Story at a glance

  • A healthy coral reef is a noisy place, and dead reefs are almost silent by comparison.
  • Scientists played the sounds of healthy reefs near dead ones and found that it caused fish, crustaceans and other species to return.
  • Bringing these species back can help ailing reefs recover after they’ve been pushed to the brink by one of the marine heatwaves that have become increasingly common under climate change.

Climate change is ravaging the world’s coral reefs. Marine heatwaves cooked the Great Barrier Reef in 2016 and 2017, killing half of all coral stretched along its roughly 1,400-mile expanse.

Scientists say we will lose 99 percent of the world’s coral reefs if the planet warms by 2 degrees Celsius or 3.6 degrees Fahrenheit. We’re already halfway there, and greenhouse gas emissions continue to increase each year. But scientists are trying to help reefs hang on as long as possible, and the latest strategy involves underwater speakers and a bit of trickery, the Washington Post reports

“Healthy coral reefs are remarkably noisy places — the crackle of snapping shrimp and the whoops and grunts of fish combine to form a dazzling biological soundscape,” Stephen D. Simpson, marine biologist and one of the authors of a new study, told the Post. 

But when ocean temperatures spike, the tiny coral animals eject the photosynthetic algae they require to survive, which causes the reef to turn white — giving “coral bleaching” its name. Bleached coral typically dies, and if enough of a reef bites the dust, the animals that live there leave en masse, leaving behind a silent, bleached ghost reef. 

And this soundscape, or its absence, doesn’t go unnoticed by creatures looking for a new home, according to new research.

During a six-week experiment in the Great Barrier Reef in Australia, scientists placed underwater speakers in reefs that had gone quiet and played the siren song of a thriving coral ecosystem. The researchers found that this more upbeat soundtrack successfully attracted new residents; there were twice as many fish at the dead coral patches where the recordings were being played compared to those that remained silent.

Bringing these species back to a dead reef might seem like a cruel bait-and-switch, but the return of fish and crustaceans can actually help a reef that may seem down for the count get up off the mat. Parrotfish, for example, can help keep harmful types of algae from running rampant, giving corals a better chance of coming back. 

Crucially, the newcomers that were drawn in by the loudspeaker stuck around. The rejuvenated community was also encouragingly diverse, according to the researchers. The number of species increased by 50 percent at the reef patches where the sounds were played, encompassing scavengers, herbivores and predators. 

If this technique can succeed elsewhere and on larger scales, it could help scientists and conservationists rebuild coral reefs around the world that have been battered by climate change, overfishing and pollution. 

Published on Dec 06, 2019