If a fish eats plastic, it can end up wanting more. In a study of baby perch from the Baltic Sea, Swedish researchers found that tiny particles of microplastic are like junk food for fish. Like junk food for humans, it's a preference that might end up killing them.
When plastic ends up in the ocean, it eventually breaks down into pieces that are less than five millimeters across, and those tiny pieces can last hundreds of thousands of years. In the study, the researchers raised fish larvae in three aquariums: one that tried to recreate the average amount of plastic in the ocean now (up to 10,000 particles per cubic meter), another without any microplastic, and a third with even higher levels.
Because plastic tends to accumulate in shallow water next to coastlines—where fish grow up—it's likely that young fish are exposed to higher levels of it. That causes problems. The researchers found that fish exposed to the most plastic were smaller, less active, and more likely to spend time completely motionless. Even worse, they no longer responded naturally to predators—so they were more likely to be eaten.
The fish raised with the most plastic also chose to eat it instead of real food. "Apparently fish are attracted to things that look different in some way—it creates a signal," says Peter Eklöv, a professor at Uppsala University and one of the authors of the paper. "That's the only explanation we have for it."
In the worst case, the fish ate so much plastic that their stomachs contained nothing else. When they were exposed to predators, all of the fish from the high-plastic tank were eaten within a day. The researchers think it may be one explanation for why perch populations are declining in the Baltic Sea, along with pike, their natural predator.
It's the first study to really look at how ocean plastic pollution is affecting ecology, though others have looked at issues like toxicology. "I think it's very important now that we go further and look more into what other interactions, how plastic can interact with the natural food web," says Eklöv.
The study looked at one of the major types of plastic pollution, polystyrene, and the researchers hope to look at other types next. They also plan to study how plastic affects other species, and whether it ends up in the food chain.
Each year, the world produces around 300 million metric tons of plastic, a number that is quickly growing. An estimated 8 million tons of that ends up in waterways and eventually the ocean.
"There are different ways we could deal with the problem," says Eklöv. "To start with, we could ban microplastics in consumer products." The U.S. ban on microbeads in consumer products, such as shower gels, will begin in 2017. The next step, he says, is better understanding where other plastic pollution comes from, so it can be stopped. Car tires, for example, are responsible for about half of plastic pollution.
"I have no solution to that," he says. "But I think if we can start a discussion and get the awareness of how we spread microplastics in the environment, we can reach into that set of policies for how we can deal with the problem."
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