Biodiversity of an unknown Antarctic Sea: assessing isopod richness and abundance in the first benthic survey of the Amundsen continental shelf

Abstract

Concerted efforts are being made to understand the current and past processes that have shaped Antarctic biodiversity. However, high rates of new species discoveries, sampling patchiness and bias make estimation of biodiversity there difficult. Antarctic continental shelf benthos is better studied in the Ross, Weddell and Scotia seas, whilst the Amundsen Sea has remained biologically unexplored largely because of severe ice conditions yearround. Here we report results from examination of the first benthic biological samples taken from the Amundsen Sea. We compare relative abundance, taxonomic richness and faunal composition of isopod families, and genera and species within two example families (i.e. Desmosomatidae and Nannoniscidae) from the Amundsen Sea with complementary sampling from the Scotia Sea. Benthic samples were taken from inner and outer Pine Island Bay (eastern Amundsen Sea) sites using an epibenthic sledge at 500 m. Similar samples were also collected from 15 Scotia arc sites at 160-to 500-m depths. The relative abundance of isopods in the Amundsen Sea samples was high and surprisingly less variable than across samples in the Scotia Sea. The abundance structure of isopods at family level was compared across different Antarctic seas. We found that in the Amundsen, Scotia and Ross Seas two families dominated abundance. In contrast, isopod abundance reported in the literature from Weddell Sea samples was much more evenly distributed across families. The Amundsen continental shelf isopod fauna appears to be rich, with 96% of individuals belonging to currently undescribed species. Most of the genera have either been described or found elsewhere, but for many of these genera it is the first time they have been recorded away from the Antarctic continental slope or deep sea. The Amundsen Sea assemblages differed greatly from the Scotia Sea sites in terms of both composition and (species and generic) richness. This was largely due to high consistency between samples compared with the highly variable Scotia Sea samples. Thorough biological analyses implementing well-structured geographic sampling regimes and the application of phylogeographic analyses on a variety of taxa are required to further explore the geographic structure of biodiversity and the evolutionary history of the Amundsen Sea.

The macro- and megabenthic fauna on the continental shelf of the eastern Amundsen Sea, Antarctica

“…Dimmler et al (1996) observed a similar composition in the megafauna Bakutis Coast region of the Amundsen Sea. The species richness observed in the larger isopods and molluscs in the Amundsen Sea AGT samples is opposite to that observed for smaller macrobenthic isopods and molluscs collected by an epibenthic sledge (EBS) at the same stations in the Amundsen Sea (Kaiser et al, 2009, Moreau et al, 2013. In the decapods, have also been recorded in the Amundsen Sea, suggesting a faunal overlap between these neighbouring regions.…”

“…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 & Kaiser, 2012).…”

The spatial structure of Antarctic biodiversity

“…Current estimates of marine biodiversity in most areas of the Southern Ocean probably reflect sampling effort ), as noted previously for the Antarctic terrestrial environment. This varies from small wellsampled locations such as King George Island, to the Amundsen Sea, which spans almost 408 of longitude, but where no fauna had been collected prior to 2008 (Kaiser et al 2009). …”

First insights into the deep-sea tanaidacean fauna of the Ross Sea: species richness and composition across the shelf break, slope and abyss

“…The debate about species richness, rarity, level of endemism and distribution patterns is ongoing because wide areas have been sparsely, if ever, sampled (Kaiser et al , 2009). Recent studies have indicated that the Antarctic slope is an important biodiversity hot spot for benthic fauna (Kaiser et al , 2011Pabis et al 2015), with a unique slope fauna in some regions of the Southern Ocean (Kaiser et al 2011).…”