The Harmful Side Effect of Cleaning Up the Ocean

In the northern Pacific Ocean, two sky-blue ships are sailing parallel to one another, several hundred meters apart. Pulled behind them is a giant U-shaped barrier, which almost looks like a fishing net. You could be forgiven for thinking they are trawlers. But they’re aiming to catch something else: plastic.

The Ocean Cleanup (TOC) is the world’s largest organization working to remove floating plastic from the ocean. Since 2021, the nonprofit has recovered 200 tons of plastic in the Great Pacific Garbage Patch, an area between California and Hawaii that is notorious for its floating waste, which is concentrated there by ocean currents. In this area, which is roughly three times the size of France, at least 400 times the amount of plastic extracted by TOC remains, to which more is added every day as it is discarded from boats or flows into the sea from rivers.

To Boyan Slat, the founder of TOC, this cleanup work “signifies an age in which we’re starting to correct the problems we ourselves have created.” To TOC’s critics, the project is costly and inefficient—a distraction from the root of the problem, which is too much plastic being discarded and not enough preventing it from getting into the sea. But more recently, new charges have been laid at the door of TOC: that its cleanup efforts are capturing not only plastic but also sea creatures that live among it. That they are, essentially, disrupting a marine habitat.

According to a new study, floating marine life, known as “neuston,” often ends up in the same places as plastic. It’s not that the plastic is somehow creating an opportunity for life to emerge, says marine biologist and corresponding author Rebecca Helm, but rather that plastic debris and organisms tend to float up and clump together in water, like cereal in a bowl. Add to this wind and swirling ocean currents, which bring plastic and neuston in from afar, and “patches” form.

Back in 2019, a rare occurrence allowed Helm, who is an assistant professor at Georgetown University in Washington, DC, to study the contents of the Great Pacific Garbage Patch. A sailing crew accompanied long-distance swimmer Benoît Lecomte as he swam right through the patch. Behind them they towed a small net along the surface of the water every day to take samples of floating marine life and plastic debris. They did the same in the periphery and outside the patch for comparison. They then photographed 22 of these samples.

Working with colleagues at the University of Hull in the UK, Helm then set about analyzing them, using image-processing software to flag different kinds of neustonic species and plastic debris in the photos. The team found that concentrations of both plastic and neuston were higher inside the patch than outside. Jellyfish-like species known as by-the-wind sailors and blue buttons were particularly visible. So too were violet snails.

It was far from a perfect method. Twenty-two photos is not a lot, and an examination of the actual samples rather than pictures of them would have been more rigorous. Plus, using “surface tows” to sample the ocean’s contents “is an imperfect art,” says Helm. Sometimes the net bounces above the waves, other times it goes below, missing some water and the plastic and organisms floating in it. But, she adds, it’s pretty clear from the photos that there’s a lot of neuston present in the garbage patch.

Helm has not shied away from publicly criticizing TOC, pointing out that the nets it uses to collect plastic could inadvertently trap neuston. Many species are not capable of swimming. By-the-wind sailors, for example, have a small stiff sail that sticks out of the water to catch the wind, while blue buttons and violet snails rely on currents to drift through the ocean. They are small creatures, but so are the meshes in the nets. And if neustonic species were killed in large numbers, it could have an impact on the turtles, fish, seabirds, and other animals that eat them.

TOC says it is well aware of the potential harm to marine life and that it has adapted the design of its plastic-catcher in recent years. The U-shaped barrier that guides the plastic into a retention zone at its far end has a net that is 3 meters deep below the surface, and it moves slowly through the water to allow mobile species to swim away. There are lights and acoustic deterrents, underwater cameras to detect protected species such as sea turtles, and escape hatches on the underside of the nets for animals that get caught. Before hoisting the nets aboard, the crew leaves them in the water for up to an hour to give animals time to escape. Nonetheless, fish, small sharks, mollusks, and sea turtles have been caught accidentally, although they make up a tiny fraction of the catch weight compared to plastic, TOC says.

