ALBERT

Description: Background: Scavenger guilds, composed of a variety of species, co-existing in the same habitat, are responsible for biomass transformation throughout 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 of the speciose superfamily Lysianassoidea are amongst the ubiquitous taxa and occupy an essential role in decomposition processes. First, we addressed the question whether scavenging lysianassoid amphipods have different feeding strategies during carcass feeding, and if their potential synergistic feeding activities influence carcass decomposition. To this end, we compared the relatively large-sized species Waldeckia obesa with the small-sized species Cheirimedon femoratus, Hippomedon kergueleni, and Orchomenella rotundifrons during carcass feeding (Notothenia spp.). Our approach combines ex situ feeding experiments, behavioural observations, and scanning electron microscopic analyses of mandibles. Secondly, we aimed to detect ecological drivers for succession patterns of scavenging amphipods in Antarctic coastal ecosystems affected by environmental disturbances. 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 records are rare, macroalgae have already colonised hard substrates. Therefore, we carried out feeding assays of the most abundant lysianassoids in Potter Cove C. femoratus and H. kergueleni, to determine their consumption rates (mg food x mg amphipods-1 x day-1) and preferences of macroalgae and fish. Results We detected two functional groups with different feeding strategies among the investigated scavenging amphipods: the 'outside-insider' (openers) and 'inside-outsider' (squeezers). Synergistic effects during carcass feeding was not statistical evident. C. femoratus showed a flexible diet when fish was not available by consuming macroalgae with a consumption about 0.2 day-1 but preferred fish with feedings rates up to 0.8 day-1. Contrary, H. kergueleni rejected macroalgae entirely and consumed fish with consumption rates up to 0.8 day-1. Conclusion This study reveals functional groups in scavenging shallow water amphipods and provides new information on coastal intraguild niche partitioning. Moreover, we conclude that dietary flexibility of scavenging amphipods is a potential ecological driver for succession and colonisation of newly available ice-free Antarctic coastal habitats.