Listening to Coral Reefs: The Sounds of Recovery
Just as a sudden silence in a classroom might signal trouble, a quiet coral reef may also indicate something is wrong. Coral reefs are alive with sound, and their natural soundscapes offer scientists valuable clues about their health and biodiversity.
Why Reef Sounds Matter
Traditionally, researchers monitored reef health by visual surveys or by calculating coral coverage. However, these methods often miss the full picture. Soundscapes — the collection of noises made by reef inhabitants — provide a richer understanding of ecological health. A reef filled with diverse and vibrant sounds is often a thriving ecosystem.
The Mars Coral Reef Restoration Project
To test this approach, scientists from two UK universities working on the Mars Coral Reef Restoration Project in central Indonesia recorded reef soundscapes in 2018 and 2019. These reefs had undergone one to three years of restoration. The recordings were then compared to the soundscapes of both healthy and degraded reefs.
The results were striking. While restored reefs did not sound identical to untouched healthy reefs, they contained a broad diversity and frequency of noises similar to them. This suggested that the restored reefs were supporting a wide range of marine life. By contrast, degraded reefs had much simpler, quieter soundscapes, reflecting their reduced biodiversity.
The Chorus of a Reef
So what exactly does a healthy or restored reef sound like? At sunrise, recordings captured growls, whoops, and even laugh-like noises. As the day progressed, the reef produced dozens of scraping sounds, likely from fish feeding. Afternoons added foghorn-like calls, while evenings brought knocks, croaks, and grunts. At night, the underwater soundtrack shifted again to purrs and raspberries, before dawn returned with the growls and grunts of a new day.
Each of these sounds comes from different creatures living in the reef — fish, crustaceans, and other marine animals all contribute to the chorus. Together, they create an underwater symphony that signals a lively, functioning ecosystem.
A New Way to Measure Recovery
By eavesdropping on reefs, scientists gain insight into recovery efforts without relying solely on visual surveys. The findings from Indonesia suggest that restored reefs can regain acoustic diversity, an encouraging sign that habitat restoration truly brings back biodiversity.
This method highlights the importance of sound as a tool in conservation. Monitoring reef soundscapes not only helps measure restoration progress but also provides early warning signals when ecosystems are under stress. A noisy reef is a healthy reef — and a quiet one is cause for concern.
