Lipids as trophic markers in Antarctic krill. II. Lipid composition of the body and digestive gland of Euphausia superba in controlled conditions

Abstract

To examine the potential of lipids as dietary markers in Euphausia superba Dana, juvenile krill were fed 4 phytoplankton diets (diatoms, cryptomonads, dinoflagellates and thraustochytrids over a range of food concentrations) and 2 species of zooplankton (rotifers and Artemia sp.) for 20 d. Lipid content, lipid class and fatty acid (FA) composition were analysed for whole krill and digestive glands (DG). Changes detected in whole krill were almost entirely associated with the lipid variability observed in DG. With marked diet-induced changes, DG lipids were the major repository for the trophic signal in krill. DG lipid content increased in krill fed on phytoplankton due to the accumulation of polar lipid (0.5 mg per DG) and triacylglycerol (up to 1.7 mg per DG). Herbivorous diets induced distinct FA signatures in the DG, characterised by higher proportions of: 16:1ω7 and 20:5ω3 in diatom-fed krill; 18:1ω9 and 18:4ω3 in cryptomonad-fed krill; 18:1ω9, 18:4ω3+18:5ω3 and 22:6ω3 in dinoflagellate-fed krill; and 14:0 and 22:6ω3 in thraustochytrid-fed krill. Dietary FA markers increased in relative proportion (% total FA) in the DG with increasing concentration of each particular food. Krill fed rotifers or Artemia sp. showed relatively low DG lipid content, with only slightly higher proportions of 18:2ω6 than observed with phytoplankton diets. Zooplankton diets induced no significant difference in FA composition in relation to the species of zooplankton used as prey or to the algal type consumed by these prey.

Trophic effects of fishing southern rock lobster Jasus edwardsii shown by combined fatty acid and stable isotope analyses

“…PCAs that used a subset of fatty acids based on metabolic relationships or ratios of n-3/n-6 polyunsaturated fatty acids (PUFA) can sometimes yield additional information (e.g. Alonzo et al 2005 dietary patterns in the present study (see Nelson et al 2002). For all species/phyla combined, at both bioregions and at fished and reserve areas, 78.8 to 82.1% of the total variance was explained by PC1 (Fig.…”

Increasing evidence for the important role of Labyrinthulomycetes in marine ecosystems

“…Several studies have attempted to trace the source of DHA in the food web (Veloza et al 2006, Alonzo et al 2005. Zooplankton incorporate fatty acids into their body from thraustochytrids they feed upon (Alonzo et al 2005, Castilo et al 2009). …”

“…The planktonic pool of dietary DHA for fish is highest in the mesozooplankton size fraction and thus the most efficient DHA transfer from planktonic food web to fish occurs through the mesozooplankton (Kainz et al 2004). Several studies have attempted to trace the source of DHA in the food web (Veloza et al 2006, Alonzo et al 2005. Zooplankton incorporate fatty acids into their body from thraustochytrids they feed upon (Alonzo et al 2005, Castilo et al 2009).…”

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

“…Details of Euphausia superba collection, experimental conditions, measurement of ingestion and faecal pellet production, krill dissection, lipid analysis and data analysis are given in Alonzo et al (2005).…”

“…Diatoms were used in this study because of their importance in the Southern Ocean food webs. Thraustochytrids are also present in Antarctic waters (Bahnweg & Sparrow 1974) and were mainly used because their FA profiles are markedly different from those of diatoms (Table 1) (Alonzo et al 2005).…”