A study led by Matthew Savoca of the National Oceanic and Atmospheric Administration (NOAA) has found that when algae grows on tiny bits of plastic in the ocean, it gives off an odor that attracts fish, leading fish to seek it out.
The study, “Odors from marine plastic debris induce food search behaviors in a forage fish,” was published in Proceedings of the Royal Society B. Savoca additionally explained his findings in layman’s terms in an article, “Bait and switch: Anchovy eat plastic because it smells like prey,” in The Conversation, published 16 August.
He found that fish – in this case, Northern anchovies – not only visually mistake microplastic for food, but also actively seek it out based on the smell it acquires.
The authors used wild-caught schools of Northern anchovy (Engraulis mordax) in numbers high enough to observe their schooling behavior. They watched how the fish moved when eating krill, and observed that the fish formed a tighter school, and instead of swimming directly into the stream varied their body positions. They then put some unscented seawater into the tank as a control and the fish did not display feeding behavior. They made two kinds of “tea” by soaking plastic debris from the ocean in seawater and by soaking clean plastic in seawater, and introduced each of these into the tank. The tea from the clean plastic induced no feeding behavior, but the tea from the plastic debris did – the fish formed a tighter school and varied their body positions, as they had done when eating krill.
They were thus able to show that the odor from the plastic debris – probably due to biofouling with algae – was attracting the fish. It was already known that fish eat plastic, but it was not clear if they just visually mistake it for food or if odor was also involved. The smell that attracts the fish may be from dimethyl sulfide (DMS) produced by the algae, which certain marine animals use to find food.
The study of anchovies is significant because the species is eaten by so many other fish, so what they eat ends up in the food chain, including many species eaten by humans.
Ron Buckhalt, director of seafood marketing at the Maryland Department of Agriculture, who worked for the federal government as director of the U.S. Department of Agriculture’s BioPreferred Program, expressed concern at the study’s results but said a solution to the problem existed.
“There is a way out,” he said. “All single-use items must biodegrade 100 percent in a marine environment. Non-compostable plastic must have a premium that would force recycling. It would have to be worldwide edict. There is also hope that as industries worldwide continue to develop new chemical pathways to produce bioplastics, these compostable products become more affordable.”
Buckhalt said the term “in a marine environment” is significant, since not all plastics labeled as “biodegradable” break down in a marine environment – the process often requires heat or sunlight.
The global problem of plastic ingestion has been further exposed by another recent report that shows plastic is increasingly appearing in tap water.
The study, commissioned by journalism site Orb, tested tap water samples from a dozen countries on five continents and found that 83 percent of samples tested positive for microplastic. The rate of prevalence varied according to the specific locales within each country, but in all of the tested cities plastic fibers were found in over 70 percent of tap water samples. In the USA, 94 percent of water samples were contaminated by plastic, including at the headquarters of the Environmental Protection Agency.
Such microscopic fragments enter the water system in multiple ways, reports Orb. In addition to the single-use items mentioned by Buckhalt (plastic forks and the like), sources include synthetic fibers from clothing, paint, dust from tires, and microbeads (which have been banned in the U.S. since 2015.)
“Plastic is all but indestructible, meaning plastic waste doesn’t biodegrade; rather, it only breaks down into smaller pieces of itself, even down to particles in nanometer scale — one-one thousandth of one-one thousandth of a millimeter,” the report said.
