For decades, ecologists have listened to the underwater world using sound recorders.
These devices capture rich soundscapes filled with cracks, snaps, and thumps, most of them produced by marine life.
But one big question has remained unanswered: which fish makes which sound? Now, thanks to a new invention, scientists are starting to decode the hidden voices of coral reefs.
A research team from FishEye Collaborative, Cornell University, and Aalto University has developed a tool that combines underwater sound recording with 360-degree video.
The device, called the UPAC-360 (short for omnidirectional underwater passive acoustic camera), can match specific sounds to the fish that produce them.
In their first field test, researchers identified the sounds of 46 different species on Caribbean reefs near Curaçao. Remarkably, more than half of those species were not previously known to make sound at all.
The discovery is groundbreaking because sound is one of the most important ways to study coral reefs. Tropical reefs cover less than 0.1 percent of the ocean floor, but they support roughly a quarter of all marine species.
They are among the most diverse ecosystems on Earth, yet they are in steep decline due to climate change, pollution, and overfishing.
With nearly a billion people worldwide relying on reefs for food, jobs, and protection, scientists urgently need better ways to monitor how these fragile ecosystems are changing.
Dr. Marc Dantzker, executive director of FishEye Collaborative and lead author of the study, compares the variety of fish sounds to birdsong in a rainforest.
“The diversity of fish sounds on a coral reef rivals that of birds in a rainforest. In the Caribbean alone, we estimate that more than 700 fish species produce sounds,” he explained.
But until now, very few of those sounds could be linked to specific species, making reef monitoring far less precise than it could be.
The UPAC-360 solves this by combining hydrophones, or underwater microphones, with a 360-degree video camera.
This technique is often used to make immersive virtual reality films but had never been applied underwater in this way.
By recording the direction of a sound and matching it with a video of the reef, the researchers can now see exactly which fish is making which noise. “When we visualize that sound and lay it over the 360° image, the result is a video that can reveal which sound came from which fish,” said Dr. Dantzker.
This breakthrough is already the largest collection of identified fish sounds ever published.
All of the recordings have been made publicly available, and the growing library could soon be used to train artificial intelligence systems to identify fish automatically. It is a vision similar to Merlin, the popular smartphone app that can identify birds by their songs.
“We’re a long way from having a Merlin for the oceans, but the sounds are useful for scientists and conservationists right away,” said Dr. Aaron Rice, a senior author of the study from Cornell University.
One of the biggest advantages of the system is that it can be left in place for long periods of time, quietly collecting data without the need for divers or boats. This allows it to capture natural fish behaviors and vocalizations that would otherwise go unnoticed.
“The fact that our recording system is put out in nature and can record for long periods means we’re able to capture species’ behaviors and sounds that have never before been witnessed,” Dr. Rice explained.
The implications for conservation are significant. By learning which fish make which sounds, scientists can begin to decode reef soundscapes in detail.
This means sound could be used as a powerful new tool to measure reef health, track biodiversity, and evaluate restoration efforts.
“By identifying which species make which sounds, we’re making it possible to decode reef soundscapes, transforming acoustic monitoring into a powerful tool for ocean conservation,” said Dr. Dantzker.
Matt Duggan, a Ph.D. candidate on the project, emphasized that many of the reef’s voices have long been drowned out by louder species like dolphins, whales, and snapping shrimp.
“By discovering the identity of these hidden voices, acoustics will become a powerful indicator of reef health and resilience and a strategy to monitor wider and deeper,” he said.
The work is just beginning. While the study identified 46 species, that represents only a fraction of the life on a Caribbean reef.
The team is now expanding its efforts, building larger sound libraries for Curaçao and moving on to reefs in Hawai‘i and Indonesia. As the catalog grows, ecologists will get closer to answering a question once thought impossible: what noise does a fish make?
