Hermit crabs are struggling to find shells to live in due to the impact of microplastic pollution.
Scientists found specimens of the crabs collected from the Irish coast and exposed to microplastics were more likely to make poor choices and end up living in low-quality shells.
"These shells are vital in protecting and enabling hermit crabs to grow, reproduce and survive," explained Dr Gareth Arnott of Queen's University, Belfast who led the study.
He said diminished ability to choose well would have serious long-term consequences for the crabs.
Hermit crabs are unusual in that they are soft-bodied and must repeatedly find new snail shells to make their home in as they grow or when their existing home is damaged.
The study found they were reluctant to seek a new shell to replace the poor-quality one they were living in, and were less able to recognise a better-quality alternative when it was offered to them.
Some 10pc of plastic waste globally ends up in the sea, and microplastics are being found all around the Irish coast and in the digestive systems of even the smallest sea creatures.
Dr Arnott said hermit crabs were vital for marine health.
"These crabs are an important part of the ecosystem, responsible for 'cleaning up' the sea through eating up decomposed sea life and bacteria," he said.
They were also an important food source for fish such as cod and ling, 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."