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The giant oceanic manta ray (Manta birostris) uses lobe-shaped structures to bounce plankton off their gill filters and into their mouth. Credit: S Kajiura/Florida Atlantic University

Science

Researchers at Oregon State University have recently discovered that manta rays are able to filter plankton from seawater using a system never seen before in the natural or industrial world. The findings, published in Science Advances, describe a unique mechanism which resists clogging and therefore offers a new approach for designing filtration systems on an industrial scale.

Manta rays are large cartilaginous fish closely related to sharks, skates and other rays. They feed by filtering small crustaceans and zooplankton through their open mouths before flushing the remaining water out through their gills. Unlike most conventional filtration systems used worldwide, manta rays can resist clogging by using leaf-shaped lobes to bounce the food away. “Manta rays appear to utilize a novel mechanism for filtering particles out of fluids," said study co-author Jim Strother, assistant professor of integrative biology in the OSU College of Science. "Their filtering apparatus has a special structure that causes plankton particles to ricochet off the filter and become concentrated in the mouth cavity, so the fish can then ingest them."

Strother and colleagues took CT scans of manta ray specimens from museum collections and then built a 3D printed replica of the filter found in the giant oceanic manta ray, Manta birostris. The replica was then placed in a flow tank with small objects and a coloured dye to represent various sized food particles. Computer modeling also helped calculate the trajectory of the particles as they entered the mouth.

This incredible design raises questions concerning the importance of manta rays to marine habitats and how they are distributed. “This system might conceivably enable larger animals to exist in areas with less food” because it’s energy efficient, says Stuart Humphries, an evolutionary biophysicist at the University of Lincoln in England who wasn’t part of the study. Rays are increasingly being targeted by illegal fishing practices and a greater understanding of the physiology of filter feeding may be useful for predicting the habitat usage of manta rays and implementing appropriate protective measures.

Furthermore, the strategy could inform better filter designs at wastewater treatment plants, which fail to catch microplastics. A filter inspired by the manta ray’s mouth might trap tiny pollutants before they escape into our oceans and harm wildlife.

By Ellis Moloney

Raj V. Divi, James A. Strother, E. W. Misty Paig-Tran. Manta rays feed using ricochet separation, a novel nonclogging filtration mechanism. (2018) Science Advances, 2, 4 (9): eaat9533 DOI: 10.1126/sciadv.aat9533

This study was supported by the CSUF Jr./Sr 2017–2018 Intramural Award, the Stephen and Ruth Wainwright Fellowship, and the Sigma Xi Grant-in-Aid of Research Award.