Effect of UV-B on lipid content of three Antarctic marine phytoplankton

The effects of UV-B radiation on the fatty acid, total lipid and sterol composition and content of three Antarctic marine phytoplankton were examined in a preliminary culture experiment. Exponential growth phase cultures of the diatoms, Odontella weissflogii and Chaetoceros simplex, and the Haptophyte, Phaeocystis antarctica, were grown at 2 (+/- 1)degree and exposed to 16.3 (+/- 0.7) Wm(-2) photosynthetically active radiation (PAR). UV-irradiated treatments were exposed to constant UV-A (4.39 (+/- 0.20) Wm(-2) and low (0.37 Wm(-2)) or high UV-B (1.59 Wm(-2)). UV-B treatments induced species-specific changes in lipid content and composition. The sterol, fatty acid and total lipid content and profiles for O. weisfloggi changed little under low UV-B when compared with control conditions (PAR alone), but showed a decrease in the lipid content per cell under high UV-B treatment. In contrast, when P. antarctica was exposed to low UV-B irradiance, storage lipids were reduced and structural lipids increased, indicating that low UV-B enhanced cell growth and metabolism. Phaeocystis antarctica also contained a higher proportion of polyunsaturated fatty acids under low UV-B in comparison with PAR-irradiated control cultures. The flagellate life stage of P. antarctica dies under high UV-B irradiation. However, exposure of P. antarctica to high UV-B irradiance increased total lipid, triacylglycerol and free fatty acid concentrations, indicating that increases in lipid content were associated with the colonial life stage. Lipid concentrations per cell also increased when C. simplex was exposed to high UV-B irradiance. This resulted from increases in free fatty acid concentration, principally saturated fatty acids, and may indicate degradation of complex lipid during high UV-B treatment. Under low UV-B, there was no statistically significant difference when compared with the control. In comparison with the PAR-exposed controls, low UV-B benefited or did not affect cellular metabolism and growth of the three microalgae examined. Our results indicate that the effect of UV-B irradiances on the lipid content of Antarctic marine phytoplankton is species-specific. Changes in ambient UV-B may alter the nutritional quality of food available to higher trophic levels.