There was a significant positive linear relationship (Figure 11.10) between percent light 
reduction and log+1 transformed biomass data, for external and internal blades combined. The linear 
regression relationship overestimates light reduction for the low epiphyte biomass samples. 
Figure 11.10 Linear regression relationship between the percent of light reduction to log(x+l) 
transformed epiphyte biomass per unit Z. marina surface area. 
Epiphytes reduced the amount of light reaching the surface of Z. marina leaves. The monthly 
range of variation in light reduction was high, ranging from 4 - 91% for external leaves, and 2-62% 
for internal leaves. The range in mean light reduction for a plant was estimated as 3 - 76 %, with an 
overall mean estimated light reduction of 53% (n=18, SE=4.6). As a result of the spatial differences in 
epiphyte biomass within the two salinity zones in the estuary, average light reduction for a plant was 
higher in Zone 1 (61%, n=72, SE=3.4) than in Zone 2 (37%, n=44, SE=4.5) as a result of the more 
heavily fouled external blades. 
11.6 Zoster a marina Light Requirements 
Minimum light requirements for maintaining and restoring SAV have been proposed for 
Chesapeake Bay (Batiuk et al., 2000) and Puget Sound (Thom et ah, 1998). Chesapeake Bay light 
criteria values were empirically estimated by measuring the maximum depth of SAV annually and 
84 
