Here’s a breakdown of the animals that crossed the Pacific on 2011 tsunami debris

About two-thirds of the creatures have never been documented off the western coast of North America

sea slugs

HITCHHIKERS  These marine sea slugs stowed away on a derelict vessel from Iwate Prefecture in Japan before being washed ashore in Oregon in April 2015. 

John W. Chapman

Life’s great diversity has revealed itself in more than 600 pieces of floating tsunami debris that have landed on the western coast of North America. Of nearly 300 living animal and protist species documented on the debris, which crossed the Pacific Ocean following Japan’s destructive 2011 tsunami, researchers analyzed in detail 237 species, which include larger invertebrates and two fish. The critters represent 15 taxonomic groups, as defined by the scientists in the Sept. 29 issue of Science. (Each box below signifies a living species; colors are different groups.)

Most of the species were mollusks, including marine snails, nudibranchs and oysters. Mollusks were followed by annelids (segmented worms), cnidarians (including sea anemones), bryozoans (moss animals that sometimes resemble coral), crustaceans and others. Some species, such as sea anemones and limpets, were able to reproduce and maintain multiple generations on these debris “islands.”

The unprecedented marine migration was possible because much of the rubbish caught up in the Pacific currents  was durable, made of plastic or fiberglass. “Years ago there were other natural disasters that potentially produced debris, but the debris was, well, organic,” says Nir Barnea, the regional coordinator for the National Oceanic and Atmospheric Administration’s marine debris program in Washington and Oregon. “Now we have plastic materials, man-made materials that remain in the marine environment for many years.”

These Pacific Ocean currents sent Japanese tsunami debris carrying a wide variety of marine critters to North American shores. E. Otwell, C. Chang

About two-thirds of the animal species (solid colors below) had never been documented along North America’s Pacific coast, while the others (crosshatched below) occur naturally or were previously introduced. If established, alien species may threaten native marine habitats, but it could take years to detect such effects.

Despite intense efforts, the researchers know they didn’t record all of the species arrivals. “We assume that there are a good deal more species that arrived that we simply never saw,” says study coauthor James Carlton, a marine scientist at Williams College in Mystic, Conn. “Just imagine the thousands, or maybe tens of thousands, of objects that landed in North America and Hawaii with living Japanese species.”

More Stories from Science News on Oceans