Songs of the Reefs
- Bianca Mata
- Aug 25, 2025
- 7 min read
Updated: Aug 26, 2025
Summary
The ocean is alive with sound, featuring a diverse array of underwater soundscapes created by marine life. This blog post showcases these sounds, immerses you in them, and discusses their importance for marine conservation, highlighting their role in protecting unique environments and the life they support.
An intriguing fact I increasingly discovered is that the underwater world is not silent. There is a distinct eerie sound when you submerge! You can still hear interactions with the world above, such as a passing boat or a nearby anchor drop, depending on how deep you are. But here, I am referring to the numerous underwater conversations which make this environment quite noisy. My snorkelling and diving sites were mainly around rocky reefs. These reefs are ideal spots to hear the sounds made by aquatic life. They serve as feeding and sheltering grounds for many species. During my explorations, I uncovered the secret language (or languages!) of the underwater world!
Reefs, whether coral, rocky, or artificial, are dynamic underwater ecosystems characterised by diverse "soundscapes". The crackling or popping sounds[1] commonly heard in these habitats originate from biological and environmental sources. They play vital roles in ecosystem function and organism behaviour across different reef types.
These sounds are made by the animals living in, on and around the reefs! The sounds reflect feeding noises, animal grunts and their bubbles (to name a few) and can be compared to the sizzling of a sausage frying in a pan or the crackling of a campfire. For example:
Snapping shrimps (from the family of Alpheidae) making snapping noises through their bubbles for predation and defense;
Fish communicating, such as damselfish (e.g., castagnola - Chromis chromis), groupers (e.g., Cernia bruna or giant grouper - Epinefel gigant), and wrasses (e.g., Donzella or Rainbow wrasse Coris julis, Donzella pavonina or Ornate wrasse Thalassoma pavo) through grunts, croaks, purrs, and whoops used in mating, territorial disputes, or distress signals;
Grazing sea urchins (e.g., Paracentrotus lividus) and other invertebrates producing low-frequency scraping and clicking sounds, especially on rocky and artificial reefs, as they feed on e.g., algae, seagrass or biofilm[2];
Movement of water over reef structures, wave breaks, and the release of gas bubbles from the substrate contribute to the background soundscape of reefs.
Studies have particularly focused on coral reefs noises because they are the most productive and diverse communities in the marine environment. But arguably, these crackling noises are heard around all types of reefs!
I noticed that the variations in frequency and the 'busyness' in the sound intensity at the snorkelling and diving sites around the Capo Carbonara Marine Protected Area[3] depended on daily factors (such as boat traffic displacing fish, changes in water currents, temperature differences, windstorms like the maestrale[4], etc.). However, on a calm day, it resembled a forest's chorus! It is often said that species diversity in reefs can rival that of rainforests[5], which are the planet's most diverse ecosystems[6]! Sound plays a crucial role for several reasons:
Provides navigation cues and habitat selection to pelagic larvae[7] of fish and invertebrates to suitable habitats, promoting recruitment and ecological connectivity. In other words, sound guides them to find their home!
It’s an indicator of ecosystem health. It is true that the health of a reef can be determined based on the sound diversity, and it can be used as a measuring tool for scientists. No wonder why an unhealthy reef is considered soundless. Or either way, that a soundless reef is considered unhealthy! As it’s portrayed in a somber landscape of a bleached or dead coral reef. Lifeless, due to a decline in its biological contributors.
It also provides acoustic cues that influence predator-prey interactions by masking prey sounds or signaling predator presence. And vice-versa, it attracts predators.
Researchers in conservation bioacoustics highlight the significance of listening to these sounds[8], noting that the World Oceans Passive Acoustic Monitoring Project (WOPAM)[9] was launched to investigate how the animals use the diversity of ocean sounds and where researches come together to listen to them! This research pins down not only habitual cues between species, the different ‘dialects’ of, for example, humpback whales, around the globe, but also how we connect with those sounds and what we are actually discovering while also understanding how human-made noises actually occupy these spaces.
Also, many artists started composing and holding concerts with ocean sounds which have been inspired from these crackling reef noises and beyond. For example, in the case of musician Alejandro Bernal from Colombia who composed an original piece of music using only animal sounds from the WOPAM recordings[10]. Or the Scottish composer, Michael Begg, who made music and held concerts using the Arctic[11] and Antarctic sounds[12]. Begg also created the Black Sea compositions[13] describing the impact of war on the fragile ecosystems of the Black Sea.
