How microplastics in the ocean will affect marine life

While there has been marine life, there has been marine snow: a relentless rain of death and debris sinking from the surface to the depths of the sea.

Snow begins as specks, which aggregate into dense, flocculent flakes that gradually sink and pass over the mouths (and mouth-like devices) of the scavengers below. But even the devouring sea snow will most likely snow again; the guts of a squid are just a rest stop on this long step into the depths.

While the term may suggest winter whites, the sea snow is mostly brown or greyish, and includes mostly dead things. For eons, the waste has contained the same things: stains from plant and animal carcasses, feces, mucus, dust, microbes, viruses, and transported carbon from the ocean to store on the seabed. Increasingly, however, sea snow is being infiltrated by microplastics: fibers and fragments of polyamide, polyethylene and polyethylene terephthalate. And this false fall seems to be altering the ancient cooling process of our planet.

Every year, tens of millions of tons of plastic enter the Earth’s oceans. Scientists initially assumed that the material was intended to float in garbage and twists, but surface studies have only accounted for about one percent of the ocean’s estimated plastic. A recent model found that 99.8 percent of the plastic that entered the ocean since 1950 had sunk below the first hundred feet of the ocean. Scientists have found 10,000 times more microplastics on the seabed than on polluted surface water.

Sea snow, one of the main routes connecting surface and depth, seems to be helping to sink plastics. And scientists have only begun to unravel how these materials interfere with the trophic networks of the deep sea and the natural carbon cycles of the ocean.

“It’s not just that sea snow carries plastics or plastic aggregates,” said Luisa Galgani, a researcher at Florida Atlantic University. “It’s just that they can help each other get to the deep ocean.”

The sunlit surface of the sea blooms with phytoplankton, zooplankton, algae, bacteria and other tiny life forms, feeding on or between the sun’s rays. As these microbes metabolize, some produce polysaccharides that can form a sticky gel that attracts the lifeless bodies of tiny organisms, small pieces of larger carcasses, foraminifera shells and pteropods, sand, and microplastics, which bind to form larger scales. “They’re the glue that holds all the components of sea snow together,” Dr. Galgani said.

Marine snowflakes fall at different rates. The little ones have a more languid descent: “as slow as a meter a day,” said Anela Choy, a biological oceanographer at the Scripps Institution of Oceanography at the University of California, San Diego. Larger particles, such as dense fecal pellets, can sink faster. “It’s just shooting to the bottom of the ocean,” said Tracy Mincer, a researcher at Florida Atlantic University.

Plastic in the ocean is constantly degrading; even something as big and floating as a jug of milk will be erased and broken into microplastics. These plastics develop biofilms from different microbial communities: the “plastisphere,” said Linda Amaral-Zettler, a scientist at the Royal Netherlands Institute for Sea Research, who coined the term. “In a way we think plastic is inert,” Dr. Amaral-Zettler said. “Once it enters the environment, it is rapidly colonized by microbes.”

Microplastics can accommodate so many microbial hitchhikers that counteract the natural buoyancy of the plastic, causing its pond to sink. But if the biofilms degrade downward, the plastic could float upward, potentially leading to a microplastic purgatory in the water column. Sea snow is anything but stable; as the flakes fall freely into the abyss, they are constantly freezing and falling apart, ripped apart by waves or predators.

“It’s not that simple: everything falls apart all the time,” said Adam Porter, a marine ecologist at the University of Exeter in England. “It’s a black box in the middle of the ocean, because we can’t stay long enough to find out what’s going on.”

To explore how snow and marine plastics are distributed in the water column, Dr. Mincer has begun tasting deeper water with a dishwasher-sized pump full of filters hanging over a cable from a research vessel. The filters are arranged from large to small mesh to filter fish and plankton. Running these pumps for 10 hours straight has revealed nylon fibers and other microplastics distributed through the water column below the subtropical gyrus of the South Atlantic.

But even with a research vessel and its expensive and difficult-to-handle equipment, an individual piece of sea snow cannot be easily recovered from the deep waters of the actual ocean. Bombs often disturb snow and scatter fecal granules. And flakes only provide little information about how quickly some snow melts, which is vital to understanding how long plastics remain, sink, or sink into the water column before settling. on the seabed.

“Are they decades?” Dr. Mincer asked. “Are they hundreds of years old? Then we can understand why we’re here and what kind of problem it really is.”

To answer these questions and work with a budget, some scientists have made and handled their own sea snow in the lab.

In Exeter, Dr. Porter collected buckets of seawater from a nearby estuary and loaded the water into continuously rolling bottles. He then sprayed microplastics, including polyethylene beads and polypropylene fibers. The constant beating, and a jet of sticky hyaluronic acid, encouraged the particles to collide and stick to the snow.

