Cellular Changes Associated with the Acclimation of the Intertidal Sea Anemone A ctinia tenebrosa to Ultraviolet Radiation

To assess the relative importance of long‐ and short‐term cellular defense mechanisms in seasonally UV ‐ R ‐acclimated A ctinia tenebrosa ( A nthozoa, A ctiniidae), individuals were exposed to summer doses of PAR , UV ‐ A , UV ‐ B and enhanced UV ‐ B (20%) for a period of 4 days. Mycosporine‐like amino acids ( MAA s) and cyclobutane pyrimidine dimer ( CPD ) concentrations were quantified, while oxidative damage to lipids and proteins, and the activities or levels of the antioxidant enzymes SOD , CAT , GR , GPOX and total glutathione were determined. Our results show that summer UV ‐ R ‐acclimated individuals had a higher UV ‐ R tolerance, with no significant increases in CPD s levels, than winter‐acclimated sea anemones possibly due to higher MAA concentrations. Summer‐acclimated individuals showed increased lipid and protein oxidation and GPOX activity only when they were exposed to UV ‐ B at 20% above ambient UV ‐ R levels. In contrast, winter‐acclimated sea anemones showed elevated levels of oxidative damage, GPOX and SOD activities after exposure to UV ‐ A or UV ‐ B at ambient and elevated levels. Thus, this study indicates that long‐term UV ‐ R acclimation mechanisms such as the accumulation of MAA s could be more important than short‐term increases in antioxidant defenses with respect to reducing indirect UV ‐ R damage in intertidal sea anemones.