EXCEPTIONAL LIPIDS AND FATTY-ACIDS IN THE PTEROPOD CLIONE-LIMACINA (GASTROPODA) FROM BOTH POLAR OCEANS

The gymnosomatous and thecosomatous pteropods, Clione limacina and its only prey Limacina helicina and L. retroversa, from Arctic and Antarc tic waters as well as particulate matter have been investigated with r espect to their lipid compositions. The close trophic relationships be tween phytoplankton-limacina-Clione were partially reflected by the fa tty acid compositions due to high amounts of 16:1(n - 7), which indica te the ingestion of diatoms in L. helicina. However, the outstanding f eature of this food chain concerns the extraordinary lipid and fatty a cid compositions of C. limacina. Up to 40.6% of its total lipid consis ted of l-O-alkyldiacylglycerol ethers, a very unusual depot lipid in t he zooplankton. The other major storage lipid were triacylglycerols, w hich occurred in similar amounts. Tn addition, the various lipid class es of C. limacina exhibited unique fatty acid compositions, due to hig h percentages of odd-chain length components, up to one third of total fatty acids. The dominant odd-chain fatty acid was 17:1(n - 8) reachi ng 18%, followed by 15:0 and 17:0, with 17:1(n - 8) enriched in the di acylglycerol ethers. Major even-chain fatty acids were 16:0, 16:l(n - 7), 20:5(n - 3) and 22:6(n - 3). in L, helicina neither diacylglycerol ethers nor odd-chain fatty acids could be detected indicating that th ese atypical lipids are not ingested with the prey by C. limacina. De novo biosynthesis of these compounds is therefore suggested. The synth esis of odd-chain fatty acids is initiated with propionate. This precu rsor may originate from dimethyl-beta-propiothetin (DMPT), which has b een described to be accumulated by L. helicina via phytoplankton uptak e. Hence, C. limacina not only represents an exceptional member of the polar zooplankton due to its extreme trophic specialisation, it has a lso developed exceptional lipid biochemical adaptations in the Arctic and Antarctic ocean. (C) 1998 Elsevier Science B.V. All rights reserve d.