Japanese tsunami flooded US with invasives

In June 2012, 15 months after a magnitude-9 earthquake struck northeastern Japan and sent a colossal tsunami hurtling through the oceans, a 66-foot slab of concrete from Misawa, Japan washed up 5,000 miles across the Pacific on Agate Beach, Oregon. A new study shows that such man-made debris from natural disasters can deposit thousands of foreign coastal invertebrates on North American shores, raising concern about the ecological and economic consequences of invasive species.

“Marine debris is a global problem that can change the way animals are moving,” said Jessica Miller, co-author on a Science paper that catalogues fauna inhabiting items conveyed by the 2011 disaster. “By documenting the suite of species and identifying those that should be paid more attention, we’ve provided tools to keep managers’ eyes open and discover invasives potentially early enough to handle them.”

Starting in 2012, Miller, an associate professor at Oregon State University, and her colleagues along the Pacific Northwest and Hawaiian coastlines collected 650 pieces of debris carrying markers that could be traced back to Japan. The objects included docks, boats, buoys, crates and plastics carrying healthy reproductive specimens, which 80 taxonomic experts around the world helped identify.

The scientists noted that at least half of the 289 species identified had not been recorded in the Pacific Northwest before, but more than 30 had been reported as invasive elsewhere.

The invertebrates Miller and her partners studied, such as the Mediterranean mussel (Mytilus galloprovincialis), a species that previously invaded Japan and the western United States and occurred on over 50 percent of the examined debris. The researchers also observed other invasive species that had already been introduced via ballast water, including the Northern Pacific sea star (Asterias amurensis) and the Asian shore crab (Hemigrapsus sanguineus). They often detected other crustaceans, worms and hydroids related to sea anemone and jellyfish, too.

“It’s likely that some species that had not yet invaded habitats outside their native range might, now that they’ve been transported such long distances on tsunami marine debris over time,” Miller said.

She believes these findings indicate how humans shape worldwide species distributions, with human-made materials surviving ocean voyages longer than natural materials and carrying with them invasive passengers.

“The development of the coastline with well-made infrastructure and durable plastics has created a transport mechanism able to carry different species longer distances than natural rafts, such as kelp or wood,” Miller said. “The intersection of coastal infrastructure, building materials we’ve made and natural disasters like large tsunamis and hurricanes could end up creating a transport vector that changes how species move around the globe.”

The biologists hadn’t thought coastal invertebrates could endure the prolonged harsh conditions at sea, but they suspect the floating junk islands’ durability and slow speed might facilitate the animals’ reproduction and adherence to surfaces.

Although prior studies examined various crustaceans and other coastal species traveling far on ocean debris and natural rafts, she said, “there’s been nothing at this scale, no documentation of such a mega rafting event, so many different items and species over six-plus years.”

Miller is part of a team building on this research by investigating the documented species’ life history traits and environmental requirements, recording more nonnative fauna on debris, identifying potential invasives and trying to understand why they survive and spread on plastic.

Despite the appearance of these invasive species on the West Coast, scientists have found no sign that they’ve established colonies there yet, but colonization is increasingly likely as plastics become more pervasive and climate change threatens to intensify extreme weather events.

“Reducing and managing the waste stream and creative adaptation and planning to deal with catastrophes” could help minimize the risks, Miller said.