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When it comes to moving home, hermit crabs are adept, often exchanging shells for the optimal abode.
But now researchers have discovered that exposure to microplastics alters this key behavior. The findings are the latest to suggest that such contamination may be having an impact on the world’s sea creatures.
“Generally, a hermit crab called ‘normal’ will always want to go for the best shell,” said Dr. Gareth Arnott, co-author of the new research from Queen Belfast University, adding that such shells are typically those of the marine snails.
“The amazing thing about this study was when [we offered them a better shell], many of the crabs that had been exposed to microplastics did not make the optimal decision to take [it],” he said.
Microplastics, pieces of plastic 5 mm or less, are a growing research topic, and previous studies show that they are present even in the deep ocean and end up in the bodies of living organisms, from seals to crabs and seabirds. .
However, while there is some evidence that exposure to such contamination has affected growth and reproduction in some animals, research on the specific effects on animal behavior and cognition is still scant.
Arnott and colleagues placed 29 female hermit crabs in a tank containing seawater, algae, and 4mm diameter polyethylene beads, at a concentration similar to levels found in the environment. Another 35 female hermit crabs were placed in a similar tank, but without the polyethylene beads.
After two hours in their new shell, each crab was placed in a deep plate of seawater and the team presented another shell, this time an ideal weight.
The team found that 25 of the crabs that had not been exposed to microplastics explored the optimally sized shells, with 21 of the crabs, 60%, residing in them.
By contrast, crabs that had been exposed to microplastics took longer to begin such an exploration, and far fewer did so: only 10 made contact with the optimally sized shells and only nine, 31% of the group, moved home.
This suggests that exposure to microplastics affects hermit crab shell selection behavior, according to the team, indicating that contamination may be affecting cognition.
“This shell selection behavior is an example of a cognitive process: the animal has to collect information about the shell and then has to decide how it is going to use that information,” Arnott said, adding that he was surprised by the results.
However, the team says there is much more to do, including looking at whether different types of microplastics have a similar effect, exploring whether microplastics actually enter the crab, and unraveling the mechanism for the effect.
“We assume that either some aspect of the polyethylene is being introduced into them to affect their decision making, or it is an indirect effect that the presence of the plastic in the tank could be influencing their feeding behavior, for example,” said Arnott .
He added that the study only looked at hermit crabs, and it will be important to explore whether the observed behavioral changes in the lab are seen in nature and have real-world implications.
“Based on the surprising finding [in this study] this would suggest that there could be a long-term impact on the natural world, but we need to do more work on that, “he said.
