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10/08/2026 | Press release | Distributed by Public on 10/08/2026 09:34

Healthy Reef Sounds Can Boost Coral and Fish Recovery Efforts

Published Date

October 08, 2026

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Coral reefs are renowned for their visual beauty, but for the marine life they support, their sounds may be just as enticing. Two new studies led by UC San Diego's Scripps Institution of Oceanography reveal how underwater acoustic enrichment - the playback of sounds from healthy reefs - can help spur the recovery of degraded coral reefs and their fish communities.

These studies - one focusing on coral larvae, and the other focusing on fish larvae - are the first to field test the effects of underwater sound on fish and coral larvae simultaneously, alongside other restoration technologies including living materials and 3D-printed settlement surfaces. The research took place in Hawaii's Kāne'ohe Bay, located off the island of O'ahu, over several spawning events in 2023 and 2024.

"We have demonstrated in a single set of field studies that acoustic enrichment works in increasing the presence of both fish larvae and coral larvae on artificial reef structures," said Scripps Oceanography researcher Aaron Thode, head of the Scripps Environmental Acoustics Lab and lead author of the coral larvae study.

Scripps Oceanography scientists led the studies in collaboration with the University of Hawai'i and other consortium partners of Rapid Resilient Reefs for Coastal Defense (R3D), a project focused on nature-based strategies to reduce wave energy, protect coastlines and improve coral resilience. The studies and broader R3D effort were funded by the Defense Advanced Research Projects Agency (DARPA).

Coral study

The newest study, published Oct. 8 in Communications Biology (part of the Nature Publishing Group), examines how acoustic enrichment affects coral larval settlement - the critical stage when free-drifting larvae search for a place to attach and begin building a reef. The research also demonstrates the potential of living materials and 3-D printed settlement surfaces to enhance coral settlement under natural spawning conditions.

"Our data indicate that when these drifting organisms detect a lot of sound from a reef, it signals to them that this is a good place to settle," said Thode. "Our analysis also provided strong evidence that synthetic chemical cues attract these organisms to reefs."

To start, the team collected sounds from a healthy reef environment off O'ahu, Hawaii. Over the course of a lunar cycle, their recorder captured the sounds of fish and numerous other organisms, including shrimp and crustaceans that produce distinctive snapping noises. (Listen to the sounds of a healthy reef under the new moon, and the distinctive "purr" of a damselfish.)

Compilation image showing views of the experiment site, including underwater perspectives and an aerial view of Moku o Loʻe. Equipment shown in the upper-left includes autonomous cameras, coral settlement and fish habitat modules, microhabitat cinder blocks, a hydrophone and a speaker. Credit: Océane Boulais

The researchers then broadcast these recordings from an underwater speaker at the study site - a flat, sandy area off the small island of Moku o Loʻe. For two weeks, the speaker played the reef recordings from sunset to sunrise.

Around the speaker, the team placed 37 artificial structures on the seafloor, at a depth of 4.5 meters (15 feet) and distances between 1 to 42 meters (3 to 138 feet) away. The structures varied in design and surface properties, and included engineered microhabitats developed in Scripps researcher Daniel Wangpraseurt's Coral Reef Ecophysiology and Engineering Lab.

These microhabitats were engineered in two ways: through their physical architecture, which created complex, protected settlement spaces, and through their living surface coating, made with BRINK - a bioactive "reef ink" containing living bacteria. BRINK was developed by former Scripps postdoctoral researcher Natalie Levy and colleagues in Wangpraseurt's lab.

Across three experiments conducted over two years, scientific divers measured coral larval settlement one and two weeks after the new moon, when spawning occurs. Using a handheld blue light and yellow filter, they counted the individual larvae that had settled on each structure.

The experiments showed that the structures closest to the speaker had the highest levels of coral settlement. Among those, the structures treated with BRINK had the best results.

