Giant sponge grounds of Central Arctic seamounts are associated with extinct seep life

Abstract

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61°E), we observe a surprisingly dense benthic biomass. 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. 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. The metabolic profile of bacteriosponge fatty acids and expressed genes indicate that autotrophic symbionts contribute significantly to carbon assimilation. 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.

Habitat types and megabenthos composition from three sponge-dominated high-Arctic seamounts

“…O. striatus is an opportunistic deposit feeder that was observed grazing upon fresh and detrital ice algae in the Nansen Basin close to the Gakkel Ridge during the minimum sea ice extent in 2012 62,63 . The mixed substrate, which can be of up to 15 cm thickness at the seamounts, may trap settled particles 50 This suggests that a combination of regional and local environmental differences likely causes the variability between the megabenthos assemblages at the Northern and Central Mount and that at the Karasik Seamount.…”

“…Demosponges of the order Tetractinellida numerically dominated the assemblages across the three seamounts, possibly owing to their unique capacity to source carbon directly from the refractory matter available on the seabed 50 , which likely makes these mostly (if not fully) independent from the water column food-supply in such a low primary productivity area 52,53 . Shrimps (Bythocaris sp.…”

“…Roberts et al 48 suggested that short-timescale environmental variability combined with the generally nutrient rich sub-surface water masses generated at the interface of intermediate and deep-sea water masses 49 might potentially enhance the development of sponge aggregations and other megafauna ( e.g ., ascidians, cnidarians, echinoderms, and demersal fish) at the Schulz Bank seamount (73.5° N, previously called Schultz Massif seamount 48 ) on the Arctic Mid-Ocean Ridge, between the Greenland Sea and the Norwegian Sea. However, very little is known about the diversity of benthic communities in seamounts at higher Arctic latitudes ( e.g ., >75° N; see also 50 ). Hence, less if anything is known about what are the key factors structuring Arctic seamount communities across different spatial scales, e.g ., do these differ from those shaping lower latitude seamount communities?…”

“…N; see also 50 ). Hence, less if anything is known about what are the key factors structuring Arctic seamount communities across different spatial scales, e.g., do these differ from those shaping lower latitude seamount communities?…”

Marine Sponge Endosymbionts: Structural and Functional Specificity of the Microbiome within Euryspongia arenaria Cells

“…Typically, the prokaryotic composition of sponge microbiomes is analyzed by high-throughput 16S rRNA gene-based sequencing approaches ( 27 – 30 , 39 – 43 ). Recently, metagenomic sequencing provided new insights into the functional gene repertoires of sponges and the metabolic pathways carried by sponge symbionts ( 26 , 44 – 46 ). However, metagenomic methods can be challenging in samples with low-microbial abundance or in those, like sponges, dominated by host DNA ( 47 ).…”