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.

Plastic waste across the world: in pictures Show all 15 1 /15 Plastic waste across the world: in pictures Plastic waste across the world: in pictures A father and son on a makeshift boat made from styrofoam paddle through a garbage filled river as they collect plastic bottles that they can sell in junkshops in Manila. The father and son team earn some three US dollars a day retrieving recyclables from the river. AFP/Getty Plastic waste across the world: in pictures A composite image of items found on the shore of the Thames Estuary in Rainham, Kent. Tons of plastic and other waste lines areas along the Thames Estuary shoreline, an important feeding ground for wading birds and other marine wildlife. Getty Images Plastic waste across the world: in pictures Children collect plastic water bottles among the garbage washed ashore at the Manila Bay. According to the United Nations Environment Programme, at current rates of pollution, there will likely be more plastic in the sea than fish by 2050. AFP/Getty Plastic waste across the world: in pictures Plastics and other detritus line the shore of the Thames Estuary. In December 2017 Britain joined the other 193 UN countries and signed up to a resolution to help eliminate marine litter and microplastics in the sea. It is estimated that about eight million metric tons of plastic find their way into the world's oceans every year. Once in the Ocean plastic can take hundreds of years to degrade, all the while breaking down into smaller and smaller 'microplastics,' which can be consumed by marine animals, and find their way into the human food chain. Getty Plastic waste across the world: in pictures A dump site in Manila in 2013. The Philippines financial capital banned disposable plastic shopping bags and styrofoam food containers, as part of escalating efforts across the nation's capital to curb rubbish that exacerbates deadly flooding. AFP/Getty Images Plastic waste across the world: in pictures Children swims in the sea full of garbage in North Jakarta, Indonesia. Getty Plastic waste across the world: in pictures An Indian woman holds a jar filled with Yamuna river water polluted with froth and toxic foam to be used for rituals at the river bank in New Delhi, India. The Yamuna River, like all other holy rivers in India, has been massively polluted for decades now. The river that originates in a glacier in the pristine and unpolluted Himalayas, and flows through Haryana, Delhi and Uttar Pradesh before merging with the Ganges River in Allahabad, once used to be the lifeline of the Indian capital. Currently, it is no more than a large, open sewer that is choking with industrial and domestic discharge that includes plastic, flowers and debris and has virtually no aquatic life. EPA Plastic waste across the world: in pictures Plastic waste is washed up on South Troon beach in Scotland. Recent reports by scientists have confirmed, plastics dumped in the world oceans are reaching a dangerous level with micro plastic particles now being found inside filter feeding animals and amongst sand grains on our beaches. Getty Plastic waste across the world: in pictures Children collect plastic to be sold and recycled, in a polluted river in suburban Manila. The city's trash disposal agency traps solid waste floating down waterways that was thrown into the water by residents of slums along riverbanks upstream. AFP/Getty Plastic waste across the world: in pictures View of the Carpayo Beach in La Punta, Callao, some 15 km of Lima. In 2013, the NGO VIDA labeled the Carpayo Beach as the most polluted in the country - 40 tons of trash on each 500m2. AFP/Getty Plastic waste across the world: in pictures Trash from Kamilo Beach in Hawaii. Gabriella Levine/Flickr Plastic waste across the world: in pictures A scavenger collects plastic cups for recycling in a river covered with rubbish near Pluit dam in Jakarta. Reuters Plastic waste across the world: in pictures Rubbish fills Omoa beach in Honduras. Floating masses of garbage offshore from some of the Caribbean's pristine beaches are testimony to a vast and growing problem of plastic pollution heedlessly dumped in our oceans, locals, activists and experts say. AFP/Getty Plastic waste across the world: in pictures A man climbs down to a garbage filled river in Manila. Plastic rubbish will outweigh fish in the oceans by 2050 unless the world takes drastic action to recycle the material, a report warned in 2016. AFP/Getty Plastic waste across the world: in pictures Garbage on East Beach, Henderson Island (Pitcairn Islands), in the south Pacific Ocean. The uninhabited island has been found to have the world's highest density of waste plastic, with more than 3,500 additional pieces of litter washing ashore daily at just one of its beaches. EPA

“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.

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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.

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