The Silence of the Shrimps: How Carbon Pollution Could Put the Sea on Mute

Ocean acidification takes the "snap" out of snapping shrimp.

April 18, 2016

Ocean acidification is making snapping shrimp much less snappy.
Photo: Ria Tan/Flickr

Imagine you’re a clown fish larva—transparent, mostly blind, with no arms, legs, or fins, just a speck of living sea dust the size of a Tic Tac being tossed to and fro in the deep, wide ocean. If you don’t find shelter among some corals soon, you’ll surely die.

Suddenly in the distance, you hear a snap-crackle-pop of hope. Below the waves, the noise carries for miles. It is the sound of the reef calling you home: the rasping of urchins, the nibbling of parrotfish, and above all, the claw-crack of snapping shrimp.

More than 620 known species of snapping shrimp make some form of ruckus in coastal ecosystems around the world. Indeed, marine sound researchers curse these crustaceans and their constant pop-pop-pops for drowning out the sounds of other sea creatures. Thanks to us, though, their noisy days may be numbered.

You might assume the clamor of our shipping, drilling, and sonar is to blame for the quieting of the shrimp—and those activities are major problems for other sea life. But new research suggests the culprit may instead be our carbon emissions (go figure). A study published last month in Proceedings of the Royal Society B found that ocean acidification, fueled by the pollution we’ve been pumping into the atmosphere, can significantly reduce how often and how loudly shrimp snap.

Snapping shrimp, or pistol shrimp as they’re sometimes called, are in the family Alpheidae. They hunt and defend themselves with powerful claws, but unlike crabs and other crustaceans, they can also close their claws so quickly and with such force that they create cavitation bubbles—tiny, underwater shock waves that can kill fish in a millisecond. (This diabolical weapon is most infamously wielded by the snapping shrimp’s distant cousin, the mantis shrimp.)

These snaps aren’t just powerful—they’re loud. At 210 decibels, shrimp snaps are second only to sperm whale clicks when it comes to sounds produced by sea animals.

To study how ocean acidification messes with these real-life popcorn shrimp, scientists from the University of Adelaide in Australia visited naturally occurring carbon dioxide vents off the coasts of Italy and New Zealand to listen in on the shrimp that live there. The vents provide a range of CO2 concentrations, so the scientists were able to test areas with pH levels similar to those currently found across the world’s oceans, as well as areas with levels close to pH projections for the end of the century. They noticed that snapping shrimp crawling in higher concentrations of CO2 were decidedly less snappy. 

Another experiment analyzed why. Using a soft brush to tickle the animals, scientists measured the strength of the shrimps’ snaps to determine whether more acidic seawater weakened their exoskeletons or reduced their physical fitness in some other way. As far as the scientists could tell, however, the shrimp in more carbon-filled waters were just as fit as more active snappers elsewhere. All of which points to a behavioral change. For whatever reason, shrimp that are overexposed to CO2 just don’t feel like making a lot of noise.

Shrimp timbre may seem like an insignificant problem, but drop a mic in the ocean nearly anywhere on earth and you’ll hear the clicks, cracks, and scratchings of life. All that clatter isn’t just background noise. It serves as an important navigational tool for fish, cetaceans, and invertebrates alike. After all, scents get pushed around by underwater currents, and visual acuity can be diminished by turbid waters, phytoplankton blooms, and of course the setting sun. Sound waves, on the other hand, can travel thousands of miles as reliable beacons in the sea.

According to the recent study, quieter seas could potentially change the structure of coastal ecosystems. As the shrimp simmer down, fish larvae could spend longer periods adrift before finding reefs to colonize. This will put them at a higher risk of predation, starvation, and frankly, homelessness—all of which could have huge impacts on fish populations and the humans who rely on them for their food and livelihoods.

And then where will we be? Like the clown fish, lost. 

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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