Baby fish are "preying" on microplastic, and it will end up in your stomach

Fish nurseries on the ocean's surface are home to more plastic than fish, and the fish are eating it.

translucent billfish larva on black background

In their earliest days, most ocean-faring fish actually reside in calm ribbons of water at the surface, taking advantage of the food and shelter they can provide. Unfortunately, these aquatic nurseries are also home to a shockingly high concentration of plastic particles — many of them the same size, shape, and color as the baby fish’s favorite foods.

Researchers found that larval fish living off the coast of Hawaii are eating an enormous amount of plastic at a time in their lives when nutrition is especially crucial. The results, published Monday in the journal Proceedings of the National Academy of Sciences, suggest that the plastic accumulating in young fish could end up in humans’ bellies.

The larvae of fish humans love to eat, like swordfish, mahi-mahi, and triggerfish (which apparently tastes like crab) all had plastic inside them, the researchers found. So did flying fish, a common prey animal for tuna, meaning plastic from them could make its way up the food chain and into your tuna salad sandwiches.

two tiny fish shown next to a dime for scale with pieces of plastic
Plastic pieces can easily mimic food, if you're a larval fish. Larval flying fish (top) and triggerfish (bottom) with ingested plastics zoomed in. Dime shown for scale.

The plastic pieces inside the fish were nearly all microfibers: polyester, nylon, polyethylene terephthalate, rayon, and artificial cellulose. And they were “primarily blue or translucent in color” — the same blue color as the fish larvae’s favored food, zooplankton.

As a result, the baby fish might confuse the plastics for their prey, the study suggests.

And the fact that plastic particles are particularly common in areas called surface slicks, or “meandering lines of convergence on the ocean surface,” is a serious problem for these juvenile swimmers, the researchers say.

Surface slicks, explained

Long, narrow ribbons of smooth water run up and down coastlines across the world. These ribbons, known as ‘surface slicks,’ are formed by internal waves and other water movement patterns. In these slicks, larval fish gather; they’re home to more than 40 percent of ocean surface dwellers, the researchers say.

This time-lapse video shows surface slick formation and movement in the coastal waters of Hawaii Island.

Surface slicks also collect most of the floating plastic in these areas of the ocean — nearly 92 percent. And the size of those plastic pieces tends to be small, the same size as the larvae’s prey. In the slicks off the coast of Hawaii, the researchers found 40 percent more prey-sized particles in slicks as compared to ambient water.

It’s perhaps no wonder, then, that the researchers found a disproportionate number of fish larvae chowing down on plastic in these areas. There’s simply more opportunity for ingestion. In the 658 fish the researchers looked at, those found in surface slicks were more than twice as likely as those found elsewhere to have eaten plastic.

The problem is only set to get worse, the study suggests. As larger plastic particles collecting in the ocean break up, they will add to the number of tiny plankton lookalikes in the slicks. Yet more not-food-that-looks-like-food for the baby fish to hoover up.

Protecting the youth

Researchers don’t know what eating plastic does to larval fish in the ocean. In lab-based studies, researchers have observed a number of adverse effects: accumulation of toxins, gut problems like blockage and perforation, and malnutrition. Plastics may even make juvenile fish less skilled at avoiding predators, hints one study.

Since these baby fish’s organs aren’t fully developed, they aren’t able to detoxify and eliminate chemicals as well as adults. As a result, eating plastic could have a “more severe” effect on them than it would on an adult fish, the researchers say.

assorted pieces of plastic
Plastic of all shapes, sizes, and colors from just one surface slick sample.

That — combined with the fact that the young fish gather in the same places as the plastic particles causing damages — sets up a dark future for the larvae, potentially impacting their chances of survival.

The findings underscore the importance of cutting down the amount of plastic that ends up in the water. Improving waste management and reducing overall plastic use could cut the plastic going into the ocean by as much as 80 percent, according to a separate study.

This is especially important, the researchers say, because surface slicks are found all over the world. The problem may not be limited to Hawaii.

In marine ecosystems, larval fish are key food sources for other animals, making them a crucial part of ecosystem functioning.

Their survival is crucial to humans, too. Larval fish grow into the fish humans all over the world depend on for vital nutrition. The more plastic-free those food sources are, the better.

Abstract:

Life for many of the world’s marine fish begins at the ocean surface. Ocean conditions dictate food availability and govern survivorship, yet little is known about the habitat preferences of larval fish during this highly vulnerable life-history stage. Here we show that surface slicks, a ubiquitous coastal ocean convergence feature, are important nurseries for larval fish from many ocean habitats at ecosystem scales. Slicks had higher densities of marine phytoplankton (1.7-fold), zooplankton (larval fish prey; 3.7-fold), and larval fish (8.1-fold) than nearby ambient waters across our study region in Hawai‘i. Slicks contained larger, more well-developed individuals with competent swimming abilities compared to ambient waters, suggesting a physiological benefit to increased prey resources. Slicks also disproportionately accumulated prey-size plastics, resulting in a 60-fold higher ratio of plastics to larval fish prey than nearby waters. Dissections of hundreds of larval fish found that 8.6% of individuals in slicks had ingested plastics, a 2.3-fold higher occurrence than larval fish from ambient waters. Plastics were found in 7 of 8 families dissected, including swordfish (Xiphiidae), a commercially targeted species, and flying fish (Exocoetidae), a principal prey item for tuna and seabirds. Scaling up across an ∼1,000 km2 coastal ecosystem in Hawai‘i revealed slicks occupied only 8.3% of ocean surface habitat but contained 42.3% of all neustonic larval fish and 91.8% of all floating plastics. The ingestion of plastics by larval fish could reduce survivorship, compounding threats to fisheries productivity posed by overfishing, climate change, and habitat loss.

Media via Jonathan Whitney, NOAA Fisheries, Credit: NOAA Fisheries, Jonathan Whitney, David Liittschwager