This study quantifies the contribution of carbonate sediments, produced in seagrass meadows and in photophilic algal communities, to the sediment budget of a beach–dune system. The contribution to the beach sediment budget represents a further ecosystem service provided by seagrass. The dependence of the beach sediment budget on carbonate production associated with coastal ecosystems has implications for the adaptation of carbonate beaches to the seagrass decline and sea level rise.