This project investigates how solar UV radiation affects planktonic food webs in the Arctic by changing the nutritional quality of the lower trophic levels. UV radiation has been documented to lead to oxidation of poly-unsaturated fatty acids (PUFAs) in phytoplankton. These PUFAs cannot be synthesized de novo by zooplankton, but are key molecules for the marine pelagic food web. A combined approach was chosen with both sampling of field data (physical as well as biological) and experiments which were carried out during two field seasons in Ny Ålesund in 2003 (april/may) and 2004 (may/june). In 2004, the main part of the field work consisted of an outdoor experiment where phytoplankton was exposed to different irradiation regimes, using the natural sunlight. Algae from all different treatments were used for feeding zooplankton in order to trace the transfer of irradiation-induced changes of the fatty acid composition in phytoplankton to the next trophic level. A number of additional parameters will be analysed as well, combined with the results of an extensive measurement series of both PAR- and UV light. The experiment was carried out on the old pier (Gamle Kaia), while the laboratory part took place in the Italian station ‘Dirigibile Italia’.