Tiny Fiddler crabs are hoovering up and breaking down microplastics, study finds

Tiny crabs have secretly been playing an “unheralded role” in cleaning up the planet by hoovering up microplastics.

A new study, published in the journal Global Change Biology, tracked a population of Fiddler crabs – which grow no bigger than the width of a Post-It note – in a highly polluted mangrove forest on the north coast of Colombia.

Here, years of urban and agricultural expansion have degraded the mangrove systems, resulting in some of the highest levels of plastic contamination reported anywhere in the world.

Despite this, researchers found that the arthropods were “thriving” and are able to ingest and break down large quantities of small plastic particles in the sediment. With the reputation of being an “ecosystem engineer”, these crabs can break down plastics within days, acting much faster than sunlight and waves.

How fiddler crabs adapt to microplastics

While scientists have previously discovered that fiddler crabs will ingest plastic in laboratory settings, this is the first study of its kind to see whether they will avoid plastic in the natural environment or “adapt to its presence”.

Researchers from Universidad de Antioquia in Turbo and Medellin, the University of Exeter, and the Corporation Center of Excellence in Marine Sciences (CEMarin) selected five one-metre-square plots of urban mangrove and sprayed 100ml solutions containing polyethylene microspheres. These are tiny plastic particles that emit bright colours when illuminated by UV light.

They repeated this process over the course of 66 days, before sampling the soil and 95 crabs.

“We wanted to learn how the microspheres are distributed among the major organs and to find out whether the crab’s interaction with microspheres resulted in their physical fragmentation into smaller particles,” says lead researcher, Professor José M. Riascos.

The study found that the crabs had accumulated microplasticsat 13 times the concentration found in the sediments. These particles were not evenly distributed in the crabs’ organs, but the greatest quantity was found in the hindguts.

Many of the microplastics were fragmented further in the process, with the team concluding that the animal’s specialised grinding gut, together with plastic-degrading bacteria, could be aiding this process. There was also a greater chance of finding fragmented particles in females than in males.

Are microplastics harming fiddler crabs?

Researchers warn that the fiddler crab’s fascinating ability may come at a cost – potentially releasing harmful nanoplastics into their tissues and subsequently into the food chain.

It highlights the importance of further research to find out whether these microplastic fragments are hindering fiddler crabs’ health and being passed on to their predators.

Researchers still don’t know exactly how – or how much – microplastics affect health outcomes. However, multiple studies have warned of potential links to serious issues such as cancer, respiratory problems and heart attack.