Not every invasive species is as dramatic or fearsome as a Burmese python or a feral hog—but that doesn’t lessen their impact on native ecosystems. Coastlines across North America and Europe have contended with the spread of the Manila clam (Ruditapes philippinarum) for at least the last century. Although a favorite among seafood lovers, the shellfish is also taking over the habitats of local shellfish, and even hybridizing with similar species.
After decades of slow conquest, the delicious mollusk is finally setting up shop along the New England coastline. According to wildlife biologists writing in the journal Biological Invasions, the region marked the Northern Hemisphere’s last holdout against the Manila clam.
“Given that Manila clams are everywhere else in the Northern Hemisphere, it was only a matter of time before they showed up here, and we’ve been keeping an eye out for them,” Aly Putnam, a study co-author and University of Massachusetts Amherst ecologist, said in a statement.
The first tip off to the mollusk’s arrival came via a photo and a text message. Last summer, Putnam received a picture from colleague and study co-author El Fernekees Hartshorn depicting a suspected Manila clam shell. Putnam and fellow researcher Carolina Bastidas were leading a biodiversity workshop on Spectacle Island in Boston Harbor at the time, and began paying attention to the coastlines. It wasn’t long before they located many more Manila clams.
Coincidentally, an entirely separate team led by the Center for Coastal Studies had recently started investigating reports of “weird clams” near Provincetown, Massachusetts. They soon combined forces, confirming that Manila clams were definitely beginning to thrive in the area.
“I realized that this was a golden opportunity to not only combine forces, but also to catch a detailed snapshot of the moment a new invasive species establishes itself,” added study co-author and Williams College marine scientist James Carlton.
The Manila clam’s origins are nowhere near Cape Cod. Instead, they’re native to Russia’s Sakhalin Islands and the coasts of Japan and southern China. The clams were introduced both intentionally and accidentally to North America and Europe during the early 20th century, where they quickly proliferated. The food industry also capitalized on the shellfish, turning them into a $7 billion-a-year industry.
While dense colonies can adversely impact local ecologies, they also offer nutritious food for crabs, small mammals, and seabirds. Now that they’re confirmed across the Northern Hemisphere, ecologists can begin to examine how the clams are spreading throughout New England, and how they will impact their new homes. Although they are likely here to stay, it’s not necessarily a terrible situation.
“On the positive side, because Manila clams can become a source of food for other animals, they can relieve pressure on native species—-for example, the predator pressure of green crabs on softshell clams,” explained Bastidas. “So, there could also be positive impacts.”
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