Lipids, trophic relationships, and biodiversity in Arctic and Antarctic krill

Environmental seasonality is a critical factor in structuring polar marine ecosystems. The extensive data now available on the lipids of Arctic and An tarctic euphausiids show that all species are characterised by a seasonally high lipid content. and neutral lipids. whether wax esters or triacylglyce rols, are primarily accumulated for reproduction. The Arctic Thysanoessa in ermis and the Antarctic Euphausia crystallorophias contain high levels of w ax esters and higher concentrations of 18:4(n-3) and 20:5(n-3) and a lower ratio of 18:1(n-9)/(n-7) fatty acids in their neutral lipids than the Arcti c Thysanoessa raschii and the Antarctic Thysanoessa macrura and Euphausia s uperba. Large amounts of phytol in the lipids of T. raschii and E. crystall orophias during winter suggest the ingestion of decaying algae originating in sedimenting material or in sea ice. Thysanoessa raschii, T. macrura, and E. superba have a high ratio of 18:1(n-9)/(n-7) fatty acids, indicating an imal carnivory. We conclude that T. inermis and E. crystallorophias are tru e high polar herbivores. while T. raschii. T. macrura. and E. superba are o mnivores with a more boreal distribution. The Arctic species Thysanoessa lo ngicaudata and Meganyctiphanes norvegica are carnivores feeding on Calanus, as indicated by high amounts of 20:1(n-9) and 22:1(n-11) fatty acids.