The dominant large copepods Calanoides acutus and Calanus propinquus were collected south of 65°S in the Antarctic Weddell Sea in late winter/early spring (October-November) and summer (January-February), and the lipid and fatty acid/alcohol compositions of copepodite stages V and females of these suspension feeders were analyzed. The lipids of C. acufus consisted mainly of wax esters. Major fatty acids in summer were 20:1(n9), 20:5(n3), 22:6(n3), 18:4(n3), 22:1(n11) and 16:1(n7). In winter the amount of 18:4(n3) decreased considerably in both stages, as did that of20:5(n3) in females, whereas the quantity of 20:i(n9) showed a strong increase in females. During both seasons the fatty alcohols in the wax esters were strongly dominated by 20:1 (n9) and 22:1 (n11). In contrast, the hulk of the lipids of C. propinquus were triacylglycerols with the principal fatty acids 22:1(n11), 22:1(n9), 16:0, 20:5(n3) and 22:6(n3). Hence, an alternative to the paradigm of energy storage by means of wax esters, typical of C. acufus and almost all other calanoid copepods from polar and temperate oceans, was found for C. propinquus. The synthesis of these energy-rich triacylglycerols occurs via an unusual marine biochemical pathway, the elongation of the 20:1(n9) to the 22:1(n9) fatty acid. Our data show the existence of very different biochemical solutions to the problem of efficient energy storage for coping with the extreme seasonality in Antarctic waters, with short periods of food plenty interchanging with long phases of food scarcity.