History in USA

Initial Introduction

The Asian Clam, Corbicula fluminea, was likely introduced to the United States in the 1920s by Chinese immigrants (6). From that introduction it quickly spread across North America, although it is likely multiple introduction events have occurred.

Spread

The Asian clam has been found to spread through ballast water, aquarium release, attachment to boat hulls (juveniles anchor to sediments due to their byssal thread), and human introduction (6). They spread rapidly in freshwater lakes, canals, streams, rivers and reservoirs throughout North America (I).

Diagram depicting spread of invasives by ballast water. Invasives spread from Point 1 to Point 3. Source

Clams and other invasive species may attach to boat hulls, thereby being transported between waters. Source

Impacts

Along with the cost of the loss of many native species, the Asian clam is estimated to cause 1 billion dollars of damage annually to the US economy as of 2005 (3). They attach to heavy machinery, clogging drain pipes and corroding surfaces of expensive equipment. All invasive species in the US cause an estimated 120 billion dollars in damages (3). They deposit high amounts of nutrients such as nitrogen, phosphorous, and calcium in the water (2). While the nitrogen and phosphorous allow for more algal blooms, which have been found to be co-located with Asian clam beds in Tahoe, the increased calcium concentrations can facilitate invasion of other species like zebra or quagga mussels (2). These other invasive species have further environmental impacts, which are economically difficult to judge in some cases.

The distribution of Asian Clam in the United States. Larger dots indicate larger concentrations of clam.
Source: USGS