ABSTRACT Mangroves play a vital role in supporting diverse associated fauna, yet information on the fish communities they host in the Philippines remains limited. In this study, we assessed fish diversity across four Philippine bioregions—Catanduanes, Batangas, Aklan, and Palawan—using environmental DNA (eDNA) metabarcoding. We analyzed 2,053,055 sequence reads of the 12S rRNA gene from water samples. We annotated 276 operational taxonomic units (OTUs), of which 159 (57.6%) were resolved to species level. OTU richness was highest in Batangas, followed by Aklan, Catanduanes, and Palawan (medians = 57, 46, 34, and 26, respectively), with many unique OTUs per site (40–48) and per habitat type (111 in fringe mangroves, 98 in riverine mangroves). However, alpha diversity, which accounts for species richness and evenness, did not differ significantly among sites or habitats, indicating overall similar diversity. In contrast, beta diversity varied significantly across bioregions, driven by biogeographic and environmental factors such as site, salinity, climate, habitat type, vegetation, and water flow. Most identified species were classified as ‘Least Concern’ ( n = 123), but the presence of ‘Not Evaluated’ ( n = 22) and ‘Data Deficient’ ( n = 12) species highlights gaps in conservation knowledge. Two Vulnerable species, the brown‐marbled grouper ( Epinephelus fuscoguttatus ) and the spotted seahorse ( Hippocampus kuda ), were also detected, emphasizing the conservation value of mangroves. More than half of the species‐level OTUs ( n = 96; 60.38%) have commercial value, illustrating the role of mangroves in supporting coastal livelihoods. Several OTUs could only be annotated to genus or family, and the presence of ‘Unknown species’ indicates unexplored biodiversity, underscoring the need to expand tropical genetic reference databases. Overall, our findings demonstrate that eDNA metabarcoding is a reliable tool for assessing fish diversity across spatial scales and has strong potential for long‐term monitoring and management to support mangrove resilience and sustainability.
Nob et al. (Sun,) studied this question.
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