Coastal change fundamentally occurs in response to changes in the balance between accommodation creation and filling, the latter in part reflecting longshore sediment fluxes. In Santa Catarina (southern Brazil), growth of the Jurerê Strandplain trapped 50–110 × 10⁶ m³ of sand, effectively halting longshore transport for 3000 years; re-initiation of headland bypassing in the last 1000 years allowed for formation of the downdrift Daniela Spit. In northern Virginia (U.S. East Coast), elongation of the Assateague Island spit-end during just the last 100 years has sequestered a similar volume of sand (∽45 × 10⁶ m³), reducing longshore transport fluxes by at least 25%, and contributing to the erosion and/or landward migration of adjacent, downdrift barrier islands. These findings demonstrate the potential for longshore sediment trapping through natural growth of updrift sediment sinks to control long-term and large-scale downdrift coastal behavior.