When you’re vacationing on a beach, it might seem like a harmless act to pick up a shell and take it home with you as a souvenir. Especially if there are a lot of shells on the beach – how could taking one, or just a few, be a bad thing? But a recently published scientific study shows just how huge of an effect this action can have. Basically, the study found that the number of shells on a popular Mediterranean beach has decreased by more than 60% over the past three decades. At the same time, local tourism has increased three-fold, and is the most likely suspect. Such shell depletion may cause serious problems for multiple walks of life that call the beach their home.
Perhaps most obviously, mollusk shells often provide important homes for hermit crabs, but several other types of animals also depend on the shells to live. For example, the shells supply shelter, protection, or a substrate for various types of algae, seagrass, fish, and other organisms. Even birds use the shells in their nests. And the chemicals that the shells are composed of (primarily calcium, in the form of calcium carbonate) need to be recycled through the ecosystem – if removed, the decreased amount of available calcium could negatively affect corals, algae, clams, oysters, urchins, lobsters, crabs, shrimp, and other marine animals that need calcium in their shells or bodies. These shells also play important roles in stabilizing beaches, which can affect an even wider variety of creatures in the area.
The study was performed on a beach in Spain (Llarga Beach). While this beach is popular with tourists, the observed three-fold increase in tourism over the last three decades is still lower than global tourism increases, which are about four-fold. Additionally, the beach is not home to any particularly beautiful or rare shells. Yet researchers still found a 70% decrese in the number of beach shells (compared to three decades ago) during tourist season (July to August) and a 60% decrease throughout the rest of the year. It is likely that more popular beaches that have more “collectible” shells have had even greater decreases that may be going unrecorded.
So while it’s tempting to take a beach shell keepsake home from a trip, it’s best to leave it where it is – the beach is its home, and the impressive diversity there relies on the shells sticking around. (And, as we’ve talked about before, to prevent the spread of potentially dangerous diseases it’s also important to not transport and release living animals in an area they’re not native to – especially amphibians and reptiles!) Instead, you could spend time picking up trash off of the beach, making it a more beautiful place for everyone to enjoy, and maybe take home some smoothed, pretty pieces of beach glass.
For further reading:
- Michal Kowalewski, Rosa Domenech, and Jordi Martinell’s article “Vanishing Clams on an Iberian Beach: Local Consequences and Global Implications of Accelerating Loss of Shells to Tourism” in PLOS ONE
- ScienceDaily’s article “Seashell Loss Due to Tourism Increase May Have Global Impact”
- University of Florida’s article “Study: Seashell loss due to tourism increase may have global impact”
- Justin Ries’s article “Ocean acidification : a risky shell game“
- Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre