Blue Planet 2: Parrotfish crunch coral with teeth made from the ‘coolest biominerals of all’

Fish 'beaks' are made of woven crystals, providing them with enormous strength

Viewers of Sunday’s episode of Blue Planet 2 were treated to the spectacle of parrotfish eating stony coral, only for it to emerge the other end as sand.

Through this process, a single parrotfish can produce around 400 kilograms of sand every year.

This digestive beach building would not be possible without the parrot-like "beaks" – actually made of modified teeth – that give these fish their name.

The hardness of these teeth is equivalent to a stack of about 88 African elephants compressed to a square inch of space.

Matthew Marcus, a researcher at Berkeley Lab, wanted to investigate the structure of this fish’s beak to find out what endowed it with such strength.

“This is a fish that crunches up coral all day, and is responsible for much of the white sand on beaches,” Mr Marcus said. “But how can this fish eat coral and not lose its teeth?”

In a new paper published in ACS Nano, Marcus and his collaborators have revealed the source of the parrotfish’s powerful bite. Their findings even suggest future designs for materials that mimic the durability of parrotfish teeth.

The researchers used X-ray techniques to reveal an “interwoven fibre nanostructure”. Crystals of a mineral called fluorapatite are woven together in a chain mail-like arrangement.

It is this structure that gives parrotfish teeth their incredible durability.

“Parrotfish teeth are the coolest biominerals of all,” said Professor Pupa Gilbert, a biophysicist at the University of Wisconsin-Madison and the leader of this study. “They are the stiffest, among the hardest, and the most resistant to fracture and to abrasion ever measured.”

Professor Gilbert suggests that “weaving crystals” to imitate this structure could be a way of producing new synthetic materials.

Efforts are already underway to replicate the structure of human tooth enamel artificially, but the teeth of parrotfish present an exciting opportunity to make something really durable.

The properties shown by their teeth would make useful additions to mechanical components found in electronics, for example, which must often withstand a lot of strain.