58 



were not as catastrophic as the 1931-32 decline, and were not well 

 documented. 



Anthropogenic and natural disturbances 



Light, wave and current energy, salinity, and temperature limit 

 eelgrass distribution, but many natural and anthropogenic disturbances 

 of varying scale and frequency destroy eelgrass beds. Certainly the 

 most important natural disturbance during this century was the wasting 

 disease, but other natural disturbances such catastrophic storms, 

 periodic storms, sediment transport, ice damage, and grazing play an 

 important role in controlling eelgrass abundance (Harlin et al., 1982; 

 Jacobs et al., 1981; Kirkraan, 1978; Orth, 1977; Rasmussen, 1977; 

 Robertson and Mann, 1984). 



Anthropogenic disturbances that may destroy seagrass beds include 

 physical disturbances (dredging, groin construction, shellf ishing, 

 propeller damage) , toxic pollution, and degradation of water 

 transparency from nutrient enrichment, topsoil runoff, and activities 

 that resuspend sediments (Cambridge, 1979; Kemp et al., 1983; Orth and 

 Moore, 1983b; Orth and Heck, 1980; Sand-Jensen and Borum, 1983; Thayer, 

 et al., 1975) . 



The cause of a particular loss of eelgrass can often be inferred 

 from the pattern and rate of loss, the rate or lack of recovery, and the 

 local history of an area. Of all the anthropogenic an natural 

 disturbances affecting eelgrass populations, severe climatological 

 events and declining water quality have had the greatest impact on 



