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

T M Morganti,U Hentschel,K Busch,B M Slaby,J J Middelburg,H Grotheer,H T Rapp,A Boetius,G Mollenhauer,J Dannheim,A Purser,A De Kluijver

doi:10.1038/s41467-022-28129-7

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.

Highlights

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its seaice cover and short productive season
The Ocean Floor Observation and Bathymetry System (OFOBS) survey data showed that the seamount summits (721–585 m) were covered by massive sponges[22] representing the densest Arctic sponge ground found to date (Figs. 1, 2)
The comparison of carbon isotopes δ13C and Δ14C using both published data and results from the present study show that the Δ14C of sponge bulk biomass was most similar to that of the bacterial fatty acid (FA) and to that of the bryozoans growing on the sponge, as well as being within the range reported for dissolved inorganic carbon (DIC)[29] in the Arctic at similar depths (Fig. 3b)

Summary

Introduction

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its seaice cover and short productive season. 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. Sponge grounds of Arctic-Boreal regions are often dominated by large highmicrobial abundance species (HMAs, i.e., sponge species which host highly diverse and dense microbial communities in their tissue) of the genus Geodia, co-occurring with Stelletta and Thenea[13] Such communities have been observed at the Faroes[4], on the North Norwegian shelf[11], and within the North-West Atlantic[3], with individuals attaining diameters of up to 1 m and WW of 25 kg[4]. To identify the food sources supporting the rich sponge community occupying these seamount summits, we combine under-ice seafloor mapping with biomass sampling to assess the bulk and compound-specific carbon (δ13C and Δ14C) and nitrogen (δ15N) isotopes and fatty acid (FA)

Methods

Results

Conclusion