The Clam That Sank a Thousand Ships

An infamous mollusk is invading new areas, buoyed by climate change and the 2011 tsunami in Japan

IMG_5272This feature originally appeared in Hakai Magazine Dec. 5, 2016

Early on a calm June morning, Nancy Treneman picks her way along the wrack line of a stretch of southwestern Oregon coast. The biologist has short, curly hair that furls in small wings from beneath her baseball cap and wears jeans patched at the knee with a denim heart. Every so often, she pauses to scrutinize a plastic bottle or lonely flip-flop, or retrieves a hatchet from her pack and skims shavings from a piece of driftwood sticking out of the bony assemblage of logs where the beach meets a steep hillside.

“The debris tells a story,” Treneman explains as she makes notes in a waterproof yellow book. “It tells you what’s going on out there. When the fishing boats are out there. When the crabbing is happening. When the hagfishing is going on.”

And today, just like 30 other days over the past three years, Treneman is looking for passages from a very particular story that may have snagged here among the rocks and sea stacks at Crook Point—a promontory inside Oregon Islands National Wildlife Refuge that happens to be a perfect catchment for Pacific Ocean castoffs. Suddenly, she spots a black plastic sphere the size of a beach ball. “Oh, oh, a new float! … This one looks freeee-esssh! Lookit! It’s got a mussel!” she cries excitedly, pointing to a delicate lacework of threads fouling its surface. “This is a tsunami float. All this stuff is old mussels.” The cluster of thumb-sized bivalves are Mytilus galloprovincialis, a Mediterranean species that has established itself along the Japanese coast.

Treneman perches on a log and punches out an email on her cellphone to marine biologist Jim Carlton, then retrieves a ziplock bag of chocolate cake from her pack and passes me a piece. “I need the bag,” she says, scraping the creatures from the float’s surface and dropping them inside.

When the magnitude 9.0 earthquake struck off the coast of Japan in 2011, it measurably shifted the country’s main island eastward, tweaked the tilt of Earth’s axis, and killed nearly 20,000 people with the towering wave that followed. The tragedy also sucked an enormous amount of buoyant stuff out to sea—fishing boats, docks, plastic flotsam—offering scientists an unprecedented look at how species raft to new environments on anthropogenic debris, a mechanism that is increasingly influencing ecosystems. With the help of volunteers, government officials, and funders, Carlton, Treneman, and more than 50 other taxonomists have identified about 300 different species that survived a journey of thousands of kilometers across the ocean to Hawai‘i, California, Oregon, Washington, British Columbia, and Alaska.

Among them is the little-known mollusk closest to Treneman’s heart: not the Mytilus, no, but the shipworm, a tunneling bivalve with a voracious appetite for wood. More…