Ecogeomorphic theory predicts that plant-sediment feedbacks regulate carbon storage in coastal vegetated ecosystems. Yet, grazers, which remove plant biomass and alter sediment properties, remain an understudied driver of carbon cycling. We used field-derived and remote sensing data to examine how consumer fronts of the keystone grazer, Sesarma reticulatum, mediate carbon storage, flux, and recovery in salt marshes. We observed accelerating rates of Sesarma front migration that led to a decrease in carbon stocks by 40-70%. Despite latitudinal differences, front migration rate had no effect on carbon stocks, flux, or replacement time. Lastly, when we included Sesarma disturbance in carbon flux calculations, we found that it may take 5-100 years for marshes to replace lost carbon, if at all. Combined, we show that small grazers cause a net loss in carbon stocks as they move through the landscape, and irrespective of migration rate, these grazer-driven impacts persist for decades.