Although clownfish are conceived on coral reefs, they spend the first part of their lives as larvae adrift in the open ocean. The fish are not yet orange, striped and do not even know how to swim. They are still plankton, a term that comes from the Greek word for “wanderer”, and they wander, at the mercy of currents in an oceanic rumminga.
When baby clownfish grow old enough to swim against the tide, they return home in high tails. The fish cannot see the reef, but they can hear its crackle, grunt, gurgle, crackle and croak. These noises constitute the sound landscape of a healthy reef, and the fish larvae rely on these landscapes to find their way back to the reefs, where they will spend the rest of their lives – that is, if they can hear them.
But humans – and their ships, seismic surveys, compressed air weapons, piles, dynamite fishing, drilling platforms, speedboats and even surfing – have made the ocean an unbearably noisy place for marine life, according to a review overview of the prevalence and intensity of the impacts of anthropogenic ocean noise published on Thursday in the journal Science. The article, a collaboration between 25 authors from around the world and various fields of marine acoustics, is the greatest synthesis of evidence on the effects of oceanic noise pollution.
“They hit the nail on the head,” said Kerri Seger, a senior scientist at Applied Ocean Sciences who was not involved in the research. “On the third page, I was like, ‘I’m going to send this to my students.’”
Anthropogenic noise often drowns out natural soundscapes, putting marine life under enormous stress. In the case of baby clownfish, the noise may even condemn them to wander the seas without direction, without being able to find their way home.
“The cycle was broken,” said Carlos Duarte, a marine ecologist at King Abdullah University of Science and Technology in Saudi Arabia and the article’s lead author. “The home soundtrack is now difficult to hear and, in many cases, has disappeared.”
Muffling the signs
In the ocean, visual signals disappear after tens of meters, and chemical signals dissipate after hundreds of meters. But the sound can travel thousands of kilometers and connect animals across ocean basins and in the dark, Duarte said. As a result, many marine species are impeccably adapted to detect and communicate with sound. Dolphins call themselves by unique names. Humming toadfish. Bearded seals chirp. Whales sing.
Scientists are aware of underwater anthropogenic noise and how far it has been spreading for about a century, according to Christine Erbe, director of the Center for Marine Science and Technology at Curtin University in Perth, Australia, and author of the article. But early research on how noise can affect marine life focused on how large animals respond to temporary sources of noise, like a whale making a detour around oil platforms during its migration.
The new study maps how underwater noise affects numerous groups of marine life, including zooplankton and jellyfish. “The extent of the noise pollution problem has only recently occurred to us,” wrote Dr. Erbe by email.
The newspaper’s idea came up with Dr. Duarte seven years ago. He was aware of the importance of the sound of the ocean for much of his long career as an ecologist, but he felt that the problem was not recognized on a global scale. Dr. Duarte found that the scientific community that focused on the soundscapes of the oceans was relatively small and isolated, with vocalizations of marine mammals in one corner and underwater seismic activity, acoustic tomography and lawmakers in other distant corners. “We have all been through our little gold rush,” said Steve Simpson, a marine biologist at the University of Exeter in England and author of the article.
Dr. Duarte wanted to bring the various corners together to summarize all the evidence gathered in a single conversation; perhaps something so grand would finally result in policy changes.
The authors examined more than 10,000 articles to ensure that they captured all the tentacles of marine acoustic research in the past few decades, according to Dr. Simpson. Patterns emerged quickly, demonstrating the damaging effects that noise has on almost all marine life. “With all this research, you realize that you know more than you think you know,” he said.
Dr. Simpson has studied underwater bioacoustics – how fish and marine invertebrates perceive their environment and communicate through sound – for 20 years. In the field, he got used to waiting for a passing ship to pass noisily before going back to studying the fish. “I realized, ‘Oh, wait, these fish try ships coming in every day,'” he said.
Marine life can adapt to noise pollution by swimming, crawling or fleeing it, which means that some animals are more successful than others. Whales can learn to bypass busy shipping routes and fish can dodge the noise of an approaching fishing vessel, but benthic creatures like slow-moving sea cucumbers have little recourse.
If the noise is more permanently established, some animals simply leave forever. When acoustic harassment devices were installed to prevent seals from hunting on salmon farms in the British Columbia Broughton Archipelago, killer whale populations declined significantly until the devices were removed, according to a 2002 study.
These forced evacuations reduce the size of the population as more animals leave the territory and compete for the same resources. And certain species that are limited to limited biogeographic ranges, such as the endangered Maui dolphin, have nowhere to go. “Animals cannot avoid sound because it is everywhere,” said Duarte.
Even temporary sounds can cause chronic hearing damage in sea creatures unlucky enough to be captured on the acoustic mat. Both fish and marine mammals have hair cells, sensory receptors for hearing. Fish can regenerate these cells, but marine mammals probably cannot.
Fortunately, unlike greenhouse gases or chemicals, sound is a relatively controllable pollutant. “Noise is the easiest problem to solve in the ocean,” said Simpson. “We know exactly what causes the noise, we know where it is and how to stop it.”
In search of peace
Many solutions to anthropogenic noise pollution already exist, and they are even quite simple. “Slow down, move the navigation route, avoid sensitive areas, change the propellers,” said Simpson. Many ships rely on propellers that cause a lot of cavitation: small bubbles form around the propeller blade and produce a horrible squeak. But quieter designs exist, or are in progress.
“The propeller design is a rapidly evolving technological space,” said Simpson. Other innovations include bubble curtains, which can involve a pile driver and insulate the sound.
The researchers also pointed to offshore mining as an emerging industry that could become an important source of underwater noise and suggested that new technologies could be designed to minimize sound before commercial mining begins.
The authors hope the review will connect with lawmakers, who historically ignored noise as a significant anthropic stress factor in marine life. The BBNJ agreement of the United Nations Law on the Sea, a document that manages biodiversity in areas outside national jurisdiction, does not mention noise in its list of cumulative impacts.
The UN’s 14th sustainable development goal, which focuses on underwater life, does not explicitly mention noise, according to Dr. Seger of Applied Ocean Sciences. “The UN had a week of noise from the ocean, where they sat, listened and then moved on to another topic,” she said.
The Science article went through three editing rounds, the last of which occurred after Covid-19 created many unplanned experiments: shipping activity declined, the oceans were relatively quiet and marine mammals and sharks returned to the waters earlier noisy where they were rarely seen. “Recovery can be almost immediate,” said Duarte.
Live with sound
A healthy ocean is not a silent ocean – hail crackling on white-crested waves, glaciers hitting the water, gases bubbling from hydrothermal vents and countless creatures squeaking, scraping and singing are all signs of a normal environment. One of the article’s 20 authors is multimedia artist Jana Winderen, who created a six-minute audio track that changes from a healthy ocean – the screams of bearded seals, crustaceans breaking and rain – to an agitated ocean, with speedboats and a pile driving .
A year ago, while studying invasive species in seagrass meadows in waters near Greece, Dr. Duarte was about to rise to breathe when he heard a horrendous crash above him: “a huge warship over me, going to full speed. ”He stuck to the bottom of the sea until the navy ship passed by, taking care to slow his breathing and not exhaust the tank. About 10 minutes later, the sound subsided and Dr. Duarte managed to rise safely to breathe. “I have sympathy for these creatures,” he said.
When warships and other anthropogenic noises cease, seagrass meadows have their own unique soundscape. During the day, photosynthetic meadows generate small bubbles of oxygen that rise through the water column, growing until they burst. Together, the explosions of the bubbles make a sparkling sound like many bells, calling larvae of fish to come home.