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The astounding quantities of discarded plastic that end up in oceans each year tend to concentrate in ring-like swirls of currents called gyres, yet most of it can be hard to spot—not because it’s not there in great quantities, but because it often takes the form of fingernail-sized microplastics. “It looks like pristine ocean until you tow your net through the water,” researcher Erik Zettler at Sea Education Association (SEA) said about the North Atlantic Gyre. “That’s when you find the plastic.”
The presence of so much plastic debris at sea poses dire threats to the marine life unlucky enough to ingest small bits of it or to become entangled in nets or plastic bags. But recent research has also revealed some of the surprising ways a few resourceful marine creatures use it to their own advantage. For some species, the tiniest scrap of plastic can offer transportation across the open sea, or access to dinner, or even an assist in reproduction. Even as science shows how much harm plastic waste can do to the natural world, it also demonstrates how, for at least a few species, garbage can prove strangely useful.
In the summer of 2009, Miriam Goldstein was a thousand miles out at sea, fishing for plastic in the most remote part of the North Pacific Ocean, when she noticed something unusual in her nets. The marine biologist and a team of researchers from the Scripps Institution of Oceanography were trawling the North Pacific Gyre. Many of the tiny bits of floating debris Goldstein and her team hauled in were carrying a strange cargo. On the surface of the plastic were the miniscule orange eggs of an extraordinary insect called the sea skater.
The open-ocean sea skater, Halobates sericeus, is one of five species of Halobates that spends its entire life on the ocean’s surface. Striding and hopping across the waves on filament-like legs, they depend on a kind of natural lifejacket to keep them afloat when swamped by waves. Tiny pockets of air trapped between layered carpets of body hair rescue them and float them back to the surface.
Just as impressive is their talent for reproductive improvisation. Sea skaters require a hard surface on which to deposit their eggs. This is not a problem for coastal insects with access to shoreline rocks. But in the remote vastness of the open ocean, a solid surface can be hard to find. In recent decades, the insects have increasingly turned floating plastic trash to their own ends, adopting it as a high-seas egg depository. In 2002, oceanographer Lanna Cheng fished from the ocean a discarded one-gallon plastic jug encrusted with 70,000 sea skater eggs, in layers 15 eggs deep. She figured about 7,000 female sea skaters must have used the same jug.
“They are desperate for anything,” Goldstein said of the sea skaters. Her research, published online in Biology Letters in 2012, showed that as plastic debris in the North Pacific has become more plentiful, the density of sea skater eggs has grown significantly along with it. Her findings counter common sense assumptions about garbage and its many harmful effects on the natural world. “It’s surprising because, with all the toxins in plastic, you’d think there might be a strong negative impact,” Goldstein said.
For some species, the tiniest scrap of plastic can offer transportation across the open sea, or access to dinner, or even an assist in reproduction.
No one knows exactly how much plastic is adrift around the world. A 2010 SEA research expedition to the North Atlantic Gyre, east of Bermuda, found the highest oceanic plastic concentration on record: 26 million pieces per square kilometer. Goldstein’s voyage in the Pacific showed that plastic concentrations there have grown 100-fold in the last 40 years.
What scientists do know is that the plastic has become braided into the life of the ocean. “Any piece of plastic larger than an inch or so may have a crab or a barnacle attached to it,” Kara Lavender Law, a SEA research professor, said. The debris draws diverse marine congregations, such as sponges, bryozoans, tubeworms, and mollusks, which can count on finding something to eat on or around it. In the nutritional desert that is the open ocean, that makes every nugget of plastic a bustling lunch spot.
SEA researchers on one cruise in the Atlantic found a 5-gallon bucket coated with algae and other organisms, but also hosting about a dozen triggerfish. The bucket had become an artificial, floating reef, offering a diverse group of organisms a sorely needed solid surface and access to nutrients.
The floating debris has also made it easier for sea life to claim new territory. David K. A. Barnes of the British Antarctic Survey wrote in Nature in 2002 that, “human litter more than doubles the rafting opportunities for biota.” Plastic trash carries mollusks, sponges, worms, and many other species to new homes, where they may threaten native populations.
The list of passengers rafting on ocean plastic also includes entire communities of microbes—microscopic organisms such as bacteria or viruses. Zettler and his fellow researchers—Tracy Mincer of the Woods Hole Oceanographic Institution and Linda Amaral-Zettler of the Marine Biological Laboratory—say that the microbial communities living on floating plastic constitute a new kind of marine ecosystem. In a paper published online last summer in Environmental Science and Technology, they dubbed it the Plastisphere.
One of their most intriguing finds had to do with what the microbes were doing to the microplastics they colonized. The researchers found curious, microscopic deformations in the plastic. These were not the usual cracks that result from weathering, but rather fields of pits seemingly hollowed out by the microbes. In the words of Emelia DeForce, a biologist who oversaw the plastic harvest examined by the researchers, the microbes seemed to have burrowed into the plastic like hot coals.
Zettler believes that it’s possible the microbes are drawn to the solid surfaces in the water because nutrients concentrate there. Other oceanographers said that it’s worth considering whether the organisms are feeding on the actual plastic. “It’s not too far a stretch to think so,” said Miriam Doyle, a research scientist at the University of Washington. She pointed to reports of oil-eating bacteria feeding on the catastrophic Deepwater Horizon oil spill in the Gulf of Mexico, and speculated that organisms might be digging into microplastics in search of nutrients. “Of all the biota out there, we know the least about these microbes.”
Whether as access to food, a ride to a new home, or a place to hatch the next generation, the marriage of marine life and plastic waste complicates any plans for any open-ocean plastic cleanup. Floating plastic is so awash in living organisms that to harvest it from the ocean likely means taking some marine life with it. That has not stopped well-meaning innovators from proposing ways to scour the ocean of plastic. One of the best-known examples is the scheme developed by Boyan Slat, a Dutch engineering student, calling for a massive system of sifting booms to span the ocean’s gyres and capture floating plastic. A video of his 2012 TEDx presentation outlining the plan became an Internet sensation.
“I’ve received hundreds of emails with ideas for cleaning up the oceans,” Goldstein said. Asked how many were promising, she answered, “For the open ocean? None.” For now, Goldstein offers her own modest proposal for countering the tide of plastic: “The best thing would be to stop putting it in the ocean in the first place.”
What may be most alarming is how thoroughly microplastic waste has insinuated itself into the life of the ocean. While the creatures that live, feed, and breed on our plastic waste might be capitalizing on this newfound resource, the real costs to the individual species and the marine ecosystem remain to be determined.
Andrew Santella has written for The New York Times Book Review, GQ, Slate, and many other publications.
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