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A shell lying on a beach isn't necessarily just a souvenir waiting to be collected. Empty shells can provide shelter for small organisms and contribute calcium carbonate to coastal environments as they gradually break down.
Hermit crabs, for example, depend on empty gastropod shells for protection. Removing large numbers of shells can therefore affect organisms that use them.
A seemingly ordinary shell can have a second life after its original animal is gone. Leaving natural material on the beach can sometimes be more beneficial than taking it home.
© U.S. National Park Service