Many of the densest deep-sea sponge grounds have been found on the shelf breaks of the North Atlantic, the Western Canadian margin, the slopes of the Hawaiian archipelago, in the Antarctic, and the Mediterranean Sea 1. Sponges are primarily filter feeders, with the densest communities often occurring where hydrodynamic conditions favor the localized concentration of particulate organic carbon 3, 4, 5, such as at the interface between two water masses 6, 7. Via their utilization of suspended material, sponges often also play an important role in nutrient and organic matter cycling between the benthic and pelagic realms 1, 2. The sponges act as ecosystem engineers: they influence community structure by providing distinct habitat niches, such as a suitable substrate for organisms to settle on, hide within or prey from, thereby enhancing local biodiversity 1. As with coral reefs, sponge grounds are characterized by a progressive accumulation of biomass produced by a limited number of long-lived benthic animal species.
We suggest that this hotspot ecosystem is unique to the Central Arctic and associated with extinct seep biota, once fueled by degassing of the volcanic mounts.ĭense aggregations of large sponges, typically known as sponge gardens or grounds 1, have been reported from intertidal to abyssal depths 1. The metabolic profile of bacteriosponge fatty acids and expressed genes indicate that autotrophic symbionts contribute significantly to carbon assimilation. Observed sponge distribution, bulk and compound-specific isotope data of fatty acids suggest that the sponge microbiome taps into refractory dissolved and particulate organic matter, including remnants of an extinct seep community. Bacteriosponges are the most abundant fauna within this community, with a mass of 460 g C m −2 and an estimated carbon demand of around 110 g C m −2 yr −1, despite export fluxes from regional primary productivity only sufficient to provide <1% of this required carbon. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61☎), we observe a surprisingly dense benthic biomass. The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season.
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