Impact of decarbonated and high pH seawater on the physiology of intertidal mussels

Marine-based electrochemical Carbon Dioxide Removal (mCDR) is a rapidly evolving subject area. Technology is being developed that facilitates atmospheric CO₂ removal by extracting Dissolved Inorganic Carbon (DIC) from seawater. Decarbonated seawater, that also has a high pH, is released into the marine environment, facilitating the drawdown of atmospheric CO­₂ into the surface ocean. Chemical perturbations also include low levels of carbon dioxide (CO₂) and bicarbonate (HCO₃^-),and increased levels of carbonate (CO₃^2-). There is no literature that investigates the impact of low carbon seawater with elevated pH on marine ecosystems. Understanding and cataloguing the effect of mCDR is fundamental for: i) determining potential impact on vulnerable systems; ii) supporting the development of any necessary mitigating actions; iii) confirming overall mCDR effectiveness; and iv) engaging the public and harnessing their support.

This work presents results from laboratory experiments that examine the physiological response of keystone organisms to decarbonated and high pH seawater. Decarbonated high pH seawater released into the environment will be diluted by mixing with ambient seawater, such that the chemical perturbations become less extreme with distance from source. Intertidal mussels (Mytilus edulis) are a keystone species that utilize DIC for major cellular functions and have poor acid-base balance. Mussels were exposed to three different dilutions of decarbonated high pH seawater (generating pH values of approximately, 10, 9.2 and 8.7). Mortality, oxygen consumption rate and filtering rate were measured after short-term (48 hr) exposure and then 48 hrs after returning to ambient seawater. Initial experiments indicate that undiluted decarbonated high pH seawater has a significant short-term impact on the physiological response of Mytilus edulis, but the species shows signs of recovery following a week in ambient seawater. Data from these and other experiments will be used to generate a risk gradient that illustrates how physiological response(s) change with dilution of low carbon, high pH seawater discharge.