Microplastic pollution threatens hermit crab populations

New research from Queen’s University Belfast and Liverpool John Moores University reveals how the microplastic pollution crisis is threatening biodiversity.

Currently up to 10 per cent of global plastic production ends up in the sea although the understanding of how this affects marine life is limited. The research, published in Biology Letters, focused on the impact of plastics on hermit crabs, which play an important role in balancing the marine ecosystem. 

Hermit crabs do not develop their own shells but instead take shells from snails to protect their soft abdomens. As a hermit crab grows over the years, it will need to find a succession of larger and larger shells to replace the ones that have become too small. These shells are vital in protecting and enabling hermit crabs to grow, reproduce and survive. 

The researchers found that when hermit crabs were exposed to microplastics, they were less likely to later touch or enter high-quality shells.

Dr Emily Bethell, Senior Lecturer in the School of Biological and Environmental Sciences at LJMU and co-author on the paper, explains: “This research shows that exposure to microplastics can disrupt hermit crab behaviour. We found that the presence of microplastics in the environment impaired their ability to select the best shells available.”

To investigate the impact of microplastics, the research team divided hermit crabs between experimental tanks, half containing microplastics while the other half had no plastic. After five days, the hermit crabs were moved into low-quality shells with the option for alternative high-quality shells offering more protection. 

Dr Arnott, lead researcher from Queen’s University, explained: “Hermit 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.

“Additionally, commercially valuable species prey on hermit crabs, such as cod, ling, and wolf-fish. 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."

Students at LJMU have the opportunity to study hermit crab shell selection behaviour and the impact of marine pollution on animal behaviour and cognition on a number of degree programmes in the School of Biological and Environmental Sciences including: BSc Animal Behaviour, BSc Wildlife Conservation, BSc Zoology.