Average salinities during 1975 to 1977 increased 4.2 ppt at the surface and 

 3.4 ppt at a depth of 3°m (Keser et al. 1978) and average temperatures were 

 1.3° C (2.3°F) lower at 0.15 m and 2.1°C (3.8°F) lower at 3 m. These changes 

 were due to increased exchange between bay waters and the colder, more saline 

 waters of the Sheepscot River when the causeway was removed. 



Two years after the causeway was removed changes in the cordgrass community 

 were observed. The mean number of shoot densities sharply decreased in 1975 to 

 1977 because of the increased salinity and colder water (Keser et al. 1978). 

 Plants 20 to 30 inches (50 to 75 cm) tall did not flower after the causeway 

 was removed. Between 1975 and 1977 average biomass decreased to 58% of that 

 of the previous years. Increased tidal amplitude, higher salinity, and lower 

 temperatures reduced vigor and fecundity in the lower marsh and eventually 

 will lead to its destruction. 



The primary producers in estuarine emergent salt marshes are phytoplankton, 

 the benthic and epiphytic algae of the mud surfaces, and emergent vegetation. 

 The relative contributions of each of these producer groups to estuarine 

 intertidal marsh production is not known. In Maine, scientists have 

 concentrated on establishing the level of production of the emergent 

 vegetation and the role it plays in supplying energy to the estuarine system 

 primarily through the detrital cycle. Data that characterizes salt marsh 

 phytoplankton and algae are scarce. 



Although phytoplankton contributes to wetland productivity, it is much more 

 important in the open estuary (see "Phytoplankton" above) . Nixon and Oviatt 

 (1973) found that in a Rhode Island salt marsh the diatoms Asterionella , 

 Thalassiosera , Nityochia , Skeletonema , and Chaetocerus dominated the larger 

 phytoplankton except during late summer when dinof lagellates were more 

 abundant. 



Epiphytic algae are small plants that grow on exposed mud surfaces and on 

 stems of emergent and submergent plants. Although detailed information on 

 their contribution to the productivity of Maine salt marshes is lacking the 

 importance of these small but numerous plants is heightened by the knowledge 

 that they are very productive during the fall and winter months, when the 

 grass communities lie senescent. Chapman (1940a) identified the algae of a 

 Massachusetts salt marsh and found that algal associations were correlated 

 with the emergent grass communities and the degree of inundation. Redfield 

 (1972) working in a Massachusetts salt marsh reported that the dwarf cordgrass 

 zone is covered almost completely with a thin layer of filamentous algae 

 during summer, principally Lyngbia sp. and Vaucheria sp. (see "Macroalgae and 

 Rooted Vegetation" above) . 



Little, if any, research has been conducted concerning the epibenthic 

 productivity of salt marshes in Maine; however, researchers have found that in 

 Massachusetts, epibenthic marsh productivity exhibits a seasonal variation. 

 Production in Great Sippewisset Marsh, Falmouth, Massachusetts, was found to 

 be low during summer and early winter but peaked in the spring (115 mg C/nr 

 /yr) and in the fall (60 mg C/m^/yr). Epibenthic production was as high as or 

 higher than the marsh phytoplankton production (Van Raalte et al. 1976). 



The most visible biotic component of the marsh, the emergent vegetation, 

 dominates the salt marsh and is the principal contributor to salt marsh 



5-121 



10-80 



