When the Tohoku earthquake occurred in Japan in 2011, immediate consequences included almost 16,000 deaths in the subsequent tsunami and the damage to the Fukushima nuclear power plants. A less obvious effect, but one we could be living with for a very long time, was the astonishing numbers of animals that were swept across the Pacific.
Scientists documenting cases of marine creatures that surfed thousands of kilometers on the tsunami's powerful waves have found 289 species, and almost certainly missed more. The number is completely unprecedented, thankfully because events like this are rare. However, humans have also been making it easier.
We know that species from spiders to monkeys have crossed vast oceans in the past, probably on mats of branches and mud. Such journeys are not quick, however, and most natural materials will degrade in the ocean environment on the way. Only a tiny proportion of those creatures ever make it to another continent. Unfortunately, plastic is much more robust, and anything that gets a lift on a non-degradable floating object in this way has a much better chance of making the distance.
Not all the animals who reached Hawaii or the west coast of America was swept the whole way in a single movement. At the mercy of currents, some turned up as many as six years later. It was expected that shore-dwelling creatures would have died over such a long period in the open ocean, but the authors of a paper in Science report this was not the case. Since previous rafting journeys have usually been limited to periods of two years, the finding marks a dramatic expansion of what is possible.
So far the authors have not found evidence of any Japanese species establishing itself in the Americas, post-tsunami. However, there are fears some could make a new home, potentially pushing out indigenous species.
“One thing this event has taught us is that some of these organisms can be extraordinarily resilient," Professor James Carlton of Williams College said in a statement. "When we first saw species from Japan arriving in Oregon, we were shocked. We never thought they could live that long, under such harsh conditions. It would not surprise me if there were species from Japan that are out there living along the Oregon coast. In fact, it would surprise me if there weren't."
Twenty percent of the ocean-crossing species identified in the study were capable of reproducing afterward. Moreover, it may not just be tsunamis that facilitate such ocean voyages. Hurricanes can also sweep lots of plastic out to sea, and we seem to be having a few of those.
We can't stop the natural disasters, but we can certainly do something about the rafts. “More than 10 million tons of plastic waste from nearly 200 countries can enter the ocean every year – an amount predicted to increase by an order of magnitude by 2025,” Carlton said.