11.2 Spatial Seagrass Patterns 
The spatial distribution of Z. marina was determined within the Yaquina Estuary from 1997 to 
the present utilizing aerial photographs and false-color near-infrared (color infrared, CIR) film (Young 
et ah, 1999). Details on how this analysis was accomplished are presented in Lee et al. (2006) and 
Appendix B. 
Permanent bed perennial shoots make up the vast majority (90%) of the eelgrass population 
(Boese and Robbins, in prep.), and almost all of this eelgrass is in the intertidal zone in both the ocean 
(Figure 11.2) and river dominated (Figure 11.3) estuarine portions. Details on the methods used to 
generate Figures 11.2 and 11.3 are presented in Appendix B. The portions of the graphs corresponding 
to depths deeper than -1.5 m (MLLW) may have errors due to limitations in mapping methods and 
bathymetric modeling. Most (97%) of the Z. marina in the Yaquina Estuary is located in ocean 
dominated estuarine portions (Figure 11.1), which is illustrated by the differences in y-axis scales in 
Figure 11.2 and Figure 11.3. Although the distribution suggests an effect of salinity on eelgrass 
distribution, Z marina appears to be able to tolerate a wide range of salinities (Nelson, 2005). 
Z. marina also appears able to survive short-term exposures to fresh water, however, net leaf 
photosynthesis decreases in waters with salinities below 5 and totally ceases in completely fresh water 
(Hellblom and Bjork, 1999; Biebl and McRoy, 1971). Within the Yaquina Estuary, Kentula and 
DeWitt (2003) found that salinity appeared to be a statistically significant factor in controlling the 
within estuary distribution of Z. marina , even though the reported mean summer and winter salinity 
ranged from 25 to 33, which are well within published tolerance limits for Z. marina (Nelson, 2005). 
The results of the Kentula and DeWitt (2003) study were complicated by changes in light attenuation 
and temperature that tended to co-vary with salinity. Results may have been further complicated since 
the bathymetry of the Yaquina Estuary changes with distance from the estuary’s mouth such that the 
amount of suitable area in the optimal depth range for seagrass growth becomes limited in upriver 
estuarine segments (Lee et al., 2006). 
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