54 



(Cottam and Munroe, 1954). When there is sufficient light available, 

 the next most important factors limiting eelgrass distribution are 

 physical energy, salinity, and temperature. 



Eelgrass is euryhaline, but is usually not found where salinities 

 persist below 5 ppt (Sand-Jensen and Borum, 1983; Bieble and McRoy, 

 1971) . In B.uzzards Bay and on Cape Cod, there are few sizable inputs of 

 freshwater, and eelgrass distribution is limited by salinity in only a 

 few areas. 



Physical energy also controls eelgrass distribution, but eelgrass 

 can has the ability to grow in diverse habitats. For example, eelgrass 

 beds can grow at sustained current velocities up to 150 cm sec" , and 

 may tolerate brief exposure to higher velocities (Fonseca et at., 1982a, 

 1983). Eelgrass beds can tolerate considerable wave exposure as well, 

 but are generally not found in the surf zone. Thus, on exposed coasts 

 eelgrass may not grow above 2 m MLW, whereas in protected areas, 

 eelgrass may be found in the intertidal. There are exceptions: clumps 

 of eelgrass can be nestled between boulders or in intertidal pools in 

 high energy areas (pers obs) . 



Eelgrass is eurythermal, and can survive between the freezing 

 point of seawater and 40° or more, therefore temperature is important 

 only in shallow stagnant waters such as salt ponds and salt marsh pans 

 which are exposed to wide temperature fluctuations or appreciable icing 

 (e.g. Keddy, 1987). In these and other shallow areas, freezing and ice 

 scour may remove beds (Robertson and Mann, 1984), and annual populations 

 of eelgrass are most common in these types of habitats. 



