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Macroalgal accumulation in a Pacific Northwest estuary - evidence of poor eutrophic condition?
Citation:
Young, D., Pat Clinton, D. Specht, R. Caldwell, AND J. Lamberson. Macroalgal accumulation in a Pacific Northwest estuary - evidence of poor eutrophic condition? Presented at Joint Aquatic Sciences Meeting, Portland, OR, May 18 - 23, 2014.
Impact/Purpose:
Application of a European Union (EU) macroalgal assessment framework for eutrophic condition to Yaquina estuary yielded misleading results. The authors conducted a five year study of benthic macroalgae in three bathymetric zones and six sites in this estuary, producing ~400 individual surveys of average macroalgal cover and biomass throughout the range of native eelgrass. When these data were applied to the EU assessment framework, approximately 85 percent of the surveys in the major eelgrass sectors were ranked as reflecting Poor or Bad eutrohophic conditions. The findings did not distinguish between areas of non-detectable and high sediment sulfides, where median levels in the eelgrass zone at one site were 50 times reported LC-50 values for marine invertebrates but essentially zero at the other site with similar macroalgal abundance. The EU framework results also did not reflect the fact that no apparent relationship between macroalgal and eelgrass biomass was found, or the fact that average macroalgal biomass decreased with distance from the estuary mouth, consistent with reports that coastal upwelling, not the watershed, is the dominant source of nutrients during the growing season. The assessment also contradicts the fact that Yaquina estuary is a major source of crabs and clams to the recreational fishery. These results raise serious questions regarding the applicability of the EU macroalgal framework for assessing eutrophication condition in Pacific Northwest coastal estuaries.
Description:
A five year study of benthic macroalgal dynamics was conducted in Yaquina estuary, Oregon, yielding 400 surveys of average macroalgal cover and biomass within three intertidal bathymetric zones at six sites covering the range of native eelgrass habitat. Application of a published macroalgal assessment framework for European Union (EU) estuaries to the results ranked the summer eutrophic condition for the major eelgrass sector as Poor to Bad. However, this framework did not reflect very different estimates of sediment porewater sulfide toxicity at the two sites of highest macroalgal and eelgrass abundance, nor the fact that highly variable average levels of macroalgae had no apparent effect on eelgrass biomass. Average macroalgal biomass decreased with distance from the estuary mouth, consistent with reports that coastal upwelling, not the watershed, is the dominant source of nutrients during the growing season. The assessment also contradicts the fact that Yaquina estuary is a major source of crabs and clams to the recreational fishery. These results raise serious questions regarding the applicability of the EU macroalgal framework for assessing eutrophication condition in Pacific Northwest coastal estuaries.