The Constellation of Creatures Inhabiting the Ocean Surface

ABOVE: © istock.com, Vaara

The open ocean and the far reaches of outer space have much in common. Stretching in their enormity from horizon to horizon, these unknowable expanses are ruled by such extreme forces that the existence of life is generally the exception rather than the rule. And yet, just as stars lie scattered across the night sky, coalescing in nebulas or falling headlong into the inescapable maw of black holes, entire ecosystems populate the sea surface, as numerous and mystifying as their celestial counterparts.

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On a foggy morning in 2007, Rebecca Helm was strolling along California’s Monterey Bay, “picking up plastic like you do when you are in love with the ocean and want to protect it,” she recalls. Among the wilting seaweed and broken shells, she saw what looked like a translucent bit of trash, and she picked it up to discard. But it turned out not to be plastic at all. Instead, it was the brittle skeleton of an animal that had washed ashore after a life spent at sea.

Helm, then a fledgling marine biologist about to begin her PhD research, recognized the organism as a by-the-wind sailor (Velella vellela), a jellyfish-like creature with a rigid sail to ferry it about the ocean surface. In that moment, she says, she suddenly understood why animals such as turtles that eat these creatures end up ingesting so much plastic—the small invertebrate mimicked its appearance and texture almost identically. And as she’d soon learn, such seagoing invertebrates often end up in the same locales as plastic, subject to many of the same forces—including wind, waves, and currents—that concentrate trash in specific areas of the ocean.

Like the 11 million metric tons of plastic that enter the ocean each year, neuston accumulate in the oceans’ “garbage patches.”

By-the-wind sailors belong to a group of enigmatic animals and other organisms called neuston that live permanently at the surface of the ocean. Their inaccessibility far out at sea means that scientists have only sporadically studied them over the last century, with only a small handful of PubMed-listed papers mentioning neuston prior to 2007, and just over 100 since. Currently, there are about 20 known species of neuston, including palm-sized crustaceans, cnidarians, snails, sea slugs, and even an insect, as well as a large protist (the floating seaweed Sargassum). Like the 11 million metric tons of plastic that enter the ocean each year, neuston accumulate in the oceans’ “garbage patches”—regions formed by large ocean currents known as gyres (see illustration on page 12) where efforts to clean up plastic pollution have focused. As Helm and others uncover more about the understudied sea surface communities that flourish in these environments—and the ecosystem services they provide—some are questioning whether those well-intentioned projects actually risk doing more damage than good.

         

“I don’t think anyone trying to pull plastic out of the ocean is also trying to kill neuston,” Helm tells The Scientist. But she describes what she sees as a reticence by certain cleanup initiatives to confront the pitfalls of their technologies when it comes to environmental impact. “I’ve noticed this absence in discussion about what would happen to [surface] ecosystems. And so I really want to insert the animals that live out there back into the broader conversation.”

Meet the neuston

In the fall of 2018, Helm, then at the University of North Carolina, Asheville, was scrolling on Twitter when she paused on a post by The Ocean Cleanup, she recalls. The company had been founded five years earlier by a high school student aiming to address plastic pollution, and while its approach has changed over the years—from a platform powered by renewables to its current iteration, two vessels that trawl the surface with a U-shaped net—the vision has remained largely the same: to recover 90 percent of the plastic in the ocean by 2040.

When she saw the tweet, Helm says, she immediately thought of neuston, which she could clearly see in some of the images of buoyed nets shared by the group. She delved into the literature looking for research on how the project might affect marine surface ecosystems. Other than a systematic characterization of surface-living species in the Pacific by a team of Russian scientists in the 1950s and 1960s, surprisingly little was known about neuston at all. Soon, she began studying the organisms herself, publishing papers and penning academic essays and articles to highlight their unacknowledged importance and call attention to the potential harm that The Ocean Cleanup could cause them. Her public support of neuston attracted collaborators interested in studying the creatures and their relationship to plastic.

We go out there on a regular basis, so we can finally get the data . . . and help fill this knowledge gap, together with other scientists, on ecosystems that we barely know.

—Matthias Egger, The Ocean Cleanup

One such scientist was Drew McWhirter, the lead scientist on a 2019 initiative called the Vortex Expedition that followed long-distance swimmer Ben Lecomte as he traversed the Pacific Ocean to draw attention to pollution. For 80 days, McWhirter lived aboard a 67-foot vessel called Discoverer, supporting Lecomte’s swim and carrying out daily net tows to sample microplastics and neuston within the Great Pacific Garbage Patch (GPGP), while Helm, back on shore, used imaging software to flag animals in the photographs.

