Effects of temperature, salinity and their interaction on growth of toxic Ostreopsis sp. 1 and Ostreopsis sp. 6 (Dinophyceae) isolated from Japanese coastal waters

Some species belonging to Ostreopsis, a benthic dinoflagellate genus, are known to produce palytoxin analogues. Around the coastal regions of Japan, the toxic Ostreopsis sp. 1 and Ostreopsis sp. 6 which are genetically divergent from other species of Ostreopsis are present from the southern to northern regions and in the southern region, respectively. The present study examined the growth responses of these strains to seven temperatures (15–35 °C) in combination with five salinities (20–40) and discusses the effects of temperature and salinity on their distribution and bloom dynamics in Japan. Tolerable temperatures and salinities ranged 15–30 °C and 25–40 for Ostreopsis sp. 1, and 17.5–30 °C and 20–40 for Ostreopsis sp. 6. The optimal temperature ranges which gave growth rates of >90 % of maximal growth rate of each strain were 22–25 °C for Ostreopsis sp. 1 and 24–30 °C for Ostreopsis sp. 6. Therefore, Ostreopsis sp. 1 is putatively tolerant to lower temperatures and thus possesses adaptability to colder waters of relatively higher latitude regions of Japan, whereas Ostreopsis sp. 6 presumably possesses adaptability to warmer waters of the southern region. We conclude that growth responses of Japanese toxic Ostreopsis sp. 1 and Ostreopsis sp. 6 to temperature-salinity affect their distribution and bloom dynamics in Japan.