Comparing the response and adaption of Antarctic tropical and temperate microalgae to ultraviolet radiation (UVR) stress

There has been concern over the increased penetration of ultraviolet radiation (UVR) over the Antarctic resulting from the depletion of stratospheric ozone layer. The adverse impact of increased UVR on microalgae can be far-reaching as they form the basis of the food chains in the Antarctic ecosystems. Although there have been many studies on the impact of UVR on Antarctic microalgae, comparative studies with tropical and temperate microalgae have not been well studied. As part of our research on stress adaptation of Antactic microalgae, the response and adaptation of Antarctic microalgae, tropical and temperate microalgae were compared to UVR stress. Microalgae of similar taxa from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237 and Navicula UMACC 231), tropical (Chlamydomonas augustae UMACC 246, Chlorella vulgaris UMACC 001 and Amphipropra UMACC 259) and temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248 and Navicula incerta UMACC 249) regions were exposed to different UVR conditions. The cultures were exposed to the following conditions: PAR (92 micromol/sq m/s), UVA (854 micro W/sq cm) + PAR and UVA + UVB (117 micro W/ sq cm) + PAR. The cultures were exposed daily to the UVA and UVB conditions for different duration, ranging from 1.5, 3 to 6 h in the light period (12:12 h light-dark cycle) for 10 days. There was no marked effect of UVA on the growth of all the algae studied. In contrast, growth of the cultures decreased with increasing exposure of UVB. The UVB exposure period causing 50% inhibition (IDsub50) was determined to assess the sensitivity of the microalgae to UVB. Both the temperate microalgae Chlamydomonas augustae UMACC 247 and Chlorella vulgaris UMACC 248 were more sensitive to UVB than Antarctic and tropical strains. In contrast, the tropical diatom Amphiprora UMACC 239 was more sensitive than the Antarctic and temperate strains. Lipid content and percentage of polyunsaturated fatty acids (PUFA) of all the microalgae studied decreased with increasing duration of UVB exposure. The decrease in percentage of PUFA due to UVB stress may affect the nutritional quality of the microalgae to organisms at the higher trophic levels.