The results, published as a preprint last year, show that while animals are ubiquitous throughout the GPGP, neither plastic nor neuston are distributed homogeneously. There is no “garbage mountain” in the middle of the ocean, says McWhirter, who has since left the sciences. Rather, “they’re dispersed, and there are clusters of items,” with abundances of neuston and of plastic correlating positively with one another. 

Although relatively little is known about neuston even today, research so far has revealed that these organisms are at once alien and familiar. As a habitat, the GPGP shares many things in common with coral reefs, including nutrient-poor water and high UV exposure, leading to similar adaptations. Like corals, some neuston have internal symbionts for extra nutrition, and almost all neuston are blue or purple, as are many corals; one hypothesis suggests that this coloration reflects more light, while another links it to camouflage, Helm says.

That camouflage plays into an open ocean food web in which neuston act as both predator and prey. The blue sea dragon (Glaucus spp.), a pelagic species of sea slug, preys upon Portuguese man-of-war (Physalia physalis), for example, which in turn ensnare small fish and crustaceans. Neuston are also a primary food source for other marine organisms, including threatened species such as loggerhead turtles (Caretta caretta) and Laysan albatrosses (Phoebastria immutabilis), and economically important fish such as juvenile Atlantic cod (Gadus morhua) and salmon (family Salmonidae).

Scientists are also now looking at roles that neuston may play on larger scales. Helm and her colleagues recently linked neuston to 28 ecosystem services, including their potential for mediating surface chemistry between the ocean and the atmosphere. Neuston live on the ocean’s skin, Helm says, and “I don’t think anyone would question the importance of the health of our skin in protecting us and our body.” In 2021, an international team similarly connected neuston to global climate regulation via their ability to absorb solar radiation, fix carbon, and mediate the “air-sea exchange of matter and energy,” the authors write in the paper. 

A World Adrift Far beyond the shore, oceans are dominated by a handful of massive gyres, circular currents that continuously suck debris into their centers. In addition to amassing pieces of floating wood and seaweed, a single gyre can also contain as many as 1.8 trillion pieces of plastic. And mixed amid all that detritus are animals—a collection of crustaceans, cnidarians, sea slugs, snails, and other organisms collectively referred to as neuston. Scientists are now studying the unique adaptations these organisms have for life on the high seas and the roles they may play in open-ocean ecosystems.

Ensnared in the cleanup debate

Helm tells The Scientist that shortly after she began sounding the alarm that The Ocean Cleanup was overlooking the potential harms of their work to neuston, the organization reached out to her about meeting to discuss her concerns. When Helm requested a public forum, however, the conversation broke down, she says. “So much of what they do, and so much of the success of their project, is because of their public-facing [communication]. And so it’s all important to me that discussions about impact happen in a public forum.” While she does speak with scientists at the organization over email, that public meeting has never taken place. 

While Helm has been one of the most vocal opponents of The Ocean Cleanup, she isn’t the project’s only critic. Across Twitter and in academic publications, other researchers have lambasted the project on everything from its carbon footprint to its financial partners. A 2021 study by the Norwegian consulting company SALT analyzed The Ocean Cleanup’s 001 system—an early iteration of their plastic-collecting technology that does not include some of the changes the group has since made to address damage to wildlife—and found that the nets could encounter as many as 40 billion zooplankton per hour, and that many of these animals would die. Several scientists have also noted that dragging a net between two ships is essentially trawling, a type of fishing that has long been condemned for its high bycatch. The Ocean Cleanup has clarified that they drag their nets slowly enough for mobile species to escape, and that each net is designed with an escape hatch that engineers can open. But previous deployments have netted turtles.

Getting really mad on the internet hasn’t stopped them from moving forward with their design, but I do think that it has put them under continuous pressure to take the impact really seriously.

—Rebecca Helm, Georgetown University

One person responding to these criticisms is Matthias Egger, the lead ocean field scientist at The Ocean Cleanup, whose role is to conduct research that helps the engineers at The Ocean Cleanup design a better product. Often, this work relates to the plastic—its sources, how it moves through the water and for how long, and the harm it could pose—but those same questions are intrinsically linked to the neuston community, he says.

While neuston weren’t included in the company’s first environmental impact assessment in 2018, a more recent iteration released in 2021 noted the potential of the nets to damage these species, and in the last few years the scientific team has begun sampling them during deployments. In a paper published in 2021, Egger and his colleagues reaffirmed that neuston and plastic are ubiquitous in the GPGP, but patchy. Their work, however, suggests neuston abundance does not directly correlate with plastic accumulation, in contrast to what Helm and her colleagues found. Egger says that, because both plastic and neuston take a variety of shapes, some are mostly shifted about by wind, while others move at the mercy of currents or waves. “For me,” says Egger, “there was no indication that they accumulate all together with plastic.”

