Combined lipid, fatty acid and digestive tract content analyses: a penetrating approach to estimate feeding modes of Antarctic amphipods
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Antarctic amphipods from the Weddell Sea and Bransfield Strait were collected to investigate the impact of various species and feeding types on lipid and fatty acid compositions. In combination with digestive tract content analyses, such information can help clarify the type of feeding mode of the various amphipod species. Micro- and macropredatory amphipod species had only small amounts of triacylglycerols as storage lipids, whereas the deposit-feeder Epimeria georgiana was rich in triacylglycerols (55% of total lipids). The fatty acids 22:6(n-3), 20:5(n-3), 18:1(n-9) and 16:0 were major lipid components of most species. Ampelisca richardsoni, a suspension feeder, had a high amount of 18:4(n-3), a major component of cryptophytes and/or haptophytes, connected with feeding on sedimenting phytoplanktonic material and with a strong bentho-pelagic coupling. In Oradarea edentata, fragments of brown algae were found almost exclusively. The major fatty acid of the macroalgae, 20:4(n-6), replaced the 22:6(n-3) in the phospholipids and 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, a typical predator, had high proportions of saturated and monounsaturated fatty acids, showing no specialisation in lipid and fatty acid composition. The fatty acid composition of Epimeria georgiana was similar to that of Eusirus perdentatus. However, high levels of triacylglycerols in Epimeria georgiana reflect periodical food plenty and starvation, due to its dependence on dead items. The fatty acid composition of the necrophage Waldeckia 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 is the major food of W. obesa.
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