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From fishing gear to food packaging, plastic is piling up far below the ocean’s surface, creating debris dumps in the deep. Viewed from above, the trash-strewn seafloor looks like a patchwork of colored carpet, says Xikun Song, a marine biodiversity researcher at Xiamen University in China.
Song and his colleagues recently found that this plastic is teeming with life. So much life, in fact, that the sunken trash may have created new biodiversity hotspots on the seafloor.
The team sifted through dozens of plastic objects, such as grocery bags and bottles, that they’d collected from several canyons in the Xisha Trough in the South China Sea between 2018 and 2020. They tallied nearly 1,200 tiny creatures—ranging in length from 0.2 millimeters to 2.5 centimeters—clinging to the debris hauled from sites as deep as 3,200 meters. Using microscopy, genetic analysis, and other methods, the researchers found that these organisms came from 49 species, from fungi and mollusks to cold-water corals—a shockingly diverse array, says Song.
They even found that some sea snails and a type of parasitic flatworm spawned on the sunken plastic. The snails deposited their eggs on the plastic, while the flatworms secreted a breeding cocoon on it. Of the many animals the team observed, one hydrozoan looked different from those known to scientists, and may be a new species altogether.
Michela Angiolillo, a marine biologist at the Italian Institute for Environmental Protection and Research who was not involved in the new study, isn’t surprised that plastic could be shifting the biodiversity in the deep sea, given that plastic provides a hard surface on an otherwise muddy or sandy seafloor. As in the extreme case of shipwrecks, she explains, marine life colonizes human litter in the search for shelter or a place to latch on.
Marine biologist Sabine Rech, of the Catholic University of the North in Chile says that, initially, it sounds great that plastic can boost biodiversity. But this ultimately means that plastic is changing the environment. “A good change for some species may be a bad change for other species,” says Rech, who was not involved in the new research. For instance, if litter on the seafloor provides a haven for certain predators, it could make life harder for their prey. And because of the complex connections within food webs, that change may spur other knock-on effects. “Eventually, a whole ecosystem may be affected,” she says.
And just like chunks of plastic at the surface, these sunken pieces will break down and pose risks to the organisms that ingest them, Rech adds. As in other remote environments, plastic is ubiquitous in the ocean, including in “places where we cannot possibly go to clean up,” she says.
There are still many unknowns as far as how the seafloor plastic will affect the ocean, cautions Song. The trash may modify food webs and oxygen availability in the water. And though the plastic appears to have created new biodiversity hotspots in the deep, Song says that these sites should be considered, primarily, as “hotspots of environmental pollution.”
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