Combined lipid, fatty acid and digestive tract content analyses: a penetrating approach to estimate feeding modes of Antarctic amphipods

Abstract. Antarctic amphipods from the Weddell Sea and Bransfield Strait were collected to investigate theimpact of various species and feeding types on lipid and fatty acid compositions. In combination withdigestive tract content analyses, such information can help clarify the type of feeding mode of the variousamphipod species. Micro- and macropredatory amphipod species had only small amounts of triacylglycerolsas storage lipids, whereas the deposit-feeder Epimeria georgiana was rich in triacylglycerols (55% of totallipids). The fatty acids 22:6(n-3), 20:5(n-3), 18:1(n-9) and 16:0 were major lipid components of mostspecies. Ampelisca richardsoni, a suspension feeder, had a high amount of 18:4(n-3), a major componentof cryptophytes and/or haptophytes, connected with feeding on sedimenting phytoplanktonic material and witha strong bentho-pelagic coupling. In Oradarea edentata, fragments of brown algae were found almostexclusively. The major fatty acid of the macroalgae, 20:4(n-6), replaced the 22:6(n-3) in the phospholipidsand triacylglycerols of the amphipod. The sponge eater, Echiniphimedia hodgsoni, was rich in 16:1(n-7)and 18:1(n-7), suggesting that the unidentifiable organic matter was of diatom origin. Eusirus perdentatus, atypical predator, had high proportions of saturated and monounsaturated fatty acids, showing no specialisationin lipid and fatty acid composition. The fatty acid composition of Epimeria georgiana was similar to that ofEusirus perdentatus. However, high levels of triacylglycerols in Epimeria georgiana reflect periodical foodplenty and starvation, due to its dependence on dead items. The fatty acid composition of the necrophageWaldeckia obesa was clearly different because of the predominance of 18:1(n-9) (>40% of total fatty acids).This dominance is probably the result of feeding on highly degraded carrion-derived organic matter, which isthe major food of W. obesa.