Summary (tl;dr)

Invasive Manila clams have successfully established reproducing populations along the northwestern Atlantic coast, specifically in Massachusetts, marking the first confirmed foothold for the species in this region.

Essential Background

The Manila clam, Ruditapes philippinarum, is a species native to the Indo-Pacific region, including areas like Russia's Sakhalin Island, Japan, and southern China. Valued as a food source, it underpins a substantial global seafood industry worth approximately $7 billion annually. Historically, the clam was introduced both accidentally and intentionally to the American Pacific Coast and European coastlines in the early 20th century, where it has since become widespread. Until recently, the northwestern Atlantic coast was considered the only major Northern Hemisphere region free from this invasive species.

The Full Story

The presence of Manila clams on the Atlantic coast first became evident in the summer of 2025, when an undergraduate attending a workshop on Spectacle Island in Boston Harbor identified a suspected Manila clam. This initial observation was followed by the discovery of numerous tiny live clams and abundant shells in areas such as Squantum in Quincy and Calf Pasture Park in Boston. Concurrently, as early as 2023, local clammers in Provincetown, located on Cape Cod, had begun reporting sightings of "weird clams." A collaborative research effort involving biologists from the University of Massachusetts Amherst, MIT Sea Grant, and the Center for Coastal Studies has now officially confirmed the establishment and reproduction of Manila clam populations in both Boston Harbor and Cape Cod. These findings, which signify an uncommon moment in invasion biology where a new species establishes itself, have been formally published in the journal Biological Invasions.

Why It Matters

The confirmed establishment of Manila clams on the northwestern Atlantic coast represents a critical turning point in invasion biology, as the species has transitioned from an occasional sighting to an established resident. This invasion raises concerns because Manila clams can outcompete native shellfish for resources and interbreed with similar native species, potentially disrupting existing ecosystems and negatively impacting local habitats that are already under conservation efforts. While the full ecological and economic implications for native shellfish populations and local fisheries are still being investigated, scientists will continue to monitor their spread and population dynamics. There is, however, a dual perspective, as the clams could potentially offer some benefits by providing a new food source for local wildlife such as seabirds, crabs, and raccoons, which might reduce predatory pressure on native species like softshell clams. Furthermore, given their marketability, the presence of Manila clams could also present new opportunities for the seafood industry.

Geographic Location

• Boston Harbor, Massachusetts, United States (established breeding populations)
• Spectacle Island, Boston Harbor, Suffolk County, Massachusetts, United States (initial suspected sighting in 2025, shells found)
• Squantum, Quincy, Norfolk County, Massachusetts, United States (live clams found)
• Calf Pasture Park, Boston, Suffolk County, Massachusetts, United States (live clams found)
• Cape Cod, Massachusetts, United States (established breeding populations and "weird clams" reported)
• Provincetown, Barnstable County, Massachusetts, United States (local clammers reported "weird clams" in 2023)
• Chatham, Barnstable County, Massachusetts, United States (commercial harvesters spotted Manila Clams)
• Wellfleet, Barnstable County, Massachusetts, United States (commercial harvesters spotted Manila Clams)
• Salem Sound, Essex County, Massachusetts, United States (northernmost occurrences documented)