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

The harmful bloom alga Fibrocapsa japonica has a worldwide distributionin temperate regions and is occasionally responsible for massmortality of fish. Little is known about requirements for optimalgrowth and survival of this species, especially about temperatureconstraints that define natural distribution. Therefore, westudied thermal traits in three Fibrocapsa strains from differentclimate regions. All strains were eurythermal and viable between4 and 32°C, explaining their presence in temperate regions.Some differences in temperature response among the strains wereobserved, not only for growth rate but also for biovolume andnet production. The implication of the observed responses wasevaluated by translating growth performance of strains in thelaboratory 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 overa much broader temperature range, despite the small temperaturefluctuations in its habitat. Interestingly, the German WaddenSea strain encounters lethal temperatures in winter and musthave 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 werein good agreement with the observed seasonal occurrence in thefield.