Table 10.1 Percentiles for benthic green macroalgae biomass (gdw nf 2 ) for Yaquina Estuary 
(1998 - 2004, Zone 1 only) and the Classification data set (2004 - 2005). 
Data set 
Percentiles for Macroalgae Biomass 
Percentile for 
Sample Size 
25 lh 
50 th 
75 ,h 
100 gdw nf 2 
Zone 1 
Yaquina 
Dry 
0 
34.9 
189.8 
62.7 % 
4432 
Wet 
0 
0 
2.9 
95.1 % 
2142 
Classification 
0 
0 
11.6 
92.9 % 
351 
Zone 2 
Classification 
0 
0 
0 
99.6 
231 
Median Zone 1 dry season macroalgal biomass between 1999-2004 in Yaquina Estuary (Table 
10.1) was less than the mean value (83 gdw nf 2 ) measured from six band transects in 1999-2000 
(Figure 10.2), and considerably higher than the median value from the Classification study. In the 
Yaquina Estuary, biomass exceeded 100 gdw nf" for 20% of the intertidal area, compared with only 1- 
6% of intertidal area for the six estuaries of the Classification Study. The Classification Study found 
that >98% of benthic green macroalgae occurred in the ocean dominated Zone 1 of the Yaquina 
Estuary (Lee et al., 2006). The reasons for the higher algal biomass found in the Yaquina Estuary 
compared to other Oregon systems studied is not clear, and makes extrapolation of information to the 
rest of the Oregon coast difficult. 
10.5 Comparisons with Findings from Other Regions 
Literature review demonstrates that there is a wide range of macroalgal densities that cause, or 
are correlated with, negative effects on estuarine organisms (Appendix D, Table D.2). Water 
temperatures reported in the reviewed literature ranged from 9 to 20 °C versus 8-18 °C for Zone 1 of 
Yaquina Estuary, and were thus reasonably similar. Approximately one-third of the studies reported 
negative ecological effects from macroalgae for percent cover values of >50% and biomass densities of 
>200 gdw m' 2 . In the Yaquina Estuary, -27% of the intertidal zone exceeded 50% cover, and -10% 
had macroalgal biomass exceeding 200 gdw nf 2 (Lee et al., 2006). We also note that this density (200 
gdw m 2 ) is twice the threshold accepted for damage by macroalgae to seagrass in Chesapeake Bay 
(Bricker et al., 2003). 
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