The green alga Haematococcus pluvialis, which accumulates astaxanthin at an optimal temperature of 20 degrees C, was cultivated under temperatures of 20 degrees C, 23.5 degrees C, 27 degrees C, and 30.5 degrees C, in order to assess the effects on algal metabolism during the growth phase. The culture growth rate declined with above-optimal increases in temperature, and the final maximum cell concentration at 30.5 degrees C reached only 35% of that attained at 20 degrees C. On the contrary, the biomass productivity was increased under all the high-temperature conditions, probably reflecting the metabolism switch from cell duplication to energy accumulation that is typically observed in algal cultures subjected to environmental stress. Moreover, an increase in the light-harvesting capability of the alga was observed by means of the total pigment balance and the photosynthesis-intensity (PI) curve measured under the different cultivation conditions. Cultures kept at higher temperatures were able to better harvest and utilize the impinging light due to photo-acclimation. Finally, the differences in the astaxanthin metabolism were elucidated by subjecting the cultures to nitrogen starvation at 20 degrees C and 27 degrees C. In the culture at 27 degrees C, a 1.4-fold increase in the astaxanthin productivity was observed when compared to that at 20 degrees C, and the latter required almost two-fold more energy for the astaxanthin production compared with the 27 degrees C culture. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.