Moreover, just as coral reefs provide vital ecosystem services[14], such as crucial food sources, coastal protection, nurseries and habitats for various marine species, migrations sites, nutrient cycling, climate regulation, and income through fisheries and tourism, as well as building materials for numerous tropical communities worldwide[15], it can be argued that any type of reef performs these roles, particularly the rocky reefs in the marine protected areas like Capo Carbonara[16][17]. Here, the reefs are conveniently situated in shallow waters, supporting diverse fish communities, local tourism and coastal protection, thus offering a local source of food and income. However, reefs face growing threats from factors such as climate change, pollution, sedimentation, rising sea levels, and overfishing.
These reefs are home to numerous animals, including the species I encountered during my dives, which I discuss in the blog series Mediterranean through My Lenses. They also sculpt enchanting underwater landscapes and majestic seamounts that evoke the surreal beauty of distant moons. Or the mysterious terrains of alien worlds!
In marine conservation and research, acoustic monitoring, using tools such as hydrophones, is being used to study the biodiversity and health of various reef systems[18]. By comparing soundscapes, researchers can assess reef resilience and the impact of human activities. In reef restoration, these recordings of crackling sounds from healthy reefs are even broadcasted on degraded reefs, attracting larvae and jumpstarting ecosystem recovery across all reef types[19][20]!
Crackling sounds are integral to the ecology of all reef types, providing vital cues for organism behavior and ecosystem health. Understanding and protecting these soundscapes across coral, rocky, artificial, and deep-sea reefs is essential for sustaining their ecological functions and biodiversity, which in return benefits us.
This experience, along with hearing the songs of the reefs near the shore, is made possible by the establishment of a marine protected area. Timing is crucial, with calm, warm days and fewer tourists being more favorable than after-storm conditions or peak holiday seasons, which typically lead to reduced biodiversity. Therefore, it is essential to support MPAs with robust regulations on activities that could affect the area and to help decision-makers grasp the rationale behind these measures.
What did you think about this story? Please comment or feedback in the comments section below. I would love to hear your thoughts! 🎶🐠🦐🐋🎶
Tips:
What can you do to listen to the crackling sounds in the water?
While on your snorkeling adventure, try to get as close to the reefs as possible (or hover above them!). Relax, stay still, slow down your breathing, and listen. Float above the soundscape, concentrating on the sounds rather than your thoughts or breathing. Alternatively, if you're an experienced freediver, you can dive down to be fully immersed in the sounds by duck diving.
When SCUBA diving, it requires more effort to refine your breathing technique. This involves taking slow, shallow breaths with a long exhale. Ensure you pause enough between breaths to hear the crackling sounds beyond the noise of your regulator and the bubbles when you breathe in and out. Meanwhile, avoid holding your breath to manage your nitrogen intake properly!
Disclaimer
***This information is intended solely for informational purposes and should not be interpreted as professional medical advice. As a diver, it's essential to prioritise your health and safety while engaging in underwater activities. Always consult with a qualified health provider or dive medicine specialist regarding any medical concerns or conditions that may affect your diving experience. Do not disregard professional advice or delay seeking it based on the content provided here.***
References
[1] The noises can be interpreted by each individual differently, but they’ve been previously referred to as crackling, snapping, frying, popping or zumzet noises.
[2] Film-like communities of bacteria or other microorganisms that stick together in a matrix of extracellular polymeric substances, covering the surfaces of marine structures.
[3] Capo Carbonara Marine Protected Area located in the south of the beautiful Italian island, Sardinia.
[4] The Italian term for "mistral". A type of cold and dry wind blowing from northwest, especially in the Mediterranean and impacting Sardinia. Its name comes from "maestro" or master, of winds, as it dominates this area most of the time.
[7] Tiny, planktonic (drifting) developmental stages of different marine species that live in the open water, far from the seafloor. These can include fish and invertebrates (crustaceans and even corals). This "drifting" helps the dispersal and repopulation of marine animals.
[9] WOPAM.
[14] Ecosystem services are the direct and indirect benefits that ecosystems offer to enhance human wellbeing and quality of life. These include practical contributions like supplying food and water and regulating the climate, as well as cultural benefits such as alleviating stress and anxiety. Indeed, the numerous services ecosystems provide can be grouped into more manageable categories: provisioning, regulating, cultural, and the somewhat less defined, supporting services. Further reading at Ecosystem services - nature’s benefits | NatureScot.
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