Study finds microplastics can impair hermit crabs’ shell selection

The mountain of plastic waste making its way into the ocean each year is undoubtedly impacting marine life, and bit by bit scientists are starting to understand the extent of these potentially disastrous effects. A new study out of the UK has revealed what this pollution might mean for hermit crabs, with an environment rich in microplastics seeming to affect their cognitive performance when selecting a home.

The study was carried out by scientists at Belfast’s Queen’s University together with researchers from Liverpool John Moores University, who set out to explore the impacts of plastic pollution on hermit crabs. These creatures play a vital role in stabilizing the marine ecosystem, through what they consume, who they are consumed by and the species they carry along for the ride.

“These crabs are an important part of the ecosystem, responsible for ‘cleaning up’ the sea through eating up decomposed sea-life and bacteria,” says Gareth Arnott, lead researcher from the School of Biological Sciences at Queen’s University. “By providing a hard, mobile surface, hermit crabs are also walking wildlife gardens. They host over 100 invertebrate species – far more than live snails or non-living substrates. Additionally, commercially valuable species prey on hermit crabs, such as cod, ling, and wolf-fish.”

A total of 64 female common European hermit crabs were recruited for the experiment, with around half placed in a tank containing small microplastic fragments, and the other half in uncontaminated water. In doing so, the team wanted to find out whether the plastic pollution impacted a key survival tactic in hermit crabs, an ability to investigate and inhabit larger, superior shells as they grow larger and wiser.

After five days in their respective tanks, both groups of crabs were placed into “suboptimal” shells inside an observation tank, where they were presented with a better alternative. The crabs that had been living amid the plastic pollution took longer to first contact the superior shells and then to enter them, than the control group. The researchers say these results suggest that the microplastic-rich environment had impaired their cognition and, by extension, their ability to carry out an essential survival behavior.

“Our research shows that exposure to microplastics can have important effects on animal behaviour,” says Arnott. “More specifically, in this case it had a detrimental effect on shell selection behaviour in hermit crabs. As this behaviour is vital for hermit crab survival and reproduction, there could be important long-term consequences.”

There are parallels between this and another interesting microplastics study from last month that found the tiny fragments could give fish aneurysms, and another last year that found they could weaken the ability of mussels to grip onto rocks. And with evidence of plastic pollution only turning up in more and more species, concerns are only growing over its broader effects on marine biodiversity.

“With these findings of effects on animal behaviour, the microplastic pollution crisis is therefore threatening biodiversity more than is currently recognised so it is vital that we act now to tackle this issue before it becomes too late,” says Arnott.

The research was published in the journal Biology Letters.

Source: Queens University

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