Effects of temperature, salinity and irradiance on growth of the novel red tide flagellate Chattonella ovata (Raphidophyceae)

To elucidate the mechanism of bloom outbreaks of the ‘novel’ noxious flagellate Chattonella ovata (Raphidophyceae), we examined the growth responses of the organism with 42 different combinations of temperature (10–35 °C) and salinity (10–35), and under various light intensities (0–381 μmol photons m−2 s−1). The three strains, CO2, CO3, and CO8 of C. ovata isolated from Hiroshima Bay, tolerated a wide range of temperature (15–32.5 °C) and salinity (10–35). The organism could grow rapidly at over 20 °C and salinity of 20, and the maximal growth rates of 1.11–1.47 divisions day−1 were found in the combination 25–30 °C and salinity of 25–30. These maximum growth rates and optimal temperatures and salinities of the C. ovata strains were clearly higher than those of Chattonella antiqua and Chattonella marina. A statistical analysis showed that growth rates of C. ovata were significantly influenced by temperature–salinity interaction. Furthermore, growth of the strain CO2 and CO8 was observed at the irradiance 15–45 μmol photons m−2 s−1 or more and was saturated at over 300 μmol photons m−2 s−1. The half-saturation constants of irradiance for the growth of C. ovata were much higher than those of C. antiqua and C. marina. These results showed that C. ovata is better adapted to higher temperature, salinity and light environments than C. antiqua and C. marina. These physiological features of C. ovata would be an ecological advantage to development of the bloom during summer seasons.