Effects of temperature and light intensity on growth in <i>Prorocentrum</i> cf. <i>balticum</i> (Dinophyceae) isolated from the Oyashio-Kuroshio Mixed Water region, North Pacific

Owing to its particular mixotrophic nutrition, Prorocentrum cf. balticum has recently been suggested to contribute significantly to the biological pump in the world’s oceans. However, the physiological attributes that facilitate its distribution have not yet been investigated. We clarified the effects of temperature and light intensity on the growth of a strain of P. cf. balticum isolated from the Oyashio-Kuroshio Mixed Water region and then estimated its potential habitat in the western North Pacific in the context of global warming. In batch cultures maintained at 5°C–30°C, the highest growth was observed at 25°C, while the viable temperature range was estimated to be 6.03°C–29.4°C. At the six different light conditions tested (20–500 µmol m−2 s−1), growth rates were positively correlated with light intensity, except at 500 µmol m−2 s−1 where photoinhibition was observed. At 20°C, the maximum specific growth rate was calculated to be 0.661 day−1 and the compensation light intensity and the saturation light intensity were 1.15 and 283 µmol m−2 s−1, respectively. These findings suggested that compared to other Prorocentrum species, P. cf. balticum is generally well suited to subtropical environments characterized by high light intensities. However, the potential to survive in mid-latitude environments that experience low temperatures during winter suggests a high probability of year-round occurrence at higher latitudes, including the Oyashio region, in the future.