Environmental deoxyribonucleic acid metabarcoding reveals fish diversity in subtropical island mangrove rivers

BACKGROUND AND OBJECTIVES: Reliable biodiversity data are essential for management in World Heritage landscapes. Nevertheless, the ichthyofaunal diversity of short mangrove rivers remains insufficiently characterized because traditional survey methods demand high logistical effort, unrestricted site access, and advanced taxonomic knowledge. The study objectives were to document fish diversity across multiple short, protected island rivers and compressed freshwater-to-mangrove gradients and to provide baseline molecular data from samples collected before the World Heritage inscription. METHODS: Environmental water samples were collected in ۲۰۱۷ and ۲۰۲۰ along freshwater-to-mangrove gradients in four river systems. Following metabarcoding analyses, operational taxonomic units were classified using reference databases, phylogenetic placement, and expert taxonomic knowledge. Sequencing-depth rarefaction, incidence-based rarefaction and coverage standardization, distance-based redundancy analysis, permutational multivariate analysis of variance, and a Procrustes-based species-richness-controlled null model were used to evaluate sampling completeness and community structure.FINDINGS: A total of ۱۷۴ operational taxonomic units representing ۴۷ families and ۱۱۰ genera were detected, including ۲۰ Red List species. Taxonomic assignment revealed that roughly ۷۴ percent of operational taxonomic units corresponded to formally recognized species. Furthermore, community compositions were largely river-specific, showing restricted overlap among the studied aquatic systems. Diversity was generally higher in lower estuarine reaches associated with mangroves. Community composition was significantly associated with salinity and location, with distance-based redundancy analysis explaining ۵۳.۴ percent of adjusted variation. Gobiidae comprised ۲۸ percent of the total operational taxonomic units and showed strong concordance with whole-community patterns, suggesting that the family is a major and ecologically characteristic component of fish assemblages in the short subtropical mangrove rivers.CONCLUSION: The historical samples documented high and spatially structured fish diversity in short mangrove rivers within a World Heritage landscape. Accordingly, the generated dataset provides an irreplaceable pre-designation molecular baseline to support subsequent monitoring and environmental evaluations. Rarefaction and coverage standardization indicated substantial completeness of the retained operational taxonomic unit dataset while confirming that river-level comparisons require caution. The high richness and freshwater‑to‑estuarine distribution of Gobiidae indicate that the family is a major component of these assemblages. Integration of this baseline dataset with contemporary monitoring programs and environmental covariates will facilitate long-term biodiversity evaluations.

کلیدواژه ها:

Aquatic biodiversity ، Community composition ، Conservation monitoring ، Environmental management ، Species richness.