Lipids of Antarctic salps and their commensal hyperiid amphipods

Antarctic salps (Salpa thompsoni and Ihlea racovitzai) and their commensal hyperiid amphipods (Vibilia antarctica, Cyllopus lucasii and C. magellanicus) were collected near Elephant Island, in the South Shetland Islands, during 1997 and the salp-rich year 1998. The sterol composition of aggregate S. thompsoni and I. racovitzai (mostly 24-methyl-5,22E-dien-3β-ol, 24-nordehydrocholesterol, cholesterol and trans-dehydrocholesterol) was reflected in the sterol composition of the commensal amphipods and was consistent with a herbivorous planktonic diet. This was not the case for solitary S. thompsoni, with 24-methylenecholesterol as the major sterol. There was a greater abundance of aggregate salp stanols in 1997 (11.7% total sterols) than 1998 (5.2%) and these different stanol levels were reflected in the commensal amphipods. Eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] were the major polyunsaturated fatty acids (PUFA) in all organisms. Octadecapentaenoic acid [18:5(n-3)] comprised 0.4-5.8% (of total fatty acids) in all 1998 salps and amphipods, but was absent in 1997 samples. This suggests a greater presence of dinoflagellates or other species rich in 18:5(n-3) in the 'salp year' 1998. Very long chain PUFA (C 24 , C 26 , C 28 ) were also only detected in 1998 samples (up to 5.3%), reflecting commensalism and greater presence of dinoflagellates or species containing very long chain PUFA. Examination of the biomarker lipids has provided an indication of trophic interactions for these Antarctic salps and their commensal hyperiid amphipods.