The Current

Putting loudspeakers in the ocean can help coral reefs, says marine biologist

Scientists say that coral reefs have a distinct sound — and it's quite different if the reefs are healthy, or dying. But by playing the sound of a healthy reef underwater, Tim Gordon says at-risk reefs can be saved.

Reefs are some of the noisiest ecosystems underwater, according to Tim Gordon

Marine biologist Tim Gordon deploys an underwater loudspeaker on a coral reef. (University of Bristol)

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A new study has found that underwater speakers and the use of sound can help to nurse dying coral reefs back to health.

Marine biologist Tim Gordon said the unusual experiment worked because while many people think of the ocean as silent, healthy coral reefs "are some of the noisiest ecosystems there are underwater."

"There's this constant crackle of shrimps clicking their claws, and invertebrates making noise as they scrape along the bottom," he told The Current.

"Fish are making all sorts of whoops and grunts and clicks and buzzes — it's a complete cacophony down there."

Listen to Tim Gordon describe the kinds of sound in a coral reef:

Marine biologist Tim Gordon describes some of the sounds you'll hear in the cacophony of a coral reef 1:03

Gordon is part of a team of scientists that studied how climate change and warming oceans are damaging reefs, focusing on the northern Great Barrier Reef off the east coast of Australia.

He explained that the noise of a healthy, bustling reef is important to attract more life, particularly juvenile fish that start life in the open ocean.

But as warming oceans have damaged reefs, the number of creatures living there has declined. That means a quieter reef, with less noise to attract new life.

Fish and other sea-life settle on coral reefs, leaving them teeming with life. (Isla Keesje Davidson/University of Bristol)

Gordon said the silence that can fall on a once-buzzing reef is "quite chilling," adding that sometimes it gets so quiet you can hear waves hitting the nearby shore.

"There's no way you could hear those [waves] in a healthy reef, because they'd just be drowned out by the diversity and abundance of other sound types going on."

Gordon's team then hit upon an idea: could they reverse that decline by sinking speakers underwater and playing the noise of a healthy reef?

"When we made the patches sound like they were healthy, we discovered … twice as many fish came back and settled onto these habitat patches, than when we didn't do anything to the sound," he said.

A coral rubble field in Sulawesi, Indonesia. (Tim Gordon/University of Exeter)

He was encouraged by the results, which were published in Nature last week, saying "that this could be a useful local-scale restoration technique." 

But he warned the technique isn't "a silver bullet" to solve the overall coral reef crisis, describing it instead as "a tool that we can add to our toolkit."

He added that it's important that "we remove the original stressor that caused the damage in the first place — in most instances worldwide, that is climate change and warming seas." 

"Without strong and decisive action on carbon emissions, any reef restoration will ultimately be fruitless."

Written by Padraig Moran. Produced by Ines Colabrese.


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