Diver over a coral reef in Indonesia, q phia/Flickr
There can be no doubt that the world’s coral reefs are in crisis. Degradation, warming and acidic seas and pollution have all contributed to their decline, and it now seems that they will not be able to recover or survive without human intervention. In recent times, researchers have realised how noisy our ocean is. Healthy coral reefs are a veritable orchestra- with snapping shrimps, fish, waves and many other sources adding to the clamour. In fact, the sound a reef produces can be indicative of its health, with thriving reefs creating louder, more diverse noises. Sound travels longer distances in water, and can be used by lots of marine animals to communicate and navigate.
Coral reefs are actually made up of lots of tiny animals called polyps, which start life floating in the water column as larvae. The larvae can choose where to settle to grow into adult polyps, triggered by a range of cues that reflect their ideal home Amazingly, they have been shown to be able to orientate themselves to the sounds produced by a reef. Unfortunately, degraded coral reefs may no longer be able to produce these cues.
This begs the question as to whether humans could intervene by having an underwater sound system playing sounds of a healthy coral reef. Playing artificial noises has already been used as a technique to attract oysters and fish to reefs. Could this possibly work to attract coral polyps too?
Fish over a coral reef. Photo: Oleksandr Sushko/Unsplash
The team of scientists created a fancy solar-powered underwater speaker system and used it to play noise collected from a healthy reef in the Virgin Islands. They collected coral larvae from adult corals and put them in cups that were isolated from any external cues with a bit of ceramic to mimic the seabed. They then selected two degraded reefs and one healthy reef with similar environmental conditions. They only played the healthy reef sounds on one of the degraded reefs, leaving a healthy reef and a degraded reef as controls. The cups were placed at different distances from the speaker and left for a day, before they counted how many larvae had settled at each site.
Extraordinarily, they found that up to 7 times more larvae settled at the sound-enriched site than the degraded site without speakers. Even the normal, healthy reef saw less settlement then the degraded site with speakers! Rates of settlement decreased with distance from the sound source, suggesting that the level of sounds affects the response by the coral polyps and further supporting the positive effects of the enhanced sound.
A diver measuring coral growth. Photo: Ryan McMinds/Flickr
This experiment suggests that using external sounds can indeed dupe baby corals into settling on degraded reefs, helping to restore them and bring them back to life. Researchers can now explore the potential of doing this on a larger scale alongside other restoration efforts.
More work is needed to understand how the specifics of timings, the level of noise and other environmental conditions will influence this method at scale, but it is certainly promising. Just settling on a reef, of course, does not ensure the survival of the corals and the recovery of the overall reef, as the polyps may be overgrown by algae or eaten. However, it certainly gives them a good a start in life, given the current state of our reefs. It would also be interesting to study how other marine animals respond to the noise to see whether sound enrichment would have wider effects on the whole ecosystem, nurturing our coral reefs back to the thriving, abundant habitats we treasure.
How we can find Another Way
This study provides a ray of hope for one of the most abundant ecosystems on earth, but restoration efforts alone won’t save our world’s coral reefs. We need a plethora of efforts, including to drastically limit and reduce carbon emissions globally. We can all play a part in reducing our personal carbon footprints, taking part in community climate action initiatives, and campaigning for better climate policies on a national and global scale. Oh, and, if you fancy, turn on the music, pretend you are a little coral larvae, and have a boogie to celebrate some positive news.
Article by Amy Bray
A coral reef from above. Photo: invisiblepower/Pexels
Source: Aoki, N., Weiss, B., Jézéquel, Y. et al 2024. Soundscape enrichment increases larval settlement rates for the brooding coral Porites astreoides. Royal Society Open Science. https://doi.org/10.1098/rsos.231514
