Kenworthy, 1987; Schubel, 1973). Eelgrass leaves reduce shear stress of 

 water motion on sediments because current velocity at the top of an 

 eelgrass canopy may exceed 1 m s"-^, whereas velocity at the base of the 

 shoots is nil (Thayer et al., 1984; Fonseca et al., 1982a). When the 

 wasting disease destroyed eelgrass beds in the 1930's, the physical 

 characteristics of adjacent beaches often changed appreciably 

 (Rasmussen, 1977) . 



Anthropogenic and natural disturbances play a significant role in 

 regulating the abundance and distribution of eelgrass and other 

 seagrasses. Certainly the most profound natural disturbance affecting 

 eelgrass abundance during this century was the wasting disease of 1931- 

 33 that eliminated at least 90% of the eelgrass in the North Atlantic, 

 including Massachusetts (Cottam, 1933, 1934; den Hartog, 1987; 

 Rasmussen, 1977). Many areas were not recolonized for decades, and in 

 some locales, eelgrass is still expanding today (den Hartog, 1987). 

 There is evidence that eelgrass populations periodically collapse 

 (Cottam, 1934) , and recent outbreaks of the wasting disease have been 

 reported (Short et al., 1986). Other natural disturbances remove 

 eelgrass including catastrophic storms, periodic storms, sediment 

 transport, ice damage, and biological removal (Harlin et al., 1982; 

 Jacobs et al., 1981; Nienhuis and van Ireland, 1978; Orth, 1975; 

 Robertson and Mann, 1984) . 



Anthropogenic disturbances include physical removal, toxic 

 pollution, and degradation of water quality (Borum, 1985; Cambridge, 

 1979; Cambridge and McComb, 1984; Fonseca et al., 1985; Kemp et. al., 

 1983; Larkum and West, 1982; Nienhuis, 1983; Orth and Moore, 1983b; 



