Coral reefs are the ocean’s vibrant underwater cities and are facing a growing crisis. These ecosystems support countless marine species and the lives of more than a billion people.

Overfishing, irresponsible tourism, coastal construction, nutrient runoff and climate change all threaten coral reefs. But hope is not lost. In a recent study, scientists used the sounds of healthy reefs to stimulate the presence of new coral species.

Reef sounds and coral restoration

Scientists at Woods Hole Oceanographic Institution have discovered that the sound of a thriving reef is inspiring a new generation of coral life. Their research focused on golf coral larvae, tiny organisms that signal the birth of new corals. The sounds made by the reef attract the larvae and they decide to settle there and grow.

“Acoustic enrichment continues to show promise as a technique for increasing the sedimentation rate of corals,” said Nadezh Aoki, a doctoral candidate at the institution.

This technique worked on two coral species and demonstrates the potential of a large-scale reef restoration tool.

Decoding the language of corals

The underwater journey of coral larvae is fascinating. Tiny organisms drift in the ocean looking for the perfect place to grow. They use chemicals, light and sound when choosing their new home.

A healthy coral reef is a symphony of purring and grunting fish as well as the persistent snapping of shrimp. This is music to the ears of a coral larva. A sick, quiet reef, on the other hand, signals organisms to continue their search.

Sounds of a healthy reef retreat

Aoki and his team collected golf ball coral larvae from the U.S. Virgin Islands in an experiment conducted in the summer of 2022. The scientists separated the larvae and placed them in two quiet sandy bays. One compartment contained a solar-powered speaker that played the sound of a nearby healthy reef.

After 24 hours, approximately 30 percent of the larvae exposed to the sounds had settled and begun to grow. After 48 hours, agreement rates were approximately 73 to 85 percent. Despite the small scale of the experiment, a similar tank-based experiment replicated the results.

Golf ball coral larvae showed significantly higher settlement rates when exposed to healthy reef sounds for the first 36 hours. After this window, the sedimentation rate remained constant regardless of the sound signals.

Excessive time for coral settlement

Senior author and marine biologist Aran Mooney explained the time sensitivity of this process. “The acoustic enhancement worked for about 36 hours. After that, they seem desperate to calm down, and healthy cues become less important.”

Golf ball corals have a short window of opportunity during the larval stage. Since they lack the resources to swim for weeks, they settle 8-36 hours after being released into the water. Initially, sound signals play a decisive role. Over time, they settle everywhere.

“We’re getting closer to some of the nuances of coral biology,” Aoki said. “There is a wide variety of reproductive strategies that corals use, and different species have different larval instars. We open up a wide range of questions about how responses to sound will differ between species.”

A symphony for coral reef restoration

The researchers also noted that corals respond to sound cues in tanks where sound reflections, aerators, and water filters make acoustics less than ideal. This discovery simplified the process of growing corals and placing them in terrestrial nurseries.

There is no one-size-fits-all solution for all coral species worldwide. Aoki and his team believe that acoustic enrichment, combined with an understanding of local coral ecology and biology, can be an effective tool for recovery.

“Finding a second species that responds to sound shows that this isn’t just a one-off and that maybe we can actually scale this up,” Mooney said.

“But we can’t throw a speaker over the side of a boat and think it will work. “We need to know this system and it needs to be integrated with other conservation and restoration efforts.”

In our quest to protect and restore the ocean’s coral reefs, the solution may not lie in our hands, but in our ears as tiny organisms listen to the symphony of life created by the reefs. The study was published in the journal JASA Express Letters.