Effects of light intensity and temperature on growth and ingestion rates of the mixotrophic dinoflagellate Alexandrium pohangense

Abstract

The newly described phototrophic dinoflagellate Alexandrium pohangense, APPH1409, fed only on the dinoflagellate Margalefidinium polykrikoides among 16 potential algal prey species tested. To explore the ecophysiology of A. pohangense, its growth and ingestion rates with and without added M. polykrikoides prey were determined as a function of light intensity (0-346 mu mol photons m(-2) s(-1)) and temperature (10-35 degrees C). Both the autotrophic and mixotrophic growth rates of A. pohangense fed on M. polykrikoides were significantly affected by light intensity. In the darkness, A. pohangense did not grow under either mixotrophic or phototrophic conditions. The compensation light intensity for the growth of A. pohangense under mixotrophic conditions (2.7 mu mol photons m(-2) s(-1)) was lower than that under autotrophic conditions (11.7 mu mol photons m(-2) s(-1)). Growth inhibition due to light stress did not occur at the tested light intensities. A. pohangense grew between 15 and 30 degrees C, but did not grow at 10 degrees C or32 degrees C. Both the autotrophic and mixotrophic growth rates of A. pohangense fed on M. polykrikoides were also significantly affected by temperature. At the same light intensity or temperature, the mixotrophic growth rate of A. pohangense was generally considerably greater than the autotrophic growth rate, with a few exceptions. Therefore, light intensity, water temperature, and prey accessibility may affect the population dynamics of this species.