10. Macroalgal Biomass as a Water Quality Response Measure 
10.1 Introduction 
Excessive algal growth is one of the major symptoms of eutrophication in coastal estuaries 
(Bricker et al., 1999). Three of the principal classes of algae are phytoplankton, epiphytic algae, and 
macroalgae. In PNW coastal estuaries, epiphytic algae (attached to other organisms) and macroalgae 
(seaweed) generally are considered to be of greater concern than is excessive growth of phytoplankton, 
which is rapidly transported out of the estuaries by tidal exchange. In this section, we report on the 
macroalgae issue as it relates to the question of eutrophication in Yaquina Estuary. 
10.2 Approach 
Beginning in 1997, numerous studies involving macroalgae have been conducted in Yaquina 
Estuary by WED. These include aerial photomapping surveys in 1997 and 1998, and intensive ground 
surveys of percent cover and biomass during 1998-2004. A listing of the individual studies conducted, 
and the analytical approaches utilized here, are presented in Appendix B. 
10.3 Results and Discussion 
10.3.1 Annual Variation: 1997 - 1998 
The aerial distributions of benthic green macroalgae documented in the aerial photography of 
July 23, 1997 and August 10, 1998 indicate a substantial increase in coverage in 1998 (Figure 10.1). 
Part of the increase very probably is due to the fact that the 1998 aerial photographs were taken two 
and one half weeks later than were those in 1997. However, based on seasonal percent cover 
distributions obtained in 1999-2000 (Figure 10.2), an increase in cover of only about 15% would be 
expected. In contrast, the benthic macroalgal cover of bare substrate on August 10, 1998 was 
approximately 250 % that on July 23, 1997 (Fig. 10.1). 
An empirical model has been developed that uses flood tide water temperatures to predict N0 3 
+ N0 2 concentrations in coastal ocean water entering Yaquina Estuary during flood tides (Brown and 
Ozretich, in review). The average concentrations predicted by this model for two-month intervals 
preceding the aerial surveys of 1997 and 1998 are 2.1 and 6.0 pM, respectively. This difference in 
average N0 3 + NO? concentration is assumed to be the result of the 1997 El Nino condition that 
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