Abstract
The noxious red tide flagellate Gymnodinium nagasakiense (Dinophyceae) was collected from Suo-Nada, in the western section of Seto Inland Sea. The effects of temperature, salinity and irradiance on growth of this organism were examined using axenic culture to evaluate the relative importance of these factors on dynamics of natural populations. The growth of G. nagasakiense was observed at the irradiance more than 10μE/m2/s and saturated at 110μE/m2/s. The growth of the flagellate was examined in 25 different combinations of temperature (10 to 30°C) and salinity (10 to 30‰) under saturated irradiance. Growth occurred at temperatures from 10 to 30°C and at salinities from 15 to 30‰. The highest growth rate was observed in the combination of 25°C and 25‰. The tolerable salinity range of growth was relatively wide at optimum temperature and was reduced to a much narrower range at suboptimal temperatures. A statistical test indicates that temperature and salinity interact in their influence on growth. The present study reveals that G. nagasakiense is an eurythermal and euryhaline organism. These physiological characteristics presumably allow them to endure the winter as motile cells, which in turn act as the seed population for the summer red tide.
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