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Mysterious marine ecosystem threatened by plastic cleanup

Ute Eberle
August 14, 2020

Little is known about the neuston, but marine biologists fear this community of organisms living on the ocean surface could be decimated as nets sweep up plastic pollution.

A blue and yellow creature floating on the surface of the water
Image: Betti Federico

In May 2017, shells started washing up along the Ligurian coast in Italy. They were small and purple and belonged to a snail called Janthina pallida that is rarely seen on land. But the snails kept coming — so many that entire stretches of the beach turned pastel. 

An unusual wind pattern had beached the animals. And for the people who walked the shore, this offered a rare encounter with a wondrous ecosystem that most of us have never heard about: The neuston. 

The neuston, from the Greek word for swimming, refers to a group of animals, plants and microorganisms that spend all or large parts of their life floating in the top few centimeters of the ocean. 

It's a mysterious world that even experts still know little about. But recently, it has been the source of tensions between a project trying to clean up the sea by skimming plastic trash off its surface, and marine biologists who say this could destroy the neuston.

Snails on a beach
The Ligurian coast has been swept by snails turning its colour pastelImage: Betti Federico

A world between worlds 

The neuston comprises a multitude of weird and wonderful creatures. 

Many, like the Portuguese man-of-war, which paralyzes its prey with venomous tentacles up to 30 meters long, are colored an electric shade of blue, possibly to protect themselves against the sun's UV rays, or as camouflages against predators.

There are also by-the-wind sailors, flattish creatures that raise chitin shields from the water like sails; slugs known as sea dragons that cling to the water's surface from below with webbed appendages; barnacles that build bubble rafts as big as dinner plates; and the world's only marine insects, a relation of the pond skater.

They live "between the worlds" of the sea and sky, as Federico Betti, a marine biologist at the University of Genoa, puts it. From below, predators lurk. From above, the sun burns. Winds and waves toss them about. Depending on the weather, their environment may be warm or cool, salty or less so.

A jellyfish
Velella velella jellyfish living on the surface of the oceanImage: Betti Federico
A sea snail
Sea snails can make up the neustonImage: Betti Federico

But now, they face another — manmade — threat from nets designed to catch trash. A project called The Ocean Cleanup, run by Dutch inventor Boyan Slat, has raised millions of dollars in donations and sponsorship to deploy long barriers with nets that will drift across the ocean in open loops to sweep up floating garbage. 

Read moreTime to clean up the ocean garbage dump

Plastic and marine life are moved by currents

"Plastic could outweigh fish in the oceans by 2050. To us, that future is unacceptable," The Ocean Cleanup declares on its website.

But Rebecca Helm, a marine biologist at the University of North Carolina Asheville, and one of the few scientists to study this ecosystem, fears that The Ocean Cleanup's proposal to remove 90% of the plastic trash from the water could also virtually wipe out the neuston. 

Read more: Dutch inventor unveils river barge to scoop plastic before it enters oceans

One focus of Helm's studies is where these organisms congregate. "There are places that are very, very concentrated and areas of little concentration, and we're trying to figure out why," says Helm. 

One factor is that the neuston floats with ocean currents, and Helm worries that it might collect in the exact same spots as marine plastic pollution. "Our initial data show that regions with high concentrations of plastic are also regions with high concentrations of life."

An Ocean Cleanup vessel at work
Image: The Ocean Cleanup
Garbage in the ocean
Waste collection in the Pacific Ocean heralded by The Ocean CleanupImage: picture-alliance/abaca/ The Ocean Cleanup

The Ocean Cleanup says Helm's concerns are based on "misguided assumptions."

"It's true that neustonic organisms will be trapped in the barriers," says Gerhard Herndl, professor of Aquatic Biology at the University of Vienna and one of project's scientific advisors. "But these organisms have dangerous lives. They're adapted to high losses because they get washed ashore in storms and they have high reproductive rates. If they didn't, they'd already be extinct."

Helm says they just don't know how quickly these creatures reproduce, and in any case recovering from passing storm is very different from surviving The Ocean Clean Up's systems which could be in place for years.

Still a lot to learn about the neuston

In December, The Ocean Cleanup and Helm participated in a symposium on the topic hosted by the Institute for Risk and Uncertainty at the University of Liverpool in the UK. Since then, direct communication between them has stopped, says Helm. "They're not interested in talking to me anymore."  

Both sides agree that much is still unknown about the neuston. But one thing that has been established is that most of the oceans' fish spend part of their lifecycle in the neuston. "More than 90% of marine fish species produce floating eggs that persist on the surface until hatching," Betti says.

The Ocean Cleanup has undertaken one of the few studies into this ecosystem, collecting data on the neuston on the relative abundance of neuston and floating plastic debris in the eastern North Pacific Ocean during a 2019 expedition to the Pacific Garbage Patch, an area where plastic pollution has accumulated on a vast scale. But it is not yet sharing what it has found. The information was being prepared for publication in an as of yet unspecified journal, probably some time next year, an Ocean Cleanup spokesperson said.   

Is the solution inshore? 

Helm believes the best way to tackle the marine plastic problem would be to position the barriers closer to land — across river mouths and bays — to catch garbage before it reaches the sea. 

Read more: Plastic waste and its environmental impact

"Stopping the flow of plastic into the ocean is the most cost-effective — and literally effective — way to ensure that it's not entering our environment," she says. 

As for the plastic already floating in open waters, she does not believe it is worth sacrificing parts of neuston and wants to see more research first. 

The Ocean Cleanup has made barriers across rivers a part of its mission. But it is also going ahead with its original vision of pulling trash from the open water. In late 2018, the project deployed a 600-meter, u-shaped prototype net into the Great Pacific Garbage Patch

The system ran into difficulties, failing to retain plastic as hoped, and needing to be brought shore for repairs and a design upgrade, after which Ocean Cleanup says it gathered haul of plastic that it will recycle and resell to help fund future operations.

Over the next two years, the project hopes to deploy up to 60 such barriers to collect drifting flotsam. Helm isn't the only one concerned about these plans.

"We should think twice about every action we take in the sea," Betti says. "In nature, nothing is as easy as we think, and often, we've done a lot of damage while trying to do a good thing."

This article has been updated. In an earlier version, the University of North Carolina Asheville was named incorrectly. Helm was not invited by The Ocean Cleanup to attend the symposium at the University of Liverpool as previously stated.