Temporal and Spatial Distribution of the Toxic Epiphytic Dinoflagellate Ostreopsis cf. ovata in the Coastal Waters off Jeju Island, Korea

The temporal and spatial distribution of the toxic epiphytic dinoflagellate Ostreopsis cf. ovata was investigated off the Jeju coastal waters, Korea, from July 2016 to January 2019. The results showed that the presence of Ostreopsis cf. ovata in 184 macroalgae was 79.3%, and it was more frequently attached to red algae and brown algae than to green algae. The abundance of Ostreopsis cf. ovata as determined by quantitative real-time polymerase chain reactions (qPCR) and microscopic analysis was 4–3204 cells g−1, and the maximum abundance observed in September 2018, when the water temperature was 24.4 °C. The abundance was higher in summer and autumn than in spring and winter. Spatially, high abundance was observed in autumn on the northern coast of Jeju Island and, in summer, in the southern and eastern coastal waters. The water temperature of Jeju coastal waters in winter remained higher than 15 °C, and this species could be overwintering in the Jeju waters. Therefore, further monitoring and research are needed to evaluate the proliferation of Ostreopsis cf. ovata, which contains a novel toxin with unidentified effects on humans.