Fatty acid content of Antarctic krill Euphausia superba at South Georgia related to regional populations and variations in diet

Abstract

The fatty acid content of Antarctic krill Euphausia superba from South Georgia was investigated during January and February 1996, a period of relatively low algal biomass. Cluster analysis of the fatty acid data revealed 3 regionally distinct groups of krill. Group A consisted primarily of sub-adults (median length 42 mm) and was characterised by high proportions of 14:0, 16:0 and 18:1(n-9) fatty acids. Group B comprised mainly juveniles and a small proportion of adults (median length 33 mm) and had a fatty acid profile similar to that of Group A. The largest group, Group C (8 of 14 stations, mostly to the east of the survey area), was almost exclusively juveniles plus a small number of sub-adults (median length 29 mm) and had unusually high percentages of polyunsaturated fatty acids [PUFA; 18:4(n-3), 20:5(n-3) and 22:6(n-3)]. Krill from Group C had the lowest total fatty acid concentrations (150 to 722 mg kg-1). These krill were surviving on the lowest algal biomass in the region and had probably resorted to carnivory on PUFA rich copepods. The pattern of fatty acids in krill from Groups A and B resembled that of krill collected from a diatom bloom in the Bellingshausen Sea, but the concentrations were generally lower. The well fed krill from the Bellingshausen Sea showed small variations in fatty acid content associated with sex and maturity, but the South Georgia results indicated that diet can have a greater impact on fatty acid content than sex and maturity stages. Fatty acid profiles were indicative of food regimes that were so distinct that the krill probably originated from spatially independent groups.