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Tuesday, May 21, 2024

The Sea Is Getting Warmer. Will the Shrimp Get Louder?

The ocean is normally a fairly noisy place, with the sounds of happy dolphins, lonely whales and diesel-chugging ships saturating the undersea world. But climate change may turn up the volume on this liquid symphony as warmer sea temperatures boost the volume of noise produced by the small but incredibly loud percussionist in this orchestra: the snapping shrimp.

This crustacean uses its oversize claw as a bubble-forming pistol of sorts, snapping it at more than 210 decibels. That’s louder than a gunshot, which is only 150 decibels. The shrimp uses these bubbles as a kind of sonic weapon to knock out its prey.

Now, marine scientists have discovered that warmer temperatures make snapping shrimp snap faster and louder, causing potential interference for submarines, fishermen, and marine life that need to communicate nearby. “It’s like going to a regular party and then someone turns up the music and the party goes wild,” says Aran Mooney, an associate scientist at the Woods Hole Oceanographic Institution who presented his work at the American Geophysical Union conference this month.

That matters, because a loud party in an undersea neighborhood disrupts life for everyone else who lives there. Mooney says fish also use sound to defend territory and to mate, so a noisier habitat could mean lower reproductive rates for some marine species. “An increase in sound could affect their neighbors as well as marine animals who rely on sound,” Mooney says. “If you increase background noise, you disrupt communication from them.”

There are more than 300 species of snapping shrimp, and they live in nearly all the world’s tropical regions. Since shrimp are cold-blooded creatures, they respond to conditions around them. As the water warms, so does a shrimp’s metabolism. Mooney listened to shrimp snap their claws in the colder water of North Carolina and compared the rates of snapping to a similar species living in the warmer tropical waters around the US Virgin Islands. He then repeated the experiments with colleagues at a laboratory at Woods Hole, Massachusetts, by taking the North Carolina shrimp and then simulating water temperatures increase due to climate change. Mooney boosted temperatures by 2 degree Celsius (3.6 degrees Fahrenheit). In the lab, they found that as the water temperature rose, so did the animals’ snapping rates.

To be sure, this is just one experiment involving one kind of marine animal. But globally, the past 10 years have been the warmest on record for Earth’s oceans. As heat is absorbed from the atmosphere, it doesn’t spread out evenly. There are hot spots of above-average heating off the northeastern US and South America, while the waters below Greenland are colder than usual. Heat from the atmosphere also goes to melting ice shelves, evaporating water, or directly reheating the atmosphere, according to a recent report by the National Oceanic and Atmospheric Administration (NOAA).

All told, the world’s oceans have absorbed more than 90 percent of the heat trapped by greenhouse gases from the atmosphere, and are warming 40 percent faster than a United Nations panel of scientists predicted they would just five years ago.

So it’s not just creatures in the tropics that are feeling the effects of a warming—and louder—ocean. So, too, are Arctic marine animals. When wind blows across open water, it creates bubbles and waves that in turn make noise. Arctic sea ice normally forms a protective layer against these environmental sounds, but ice coverage has declined dramatically as the result of atmospheric warming, creating bigger areas and longer periods of open water. Some areas of the Barents Sea now have four more months each year of open water than they did 30 years ago, says Kate Stafford, a senior oceanographer at the University of Washington’s Applied Physics Laboratory.

Stafford’s own research in the Arctic has shown that ambient sound levels are increasing as the result of the loss of sea ice. “We are altering the soundscape of the Arctic,” Stafford says.

Commercial activities are injecting low-frequency sounds into an ecosystem that has not evolved to deal with such a disturbance, Stafford says. Animals like the bowhead whale that once lived in relatively quiet waters are now dealing with more noise now that there’s less sea ice, as well the sounds from a boom in both ship transportation and oil exploration that has been fueled by the ice melt. Bowhead whales are communicating less with each other as the result of increasing noise, Stafford says, citing a colleague’s research.

“At some point, as drilling noise gets louder, they stop calling altogether,” Stafford says. “It’s just not worth talking at all.” The animals also use sound to find their prey, so more noise means it's harder for them to hunt.

And the noise levels may only get worse: Chinese officials are considering a transpolar sea route later this century, while energy firms from Europe, Russia, and the US are looking to the Arctic to fuel their economies.

Annebelle Kok, a postdoctoral researcher at the Scripps Institution of Oceanography who is studying the effects of noise on marine life, agrees that a noisier ocean—whether from passing ships or riled-up snapping shrimp—isn’t so good for the creatures that live there. “This might seem like a small thing, but behavioral changes can have big consequences,” says Kok, who is not involved in Mooney’s work. “If marine mammals change the way they hunt to avoid a ship, that can have consequences for their fitness or survival. Fish get distracted by boat noise and can get eaten more quickly if there’s a boat nearby.”

As for Mooney, he believes that it’s too early to tell if the snapping shrimp will continue their raucous behavior as their habitat warms. They could move north to cooler waters, for example. Fish that don’t like the snapping might do the same, but jumping into another fish’s territory up north can lead to unpredictable results, and increased competition, for all the species involved.

Mooney says his next project is studying whether the noise from the construction of offshore wind turbines might disturb squid off the Massachusetts coastline. That’s a big concern for squid fishermen, as well as marine mammals and fish that rely on squid for their diet.

And if the snapping shrimp are any example, their obnoxious noise-making may be just one of the first signs that a warming ocean is beginning to have hard-to-predict effects up and down the food chain.

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