Microplastics prevent hermit crabs from choosing the best shells

Hermit crabs always have one eye on upgrading their homes, often swapping their shells for others that are a better fit.

But researchers have now warned plastic pollution in the oceans is impairing the crustaceans’ judgement about their optimal abode.

This disruption could have wide-ranging consequences for marine ecosystems due to hermit crabs’ role as “walking wildlife gardens” which host more than 100 other species.

Experiments conducted by biologists at Queen’s University Belfast and Liverpool John Moores University found crabs exposed to microplastics were less likely to touch or enter more suitable shells when available.

Dr Gareth Arnott, lead researcher at the Northern Irish university’s School of Biological Sciences, said: “Our research shows that exposure to microplastics can have important effects on animal behaviour.

“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.”

Hermit crabs do not develop their own shells, instead taking those of snails to protect their soft abdomens. As the crabs grow over the years, they seek out a succession of larger shells to move into.

Australian scientists warned last year that plastic pollution was killing hermit crabs on a vast scale. More than 560,000 have died after being trapped inside waste littering the shores of the Cocos Islands in the Indian Ocean and Henderson island in the Pacific, according to a study published by biologists at the University of Tasmania.

Up to 10 per cent of the plastic produced worldwide ends up in the sea, according to Greenpeace research.

To investigate the impact of microplastics on the crustaceans’ behaviour, Dr Arnott and his colleagues kept 35 female crabs in tanks containing seawater, seaweed and polyethylene beads for five days. A second group fo 29 crabs were placed in tanks without plastic.

All the crabs were then transferred to into “suboptimal” shells and placed into observation tanks with a better-fitting shell.

The crabs that had been exposed to plastic were less likely than the control group to investigate or enter their optimal shell, and those that did took longer on average to move into it.

In a study published in the journal Biology Letters, researchers said their findings suggested microplastics “impair cognition” in hermit crabs, “disrupting an essential survival behaviour”.

Dr Arnott said: “Our research shows for the first time how microplastics are disrupting and causing behavioural changes among the hermit crab population.

“These crabs are an important part of the ecosystem, responsible for ‘cleaning up’ the sea through eating up decomposed sea-life and bacteria.

“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.”

Commercially fished species such as cod, ling, and wolf-fish also prey on hermit crabs, noted Dr Arnott.

He added: “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.”

The team said more research was needed to establish why microplastics changed crabs’ behaviour, the impact of different plastics, and how other species were affected.