Abstract: The disclosed systems, methods, and apparatuses may combat coastal erosion using a shell module shaped to enable retention of sand on a beach and shore face. The shell module may be shaped to minimizing interference with recreational use of the beach and providing a beneficial environment for desirable sea life. The modular shell can be conveniently transported and emplaced in shell reefs. These shell reefs may comprise multiple, optionally interlocking shell modules. These shell reefs can prevent fill, such as sand, de-watered sand, or sand slurry from being scoured and sluiced out to sea. The disclosed systems and methods harness the energy of incoming and returning waves, including tidal and surf action, to assist in spreading the fill, recreating a natural beach, complete with layers of sand capable of resisting the scouring force of ocean waves and currents.