Abstract
Sea snakes are a major component in many coral reef ecosystems, as predators on fishes. Emydocephalus ijimae is a dietary specialist on demersal fish eggs, but it is not well understood how wide a variety of fish species are involved in this unique predator–prey system. To clarify the feeding ecology of E. ijimae on a mid-latitude coral reef, we identified fish eggs taken from the snakes’ stomachs using DNA barcoding. Relative abundances of potential prey species in the snake’s habitat were also estimated by environmental DNA metabarcoding analysis. A total of 209 stomach contents were obtained in monthly field surveys from May 2017 to December 2019, and these consisted of 618 presumptive fish egg clutches of at least 30 species and 14 genera in 5 families. Snake predation peaked in June, with 3.38 clutches/stomach on average, and dropped to 0.04 in December–January. It was estimated that 473 clutches/hectare were consumed at our sites by E. ijimae in June. Pomacentridae (22 species) comprised 93.4% of the total clutches, followed by 4.05% Plesiopidae (2 species), and 1.94% Gobiidae (4 species). The predation frequencies for prey species generally were correlated with their relative abundances in the habitat, suggesting that E. ijimae preys on fish eggs largely in proportion to their availability. Nonetheless, predation frequencies for several pomacentrid species deviated significantly from their abundances in the community, suggesting a certain degree of prey selectivity by E. ijimae. These findings provide an important basis for further studies on this unique system.
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Acknowledgements
We thank Yuji Sano, Keitaro Sano and Ryutaro Sano for assistance with field surveys, Takenobu Tokuyama for his help with the molecular experiments, and Nakatada Wachi for his suggestions on the data analysis. Also, we would like to express our sincere thanks to Dr. Alan H. Savitzky for his constructive comments and English editing on our manuscript. We also thank two anonymous reviewers for their comments and suggestions to improve our manuscript. This study was conducted under permission from the Japan Ministry of the Environment for capturing the sea snakes and for installation of the water temperature logger in Kerama Islands National Park (Ministry of the Environment of Japan: Kyushu District: Naha Office, 1606062, 1707283, and 1807251).
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TY collected data in a field survey, analyzed the data and wrote the manuscript. MT participated in data analysis and wrote the manuscript.
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Yamamoto, T., Toda, M. Dietary variation and seasonal changes in the fish egg eating specialist, Emydocephalus ijimae (Squamata: Reptilia) in mid-latitude coral reefs. Coral Reefs 44, 451–466 (2025). https://doi.org/10.1007/s00338-025-02615-y
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DOI: https://doi.org/10.1007/s00338-025-02615-y