Fish Prefer Eating Dangerous Plastic Pollution

When European perch were exposed to polystyrene microplastics, their survival rate dropped, a new study shows.
Perch larvae that ingested plastic particles ignored signs of predators like this juvenile pike, cutting their survival rate. (Photo: Oona Lönnstedt)
Jun 2, 2016· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

Just as humans often love to shove sugar and fat into their mouths, a new study finds that some fish can’t stop eating dangerous plastics. And just as with people, this unnatural diet is killing them.

For the study, published Thursday in Science, researchers from Uppsala University in Sweden collected European perch eggs from the Baltic Sea, took them into the lab, and exposed them to varying levels of polystyrene microplastics. The plastics, they found, reduced the hatching rates by about 15 percent and made the larvae that survived less active.

The exposed larvae ignored the scent of nearby predators, dramatically reducing their chances of reaching adulthood. They also showed a preference for eating plastic particles even when real prey were also present, completely ignoring readily available supplies of zooplankton, their normal food.

“I remember looking at larvae in the microscope and just seeing so many little plastic pieces in the stomachs of fish after fish,” said marine biologist Oona Lönnstedt, the study’s lead author. “It was terrifying and very sad.”

A larval perch from the Baltic Sea has a stomach full

of microplastic waste particles. (Photo: Oona Lönnstedt)

Lönnstedt and coauthor Peter Eklöv focused on European perch because the species has experienced a dramatic population decline since the mid-1990s. “We decided to examine if there could be a link to microplastic pollutants which accumulate in shallow coastal habitats, which are a growing threat in the Baltic Sea,” she said.

Earlier studies showed declining perch abundance during earlier life stages, but the cause remained unclear, Lönnstedt said. This study may explain that collapse.

The study differs from some previous studies on microplastics and marine life, said Lönnstedt, because it demonstrates that plastic particles affect not only physiology but also behavior. “This is a serious cause for concern, in particular since microplastic waste often accumulates in shallow coastal areas where many developmental stages of aquatic organisms can be found,” she said.

The finding comes at a critical time for the Baltic Sea, where declines in perch and another large predator, the pike, have created cascading effects in the local ecosystem. Lönnstedt said the populations of smaller predators, such as the three-spined stickleback and sprat, have “dramatically increased in coastal and offshore habitats” without the larger predators to keep them in check. That has led to over-predation on smaller plant-grazing fish, which in turn has allowed algae to bloom to nuisance levels.

Perch and pike are both popular fish among recreational anglers, whose industry has suffered as a result of the fishes’ decline.

Previous studies cited in the new study found an average of 7,000 to 10,000 microplastic particles per cubic meter along the Swedish coast.

Lönnstedt said the research continues on multiple fronts. She and Eklöv have conducted similar polystyrene experiments with pike, flounder, and damselfish, all of which “seem to respond in a very similar manner as perch,” she said. “We will continue to examine how different species are affected by microplastic particles to see how wide-ranging this is.”

They’re also looking at how other types of plastic affect various species. “Now we know that polystyrene is bad, but we also need to compare it to the other common polymers, such as polyethylene and PVC,” she said.

The team is also studying fish in the environment to see if they are changing their diets in favor of plastic. “We have collected larvae from the field and found that they have indeed ingested plastic, but this needs to be studied more in depth,” Lönnstedt said.