Click, clack and pop: sounds indicate health of coral reefs, study finds

The sound of the submarine world is the sound of the popping sound that you hear when you put your head under water. Fish chat to each other, or move water with their fins, hard-shelled creatures scraper against the surface, and molluscs drag themselves to their nooks.

There is more to these clicks, clacks and pops than just the wonder of it all. Oceanographers say that monitoring the sounds of coral reefs can serve as a non-intrusive, inexpensive and efficient method for tracking the state of their health.

A new research shows that coral communities that are degraded do not sound as vibrant as healthy ones because they have less biodiversity.

"Soundscaping gives us this really nice heartbeat of what's going on on the reef," said Lauren Freeman, senior oceanographer at the Naval Undersea Warfare Center, while presenting these findings to the Acoustical Society of America.

The team monitored the acoustics in the reefs off Hawaii between the years of 2020 and 2019. They recorded sounds for up to six months.

They tried to reconstruct what was happening underwater by breaking down the sounds and analyzing them by the microsecond.

The sun sets and rises before most reefs are full of noise. Many species give birth in spring when the weather is hot, while dusk and dawn represent a sort of underwater activity.

The researchers found that coral communities sound less vibrant and emit more high-frequency sounds. While healthy reefs give readings 0f 2-8 kilohertz, less diverse reefs tend to be above 12kHz, as they become overpopulated with macroalgae, which create bubbles of oxygen that float to the surface and pop.

More researchers will be able to use the findings to study reefs and monitor restoration projects. There are many challenges associated with traditional surveying of reefs, such as time limitations for divers underwater, the small areas of reef that can be covered, and the fact that there are simply too many reefs to monitor. Sound surveys could change that.

Katey Lesneski, director of restoration science at Coral Vita, a land-based coral farm for reef restoration, was not involved in the study but said more research would be needed to characterise what a healthy reef sounds like in different regions of the world.

She said that the data collection could be highly cost-effective, cover a large area and be a constant source of information.