Culture method and growth characteristics of marine benthic dinoflagellate Ostreopsis spp. isolated from Japanese coastal waters

Abstract

Blooms of toxic dinoflagellates of the genus Ostreopsis, which is known as a producer of palytoxin (PTX) analogs, may pose a threat to human health in tropical, subtropical, and temperate regions around the world. In the present study, we established a suitable culture method for Ostreopsis spp. isolated from Japanese coastal waters and characterized their growth potential using the method to discuss their bloom dynamics. Each clonal strain of Ostreopsis cf. ovata, Ostreopsis sp. 1, Ostreopsis sp. 5, and Ostreopsis sp. 6 was incubated in 25 × 150 mm test tubes with a flat bottom containing various kinds of medium. Since Ostreopsis spp. strains grew well in IMK and/or f/2 media, we selected these media for cultivation of all the Ostreopsis spp. isolates. Growth rates of O. cf. ovata (0.834 divisions/day), Ostreopsis sp. 1 (0.619 divisions/day), and Ostreopsis sp. 6 (1.04 divisions/day) that produce PTX analogs significantly differed (p < 0.05) respectively and are clearly higher than those of other reported epiphytic dinoflagellate Gambierdiscus toxicus, Prorocentrum lima, and Coolia monotis cultures, which suggest that these species have ecological advantages to predominate through the algal succession in Japanese coastal waters, resulting in a potential risk to human health in this region.