“Weird Clams” Reveal a New Invasion Along the U.S. Northeast Coast
By University of Massachusetts Amherst
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| Empty Manila clam shells blanketing the intertidal zone in Boston Harbor’s Spectacle Island. Credit: Aly Putnam |
A stretch of Atlantic shoreline that had remained free of Manila clams now appears to support reproducing populations of the invasive shellfish.
Biologists led by the University of Massachusetts
Amherst, MIT Sea Grant at the Massachusetts Institute of Technology
and the Center for Coastal Studies confirmed that Ruditapes
philippinarum has established itself along the northwestern Atlantic
coast. Published in Biological Invasions, the findings capture a
rarely documented stage of biological invasion, when a species is
first becoming established and beginning to spread through a new region.
Manila clams are native to waters extending from Russia’s
Sakhalin Islands through Japan and southern China. Since at least the early
20th century, however, people have introduced them both intentionally and
accidentally to the Pacific coast of North America and to Europe, allowing the
species to spread across much of the Northern Hemisphere.
The clams are widely valued as food and support an industry
worth about $7 billion annually. At the same time, dense populations can
compete with native shellfish, hybridize with related species, and alter
surrounding ecological communities.
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| Co-author Bastidas in Squantum, Massachusetts, holding a native quahog clam. Mussels and Manila clams are visible in the tray. Credit: Carolina Bastidas |
Their arrival may also bring some benefits. Manila clams can provide abundant food for seabirds, crabs, raccoons, and other animals that prey 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.
A text message starts the search
The Northeastern U.S. had represented the last major gap in
the Manila clam’s Northern Hemisphere range. Evidence that the species had
reached this coastline emerged from something remarkably ordinary: a text
message.
During the summer of 2025, Putnam was leading a small
workshop on intertidal biodiversity at Spectacle Island in Boston Harbor when
El Fernekees Hartshorn sent her a photograph of an unfamiliar clam. Fernekees
Hartshorn, a recent University of Rhode Island graduate who had worked with
Putnam on regional Rapid Assessment Surveys for marine invasive species,
suggested that the shellfish might be a Manila clam. Fernekees Hartshorn is
also a co-author of the paper.
Carolina Bastidas, a research scientist with MIT Sea Grant and Putnam’s co-investigator, was also participating in the Spectacle Island trip. The two began searching the shoreline for Manila clam shells and soon found them in large numbers.
At the same time, another group led by Owen Nichols of the
Center for Coastal Studies had been following separate reports. Beginning in
2023, local clammers had described finding “weird clams” around Provincetown at
the northern end of Cape Cod and at other locations across the Cape.
The Boston Harbor and Cape Cod investigations might have
continued independently if James T. Carlton had not connected them. Carlton, an
emeritus professor of marine sciences at Williams College and a leading
authority on invasive marine species, learned about the shells found on
Spectacle Island and urged Putnam and Bastidas to determine whether they
represented an established population rather than discarded food or bait.
“Find me living clams,” he told the group—especially baby
clams and clams that showed evidence of having reproduced.
Young clams confirm a new population
Putnam and Bastidas soon found the evidence Carlton
requested. After spending hours digging at Squantum in Quincy and Calf Pasture
Park in Boston, the researchers used sieve-based sampling to recover dozens of
small living clams. The juvenile specimens showed that Manila clams had
recently reproduced and that young clams were joining the population.
Nichols’s group then investigated the unusual clams reported
around Cape Cod. They found female Manila clams that also showed evidence of
reproduction, strengthening the case that the species was established at
multiple locations rather than appearing only as isolated individuals.
“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.”
The ecological consequences remain uncertain
Researchers do not yet know how Manila clams reached the northwestern Atlantic or what their establishment could mean for coastal waters in the Northeastern U.S. Their presence could affect commercial shellfishing, native species and broader ecological relationships, but the direction and scale of those effects remain unclear.
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.”
Reference: “Completing the journey in the global north: the
Manila clam (Ruditapes philippinarum) (Bivalvia: Veneridae) arrives in the
Northwest Atlantic Ocean” by Alysha B. Putnam, Carolina Bastidas, Owen C.
Nichols, Jeff C. Clements, El Fernekees Hartshorn, Diana W. Chin, Alison Frye,
Renee Gagne, Megan Lynn Geiger, Rachel Hutchinson, Vania Rivera Leon, Alexis J.
Neffinger, Joshua Reitsma, Tommy Tucker, Isabella C. Yeung and James T.
Carlton, 4 July 2026, Biological Invasions.
DOI:
10.1007/s10530-026-03861-z
