Isolation and cultivation of microalgae select for low growth rate and tolerance to high pH

► Growth and production rates of the red tide dinoflagellate Heterocapsa triquetra varies widely between strains under identical experimental conditions and is in general higher in recently established strains. ► Recently isolated strains have lower upper pH tolerance limits for growth than strains kept in the laboratory for more than 20 years. ► These findings suggest that the laboratory environment selects for high tolerance to elevated pH and lower growth and production rates. ► In order to incorporate data derived from culture experiments in conceptual and mathematical model formulations of microalgal blooms, the cultivation age and the levels of intra-specific variability need to be addressed.