From Prey To Predator: Microplastics Found To Move Up The Marine Food Chain

Half of all observed seal scat contained plastic particles. David J. Martin/Shutterstock

It’s been shown that fish not only mistake plastic for food, but may in fact actively seek it out. Now, researchers say microplastics are making their way up the food chain.

For the first time, scientists found that little plastic bits eaten by fish can transfer to the marine predators that eat them. The new finding was published in Elsevier

It’s a process called trophic transfer and it has been observed in animals further down the food chain, like mussels and crabs. Researchers have long assumed it happens in marine mammals as well but lacked the evidence to prove it. Until now.

“We have shown that trophic transfer is an indirect, yet potentially major, route of microplastic ingestion for these predators," said lead author Sarah Nelms in a statement. "By examining scat from captive animals and the digestive tracts of fish they were fed upon, we could eliminate the possibility that the seals were eating plastic directly and be sure that any microplastics we found in their scat came via the fish."

Since it would be difficult to tell whether the wild animals were directly consuming plastics, researchers studied the feces of captive grey seals and the digestive tracts of wild-caught Atlantic mackerel fed to the seals. They found one-third of the mackerel and half of the seal poo contained microplastics.

It seems wildlife can’t escape humanity’s fixation with plastic. Nearly every continent and every body of water is accumulating plastic – it's even building up in the remote Arctic.

Animals as small as zooplankton and as large as whales have been recorded eating plastic. When consumed, plastics can obstruct the digestive system, as well as cause internal physical damage, inflammation of the intestines, and difficulties eating.

In an unrelated study, researchers found 73 percent of Northwest Atlantic deep-sea fish are also consuming microplastics – the highest reported frequency of plastic-eating fish in the world. 

Microplastics are plastic fragments broken down from larger items and can come from all sorts of things. Take, for example, the plastic that is shed each time you wash your clothes or the little dots in your toothpaste. Just like Nemo, both eventually make their way to the ocean.

In the case of seal scat and mackerel guts, researchers say ethylene propylene was most frequently detected. It’s one of the most commonly used and fastest growing rubbers and is found in everything from roofing materials to car windows to garden hoses. Particles averaged around 2 millimeters long and were mainly black, clear, red, and blue in color.

If seals are ingesting plastic from fish, that means people could be too.

“The world is awakening to the gravity of the plastic problem and the possible negative impacts of microplastics in the marine environment," said researcher Professor Brendan Godley.

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