Underwater Speakers Can Restore Dying Reefs, Study Finds

Record-high ocean temperatures around the world have led to unprecedented levels of coral bleaching and degradation in recent years. Scientists have been searching for ways to restore degraded reefs, and it turns out underwater speakers might hold the answer. 

A new study published in the Royal Society Open Science journal found that speakers used to play the sounds of a healthy reef helped coral larvae settle at rates up to seven times higher than usual. The team attempted the study to expand on prior research showing that coral larvae drop out of water currents and find a place to settle and become reefs when they hear healthy reef sounds like fish splashes or calls. 

Study author Nadège Aoki, a marine biologist at Massachusetts' Woods Hole Oceanographic Institution, told ABC News that researchers have observed that healthier reefs tend to have complex soundscapes and a more diverse arrays of fishes. 

"They have a sound environment that is distinctive and gives kind of an acoustic signature to the reef," Aoki said. This often includes the sounds fish make by eating or scratching against coral or strumming on their swim bladder. 

To reach their conclusions, the researchers collected larvae from adult mustard hill coral colonies and placed them at distances of one, five, 10, and 30 meters from solar-powered speakers that played the sounds of a healthy reef recorded about 10 years earlier. Upon further inspection, they found that the larvae that were closest to the speakers settled at a rate of about twice as much. "This effect decreased as you got farther away from the speaker," Aoki said. "Low-frequency sound appears to have an impact on their settlement behavior as well."

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The findings are promising for those hoping to preserve the beauty of coral reefs in the coming decades as we continue to deal with climate issues above and below the water's surface. 

"We're observing thermal heating and bleaching events happening at more regular frequencies than they have in the past," Aoki explained. "That makes it very difficult for reefs to have sufficient time to recover and grow back in between these disruptive events."

Reef populations have been dying in the past several decades due to warming water temperatures, increased ocean acidity, pollution, and habitat loss, with some scientists estimating as much as half of all of Earth's reefs have died since the 1950s. Looking forward to the future, then, reefs will need as much help from humans as possible to continue to live.