HERBIVOROUS OR OMNIVOROUS - ON THE SIGNIFICANCE OF LIPID COMPOSITIONSAS TROPHIC MARKERS IN ANTARCTIC COPEPODS

Three dominant Antarctic copepods, Calanoides acutus, Rhincalanus giga s and Metridia gerlachei (copepodite stages V and females), were colle cted during summer (January/February) in the southern Weddell Sea sout h of 70-degrees-S. Detailed analyses of their lipid and fatty acid/alc ohol compositions were carried out. The trophic positions of these cop epods were elucidated by means of the lipid compositions (''marker lip ids''). High amounts of wax esters were found in C. acutus (92% of tot al lipids) and in R. gigas (84-86%). The level of wax esters in M. ger lachei was relatively low (27-42%), while the accumulation of triacylg lycerols tended to be higher (19-22%). Characteristic lipid components of C. acutus were the long-chain monounsaturated fatty acids and fatt y alcohols 20:1 (n-9) and 22:1 (n-11). These components together with elevated amounts of the 18:4 (n-3) and, to a lesser degree, of the 16: 1 (n-7) fatty acids, typical of phytoplankton lipids, indicate herbivo rous feeding for C. acutus. Other abundant fatty acids were 20:5 (n-3) and 22:6 (n-3). The fatty acid composition of M. gerlachei was charac terized by very high amounts of these 22:6 and 20:5 acids. Other impor tant fatty acids were 18:1 (n-9) and 16:0, but only small amounts of 1 6:1 (n-7) and 18:4 (n-3) occurred. In contrast to C. acutus the fatty alcohols of M. gerlachei consisted almost exclusively of the short-cha in components 14:0 and 16:0. M. gerlachei is known as an omnivorous sp ecies, which was clearly reflected by its lipid and fatty acid/alcohol pattern. Few data are available on the feeding of R. gigas, but it is usually described as an herbivorous small-particle feeder. R. gigas s howed fatty acid/alcohol characteristics typical of either C. acutus o r M. gerlachei. Higher amounts of the 16:1 (n-7) and 18:4 (n-3) fatty acids suggest herbivorous feeding, whereas the dominance of short-chai n alcohols (14:0 and 16:0) resembled the lipid pattern found in the om nivorous M. gerlachei. Hence, the lipid composition of R. gigas showed an intermediate pattern, which implies a tendency towards an opportun istic feeding mode, positioned somewhere between the other two species .