Molecular species diagnosis confirmed the occurrence of Kumamoto oyster Crassostrea sikamea in Korean waters

In order to develop an appropriate natural resource management policy, it is important to elucidate the cryptic habitats of species. Oyster species are likely to have such unrecognized habitats owing to the difficulty involved in morphological species identification. In this study, we discovered a novel cryptic habitat of the Kumamoto oyster Crassostrea sikamea, a sibling species of the Pacific oyster C. gigas, in Korean waters. We collected 50 oyster samples from Suncheon Bay, located in the southern Korean Peninsula, among which 20 individuals of C. sikamea, 29 of C. gigas, and one C. sikamea/C. gigas hybrid were identified based on mitochondrial and nuclear DNA markers. There were no significant differences in shell morphology between the two species, which is consistent with how difficult it is to delineate them based on their shell features. Our identification of this novel C. sikamea habitat should help to improve the resource management of East Asian oysters.