Haematococcus pluvialis grows as motile bi-flagellated green cells under optimum growth conditions. Due to changes in environmental conditions, such as increased light intensity, high temperature, nutrient limitation or high salt concentrations, the healthy green cells undergo morphological and biochemical changes as their survival strategies. They turn into red cysts, lose their motility, increase cell size, thicken cell walls, and induce carotenogenesis. In particular they accumulate significant amounts of astaxanthin esters that may constitute up to 95% of the total carotenoids.
Commercially, Haematococcus pluvialis is cultivated as a two-stage process under photoautotrophic conditions. The first (green) phase is maintained under low light, as most of the strains are sensitive to light, for induction of carotenogenesis. This first phase is focussed on generating enough actively growing green biomass, which then after gentle harvesting, is transferred to the second (red) phase which consists of a stress medium and/or high-light condition for cellular morphogenesis with appropriate biochemical changes, especially the accumulation of carotenoid astaxanthin.