Microalgal starch is a potential feedstock for biofuel production. The effects of KNO3 and MgSO4 concentrations and light intensity on biomass and starch production by the marine microalga, Tetraselmis subcordiformis, were investigated. Under 200 mu mol m(-2) s(-1) irradiance and sulfur-deprived conditions, a starch productivity of 0.62 g L-1 d(-1) and a starch content of 62.1% based on dry weight (DW) was achieved. A starch content of 54.3% was achieved under low irradiance and nitrogen starvation, which was 6.5% higher than that under nutrient- and light-sufficient conditions. Photosynthetic activity was indispensable for starch accumulation. It is difficult to reach high starch productivity and starch concentration simultaneously. Proper nutrient concentrations are necessary to achieve high starch productivity or starch concentration based on the target. The high starch productivity and starch content suggest that T. subcordiformis is a promising microalgal starch producer. (c) 2012 Elsevier Ltd. All rights reserved.