A seashell may look like one of the most harmless souvenirs a beach can offer. It is small, already detached from its animal and, unlike a piece of coral or live wildlife, seems to have no obvious role left to play.
But on a beach, an empty shell is not necessarily an ecological leftover.
Scientists studying coastlines in India and elsewhere have found that the availability and physical movement of shells can matter to the ecosystems around them.
That does not mean every tourist who slips one shell into a pocket is causing measurable beach erosion. But it does raise a different question when thousands of people repeatedly remove shells from the beach.
Shells are made largely of calcium carbonate. Once molluscs die, their shells can remain on the shoreline, where waves, tides and abrasion gradually break them down and return that material to the coastal sediment system.
A particularly important study came from Portugal. In a 2014 PLOS ONE paper, Michał Kowalewski, Rosa Domènech and Jordi Martinell compared shell abundance and tourism at Praia de Faro over two periods, 1978–81 and 2008–10.
#Beaches aren’t just ours, they’re home to a multitude of creatures.🦞🦀🐌🐜🏝️
Thousands of hermit crabs die after getting trapped in marine plastic litter. The remote beaches in #Nicobar Islands are of no exception. Our recent study published in Marine Pollution Bulletin… pic.twitter.com/ZCWuDM1XBk
— Wildlife Institute of India (@wii_india) November 6, 2025
They found that tourist arrivals had increased 2.74 times, while the abundance of mollusc shells on the shoreline had fallen by 2.62 times. The relationship between tourism and shell abundance was statistically significant, with the correlation becoming stronger during months with high tourist arrivals.
The researchers did not claim that every individual shell removed by a visitor causes erosion. Instead, they proposed several possible consequences of substantial shell depletion.
One is physical.
Shells scattered across a shoreline can form a coarse layer or “pavement” that can inhibit sediment movement. Removing large quantities of this material, the researchers wrote, may change the rates and patterns of sediment erosion. Shell removal can also reduce the amount of calcium carbonate returning to the coastal system.
The scientifically defensible takeaway is not “take one shell and cause erosion.” It is that large-scale depletion of shells can potentially modify beach sediment dynamics.
And India’s beaches provide an important context for understanding why.
India’s eastern coast is constantly processing shells
A study published in Estuarine, Coastal and Shelf Science examined 8,670 dead bivalve specimens collected across roughly 2,500 km of India’s eastern coast, covering sandy beaches, mixed sandy-rock and sandy-clay beaches, as well as beaches associated with tidal flats and seagrass habitats.
The researchers found that, after molluscs die, their shells are transported to beaches and subjected to continuous swash and backwash, producing abrasion and gradually changing the shells.
In other words, the shells lying on an Indian beach are part of an ongoing coastal process in which biological material is transported, broken down and incorporated into the beach environment.
This does not establish that tourist shell collection is causing erosion along India’s coast. Coastal erosion is driven by many interacting factors, including waves, currents, storms, sediment supply, coastal construction and changes in sea level.
And then there are the animals that need them
The strongest ecological argument for leaving shells behind has less to do with erosion, and more to do with hermit crabs. India is home to over 110 species of hermit crabs.
Unlike most crabs, hermit crabs do not have a hard abdomen.
The shells lying on an Indian beach are part of an ongoing coastal process in which biological material is transported, broken down and incorporated into the beach environment. Photograph: (Hartmann Linge)
They therefore occupy empty gastropod shells, using them as portable protection from predators, physical stress, drying, and fluctuations in salinity.
A 2023 study by Rema Reshmi, Preetha Karnaver and A Bijukumar, published in the Records of the Zoological Survey of India, examined shell selection by hermit crabs along the Kerala coast. The researchers studied 35 hermit-crab species and documented the different gastropod shells they use. They describe empty shells as an important form of mobile habitat for these animals.
So the shell that looks abandoned to a tourist may be anything but useless to a hermit crab.
Gujarat offers another example
On the Kathiawar Peninsula of Gujarat, researchers Jatin V Raval, Pradip Kachhiya, Paresh Poriya and Rahul Kundu studied two intertidal hermit crabs, Clibanarius infraspinatus and Diogenes avarus.
Their 2016 study found that gastropod shell resources at the rocky-muddy intertidal site were scanty. The two crab species used shells from nine and 19 gastropod species, respectively.
The researchers also found that larger crabs were disadvantaged by a shortage of suitably large shells, contributing to competition for available shell resources.
India’s beaches also show why the story cannot be reduced to tourism
Along the coast of Kattupalli in Tamil Nadu, Irular families traditionally gather kilinjal, or seashells, washed ashore during high tides.
Not every shell removed from a beach is a tourist souvenir, and not every form of shell collection has the same ecological or social implications. In some coastal communities, shells are part of livelihoods and local economies.
The question, therefore, is scale, context, and what the beach can naturally replenish.
So, should you take that shell home?
Shells perform several functions once they enter the coastal environment. They are gradually recycled into sediment; large accumulations can influence sediment movement, and empty gastropod shells can become essential shelters for hermit crabs.
And coastal ecosystems are already dealing with pressures ranging from tourism and litter to pollution, changing sediment dynamics and development.
That shell may have already sheltered a mollusc, may eventually become part of the sediment, or may be exactly the size a hermit crab is waiting for.
And that is reason enough to admire it where you found it, and leave it there.
