Tech & Science

The Garbage Eaters

In the Magazine
Plastic Trash found in the oceans of the world. Richard T. Nowitz/Corbis

On the surface of the most desolate parts of the world's oceans, billions of tiny pieces of plastic swirl and churn. They are festering pockets of pollution, but the ocean is a resilient beast. And even in these incredibly remote areas, where nothing much ever happens, this human garbage has begun to attract communities of life. Recent research suggests the ocean's plastic patches are instigating a new evolutionary pathway for microbes and creating a food chain out of thin air—and water.

You've probably heard about the ocean's garbage patches—large areas of water where waste plastic collects. It's a phenomenon that didn't exist until the 1970s, when Styrofoam started showing up en masse. A slew of other plastic items followed, so much so that in 2012, scientists announced that the amount of plastic in the ocean had grown 100 times over four decades. The United Nations Environment Program has estimated that you can now find about 46,000 pieces of plastic in every square mile of sea. There are 18 million tons of plastic in the Pacific Ocean alone, and the biggest island of trash is roughly the size of Texas.

A lot of that garbage came from ships that dumped their waste whenever they were too far from port. In the mid-1970s, though, the International Maritime Organization banned dumping and attempted to minimize the pollution caused by oceangoing vehicles. Today, plastic garbage mostly comes from rivers. Left on beaches or swept up in the wind, plastic makes its way downstream and gets caught in levies where rain washes it into the ocean.

Dense plastics found in bottles, like polyethylene terephthalate, commonly known as polyester, sink to the ocean floor after weather and oxidation from the sun tear them apart. Scientists have very little knowledge of what happens to these bits of plastic once they descend. They estimate that, for all the plastic they're able to see on top of the ocean, there is 10 times more at the bottom.

The rest of that plastic gets trapped in one of the ocean's five gyres—a worldwide network of surface currents created by the Earth's wind patterns and the spinning of the planet. Plastic caught in the gyres gets tossed around, broken down into small pieces and then sucked into a vortex at the center of each current. According to Tracy Mincer, a geochemist at the Woods Hole Oceanographic Institution who studies the properties of the garbage patch, it takes about six weeks for a plastic bottle or piece of Styrofoam to make its way from the East Coast of the U.S. to the center of a gyre.

"These currents are powerful and swift, and there's no chance to [escape] and reach land," he says. Once the small pieces make it to the center, "they sit there and churn. If the wind is blowing and there's a one- or two-foot wave, you'll never see this stuff. But if the seas are very calm and glassy, you'll see things that look like paint chips or confetti floating up to the top. The sun and wave action break this stuff down into millimeter and tens of millimeter chunks of plastic that hang out and persist for a very long time."


4.11_NW0315_Plastisphere_illo There is an island of trash the size of Texas in the Pacific thanks to a worldwide network of gyres driven by currents and wind that trap light plastic waste. Ocean current data courtesy of NOAA and Greenpeace John Grimwade

The final resting places for these chips are extremely desolate areas of the sea, where the water is deepest and there are no islands or other surfaces for miles. For the animals that live there—mostly small shrimp and tiny plants—it's an extremely competitive place, where any available nutrients are immediately spoken for.

Those billions of small garbage chips have created a surface where none existed before. And whenever you add a surface to water, rare and sparse nutrients that would otherwise be inaccessible to life begin to collect. Much like how dust forms in a layer on the outside of your windows or dirt accumulates on the hood of your car, nutrients form a thin film on the surface of these plastic chips.

What scientists have recently discovered is that the sudden appearance of concentrated nutrients is waking up and attracting dormant microbial life. "They're very aware of their environment and can find their way toward nutrients. They head toward the chemicals they want—they can follow a plume of nutrients towards a more concentrated bit," says Mincer.

Once these microbes find a surface covered in nutrients they can eat, they lay down anchors on the plastic and begin to propagate. Researchers are finding thousands of different microbes are now making their homes on the ocean's plastic confetti. Many of them are diatoms—single-celled plants that eat the nutrients off the plastic and harvest light from the sun for energy.

