Zooplankton? No thanks. Some baby fish now prefer plastic, say scientists

Humanity's plastic debris isn't just polluting the ocean, it's also changing some of its young inhabitants' dietary preferences.

Baby fish exposed to microplastics tended to eat the plastic particles instead of free-swimming zooplankton, their own natural food source, a study published in the journal Science has found. Researchers at Uppsala University found that the larval fish that were exposed to microplastic particles displayed a shift in behavior and stunted growth, leading to higher mortality rates.

Microscopic plastic particles, which are defined as being smaller than five millimeters, originate from larger plastic waste that ends up fragmenting, or from microscopic manufactured plastics, such as microbeads in hygiene products. They enter the ocean as waste from waterways and tend to concentrate in shallow parts of the ocean, along the coasts, threatening the development of fish. While there has been concern that microplastic waste accumulation could impact the marine ecosystem, this has been the first study to illustrate the effects on developing fish.

"Fish reared in different concentrations of microplastic particles have reduced hatching rates and display abnormal behaviors," said lead author Oona Lönnstedt from Uppsala University, in a press release. "The microplastic particle levels tested in the current study were similar to what is found in many coastal habitats in Sweden and elsewhere in the world today."

Researchers found that the growth of larval perch exposed to microplastic polystyrene particles was stunted, a condition the scientists attributed by the fish's preference for eating plastic while ignoring their natural zooplankton food source.

"This is the first time an animal has been found to preferentially feed on plastic particles and is cause for concern," said Peter Eklöv, an ecologist at Uppsala University.

Dr. Lönnstedt added that larvae that were exposed to microplastic particles during their development also displayed a change in behavior and were less active than fish that grew up in water free of microplastic particles. "Furthermore, fish exposed to microplastic particles ignored the smell of predators which usually evoke innate antipredator behaviors in naive fish," said Lönnstedt.

Without any behavioral defenses, larvae were more vulnerable to predators. For example, when they were put in the same location as pike, a natural predator, the fish exposed to microplastic particles were four times more likely to be eaten than those who were not exposed. Within 48 hours, all the fish exposed to microplastics were dead.

The study sheds light on the consequences of microplastic waste particles in marine ecosystems, illustrating the need for "biodegradable" products in order to reduce how much microplastic waste enters the oceans. A report from the United Nations released in May, however, suggests that the disintigration rates of so-called biodegradable plastics in the oceans are grossly exaggerated.