Composition and influencing factors of the amphibian community in Hainan Dongzhaigang National Nature Reserve

Aims: As vertebrates in the transition from aquatic to terrestrial life, amphibians are an essential indicator of environmental health. The wetland-type Hainan Dongzhaigang National Nature Reserve protects a major natural area of mangrove forests. Information on amphibian resources in mangrove wetland-type reserves remains limited. We aim to better understand the community characteristics and spatial distribution pattern of amphibians and their influencing factors in Hainan Dongzhaigang National Nature Reserve. Further, we provide a scientific basis for the conservation and management of amphibians in mangrove wetland-type reserves. Methods: Three rounds of line transect surveys at night were conducted for amphibians in the reserve from July 2022 to April 2023. We used a total of 39 fixed sample lines with a length of 200 m in the reserve, with a spacing of more than 500 m between sample lines. Every night from 19:00 to 24:00 we surveyed each sample line once and repeated this routine for 3 days. The Mann-Whitey U-test analysis was applied to determine if there were differences in amphibian richness and abundance between the two sample areas. Differences in amphibian community composition between breeding periods were compared by Chi-square test. Pearson analyses were used to determine the relationship of each factor with amphibian abundance, richness, and Shannon’s diversity index. Results: Seven species of amphibians from five families were distributed in the reserve, including dominant species Fejervarya moodiei, suboptimal species Hylarana guentheri, and unfrequent species of Fejervarya multistriata, Duttaphrynus melanostictus, Microhyla fissipes, M. pulchra, and Polypedates megacephalus. Each sample line averaged a record of 2.67 amphibian species within the buffer and experimental zones, whereas the majority (94.44%) of sample lines recorded only a single species Fejervarya moodiei in the core zone. The seven amphibian species were recorded in the nearshore habitats of the reserve, while the near-sea habitats were inhabited only by Fejervarya moodiei. Species richness (P < 0.01) and abundance (P < 0.01) of nearshore amphibians were negatively correlated with seawater salinity. Further, their abundance was negatively correlated with ambient humidity (P < 0.01) and water pH (P < 0.01), but positively correlated with tidal height (P < 0.01), air temperature (P < 0.001), and water temperature (P < 0.001). Conclusion: Our research shows that there are spatial differences in amphibian community composition, and seawater salinity and animal dispersal may contribute to these differences. We observe differences in amphibian community composition, with inter-monthly variations in breeding activities and ambient temperature being important factors. Additionally, we find that tidal height, humidity, and water pH significantly influence the variation of amphibian abundance in the reserve.