MEPS 296:81-91 (2005)  -  doi:10.3354/meps296081

Lipids as trophic markers in Antarctic krill. III. Temporal changes in digestive gland lipid composition of Euphausia superba in controlled conditions

Frédéric Alonzo1,2,3,5,*, Patti Virtue1, Stephen Nicol2, Peter D. Nichols3,4

1Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart, Tasmania 7001, Australia
2Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050, Australia
3CSIRO Marine Research, Castray Esplanade, GPO Box 1538, Hobart, Tasmania 7001, Australia
4Antarctic Cooperative Research Centre, University of Tasmania, GPO Box 252-77, Hobart, Tasmania 7001, Australia
5Present address: Institut de Radioprotection et de Sûreté Nucléaire, Centre de Cadarache, BP 3, 13115 Saint-Paul-Lez-Durance cedex, France

ABSTRACT: Two phytoplankton diets with markedly different fatty acid (FA) profiles (thraustochytrid and diatom over a range of concentrations) were fed to juvenile Euphausia superba Dana to evaluate the time lapse required for the development of trophic lipid signatures in the digestive gland (DG). Krill were collected after 5, 10 and 20 d of feeding on thraustochytrids. Krill fed on thraustochytrids for 20 d were also collected after a further 5, 10 and 20 d of feeding on diatoms. An accumulation of polar lipid (0.4 mg per DG) was observed after 5 d of feeding on thraustochytrids at every concentration of food. The deposition of triacylglycerol (0.25 mg per DG) required 10 d of feeding and only occurred at the 2 highest food concentrations. Amounts of thraustochytrid-derived FA, 14:0, 16:0 22:6ω3 and 22:5ω6, increased after 10 d of feeding. The final concentration of 22:6ω3 was dependent on food concentration. Though it was absent in the diet, the essential FA 20:5ω3 accumulated from the retroconversion of 22:6ω3 after 20 d. Changing the krill diet to diatoms resulted in a marked decline in thraustochytrid FA, particularly 14:0 and 22:6ω3, after 5 d, whilst diatom FA, 16:1ω7 and 20:5ω3, remained constant. Thraustochytrid signatures were completely erased from the FA profiles of DG after 20 d feeding on diatoms. Slow accumulation of storage lipid and short residence time of dietary FA suggest that lipid turnover rates are high in Antarctic krill DG.

KEY WORDS: Euphausia superba · Antarctic krill · Lipid class · Fatty acid · Digestive gland · Trophic signature · Temporal scale

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