72 Chapter 2 might increase benthic methane release into the water column and potentially coastal methane emissions to the atmosphere. This is particularly relevant for relatively shallow coastal sites, such as Site 7 in the Stockholm Archipelago. Genes encoding F420-dependent sulfite reductases have been found in ANME-1, ANME-2, and ANME-3 genomes (Chadwick et al., 2022), suggesting that sulfide-driven sulfite toxicity may be a commonly encountered environmental pressure by ANME and, therefore, a widespread control on AOM activity. In conclusion, our data suggest that ANME-2 archaea might be able to compensate for methane increases under hypoxic conditions, but are unable to thrive under euxinic conditions because of sulfide-driven toxicity. This disruption of the methane biofilter results in increased benthic methane release into the water column in coastal ecosystems severely impacted by eutrophication and bottom water deoxygenation. Further studies should investigate if increased methane concentrations in euxinic waters result in increased methane emissions to the atmosphere. Moreover, future studies are required to characterize the methaneoxidizing activity of ANME archaea under changing bottom water redox conditions, as well as the metabolism and terminal electron acceptors utilized. Data availability Adapter-trimmed 16S rRNA gene reads and MAGs have been deposited on NCBI under BioProject PRJNA805085. All geochemical data in this study are provided in Supplementary Table 3. Author contributions PDM and NAGMvH designed the study. PDM, WKL, MH and NAGMvH collected sediment cores and conducted fieldwork. PDM, JPRCdM, WKL, AJW, MJEM, MH and NAGMvH performed biogeochemical and microbiological measurements. PDM led computational analyses, data visualization and manuscript writing. CUW, MSMJ and CPS guided sampling design and data analyses. All authors edited the manuscript and agreed on its final version.
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