Coastal zones are among the world's most productive ecosystems. They store vast amounts of organic carbon, as 'blue carbon' reservoirs, and impact global climate change. Archaeal communities are integral components of coastal microbiomes but their ecological roles are often overlooked. However, archaeal diversity, metabolism, evolution, and interactions, revealed by recent studies using rapidly developing cutting-edge technologies, place archaea as important players in coastal carbon

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... cal cycling. We here summarize the latest advances in the understanding of archaeal carbon cycling processes in coastal ecosystems, specifically, archaeal involvement in CO2 fixation, organic biopolymer transformation, and methane metabolism. We also showcase the potential to use of archaeal communities to increase carbon sequestration and reduce methane production, with implications for mitigating climate change.