You might think twice next time you snag a seashell from the beach and drop it into your pocket: You might be altering the seaside environment.
In a study more than 30 years in the making, researchers have found that the removal of shells from beaches could damage ecosystems and endanger organisms that rely on shells for their survival.
The study focused on a stretch of coastline on Spain's northeastern Mediterranean shore called Llarga Beach, where the researchers conducted monthly surveys of seashell abundance between 1978 and 1981.
At the time, they weren't thinking of ecology: They were doing paleontology research to understand what happens to shells after the organisms that inhabit them die.
“Only later did our research group realize that this quantitative data set offered us a unique opportunity to evaluate changes in shell abundance on a beach that was increasingly frequented by tourists,” said study leader Michal Kowalewski, a curator at the Florida Museum of Natural History.
The researchers focused on the empty shells of three types of clams. When they returned to the same beach three decades later, they found that the abundance of seashells had decreased by 60 percent, while tourism had increased in the area by 300 percent.
Even though other factors might play a role in the shells' decline, it is hard not to think that human behavior is to blame for the decline in seashells.
Humans seem even more culpable when you factor in the seasonal pattern: Shell abundance was especially low in the tourist-heavy summer months of 2008 to 2010, compared with the rest of the year. And the loss of seashells can't be attributed to fisheries, since the area hasn't seen any new commercial fisheries since the 1970s, the researchers found. Nor has there been much urban development. And there haven't been any major ecological or environmental changes that might account for the decline.
But could beachgoers who pocketed seashells – or bought them at beach shops – really account for what Kowalewski found? Probably not.
“Shell collecting by beachcombers is an intuitively obvious explanation,” he said, “but many other processes with tourism can lead to removal or destruction of shells.”
Grooming the sand with heavy machinery to make a more comfortable beachgoing experience, for example, can destroy shells. Such grooming is common at tourist beaches around the world. Another way in which tourism contributes to shell decline, the study suggested, is through the use of recreation vehicles on the sand.