So now there is a whole new colony of life growing and breeding in the middle of the ocean's desert. And, it turns out, these microbes are producing carbon and other nutrients that larger animals want to eat.

One of Earth's largest migrations of life happens every night. When the sun goes down, visual predators (who determine what they eat based on the color pattern and behavior of their prey) swim up from the ocean's depths. Millions of fish and other hungry species surface in search of food.

Normally, in the deepest parts of the ocean they'd have little food to find. But in one of the most recent findings about the plastic colonies, scientists have discovered that the types of microbes attaching themselves to plastic have the ability to bioluminesce. In other words, when the sun goes down, the plastic-loving microbes begin to glow.

Visual predators are 10 times more likely to eat food that luminesces than food that doesn't. It's an instinct that helps them find the most nutritious meals. And scientists studying the fish that live around the garbage patch have discovered that 10 percent of them have plastic in their guts. It turns out, the glowing microbe colonies are a delicious draw.

All of this has led scientists to speculate that the plastic has created a false food web, most likely spurred by the microbes' end-goal of getting into fish stomachs, where they have access to an endless stream of nutrients that would otherwise be unavailable to them. "This is like a bait-and-wait situation for these microbes," says Mincer. "As we look closer at their genes, we see they have the ability to colonize intestinal tissue." Mincer is part of a team of scientists from Woods Hole and the Sea Education Association who have received funding from the National Science Foundation to better understand this new ocean world they have dubbed the "plastisphere."

Through DNA analysis and cultivation of the microbes in the lab, they're hoping to prove their theory that these microbes have evolved to use the plastic as a means to an end. Ultimately, this will help them develop a clearer picture of the change that plastic has wrought on the ocean environment. Right now, they can only see the short-term effects of the pollution. But if they can demonstrate that the plastic is causing evolutionary change in local animal species, they'll have proved their theory that our garbage is having an even greater long-term environmental impact than we thought. And according to Mincer, there is good evidence they're correct.

First, scientists have never seen microbes attempt to get into fish guts by colonizing plastic.

Next, the microbes that live on the plastic are different from any other microbes that scientists have found floating around them. This means that probably only a minuscule seed bank population of them is living in the open water—the gathering on the plastics is the biggest congregation of these particular microbes ever seen.

Last, they have to be able to latch on to plastic. The surface of plastic is waxy and oily—it's hydrophobic, meaning even water can't attach to it. "For things to stick, there are some tricks they need," says Mincer. All bacteria attach to surfaces by using their flagellum—teeny-tiny tentacles—to test out the surface to see if they can adhere. Then they send out a bunch of fibers that tether them to the surface. Finally, they secrete a bunch of protein and polysaccharides to glue themselves in place. But some of the microbes they've found in the plastisphere are able to latch on to plastic in just five minutes. "They know it's plastic, and they want it," Mincer says. They think that, with these guys, some of their fibers are actually hydrophobic—just like the surface of the plastic. But it's too early to know for sure.

The science team is now specifically looking to find genes that might be responsible for the microbes' super-colonizing behavior. According to Mincer, the main question is: "Did the organisms on plastic go through a specific selective event that forced a rapid bottleneck or type of evolution?"

By studying how these microbes evolved to attach themselves onto the ocean's garbage patch, scientists may find a way to reverse the human-made destruction. Given that it's unlikely that the world will unilaterally refrain from tossing plastic into the ocean, scientists are taking a different route: Mincer says that if they can identify "the right kinds of microbes to colonize and degrade in a natural fashion," manufacturers could start to add microbe-attracting materials into the plastics they make. In other words, we can engineer our plastics so that microbes eat up our trash, and clean the oceans for us.

It's clear that humans certainly aren't the best influence on the Earth. But even if we throw billions of pieces of plastic at it, the ocean will adapt and life will find a way.

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