Temperature constrained growth of O. cf. ovata within a window of 18-30 掳C, while best performances were recorded at 22 and 26 掳C. Growth was maximum at 12 h daylength, whereas it was limited by photon flux density at short daylength (9 h) and often showed photosaturation at the longest daylength (15 h). Cells with anomalous shape were found during the exponential phase at the lowest and highest temperatures, while cells with a reduced size were produced at all conditions except 18 掳C. Total toxin concentration varied between the different environmental conditions and between exponential and post-exponential growth phases without a clear pattern, whereas toxin composition was less variable. Our results suggest that O. cf. ovata is adapted to intermediate temperatures and daylength conditions such as those recorded in the natural environment at the beginning of summer and/or at the beginning of autumn, when this dinoflagellate builds up its biomass along the coast of the Mediterranean Sea. Photosaturation instead occurs at the highest temperature and irradiance conditions, thus supporting the observations of generally lower cell abundances in late July-August.
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