Do fish make noise? New technology lets the public hear coral reefs up close

Coral reefs are necessarily gorgeous in color and movement, but below the waves there is a similarly colorful world of sound. Underwater, there is a soundscape of snapping shrimp, grunting fish, and other animals that fill the scene. Scientists have long believed that these soundscapes are vital for survival, giving animals sonic cues to use to find shelter, avoid predators, and even choose where to reside. But until recently, scientists struggled to record the full gamut of reef acoustics.

But today, researchers have developed a system that marries 360-degree video with spatial recording audio to map reef sounds in exquisite detail. The device does not just capture sound—it reveals who's making it, from which direction it is coming, and what that says about the health of the ecosystem. By enabling you to view and listen to reefs in a whole new way, the project can rescale how scientists study these vulnerable ecosystems and the rest of us connect with them.

It is simple to overlook the significance of underwater sound. Light disappears rapidly on the sea floor, but sound can travel vast distances. Some young fish and invertebrates depend on reef sounds to lead them home to shelter. Predators ambush with weak signals, and their prey species carefully listen for signs of danger. Vibrant reefs are noisy and healthy reefs, whereas degraded ones are abnormally silent.

For years, scientists had watched reef health by visual observation mostly, counting fish and describing corals. That told them much but missed the underwater symphony that often tells a more honest story. Traditional recorders captured only flat, two-dimensional sound, leaving it all but impossible to discern from which animal a given call came from. The new technology changes that by recording in all directions at once and combining the signals into a three-dimensional sound map.

At the heart of this innovation is what the team has dubbed an Omnidirectional Underwater Passive Acoustic Camera, or UPAC-360. Imagine a camera that does not only record but also hears in surround sound. The technology employs hydrophones, or underwater microphones, to record spatial audio. The sounds replicate the method your ears determine where sound is in space, a process called Ambisonics.

With a 360-degree video camera added to it, the experience is completely immersive. When you turn your head towards a group of fish in the video, the audio also shifts, as if you're swimming along with them. This sync view enables you to pair certain sounds with certain fish or shrimp. As executive director of FishEye Collaborative and lead author on the study, Dr. Marc Dantzker explains, "When we map that sound and put the image on top of the 360° image, what you end up with is a video that can tell you which sound was made by which fish."

The researchers field-tested their gear on Caribbean reefs near the island of Curaçao. Attached to the seafloor, the system recorded hours of reef activity. Shrimp snaps and the calls of larger fish were all picked up by the microphones. Comparing the sound and vision, the team identified 46 species of fish that made a noise, over half of which were not known to make a sound before.

This discovery is the largest published set of reef fish soundings. Results were released in the journal Methods in Ecology and Evolution, and recordings are now publicly available here. Dantzker compares the sonic complexity of a coral reef to birdsong, saying, "The sonic diversity of fish on a coral reef is comparable to that of birds in a rainforest. In the Caribbean alone, we estimate more than 700 species of fish make sounds."

Audiological complexity—the complexity of sounds—was a good indicator of reef health. Healthy reefs produced a rich and complex sound, while damaged reefs produced thin and monotonous-sounding reefs. This makes acoustic monitoring an efficient method of tracking ecosystem change, especially as it functions even at night or in dirty water when vision is poor.

The method also identifies overlapping tones more clearly than earlier systems. That allows scientists to determine what species are happening, make notes of interactions such as predator-prey encounters, and even document behavior never witnessed by divers. "Because our recording setup is deployed in the wild and can record continuously for extended periods, it allows us to collect species' behaviors and sounds never before observed," comments Dr. Aaron Rice, a senior author of the study at Cornell University.

The research doesn't end in Curaçao. The team plans to expand the sound library across other reefs, including those in Hawai‘i and Indonesia. The goal is to build a global reference database, similar to how bird songs are catalogued for identification apps like Cornell Lab of Ornithology’s Merlin. With enough data, machine learning systems could automatically recognize reef species by sound alone. We are far from being able to construct 'Merlin' for the seas, but the sounds are of direct utility to scientists and conservationists immediately," Rice said.

Graduate researcher Matt Duggan highlighted how the instrument unearths hidden voices. "Until now, the 'noisiest' animals, like dolphins, whales, and snapping shrimp, have ruled the many others in the ocean. By determining who these hidden voices belong to, acoustics will be a powerful indicator of reef resilience and health."

The science is not just a scientific technique but also a way of creating public interest. Virtual reality experiences made from the recordings enable you to see and hear reefs like you are underwater. The interactive experience can evoke emotional connections that photo reports or images cannot do. Museums, classrooms, and even local community centers could use these recordings to teach about reef conservation in a vivid, personal way.

For people whose lives depend on reefs, to listen to the difference between a healthy reef and an unhealthy one puts things into perspective. Citizen science is also a vision of the researchers. Local communities and volunteers could use inexpensive versions of the recording device to supply data, making monitoring worldwide more comprehensive.

Reefs cover only 0.1% of the oceanic bottom but are home to a quarter of all sea life. They are under an extremely severe threat from pollution, overfishing, and climate change. Nearly a billion people worldwide depend upon reefs for livelihood and food. Effective conservation is only possible if one understands how reefs are responding to damage as well as to restoration.

"These reefs are depreciating rapidly, threatening not just biodiversity but also the livelihood and food security of nearly one billion people who depend on them," Dantzker warned. "In response, governments and NGOs are investing billions protecting and restoring the reefs. That still isn't enough, so we need to ensure that we use these limited funds wisely."

By making reefs more accessible to scientists and easier for the public to visit, the new acoustic camera offers a promising step towards this goal.

This emerging technology offers scientists more precise tools for tracking reef health without invasive methods. By linking sound diversity to ecosystem strength, it presents a fast and reliable monitoring system. And unlocking the sound library will allow machine learning to become the key to identifying species, a development that may transform conservation science in the same manner that bird-song recognition apps have.

To the public, the immersive audio-visual experience offers a new way of connecting with coral reefs, translating abstract conservation issues into personal encounters.

Citizen scientists can even contribute to data gathering soon, giving communities a vested interest in the conservation of nearby reefs. The technology can also be used beyond the reefs in other habitats, including mangroves and wetlands.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.