First record of Pseudadenoides kofoidii, a marine sand-dwelling dinoflagellate, from Geoje Island, Korea: morphology, phylogeny, and growth and fatty acid content under different temperature conditions

To clarify an unidentified marine sand-dwelling dinoflagellate isolated from samples collected at a sandy beach of Geoje Island, Korea, its morphology and molecular phylogeny based on the small and partial large subunit rRNA gene sequences were examined. In addition, growth responses and fatty acid content of the isolate under different temperature conditions were investigated to assess its physiological traits and aquaculture potential. Cells were 26.3–41.5 μm long (34.8 ± 3.6 μm) and 19.8–40.8 μm deep (28.9 ± 4.8 μm), and a nucleus located in the dorsal half of the cell and pyrenoid surrounded by a starch sheath were observed. Scanning electron microscope observations revealed that the cells were characterized by a lack of precingular plates, scattered thecal pores, a single flagellar pore and a shallow anterior cingulum. One or two pores were present on the plate 3p, and one pore was consistently observed on plate 4p. The phylogenetic analyses revealed that the Korean isolate can be identified as Pseudadenoides kofoidii that has not previously been described in Korean coastal area. In the growth experiments, the isolate appeared to prefer moderate temperatures (15 and 20°C) rather than higher temperature (25°C). Although this species exhibited temperature-dependent variation in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) production, P. kofoidii maintained remarkably high levels of DHA and EPA in its fatty acid composition (>42% of total fatty acids), highlighting its potential as a promising marine source of fatty acids for aquaculture applications.