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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’.
Plankton of shallow polar freshwater water bodies is exposed to increasing levels of ultraviolet radiation (UVR) due to the limited water depth. Daphnia (Crustacea, waterflea) and algae are common representatives of the food chain in these water bodies. Daphnia almost exclusively use lipids for energy storage, which they obtain from their food (mainly algae). Therefore, Daphnia and algae are closely linked to each other. Preliminary experiments on the UV-induced damage in phyto- and zooplankton point to lipids as one of the key players. With this application we want to identify how algae specific lipids and fatty acids (FA) are modified by UVR. The factors modifying UV-doses to the animals and their food are depth of the waterbody and DOC (absorbs UV). A pondsurvey shall provide a wide spectrum on ponds which vary in DOC and depth. Lipid analysis of Daphnia and their food of these ponds as well as physical parameters of the pond waters shall identify correlations between UV-exposure and specific fatty acids. This shall enable us to estimate the effect of solar UVR on the freshwater plankton community in polar ponds.
The polar pteropod Clione limacina is characterised by high quantities of lipids with ether components (1-O-alkyldiacylglycerol=DAGE) in combination with odd-chain fatty acids. It is unknown why Clione and probably other pteropods have specialised in this manner. Furthermore the precursor of the biosynthesis of these compounds is still unknown. Therefore samples of Clione limacina and its only prey Limacina helicina will be collected by using plankton nets from small boats. The species will be kept in aquaria and feeding experiments with both species and food of different composition and nutritional value are planed.