Listening to the sound coral reefs make could be a way to monitor their health

If you thought corals were soundless, think again! Scientists have revealed that listening to the noise produced by reefs can even help in monitoring the health of these organisms: the more sound they emit, the more likely they are to be well preserved. An important takeaway as corals are one of the underwater species most threatened by global warming.

If you are planning to go diving this summer and you have the chance to contemplate any corals, don't forget to pay attention to what you hear. Because these reefs emit sounds. And according to oceanographers at the US Naval Undersea Warfare Center (NUWC), listening to them could be an inexpensive and effective way to monitor their health. 

To reach this conclusion, an NUWC team led by US oceanographer Lauren Freeman monitored reef acoustics off Hawaii between 2019 and 2020, introducing underwater microphones over a six-month period. They then compared them to other sounds collected near Bermuda and New England. 

Overall, the hundreds of thousands of animals that live in the reef make sounds similar to radio static, crackling, or the "pop of a bowl of Rice Krispies" as milk is poured, the study explains. Highly precise descriptions that correspond to when the coral reef is well preserved, in good health. "The sound changes for reefs that are not healthy, becoming quieter and less diverse," the study authors note. 

Another study carried out by English researchers from the University of Exeter and published at the end of May makes a similar observation. The researchers reconstructed sounds using an artificial intelligence tool, with which they detected differences in sound frequencies depending on the health of the reefs. The authors of the work found that preserved corals emitted louder sounds than those more exposed to bleaching.

Well-preserved corals remain in some regions of the planet

Essential to biodiversity and human health, coral reefs are severely taxed by marine heat waves, which are becoming increasingly frequent due to climate change. The increase in water temperatures leads to an acidification of the oceans, thus generating significant thermal stress on corals, which eventually leads to bleaching, i.e., the death of these reefs.

According to an Australian government report released in mid-May, about 91% of Australia's Great Barrier Reef suffered "bleaching" due to a prolonged heat wave during the austral summer. Fortunately, some of them located in other parts of the world seem to be resisting better.

One such example can be seen in Tahiti, where totally preserved reefs were recently discovered by an international team of researchers. Others were seen near Hawaii, according to a recent studyby American researchers from Oregon State University. 

© Agence France-Presse