AME prepress abstract  -  doi: 10.3354/ame01201

ABSTRACT: The effects of ambient solar UV radiation (280 – 400 nm) were determined using three natural marine protist communities incubated in 650 l tanks (minicosms) for 13-14 d over the summer of 2002/03 at Davis Station, Antarctica. Minicosms were exposed to ambient light that was variously attenuated to give treatments of photosynthetically active radiation (PAR, ≥385 nm wavelength), PAR+ ultraviolet A (UV-A) radiation (315-385 nm), and PAR+UV-A+4 different treatments of ultraviolet B (UV-B) radiation (280-315 nm) that simulated a range of equivalent depths (ED) in the water column from 4.43 to 7.15 m. Results showed a seasonal progression in the response of microbial communities to UV radiation exposure. The first experiment in November showed the microbial community was significantly inhibited in the PAR+UV-A-exposed treatment but this inhibition declined with increasing addition of UV-B radiation. The second experiment in December showed UV-A or UV-B radiation had few significant effects. Like in experiment 1, some taxa were inhibited by PAR+UV-A or promoted by UV-B but most were inhibited at the highest UV-B irradiances (≤ 4.43 m ED). The last experiment in January showed UV-B-induced inhibition of all but one of the dominant taxa. The seasonal transition in UV wavelengths responsible for inhibition of protists may be due to ozone reduction, the light history of protists, and/or changes in species composition. The increasing UV-B-induced inhibition we observed over summer corresponded to a decline in ozone concentrations over Davis. This recurrent decline in ozone over Antarctica between January and April coincides with blooms of diatoms that appear to have low UV-B-tolerance but are responsible for ~ 47% of annual primary production in Antarctic waters.