(Photo: Pavel Ahmed/Flickr)

Entire communities of new marine and seashore organisms have arrived in Hawaii and along the West Coast in the aftermath of the 2011 Tōhoku earthquake and tsunami.

Almost 300 species, including fish, snails, sponges, and many microorganisms, survived the 5,000-mile drift as organic clumps around floating islands of the rubble that was swept from the shores of Japan by the tsunami's relentless waves. Such a large and concentrated swarm of new arrivals is highly unusual and presents a potential invasive species threat, according to a new study published in the journal Science.

Greg Ruiz, a marine invasive species researcher with the Smithsonian Environmental Research Center who co-authored the paper, says floating colonizations by invasive species are rare events.

"There are no [previous] records of material coming from the shores of Asia to the shores of North America, and the search record is quite extensive," Ruiz says, adding that earler colonizations happened via other mechanisms like ship traffic.

"One of the things that really blew me away is that so many of these organisms could survive in open ocean for five to six years," Ruiz says, alluding to the journey of a tiny Japanese coastal fish that washed ashore near Long Beach in the stern well of a rusty fishing boat. "We didn't think they would find enough food. Our study shows that's not the case."

These Japanese sea stars arrived in Newport, Oregon, in 2012 aboard a floating fisheries dock. (Photo: John W. Chapman/Oregon State University)

After studying the accretions of rubble and organisms, Ruiz suggests that the huge amount of plastic debris in the ocean, including material mobilized by the tsunami, made the rafts sturdy enough to withstand the long trip.



Some of the debris was quite large, including a 60-foot floating dock encrusted with shellfish and other organisms, as well as 60 to 70 boats of various sizes. A lot of the species the team documented were in good physical shape and actively reproducing.

Now that they are here, the team says, it's time to start thinking about a response, because the flotilla of new organisms could harbor potential threats to human health and ecosystems, as well as to important economic resources like fisheries and tourism. An unrelated recent study found, for example, that potentially harmful microbial communities are forming in areas where plastic pollution is dense.

Ruiz says the big-picture solution is to reduce global plastic pollution, but some short-term measures aimed at prevention could save a lot of money down the road. Once damaging aquatic invaders are established, it's extremely hard to get rid of them. Zebra and quagga mussels caused losses of up to $5 billion on the economy of the Great Lakes region in the late 1990s by clogging water intakes and degrading fisheries.

The latest study helps identify where the pollution is washing up, which could guide early monitoring and targeted clean-ups, aimed at preventing new species from gaining a foothold.

Aquatic species started hitchhiking when prehistoric people launched their first dugout canoes, and spread globally when seafaring Phoenicians and Vikings took to the seas. On land, Marco Polo's camels no doubt carried their share of pests between Europe and Asia. Biological invasions are, in a way, the story of life on Earth.

Marine sea slugs washed ashore in Oregon in 2015 aboard a derelict Japanese vessel. (Photo: John W. Chapman/Oregon State University)

But the scope of this latest migration across the Pacific is probably unprecedented. Altogether, the team counted 289 living invertebrate and fish species arriving from Japan. Many species were just recorded on one piece of debris, so the scientists estimated that the real number of species is much higher.

Most frequent among the new species were mollusks, but there were also many types of worms, anemones, and jellyfish relatives and crustaceans, as well as branching colonies of underwater bryozoans. None of the organisms would be expected to survive such a long time at sea—up to six years for some of them—because open ocean conditions are usually not tolerable for coastal species. The findings suggest that the slower speed of the rafts compared to ships may have let the organisms gradually adapt during the trip.

Ruiz said that several of the species they identified—especially parasites associated with mussels and some starfish, as well as algal species—have shown invasive behavior in other ecosystems. The hotspots for tsunami debris accumulation are along the coast in Washington and Oregon, and to a lesser degree in California.

Until now, the scientists hadn't documented any colonization by the new species. It can take several years for invaders to establish a foothold, and that opens a window of opportunity for prevention.

Still, for now, the best-practices handbook for responding to marine invasive species is pretty thin.

"For terrestrial systems, probably for economic reasons, we've developed pretty good tools for detection and treating, controlling or eradicating new pests that come in," Ruiz says.

For aquatic systems, there are some controls, but there's not a robust response or regulatory framework. Nevertheless, there have been successful eradications of marine invasive species: Ruiz said that, by acting fast, biologists were able to eradicate a potentially harmful mussel from a harbor in Western Australia, as well as parasites associated with abalone that landed on the central California coast some years ago, and invasive algae in Southern California.

Prevention starts with continued monitoring for potentially threatening new arrivals. The next step is studying the various species to determine if there are pathogens or parasites that present a threat to human health, native ecosystems or fisheries and recreation, followed by targeted clean-ups.

Most of all, Ruiz says the study shows the urgent need to reduce plastic pollution in the oceans. Much of the debris the scientists found was made of fiberglass or other plastic materials that made the new large-scale invasion possible.

"The growing amount of plastics and microplastics in the oceans may have big impacts for animals and ecosystems. There should be some attention to this as we consider the consequences of plastic pollution," Ruiz concludes.