Devil rays' filter-feeding inspires microplastic pollution innovation
Devil rays are colossal animals but they feed on some of the smallest critters in the ocean and the rays' mouth filter shape has puzzled scientists for decades. New research might have now found some answers on how the shape might affect the species ability to filter plankton, while also paving the way for the development of bio-inspired filters.
Researchers exploring the mysteries of how devil rays filter feed on some of the ocean’s tiniest critters believe they may have just stumbled on a unique nature-inspired design that could be replicated to treat wastewater and filter out microplastic pollution.
Known as gentle giants of the ocean, devil rays – or mobula rays – are colossal marine animals that can grow up to 5.2cm in disc width. Despite their size, these creatures feed on some of the smallest organisms found in the marine environment.
Swimming through the ocean with their mouths open, devil rays are designed to take in vast quantities of water and filter out and feast on tiny plankton. To do this, they use a filter that is unlike any you might encounter in everyday life. And it’s a design which, researchers believe, could just change our approach to filtering out the ocean’s nastiest polluters: microplastics.
The devil ray’s filter is made from a large array of small plates, which are oriented in the mouth so that water slides over the tips of the plates. On a mission to understand why the filter has such an unusual shape and how that shape affects the species ability to filter plankton, researchers from the University of Florida’s Whitney Laboratory for Marine Bioscience and California State University, Fullerton joined forces and got to work searching for an answer.
To start, the team created a 3D digital model of a devil ray’s filter using a CT scanner, similar to the equipment used at a hospital for diagnosing injuries.
To better understand how flow moves through the filter, the team then created 3D-printed replicas that could be studied up close in laboratory flow tanks that reproduce the conditions that occur in real animals. They also ran a series of computational simulations to understand the physics behind what they were seeing in the lab.
The research produced surprising results, some that may even pave the way for the development of new bio-inspired filters with improved performance for treating wastewater and mitigating the scourge of microplastics pollution.
The latest study into microplastic pollution has drawn strong links with the growth of bacterial communities responsible for diseases in both humans and animals. The study described that the number of estimated microplastics in the ocean currently exceeds 171 trillion pieces. Microplastics are notoriously difficult to filter owing to their size. These plastic particles, measuring at under 5mm are, however, a widespread environmental pollutant.


A traditional sieve filter operates by trapping large particles in small holes, like a colander that retains pasta while allowing water to drain. As you might expect, sieve filters with smaller holes collect smaller particles, but are more prone to clogging and require higher pressures. However, experiments on devil ray filters indicated something else was happening. As water passed over the unusual small plates of the filter, it created swirling pockets of water in the openings.
This rotating flow caused plankton to bounce off the filter rather than becoming trapped on the surface. When the team examined filters with smaller or larger openings, they found that the swirls of fluid changed size but the filtration properties were mostly unaffected.
This unusual mechanism allowed devil rays to filter out plankton from the surrounding water at higher flow rates and with less clogging than would be possible using a simple sieving filter. These results provide new insights into the biology of this ecologically important group of animals.
Read the full study here.

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