A fast-spreading, highly contagious cancer is decimating soft-shell clam populations along the West Coast, alarming scientists and impacting a prized resource for high-end restaurants.
Bivalve Transmissible Neoplasia on the Rise
The disease, known as bivalve transmissible neoplasia, is passed between clams through seawater via living cancer cells. While previously identified on the Atlantic Coast, its recent surge in Pacific Northwest waters marks a significant and concerning development. A study published last month revealed that over 75% of soft-shell clams at two surveyed locations in Washington state were afflicted, representing one of the most severe outbreaks documented.
Scientists first detected the cancer in Washington's Puget Sound in 2022, when it affected 45% of the local clam population. In just two years, that figure has risen to 75%. "We were surprised to find a transmissible cancer spreading at this level in Pacific Northwest clams," stated Michael Metzger, Ph.D., senior author of the study and Associate Investigator at the Pacific Northwest Research Institute (PNRI). "The scale of the outbreak makes it an important system for understanding how these rare cancers emerge and move through wild populations."
Ecosystem and Industry Impact
Clams play a crucial role in marine ecosystems by filtering plankton and bacteria from the water. Their decline poses a threat to the overall health of the environment. These soft-shell clams, which are not native to the West Coast and were likely introduced from Atlantic populations in the 1870s, are also a staple in many top U.S. restaurants. Early research suggests that hybrids involving the Japanese species, Mya japonica, may exhibit greater resistance to the cancer, prompting further investigation into genetic factors influencing cancer transmission and immunity.
Beyond cancer, West Coast shellfish face mounting pressures from pollution and climate change impacts such as ocean acidification and rising temperatures. A 2021 heatwave, for example, caused widespread shellfish die-offs on Washington beaches. Experts note that increased heat and pollution can exacerbate the vulnerability of clams to diseases like cancer.
Origin and Future Outlook
While the exact pathway of the cancer's arrival on the West Coast remains unclear, researchers believe human activity is the most probable vector. "The most likely explanation is accidental human-assisted transport of an infected clam or seawater containing cancer cells, but we don’t yet have evidence that allows us to determine the precise route," Metzger explained. "Understanding how transmissible cancers move between regions will be critical for monitoring and managing future outbreaks."
While there is concern the cancer could spread further south to Oregon and California, scientists currently assess the risk as low. The current outbreak's early stages offer an opportunity for researchers to study how clam populations adapt to the disease in their natural habitat. It is important to note that the cancer does not pose a risk to human health, and affected clams are considered safe for consumption. However, in a separate issue, Washington clams have also been linked to norovirus contamination, leading to a recall of certain harvested clams in March due to potential contamination with the virus.