2021-02-04 19:17:33 | In the Oceans, the Volume Is Rising as Never Before

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Story by: Sabrina Imbler The New York Times World News

Although clown fish are conceived on coral reefs, they spend the first part of their lives as larvae drifting in the open ocean. The fish are not yet orange, striped or even capable of swimming. They are still plankton, a term that comes from the Greek word for “wanderer,” and wander they do, drifting at the mercy of the currents in an oceanic rumspringa.

When the baby clown fish grow big enough to swim against the tide, they high-tail it home. The fish can’t see the reef, but they can hear its snapping, grunting, gurgling, popping and croaking. These noises make up 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 guns, pile drivers, dynamite fishing, drilling platforms, speedboats and even surfing — have made the ocean an unbearably noisy place for marine life, according to a sweeping review of the prevalence and intensity of the impacts of anthropogenic ocean noise published on Thursday in the journal Science. The paper, a collaboration among 25 authors from across the globe and various 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 Applied Ocean Sciences who was not involved with the research. “By the third page, I was like, ‘I’m going to send this to my students.’”

Anthropogenic noise often drowns out the natural soundscapes, putting marine life under immense stress. In the case of baby clown fish, the noise can even doom them to wander the seas without direction, unable to find their way home.

“The cycle is broken,” said Carlos Duarte, a marine ecologist at the King Abdullah University of Science and Technology in Saudi Arabia and the lead author on the paper. “The soundtrack of home is now hard to hear, and in many cases has disappeared.”

In the ocean, visual cues disappear after tens of yards, and chemical cues dissipate after hundreds of yards. But sound can travel thousands of miles and link animals across oceanic basins and in darkness, Dr. Duarte said. As a result, many marine species are impeccably adapted to detect and communicate with sound. Dolphins call one another by unique names. Toadfish hum. Bearded seals trill. Whales sing.

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Scientists have been aware of underwater anthropogenic noise, and how far it propagates, for around a century, according to Christine Erbe, the director of the Center for Marine Science and Technology at Curtin University in Perth, Australia, and an author on the paper. But early research on how noise might affect marine life focused on how individual large animals responded to temporary noise sources, such as a whale taking a detour around oil rigs during its migration.

Dr. Simpson has studied underwater bioacoustics — how fish and marine invertebrates perceive their environment and communicate through sound — for 20 years. Out in the field, he became accustomed to waiting for a passing ship to rumble by before going back to work studying the fish. “I realized, ‘Oh wait, these fish experience ships coming by every day,’” he said.

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Marine life can adapt to noise pollution by swimming, crawling or oozing away from it, which means some animals are more successful than others. Whales can learn to skirt busy shipping lanes and fish can dodge the thrum of an approaching fishing vessel, but benthic creatures like slow-moving sea cucumbers have little recourse.

Many solutions to anthropogenic noise pollution already exist, and are even quite simple. “Slow down, move the shipping lane, avoid sensitive areas, change propellers,” Dr. Simpson said. Many ships rely on propellers that cause a great deal of cavitation: Tiny bubbles form around the propeller blade and produce a horrible screeching noise. But quieter designs exist, or are in the works.

“Propeller design is a very fast-moving technological space,” Dr. Simpson said. Other innovations include bubble curtains, which can wrap around a pile driver and insulate the sound.

The researchers also flagged deep-sea mining as an emergent industry that could become a major source of underwater noise, and suggested that new technologies could be designed to minimize sound before commercial mining starts.

The authors hope the review connects with policymakers, who have historically ignored noise as a significant anthropogenic stressor on marine life. The United Nations Law of the Sea B.B.N.J. agreement, a document that manages biodiversity in areas beyond national jurisdiction, does not mention noise among its list of cumulative impacts.

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The U.N.’s 14th sustainable development goal, which focuses on underwater life, does not explicitly mention noise, according to Dr. Seger of Applied Ocean Sciences. “The U.N. 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 occurred after Covid-19 had created many unplanned experiments: Shipping activity slowed down, the oceans fell relatively silent, and marine mammals and sharks returned to previously noisy waterways where they were rarely seen. “Recovery can be almost immediate,” Dr. Duarte said.

When warships and other anthropogenic noises cease, sea grass meadows have a soundscape entirely their own. In the daytime, the photosynthesizing meadows generate tiny bubbles of oxygen that wobble up the water column, growing until they burst. All together, the bubble blasts make a scintillating sound like many little bells, beckoning larval fish to come home.


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Source References: The New York Times World News

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