Abstract
Deep-sea sponge grounds are habitat-forming benthic communities characterized by high biomass and structural complexity. Despite their ecological significance, their role for the deep-sea environment remains poorly understood and their functioning is often inferred from ex situ studies. We hypothesized that deep-sea sponge grounds exhibit substantially higher respiration and nutrient turnover than surrounding soft sediments, making them hotspots of carbon and nutrient cycling in the deep sea. Integrated respiration and nutrient cycling were quantified in a sponge ground on the summit of an Arctic seamount (Schulz Bank, ~ 580 m depth). We used in-situ incubation chambers measuring oxygen consumption, prokaryotic cell removal, and inorganic nutrient fluxes. Respiration rates ranged from 0.13 to 0.93 mmol O₂ m⁻² h⁻¹, which is comparable to cold-water coral reefs and up to 7–21 times higher than reported for soft sediments of the Arctic deep sea. This indicates a high organic carbon demand exceeding surface-derived supply, suggesting the uptake of additional food resources. All incubations showed net release of ammonium, phosphate, nitrite and nitrate, with fluxes correlating with sponge biomass. Our results demonstrate that deep-sea sponge grounds function as hotspots of carbon and nutrient cycling and suggest distinct functional contributions of sponge groups and their microbiome.
Data availability
The data supporting this study are available from the corresponding author upon request.
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Acknowledgements
We thank the crews and scientific parties of RV G. O. Sars cruise GS2017110 for their technical support. We thank Stig Vågenes and his ROV Ægir 6000 team for the exceptional skill and precision during the dives.
Funding
Open Access funding enabled and organized by Projekt DEAL. This research has been performed in the scope of the SponGES project, which received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 679849. I acknowledge support by the Open Access publication fund of Alfred-Wegener-Institut Helmholtz- Zentrum für Polar- und Meeresforschung. Open Access funding enabled and organized by Projekt DEAL.
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UH, BM, MB, JMG, FM designed the study. UH, BM, MB, JMG, FM, HTR participated in sampling. UH, BM, MB, JMG, FM conducted the incubations. KB did microbial analyses. HTR conducted sponge taxonomic analysis. UH performed the data analysis and visualization. UH wrote the manuscript. UH, BM, MB, JMG, FM, KB, GJR discussed the results, reviewed and edited the manuscript.
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Hanz, U., Mueller, B., Bart, M.C. et al. Unveiling in situ oxygen, carbon and nutrient cycling of a sponge-driven biological hotspot in the arctic. Sci Rep (2026). https://doi.org/10.1038/s41598-026-41798-4
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DOI: https://doi.org/10.1038/s41598-026-41798-4
