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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.
