Abundance of Ciguatera-Causing Dinoflagellates from Coastal Waters off West-sea, South Korea

Sea surface temperatures have shown a long-term increasing trend along the Korean coasts in association with climate change. Consistent with this warming trend, subtropical benthic dinoflagellate genera, including Gambierdiscus, Ostreopsis, Coolia, Prorocentrum, and Amphidinium, were first reported from the coastal waters of Jeju Island in 2009. These genera include toxin-producing species associated with ciguatera fish poisoning (CFP) and therefore warrant continued monitoring because of their potential implications for marine ecosystems, fisheries, and aquaculture. This study surveyed the dominant macroalgal species along the west coast of Korea and compared the occurrence patterns of five genera of subtropical benthic dinoflagellates epiphytic on these macroalgae during 2022 and 2023. Prorocentrum cf. lima and Ostreopsis sp. were consistently detected during spring, summer, and autumn over two consecutive years in the coastal waters of Seocheon, Buan, and Gochang, whereas they were absent during winter. These findings indicate that these subtropical benthic dinoflagellates are capable of surviving in the highly dynamic intertidal environment of the West Sea, characterized by a large tidal range. Their repeated seasonal occurrence over two consecutive years suggests that they are recurring components of the western Korean coastal ecosystem and highlights the need for continued monitoring under ongoing ocean warming.