suppressed normal upwelling of nutrient-rich subsurface water that year (Corwith and Wheeler, 2002). 
The ~ 300 % increase in the modeled nutrient concentration agrees well with the ~ 200 % net increase 
in intertidal macroalgal cover between 1997 and 1998 surveys. 
10.3.2 Seasonal Variation: 1999-2000 
Monthly averages (+ 1 std. error) for percent cover and biomass of benthic green macroalgae 
were measured for six sites (Appendix B) in Zone 1 during 1999-2000 (Figure 10.2). Maximum 
values occurred in September - October for both percent cover (~ 50 %) and biomass (~ 200 gdw m‘“), 
with rapid declines in November. Between December 1999 and May 2000 the respective averages 
were below 5 % and 5 gdw m‘“. In Zone 1 more than 95% of the intertidal cover and biomass 
accumulation for benthic green macroalgae occurred during the dry season. 
Macroalgal composition was assessed in 2001, and consisted of taxa most closely resembling 
Ulva lima : ~60%; U. fenestrata : ~30%; U. flexuosa : ~10%; U. intestinalis: <5%; (WED unpublished 
data). The seasonality and peak biomasses are consistent with historical data sets from the lower 
portion of Yaquina Estuary. Davis (1981) observed mean biomass of 400-500 gdw m' for green 
macroalgae during June to September, 1980 and Garber et al. (1992) observed green macroalgae 
biomass of 185-370 gdw m" during June to October of 1984 and 1985. These comparisons suggest 
that there was no increase in the frequency or intensity of macroalgal blooms within Yaquina Estuary 
over this 20 year period. 
66 
