Although narwhals are conceived on coral reefs, they spend the first part of their lives as larvae floating in the open ocean. The fish is not yet orange, striped or can even swim. They are still plankton, a term derived from the Greek word for ‘wanderer’, and they wander, drifting at the mercy of the currents in an oceanic rum spring.
When the baby’s narwhal grows big enough to swim against the tide, they pull it home. The fish cannot see the reef, but they hear it breaking, grunting, gurgling, popping and croaking. These sounds form the soundscape of a healthy reef, and larval fish rely on these soundscapes 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, air rifles, pole drivers, dynamite fishing, drilling platforms, speedboats and even surfing – have made the sea an unbearable noise for marine life, according to a comprehensive survey of the occurrence and intensity of anthropogenic effects. ocean noise published in the journal Science on Thursday. The paper, a collaboration between 25 authors from around the world and different fields of marine acoustics, is the largest synthesis of evidence on the effects of oceanic noise pollution.
“They hit the nail on the head,” said Kerri Seger, a senior scientist at the Applied Ocean Sciences, who was not involved in the research. “On the third page, I said, ‘I’m going to send this to my students. ‘
Anthropogenic noise often drowns out the natural soundscapes and puts marine life under tremendous stress. In the case of baby narcissus, the noise can even condemn them to stray from the sea without finding their way home.
“The cycle has been broken,” said Carlos Duarte, a marine ecologist at King Abdullah University of Science and Technology in Saudi Arabia, and the paper’s lead author. “The soundtrack of the house is now difficult to hear and has disappeared in many cases.”
Drowning the signals
In the ocean, visual cues disappear after ten meters, and chemical cues disappear after hundreds of meters. But sound can travel thousands of miles, connecting animals across ocean basins and in the dark, said Dr. Duarte said. As a result, many marine species have been impeccably adapted to detect and communicate with sound. Dolphins call each other by unique names. Toadfish hum. Beard seals tremble. Whales sing.
According to Christine Erbe, director of the Center for Marine Science and Technology at Curtin University in Perth, Australia, scientists have been aware of anthropogenic noise underwater for a century and how far it propagates. But early research on how noise can affect marine life has focused on how individual large animals respond to temporary noise sources, such as a whale taking a turn at the oil rigs during migration.
The new study maps how underwater noise affects numerous groups of marine life, including zooplankton and jellyfish. “The scale of the problem of noise pollution has recently dawned on us,” said Dr. Erbe written in an email.
The idea for the paper was presented to Dr. seven years ago. Duarte came. For much of his long career as an ecologist, he was aware of the importance of ocean sound, but he felt that the issue was not being recognized on a global scale. Dr. Duarte found that the scientific community focused on the ocean soundscapes was relatively small, with vocalizations of marine mammals in one corner, and underwater seismic activities, acoustic tomography, and policymakers in other, remote corners. “We all had our little golden rush,” said Steve Simpson, a marine biologist at the University of Exeter in England, and a writer on the paper.
Dr. Duarte wanted to bring the different corners together to synthesize all the evidence they had gathered in a single conversation; perhaps something that this wonderful policy will eventually lead to policy changes.
According to author Simpson, the authors have selected more than 10,000 articles to ensure that they have captured every trend of research on sea acoustics over the past few decades. Patterns quickly emerged that show the detrimental effect that noise has on almost all marine life. “With all the research, you realize that you know more than you think you know,” he said.
Dr. Simpson studied underwater bio-acoustics for 20 years – how fish and invertebrates in the area perceive their environment and communicate through sound. Out in the field, he got used to waddling on a passing ship before going back to work to study the fish. “I realized, ‘Oh, wait, this fish experiences ships every day,'” he said.
Marine life can adapt to noise pollution by swimming, crawling or washing away, which means that some animals are more successful than others. Whales can learn to attract busy ship lanes, and fish can dodge the drum of an approaching fishing vessel, but botways like slow-moving sea cucumbers have little use.
If the noise moves in more permanently, some animals simply leave forever. When acoustic harassment devices were installed to ward off seals from prey on salmon farms in the Broughton Archipelago in British Columbia, orcas’ populations declined significantly until the devices were removed, according to a 2002 study.
These forced evacuations reduce population size as more animals give up land and compete for the same pool of resources. And certain species that are restricted to limited biogeographic ranges, such as the endangered Maui dolphin, have nowhere else to go. “Animals can’t avoid the sound because it’s everywhere,” said Dr. Duarte said.
Even temporary noises can cause chronic hearing damage in marine animals that are unfortunate enough to get caught up in the acoustic effects. Both fish and marine mammals have hair cells, sensory receptors to hear. Fish can regrow these cells, but marine mammals probably can not.
Fortunately, noise, unlike greenhouse gases or chemicals, is a relatively controllable pollutant. “Noise is about the easiest problem to solve in the sea,” said dr. Simpson said. “We know exactly what causes noise, we know where it is, and we know how to stop it.”
Looking for silence
There are already many solutions to anthropogenic noise pollution, and are even quite simple. “Slow down, move the shipping lane, avoid sensitive areas, change propellers,” said Dr. Simpson said. Many ships rely on propellers that cause a lot of cavitation: small bubbles form around the propeller blade and make a terrible screaming noise. But there are quieter designs, or it’s working.
“Screw design is a very fast-moving technological space,” said dr. Simpson said. Other innovations include bubble curtains, which can wrap around a stacker and isolate the 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 designed to minimize noise before commercial mining began.
The authors hope the review joins policymakers who have historically ignored noise as a major anthropogenic stressor on marine life. The BBNJ Convention on the Law of the Sea, a document that governs biodiversity in areas outside national jurisdiction, does not mention noise in the list of cumulative consequences.
According to Seger of the Applied Ocean Sciences, the expression of the UN’s 14th Sustainable Development Goal, which focuses on underwater life, is not explicitly mentioned. “The UN had an ocean noise week where they sat down and listened to it and then went on to another topic,” she said.
The paper in Science went through three rounds of editing, the last of which took place after Covid-19 created many unplanned experiments: Shipping activity slowed, the oceans became relatively quiet and marine mammals and sharks returned to previously noisy waterways where they were rarely seen. “Recovery can be almost immediate,” said Dr. Duarte said.
Live with sound
A healthy ocean is not a quiet ocean – hail crackling in white crest waves, glaciers plunging into water, gases bubbling out of hydrothermal vents, and numerous creatures biting, rasping and singing are all signs of a normal environment . One of the 20 authors on the page is multimedia artist Jana Winderen, who created a six-minute soundtrack that shifts from a healthy ocean – the calls of bearded seals, funny crustaceans and rain – to a disturbed ocean of motorboats and staple. row.
While dr. Duarte was studying invasive species in seagrass meadows in waters near Greece a year ago, he was about to get into the air when he heard a terrible rumble above him: ‘a large warship on top of me which goes at full speed. He remained stuck on the seabed until the naval vessel passed, careful not to slow down his breathing and not to sink his tank. About ten minutes later the sound dropped and Dr. Duarte rises safely for air. “I sympathize with these creatures,” he said.
When warships and other anthropogenic sounds cease, seagrass meadows have their own soundscape. During the day, photosynthesis produces meadows with small oxygen bubbles that swirl and grow in the water column until it bursts. All in all, the bubble explosions make a dazzling sound like very small bells, signaling the larval fish to come home.