The group has used that information to refine their plastic-tracking models, which The Ocean Cleanup crew uses to target its efforts to the most polluted areas and to identify plastic hotspots that may also be populated by fewer animals, Egger says. In addition, he now samples neuston ahead of and behind the net to determine what changes, if any, are happening at the community levels. “With these new data, we aim to refine that understanding of which are really the key species we need to look out for.” Moreover, project engineers have made changes to the nets, including a larger mesh size, to minimize capture of marine life, and prior to hauling the nets onboard, the crew allows them to sit for up to an hour to give animals time to escape. The risk of damaging marine life is one Egger takes seriously, he says, and is “exactly why we currently have one [cleanup] system in there, and not ten.”

Regardless, Helm has continued to voice her criticisms, in part because she believes that the science should come ahead of the cleaning. “Getting really mad on the internet hasn’t stopped them from moving forward with their design, but I do think that it has put them under continuous pressure to take the impact really seriously,” she says. 

         

She points to the way another group, the California-based Ocean Voyages Institute, has approached the problem of ocean plastic more thoughtfully. The group divvies out geolocating tags to volunteers passing through the GPGP to flag large pieces of debris such as ghost nets, disused fishing nets that float aimlessly through the ocean. Tagging the trash not only allows vessels to avoid them, but also turns them into beacons for tracking ocean currents. Once enough pieces have been marked, a sailboat journeys out to retrieve the tags and the garbage they mark. In 2020, the Ocean Voyages Institute completed the largest single cleanup in history, recovering 103 tons of trash. Helm says that targeting individual pieces of tagged trash accomplishes far more with less environmental impact. 

Not everyone agrees with Helm that The Ocean Cleanup’s approach is entirely inappropriate, however. Many researchers who spoke to The Scientist point to the sheer size of the ocean, the speed at which neuston repopulate, and the immediate threat of plastic pollution as reasons to push ahead. “The thought of not cleaning up the ocean because of it affecting the neuston life is pretty ridiculous,” McWhirter says, adding that the mesh of the nets from The Ocean Cleanup that he has seen is “big enough for neuston life to pass through.” Lanna Cheng, a professor emeritus at the University of California, San Diego, who spent her career studying neuston species of the insect genus Halobetes, similarly notes that dense floating aggregations of anything at sea, plastic or neuston, are rare. “Therefore . . . it’s not going to really affect the surface ocean community that much, even if we try some cleanup.”

Rui Albuquerque, a PhD student at the University of Aveiro in Portugal whose dissertation focuses on neuston, says that his research so far suggests those species have enough functional redundancy—meaning many species can perform a similar ecological role—that any compositional changes would be compensated for by other members of the community. “I think the take-home message is [that] neuston appear to be a lot more resilient than we would have thought,” he tells The Scientist. “Even if you remove one of the groups, another one could always replace that niche, and even if the environmental conditions change, it appears that the neuston can adapt.”

Conducting research while taking out the trash

Beyond The Ocean Cleanup’s own research, Egger is also offering to collect data for other scientists on the lengthy, expensive trips to sea that the group makes each year. He recently partnered with the Smithsonian Environmental Research Center, for example, to interrogate whether invasive species are traversing the Pacific, possibly hitchhiking on debris, and feeding on neuston to fuel their voyage. The Ocean Cleanup crew has also collected samples for Cheng to probe how Halobetes interacts with plastic. “We go out there on a regular basis, so we can finally get the data . . . and help fill this knowledge gap, together with other scientists, on ecosystems that we barely know,” Egger says.

Helm, meanwhile, recently relocated to Georgetown University and is gearing up for a new phase of her career. Many of the questions her lab has started to answer remain largely unexplored, including what neuston communities look like in oceans around the world, whether they have seasonal patterns, and how significant their contributions are to global processes. What researchers need, she says, is more data, and to that end, she and several colleagues recently established the Global Ocean Surface Ecosystem Alliance to encourage the public to report sightings of neuston and plastic. With this crowdsourced data, Helm says she hopes to continue unveiling the mysteries of the open ocean. “There’s definitely a lot of work left to do, and I’m excited to be a part of it.”

When she first encountered a desiccated by-the-wind sailor on a lonely beach, Helm says she could never have guessed that she would one day become a leading voice for high seas biodiversity. But as she noted years later, the living things persisting at the interface between sea and sky had changed her life. “I never meant to study the sea surface,” she shared on Twitter in 2021. “[B]ut now I believe this forgotten world is one of the MOST IMPORTANT places on Earth.”