Jun 6, 2019 - Energy & Environment

Microplastics lurk in the deep sea

Microplastic in the ocean

Photo: Tunatura/Getty Images

Huge quantities of microplastics can be found in the twilight zone depths of the ocean, where sunlight does not penetrate, a new study conducted in Monterey Bay finds.

Why it matters: The research, published Thursday in Scientific Reports, indicates that microplastics — tiny plastic particles less than 5 millimeters across — are entering the deep sea and being consumed as part of the marine food web. It's thought that these particles may be harming ocean life, but the details on that are just emerging.

What they did: A team of researchers used remotely operated vehicles outfitted with specialized sampling devices to capture and analyze microplastics at various depths.

They also studied the presence of microplastics in two filter-feeding species: giant larvaceans and pelagic red crabs.

  • The species migrate from deep ocean waters to the near surface each day in order to feed.
  • Pelagic red crabs, which are a food source for larger fish, can collect food and bits of plastic via tiny hairs on their exoskeleton.
  • Larvaceans, which resemble tadpoles, manufacture mucus filters called "mucous snot houses" that collect material — including microplastics — and discard it when they're full. Those sacs, known as sinkers, then fall toward the ocean floor and are eaten by other animals as they descend.

Scientists also analyzed the chemical composition of the microplastics.

What they found: The levels of microplastic pollution in the gastrointestinal systems of the creatures studied indicates that there is as much, if not greater, plastic pollution at some depths as there is in the well-known Great Pacific Garbage Patch, researchers tell Axios.

  • One of the largest plastic reservoirs of marine microplastics can be found within the water column and animals of the deep sea, the study shows.
  • “We found microplastics in their guts, every specimen we collected had microplastics in them," co-author Anela Choy of the Scripps Institution of Oceanography, tells Axios.
  • The researchers found similar concentrations of microplastic particles from near the surface and in the deepest waters surveyed.

Surprisingly, they found about 4 times the concentrations of microplastic particles in the midwater range, from about 600 feet down to about 2,000 feet, compared to surface waters. “We may be missing the largest reservoir of microplastics in the ocean,” Choy said of studies to date that have focused mostly on the ocean surface.

  • Scans of the microplastics found in the study showed about 40% of them contained polyethylene terephthalate (PET) as well as polyamide and polycarbonate — all of which are mainly used for consumer products rather than in fishing lines and other sources of marine plastic.

What we don't know: Scientists are just beginning to investigate the risks of microplastic pollution on human and animal health, so expect more news on this front in the next few years.

What they're saying: Kyle S. Van Houtan, chief scientist at the Monterey Bay Aquarium and a study co-author, tells Axios the study contains many concerning findings, but he is optimistic since much of the plastic in the deep sea can be reduced by phasing out single-use plastics on land.

“This is something we can make a big difference on by making changes in our lives," he says.

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