Growth and chemical composition of the toxic dinoflagellate Gymnodinium galatheanum in relation to irradiance, temperature and salinity

Abstract

Gymnodinium galatheanum Braarud shows optimum growth (0.57 d-1) at 20 to 24°C and 24‰ S, within a temperature/salinity range of 7 to 24°C and 10 to 34‰ S, respectively. The growth rate is significantly affected by temperature and salinity, but no temperature-salinity interaction is found. No photoinhibition is found below 500 μmol photons m-2 s-1. Optimum irradiance for growth is ~120 μmol m-2 s-1, while the optimum for the growth-relevant chl a-normalized C fixation rate is >500 μmol m-2 s-1. This difference in optimum irradiance for the growth and photosynthetic rate is related to a decrease in the cellular chl a/carbon ratio with increasing irradiance. Carbon, nitrogen and phosphorus contents per cell are significantly affected by temperature, salinity and irradiance. The high and low P/C and N/P ratios, respectively, for nutrient saturated cells indicate that G. galatheanum has a large storage capacity for phosphorus.