| Summary: | Unraveling food webs is a first step towards understanding of ecosystem functioning and a requirement to forecast climate-induced ecosystem responses. The organisms under study are benthic copepods (order Harpacticoida) inhabiting a fjord-like environment on the southern coastline of King George Island, one of the most rapidly warming regions on earth at the north-western tip of the Antarctic Peninsula. Despite increased understanding of Antarctic food web structures, little is known about the feeding ecology of benthic copepods in these systems. A fatty acid trophic marker strategy was used to unravel the diet composition of Antarctic harpacticoid copepod species or assemblages collected from distinct habitats in summer. Their diverse storage fatty acid composition revealed the occupation of different trophic niches associated with their specific life-styles, i.e., endobenthic, epiphytic with ( Alteutha spp.) or without ( Harpacticus sp.) frequent water column excursions. Moreover, prevalence of biosynthesized ɯ7 long-chain monounsaturated fatty acids in Harpacticus sp. and ɯ9 fatty acids in Alteutha spp. further suggested adaptations to particular habitats in polar ecosystems as different dietary precursors 16:1ɯ7 (microphytobenthos, epiphytic diatoms) or 18:1ɯ9 (flagellates) fuel these elongation pathways.
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