| Abstract |
The genus Gambierdiscus produces ciguatera toxins, which has led to extensive studies of this genus. Epiphytic dinoflagellate cells were isolated from coralline macroalgae collected from the coastal waters of Jeju Island, Korea, and two clonal cultures were established. The morphology of these cells was examined using light and scanning electron microscopy, and the sequences of the small subunit (SSU), large subunit (LSU), and internal transcribed spacer (ITS) region of rDNA were determined. The phylogenetic trees based on SSU, LSU (D1-D3), and LSU (D8-D10) rDNA showed the two Korean isolates forming a clade with unidentified strains named Gambierdiscus sp. type 2. This clade showed a clear divergence from the two closest clades containing of the G. caribaeus and G. carpenteri strains. Morphologically, the Korean isolates had an anteroposteriorly compressed cell shape having a smooth theca ornamentation. Growth of the Korean isolates ceased when water temperatures were <20 °C or >30 °C with an optimum at 26 °C. This temperature preference may account for why Gambierdiscus sp. type 2 has only been isolated from the temperate waters of Korea and Japan. However, the two most closely related species G. caribaeus and G. carpenteri have broader temperature ranges tolerating as high as 34-36 °C and are globally distributed. Based on these results, the Korean isolates are proposed as a new species in the genus Gambierdiscus and named Gambierdiscus jejuensis sp. nov. Furthermore, it is suggested that the unidentified strains belonging to the Gambierdiscus sp. type 2 be transferred to the new species, G. jejuensis.
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