Ocean acidification modulates material flux linked with coral calcification and photosynthesis

Coral reefs are essential for the foundation of marine ecosystems. However, ocean acidification (OA), driven by rising atmospheric carbon dioxide (CO₂) threatens coral growth and biological homeostasis. This study examines two Hawaiian coral species-Montipora capitata and Pocillopora acuta to elevated pCO₂ simulating OA. Utilizing pH and O₂ microsensors under controlled light and dark conditions, this work characterized interspecific concentration boundary layer (CBL) traits and quantified material fluxes under ambient and elevated pCO₂. The results of this study revealed that under increased pCO₂, P. acuta showed a significant reduction in dark proton efflux, followed by an increase in light O₂ flux, suggesting reduced calcification and enhanced photosynthesis. In contrast, M. capitata did not show any robust evidence of changes in either flux parameters under similar increased pCO₂ conditions. Statistical analyses using linear models revealed several significant interactions among species, treatment, and light conditions, identifying physical, chemical, and biological drivers of species responses to increased pCO₂. This study also presents several conceptual models that correlate the CBL dynamics measured here with calcification and metabolic processes, thereby justifying our findings. We indicate that elevated pCO₂ exacerbates microchemical gradients in the CBL and may threaten calcification in vulnerable species such as P. acuta, while highlighting the resistance of M. capitata. Therefore, this study advances our understanding of how interspecific microenvironmental processes could influence coral responses to changing ocean chemistry.