Effects of temperature and light intensity on the growth and toxicity of<i>Heterosigma akashiwo</i>(Raphidophyceae)

Abstract

The effects of temperature and light intensity on the growth and toxicity of Heterosigma akashiwo (Hada) were studied in the laboratory. The growth and toxicity of this organism were found to be greatly influenced by temperature and light intensity. The best growth was found at 25 °C where the toxicity was very low. On the other hand, cells were found to be most toxic at 20 °C (0.087 ± 0.005 FU), although the growth was much less than at 25 °C. The lowest toxicity was observed at 30 °C with a toxicity of 0.011 ± 0.005 FU. The toxicity of this species also differed markedly at different light intensities. It gave the maximum toxicity at 200 μE m−2 s−1, but poor growth. The best growth occurred at 100 μE m−2 s−1, but with a marked toxicity drop. In toxin composition studies, the amounts of most of the toxic fractions were lower at 25 °C and 100 μE m−2 s−1 where the growth was most conspicuous.