Environmental DNA metabarcoding reveals geologic, not geographic, drivers of coral community structure in Palau

Coral reefs in tropical and subtropical oceans are complex ecosystems characterized by high biodiversity. Zooxanthellate scleractinians are a major component of these reefs. However, the factors influencing coral community establishment and the diversity of coral genera remain poorly understood. A scleractinian-specific environmental DNA metabarcoding (Scl-eDNA-M) method offers a comprehensive and comparative approach to analyzing coral communities across different reef sites. In this study, 10 reef sites in the Republic of Palau, each with distinct geographic features, were monitored using the Scl-eDNA-M system. This system is technically capable of identifying all 69 known scleractinian coral genera in Palau; approximately 60 genera were detected in this study. Acropora , Porites , Montipora , Pocillopora , Goniastrea , and Merulina were the dominant genera, while Leptoria , Platygyra , Pavona , Favites , Isopora , Cyphastrea , and Hydnophora were sub-dominant. The visual census method supported the eDNA metabarcoding results. Clustering analysis based on coral diversity at the genus level indicated that the 10 sites could be grouped into three categories, primarily based on the dominance of Acropora , Porites , Montipora , or Pocillopora . These community profiles were not associated with geographic features such as north versus south or east versus west, but rather with geological features such as lagoons, moats, or reef slopes. In contrast, several genera were identified only at specific geographic locations, including the western outer reefs. Although a larger-scale survey is needed, this study provides an insight into how coral communities in the Palau Islands may have formed in relation to geographic and geological factors.