# Ocean acidification modulates material flux linked with coral calcification and photosynthesis

## TL;DR

This study shows how ocean acidification affects two coral species differently, impacting their calcification and photosynthesis processes.

## Contribution

The study introduces new insights into how ocean acidification influences coral calcification and photosynthesis through microsensor measurements of boundary layer dynamics.

## Key findings

- Pocillopora acuta showed reduced dark proton efflux and increased light O2 flux under elevated pCO2.
- Montipora capitata showed no significant changes in flux parameters under elevated pCO2.
- Elevated pCO2 exacerbates microchemical gradients in the boundary layer, potentially threatening calcification in vulnerable species.

## Abstract

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.

The online version contains supplementary material available at 10.1038/s41598-025-30818-4.