked only by 

 microbes and, in the case of lignins, very 

 slowly. Algae, on the other hand, are 

 eaten readily by benthic animals, as has 

 been demonstrated by excluding mud snails 

 from marsh areas and observing the 

 increase in algal biomass (Pace et al. 

 1979). Pace et al. (1979) found that the 

 snails only reduced algal populations by 

 grazing and caused no related increases in 

 algal productivity in their Georgia marsh. 

 On the other hand, Connor et al. (1982) 



found that at moderate population levels, 

 the nutrients (ammonia) excreted by the 

 snails stimulated algal production. An 

 increase in production when grazers are 

 excluded has also been shown in early 

 spring when blooms of Beggiatoa were 

 produced in Great Sippewissett Salt Marsh 

 by fencing Fundulus out of marsh creeks 

 (J.M. Teal, unpubl. data). 



Salt marsh phytoplankton productivity 

 may be high, especially at high tide when 

 the water is clear from being filtered by 

 the marsh and nutrient levels are 

 maintained by marsh-to-water exchanges. 

 In Georgia marshes, phytoplankton are 

 estimated to contribute about half as much 

 to the system as do benthic algae (Pomeroy 

 and Wiegert 1981); in Massachusetts, 

 phytoplankton productivity may be about 

 equal to that of benthic algae (Van Raalte 

 et al. 1976). Pomeroy and Wiegert (1981) 

 showed that phytoplankton photosynthesis 

 in Georgia is inhibited by low 

 temperatures in winter; Glibert et al. 

 (1984) have found high levels of 

 phytoplankton photosynthesis in 

 Massachusetts coastal inshore waters 

 during winter. If this difference is 

 real, then phytoplankton may be even more 

 important to New England marsh creeks than 

 we previously thought. 



Algal production in surface pools of 

 a salt marsh was measured by Ruber et al . 

 (1981). They estimated an ash-free dry 

 weight value of 514 g/m 2 /yr, which is a 

 little more than the production of dwarf 

 Spartina in New England and slightly less 

 than half that of tall Spartina . 

 Planktonic diatoms and dinof lagel lates 



Table 4. Production of benthic algae in salt marshes along the Atlantic coast. 



31 



