The deepest part of the ocean is one big cacophonic orchestra. Hidden in its burrows are the loudest invertebrates: the snapping shrimps.

With the crackling, crunchy sound of its asymmetrical claws, the snapping shrimp is a real "treble-maker" for all marine life recordists. But the sound is essential because the animal uses it as a hunting mechanism as well as a warning sign to scare off predators.

This snappy marine creature produces the most ubiquitous sound in shallow temperate waters, and can be heard like a crackling popcorn. In fact, the snapping shrimp produces sounds of up to 210 decibels.

Unfortunately, the strange snapping shrimps are in danger of being silenced, all because of ocean acidification, a new study revealed.

Falling Silent

Tullio Rossi, one of the study researchers, said coastal reefs are far from being quiet environments because they are filled with loud, crackling sounds.

"Shrimp 'choruses' can be heard kilometers offshore and are important because they can aid the navigation of baby fish to their homes," said Rossi. "But ocean acidification is jeopardizing this process."

Scientists have known for a while that the continuous acidification of oceans is causing some change to marine creatures with a calcium carbonate shell.

How are the snapping shrimps affected? Rossi and his colleagues found that for snapping shrimps, whose habitats are at natural CO2 volcanic vents, there is a change in behavior rather than any physical injury to the creature's claw.

Along with Ivan Nagelkerken and other scientists, the research team studied the snapping shrimp sound in field recordings conducted at CO2 volcanic vents in three various locations in the ocean. The team also analyzed the sound under laboratory conditions.

At CO2 volcanic vents, the ocean is much more acidic. Turns out, there were significant reductions in the levels of sound produced by shrimps, as well as the frequency of their snaps.

A Worrisome Outcome

Nagelkerken said sound is one of the most dependable cues for direction and location in the ocean because it can carry up to thousands of kilometers with little change.

In contrast, scents and visual cues are affected by water clarity, light and turbulence.

In the end, the results of their study are quite "disturbing," Nagelkerken said.

If the carbon emissions induced by human activity remain unabated, ocean acidification will turn noisy and lively reefs into relatively silent ones, he said.

"Given the important role of natural sounds for animals in marine ecosystems, that's not good news for the health of our oceans," he added.

The team's findings are featured in the journal Proceedings of the Royal Society B.

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