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Ship noise disrupts camouflage abilities of shore crabs

Ship noise causes shore crabs to change color and seek shelter more slowly. Photo by Emily Carter/Exeter
Ship noise causes shore crabs to change color and seek shelter more slowly. Photo by Emily Carter/Exeter

March 9 (UPI) -- The shore crab is the most common crab on the coasts of the British Isles. Its color changing abilities help the crab blend in to its surroundings, but new research suggests ship noise is undermining the crab's camouflage.

Most research into the effects of noise pollution has focused on marine mammals, like whales and dolphins, that use sonar to communicate and hunt for prey.

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The latest research, published this week in the journal Current Biology, showed shore crabs subjected to elevated ship noise were slower to change colors as they moved through their underwater environs.

"Shore crabs don't depend heavily on sound -- so our finding that noise affects their behavior and ability to camouflage themselves suggests ship noise might affect a very wide range of species," lead study author Emily Carter, researcher at the University of Exeter, said in a news release.

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For the research, scientists tracked the movements and color changes of juvenile shore crabs in a series of tanks. Juvenile crabs can alter their appearance more quickly and dramatically than mature crabs, especially after molting, the act of shedding their shells as they grow.

"Our study shows that humans and noise pollution can substantially affect features of animals such as their coloration that are crucial to survival," said study co-author Martin Stevens, professor of sensory ecology and evolution at Exeter. "If crabs are less well concealed, and less likely to run away, they are more likely to get eaten by predators."

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In the test tanks, crabs were exposed to either a loud ship noise or a quiet ship noise, once every hour. To start, the crabs were all dark-shelled, but over the course of eight weeks, became paler as a result of life in the pale-bottomed tanks.

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The crabs exposed to ship noise changed color more slowly than the control group, which were left undisturbed by noise. When scientists simulated the presence of a predator, a bird flying over head, 85 percent of the crabs -- both those exposed to loud and quiet noise -- scurried for cover. However, when the predator simulation occurred at the same time as the house ship noise, the crabs were slower to seek shelter.

While adult shore crabs have other defense mechanisms, juvenile crabs are more reliant on their color-changing and shelter-seeking abilities, both of which are harmed by noise pollution.

"Previous studies have suggested that a lot of energy may be used during color change, and stress is also thought to be costly in terms of energy," Carter said. "So, the most likely explanation for our findings is that the stress caused by ship noise means crab don't have as much energy to devote to camouflage."

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