Temperature constrained growth of O. cf. ovata within a window of 18–30 8C, while best
performances were recorded at 22 and 26 8C. 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 8C. 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.