| Summary: | The destruction of the ozone layer, concomitant with a projected enhancement in ocean stratification, will increase the dosage of ultraviolet radiation (UVR), as well as sea surface temperature and incident light level. The diatom Fragilariopsis cylindrus and other Antarctic phytoplankton will therefore be exposed to, and require protection from, increasing levels of damaging UVR, under elevated temperatures and light conditions. It has been hypothesized that phytoplankton utilize photoprotective pigments and the production of mycosporine-like amino acids as strategies against UVB-induced production of reactive oxygen species (ROS). The goal of this research was to investigate photoprotective mechanisms employed by F. cylindrus, following exposure to enhanced UVB. Interactive effects of temperature and light level were explored, as cultures were subjected to temperatures of 0°C or 4°C and light levels of 15 µE m−2 s−1 or 100 µE m−2 s−1, in order to approximate current and future Southern Ocean stratification conditions. Growth rate and photosynthesis significantly declined by 40–80% and 50-90%, respectively, following exposure to high UVB relative to control conditions. This decline in physiological health was accompanied by a 50–300% increase in photoprotective mechanisms. Exposure to high UVB under current climate conditions resulted in the least amount of photodamage and photoprotection. Conversely, elevated light level resulted in the greatest decrease in growth and photosynthesis, accompanied with the greatest increase in photoprotection when exposed to high UVB. Under both light levels, the elevated temperature appeared to mitigate damage caused by high UVB exposure. The results of this study shed light on the mechanisms utilized by F. cylindrus in response to oxidative stress induced by UVB, and how these mechanisms may be expected to change under future ocean stratification conditions.
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