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The impact of ultraviolet radiation (UVR) on a semi-natural, soft-bottom diatom commu- nity from Potter Cove, King Georg Island, Antarctica, was investigated. The objective was to estimate the impact of UV-B (280 to 320 nm) and UV-A (320 to 400 nm) on photosynthetic efficiency, pigments, DNA damage and repair. The diatom community was exposed to different doses of radiation treat- ments: PAR + UV-A + UV-B (PAB), PAR + UV-A (PA) and PAR (P). The most frequently observed spe- cies were Pleurosigma obscurum and Gyrosigma fasciola. Within the 0.7 mm substrate, UV radiation significantly reduced the Photosystem II (PS II) maximum efficiency (Fv/Fm). Complete recovery was observed after 6 h post-cultivation under dim white light. The accumulation of diatoxanthin increased with exposure time for the P and PA treatments, but not for the PAB treatment, indicating a UV-B-related blocking of the de-epoxidation process within the xanthophyll cycling process. The ratio of diatoxanthin:(diatoxanthin+diadinoxanthin) decreased again to initial values after 24 h of recovery. The amount of DNA damage, measured as accumulation of cyclobutane pyrimidine dimers (CPDs), was minimal and increased with increasing UV-B dose, but DNA lesions were completely repaired within 24 h under dim white light. Regardless of possible avoidance strategies, e.g. vertical migration, negative UV treatment effects were observed. However, these effects were transient, facilitated by the dynamic recovery of photoinhibition and an efficient DNA damage repair mecha- nism. Although results from laboratory experiments using artificial radiation can only be extrapolated to field conditions with great caution, we conclude that Antarctic marine benthic diatoms inoculated into a semi-natural habitat are resilient to unnaturally high UVR.

UV radiation effects on pigments, photosynthetic efficiency and DNA of an Antarctic marine benthic diatom community