Researcher Natalie Levy uses a UV flashlight to inspect microhabitat structures for signs of coral larvae settlement. Credit: Océane Boulais
Natalie Levy inspects the adhesion of microhabitat structures to concrete blocks near the study site. Credit: Océane Boulais

"The acoustics help, and with the living biofilm, it's a lot better," said Thode. "When combined with structures that had crevices, acoustic enrichment worked very well for the coral larvae settlement."

The study noted that specialized 3D-printed structures developed by colleagues at the Hawaiʻi Institute of Marine Biology also performed well, but those structures were only tested with sound alone and not BRINK. For future experiments, the team recommends combining acoustic enrichment with these more complex structures coated with BRINK for the best chance of coral settlement success.

"We now have evidence that several of these technologies can work in the field, which is a major step forward," said Wangpraseurt, who is also UC San Diego's lead principal investigator for the R3D project and a co-author of the study. "It brings us closer to the vision of hybrid reefs, a new class of living coastal infrastructure that combines engineering and biology to protect our shores while supporting the growth and recovery of reef ecosystems."

Reef fish study

In a related study published recently in Scientific Reports, Scripps PhD candidate Océane Boulais and colleagues used custom-built autonomous cameras to document an increase in fish larvae during the same acoustic enrichment field deployments.

"Fish are important components of healthy coral reefs, because certain species feed on smothering microalgae that would otherwise make it difficult for coral larvae to settle and grow," said Boulais, the lead author of the study.

Because fish are easily disturbed by humans, monitoring their activity while scuba diving presents a challenge, one Thode likened to "Godzilla trampling through a city and trying to get an accurate count of all the humans scurrying away." As a solution to this problem, Boulais developed an array of low-power autonomous cameras capable of continuously detecting and counting fish larvae for up to three weeks.

Boulais positioned the cameras near the entrances of complex, 3D-printed structures that functioned as "fish hotels," documenting fish as they entered and left while also tracking the presence of larvae.

"By developing these non-invasive cameras, we can essentially spy on the fish and observe a lot of their natural behavior," said Boulais. "The autonomy and long-term monitoring design of these cameras enable us to observe which animals show up, and how long they stay."

An autonomous camera documented the activities of larval fish schools at an artificial reef structure during the acoustic experiments. Credit: Océane Boulais

One of the custom-built, autonomous cameras used for recording time lapses of fish larvae during the acoustic enrichment studies. Credit: Océane Boulais

The cameras were deployed at two sites: one near the underwater speaker providing acoustic enrichment, and one at a control site where an identical speaker did not emit any sound.

Larval counts at both sites peaked around the new moon, but the acoustically enriched site attracted 4 to 14 times more fish larvae overall - a promising indication that the added sound helped draw young fish to the structures. The results held even when the team swapped locations of the true speaker and control speaker.

"The cameras are relatively new, but they're already helping us learn so much about the early life stages of reef fish, and how sound might enhance their presence on a reef," said Boulais.

Next steps

DARPA plans to install a $22 million hybrid reef structure off Oʻahu this fall, with corals likely to be outplanted in late 2026 or early 2027. The Kalaeloa Hybrid Reef will span 50 meters (164 feet) and incorporate technologies tested through the R3D program, including Scripps-developed microstructures and an acoustic enrichment system.

A birds-eye view of the field deployment crew (Maddie Hardt and Natalie Levy) placing a fish habitat module around the playback speaker before the acoustic enrichment experiments. Credit: Océane Boulais

After installation, DARPA will transition ownership of the prototype living breakwater to the Hawai'i Department of Transportation, a transition partner for the R3D program.

More than 50 researchers and R3D consortium members contributed to the studies as co-authors. View the coral larval study and the fish larvae study online to see the full list of authors.

To learn more about Scripps-led acoustic enrichment research, visit Birch Aquarium's Living Seas Tropical Pacific exhibit, which features samples of the reef sounds used in these studies.

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