Ship Noise Leaving Crabs Too Stressed to Hide From Danger

(CN) – Human-caused undersea noise from ships stress out shore crabs, weakening their defenses and leaving them vulnerable to predators, according to research released Monday.

A study published in the journal Current Biology details how ship noise stresses out crabs and hampers their ability to change their shell color in order to blend in with their environment.

A juvenile shore crab blends in with light-colored rocks (Photo courtesy of Martin Stevens)

“Prior work had shown that ship noise can be stressful for shore crabs, so in this study, we wanted to address how that stress might affect behaviors they rely on for survival,” said first author Emily Carter, a graduate from the University of Exeter.

While crabs don’t rely primarily on sound, the research finds that noise pollution still affects their ability to respond to predators.

To determine the effects of noise pollution, the scientists put young shore crabs into two tanks. In one, they played the sounds of a container ship, cruise ship and oil tanker. The other tank, acting as a control, was exposed to natural water sounds played at various volumes.

The researchers discovered over the course of eight weeks that the crabs exposed to ship noise lightened their color to match the tank only half as much as the crabs in the control tank. Carter said she thinks this is due to the effect of the ships’ noise pollution.

“Color change in shore crabs is a slow, energetically costly process that’s controlled by hormones that activate specialized pigment cells across their shell,” Carter said. “Stress consumes energy and disrupts hormone balance, so we believe that the stress caused by ship noise either drains the crabs of the energy required to change color properly or disrupts the balance of hormones necessary to make that change.”

The scientists also noted physiological changes to the crabs, as they grew and molted slower than the control group. They also discovered that the crabs subject to noise pollution failed to respond to a simulated bird attack.

“About half of the crabs exposed to ship noise did not respond to the attack at all, and the ones that did were slow to hide themselves,” Carter said. “Similar to how people have trouble concentrating when stressed, the nature of their response indicates that they couldn’t process what was happening, as if that awareness and decision-making ability just wasn’t there.”

While most noise pollution research has focused on animals who directly use sound, Martin Stevens, professor at the University of Exeter, said the results show that more studies are needed on a wider range of ocean life.

“This work shows how processes like color change, which are not directly linked to acoustics, can still be affected by noise and how even animals like crabs are impacted by noise pollution–not just species that actively use sound, such as many fish or mammals,” says Stevens.

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