Sep 28, 2017

Debris from 2011 tsunami carried invasive species to North America

Oregon Coast Aquarium employees recover fish from a boat washed ashore from JapanCredit: Oregon Coast Aquarium

The 2011 Japanese earthquake and subsequent tsunami washed massive amounts of debris into the sea. Boats, docks and parts of houses circulated in the Pacific and landed on the shores of North America, carrying animals native to Japan with them. In a paper published Thursday in the journal Science, researchers documented the scope of this unprecedented event for the first time.

Why it matters: The authors are concerned this might be a glimpse of the future. More people live along the seashore than ever before, and as major storms and associated surges become more common, massive rafting events like this may also increase, speeding the distribution of invasive species across the oceans.

"If you look at the Caribbean and the Florida Keys right now, there are entire neighborhoods gone. We know that this debris went into the ocean," study author James Carlton, a marine biologist at Williams College, tells Axios.

Tsunamis have washed manmade structures out to sea in the past, but they generally decayed before they made it to shore. The study authors found no record of debris washing up in North America following Japanese tsunamis in 1896 and 1933. But the advent of plastics has created structures capable of surviving the open ocean for decades. Carlton says that a rapid dispersal of species like this has never been seen before.

What they did: A team of marine scientists surveyed 634 pieces of Japan-originating debris that washed up in North America since 2012. This included chunks of docks, crates of wood and entire boats.

What they found: The scientists found 289 different marine species native to Japan, including invertebrates like worms, seastars, snails and shellfish like mussels to actual fish.

Even vertebrates like fish have survived the journey. In 2016, a school of 20 yellowtail jacks and one barred knifejaw were found in a Japanese boat that washed up on the shore of Oregon. They were trapped in the boat's hull for five years and highly emaciated. Six jacks and the knifejaw survived, and are currently on display at the Oregon Coast Aquarium, say Aquarium officials.

Over time, the diversity of species washing up on North American shores decreased. That's because the longer the debris drifts at sea, the hardier the species have to be to survive. It's likely, says Carlton, that the animals that can survive the journey could also be successful invasive species.

Wait and see: No breeding populations of invasive species from Japan have been found yet, but that doesn't mean they aren't established. It can take a while for a population to reach a noticeable size, says Carlton.

Look back: This rafting event and related migration is unprecedented in its size and scope. But rare, smaller rafting events have happened naturally. Their fingerprints are visible in the distribution of species around the globe, but this is the first time one has ever been observed in real time.

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