Synergy of Ocean Alkalinity Enhancement with Biological Carbon Pump for Marine CO2 Removal in the Coastal Ecosystem with Oysters

Abstract Ocean Alkalinity Enhancement (OAE) and bivalve farming offer two promising marine carbon removal strategies. However, their combined effectiveness in coastal seas remains poorly understood due to the opposite effects of the calcification and nutrient excretion of bivalves on water CO2. Through manipulative experiments with mesocosms, here we identify that moderate OAE (2700 μmol·kg-1) acted synergistically with oyster farming in carbon storage and sequestration. Although OAE alone did not significantly alter primary production and biodeposition, the combination of moderate OAE and oyster farming boosted the two parameters, shifting carbon storage from inorganic toward organic dominance. The combination enhanced total carbon storage, refractory carbon, and protein production by 129%, 38%, and 52%, respectively, relative to oyster farming only. In contrast, these effects diminished in higher OAE (3150 μmol·kg-1). These findings highlight that integration of moderate OAE with oyster farming aligns with global sustainability goals of combating climate change and enhancing food security.