29 Sep 2017

Animals make six-year debris-surfing voyage - study

5:09 pm on 29 September 2017

American researchers say in the six years since a massive tsunami struck Japan, at least 289 species of animals have travelled to the United States on rafts of rubbish.

The uninhabited Henderson Island in the South Pacific

Photo: Jennifer Lavers

Thousands of non-native marine crustaceans, fish, molluscs and anemones continue to land on the American west coast on rafts of plastic, fibreglass and other debris that was washed out to sea in 2011.

According to a paper describing the phenomenon, published today in the journal Science, as many as 65 percent of the species are not native to US waters.

Scientists said the phenomenon, which had "no known historical precedent", was still unfolding.

Study co-author Professor Jim Carlton from Williams College in Massachusetts feared if any were able to colonise, there could be devastating consequences.

"The immediate concerns are the potential economic and environmental impacts of any given invasion, like the North Pacific sea star in Australia," he said.

Objects ranging from barges and fishing vessels to plastic bags and buoys were washed out to sea in a "massive debris field" during the 2011 tsunami.

This deluge of flotsam was then sucked into the Pacific trash vortex - a gyre of circulating marine rubbish that brushes the coast of Japan and circulates clockwise around the North Pacific Ocean.

Each spring, as offshore currents pushing off the US coast ease, "spring pulses" of trash wash ashore on the US west coast.

The scientists said it was unclear yet whether any animals arriving on the rafts had been able to successfully colonise.

"We are in the establishment window. The lag time between their arriving and becoming established and detected can be a while," Professor Carlton said.

Upheaval to species dispersal

What has scientists really amazed is the length of time these animals have been able to survive in the open ocean, which they put down to the longevity of the plastic and fibreglass that make up much of the debris.

"Six years at sea [is] four or more years longer than previous documented instances of the survival of coastal species rafting in the ocean," the paper states.

The paper's authors make the case that massive coastal development and climate change are converging to completely reshape the way species are dispersed around the globe.

"If we advance the climate change models that argue that hurricanes and typhoons and other storms will be increasing in frequency and size, then we enter an era in the 21st century where larger and more frequent storms are for the first time interfacing with the densest populations and infrastructure that we've ever had on [our] coastlines," Professor Carlton said.

Professor Steven Chown from Monash University said the research would "change our view of the world".

"Their research is amazing in actually documenting this pulse event, and then demonstrating that we might have to expect more such large-scale events given the huge increase in infrastructure globally along with, of course, increasingly extreme weather events," he said.

"That's what changes the game for me."

Rafting creates 'extremely difficult' biosecurity challenge

Professor Chown - whose research interests include Antarctica, biological invasions and climate change - said it was not a matter of if, but when, these invading species would establish.

He warned the challenges to biosecurity were enormous.

"We know from the ecology of marine invasions that some will [establish], and they'll be hard to detect in the beginning," he said.

"If you think about surveillance operating through borders, checking of cargo detects quite a lot of stuff. But actually doing surveillance along a whole coastline for potential species which could have huge impacts is extremely difficult."

In the US, researchers have enlisted the help of citizen scientists to report and check debris from Japan that washes up on the coast.

Although the amount of material arriving has been declining, they say they are expecting another spring pulse next year.

And while the reduction in pollution washing up in the US is welcome news, scientists fear any species strong enough to survive seven or more years at sea may well have the characteristics of a successful invader.


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