Coral reefs worldwide are facing unprecedented threats due to the widespread effects of climate change and human activities. Although research on the ecological functions of coral reefs in sustaining fish biodiversity has gained momentum, most studies rely on simplified proxies, such as coral cover. This omission of the ecological functions of other habitat-forming species may hinder more accurate assessments. In this study, using global data from over 3,000 survey transects, we modeled the relationship between the composition patterns of habitat-forming species on coral reefs and fish richness using eXtreme Gradient Boosting (XGBoost) models and SHapley Additive exPlanations (SHAP) methods. Additionally, we estimated the ecological functions of coral reefs in sustaining fish species richness across various global marine ecoregions using the fitted XGBoost models. The results indicate that habitat-forming algae generally reduce fish species richness, whereas habitat-forming corals tend to enhance it. Furthermore, habitat-forming algae have a stronger average impact on fish species richness compared to habitat-forming corals, with impacts 2.3 times greater. We also found that marine ecoregions near Indonesia are hotspots, while those in the eastern tropical Pacific Ocean are cold spots for coral reefs' role in sustaining fish species richness. These findings have important implications for the sustainable management of coral reef ecosystems globally.

coral reefs, ecological function, fish biodiversity, habitat-forming species