DIET-INDUCED CHANGES IN THE FATTY-ACID COMPOSITION OF ARCTIC HERBIVOROUS COPEPODS - EXPERIMENTAL-EVIDENCE OF TROPHIC MARKERS

To verify the potential of fatty acids as trophic markers, feeding experiments were carried out with the dominant herbivorous copepods Calanus 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 16:1(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.