What does a thriving coral reef sound like? Researchers from Woods Hole Oceanographic Institution monitored the acoustics of a healthy coral ecosystem in the U.S. Virgin Islands and rebroadcast the recordings at degraded sites to attract settlement by coral larvae.

After documenting 12-hour soundscape recordings of a healthy reef, researchers installed solar-powered underwater speakers at sparsely populated sites. Captured mustard hill coral larvae contained in screened cups were then zip-tied to rebar stakes hammered into the sand at each reef, at distances of 1 m to 30 m from the speakers and exposed to rebroadcasts of healthy reef sounds for three nights.

On average, coral larvae settled at rates up to seven times higher with the enriched sound environment relative to test sites receiving no sound input. The highest settlement rates were observed at 5 m from the speakers, but even the polyp-bearing cups placed 30 m away had more larvae settling to the bottom than at the sites lacking the stimulatory effect of sound.

“The fact that settlement is consistently decreasing with distance from the speaker, when all else is kept constant, is particularly important because it shows that these changes are due to the added sound and not other factors,” explained the researchers. “This gives us a new tool in the toolbox for potentially rebuilding a reef.”

The research is published in Royal Society Open Science.