intertidal salt marshes primary producers (plants) capture the energy of the 

 sun and produce biomass through photosynthesis. Much of the energy produced 

 by photosynthesis is consumed in plant respiration. In marshes the energy 

 produced by photosynthesis is greater than that consumed by respiration, so 

 organic matter accumulates and becomes available to the system as a source of 

 energy for consumers. 



In the salt marshes of Maine, primary producers are the phytoplankton, algae, 

 and emergent vegetation (figure 5-47). Emergent vegetation in the forms of 

 cordgrass, salt hay, and black rush dominates the primary productivity. 

 Primary production in the form of plants is ingested directly by herbivores. 

 In wetland habitats, phytoplankton and, to some extent, algae are consumed by 

 a variety of filter-feeding invertebrates and larvae. Leaf loss to herbivores 

 was about 23.3% in a northern population of cordgrass (Hatcher and Mann 1975), 

 but no significant population of grasshoppers or other herbivorous insects was 

 observed in a Rhode Island salt marsh (Nixon and Oviatt 1973). 



Most of the primary production of salt marshes enters the food web as 

 detritus, but some is stored in the sediments as peat. As emergent plants 

 die, much of their above-ground biomass is transported from the marsh surface 

 to the water column by tides and exported to the adjacent estuary. In Maine, 

 scoring of the intertidal marshes removes virtually all of the cordgrass. 

 (McGovern, 1978, found no unsenescent above-ground cordgrass in December and 

 April). Dead vegetation (detritus) is colonized by microbes which decompose 

 the vegetation to particulate form. As detrital particles are further 

 decomposed, they are converted into an enhanced nutritious food source which 

 includes the colonizing microbes (figure 5-48) and is consumed by a variety of 

 filter- and deposit-feeding organisms. 



Salt marshes may import energy from the terrestrial habitats that border them, 

 the riverine systems that flow into them, the atmosphere, and the estuarine 

 open water systems that are contiguous to them. Litter from bushes, trees, 

 and grasses may be transported to salt marshes by rain, runoff, and wind. 

 Some terrestrial consumers (e.g., mice and rabbits) browse the salt marsh 

 vegetation and leave nutrient-rich fecal droppings. 



Runoff from rain potentially can carry a variety of inputs into the upper 

 areas of marshes. Natural items (e.g., litter, debris, and sediment) may be 

 transported into the marsh, but non-natural inputs, such as heavy silt from 

 construction activities, oil and grease from highways or parking lots, and 

 pesticides from fields also can be transported into the salt marsh. 



The riverine system carries organic material, dissolved nutrients, fresh water 

 animals, and potential pollutants (pesticides, sewage, heavy metals, and 

 hydrocarbons) from the inland systems to the estuarine salt marshes. It is 

 extremely difficult to quantify the amounts of these materials entering the 

 wetland system. However, it is clear terrestrial and riverine systems have a 

 direct, if not well-understood, relationship with the intertidal wetland 

 habitats. Most researchers agree that estuarine intertidal wetlands export 

 more energy than they import (Teal 1962; and Nixon and Oviatt 1973). 



5-128 



