“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.