The biochemical profile and growth of the coastal diatom Skeletonema marinoi was investigated under four different daily blue light doses (sinusoidal light peaking at 88, 130, 250 and 450 μmol photons m(−2) s(−1), respectively). Ability of cells to regulate the light energy input caused alterations in growth and different biosynthetic pathways. The light saturation index for photosynthesis (E(k)), which governs the photoacclimative processes, ranged between 250 and 300 μmol photons m(−2) s(−1). Cells that were adapted to low light (<E(k)) enhanced their carotenoid, lipid and protein contents and lowered carbohydrate content, and vice versa under high light (≥E(k)). Variations in fatty acid, pigment and amino acid compositions were a result of light adaptation. Our data show that light is a potent factor for manipulating biomass synthesis in microalgae, such as diatoms for microalgal biotechnology.