Temperature responses of three Fibrocapsa japonica strains (Raphidophyceae) from different climate regions

Abstract

The harmful bloom alga Fibrocapsa japonica has a worldwide distribution in temperate regions and is occasionally responsible for mass mortality of fish. Little is known about requirements for optimal growth and survival of this species, especially about temperature constraints that define natural distribution. Therefore, we studied thermal traits in three Fibrocapsa strains from different climate regions. All strains were eurythermal and viable between 4 and 32°C, explaining their presence in temperate regions. Some differences in temperature response among the strains were observed, not only for growth rate but also for biovolume and net production. The implication of the observed responses was evaluated by translating growth performance of strains in the laboratory to potential performance in the natural habitats. Only the Japanese strain seemed to be well adapted to its environment, while the New Zealand strain exhibited growth and survival over a much broader temperature range, despite the small temperature fluctuations in its habitat. Interestingly, the German Wadden Sea strain encounters lethal temperatures in winter and must have a resting stage, able to survive temperatures <4°C, to explain its occurrence in this region. However, in general, the responses of the three F. japonica strains in culture were in good agreement with the observed seasonal occurrence in the field.