Optimal culture conditions were investigated for the continuous culture of Isochrysis affinis galbana (T-Iso) by assessing the effects of irradiance, temperature, pH and nitrogen and phosphorus requirements. Assessment of the growth rate-irradiance relationship in a turbidostat experiment highlighted that an optimum irradiance efficiency for growth (E-mu) occurred at irradiance much lower than the saturating level. Furthermore, our modeling approach for productivity pointed out that an optimal set of irradiance and dilution rate could be achieved in order to maximize irradiance efficiency. Optimal conditions for growth were assessed for temperature, pH and irradiance by means of a factorial design experiment. The resulting model predicted that optimal culture conditions occurred at pH = 6.8, irradiance = 780 mu mol photons.m(-2).s(-1) and temperature = 30 degrees C and emphasized significant pH-temperature and pH-irradiance interactions on growth. The critical N:P ratio was shown to be a decreasing function of the growth rate and revealed high requirements of T-Iso for nitrogen relative to phosphorus. Finally, we propose an integrative optimization procedure for the continuous culture of I. affinis galbana and outcomes are discussed. (C) 2011 Elsevier B.V. All rights reserved.