How fishy sounds save many a mud crab

Fish use their watery voices to relay distress, find prey, defend their nests, and attract mates but the sounds they make also help marine crabs to hide from predators. Researchers have found that marine crabs too have the capability to hear.

The auditory ability of marine crabs plays an important role in their response to fish predators, the findings showed.

"We showed that these crabs change their behaviour in response to acoustic signals," said Randall Hughes, assistant professor of marine and environmental sciences at Northeastern University in the US.

In the first step of the experiment, the researchers looked at whether mud crabs respond to fish sounds.

They put the crabs into mesocosms -- experimental environments designed to mimic the natural world -- containing food in the form of juvenile clams.

They then submerged a microphone into the tank and transmitted various types of sound recordings of oyster toadfish, hardhead catfish and black drum fish.

"We pretty quickly saw that the crabs were not feeding as much in response to the predator sounds," Hughes added.

By examining the response of the crabs to implanted electrodes into the "statocyst" at the base of the mud crabs' antennae, the researchers confirmed that this was due to the crabs' ability to actually hear them, rather than some other hidden variable.

The findings appeared in the journal Proceedings of the Royal Society B.