Quantifying and valuing carbon flows and stores in coastal and shelf ecosystems in the UK

•Offshore shelf sea sediments are a manageable carbon store important as forests.•Offshore shelf sea sediments are currently not protected by international agreements.•With scenario analysis (25-years) we estimate damage costs up to US$12.5 billion.•Uncertainties: estimates of UK shelf sediment sedimentation rates and trawling impact.•The main challenge: protect marine habitats whilst maintaining food security.