118 



after the first patches of eelgrass appeared. 



The percent cover of eelgrass beds at peak abundance also varied 

 among sites. In high energy environments like Megansett Harbor, 

 Falmouth, wave scour and storms frequently remove patches of eelgrass of 

 various size, so some habitats never exceed 50% cover, even over 

 decades. In shallow areas like this, eelgrass beds survive and 

 recolonize in the troughs of migrating sand waves (Fig. 21a). In 

 contrast, eelgrass beds eventually cover virtually all of the bottom in 

 quiescent areas. 



Differences in both colonization rate and peak cover can be 

 explained by differences in disturbance size, disturbance frequency, 

 vegetative growth rate, and seedling recruitment rate that can be 

 measured from photographs. These variables were included in a computer 

 simulation that accurately predicted changes observed on sequences of 

 photographs (Costa, 1988 and in prep.). Results of this simulation 

 suggest that physical removal of patches of eelgrass less than 10 m'' 

 have little effect on rate of colonization or peak cover, even when 25% 

 of the bed is removed each year. Other disturbances, such as declining 

 water quality or catastrophic storms may lead to sizeable and 

 longlasting losses. 



The pattern of eelgrass colonization on a larger scale (lOO's to 

 lOOO's of ha) is distinct from the small scale pattern of colonization. 

 On large parcels of coast, such as around Great Neck (above) or high 

 energy areas like Wianno Beach on Cape Cod (in preo.) eelgrass took 20 

 to 30 years to reach peak abundance after onset of colonization. Growth 

 on a large scale is not logistic, rather staggered or linear because of 



