Plastic rafting: the invasive species hitchhiking on ocean waste | Oceans
The 2011 tsunami in Japan was catastrophic, killing nearly 16,000 people, destroying homes and infrastructure, and sweeping across a estimated at 5 million tonnes of debris at the sea.
However, this debris did not disappear. Some drifted across the Pacific, reaching the coasts of Hawaii, Alaska and California – and with it, hitchhikers.
Almost 300 different non-native species crossed the ocean in what can be considered a “mass rafting” event. The Smithsonian Environmental Research Center in 2017 counted 289 Japanese marine species that were transported to distant shores after the tsunami, including sea snails, sea anemones and isopods, a type of crustacean.
Plastic rafting is a huge and mostly unknown danger. Invasive species that carry plastic waste to new shores can reduce the habitats of native species, be carriers of disease (microalgae are a particular threat) and puts additional pressure on ecosystems already strained by overfishing and pollution. According to David Barnes, marine benthic ecologist with the British Antarctic Survey and guest lecturer at the University of Cambridge, rafting increases the “risk of extinction. [while] reduce the biodiversity, function and resilience of ecosystems ”.
The tsunami also showed something new: Many animals survived adrift for more than six years, longer than previously thought.
Rafting – or ocean dispersal – is a natural phenomenon. Marine organisms attach themselves to marine litter and travel hundreds of kilometers. Tufts of floating algae such as Sargassum, sometimes 3 meters thick, shelter certain “rafting species” in the Atlantic, such as reef fish, or pipefish and seahorses, both of which are bad swimmers.
Prof. Bella Galil, curator at the Steinhardt Museum of Natural History, Tel Aviv University, said: “Transoceanic rafting is a fundamental feature of evolutionary marine biogeography and ecology, often cited to explain the origins of marine life. global patterns of species distribution.
But while it is relatively rare for a non-native species to survive in a new environment, she says, the huge increase in litter dumped at sea, as well as abandoned fishing gear, allows biological fouling: aquatic organisms attaching themselves where they are not wanted.
It turns “a rare and sporadic evolutionary process into an everyday process,” she says. Invasive species can threaten biodiversity, food security and human well-being. Sea grapes from Australia that arrived in the Mediterranean in 1990, for example, displaced other marine algae, causing a domino effect that ultimately led to a reduction in native gastropods and crustaceans.
One of the most powerful corridors for marine invasions is from the Red Sea, via the Suez Canal, into the Mediterranean. Galil notes that of 455 alien marine species currently recorded in the eastern Mediterranean, most are believed to have passed through the canal, either through the mainstream northward or via ballast water, by hitchhiking. mainly on plastics.
These invasive species don’t just hang around. Many have spread to the central and western Mediterranean, again often colonizing floating litter. In addition to negatively affecting critical habitats, says Galil, some are “harmful, poisonous or poisonous and pose a clear threat to human health.” Long-spined sea urchins and nomadic jellyfish, both poisonous and both native to the Indian Ocean, are just two examples that are now wreaking havoc in the Mediterranean.
The route is likely to become even more popular after the widening of the canal, Egypt’s response to the container ship Ever Given grounding earlier this year. “Bigger canal, bigger ships [will mean] probably a greater volume of species from the Red Sea arriving in the Mediterranean, ”explains Galil.
Plastic rafting is far from being limited to the Mediterranean. There was one hundredfold increase in marine plastics over the past two decades, what Barnes calls an “ecosystem changer”.
“Plastic, in particular, has dramatically increased the possibilities for transportation in terms of the amount of wreckage, variety (size and structure), where it goes and how long it floats,” he says. “In addition, plastic can increase the local spread of invasive species when they arrive and become established.” A compilation of 2015 listed 387 species, from microorganisms to algae and invertebrates, found themselves rafted on marine litter, in “all the great ocean regions”.
Barnes even found invaders of plastic rafts in the Southern Ocean, refuting the idea that the freezing temperatures of Antarctica would keep them at bay. Antarctica can be particularly susceptible to such invasions, as its endemic species have evolved in near isolation and under a very narrow range of environmental conditions. “Any species lost here is a loss of global biodiversity: they only live around Antarctica, and blue carbon [CO2 held in oceans] they store provides some powerful retorts against climate change, ”he says – blue carbon refers to carbon held by ocean life, such as kelp and coral polyps.
With the ocean’s surface now strewn with plastic, there is no limit to where it can travel, taking invaders with it. Tens of thousands of species can migrate from “anywhere to anywhere, for times ranging from days to decades,” says Barnes.
One of the main interchanges in this network of maritime highways is the North Pacific Gyre, home to the Great Pacific Garbage Patch, the largest concentration of plastic in our oceans. Here, currents and marine debris converge, and the currents then disperse the waste to the most remote corners of the planet. Likewise, the South Pacific Gyre is believed to be responsible for the waste (mostly plastic) on the beaches of Rapa Nui (Easter Island).
According to a 2018 study in Marine Pollution Bulletin by researchers at the Spanish University of Oviedo, 34% of the debris examined on Easter Island carried organisms from elsewhere. These included water surveyors, a stony coral called Pocillopora and Major aircraft, a species of crab. Another study by the same authors found plastic rafting along about 120 miles (200 km) of coastline on the Bay of Biscay, with plastic fishing, hobby, and household items carrying non-native invasive species such as the giant pacific oyster and the Australian goose.
Some of the world’s most precious environments could be at risk, including the Galapagos Islands. With a plastic crisis so bad that 400 plastic particles were found per square meter on the most affected beaches of the islands, and some of this plastic already known to harbor non-native species, it’s not hard to imagine an invasive species soon threatening the famous unique fauna of the islands. Other remote islands such as Saint Helena, Ascension and Tristan da Cunha are also “very vulnerable to invasion”, reported Barnes, due to “little sea traffic and endemic species intact”.
In 2018, Barnes went further, describing marine plastic as an ecosystem in its own right, with the only winners being colonizing wildlife, which he called the “plastisphere”.
So what can be done about the plastisphere and who is responsible? In the context of the Suez Canal, Galil says: “If we adhere to the ‘polluter pays’ principle, Europe is complicit – the canal mainly serves Europe. But she also calls for an immediate reduction in the amount of plastics in the environment – and “until then, a strictly enforced ban on discharges into the oceans.”
Tracking technology can also help, such as Integrated marine debris observation system (IMDOS), a proposed – but not yet implemented – system that would combine satellite imagery, trawl surveys, vessel observations and data submitted to various organizations to track marine litter.
Another effort to standardize marine plastic monitoring is Floating ocean ecosystems (FloatEco), a multidisciplinary project, partly funded by NASA, to “better understand the dynamics of floating plastics in open ocean environments”. And there are organizations such as Ospar, which brings together 15 governments and the European Union to cooperate in protecting the environment of the northeast Atlantic Ocean.
“A global problem like marine plastic litter, and all the challenges it creates, is impossible to solve without collaboration,” says Eva Blidberg, former project manager for blastic, a recent EU initiative to map and monitor marine plastics in the Baltic Sea.
But with the pandemic leading to an estimate 1.6 million tonnes of single-use PPE thrown away daily, some of which end up in the ocean, the problem only gets worse. When Barnes first reported the threat of plastic rafting in 2002, he struggled to convince people it was a cause for concern. “Now society is so in the spotlight in a blizzard of climate and biodiversity issues that it’s still hard to convince people that it’s worth worrying about,” he says.
Since organisms cannot be stopped from doing what they want, the only real way to repel invaders from rafts is to take their rafts away from them. Monitoring and collaboration are important, says Blidberg, but she adds, “The most important thing is to plug in the marine debris valve. “