The microalgae Tetraselmis suecica in mesocosms under different light regimes

Pigment profiles and pheopigment accumulation of the microalga Tetraselmis suecica were studied under different spectral irradiances. Irradiance conditions typical of coastal waters with (‘clear’) and without (‘coloured’) chromophoric dissolved organic matter (C-DOM) were simulated in mesocosm cultures. The lag, growth and stationary phases were found to follow a logistic model, as light limitation controlled growth where maximum carrying capacity and incremental growth were sensitive to irradiance conditions, both being higher in mesocosms with full irradiance conditions (clear sea conditions without attenuation due to C-DOM). Through daily measurements of chlorophylls, carotenoids and pheopigments, it was found that the highest concentrations of pigments occurred in the growth phase: in particular in the clear sea conditions. Lower concentrations of lutein were measured in the coloured mesocosms showing their protective function against photo-oxidation. Pheopigment concentrations increased linearly throughout the experiment, being highest in the mesocosm with clear sea conditions. In general, clear sea conditions, including ultraviolet irradiance, showed the higher production of primary and secondary pigments, demonstrating the high tolerability of T. suecica to a range of solar irradiance conditions.