Pteropods (Gastropoda: Opisthobranchia) in the Southern Ocean: First results from fatty acid and stable isotope analyses on the SYSTCO material

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The Antarctic Ocean is a complex ecosystem including planktonic herbivores like krill, salps, copepods a s w ell a s c arnivores l ike a mphipods, c tenophores, c nidarians and which are f ed upon by birds, fish, squids, seals and baleen whales. Although there are many reports about the che mical com ponents of t he Antarctic krill species Euphausia superba, as w ell as f or calanoid copepods, which are key organisms in the planktonic food web of the Antarctic Seas, there is yet little inf ormation available on the bi ochemical c onstituents of ot her c ommon species, like pteropods, which are frequently found in planktonic hols in the Southern Ocean. To find out more about the feeding ecology as well as the trophic position of these organisms, zooplankton samples were taken during the SYSTCO expedition, and preserved in order to conduct biochemical analyses, more precisely estimating stable isotope ratios and identifying fatty acid signatures. This approach will here be presented on four pteropod species (Clione limacina, Limacina helicina, Spongiobranchaea australis, Clio pyramidata sulcata). One aim of this study is to analyse and compare the fatty acid composition of these animals to discover possible adaptations to the polar environment as well as to identify the major food sources that are utilized. Furthermore, an approach is undertaken to define the trophic position of the studied animals. Preliminary results from stable isotope 13C and 15N analyses indicate a very basal position of all investigated pteropod species.