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Amphipoda from the superfamily Lysianassoidea Dana, 1849 play an important role in Southern Ocean benthic food webs due to their high biomass, abundance and predominantly scavenging mode of feeding. Our knowledge on the lysianassoid fauna, even in well-studied areas of the Western Antarctic Peninsula, is incomplete. Here we report the findings of an integrated study of lysianassoid amphipods of Potter Cove, King George Island/ Isla 25 de Mayo (KGI), combining morphological and molecular species identification (COI barcoding) methods, investigating more than 41,000 specimens from baited traps. For comparison, 2039 specimens from the adjacent Marian Cove were analysed. Ten lysianassoid species were recorded in the deeper outer Potter Cove, whereas the inner cove (<50 m) was dominated by a single species, Cheirimedon femoratus Pfeffer, 1888 (99.44% relative abundance). It is hypothesized that the impoverished lysianassoid fauna inside the meltwater-influenced inner cove represents a 1model for future conditions along the Western Antarctic Peninsula under conditions of increased glacial melting. 2Abyssorchomene charcoti (Chevreux, 1912)

BackgroundScavenger guilds are composed of a variety of species, co-existing in the same habitat and sharing the same niche in the food web. Niche partitioning among them can manifest in different feeding strategies, e.g. during carcass feeding. In the bentho-pelagic realm of the Southern Ocean, scavenging amphipods (Lysianassoidea) are ubiquitous and occupy a central role in decomposition processes. Here we address the question whether scavenging lysianassoid amphipods employ different feeding strategies during carcass feeding, and whether synergistic feeding activities may influence carcass decomposition. To this end, we compared the relatively large species Waldeckia obesa with the small species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during fish carcass feeding (Notothenia spp.). The experimental approach combined ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Furthermore, we aimed to detect ecological drivers for distribution patterns of scavenging amphipods in the Antarctic coastal ecosystems of Potter Cove. In Potter Cove, the climate-driven rapid retreat of the Fourcade Glacier is causing various environmental changes including the provision of new marine habitats to colonise. While in the newly ice-free areas fish are rare, macroalgae have already colonised hard substrates. Assuming that a temporal dietary switch may increase the colonisation success of the most abundant lysianassoids C. femoratus and H. kergueleni, we aimed to determine their consumption rates (g food x g amphipods−1 x day−1) and preferences of macroalgae and fish.ResultsWe detected two functional groups with different feeding strategies among scavenging amphipods during carcass feeding: carcass ‘opener’ and ‘squeezer’. Synergistic effects between these groups were not statistically verified under the conditions tested. C. femoratus switched its diet when fish was not available by consuming macroalgae (about 0.2 day−1) but preferred fish by feeding up to 80% of its own mass daily. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with a maximal rate of 0.8 day−1.ConclusionThis study reveals functional groups in scavenging shallow-water amphipods and provides new information on coastal intraguild niche partitioning. We conclude that the dietary flexibility of C. femoratus is a potential ecological driver and central to its success in the colonisation of newly available ice-free Antarctic coastal habitats.Electronic supplementary materialThe online version of this article (10.1186/s12983-017-0248-3) contains supplementary material, which is available to authorized users.

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