Marine sea slugs from a Japanese vessel that washed ashore in Oregon in April 2015. Image: John Chapman

When a powerful earthquake rocked the Pacific coast of Tōhoku in March 2011, it didn’t just upend life in Japan. A massive tsunami wave swept countless coastal organisms into the open ocean, clinging to human garbage. An “extraordinary” trash-fueled migration from Japan to to North America ensued, the likes of which scientists have never seen.

That is the startling conclusion of a paper published today in the journal Science, which documents nearly 300 Japanese marine coastal species from 16 phyla that rafted across the Pacific, to Hawaii and the west coast of North America, in the six years following Great East Japan Earthquake, the most powerful quake ever recorded in Japan. Many of these hapless migrants made the long journey on human-made objects—Styrofoam cups, bottles, tires, ships, and pieces of docks—which collectively fueled the “longest transoceanic survival and dispersal of coastal species by rafting.”

It’s a bizarre event, but one we might see more of in the future, as booming, trash-producing coastal cities collide with earthquakes, hurricanes, and potentially, climate change-juiced natural disasters.

“I didn’t think that most of these coastal organisms could survive at sea for long periods of time,” study co-author Greg Ruiz, a marine biologist at the Smithsonian Environmental Research Center, said in a statement. “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.”

Japanese vessel washed ashore in Longbeach, Washington. Image: Russ Lewis

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Just as low levels of radiation from the Fukushima nuclear disaster seeped across the Pacific, debris stirred up by the quake and subsequent tsunami has been washing up on shorelines from Hawaii to Alaska to California since 2012. For the new study, researchers from Williams College, the Smithsonian Environmental Research Center and elsewhere partnered with government officials, private citizens and coastal cleanup crews to collect and analyze 634 pieces of “Japanese marine tsunami debris” that harbored live animal communities. The authors note that the debris, collected over a five year span following the 2011 quake, represents “only a fraction” of the total junk that washed ashore—many other items weren’t reported, weren’t recognized as tsunami debris, or were in areas impossible to reach.

Still, this small sampling of quake-driven flotsam contained an impressive array of would-be colonists: at least 289 living invertebrate and fish species, “none of which were previously reported to have rafted transoceanically between continents,” according to the new study. These critters run the gamut from single-celled protozoans to Asian isopods, shipworms, and enormous colonies of mussels and barnacles. Amazingly, the flow of debris didn’t appear to taper off from 2012 to 2016, although the number of highly-diverse rafted communities declined over time.

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“It is surprising that living species from Japan continue to arrive after nearly 6 years at sea, 4 or more years longer than previous documented instances of the survival of coastal species rafting in the ocean,” the authors write, noting that the population structure of the rafted colonies suggests many animals, despite their hardship, still managed to reproduce en route.

Time will tell whether any of these ocean-swept migrants establish themselves on new shores—that question was beyond the scope of the study. But the researchers do note that 35% of the species identified were already known to occur on the Pacific coast, suggesting “a climactic match as well as a broad range of matching habitats.”

Japanese sea stars found on a fisheries dock near Newport, Oregon. Image: John Chapman.

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Since the time of Darwin, ecologists have been aware that animals establish themselves in new parts of the world by rafting across the high seas. But there’s a longstanding debate over how often this occurs, and how important the process is in shaping global biodiversity. As Lawrence Heaney, Curator and Head of the Division of Mammals at the Field Museum, told Earther, the new study offers one of the richest datasets yet that can help address that question.

“In terms of scientific impact, this is a fabulous experiment,” Heaney, who wasn’t involved with the study, told Earther, noting that the research supports the idea that catastrophic events have a disproportionate impact on the global species shuffle. “What we’re learning is that what happens ordinarily isn’t necessarily the thing that determines what happens globally over the long term. Rare events can have an enormous impact.”

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Bruce Patterson, the MacArthur Curator of Mammals at the Field Museum of Natural History, who also wasn’t involved, voiced a similar sentiment. “As a terrestrial biologist, and one fascinated by questions of how and when did the ancestors of New World monkeys and guinea pig-like rodents cross the South Atlantic, rafting offers a critically important if highly infrequent event,” he told Earther in an email. “This article shows how extended those events can be, lasting for years beyond their environmental-geological trigger.”

A Japanese barnacle alongside a native gooseneck barnacle found in 2014 in Long Beach, Washington. Image: James Carlton

The fact that so many animals hitched a ride on garbage adds an Anthropocene-era twist to an age old story of species dispersal. As the authors note, many human-made materials don’t decompose readily, meaning they can potentially serve as lifeboats over incredibly long distances and timespans.

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“We’ve known for a long time that human debris in the ocean is bad, but normally it’s put in the context of animals eating them or being affected by BPA in the water,” Allison Fritts-Penniman, a marine zoologist at the California Academy of Sciences, told Earther via email. “The idea that it facilitates long-distance dispersal via rafting, and potentially leads to species invasions, is new and fascinating, especially because human-made rafts last longer than natural rafts.”

“I simultaneously love and am terrified by the fact that some species reproduced while on their raft,” Fritts-Penniman added. “I love it because it paints a nice picture of survival for this little island community traveling the world, but it terrifies me because it means these species probably have a good chance of surviving as an invasive species wherever they land.”

The study’s authors seem to agree that more rafting-driven colonization could be in our future, seeing as coastal populations are booming and dumping their garbage into the ocean at staggering rates. While there’s still plenty of research to be done, it’s another plausible avenue by which humans are inadvertently scrambling the tree of life.

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It also reminds us that trash is far more than an eyesore—it has become an inextricable part of Earth’s ecosystems.

[Science]