The 2011 Tsunami Flushed Hundreds of Japanese Species Across the Ocean

After the Fukushima disaster, a surprising number of coastal creatures survived a multi-year journey by clinging to floating debris

Tsunami Hitchhikers
Japanese sea slugs that washed ashore in Oregon in 2015 John Chapman

The 2011 earthquake and tsunami in Fukushima, Japan, released more than just radiation. The catastrophe, which killed 18,000 people and created one of the worst nuclear crises in history, also swept at least 289 Japanese species across the Pacific Ocean who hitched a ride on some of the tons of debris the tsunami sent flying.

Rafting is a biological process in which organisms are swept by ocean waters from one land mass to another, surviving by floating on pieces of debris. It’s a rare event, but it’s likely how monkeys made it from South America to Central America and how most of the animals in Madagascar made it to the island.

Before the 2011 tsunami, however, there wasn't record of critters making the long and brutal journey across the Pacific from Japan to North America, Ed Yong reports for The Atlantic. In fact, there wasn't even a record of debris that had washed up along the coast from Japan. “[A]nd it wasn’t for lack of looking,” James Carlton of Williams College, tells Yong. “Marine biologists have populated that coastline since the 1950s. I’ve personally walked those beaches for decades. If it happened, it was rare enough that it was beyond detection.”

But in a new study, published in the journal Science, Carlton and his co-authors worked with a network of volunteers to survey Japanese tsunami marine debris down the Pacific coast of North America from Alaska through California. They found more than 600 pieces of debris colonized by nearly 300 species native to Japanese shores—sea slugs, oysters, barnacles and more. Two species of fish even made it across the 4,000-mile-wide ocean.

“I didn't think that most of these coastal organisms could survive at sea for long periods of time,” Greg Ruiz, study co-author and marine biologist at the Smithsonian Environmental Research Center says in a press release. “But in many ways they just haven't had much opportunity in the past. Now, plastic can combine with tsunami and storm events to create that opportunity on a large scale.”

As Martin Fackler at The New York Times reports, it’s hard to say whether any of the species that crossed the ocean will become residents of North America. But the survey suggests that, while rafting is a natural phenomenon, human influence has dramatically changed the process. Without man made materials like plastics and polystyrene that can stay afloat for years, it’s unlikely any of the creatures would have survived the trip. "Wood carried away by the tsunami probably sank, waterlogged or bored with holes by sea creatures," writes Ben Guarino for The Washington Post

The species that survived were all very young, which suggests the bustling colony was created by the reproduction of creatures on the detritus rafts over the years it took to cross the ocean.

“We have created a new ecological process, the process of mega-rafting,” Steven L. Chown, biologist at Monash University who wrote a commentary on the study in Science, tells Fackler. “The development of materials that can float for ages, and the rising levels of seas due to climate change, make the possibility of these events larger and larger.”

The debris found in the survey included lots of large-scale objects, like docks colonized by over 100 species and fiberglass fishing boats with barnacles clinging to their hulls. But even small bits of trash can act as a raft for species to cross oceans, Charitha Pattiaratchi from the University of Western Australia tells Yong. “The tsunami provided lots of large debris that could be studied,” he says. “But what is more important is what happens at the smaller scale—even very small plastics can be transported between ocean basins, and these have their own ecosystems.”

The plastic pollution in the ocean along with major development along the coasts has changed what makes it into the ocean after a tsunami or hurricane, Carlton tells Guarino. In 1933, for example, when a major Tsunami hit the Japanese coast, most of the debris was wood from small villages. Now, coastal mega-developments flush tons of plastic debris into the ocean during natural disasters, which could lead to more mega-rafting events.

Get the latest stories in your inbox every weekday.