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The Silence of the Shrimp

The loudest invertebrates in the ocean, snapping shrimps, may be silenced as the oceans become more acidic due to high levels of CO2, a University of Adelaide study has found.

Ocean acidification is expected to have profound consequences for many species that rely on sound cues for information about the location and quality of food, shelter, partners and potential predators.

“Shrimp ‘choruses’ can be heard kilometres offshore, and are important because they can aid the navigation of baby fish to their homes,” says PhD candidate Tullio Ross. “Ocean acidification is jeopardising this process.”

The snapping shrimp are the most common and noisiest of the sound-producing marine animals in coastal ecosystems (www.tinyurl.com/hljjhgx). They can produce sounds of up to 210 dB through the formation of bubbles created by rapidly closing their snapping claw as a warning sign to scare off predators.

Rossi and supervisors A/Prof Ivan Nagelkerken and Prof Sean Connell measured the sound produced by shrimp in field recordings at natural CO2 volcanic vents at three different ocean locations and under laboratory conditions. They found substantial reductions in both the levels of sound produced and in the frequency of snaps. The results were published in the Proceedings of the Royal Society B (www.tinyurl.com/jt8z8sv)

“Our results suggest that this is caused by a change of behaviour rather than any physical impairment of the claw,” Nagelkerken says. “This outcome is quite disturbing. Sound is one of the most reliable directional cues in the ocean because it can carry up to thousands of kilometres with little change, whereas visual cues and scents are affected by light, water clarity and turbulence.

“If human carbon emissions continue unabated, the resulting ocean acidification will turn our currently lively, noisy reefs into relatively silent habitats. And given the important role of natural sounds for animals in marine ecosystems, that’s not good news for the health of our oceans.”