Effects of irradiance and temperature on the growth and feeding of the obligate mixotrophic dinoflagellate Gymnodinium smaydae

Abstract

Gymnodinium smaydae is a fast-growing mixotrophic dinoflagellate. This study investigated whether light intensity (0–346 µmol photons m−2 s−1) and temperature (5–35 °C) affect the autotrophic or mixotrophic growth rate or ingestion rate of Gymnodinium smaydae GSSH1005. At all light intensities tested, G. smaydae GSSH1005 showed negative autotrophic growth rates, but positive mixotrophic growth rates when feeding on Heterocapsa rotundata. However, both autotrophic and mixotrophic growth rates were significantly affected by light intensity. The mixotrophic growth rates at 0–6 µmol photons m−2 s−1 were 0.67–0.72 day−1; they increased up to 1.28 day−1 at 58 µmol photons m−2 s−1, but became saturated at higher light intensities. The ingestion rates were also significantly affected by light intensity. The maximum ingestion rate of 2.3 ng C predator−1 day−1 was achieved at 58 µmol photons m−2 s−1. Although the autotrophic growth rates were negative at all temperatures tested, the mixotrophic growth rates were positive at 10–32 °C. Both autotrophic and mixotrophic growth rates were significantly affected by temperature. The maximum mixotrophic growth rate of 1.55 day−1 was noted at 25 °C. The ingestion rates were also significantly affected by temperature. The maximum ingestion rate of 4.2 ng C predator−1 day−1 was noted at 32 °C. Therefore, both light intensity and temperature can affect the population dynamics of G. smaydae GSSH1005.