Possible evidence of range expansion of the tropical ghost crab Ocypode ceratophthalmus to a temperate region driven by climate change

Recent rapid climate change caused by global warming has significantly affected marine organisms, and species normally found in tropical zone have been reported in temperate zones. This cryptic range expansion may influence ecosystems due to interspecific competition for habitats, prey, and population reproductive resources with native species. In September 2021 and August 2022, we identified the tropical ghost crab species Ocypode ceratophthalmus in the southern region of the Korean Peninsula. To date, only three species of ghost crabs, O. stimpsoni , O. cordimana , and O. sinensis , had been reported. Morphologically, all specimens possess a stridulating ridge composed of two parts of circular and horizontal lines but lack prolonged eyestalks. Species identification was confirmed using a partial sequence of the mitochondrial cytochrome c oxidase subunit I ( mtCO1 ) gene for each individual given their morphological immaturity. Additionally, population genetic analyses using the mtCO1 and nuclear sodium‑potassium ATPase α-subunit ( NaK intron) genes revealed the high genetic connectivity between Korean populations and the neighboring populations in Northeast Asia. The results of the neutrality test and mismatch distribution indicated that the Jeju population in South Korea experienced a recent population expansion. Given the oceanic flow of the Kuroshio Current and the smaller currents branching off, the genetic homogeneity of populations is anticipated to be a result of continuous immigration of individuals from more southern localities. These findings provide pivotal insights into the habitat expansion of the tropical crabs into temperate zones. Additionally, they inform conservation strategies for native crabs by enabling effect-based estimation of species range expansion and settlement. • This is the first record of the tropical ghost crab Ocypode ceratophthalma in South Korea. • Genetic markers showed high connectivity between Korean and other Northeast Asian populations. • The Jeju population exhibited genetic signals of recent expansion into a temperate habitat. • Cimiate change might have induced range shifts of this tropical crab.