In addition to collecting plastic, TOC conducts its own ocean research, as well as environmental impact assessments that determine and describe the potential damage of the cleanups. But as a private player operating in international waters where few rules apply, TOC is not required to publish these. “We do much more than just clean, which is difficult enough. We also actively contribute to the understanding of an ecosystem that we barely know,” says Matthias Egger, whose role is to conduct research that helps TOC engineers further develop and scale up its cleanup system. In recent years, neuston have become a particular focus.

Egger and his team have been sampling the surface water in front of and behind the cleanup system on a weekly basis to compare the composition of neuston, to understand which species to look out for, what effect the cleanup system has, and whether there are seasonal differences in how many neuston are present. The data is currently being evaluated and is due to be published this year. “But for the initial results, we are really happy to see very little impact,” says Egger.

Egger stresses that TOC wants to make sure its plastic-cleaning efforts are helping marine life, not harming it. But it’s more complicated than simply trying to minimize the amount of marine life taken out of the ocean along with plastic, he says. If crustaceans or sea anemones from other regions cling to plastic debris and hitch a ride to the middle of the Pacific Ocean, they could feed on neuston there. Is it then right or wrong to remove these invaders, who may be disrupting the local ecosystem? “There is always marine life associated with the plastic,” says Egger. “But very often, it’s marine life that does not belong there, because the plastic does not belong there.”

A study published in mid-April offers some clues as to which traveling species could pose a problem. Researchers at the Smithsonian Environmental Research Center examined 105 pieces of plastic debris they had obtained in frozen form from TOC. They found traces of species normally found in coastal waters that had used floating plastic as rafts and ended up in the Great Pacific Garbage Patch—in particular nets, ropes, buoys, boxes, and cylindrical eel traps from the fishing industry. Some species also appeared to reproduce in their new offshore home. For example, some shrimp-like amphipods were carrying eggs in their brood pouches.

This isn’t surprising, says Martin Thiel, a professor of marine biology at the Catholic University of the North in Chile. Marine organisms have been found colonizing all sorts of floating materials in the ocean, including volcanic pumice, seaweeds, and wood, at least until these items start to degrade and sink. Whether it’s organisms that settle on more durable plastic debris or that float at the surface next to it, Thiel says that they can’t simply be separated from plastic. “What’s out there, we better leave it in peace, because by removing it, we may do more harm,” he says.

Lanna Cheng, research scientist emeritus at the Scripps Institution of Oceanography at the University of California, San Diego, is somewhat less concerned. Sometimes neuston are floating among plastic, sometimes not. Some neuston are able to swim up and down. And storms can come along and mix things up. Because neuston aggregations appear to be so patchy, accidental catches would likely not significantly affect their populations, she says. And because TOC invests so much time and resources in offshore trips, she welcomes the organization’s contribution to science by offering marine biologists like her opportunities to collect samples. “The surface community [of marine life] is a community that was hardly studied until plastic pollution became a problem. Part of the reason was that there was very little economic value,” she says. Cheng herself has spent her career studying insects that have evolved to literally walk on the open ocean and survive.

Helm, however, remains critical, in part because she believes that studies should first show that there is no impact on neuston, before cleanups are carried out. “If they really do the work and demonstrate that their efforts have no impact on ocean surface life, then I will be excited to see that they took the criticism and made changes,” she says. One change crucial to neustonic species was made recently. In May 2023, TOC more than doubled the length of its net barrier, which now extends to 1,750 meters. As part of the upgrade, the mesh size of the nets in the retention zone, where plastic is held before being hoisted onto the ships, has been increased from 10 to 50 millimeters square. This should allow very small creatures like blue buttons and violet snails to pass through the nets, but by-the-wind sailors, for example, can grow larger than this. However, increase the mesh size any more than this, and pieces of debris could start to seep through.

The two sky-blue ships are currently cruising across the Great Pacific Garbage Patch again, testing the updated barrier in the hope that they can collect more plastic per trip. Ridding the open ocean of plastic remains a Sisyphean task. As more plastic enters the patch, and scientists learn more about the creatures living there, TOC still has many obstacles to overcome before it can scale up its operations. “Our purpose is to help those organisms out there, but you need to make sure that the way you help is actually helping them,” says Egger. “And that’s what we’re trying to figure out.”

Updated 5-11-2023 10:30 am BST: Lanna Cheng’s affiliation was clarified.