Benthic biodiversity under Antarctic ice-shelves - baseline assessment of the seabed exposed by the 2017 calving of the Larsen-C Ice Shelf

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Regional climate change is well established in the Antarctic, particularly in the Antarctic Peninsula region. Details of the underlying drivers of climate change and its physical consequences are increasingly well understood. Changes in the physical properties of the marine system are especially important for biological components and include, inter alia, changes in ocean temperature and ocean acidification, reductions in the extent and timing of seasonal sea-ice and the retreat and collapse of ice shelves and glaciers. Nevertheless, the implications for biological systems remain poorly understood, above all, for how rapidly physical changes might cascade through marine foodwebs. It is therefore important that ecological studies that facilitate long-term comparisons are established, and in order to develop projections of the future consequences of climate change. These studies are best undertaken in the absence of any effects caused by other human activities. In this respect, ice-shelf collapse is of special importance as it opens up new habitats for biological colonisation and ecological succession, and impacts established biogeochemical cycles.A recent review by Trathan et al. highlighted how 50-years of retreat in ice shelves and coastal glaciers around the Antarctic Peninsula has exposed at least 2.4 x10^4 km^2 of new open water. These newly revealed habitats appear to have allowed new phytoplankton blooms that were rapidly followed by new marine zooplankton and seabed communities. In general, the fauna under existing ice shelves exists in oligotrophic, deep-sea-like conditions and, because ice shelf collapse may lead to greater nutrient input, there may be a shift in community structure through the loss and gain of species. Ice-shelf loss will allow increased levels of marine snow and benthic-pelagic coupling that will alter benthic nutrient cycling and may result in additional carbon storage. Further, terrigenous material may also be deposited in some of these habitats, potentially impacting upon the existing benthos and modifying conditions for future colonisation.The benthic communities of the Antarctic shelf show high levels of gigantism, longevity, slow growth, late maturity and endemism, meaning that many species are susceptible to disturbance. However, these communities are also potentially more dynamic than so far assumed and can show surprising rates of change, even over relatively short time periods. Nevertheless, they remain susceptible to environmental variability and change. Therefore, the regional nature of ongoing climate change coupled with the high levels of endemism mean that community processes will vary across a range of sites. Gaining early sight of communities will be key, prior to the commencement of species loss, or future colonisation.The Antarctic shelf ecosystems that form following ice-shelf loss will be susceptible to colonisation by species from immediately adjacent areas; however, other complex processes may also take place as ocean currents may create opportunities for species to return that were last present in the last interglacial, a warmer period than at present.Our project will use a four-fold approach:1) Characterisation of the benthic community formerly under A68, their assemblages and spatial distribution at a range of nested scales in relation to the distance from the former ice-shelf front. 2) Samples returned to the UK (preserved in ethanol, RNAlater, or stored at -80C) for future molecular genetic and genomic analysis of phylogeography, evolutionary history and metagenomics.3) Collection of macro- and megafauna and dietary sources such as ice-algae, plankton and organic matter in the sediment for food web analysis using bulk stable isotopes of delta 13C, 15N and 34S, and lipid analysis.4) In-vitro incubation whilst at sea to explore 13C uptake by infaunal meio- and macrofauna in multicorer-tube microcosms.