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Today, I’m going to be your DJ and guide you through a different kind of playlist: a fantasia of sound that tells a story about the ocean. Let’s start with the cacophonous clip below.
What are your impressions? Did it sound chaotic to you? Maybe it felt familiar in some way, as if someone were laughing while rain poured heavily in the background. Like you were listening to an underwater carnival. You were, in a sense. You were hearing a healthy coral reef.
Coral reefs are among the largest, most ancient, most diverse, and most threatened animal-built structures on the planet. Around 800 species of hard corals, the building blocks of reef ecosystems, are home to 25 percent of marine life. Thousands of organisms—including algae, crustaceans, fish, sharks, rays, sea turtles, and marine mammals—rely on coral reefs to reproduce, grow, feed, and survive.
Fish sounds include popping, croaking, grunting, whooping, and trumpeting.
And the sounds of a coral reef are as diverse as its residents.
Snapping shrimps, for example, from the family Alpheidae, are major musicians. When it’s feeding time, this crustacean creates a network of bubbles with its unique and characteristic claw, which can stun or kill its prey. When many are hunting at the same time, their claws create a sound similar to that of rain, as you heard in the audio clip—a noise so loud it can compete with the sound produced by the loudest whales in the ocean.
Fish also like to gather and communicate with each other within coral reefs. Some of their sounds include popping, croaking, grunting, whooping, and trumpeting. They tend to make these sounds while hunting, arriving in new territory, mating, or when predators are near.
Listen to the purrs of the sergeant majors
Listen to the whoop of the damselfish
Listen to the laughing of an unidentified fish
Coral reef soundscapes are more than a simple chorus of animal noises combined. With the help of research and technology, scientists have discovered that they tell detailed stories.
When looking for places to reproduce and grow, fish and other invertebrates rely in part on sound waves to detect the best places to do so. Sound moves through water quickly and carries a long way from its source, which means that fish far from a particular reef can hear it and receive information about the presence, behavior, diversity, and abundance of the organisms living in it.
The sounds produced by marine life in a healthy coral reef indicate that the reef is a vibrant place to live. A dynamic coral soundscape is like a big billboard in the ocean declaring, “The home of your dreams is right here!”
Snapping shrimps are major musicians.
Sound also plays a critical role in coral growth. Corals of the same species in a particular area synchronize to liberate eggs and sperm into the water column in an event called coral spawning. When these gametes find each other and fertilization occurs, the larvae will search for a surface on which to settle and grow—hopefully into a colony. In a recent study, scientists explain that the larvae of the coral species Porites astreoides tend to prefer settling in places that have a more vibrant soundtrack; that is, a dynamic soundscape that can improve the rate of baby corals’ settlement in a reef.
And coral soundscapes don’t just help marine life. Researchers can use them as tools to measure the health and biodiversity of coral reefs.
Earlier this year, scientists discovered that the fourth global coral bleaching event on record (and the second in the last 10 years) had begun. Climate change, and especially marine heat waves, increase water temperature, which puts stress on corals. This stress breaks their vital relationship with zooxanthella, the microalgae living within their tissues, and causes them to become white and weak. As they lose their colors and strength, coral reefs stop being the nourishing and vibrant places they once were, so their residents leave. In the space left behind is a heartbreaking sound.
Gone is the diversity and complexity we heard earlier. No more laughing or whooping—only shrimps snapping. When comparing soundscapes, scientists from the University of Exeter at the Great Barrier Reef heard a sharp reduction in sound following the massive bleaching events of 2016.
The loss of coral reefs isn’t just devastating for marine life. Reefs also play a crucial role in the lives of the nearby communities. Approximately 1 billion people rely on coral reefs for food, coastal protection, culture, and tourism. And so, around the world, numerous efforts are being made to grow coral fragments in order to restore and bring reefs back to life.
As part of these efforts, scientists have been using the power of sound. At the Great Barrier Reef in Australia, an international team of scientists installed loudspeakers playing the soundtrack of a healthy coral reef on patches of degraded corals. Afterward, twice as many fish were attracted to (and stayed in) these sites than to those without sound. Fish of all trophic levels were present—some that eat algae and plankton and some that eat other fish, for example—helping to make the ecosystem complex and dazzling once again. This technique, called acoustic enrichment, is another tool for professionals working on coral reef restoration all around the world.
Rachel Carson’s revolutionary 1962 book, Silent Spring starts with the story of an imagined village grappling with the effects of pesticides:
And there was a strange stillness … It was a spring without voices. In the mornings, which had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices, there was now no sound; only silence lay over the fields and woods and marshes.
More than 60 years later, our marine habitats aren’t far removed from Carson’s town. Coral reefs are bleaching as well as being degraded by illegal fishing and killed by bacterial diseases. We might very well wonder if “a spring without voices” is the next season for the ocean.
As the audio clips above reveal, sound is much more than a vibrating wave traveling through a medium. It can carry information, guidance, and hope. The ocean is telling a story with every sound it makes. And if there is no sound, there is no life. Silence isn’t an option. 
Adapted with permission from an earlier version of this article, to which Rachel Small contributed.
Lead photo by Beth Watson, Ocean Image Bank
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