How Seashells End Up on the Beach

From Living Mollusk to Shoreline Treasure

Seashells are the exoskeletons of marine mollusks (gastropods, bivalves, chitons) made of calcium carbonate. Their journey to the beach involves several processes:

1. Natural Death & Deposition: Shells settle on the seafloor after the animal dies.
2. Wave & Current Transport: Tides, longshore drift, and storm surges move shells shoreward over weeks to years.
3. Predator Discards: Crabs, fish, birds, and octopuses crush or pry open shells, dropping fragments that wash ashore.
4. Human Activity: Dredging, trawling, and shell collecting redistribute shells; some are discarded as bycatch.
5. Coastal Erosion: Bluff retreat releases shells from Pleistocene deposits onto modern beaches.

Once on the beach, tumbling in the swash zone rounds edges, polishes surfaces, and sorts shells by size/shape—creating the familiar strandline mosaic.