Why the warming oceans will get louder

Every 10 minutes, the relentlessly warming oceans absorb 50 megatons of energy, the amount of energy released when detonating the largest-ever atomic bomb.

These warming seas — which soak up over 90 percent of the heat humanity traps on Earth — harbor a particularly loud critter found all over the world: the snapping shrimp. The shrimp make an omnipresent background noise similar to static, or frying bacon, or crinkled paper. And new evidence points to a future where snapping shrimp may get significantly louder as the oceans continue to warm — a big environmental change for the many creatures inhabiting bustling reefs.

Marine scientists from the Woods Hole Oceanographic Institution recently gathered some 200 snapping shrimp from waters off of North Carolina. The researchers found the already-clamorous species become markedly louder when introduced to warmer temperatures, and will present their research Friday at the 2020 Ocean Sciences Meeting.

"The sea is a pretty noisy place," said Aran Mooney, a marine biologist at Woods Hole who coauthored the research.

"We’ve been worried about human-produced noise in the ocean," he said. "But we haven't thought about natural sounds."

The sound of snapping shrimp (which is likely an involuntary, automatic response) in coral and oyster reefs is truly ubiquitous. "If you're listening to a healthy coastal ecosystem, you’ll hear snapping shrimp," said Michelle Fournet, a postdoctoral researcher at the Center for Conservation Bioacoustics at Cornell University.

"We hear them almost every hour of every day," Fournet, who had no involvement in the research, added.

Each "snap" is made when shrimp quickly close their claws and pop a little bubble of air. Listen for yourself:

The Woods Hole researchers exposed the shrimp to three main temperatures: 10 degrees Celsius (50 F), 20 C (68 F), and 30 C (86 F). For reference, the shrimp usually experience 10 C temperatures in the winter, and about 28 C during the summer.

The difference in noise levels between 10 C and 30 C, measured in decibels, was dramatic. In the warmer conditions, the snapping was 20 decibels louder, which equates to being ten times as loud, explained Wood Hole's Mooney.

Overall, ocean temperatures have risen by about 2 F over the last 100 years, so each season, whether summer or winter, presumably has boosted overall temperatures and loudness, explained Mooney.

Critically, the U.N. International Panel on Climate Change (IPCC) expects surface ocean waters to warm by at least another 1 degree Fahrenheit or so by 2050. The warming will continue until human-made carbon emissions drop to zero — and there's no evidence of that happening for at least decades. (Emissions are still on the rise.)

The link between temperature and snapping is clear, said Mooney, and suggests that it's almost certainly going to get louder in ocean reefs, which teem with life (Though, like all novel research, these compelling results must be reproduced again). The looming question, however, is what does this boost in noise mean for ocean animals?

Snapping shrimp in a petri dish. Credit:

The ocean's heat content is rising. Credit: noaa

"The ecological implications of this are wide open," said Cornell's Fournet.

"We don't know what these effects are," agreed Mooney.

This research opens up the door to find answers, he said, by further researching snapping shrimp and animals, potentially in wild places.

Louder environments could easily cause problems for fish and other creatures. The boosted volume can mask sounds of the reef, as animals look for food or avoid predators. To us, reefs might appear quiet, but when recorded with underwater microphones, it's a bustling place. Toadfish whistle, groupers make low-frequency sounds, and many fish "puff."

"Fish make a lot more sounds than people think," said Fournet.

Or, the amplified snapping could be like having excessively loud neighbors, said Mooney. In that case, the noise would be incessantly stressful.

Already, civilization's warming of the oceans — stoked by dramatically boosted levels of atmospheric carbon dioxide to amounts likely not seen in millions of years — has resulted in animals fleeing from their homes and may also blind some sea creatures.

Now, we're likely altering the way their world sounds.

"We’re changing the soundscape," said Mooney.