Invasive Manila clams documented along Massachusetts coast

Marine biologists have confirmed that the invasive Manila clam has established itself along the Massachusetts coastline, marking the first time the species has been documented in the northwestern Atlantic. Researchers from the University of Massachusetts Amherst, Massachusetts Institute of Technology Sea Grant and the Center for Coastal Studies conducted the investigations.

Their findings were published in the peer-reviewed journal Biological Invasions.

Discovery process The confirmation emerged from two parallel investigations.

In the summer of 2025, a text message with a photo of a clam prompted researchers to search Spectacle Island in Boston Harbor. They found shells in abundance and later dug up dozens of tiny live clams at sites in Quincy and Boston. Researchers with the Center for Coastal Studies had been hearing reports from clammers in Provincetown of "weird clams" since 2023.

Their investigation uncovered female Manila clams that had also reproduced.

Geographic spread and background The species has now been found from Boston Harbor to Cape Cod. The Northeast had been the last region in the Northern Hemisphere without Manila clams. Native to waters stretching from Russia's Sakhalin Islands through Japan and southern China, the Manila clam has spread widely since the early 20th century. Today, it represents a $7 billion global industry.

Potential effects Scientists remain unsure how the clams reached New England waters or how quickly they may spread. They warn that the clams could cause problems by crowding out native shellfish and reshaping coastal habitats if their populations get too big.