The compositions of wax esters, triacylglycerols and phospholipids in Arctic and Antarctic copepods: evidence of energetic adaptations

The fatty acid and fatty alcohol compositions of wax esters, triacylglycerols and phospholipids were determined in the Antarctic copepods Calanoides acutus, Calanus propinquus, Metridia gerlachei, Euchaeta antarctica and Euchirella rostromagna and in the Arctic copepods Calanus hyperboreus, C. glacialis, C. finmarchicus and M. longa to reveal similarities and differences between the nine species. The wax esters of the herbivorous species were clearly characterised by the long-chain monounsaturated fatty acids and alcohols 20:1 (n-9) and 22:1 (n-11), whereas the omnivorous and carnivorous species usually had high relative amounts of the 18:1 (n-9) fatty acid and of the short-chain saturated alcohols 14:0 and 16:0. The wax ester-storing copepods contained only small amounts of triacylglycerol, but the latter was the dominant depot lipid in the Antarctic C. propinquus and E. rostromagna. The triacylglycerol fatty acid composition of C. propinquus deviated strongly from those of all other species due to large amounts of the two isomers 22:1 (n-11) and 22:1 (n-9). The wax ester molecules of the herbivorous species had the highest energetic content, although the triacylglycerols of C. propinquus reached very similar energy levels. The wax ester-storing herbivorous species have developed similar lipid biochemical adaptations in both polar oceans. In contrast, predominantly triacylglycerol-storing species occur only in Antarctic waters. The phospholipids contained very high levels of polyunsaturated fatty acids, especially 22:6 (n-3), which was about twice as abundant as 20:5 (n-3) and 16:0, the other characteristic fatty acids. In both, Arctic and Antarctic species, the fatty acid compositions of the phospholipids showed a pronounced uniformity. The extremely high degree of unsaturation is extraordinary as compared to other marine taxa.