Although clownfish are conceived on coral reefs, they spend the first part of their lives as larvae floating in the open ocean. The fish are not yet orange, striped or even swimming. They are still plankton, a term derived from the Greek word for “wanderer”, and they migrate by being exposed to the currents in an oceanic rumspringa.
When the baby clownfish get big enough to swim against the tide, they pull them home. The fish cannot see the reef, but they can snap, grunt, gurgle, pop, and croak. These noises form the soundscape of a healthy reef, and larval fish rely on these soundscapes to return to the reefs, where they will spend the rest of their lives – if they can hear them.
But humans – and their ships, seismic surveys, air rifles, pile drivers, dynamite fishing, drilling rigs, speedboats, and even surfing – have made the ocean an excruciatingly noisy place for marine life, according to a comprehensive review of the spread and intensity of the effects of anthropogenic sea noise , published Thursday in Science magazine. The paper, a collaboration of 25 authors from around the world and different fields of marine acoustics, is the largest synthesis of evidence on the effects of ocean noise pollution.
“You 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 said, ‘I’ll send this to my students.'”
Anthropogenic noise often drowns out the natural soundscapes and exposes marine life to immense stress. In the case of baby clownfish, the noise can even doom them to wander the seas with no direction and unable to find their way home.
“The cycle is broken,” said Carlos Duarte, marine ecologist at King Abdullah University of Science and Technology in Saudi Arabia and lead author of the paper. “The soundtrack from home is now difficult to hear and in many cases has disappeared.”
The signals drown out
In the ocean, visual cues disappear after ten meters and chemical cues disappear after hundreds of meters. But sound can travel thousands of kilometers and connect animals across oceanic basins and in the dark, said Dr. Duarte. As a result, many marine species are perfectly adapted to recognize and communicate with sound. Dolphins call each other by unique names. Toad fish buzz. Bearded seals trill. Whales sing.
According to Christine Erbe, director of the Center for Marine Science and Technology at Curtin University in Perth, Australia and an author of the paper, scientists have been aware of underwater anthropogenic noise and its spread for about a century. However, early research on how noise could affect marine life focused on how individual large animals reacted to transient sources of noise, such as a whale making a detour around oil rigs while migrating.
The new study shows how underwater noise affects myriad groups of marine life, including zooplankton and jellyfish. “The magnitude of the noise problem has only recently occurred to us,” wrote Dr. Inheritance in an email.
The idea for the paper came from Dr. Duarte seven years ago. He had been aware of the importance of ocean noise for much of his long career as an ecologist, but felt that the problem was not being recognized on a global scale. Dr. Duarte noted that the scientific community focused on marine soundscapes was relatively small and goofy, with marine mammal vocalizations in one corner and underwater seismic activity, acoustic tomography, and policymakers in other far corners. “We were all on our little gold rush,” said Steve Simpson, a marine biologist at the University of Exeter in England and author of the paper.
Dr. Duarte wanted to bring the different corners together to bring all of the evidence they’d gathered into a single conversation. Maybe something so great would ultimately lead to policy changes.
According to Dr. Simpson, the authors screened more than 10,000 articles to ensure they covered all of the tendrils of marine acoustics research over the past few decades. Patterns quickly emerged showing the harmful effects of noise on almost all marine life. “In all this research, you realize that you know more than you think you know,” he said.
Dr. Simpson has been studying underwater bioacoustics for 20 years – how fish and marine invertebrates perceive their environment and communicate through sound. Out in the field, he got used to waiting for a passing ship to rumble by before going back to work to study the fish. “I realized, ‘Oh wait, these fish see ships that come by every day,'” he said.
Marine life can adapt to noise pollution by swimming, crawling, or oozing away, meaning some animals are more successful than others. Whales can learn to bypass busy shipping lanes and fish can avoid the roar of an approaching fishing vessel, but benthic creatures like slow-moving sea cucumbers have little recourse.
When the noise becomes more permanent, some animals simply leave for good. When acoustic harassment devices were installed to deter seals from hunting on salmon farms in British Columbia’s Broughton Archipelago, killer whale populations declined significantly until the devices were removed, according to a 2002 study.
These forced evacuations reduce the population size as more animals give up their territory and compete for the same resource pools. And certain species tied to limited bio-geographical areas, like the endangered Maui dolphin, have nowhere else to go. “Animals can’t avoid the sound because it’s everywhere,” said Dr. Duarte.
Even transient noises can cause chronic hearing damage in marine animals that are unlucky enough to be caught in acoustic wake. Both fish and marine mammals have hair cells, sensory receptors for hearing. Fish can grow these cells back, but marine mammals likely cannot.
Fortunately, unlike greenhouse gases or chemicals, sound is a relatively controllable pollutant. “Noise is the easiest problem in the ocean to solve,” said Dr. Simpson. “We know exactly what is causing noise, we know where it is and we know how to stop it.”
Looking for peace
There are already many solutions to anthropogenic noise pollution that are actually quite simple. “Slow down, move the lane, avoid sensitive areas, change propellers,” said Dr. Simpson. Many ships rely on propellers, which cause a lot of cavitation: tiny bubbles form around the propeller blade, creating a terrible screeching sound. But quieter designs exist or are in the works.
“Propeller design is a very fast-paced technological space,” said Dr. Simpson. Other innovations are bubble curtains that wrap around a pile driver and can isolate sound.
The researchers also identified deep-sea mining as an emerging industry that could become a major source of underwater noise and suggested that new technologies could be developed to minimize the noise before commercial mining began.
The authors hope the review is related to policy makers who have historically ignored noise as a major anthropogenic stressor on marine life. The United Nations BBNJ Convention on the Law of the Sea, a document that manages biodiversity in areas outside national jurisdiction, does not mention noise in its list of cumulative effects.
The 14th United Nations Sustainable Development Goal, which focuses on life underwater, mentions according to Dr. Seger of Applied Ocean Sciences doesn’t explicitly mention noise. “The UN had a week of sea noise where they sat down and listened to it and then moved on to another topic,” she said.
The paper in Science went through three rounds of processing, the last of which came after Covid-19 conducted many unplanned experiments: shipping activity slowed, the oceans became relatively still, and marine mammals and sharks were returning to previously noisy waterways where they were rarely found seen. “Recovery can be almost instant,” said Dr. Duarte.
Lively with sound
A healthy ocean is not a quiet ocean – hail crackling in white-capped waves, glaciers crashing into water, gases escaping from hydrothermal springs, and myriad creatures chittering, scratching, and singing are all signs of a normal environment . One of the paper’s 20 authors is multimedia artist Jana Winderen, who created a six-minute audio track that moves from a healthy ocean – the calls of seals, the crackling of crustaceans, and rain – to a disturbed ocean with motorboats and piles of driving .
A year ago when Dr. Duarte investigated invasive species in seagrass beds in waters near Greece, he was about to take a breath when he heard a terrible rumble overhead: “A huge warship above me, sailing at full speed. “He stayed glued to the seabed until the naval ship passed, being careful not to slow his breathing and not to deplete his tank. About 10 minutes later the noise subsided and Dr. Duarte was sure to get a breath. “I have sympathy for these creatures,” he said.
When warships and other anthropogenic noises stop, seagrass meadows have their very own soundscape. During the day, the photosynthetic meadows create tiny bubbles of oxygen that wobble up the water column and grow until they burst. All in all, the bubble explosions make a sparkling sound like many small bells and lure larval fish home.