Abstract
We performed a series of experiments with Antarctic natural phytoplankton communities exposed to natural levels of solar radiation in order to quantify the effect of ambient ultraviolet radiation (UVR) on phytoplankton growth, cell death and their balance. Treatments in which UVR was excluded showed a high increase in biomass, dominated by diatoms, with chl a (chlorophyll a) reaching values as high as 22 mu g l(-1), 9 times larger than initial values. In contrast, chl a values remained low at the end of the experiments under treatments with full solar radiation. Phytoplankton growth rates were also inhibited by UVR, increasing up to 5 times in UVR-excluded treatments. The percentage of dead cells within Antarctic phytoplankton communities decreased in treatments with UVR blocked. The Antarctic phytoplankton populations studied appeared to be strongly controlled by UV at surface irradiances with biomasses inhibited by up to 80-90%. This suggests that increased UVR levels over Antarctica may reduce phytoplankton growth rates and cause cell death, thus reducing the phytoplankton stock. These effects may have important consequences for the food web in Antarctic waters.