Why is the sound of coral reefs important? Explained. 

Take a deep breath. Immerse yourself. Imagine diving onto a coral reef. Multicoloured arms reach up from the seabed, fish fly by on their busy way, shrimps clean their clients, anemones wave in the water.

Energy and movement surround these bustling underwater cities. Let us explore the sounds of coral reefs (and let’s see how many synonyms for noise we can get in).  

Had we asked you to put yourself in the jungle, or on a busy city street, you would have probably filled your ears with the calls of unseen birds and insects, or the honking of a taxi and chatter of fellow bipeds. The sounds of bustling coral reefs are just as diverse and entrancing.  

What sounds can you hear on a coral reef? 

Whistles, pops and hums. This background noise often stays as exactly that: background, largely unnoticed. Yet through advancements in bioacoustic research, we have begun to dissect the noises coral reefs make and realise their importance. 

If you take deliberate notice you will begin to hear the background crackle produced by the sharp pops of pistol shrimp. Pistol shrimp produce sounds exceeding 200 decibels at the source – a conversation is around 60 dB, city traffic 85dB and a jet engine 30m (100ft) away is approximately 150dB. Using their specially modified claws, they rip the water apart, creating cavitation bubbles that briefly reach temperatures comparable to the sun’s surface (up to 4,700°C).  

Then you hear the grunts of clownfish families talking to each other in their anemones. Gradually the other croaks, growls and even fish blowing raspberries come to your attention, and where there was only white noise is now a rich tapestry of sound. Coral reefs are bursting with sound and life. In fact, reefs support over a quarter of all marine life. 

Why is sound so important for coral reefs?  

The coral reef soundscape is crucial not only for the individuals communicating with each other, but for the survival of the reef itself. 

Residents of coral reefs use sound in different ways. The ambon damselfish can be heard singing to attract a mate; saddleback clownfish grunt to other members of their colony, warning of potential predators. And predators use sound to co-ordinate their hunts.  

Each coral reef has its own acoustic signature, defined by the population it supports.  

We now understand that young animals will listen out from the open sea and select their future home by listening to it.  

This means that the health and resilience of coral reefs depends (at least in part) on their residents’ din. Recently, even coral larvae have been shown to move towards the sounds of a healthy reef, called home by the hubbub.  

Each whistle and whoop add to the cacophony of the reef: a healthy reef is a loud one.

Why is listening to coral reefs important?  

Marine biologists are unpacking the cacophony for science. By listening in and identifying the various reef rumblings, we can identify who’s there.  

This is better than just looking at coral reefs, as we can find the species good at hiding and the nocturnal. We’re even putting AI to work to identify the sounds for us. 

How does human noise impact coral reefs? 

There are some new faces on the coral reef: us. Say what you will about people, but we are rarely subtle.

Our visitations to the marine world bring our own katzenjammer. Motorboats busy themselves buzzing around, whilst seismic surveyors searching for oil and gas fill the water with explosions, and construction work hammers the sea bed with steel piledrivers. 

Most of the noise on coral reefs comes from our boats – engines chugging and rattling, propellers producing bubbles through cavitation just as the pistol shrimp do – these bubbles bursting with a screech. We create an ‘acoustic fog’ – as described by bioacoustic researcher, Steve Simpson.

We are realising with more clarity the effect of our racket. When motorboat noise is present, fish are more vulnerable to predation, perhaps due to warning calls being drowned out, or confusion slowing reaction times.  

Fish show signs of stress and stop their usual activities, including parents fanning their eggs with oxygen-rich water. This can mean young fish don’t develop properly and less of them will survive.  

As healthy reefs are noisy, the opposite is also true: damaged or dying reefs lose their song.  

Coral reefs face many threats: from warming seas causing them to bleach and die, to increasing acidity making it harder for them to build their skeletons.  

In 2016, the most famous reef of them all, the Great Barrier Reef, boiled in hot seas and an estimated two-thirds of coral in the north of the reef died. With this we also lose its noise. In the north part of the reef, it’s 75% quieter than before.  

The reef lost its voice.  

As our fog of noise descends and reefs quieten under the stresses created by us, young crabs, coral and fish listening as they drift in the Ocean can’t hear their homes call to them. Less offspring to fill these underwater cities puts their future in further doubt. 

What can we do to protect coral reef soundscapes? 

But hope isn’t lost! Whenever we give it a chance, nature exceeds our expectations to recover. 

The growing research in bioacoustics is pushing our understanding of the noisy world under the waves. As we learn more about our Ocean’s audio, the desire and ability to protect it grows too.  

“Sound is a pollutant we have the most control over, and we can really fix things” – Prof Steve Simpson 

Ongoing research is decreasing the noise of our engines, and protection of our marine areas is growing. We now know minimising our audio footprint will improve feeding and mating behaviours of the animals on the reef, allow parents to feed and nurture their young better, and give fish a better chance to avoid predators.  

We can now listen to a reef and learn how healthy it is. Phonic richness – the diversity of animal produced sounds – is greater on a healthy reef. 

Early experiments with acoustic enrichment show promise. When speakers play healthy reef sounds, they attract significantly more juvenile fish and some invertebrates than areas where no sound was played.   

While still experimental, this approach could potentially become one tool in the coral reef restoration toolkit. Read more about the other approaches to reef restoration here. 

Our Ocean is resilient and, as we deepen our understanding of it, we can more effectively protect it. 

Dunk your head again onto your imaginary coral reef, take a deep breath. Close your eyes. Just listen to the Ocean sing.  

(Final noise synonym count: 11) 

Post by

Will Steen