Ecophysiology of the kleptoplastidic dinoflagellate Shimiella gracilenta: II. Effects of temperature and global warming

Water temperature affects plankton survival and growth. The dinoflagellate Shimiella gracilenta survives using theplastids of ingested prey, indicating kleptoplastidy. However, studies on the effects of water temperature on kleptoplastidicdinoflagellates are lacking. We explored the growth and ingestion rates of S. gracilenta as a function of water temperature.Furthermore, using data on its spatiotemporal distribution in Korean coastal waters during 2015–2018, we predictedits distribution under elevated temperature conditions of +2, +4, and +6°C. Growth rates of S. gracilenta with andwithout Teleaulax amphioxeia prey as well as ingestion rates were significantly affected by water temperature. Growthrates of S. gracilenta with and without prey were positive or zero at 5–25°C but were negative at ≥30°C. The maximumgrowth rate of S. gracilenta with T. amphioxeia was 0.85 d-1, achieved at 25°C, and 0.21 d-1 at 20°C without prey. The ingestionrate of S. gracilenta on T. amphioxeia at 25°C (0.05 ng C predator-1 d-1) was greater than that at 20°C (0.04 ng Cpredator-1 d-1). Thus, feeding may shift the optimal temperature for the maximum growth rate of S. gracilenta from 20 to25°C. In spring and winter, the distributions of S. gracilenta under elevated temperature conditions were predicted notto differ from those during 2015–2018. However, S. gracilenta was predicted not to survive at some additional stationsunder elevated temperature conditions of +2, +4, and +6°C in summer or under elevated temperature conditions of +6°Cin autumn. Therefore, global warming may affect the distribution of S. gracilenta.