Plastic bringing waves of alien crabs and fish to shores around the world, scientists warn

Hundreds of alien species are being carried around the world on a tide of ocean plastic, posing a significant threat to native wildlife.

Crabs, clams and even large fish are among the creatures hitching a ride on top of or inside plastic vessels, crossing vast stretches of ocean.

Considering the harm foreign species can cause when introduced to new environments, scientists are concerned this quiet invasion is a disaster waiting to happen.

For Professor Jim Carlton, alarm bells began to ring as he investigated the sheer number of species that had arrived on American shores from Japan after a massive tsunami struck in 2011.

So far he has found nearly 400 Japanese creatures inhabiting the shorelines of Hawaii and mainland US after travelling thousands of miles across the sea, but he said on a global scale this is a drop in the ocean.

“I think it’s a globally vastly underestimated phenomenon,” said Professor Carlton, who is based at Williams College.

“It’s a sad situation. We have marine debris washing ashore in the Arctic, the Antarctic, and everywhere in between.”

After the tsunami, millions of plastic items were flushed into the oceans after waves engulfed coastal towns.

Ever since, Professor Carlton and his collaborators have discovered many recognisably Japanese items washed up on American shores, together with their living cargo.

Creatures like mussels and anemones had made the journey attached to the plastic, while some free-swimming animals had been caught inside vessels and released on arrival.

Many of these new arrivals have already proved problematic, bringing disease or wiping out local species in their new habitats.

One of the largest fish known to have been transported from Asia was a barred kninfejaw, which scientists have watched thrive since it was spotted in 2014 off the coast of San Francisco.

“The ecological roulette is that of these 400 species some are finding a perfect temperature match in the Pacific Northwest, or on the west coast in general, and while they have no previous invasion history, could – if they become established – easily become serious pests or nuisances,” said Professor Carlton.

The marine ecologist presented his work at the American Association for the Advancement of Science (AAAS) annual meeting in Washington DC, and said a growing body of research was throwing up misplaced species in strange parts of the world.

Last year scientists warned that British overseas territories like the island of St Helena were facing a barrage of plastic waste and its living cargo.

While creatures have always been transported between continents on rafts made of biological material like wood, these natural rafts have a limited lifespan.

Plastic, on the other hand, takes hundreds of years to decompose, meaning it can transport seafaring creatures incredibly long distances.

There is also the concern that as climate change warms up the world’s oceans, regions will become colonised by creatures that could never previously have thrived there.