On March 11, 2011, an unprecedentedly powerful earthquake struck the Tōhoku region of Japan. It destroyed hundreds of thousands of buildings, wrecked the Fukushima Daiichi nuclear plant, created a tsunami that reached 40 meters in height, and shifted the entire planet a few inches on its axis. But among these catastrophic consequences, there were also subtler ones. For example, the tsunami inundated a small blue-and-white fishing boat called the Sai-shou-maru, ripping it from its moorings and casting it out to sea.

The boat drifted eastward through the Pacific, never capsizing. Then, on March 22, 2013, a couple weeks after the two-year anniversary of the quake, it washed ashore on Long Beach, Washington. Its hull was encrusted with seaweed and barnacles, and one of its compartments was full of water. And living in that water were five striped beakfish. The fish were youngsters, just four inches long. They had probably been swept into the boat as larvae, and spent their entire lives growing up within this ersatz aquarium. For two years, the boat was their entire world.

Four of those fish were euthanized by the Washington Department of Fish and Wildlife, but the fifth—now known as the “tsunami fish” was relocated to Oregon’s Seaside Aquarium. Its story astonished John Chapman, an ecologist at Oregon State University who studies aquatic invasive species. Somehow, this coastal species had endured a two-year, 4,000-mile voyage across the open ocean, in the tiniest of living spaces. “We said this couldn’t happen,” Chapman told OregonLive. “And nature is like: Oh yes it can.”

Of late, nature has been saying that to Chapman a lot.

In the last five years, he and his colleagues have documented 634 pieces of debris that were swept away by the Tōhoku tsunami and eventually washed up on the coasts of North America. And it hasn’t stopped coming yet. Between them, these bits of ocean-hopping junk carried 289 species that are typically found along Japanese coasts—a vast horde of sponges, sea stars, sea anemones, mussels, limpets, barnacles, and fish.

Nothing like this has happened before. Sure, animals can raft across large distances by clinging to natural debris that’s been swept to sea by storms—that’s how lemurs got to Madagascar, how monkeys and guinea pigs got to South America, and how iguanas got the Galapagos. But none of the 289 species that the team identified had previously been known to raft across oceans—let alone an ocean as immense as the Pacific.

Until 2012, there were no records of Japanese debris floating to North America, “and it wasn’t for lack of looking,” says James Carlton from Williams College, who worked with Chapman on his census of drifters. “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.”

Partly, that might be because the 2011 Tōhoku earthquake was one of the strongest in history. But Carlton thinks that it’s also because humans have changed the world, by just introducing a lot more stuff to it. “A similar tsunami occurred in the same place in 1933,” he says. “We’ve looked at photos of that coast in 1933, and there are small villages with wooden homes. Advance to 2011, and we have a vast infrastructure. In the last 50 years, we’ve poised, on the edge of the world, this massive amount of material that’s ready to be washed into the ocean.”

Carlton, Chapman, and their colleagues first realized what was happening on June 2012, when a huge Japanese dock washed ashore in Agate Beach, Oregon, not five miles away from Chapman’s lab. The hulking mass of steel and concrete was the length of a tennis court, and half as wide. Based on a small plaque on its side with Japanese characters, the team traced its origins to the fishing port of Misawa. And they saw that it was positively dripping with over 100,000 mussels, and at least 100 other marine species. They removed as many of the organisms as they could for study and, fearing the potential for ecological invasions, they told state officials to destroy everything else.

The Misawa dock at Agate Beach (Reuters)

A few months later, a second dock washed up at Olympic National Park, once again festooned with Japanese creatures. More months ticked by, and the debris kept arriving: small ships like the Sai-shou-maru, buoys, crates, fragments of wood, children’s toys. They washed up everywhere from southern Alaska to central California. The team assembled a network of colleagues and citizen scientists to alert them of any new arrivals, so they could scrape off biological samples before the objects were quarantined and destroyed.

To Carlton, it’s astonishing that the junk is still arriving, more than six years after the earthquake and the tsunami. A bucket in Manzanita. A pallet in Newport. Two buoys in Long Beach. And two huge docks, like the ones that washed up in 2012, are still unaccounted for. Each new arrival brings previously undetected species with it, which suggests that the team is nowhere close to identifying the full extent of the displaced menagerie. “I wouldn’t be surprised at all if, 10 years after the tsunami, a fiberglass fishing boat showed up on a beach in Oregon,” he says. “The real question is how long these species will stay alive on this debris.”

That they survive at all is surprising. In the open ocean, food is scarce, shade is absent, and conditions are unpredictable. Sun, sea, salt, and starvation should all exert a heavy toll on animals that are adapted to Japan’s rich coastal waters. And yet, these drifters aren’t just surviving at sea; they’re also breeding. On the beached junk, the team found many generations of several species, which had clearly been reproducing on their floating islands.

It used to be that animals would raft across oceans on logs and other bits of vegetation that would slowly dissolve beneath them. But humans have added far more durable materials into the mix—steel, concrete, and plastic, which can endure longer treks. Ships can obviously take animals across the same distances, but their speed makes it harder for hitchhikers. Passively floating junk, however, gives them a chance to acclimate. And since they drift randomly, rather than docking at specific ports, they expose a much wider range of coastal habitats to invasive species.

“The tsunami provided lots of large debris that could be studied,” says Charitha Pattiaratchi from the University of Western Australia. “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.” Half of all the plastic that has ever existed was made in the last 13 years, and 5 trillion tiny pieces now float in the surface layer of the oceans.

“Often, plastic debris is found on beaches, but its origins are unknown,” says Jenn Dijkstra from the University of New Hampshire. But since the team could trace each object back to Japan, and since they knew the date of the tsunami, “they showed that a number of species could live for years, crossing oceans and reaching shorelines with individuals capable of reproducing and potentially establishing populations in their new environment.”

For now, the team hasn’t detected any cases where Japanese species that were pushed over by the tsunami have established themselves in North American waters. But it’s too early to detect such invasions, Carlton says. They may be happening, but we wouldn’t know. And they’ll probably be a recurring feature of the future.

Most of the world’s megacities have been built on coasts. They’re made of persistent materials that can withstand oceanic voyages. And such materials are at more risk than ever of being swept out to sea because hurricanes and typhoons are becoming more frequent, thanks to climate change. As Carlton says, “We’ve piled up so much stuff on the coasts, in a world where the probability of it all being washed into the ocean has increased dramatically.”