Ocean acidification, driven by increased atmospheric CO2 absorption, poses significant threats to marine ecosystems, particularly coral reefs. This longitudinal study monitored coral health, biodiversity, and water chemistry at 12 reef sites across the Indo-Pacific over 18 months. We documented pH decreases of 0.15 units and corresponding 28% declines in coral calcification rates. Species diversity decreased by 22% in the most affected areas, with branching corals showing greater vulnerability than massive species. Our research includes novel methods for community-based monitoring and provides actionable recommendations for reef conservation and restoration efforts.