march 11, 2011, started like
any other day for the many mussels along Japan’s eastern coastline—clinging to docks and straining their snacks out of the water—until 2:46 p.m., that is, when two colliding chunks of the Earth’s crust set off six minutes of ground-shattering quakes, then a series of gigantic waves powerful enough to crush three-story buildings and rip docks off their moorings.
That earthquake and tsunami killed about 18,000 people and caused more than $200 billion in damage. Simply clearing away the debris took about four years. But not all of the debris stayed in Japan, and the untold story of what was sent adrift offers a revealing glimpse of how natural disasters reshape the world, often in the most unexpected ways.
The tsunami marked the moment when thousands of those mussels set off on an incredible adventure across the Pacific Ocean. In the past six years, debris from Japan has landed on the beaches of Hawaii and all along the western coast of North America. And according to a study of the tsunami’s aftermath published September 29 in Science, a small sample of that debris—much of it plastic—brought with it living specimens of almost 300 species.
The report offers a “minimum picture” of the tsunami wreckage transported to North America, says James Carlton, lead author on the project and a marine ecologist at Williams College. And the debris is still arriving, he reports. “We had no idea it would last until 2017 and beyond.”
The long trail of debris means hundreds of species got a foothold in new ecosystems. Scientists have known for a long time that species hitch rides on logs, but it’s incredibly difficult to track a piece of debris from takeoff to landing. “This is really the first largescale [migration] event that we are basically witnessing as it unfolds,” says Martin Thiel, an ecologist who studies species movement at the Catholic University of the North in Chile and wasn’t involved with the study. ”
Ecologists could track most of the tsunami debris because it was relatively easy to identify. In many cases, an entire dock or boat washed ashore, complete with registration numbers or other identifying information.
For the study, the team examined 634 pieces of debris believed to stem
from the tsunami, then tallied the animals each piece was carrying, aided by 80 scientists from around the globe. The final tally: living critters from 289 species, including Japanese skeleton shrimp, Pacific seastar and barred knifejaw fish.
Some of those creatures may not have made the whole journey—they may be descendants born on the voyage—but they all have the chance to live in a new habitat. And the researchers estimate that many more living organisms have the same opportunity, given the large amount of unstudied debris in the oceans. Most of these “debris hitchhikers” won’t survive because they didn’t happen to be deposited in a habitat that suits them, but any that do get lucky could become an invasive species, able to thrive so well that native species suffer.
There’s no telling which species might do that kind of harm—carlton compares the process to “ecological roulette,” because predicting which new arrivals will not meet natural predators in a new location is impossible. The past can be informative, however—mediterranean mussels, one of the 289 species found in the debris, have invaded other places—so scientists are monitoring coastal habitats in Hawaii and North America for early signs of an invasion.
The amount and variety of debris still washing ashore six years after the Japanese tsunami is staggering. Natural debris like wood petered out after the first few years, since it often breaks down en route. But the plastic keeps coming. “We have basically a huge armada of plastics, and those are the ones that have been making it along this very long trip,” Thiel says.
Tsunami debris is just a fraction of all the plastic in Earth’s oceans, so the same odysseys being documented here could be more common than we realize. “We know that plastic in the ocean is not a good thing for many different reasons, and this is one of the reasons,” Thiel adds. He’s referring to ugly surprises, like the Japanese orangespotted sea anemones that came ashore from southern Oregon to central California during the spring of 2016, the first time the anemone was spotted on any tsunami debris.
“The tsunami event was this obviously human tragedy,” says Cathryn Clarke Murray, a marine ecologist at the North Pacific Marine Science Organization in British Columbia, which has been supporting Carlton’s research and other projects studying the impact of tsunami debris. But, she says, the study has provided new insights into how species move around the world. “It really changed our perception of coastal ecology.”
Carlton and Thiel both note that the study is timely, given the paths of Hurricanes Irma and Maria across Florida and the Caribbean, knocking plastic and other debris into the ocean. Many species could easily have hitched a ride to travel along the Gulf Stream and eventually land in Europe. And if current trends continue, more and more of that debris will be longfloating plastic. That’s welcome news for accidental adventurers, since no one wants to be stranded in the middle of an ocean. There’s no telling, however, how these wanderers will be greeted once they make landfall.
Most “debris hitchhikers” won’t
survive, but lucky ones could become an invasive species.
CRUISE, NO CONTROL Some of the debris created by an earthquake and tsunami in Japan drifted across the aci c including a barge that made land in ong each, alifornia , bringing with it many accidental tourists.