Regional variability of Antarctic krill (Euphausia superba) diet as determined using lipid, fatty acid and sterol composition

Nicole Hellessey1, Jessica A Ericson2, Peter D Nichols3, So Kawaguchi4, Stephen Nicol5, Nils Hoem6 and Patti Virtue1, (1)Institute for Marine and Antarctic Studies, Ecology and Biodiversity, Hobart, TAS, Australia, (2)Cawthorn Institute, Nelson, New Zealand, (3)Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Hobart, TAS, Australia, (4)Australian Antarctic Division, Krill Aquarium, Kingston, TAS, Australia, (5)Institute for Marine and Antarctic Studies, Taroona, TAS, Australia, (6)Aker BioMarine, Cheif Scientist, New York, NY, United States
Antarctic krill (Euphausia superba) are a circumpolar species with an omnivorous diet. Knowledge of krill diet in different oceanic regions will help predict how regional-scale environmental change may impact local krill populations. Krill from the Atlantic, Indian and Pacific sectors of the Southern Ocean were compared. The total lipid, lipid class, and neutral fraction fatty acid and sterol content and composition of whole krill, their digestive glands and stomachs during the late-summer were examined. Krill from the Indian sector had a distinctly different diet to the Atlantic and Pacific sectors based on their fatty acid profiles (p: < 0.001). Indian sector whole krill had higher phospholipids (55.0 ± 8.9%, as % total lipids) compared to Pacific (45.9 ± 3.6%) and Atlantic sector krill (43.7 ± 8.2%). Indian sector krill digestive glands showed lower phospholipid levels (Indian: 29.4 ± 8.5%, Pacific: 52.5 ± 5.7%, Atlantic: 52.5 ± 5.9%). Indian sector krill had a more carnivorous and diatomaceous diet (higher levels of 16:1n-7c, 14:0 and 20:1 and 22:1 isomers), with less flagellate input (lower 18:4n-3, 21:5n-3 and 18:3n-6) than other regions. One site in the Indian sector had particularly high 22:6n-3. Indian Ocean sector krill had lower cholesterol levels in their stomachs (52.5 ± 14.1%, as % total sterols) than Pacific and Atlantic sector krill stomachs (62.8 ± 1.9 % and 60.9 ± 4.9%, respectively). This study is, to our knowledge, the first to detail the regional differences in late-summer krill diet by assessing the lipid, neutral fraction fatty acid and sterol content and composition of different tissue types.