Water Chemistry and Habitat Size Predict Spawning Success in Endangered Hynobius yangi: Feeding Ecology and Implications for Urban Wetland Design

Urbanization threatens amphibians through habitat loss and fragmentation. The critically endangered Hynobius yangi, endemic to Korea, faces severe habitat destruction from urban development. No previous study has simultaneously assessed physicochemical habitat quality and larval feeding ecology across restored and alternative wetlands for this species using fecal DNA metabarcoding. We compared 25 H. yangi spawning sites in Sasong New Town through long-term monitoring (April 2021–September 2024; 364 surveys) and fecal DNA metabarcoding (18S V9, COI313, and blocking primers) from 60 larvae. Egg sac abundance showed negative associations with habitat area (r = −0.21), pH (r = −0.23), and conductivity (r = −0.21); however, none retained significance after Bonferroni correction, and each explained only 4–5% of variance, indicating exploratory associations. Associated conditions included area 115.5 ± 16.2 m2 (mean ± SE), circularity 44.2 ± 2.4%, pH 7.55 ± 0.10, and conductivity 53.0 ± 2.7 μS/cm. Dietary analysis identified 17 prey taxa. Larvae in alternative areas showed generalist feeding favoring Perlidae and Tubificidae, while restored-area larvae showed specialist patterns dominated by Chironomidae, Nematocera, and Psychodidae. Both habitat types supported H. yangi populations. These preliminary findings suggest that appropriately designed alternative areas may complement traditional restoration, pending multi-site validation.