Research papersThe macro- and megabenthic fauna on the continental shelf of the eastern Amundsen Sea, Antarctica
Introduction
The Amundsen Sea in western Antarctica is in the Pacific sector of the Southern Ocean and is one of the most remote, least explored and most rapidly changing regions of Antarctic waters. Despite being a region with large and prolonged sea ice cover, two extremely productive polynyas, the Amundsen Sea and the Pine Island Bay polynyas, occur in this region (Arrigo et al., 2012; Yager et al., 2012). Based on satellite derived chlorophyll a data, the better studied Amundsen Sea Polynya is the most productive of the Antarctic polynyas (Arrigo and van Dijken, 2003). Over the last 30 years the summer sea ice extent has declined and the opening of the Amundsen Sea Polynya has occured earlier (Yager et al., 2012). During the Austral springe polynyas are locations of significant phytoplankton blooms and intensive sedimentation (Smith and Comiso, 2008, Ducklow et al., 2008); both of which will have an effect on the distributions and abundance of the underlying benthic fauna (Corliss et al., 2009, Sun et al., 2006). To date, the biodiversity and distribution of the benthic fauna in the Amundsen Sea is unstudied, while marine geological and oceanographic cruise activities in the region have increased substantially (Lowe and Anderson, 2003, Jenkins et al., 2004, Thoma et al., 2008, Jacobs et al., 2011). This increased interest follows land-based geophysical research on the West Antarctic Ice Sheet (WAIS) glaciers and the ice streams of Marie Byrd Land showing that these are thinning faster than any other glaciers in Antarctica (Shepherd et al., 2001, Holt et al., 2006). As a result, The Amundsen Sea Embayment is a major drainage basin for the WAIS (Rignot, 1998, Evans et al., 2006). Of particular interest in the recent debate on climate change and sea level rise is how increased melting of the WAIS might lead to its collapse and what the influence on global sea-level rise could be (Vaughan, 2008, Bamber et al., 2009). Initial bathymetric investigations of the seafloor topography showed that the continental shelf of the Amundsen comprises several deep troughs and basins which were formed during past ice ages and reach more than 1600 m in depth (Dowdeswell et al., 2006, Noormets et al., 2009, Graham et al., 2010). One of these deep basins is located in Pine Island Bay (Graham et al., 2010) and was a particular focus of attention in this study.
Recent studies on the biogeographic distribution of the Antarctic benthic and pelagic faunas highlight the AS as a completely unsampled region (Linse et al., 2006, Griffiths et al., 2009, Griffiths, 2010). During a geology-focused expedition on RV Polarstern in 1994 (Miller and Grobe, 1996) three biological stations were sampled off the Bakutis Coast in the Amundsen Sea using a remote operating vehicle with an underwater video camera and an Agassiz trawl and the observed megafauna analysed (Starmans et al., 1999). In 2008 the British Antarctic Survey (BAS) BIOPEARL II (Biodiversity Dynamics: Phylogeography, Evolution and Radiation of Life) cruise on RRS James Clark Ross sampled the benthic animals of the Amundsen Sea Embayment and Pine Island Bay for the first time. The deep shelf basin of Pine Island Bay is of particular interest for evolutionary studies on the survival of benthic fauna on the Antarctic shelf during glacial maxima when ice sheets covered most shelf areas (Barnes and Hillenbrand, 2010). These basins may have acted as refugia for shelf species. Alternatively, the link with the Antarctic Circumpolar Deep Water through the shelf troughs might have supplied the Pine Island Bay basin with deep-sea species since the Last Glacial Maximum (Riehl and Kaiser, 2012). Preliminary identifications of macro- and megafauna collected during the BIOPEARL II cruise found isopod species in this shelf area that had only previously been reported from the Antarctic deep sea (Kaiser et al., 2009). Initial investigations on the holothurians and isopods from this region have revealed species new to science from the Amundsen Sea Embayment and Pine Island Bay (Brandt, 2009, O′Loughlin et al., 2010, Riehl and Kaiser, 2012).
The main objective of this study is to describe the benthic assemblage structure in the southern Amundsen Sea collected by Agassiz (AGT) trawl. Species composition and richness will be assessed and compared with those of the Ross, Scotia and Weddell seas.
Section snippets
Study area
The main study area was the eastern Amundsen Sea embayment and Pine Island Bay (Fig. 1). Comparative and replicate samples were taken in the southern Bellingshausen Sea and in the adjacent deep sea at the Mary Byrd Seamount (Fig. 1).
The Amundsen Sea Embayment is one of the three major drainage basins for the West Antarctic Ice Sheet (Rignot, 1998, Evans et al., 2006). Several large ice shelves discharge into the Amundsen Sea Embayment and Pine Island Bay, and large parts of the area are covered
Results
The investigations of shelves, slopes and deep sea of the southern Bellingshausen and eastern Amundsen seas, based on 37 AGT catches, yielded 5469 specimens belonging to 16 phyla, at least 20 classes and more than 270 species (Table 2, Table 3, Supplement 1). The total collected wet mass was 24.495 kg (Table 1).
Taxon richness
This study is based on the first benthic samples to be collected in the eastern Amundsen Sea, and suggests that the higher taxon richness (e.g. phylum, class and order levels) is as high as that of other Antarctic regions (Gambi and Bussotti, 1999, Arntz et al., 2005, Rehm et al., 2006, Linse et al., 2007, Griffiths et al., 2008, Cummings et al., 2010). However, the taxonomic composition of the Amundsen Sea benthic fauna is different from the Dumont D′Urville, Weddell and Ross Seas, and the
Acknowledgments
Thanks to Captain Jerry Burgan and his crew of RRS James Clark Ross for help and support on board and especially for getting us into Pine Island Bay. We are grateful to Dr Rob Larter and his team for swath support and to Dr Julian Gutt and two unknown reviewers for valuable comments on the manuscript. This study is part of the British Antarctic Survey Polar Science for Planet Earth Programme funded by The Natural Environment Research Council.
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2020, Marine GeologyCitation Excerpt :Therefore, understanding the heterogeneity of habitat features is important for understanding local-scale diversity patterns and community structure. The importance of the continental slope as a distinct habitat has been the focus of previous studies that have sought to understand connectivity between Antarctic shelf, slope and abyssal faunas (Barnes and Kuklinski, 2010; Kaiser et al., 2011; Linse et al., 2013; Neal et al., 2018; Pabis et al., 2015). Determining the degree to which benthic communities in these regions are distinct has important implications for assessing conservation priorities, and for understanding colonisation and evolutionary history, particularly the potential of the slope and abyss to act as a source for shelf recolonisation following glaciations (e.g. Kaiser et al., 2011; Thatje et al., 2005).
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Current address: Hatfield Marine Science Center, Department of Zoology, 2030 S.E. Marine Science Drive, Newport, Oregon 97365, USA.