Ocean Romance: Japanese Treefrogs Exploit Coastal Pools for Breeding Under Salinity and Habitat Constraints

Understanding amphibian microhabitat selection in coastal landscapes offers insight into patterns of local ecological adaptation in coastal island populations. This study examined whether coastal pools can sustain populations of the Japanese Treefrog, Dryophytes japonicus, a species whose coastal breeding ecology remains poorly understood. Additionally, we tested the prediction that salinity strongly influences breeding site use. We combined a meta-analysis of 95 published studies with single-time-point field surveys of 810 tadpoles from 84 coastal pools across five topographically varied sites on Jeju Island, Republic of Korea. Using random forest and partial dependence analyses, we assessed eight environmental factors shaping tadpole occurrence. Across all studies reviewed, publication patterns showed no thematic or temporal bias across decades. However, more than 70% of studies focused on agricultural habitats, while fewer than 5% examined natural coastal pools, revealing a major knowledge gap. Empirical field data integrated with statistical modeling showed that, although salinity was the focal predictor of our study, distance to the coastline emerged as the strongest determinant of tadpole occurrence, with greater occurrence in pools positioned farther inland. The species consistently bred in shallow, low-salinity pools located away from both the forest edge and the immediate shoreline, revealing clear spatial filtering within the coastal landscape. Dissolved oxygen also contributed to tadpole occurrence, particularly in coastal pools, underscoring the importance of well-oxygenated water for successful breeding. Together, these results provide ecological insight into how D. japonicus persists in coastal landscapes under multiple environmental constraints.