Natural alkalinity enhances coral physiology and what this means for restoration

Ocean acidification and its role in disrupting ecosystem dynamics has been extensively documented in contemporary marine science. Ocean acidification results from the oceans absorbing approximately one-third of all CO₂ released into the atmosphere generating downstream shifts in seawater carbonate chemistry. Governing bodies worldwide are incentivizing marine Carbon Dioxide Removal (mCDR) technologies to mitigate anthropogenic climate change. Among these strategies, Ocean Alkalinity Enhancement (OAE) has been proposed as a dynamic method to remove carbon and offset ocean acidification. However, OAE remains a ‘black box’ with many foundational questions still unanswered. There is growing evidence for potential co-benefits of OAE at the ecosystem level, but further research is needed to capture how OAE integrates at the organismal level. Here we present a novel dataset highlighting how naturally occurring alkalinity enhancement positively modulates coral physiology. Three biogeochemically distinct substrate types were identified in Bocas del Toro, Panama. Ten coral colonies of the branching species, Porites porites (n = 10), were deployed within 50 m x 50 m matrices in dense and sparse T. testudinum meadows (n = 3) as well as in intact coral communities (n = 3; >30% live coral cover). We found that belowground respiration within intact communities of T. testudinum generated an alkalinity-rich environment significantly increasing calcification and fitness. Perhaps most compelling is that this phenomenon persisted despite corals experiencing weak to moderate hypoxia (£ 4.5 mg L^-1) due to nighttime respiration.We believe this research provides critical evidence for how Ocean Alkalinity Enhancement could modulate organismal physiology in at-risk marine communities.