The most dramatic effects of Antarctic climate change are predicted around the Antarctic Peninsula. The temperature increase and glacier retreat are already affecting the marine environment. Here, the planktonic primary productivity is not sufficient to cover the carbon demand by benthic fauna. Hence, benthic microalgal productivity is of uttermost importance for the ecosystem functioning. In an outdoor set-up we tested the effects of increased temperature on benthic microalgal communities (primarily pennate diatoms) sampled from 5-7 m water depth. During 12 days, the diatoms were exposed to a temperature gradient in steps of ca 2°C, from ambient (2°C) up to ca 10°C. No effects on total cell numbers (growth) were observed (diatom composition remains to be analysed). Treatment effects in ΔF/Fm’ were found with highest yield at the highest temperature. In parallell to the outdoor experiment, a laboratory experiment was set-up to test the effect of decreased salinity from ambient salinity 33 to 21 units. Over 11 days, no treatment effects on cell number (growth) or photosynthetic activity (Fv/Fm) were observed. Therefore, an additional treatment with salinity 14 was set-up. Only Fv/Fm was tested but over 7 days, again no treatment effects were observed compared to the control. However, significantly lower NPQ values were found for salinity 33. Samples for analyses of bacterial biomass, photosynthetic pigments (HPLC), lipid peroxidation (thiobarbituric acid reactive substances (TBARs) assay) and biomass of heterotrophic bacteria are currently transported to Sweden. In conclusion, our preliminary results show that the benthic diatoms studied have a wide tolerance to rapid changes in both temperature and salinity, and as a community these diatoms do not seem affected by effects of the ongoing climate change around King George Island.