They’re here: Biologists identify first established colonies of invasive clam in Northeastern US
Team led by UMass Amherst in collaboration with MIT Sea Grant and Center for Coastal Studies find reproducing populations of Manila clam in Cape Cod and Boston Harbor
University of Massachusetts Amherst
image:
Aly Putnam holding a baby Manila clam, much smaller than a thumbnail. Newly born clams are evidence that the species has established itself.
view moreCredit: Aly Putnam
AMHERST, Mass. — A collaborative team of biologists led by the University of Massachusetts Amherst, MIT Sea Grant at the Massachusetts Institute of Technology and the Center for Coastal Studies has discovered that the invasive Manila clam, Ruditapes philippinarum, has established itself along the northwestern Atlantic coastline — the last place in the northern hemisphere to have remained Manila-clam free. The team’s findings, published in Biological Invasions, document an exceedingly rare moment when an invasive species first takes hold in a new environment and begins to spread.
The home range of the Manila clam is from the coast of Russia’s Sakhalin Islands through Japan and southern China, but since at least the early 20th century they have been spreading to coastlines throughout the northern hemisphere. This is because they were introduced accidentally and intentionally to the American Pacific coast and to Europe. They are a delicious clam, prized in many cultures’ cuisines, and now represent a $7 billion per year industry. However, the clams can also outcompete native shellfish, hybridize with similar species and, in colonies dense enough, affect the local ecological community.
But it’s not all bad. Aside from their marketability, they can also be a rich food source for seabirds, crabs and other animals, like racoons, that feed on shellfish.
“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,” says marine scientist, Aly Putnam, who is a postdoctoral researcher at UMass Amherst and lecturer at Smith College, as well as the paper’s lead author.
As it turns out, the Manila clam has now reached the final major gap in its Northern Hemisphere distribution: the coastlines of the Northeastern U.S. We owe this new information to a simple text message.
In the summer of 2025, Putnam, who was leading a mini workshop on intertidal biodiversity on Spectacle Island in Boston Harbor, received a text from El Fernekees Hartshorn, a recent undergraduate student from the University of Rhode Island, who had worked alongside Putnam through regional Rapid Assessment Surveys for marine invasive species. Fernekees Hartshorn, also one of the paper’s co-authors, had texted Putnam a picture of a clam and suggested it might be a Manila clam. Putnam’s co-investigator Carolina Bastidas, research scientist with MIT Sea Grant, was also along on the trip to Spectacle Island, and the two decided to keep an eye out for Manila clam shells—which they found in abundance.
Unbeknownst to Putnam and Bastidas, another research group, led by the Center for Coastal Studies’ Owen Nichols, had also begun hearing reports from local clammers in 2023 of “weird clams” in Provincetown, at the northern tip of Cape Cod, and other sites around the Cape.
The two groups would have continued researching along parallel tracks were it not for James T. Carlton, emeritus professor of marine sciences at Williams College and one of the world’s foremost authorities on marine invasive species, who brought the Boston Harbor and Cape Cod groups together. When Carlton heard of the shells on Spectacle Island, he told Putnam and Bastidas to make sure they weren’t just the remains of someone’s dinner or discarded bait shells. “Find me living clams,” he told the group—especially baby clams and clams that showed evidence of having reproduced.
It didn’t take long for Putnam and Bastidas to do just that—the team spent hours digging at Squantum in Quincy and Calf Pasture Park in Boston. Using sieve-based sampling, they yielded dozens of tiny, live specimens, confirming recent reproduction and recruitment.
And then, when Nichols’s team investigated the weird clams on Cape Cod, they found female Manila clams that showed evidence of having reproduced.
“When I learned about what each group was working on,” Carlton says, “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.”
“As a marine biologist, I have worked with invasive species and with Rapid Assessment Surveys from the Northeast Aquatic Nuisance Species (NEANS) Panel for 11 years now,” says Bastidas. “Collaboration is invaluable for these sorts of efforts, and the fact we had already a network of people looking into Manila clams, means that we could catch them at the moment they established themselves.”
It’s not clear how the clams arrived in the northwestern Atlantic, nor is it clear what the future holds for the Northeastern U.S.’s waters now that they’re here. Bastidas says, “We do need more research to understand the Manila clam’s potential effects on the shellfishing industry and ecological communities. 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 predatory pressure of green crabs on softshell clams. So, there could also be positive impacts.”
“Discoveries like this remind us how much there is still a lot to learn about our coastal ecosystems,” said Putnam. “Finding the species is only the beginning. Now we are working to understand its distribution, if these populations are expanding and how these clams interact with other species in New England coastal systems. This research will help us determine whether this newcomer becomes a minor addition to the ecosystem or a more influential player in the years ahead.”
Researchers at the Northeastern University, Massachusetts Bays National Estuary Partnership, Massachusetts Office of Coastal Zone Management, Fisheries and Oceans Canada and Cape Cod Cooperative Extension Woods Hole Oceanographic Institution Sea Grant; and Salem Sound Coastwatch also contributed to this study.
A media kit with photos and all caption and credit information is available here.
Contacts: Aly Putnam, aputnam@umass.edu
Carolina Bastidas, bastidas@mit.edu
Daegan Miller, drmiller@umass.edu
About the University of Massachusetts Amherst
The flagship of the commonwealth, the University of Massachusetts Amherst is a nationally ranked public land-grant research university that seeks to expand educational access, fuel innovation and creativity and share and use its knowledge for the common good. Founded in 1863, UMass Amherst sits on nearly 1,450-acres in scenic Western Massachusetts and boasts state-of-the-art facilities for teaching, research, scholarship and creative activity. The institution advances a diverse, equitable, and inclusive community where everyone feels connected and valued—and thrives, and offers a full range of undergraduate, graduate and professional degrees across 10 schools and colleges and 100 undergraduate majors.
About MIT Sea Grant
Based at the Massachusetts Institute of Technology, MIT Sea Grant is a federal-institute partnership with NOAA that promotes the conservation and sustainable development of coastal and marine resources through research, education, and outreach. MIT Sea Grant works across four focus areas: Healthy Coastal Ecosystems; Environmental Literacy and Workforce Development; Resilient Communities and Economies; and Sustainable Fisheries and Aquaculture.
Empty Manila clam shells blanketing the intertidal zone in Boston Harbor’s Spectacle Island.
Credit
Aly Putnam
Journal
Biological Invasions
Article Title
Completing the journey in the global north: the Manila clam (Ruditapes philippinarum) (Bivalvia: Veneridae) arrives in the Northwest Atlantic Ocean
