< 2019 Annual Report Photo by Susan von Thun

Finding microplastics in ocean food webs

Many people have heard of the “Great Pacific Garbage Patch,” a vast area of ocean between California and Hawaii, where ocean currents concentrate plastic pollution. However, it turns out there may also be a lot of plastic far below the ocean’s surface.

A joint research project between MBARI and the Monterey Bay Aquarium showed that plastic debris less than five millimeters (0.2 inches) across, known as microplastic, is common from the surface to the seafloor. It may also be entering marine food webs, both at the surface and in the deep. Most of this microplastic is coming from consumer products.

This groundbreaking study is the first to look systematically at microplastics, with repeated sampling at the same locations and range of depths, from just beneath the ocean surface to 1,000 meters (3,281 feet).

The study, conducted in California’s Monterey Bay National Marine Sanctuary, also found that small ocean animals are consuming microplastics, which introduces the particles into food webs from near-surface waters down to the deep seafloor.

“Our findings buttress a growing body of scientific evidence pointing to the waters and animals of the deep sea, Earth’s largest habitat, as the biggest repositories of small plastic debris,” said Anela Choy, the study’s lead author. “Our study demonstrates a link between microplastics distributed across the water column and entry of this foreign material into marine food webs by important marine animals, such as pelagic crabs and giant larvaceans.”

The researchers discovered microplastic particles inside deep-sea larvaceans (left) and pelagic red crabs (right). Right image courtesy of Monterey Bay Aquarium. The giant larvacean, Bathochordaeus mcnutti, is a few centimeters long, but its mucous filter "house" can reach 1 meter (about 3 feet) in diameter. Pelagic red crabs, Pleuroncodes planipes, can reach up to 13 centimeters (five inches) long.

Choy conducted the research while serving as a postdoctoral fellow at MBARI. She is currently an assistant professor at Scripps Institution of Oceanography at the University of California, San Diego.

MBARI Principal Engineer Kakani Katija, a co-author of the microplastics study, noted: “This research shows how we can leverage scientific, engineering, and conservation expertise to develop new technology that provides powerful insights into how humans are impacting the ocean.”

Microplastics are pervasive from the surface to the seafloor

Using MBARI remotely operated vehicles (ROVs) equipped with sampling devices designed specifically for this project, the researchers filtered plastic particles out of seawater on multiple occasions at two different locations and various depths—from five to 1,000 meters (16 to 3,281 feet) below the surface in the Monterey Bay. Some samples were collected just offshore from Moss Landing Harbor, but the majority were collected about 25 kilometers (15.5 miles) from shore, in the deep waters of Monterey Canyon.

The results surprised the team. They found nearly identical concentrations of microplastic particles near the surface and in the deepest waters surveyed. Perhaps more startling, they found roughly four times the concentration of microplastic particles in the midwater range (200 to 600 meters, or 656 to 1,969 feet) than in the surface or deepest waters sampled.

MBARI engineers spent considerable time and effort developing a device to avoid contamination and carefully collect and filter microplastics deep below the surface of Monterey Bay.

Microplastics were discovered in all animals sampled

In addition to sampling the water, the researchers looked at concentrations of microplastic particles in specimens of two marine species that filter-feed in the water column—pelagic red crabs and giant larvaceans. The team found microplastics in the bodies of all of the animals they examined.

Pelagic red crabs and tadpole-like giant larvaceans are critical components of ocean food webs. Pelagic red crabs are commonly found in large numbers near the ocean’s surface, where they are consumed by many species of fishes, including tunas, and some marine mammals. Larvaceans create large mucus filters that collect organic material—and microplastic—and then discard those filters, which other animals consume as they sink to the seafloor.

More microplastics in samples originated from consumer products than fishing gear

Plastic found in the depths of Monterey Bay were the same types commonly found in consumer goods, as seen here washed up on a Monterey Bay beach. Image courtesy of Hank Armstrong, Monterey Bay Aquarium.


Equipped with a microscope and a laboratory technique called Raman spectroscopy, researchers from Arizona State University contributed to the study.

The most abundant plastics found—polyethylene terephthalate (PET), polyamide, and polycarbonate—are commonly used in consumer products, including food and beverage packaging such as single-use drink bottles and to-go containers. Most of the microplastic particles the researchers discovered were highly weathered, suggesting they had been in the environment for many months or years.

Even though Monterey Bay is home to commercial fisheries, the researchers found very few particles of polypropylene or other plastics commonly used in local fishing gear. They also detected more microplastic particles offshore than nearshore.

“This suggests that most of the particles did not originate from local fishing gear,” explained Kyle Van Houtan, chief scientist at Monterey Bay Aquarium and one of the study’s co-authors. “It also suggests that at least some of the microplastic was transported into the area by ocean currents.”

This finding could indicate that plastic is widely distributed offshore.

Bruce Robison, a senior scientist at MBARI and co-author of the paper, added: “These results are intriguing and show the need for similar deep-water surveys in other locations so we can find out how widespread the problem is.”

The research team is now developing “plastic ingestion profiles” for a broader suite of midwater animals that comprise the deep pelagic food web of Monterey Bay. They will study whether plastic transfers through feeding and whether particular animals that feed a certain way, or live at a specific depth, ingest more plastic than others. Researchers will also focus on whether the concentrations of toxins associated with plastics are correlated with the plastic loads in the gastrointestinal tracts of the same species.

The research team is sharing study results with a range of audiences. Some 30,000 people have viewed a video jointly produced by the Monterey Bay Aquarium and MBARI about the study. MBARI’s Katija shared her expertise with students participating in the National Geographic GeoChallenge to generate solutions to the critical ocean-plastics problem.

Policy experts at the Monterey Bay Aquarium indicate that making and using less plastic is the most effective means of addressing the ubiquitous presence of plastic pollution throughout the water column. It may be virtually impossible to remove existing microplastics from the deep sea, but slowing the flow of plastic from land will decrease how much plastic accumulates in our global ocean.

Bioluminescence: Behavior, biochemistry, and genomics

Researchers are teasing out the mysteries of bioluminescence for deep-sea organisms that create their own light.

Learn more