Disentangling ocean acidification organismal effects through an experimental system that allows automated and dynamic carbonate chemistry manipulations

Chair: Thomas Trull

Iria Gimenez (1)*, George G. Waldbusser (2), Burke Hales (3)

1 College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, USA
2 College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, USA
3 College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, USA

Background
Ocean acidification (OA)-driven pCO2, pH, and saturation state changes are tightly coupled within oligotrophic open ocean regimes, but can decouple across regimes or within dynamic coastal and estuarine waters. Laboratory OA experiments relying on CO2 gas injection or addition of mineral acid result in covariance of these carbonate system variables distinct from natural settings where they may change simultaneously and independently. These approaches do not allow determination of the carbonate parameter driving sensitivity, and thus difficult mechanistic interpretation of physiological responses.

Methods
Building on previous batch-culture work, we developed a system that allows long-term experimental decoupling of carbonate parameters. The system independently manipulates alkalinity and dissolved inorganic carbon (DIC) to and consists of two parts: 1) an analyzer that monitors source-water pCO2 and DIC in real time, 2) a dynamic feed-forward controller system that performs automated, precise acid and carbonate reagent additions through computer-controlled syringe pumps.

Findings
After overcoming several implementation challenges, we have been able to simultaneously manipulate water on three different experimental treatments to results less than 3% from respective DIC and alkalinity targets. Preliminary tests show that extremely sensitive embryos and young larvae develop and grow normally in water manipulated to mimic control chemistry, while harmful conditions resulted in poor larval success. We will present data from precision and accuracy tests and preliminary physiological data from experiments to evaluate saturation state and pH integrated effects over the entire mussel larval period.

Conclusions
We constructed an experimental system providing opportunity to run OA experiments over long timescales in a flow-through setting providing more consistent experimental conditions. This system allows better mechanistic understanding of physiological responses to OA through a clear separation of effects due to different carbonate parameters and can be used on multiple organisms, allowing greater understanding of OA responses in ocean-margin waters that show decoupling.