Filling the monitoring gap: Aquatic ecosystem metabolism as a cost-effective, scalable tool for assessing marine carbon dioxide removal

Emily J Chua, Hilary I Palevsky

Marine carbon dioxide removal (mCDR) is an emerging climate mitigation solution increasingly recognized as necessary to supplement greenhouse gas emission reductions. Various mCDR methods, from biotic to abiotic measures, are being piloted, fueled by enthusiasm from governments and the private sector. As companies start to sell carbon credits, standards for monitoring, reporting, and verification (MRV) to assess removed carbon and environmental impacts have begun to lag behind, putting the credibility of mCDR at risk. Currently proposed assessment frameworks require costly, complex measurements that can pose a practical barrier, especially for smaller projects. Although dissolved oxygen is easily measured and often included as a required monitoring parameter, its role in evaluating ecosystem status remains poorly defined—highlighting gaps in MRV interpretation and implementation. To address this monitoring bottleneck, we propose the widespread adoption of aquatic ecosystem metabolism metrics in the MRV pipeline. Ecosystem metabolism, which can be calculated using low-cost, autonomous oxygen sensor measurements, provides real-time, integrative insights into how mCDR interventions affect carbon cycling and ecosystem function. Here, we review how metabolism has been used as an effective tool in environmental management and highlight parallels with mCDR assessment needs. We then present a synthesis of metabolism measurements in coastal ecosystems and describe how scaling these measurements can address key mCDR assessment challenges. We also discuss practical considerations and opportunities for incorporating metabolism into MRV frameworks. By tracking ecosystem responses across mCDR methods and deployment sites, metabolism provides a readily measured and communicated metric that serves as a practical addition to the mCDR monitoring toolkit.