Anela Choy studies the things that deep-sea creatures eat, which means that, in effect, she is often studying plastic. Over the years, pieces of debris would show up again and again in the stomachs of certain fish, species that rarely come to the surface to feed. The plastic, she realized, must be going down to them.
Microplastics—tiny pieces less than five millimeters in size—have largely been studied as a problem of the ocean surface. Plastic tends to be buoyant, the thinking goes, and the ocean surface is frankly easier to study. But Choy, who is a biological oceanographer now at the University of California at San Diego, wanted to go deeper. In 2017, she and a team sent a specially designed remote-operated vehicle (ROV) down 3,200 feet in California’s Monterey Bay, systematically sampling up and down the water column.
It turns out that far more microplastics are hidden deep in the ocean than on the surface. The ROV found the highest concentrations of microplastics in water 200 to 600 meters, or 650 to 2,000 feet, below the surface. What’s more, those levels were comparable to the concentration closer to the surface of the infamous Great Pacific Garbage Patch, where ocean currents trap microplastics.
If anything, Monterey Bay is famously clean. “The Monterey Bay is considered a success story. It’s a beautiful place. The sardine and fish population have come back from crashes in the mid-1900s,” says Kyle S. Van Houtan, the chief scientist at the Monterey Bay Aquarium and a co-author of the study. “However, if you go below the surface, there’s more of a concentration of plastic than where many people consider the dirtiest: the Great Pacific Garbage Patch.”