Effect of UV stress on the fatty acid and lipid class composition in two marine microalgae <Emphasis Type="Italic">Pavlova lutheri</Emphasis> (Pavlovophyceae) and <Emphasis Type="Italic">Odontella aurita</Emphasis> (Bacillariophyceae)

Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA), are abundantly synthesized by some phytoplankton species and play a key role in the marine food chain. However, they are generally considered to be sensitive to oxidation by UV radiation (UV-R). In order to investigate the effect of UV-R on the lipid composition of two marine microalgae, Pavlova lutheri and Odontella aurita, they were exposed to a combination of UVA-R and UVB-R with a total UV-R daily dose of 110 kJ m⁻². Chlorophyll a, photochemical efficiency, and lipid composition were then determined on days 3, 5, and 8 of UV-R exposure. In P. lutheri, exposure to UV-R treatment led to a decrease in the proportions of PUFAs, such as EPA and DHA, especially into structural lipids (glycolipids and phospholipids). Our findings reveal a reduction of 20% in EPA levels and 16% in DHA levels, after 8 days of UV-R treatment. In O. aurita, exposure to UV-R did not change the fatty acid composition of the total lipids and lipid fractions of the cells. EPA levels remained high (27–28% of total lipids) during the 8 days of treatment. Consequently, the n-3 fatty acid content of P. lutheri was altered which highlights the sensitivity of this species to UV-R, whereas the results obtained for O. aurita suggest a more UV-R resistance. As a result, in latitude countries with medium UV-R level, outdoor “race-way” culture of O. aurita could yield a high-EPA algal biomass, whatever the seasonal variations in UV-R.