As It Happens

A chemical in plastic is tricking hermit crabs into thinking trash is food

It’s hard to avoid garbage when you’re chemically attracted to it. But such is the life of a hermit crab.

The crabs get 'excited' and 'almost hyperactive' when exposed to the chemical additive oleamide

A common hermit crab forages on the seafloor. (Sven-Erik Arndt/Arterra/Universal Images Group/Getty Images)

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It's hard to avoid garbage when you're chemically attracted to it. But such is the life of a hermit crab.

Hermit crabs are physically drawn to a chemical additive commonly found in plastic products, in much the same way that they are drawn to the scent of food, according to a new study out of the University of Hull in England.

"This is just speculation, of course, but we can assume that if they go around looking for food, they are foraging and they mistake a piece of plastic for food, they would waste a lot of time and energy foraging," Paula Schirrmacher, a PhD candidate in marine science and biology and co-author of the study, told As It Happens guest host Nil Köksal.

"In the world that's already full of lots of different stressors with climate change and ocean acidification, for example, this is just another stressor that makes them waste potentially time and energy."

The findings were published this month in the journal Marine Pollution Bulletin. 

Hermit crabs walk all over a discarded used medical face mask at the bottom of the Adriatic Sea. (Andrey Nekrasov/Barcroft Media/Getty Images)

The researchers wanted to test how hermit crabs off the coast of Yorkshire respond to oleamide, a chemical commonly added to plastic to make it more malleable. 

Oleamide is often found in ocean pollution and it leaches into water, Schirrmacher said.

When exposed to low concentrations of oleamide, the crabs' hearts started racing and their respiration rates increased. That's the same reaction they have to food stimulants. 

"We found that they are excited," Schirrmacher said. "They almost get hyperactive."

No, not that kind of attraction 

A university press release about the study initially misreported the crabs are "sexually attracted" to plastic waste. The error was then reproduced in several news articles. 

Schirrmacher blames that mistake on a "miscommunication with our press office" conflating the study with earlier research that found oleamide may act as a sexual stimulant for male feeder shrimps.

But for the crabs, she said, it's all about finding their next dinner.

"This indicates that oleamide … might be interpreted by other animals in a very different way," she said. "So this problem is much larger than this one particular species, hermit crabs, attracted to this one particular plastic additive. There might be more."

Paula Schirrmacher is a PhD candidate in biology and marine sciences at Hull University in England. (Submitted by Paula Schirrmacher)

The researchers suspect the crabs are "tricked" into thinking plastic is food because oleamide is similar in composition to oleic acid, a chemical released by arthropods during decomposition.

And hermit crabs are scavengers that are attracted to "the smell of death and decay," says Schirrmacher.

She explained that this research is in the early stages and there's still plenty to learn about how plastic affects the natural habits of sea creatures.

We already know the hermit crabs aren't alone in their hunger for dangerous trash. A 2020 study found that sea turtles may also be drawn to the food-like smell of plastic pollution

And scientists have often found piles of of plastic debris lodged in the stomachs of various marine creatures, including turtles, whales and seabirds

"This is definitely a huge problem for wildlife, not just for hermit crabs. It might look cute when the hermit crab has this little bottle cap as a shell, but it is a huge problem that we're facing now," Schirrmacher said.

"We are always hearing about the toxicity of plastic, with entanglement and ingestion of plastic particles by marine life. But what we're kind of forgetting here is why are those animals attracted to the plastic in the first place? And that was one of the main focus of our study here."


Written by Sheena Goodyear. Interview produced by Sarah Jackson.

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