“Obviously we don’t have 300 meters of pipe to sink it,” Dr. Porter said. “By rolling it, what you’re doing is creating an endless column of water for the particles to fall off.”

After rolling the bottles for three days, he pipetted the snow and analyzed the number of microplastics on each scale. His team found that all the types of microplastics they tested added to sea snow and that microplastics such as polypropylene and polyethylene, usually too floating to sink on their own, easily sank once incorporated into the snow. neu marina. And all microplastic-contaminated sea snow sank significantly faster than natural sea snow.

Dr. Porter suggested that this potential change in snow speed could have major implications for how the ocean captures and stores carbon: faster snowfalls could store more microplastics in the deep ocean, while slower snowfalls could make plastic-laden particles more available. to predators, which can starve to the deepest trophic networks. “Plastics are a diet pill for these animals,” said Karin Kvale, a carbon cycle scientist at GNS Science in New Zealand.

In experiments in Crete, funded by the European Union’s Horizon 2020 research program, Dr. Galgani has attempted to mimic sea snow on a larger scale. He dropped six mesocosms – huge bags containing nearly 800 gallons of seawater and recreated the natural movement of water – into a large pool. Under these conditions sea snow formed. “In the field, mostly make observations,” Dr. Galgani said. “You have very little space and a limited system. In the mesocosm, you’re manipulating a natural system.”

Dr. Galgani mixed microplastics into three mesocosms in an attempt to “recreate a sea and perhaps a future ocean where a high concentration of plastic can be found,” he said. Microplastic-laden mesocosms produced not only more sea snow but also more organic carbon, as plastics provided more surfaces for microbes to colonize. All of this could sow the deep ocean with even more carbon and alter the ocean’s biological pump, which helps regulate the climate.

“Of course, it’s a very, very big picture,” Dr. Galgani said. “But we have some signs that it can have an effect. Of course, it depends on how much plastic there is.”

To understand how microplastics can travel through the trophic networks of the deep sea, some scientists have resorted to creatures to look for clues.

Every 24 hours, many species of marine organisms embark on a synchronized migration up and down the water column. “They do the equivalent of a marathon every day and night,” Dr. Choy said. Guilherme VB Ferreira, a researcher at the Federal Rural University of Pernambuco in Brazil, asked, “Is it possible that they carry plastics up and down?”

Dr. Ferreira and Anne Justino, a doctoral student at the same university, collected vampire squid and water squid from a stretch of the tropical Atlantic. They found a lot of plastics in both species: mostly fibers, but also fragments and pearls.

This made sense for medium-sized squid, which migrate to the surface at night to feed on fish and copepods that eat microplastics directly. But vampire squid, which live in deeper waters with fewer microplastics, had even higher levels of plastic, as well as foam, in their stomachs. Researchers have hypothesized that the main diet of sea snow vampire squid, especially more meaty fecal pellets, may be channeling plastics into their bellies.

“It’s very worrying,” said Ms. Justin. Dr. Ferreira said, “They are one of the most vulnerable species to this anthropogenic influence.”

Mrs. Justino has excavated fibers and pearls from the digestive tract of lantern fish, hatcha fish and other fish that migrate up and down the mesopelagic, from 650 to 3,300 feet down. Some microbial communities that settle into microplastics can biolumines, attracting fish like bait, said Dr. Mincer.

At Monterey Bay Canyon, Dr. Choy wanted to understand if certain species of filters were ingesting microplastics and transporting them to the trophic networks in deeper water. “Sea snow is one of the main things that connects food webs across the ocean,” he said.

Dr. Choy focused on the giant larvae Bathochordaeus stygius. The larvae resemble a small tadpole and live inside a palatal mucus bubble that can grow up to a meter long. “It’s worse than the dirtiest booger you’ve ever seen,” said Dr. Choy. When their mucus houses become clogged with food, the larvae move and the heavy bubbles sink. Dr. Choy found that these mucus palaces are full of microplastics, which are sent to the depths along with all their carbon.

Giant larvae are found in the world’s oceans, but Dr. Choy noted that her work focused on the Monterey Bay Canyon, which belongs to a network of marine protected areas and is not representative of other seas. more polluted. “It’s a deep bay on a country coast,” Dr. Choy. “Extend the scale and think about how big the ocean is, especially the deep water.”

The individual snowflakes are small, but they add up. A model created by Dr. Kvale estimated that in 2010, the world’s oceans produced 340 trillion aggregates of sea snow, which could carry up to 463,000 tons of microplastics to the seabed each year.

Scientists are still exploring exactly how this plastic snow is sinking, but they know for a fact, said Dr. Porter, that “everything is finally sinking into the ocean.” Vampire squid will live and die and eventually turn into sea snow. But the microplastics that pass through them will remain and eventually settle to the seabed in a stratigraphic layer that will mark our time on the planet long after humans have disappeared.

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