On the surface, the Arctic Ocean is pure serenity: chunk after chunk of brilliant white ice, lazily floating around. What you can’t see is that its underside is covered in green snot, à la the ectoplasm of ghost Buster—an underwater forest of Melosira arcticaalgae growing in sticky, dangling “trees” several feet long.
Even if it’s unappetizing for you or me, Melosira arctica forms the basis of the Arctic Ocean food chain. During spring and summer, its individual photosynthetic cells grow rapidly, absorbing the sun’s energy and forming long chains. These become food for small surface-dwelling creatures known as zooplankton, which in turn are eaten by larger animals, such as fish. Clusters break off and also sink thousands of feet to feed sea cucumbers and other seafloor scavengers.
But now this algal ecosystem, like literally everywhere on the planet, is completely infested with microplastics, which ride the currents and arrive from distant metropolises to settle on ice and snow. This is likely to have important consequences not only for Arctic organisms but also for the way the ocean sequesters carbon from the atmosphere. An article published today in the magazine Environmental sciences and technologies finds that, on average, this alga contains 31,000 plastic particles per cubic meter, thanks to its gelatinous tendrils. “The algae form long filaments or curtain-like structures and produce a sticky mucus that probably helps trap microplastic particles efficiently from their surroundings,” says marine biologist Melanie Bergmann of the Alfred Wegener Institute in Germany, lead author of the study. ‘item.
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In fact, the concentration of microplastics (or particles smaller than 5 millimeters) in algae is 10 times higher than the 2,800 particles scientists have found per cubic meter of water. Sea ice is even more contaminated, Bergmann’s previous research found 4.5 million particles per cubic meter. This astronomical figure is due to the ability of floating sea ice to “clean” particles from seawater as it freezes, all while being dusted with atmospheric microplastics that fall from above.
AS Melosira arctica grows on this ice, its viscosity attracts microplastics from the surrounding water. Later, when the ice melts, those trapped particles are released, releasing a concentrated dose of microplastics. A whopping 94 percent of the microplastics the researchers found in the algae were smaller than 10 microns, or one-millionth of a meter. “Because it’s a filamentous alga and the cells are quite small, it preferentially picks up all the little things,” says Deonie Allen, co-author of the paper and a microplastics researcher at the University of Birmingham and the University of Canterbury. “And all the really small things end up having the biggest impact on the ecosystem.”
The smaller a particle is, the more organisms it can enter. Plastics can break down so small that they enter individual cells of the algae or zooplankton that feed on them.
Researchers still can’t tell if all that microplastic is doing harm Melosira arctica. But further laboratory research has found that the plastic particles can be toxic to other forms of algae. “In experiments with very high doses of microplastics, small microplastics damaged and entered algal cells, leading to stress responses such as damage to chloroplasts and thus inhibition of photosynthesis,” says Bergmann.
There’s another concern, too: If enough plastic builds up on the algae, it could block sunlight from reaching the cells, further interfering with photosynthesis and growth. “This study really contributes to a growing body of research showing that these microscopic organisms and these microscopic plastics can combine and become a really macroscopic problem,” says Anja Brandon, associate director of US plastics policy at the Ocean Conservancy. that wasn’t involved in the study. “These algae in the Arctic and phytoplankton throughout the marine environment form the fundamental backbone of the marine food web.”
But the proliferation of plastics could wreak havoc on that network. As summer temperatures rise and Arctic sea ice deteriorates, more and more clumps of algae can break free and sink, carrying those microplastics with them into new ecosystems. This may be why scientists are also finding particle droplets in Arctic Ocean sediments. “There’s a whole community right under where the ice is melting,” says Steve Allen, a microplastics researcher at the Ocean Frontiers Institute and co-author of the new paper. The sinking seaweed is a sort of food “conveyor belt” for benthic creatures like sea cucumbers and brittle stars, he says.
In this sensitive ecosystem, food is relatively scarce compared to, for example, a tropical coral reef. If a sea cucumber is already making do with limited amounts of food oozing from the surface, it would be wrong to load that food with inedible plastic. This is known as ‘food dilution’ and has been shown to be a problem for other small animals, which become full of microplastics reducing their appetite for real food.
Jagged plastic particles can also cause severe scarring of the gut, as was recently demonstrated in seabirds with a new disease known as plasticosis. And that’s not to mention the potential chemical contamination of an animal’s digestive system: At least 10,000 chemicals have been used to make plastic polymers, a quarter of which scientists consider worrisome.
Microplastic contamination of Melosira arctica it could also have serious effects on the carbon cycle. As the algae grow, they absorb carbon, as plants do on land. When it sinks to the bottom of the sea, it sequesters that carbon in the depths. But if the microplastic inhibits their growth, the algae will absorb less material. Or, if the pollutant makes the algae break down more easily, that will give scavengers in the water column more opportunities to consume it, thus preventing some of the carbon from reaching the seabed. And if scavengers eat the plastic, their waste may also be less likely to reach the ocean floor: When scientists fed microplastics to zooplankton known as copepods in the lab, the particles made their fecal pellets slower to digest. sink and easier to break apart. This is bad for both carbon sequestration and for the animals that rely on this waste as a food source.
All of this is fueling the dramatic transformation of the Arctic, which is now warming more than four times faster than the rest of the planet. Atmospheric plastics that settle on sea ice, especially fragments of black car tires, absorb more energy than the sun and can accelerate melting. This exposes darker ocean waters, which absorb more heat and melt more ice. Overall, there is less sea ice, and therefore less room for Melosira arctica to do its job of absorbing carbon and more melting, which releases a flood of built-up plastic.
Bergmann thinks this situation will only get worse as a warmer Arctic leads to more human development, and therefore more plastic waste. “As the sea ice retreats, human activities in the region increase,” Bergmann says. “In fact, they already have — fishing, tourism, shipping — that will perpetuate the pollution.”
