64 



of bays. In more enriched areas, particularly near polluted streams or 

 near enriched groundwater inputs, green algae such as Ulva and 

 Enteromorpha replace the red algae that dominate less enriched areas 

 (Lee and Olsen, 1985; Pregnall, 1983; pers. obser.). This difference in 

 species composition can be explained by the fact red algae are effective 

 in storing "pulses" of nutrients, whereas these green algae grow quicker 

 under more continuous exposure to high nutrients (Fujita, 1985). 



Drift material may also consist of shed eelgrass leaves and 

 detached Codium. Algae that are abundant on eelgrass such as the red 

 alga Polysiphonia, are abundant in drift material in these areas. 



Recolonization and interpreting historical changes 



Eelgrass may decline in some areas due to disturbance, but will 



« 

 recolonize any devegetated area, as well as newly created habitat, if 



conditions are conducive to lateral growth of vegetative shoots or 



germination and survival of seedlings. Colonization rates have been 



documented in transplant studies. For example, Fonseca et al. (1979, 



1982b) state that full coverage can be obtained in one year by 



transplanting 20 shoots on a 1 m grid. Similarly high rates of 



expansion have been noted in other studies (Araski, 1980; Goforth and 



Peeling, 1979). 



In related work (in prep.), I have studied the colonization of 



bare substrate by eelgrass using sequences of aerial photographs. From 



these photographs, vegetative growth rate, recruitment rate, disturbance 



size and frequency (= bed mortality) can be measured and these four 



parameters, were incorporated in a computer simulation. The results of 



