Healthy reef sounds inspire coral larvae growth

Coral reefs are the ocean’s vibrant underwater cities, and they face a growing crisis. These ecosystems support countless marine species and over a billion human lives.

Overfishing, irresponsible tourism, coastal construction, nutrient runoff, and climate change are all threats to coral reefs.

However, hope is not lost. In a recent study, scientists used the sounds of healthy reefs to coax new coral species into existence.

Reef sounds and coral restoration

Scientists at the Woods Hole Oceanographic Institution discovered the sounds of a flourishing reef inspire a new generation of coral life. Their research focused on golfball coral larvae, tiny organisms that signal the birth of new corals.

The sounds of the reef draw the larvae and they choose to settle and grow in these areas.

“Acoustic enrichment is continuing to show promise as a technique to enhance coral settlement rates,” said Nadège Aoki, a doctoral candidate at the institution.

This technique worked on two coral species and indicates potential as a broad-based tool for reef restoration.

Decoding the language of corals

The underwater journey of a coral larvae is fascinating. Searching for the perfect place to mature into adulthood, the tiny organisms drift through the ocean. They use cues from chemicals, light, and sound to choose their new home.

A healthy coral reef is a symphony of purrs and grunts from fish, along with the persistent crackle of snapping shrimp. It is music to a coral larva’s ears.

On the other hand, a sick, silent reef signals the organisms to keep searching.

The draw of healthy reef sounds

In an experiment in the summer of 2022, Aoki and her team collected golfball coral larvae from the U.S. Virgin Islands.

The scientists divided the larvae and placed them in two quiet, sandy bays. One bay had a solar-powered speaker playing the sounds of a nearby healthy reef.

After 24 hours, about 30 percent of the larvae exposed to the sounds settled and began to grow. After 48 hours, the settlement rates were around 73 to 85 percent.

Despite the experiment’s small scale, a similar tank-based experiment echoed the results.

Golfball coral larvae showed significantly higher settlement rates when exposed to healthy reef sounds during their first 36 hours. After this window, the settling rate remained the same regardless of the sound cues.

Crunch time for coral settlement

Senior author and marine biologist Aran Mooney explained the time-sensitivity of this process. “Acoustic enrichment worked for 36 hours or so. After that, they seem desperate to settle, and healthy cues become less important.”

Golfball corals have a short window of opportunity in their larval stage. Without the resources to float around for weeks, they settle within 8 to 36 hours of being released into the water.

Early on, sound cues play a crucial role. As time runs out, they settle anywhere.

“We’re getting at some of the nuances of coral biology,” Aoki said. “There’s a huge range of reproductive strategies that corals use, and different species have different larval periods. We’re opening up this broad range of questions about how responsiveness to sound will vary between species.”

A symphony for coral reef restoration

The researchers also noted corals responded to auditory cues in tanks where sound reflections, aerators, and water filters make acoustics less ideal. This discovery simplified the process of getting corals to reproduce and settle in land-based nurseries.

There is no single solution suitable for all coral species worldwide. Aoki and her team believe acoustic enrichment combined with an understanding of local ecology and coral biology can be an effective tool for restoration.

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

“But we can’t just throw a speaker over the side of a boat and think it’s going to work. We have to know the system and it has to be integrated with other conservation and restoration efforts.”

In the quest to protect and restore the ocean’s coral reefs, the solution might lie not in our hands, but in our ears as the tiny organisms listen to the symphony of life produced by reefs.

The study is published in the journal JASA Express Letters.

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