The family Ostreidae (Mollusca, Bivalvia) is an important component of marine ecosystems. The unique location and marine environment of Hainan Island provide diverse habitats for oysters. However, in recent years, oyster resources of Hainan Island have been under severe threats due to environmental pollution and habitat destruction. To better protect and utilize these biological resources, this study conducted systematic identification of naturally distributed oysters on Hainan Island using DNA barcoding technology. The results revealed the presence of 17 lineages, belonging to 14 species of oysters. The interspecies genetic distances for the COI gene sequences ranged from 10.09% to 31.72%, with notable DNA barcode gaps observed between intra- and interspecies. Additionally, the interspecies genetic distances for the 28S rRNA gene sequences varied between 0.24% and 14.03%. The DNA barcoding analysis indicated the existence of cryptic lineages within Saccostrea cuccullata (Born, 1778). Furthermore, the study highlighted that Saccostrea malabonensis (Faustino, 1932) is the most prevalent and dominant species along the Hainan Island coastline, attributed to its ability to adapt to a wide range of salinity levels. When comparing the species diversity of oysters between the western and eastern coasts of Hainan Island, it was found to be higher on the western coast. This disparity is likely influenced by geographical factors and human activities. Specifically, the western coast, situated in the Beibu Gulf, benefits from relatively stable water quality and numerous river inflows, providing abundant phytoplankton and optimal growth conditions for oyster larvae. Conversely, the eastern coast experiences frequent human activities, such as aquaculture and tourism, which may contribute to the decline in species diversity in this region. Overall, this study enhances our understanding of the species diversity of oysters on Hainan Island and provides scientific evidence that is crucial for the development, protection, and sustainable utilization of these valuable oyster resources.
