Plastic litter is now virtually inescapable throughout every crevice of the world's oceans, and a newly published study finds, for the first time, that the creatures living in the deepest, most remote environs on Earth are eating it in startling amounts.
A British research team captured amphipods, tiny shrimp-like crustaceans that scavenge on the seabed, from six of the world's deepest ocean trenches and took them back to their lab. There, they discovered that more than 80 percent of the amphipods had plastic fibers and particles in their digestive systems, known as the hindgut. The deeper the trench, the more fibers they found. In the Mariana Trench, the deepest at more than seven miles beneath the waves in the western Pacific, the scientists found fibers in 100 percent of the samples–in every amphipod collected. Prior studies of plastic particles ingested by marine organisms caught near the surface have found far smaller percentages.
The new research, published in the journal Royal Society Open Science, adds new details to earlier research that only discovered plastic bits in sea floor sediment in 2014. But it fleshes out the picture shaping up of ocean trenches as the final sink for marine debris. That is not good news.
Once the plastic particles sink to the deep sea, they've got nowhere else to go.
“If we could magically snap our fingers over 10, 20, 50 years time and stop making plastic, what would happen to the plastic in the river? It would flush and wash out,” says Alan Jamieson, a marine biologist at Newcastle University and the study's lead author. “The coastlines would dilute and disperse. In the open ocean, the UV and wave action would act on that plastic and the surface would be clean again. What happens when you get to the deep sea, there's no dispersal or flushing. It's only going to get more and more and more.”
He adds: “This is not a one-off find. The Pacific Ocean covers half the planet. Our study sites were off Japan and Peru and Chile in places separated by thousands of miles. We can now say with confidence that plastic is everywhere. Let's not waste our time looking for more. Let's concentrate our efforts on what it is actually doing.”
How did they sample so deep?
The research team sampled five trenches throughout the western Pacific and one deep-sea trench off the west coast of South America. Researchers deployed traps with bait wrapped carefully to avoid falsely contaminating a creature's insides with plastic.
A whale shark swims beside a plastic bag in the Gulf of Aden near Yemen. Although whale sharks are the biggest fish in the sea, they're still threatened by ingesting small bits of plastic.
Once collected, they studied a deep part of the creature's digestive system called the hindgut. They wanted to ensure no plastic ingested after the amphipods were caught was making its way into their results.
Inside, they found a rainbow of plastic items.
Sixty-six percent of the plastic they found was blue fibers. Black, red, and purple fragments were also present, along with blue and pink fragments.
No trench was fiber-free, and more than 80 percent of the amphipods contained them. When tested, the fibers were the same used in textiles, and the study suggests they entered the ocean after leaching from washing machines.
Richard Thompson, a marine scientist at the University of Plymouth, whose 2014 study discovered the microplastics on the deep see floor, says the new work is “a missing piece of the jigsaw puzzle.”
“The next thing is: is it causing any harm,” he asks. “It's a risk assessment. They more plastic you've got, the more likely a large number of creatures are going to interact with it. There are so few studies in the deep ocean, we are only beginning to understand it.”
What does it mean for ocean food chains?
Jamieson says the reactions he gets to the revelation that marine life at the bottom of the sea is eating plastic falls into two categories. The first is horror that no place on the planet has escaped the plastic invasion. The other category stuns.
“Believe it or not, they say, 'That's great. It means the contamination from land is now at the bottom of the sea and that’s a good result, isn’t it?'” he says. “It’s crazy that people like to think that way.”.
“Humans have an odd relationship with depth,” Jamieson says. “When you talk about seven miles underwater, people freak out. Flip that 90 degrees. Seven miles is half the length of Manhattan. A marathoner could run it in 20 minutes. It’s a small world in many respects and throwing something into the sea, it can sink to places that you think are far away, which are not really.”
Jamieson says the ocean should be considered in a different light—as part of one continuous body of water that covers most of the Earth’s surface, full of millions of animals all interacting with each other.”
Susanne Brander, an Oregon State University toxicologist who researches the effects of microplastics on larval fish, says the amphipods are becoming a vector to transport plastic particles into the food web.
“The amphipods they are finding fibers in are prey for larger fish and those larger fish are prey for even larger predators,” she says. “These zooplankton at the base of the food chain are taking up the microfibers because they are similar in size to the phytoplankton they eat. And that puts these fibers into the food web. We are finding larger organisms with intestines lined with microfibers. They found a baleen whale that had been beached and when they cut it open, the intestines were lined with these smaller particles. They give us a snapshot of what's happening in a larger sense.”
There are as many as 51 trillion pieces of plastic in the ocean, and 90 percent of that ocean plastic is microscopic. Scientists have previously likened it to a kind of “soup.”
Last December, researchers from Japan warned National Geographic of the urgency to learn more about these remote places. Recreating the intense pressure of the deep sea in labs is difficult, and the full impacts of plastic on deep-sea organisms is still unknown or unconfirmed.
This article has been updated with additional information.