ALBERT

Description: To verify the potential of fatty acids as trophic markers, feeding experiments were carried out with the dominant herbivorous copepods Ca/anus finmarchicus, C. hyperboreus and C. glacialis from the Greenland Sea during two Arctic expeditions in June/July 1991. Depending on the fatty acid composition of these copepods, the diatom Thalassiosira antarctica or the dinoflagellate Amphidinium carterae were offered as food to induce deviating fatty acid compositions. Since the copepodite Stages CV of C. finmarchicus had very low amounts of the 16: 1(n-7) fatty acid but high amounts of 18:4(n-3), the specimens were fed on T. antarctica rich in 16: 1(n-7) over a period of up to 42 days. At the end of the feeding experiment the portion of the 16:1(n-7) fatty acid had strongly increased by 11%, while the 18:4(n-3) fatty acid was almost depleted. In contrast, high amounts of the 16: l(n-7) fatty acid in C. hyperboreus (CV) suggested feeding on diatoms, therefore its diet was changed to A. carterae dominated by high amounts of the 18:4(n-3) fatty acid. After 47 days the portion of 18:4(n-3) increased by 8%, whereas 16:1(n-7) decreased by 3%. In female C. glacialis the changes in the fatty acid composition after feeding with A. carterae were less pronounced as compared to the other species, due to a severe lipid loss during the experiment. The feeding experiments document the incorporation and turnover of dietary fatty acids under controlled laboratory conditions and provide clear evidence for the potential of specific fatty acids as trophic marker lipids.Keywords: Arctic; Copepod; Feeding; Lipid; Fatty acid; Alcohol; Trophic marker

Description: Three dominant Antarctic copepods, Calanoides acutus, Rhincalanus gigas and Metridia gerlachei (copepodite stages V and females), were collected during summer (January/ February) in the southern Weddell Sea south of 70°S Detailed analyses of their lipid and fatty acid/ alcohol compositions were carried out. The trophic positions of these copepods were elucidated by means of the lipid compositions (marker lipids). High amounts of wax esters were found in C. acutus (92% of total lipids) and in R. gigas (84-86%). The level of wax esters in M. gerlachei was relatively low (27-42%), while the accumulation of triacylglycerols tended to be higher (19-22%). Characteristic lipid components of C. acutus were the long-chain monounsaturated fatty acids and fatty alcohols 20:1 (n-9) and 22:1 (n-il). 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, indicatc herbivorous feeding for C. acutus. Other abundant fatty acids were 20:5 (n-3) and 22:6 (n-3). Thc fatty acid composition of M. gerlachei was characterized by very high amounts of these 22:6 and 20:5 acids. Other important fatty acids werc 18:1 (n-9) and 16:0, but only small amounts of 16:1 (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-chain components 14:0 and 16:0. M. gerlachei is known as an omnivorous species, which was clearly reflcctcd by its lipid and fatty acid/alcohol pattern. Few data arc available on the feeding of R. gigas, but it is usually describcd as an herbivorous small-particle feeder. R. gigas showed fatty acid/alcohol characteristics typical of either C. acutus or 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-chain alcohols (14:0 and 16:0) resembled the lipid pattern found in the omnivorous M. gerlachei. Hence, the lipid composition of R. gigas showed an intermediate pattern, which implies a tendency towards an opportunistic feeding mode, positioned somewhere between the other two species.

Description: Lipid compositions of the dominant Antarctic copepods Calanoides acutus, Rhincalanus gigas and Calanus propinquus from the Weddell Sea have been investigated in great detail. Copepods were collected during summer in 1985 and late spring/early winter in 1986. The analyses revealed specific adaptations in the lipid biochemistry of these species which result in very different lipid components. The various copepodite stages of C. acutus synthesize wax esters with long-chain monounsaturated moieties and especially the alcohols consisted mainly of 20:1(n-9) and 22:1(n-1 1). R. gigas also generates wax es-ters, but with moieties of shorter chain length. The fatty alcohols consisted mainly of 14:0 and 16:0 components, while the major fatty acids were 20:5, 18:4 and 22:6, of which 18:4 probably originated from dietary input. In contrast, C. propinquus accumulates triacylglycerols, a very unusual depot lipid in polar calanoid copepods. Major fatty acids in C. propinquus were the long-chain monounsaturates 22: l(n-9) and 22: 1(n-l 1), which may comprise up to 50% of total fatty acids. In C. acutus and C. propinquas there was a clear increase of long-chain fatty acids with increasing developmental stage. In contrast, the fatty acid and alcohol composition of the R. gigas copepodite stages were characterized by the dominance of the polyunsatu-rated fatty acids as well as high amounts of the monoun-saturates 18:1(n-9) and 16:1(n-7). There was a considerable decrease of the dietary fatty acid 18:4(n-3) towards the older stages during summer; in late winter/early spring 18:4 was only detected in very low amounts. This tendency was also found in the other two species, but was less pro-nounced. In all three species dry weight and lipid content increased exponentially from younger to older stages. Thehighest portion of wax esters, or of triacylglycerols in C. propinquus, was found in the adults. Dry weight and lipid content were generally higher during summer. In late winter/early spring the variability was more pronounced and lipid-rich specimens showed a selective retention of long-chain monounsaturated fatty acids, whereas in lipid-poor specimens these fatty acids were very much depleted.