We explored the relationship between organic carbon and mud (i.e. silt and clay) contents in seagrass ecosystems to address whether mud can be used to predict soil C content, thereby enabling robust scaling up exercises at a low cost as part of blue carbon stock assessments. We show that mud is not a universal proxy for blue carbon content in seagrass ecosystems, but it can be used to estimate soil Corg content when low biomass seagrass species (i.e. Zostera, Halodule and Halophila) are present.