Deep-sea megabenthos communities of the Eurasian Central Arctic are influenced by ice-cover and sea-ice algal falls

Abstract

Quantitative camera surveys of benthic megafauna were carried out during the expedition ARK-XXVII/3 to the Eastern Central Arctic Basins with the research icebreaker Polarstern in summer 2012 (2 August-29 September). Nine transects were performed for the first time in deep-sea areas previously fully covered by ice, four of them in the Nansen Basin (3571-4066m) and five in the Amundsen Basin (4041-4384m). At seven of these stations benthic Agassiz trawls were taken near the camera tracks for species identification. Observed Arctic deep-sea megafauna was largely endemic. Several taxa showed a substantially greater depth or geographical range than previously assumed. Variations in the composition and structure of megabenthic communities were analysed and linked to several environmental variables, including state of the sea ice and phytodetritus supply to the seafloor. Three different types of communities were identified based on species dominating the biomass. Among these species were the actiniarian Bathyphellia margaritacea and the holothurians Elpidia heckeri and Kolga hyalina . Variations in megafaunal abundance were first of all related to the proximity to the marginal ice zone. Stations located closer to this zone were characterized by relatively high densities and biomass of B . margaritacea . Food supply was higher at these stations, as suggested by enhanced concentrations of pigments, organic carbon, bacterial cell abundances and nutrients in the sediments. Fully ice-covered stations closer to the North Pole and partially under multi-year ice were characterized by lower concentrations of the same biogeochemical indicators for food supply. These stations nevertheless hosted relatively high density and biomass of the holothurians E . heckeri or K . hyalina , which were observed to feed on large food falls of the sea-ice colonial diatom Melosira arctica . The link between the community structure of megafauna and the extent and condition of the Central Arctic sea-ice cover suggests that future climate changes may substantially affect deep ocean biodiversity.

Vertical distribution of megafauna on the Bering Sea slope based on ROV survey

“…For example, Kolga nana Théel, 1879 aggregations were found in the Charlie-Gibbs Fracture Zone (Gebruk & Krylova, 2013) with densities of up to 76 ind/m 2 and in the Porcupine Seabight in the North Atlantic (Billett & Hansen, 1982) with a mean density of 34 ind/m 2 at depths at around 4,000 m. Specimens of K. nana were observed in the Charlie-Gibbs Fracture Zone feeding on the soft sediment mainly in flat and gentle slope areas (Rogacheva, 2012). Another species of this genus, K. hyalina Danielssen & Koren, 1879, was abundant in the Central Arctic Basins with densities significantly dependent on seasonal ice-algae supply to the seafloor (Rybakova et al, 2019). The density of K. kamchatica in our study (17 ind/m 2 ) was lower than in the mentioned reports, although it was still relatively high.…”

Reliance of deep-sea benthic macrofauna on ice-derived organic matter highlighted by multiple trophic markers during spring in Baffin Bay, Canadian Arctic

“…Coinciding with reductions in sea-ice cover and warming waters, shifts in both benthic biomass and species composition have been described for some Arctic regions, suggesting that climate change may also impact biological diversity in these deep-Yunda-Guarin et al: Importance of sympagic carbon for Arctic benthic communities in spring Art. 8(1), page 11 of 18 sea ecosystems (Grebmeier et al, 2018;Rybakova et al, 2019). Predictions point to future alterations in primary production in the Arctic Ocean due to a reduction in seaice extent and changes in its phenology (Tedesco et al, 2019).…”

What Feeds the Benthos in the Arctic Basins? Assembling a Carbon Budget for the Deep Arctic Ocean

“…As the water depth increases over the slopes, the benthic biomass decreases by a factor of ∼5-20 ( Figure 1) due to decreasing abundance of organisms (Levin et al, 2001;Bluhm et al, 2011;Degen et al, 2018;Vedenin et al, 2018), as well as by declining body sizes (Wei et al, 2010). Even though the position of the marginal ice zone determines the primary production, which in turn influences the benthic biomass distributions (Degen et al, 2018;Rybakova et al, 2019), benthic organisms of all size fractions populate the AO basins (MacDonald et al, 2010;Bluhm et al, 2011;Degen et al, 2018;Vedenin et al, 2018;Rybakova et al, 2019). This clearly reflects that there must be sufficient carbon input to sustain their present densities.…”

“…Macrofaunal biomass ranges from 0 to 4.4 g C m −2 with an average of 0.5 g C m −2 below 1000 m (Figure 1). The epifaunal megabenthos is often dominated by brittle stars, sea cucumbers, and zoarcid, liparid, and rajid fishes in soft sediments of the AO basins (Bergmann et al, 2011;Taylor et al, 2016;Rybakova et al, 2019;Zhulay et al, 2019). Abundances are mostly ≤1-5 ind.…”

“…Zhulay et al, 2019), but epifaunal densities may be enhanced at hot spots on glacial drop stones (mainly by cnidarians and sponges, Meyer et al, 2016;Zhulay et al, 2019). Given that Arctic deep-sea epifauna is primarily assessed photographically, their biomass estimates are even sparser than abundance estimates, but new estimates yield <0.001-0.2 g C m 2 (≥1000 m; Rybakova et al, 2019;Zhulay et al, 2019). Hyperbenthic taxa such as benthic jellyfish, ctenophores, highly mobile polychaetes, and mysids have been documented in the AO basins (MacDonald et al, 2010;Zhulay et al, 2019), but estimates of their abundance, biomass, or carbon demand are lacking.…”