Diversity and distribution of the coral-associated endolithic algae Ostreobium in the Southwestern Caribbean

Coral reefs are facing significant environmental challenges. Ocean acidification has the potential to induce the dissolution of coral reefs. The community of micro-bioerosion exhibits a heightened level of concern in the context of ocean acidification. Comprehending the close interplay between bioeroders and corals is of utmost importance in predicting the trajectory of these vulnerable ecosystems. The genus Ostreobium, which belongs to the order Bryopsidales (Chlorophyta) and comprises euendolithic chlorophyte algae, has been identified as the primary cause of reef dissolution among microbioeroders. The objective of this study was to comprehend the inherent distribution of rbcL clades of Ostreobium in the Southwestern Caribbean corals within a gradient of reef depth. The Ostreobium rbcL variants were found to be linked with corals belonging to the Agariciidae, Merulinidae, Poritiidae, Siderastreidae, Astroconeiidae, Montastreidae, Mussidae, and Pocilloporidae families. The individuals selected for the current investigation are categorized as members of either the "complex" or "robust" coral groups. Our findings indicate that solely the corals categorized as complex exhibit close memberships with the three Ostreobium superclades. In general, the dispersion of Ostreobium within the Southwestern Caribbean region exhibits differentiation among various coral groups and is influenced by geographical and bathymetric factors. The Ostreobiums diversity is primarily composed of ecological specialists, wherein most clades are linked to particular hosts. Conversely, only a few ecological generalists are associated with multiple hosts, akin to zooxanthellae. Ostreobium exhibits greater diversity on encrusting corals such as agariciids, which are among the most abundant and widespread coral species in the Caribbean.