HMSC Research Seminar: The Response of the Olympia Oyster (Ostrea lurida) to Increased Alkalinity: Implications for Ocean Alkalinity Enhancement.

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Speaker: Ben Epley, Ph.D. Student, College of Ocean, Earth and Atmospheric Sciences, Oregon State University

Topic: Ocean Alkalinity Enhancement (OAE) is a proposed marine carbon dioxide removal (mCDR) technique which increases the ocean’s capacity to absorb carbon dioxide and simultaneously mitigates ocean acidification. While ostensibly beneficial, the effect a rapid increase in alkalinity would have on most marine organisms remains poorly constrained. The Olympia Oyster (Ostrea lurida) is a brooding species native to the US west coast. In previous work, the PD1 larvae have demonstrated an acute sensitivity to alkalization, raising questions about sensitivity at subsequent life stages. We exposed adult Olympia Oysters to alkalization scenarios ranging from a control (no alkalinity addition) to approximately double the control, ~4000 µmol kg-1, while maintaining near atmospheric CO2 equilibrium to isolate the effect of alkalinity additions on physiology. Responses were quantified with physiological rate measurements of biomineralization and respiration, shell/tissue growth, and measurements of shell composition. We found statistically significant increases in biocalcification rate when ΩCa is greater than ~ 8, with no observable change in respiration or growth rate. However, changes in shell Mg:Ca and proportion metabolic carbon across treatment conditions are suggestive of a weakening control over biocalcification. Finally, we observed a notable increase in mortality rate with increasing alkalinity following a domoic acid (DA) exposure related to a harmful algal bloom, adding to previous work linking the toxicity of domoic acid to oysters in buffered seawater. This work demonstrates that while OAE has a minor direct effect on adult O. lurida physiology, the community needs to explore both ecosystem level responses to OAE and fundamental biocalcification mechanisms to predict responses across species and life history stages.