Mud Crabs Can Hear: Crustacean Behavior Impacted by Predatory Fish Noise

As shipping traffic and exploration activities increase, the world's oceans are becoming a noisier place. Unfortunately, this impacts the fish living there-creatures that rely on sound to communicate, just like their terrestrial counterparts. Now, scientists have discovered that crustaceans, such as crabs, also hear and rely on sound to tell them about a predatory fish's approach.

Until now, no one has studied the way prey species react to fishes' auditory cues. That's why scientists decided to take a closer look. The researchers examined whether mud crabs respond to fish sounds by putting the crustaceans into mesocosms, which are experimental environments designed to mimic the natural world, containing food in the form of juvenile clams. Then, the researchers submerged a microphone into the tank and transmitted various types of sound recordings of oyster toadfish, hardhead catfish and black drum fish.

The researchers found that the catfish and black drum fish sounds had the most pronounced effect on the crabs' behavior. This is possibly because they move on and off the reef during feeding times, while the toadfish stick around all the time.

"Prey usually respond differently if the cue is constant versus variable," said Randalla Hughes, one of the researchers, in a news release. "It makes sense-if a cue is constant, you're going to have to eat sometime, so you become desensitized to it."

The findings reveal that the prey do indeed change their behavior due to predator sounds. This shows that crabs have the ability to hear, and rely on sound in order to increase survival rates. That said, if the ocean is too noisy for them to hear, then it's possible that their ability to survive may decline.

Currently, the researchers plan to examine whether mud crabs on all reefs show the same behaviors, or if they're only sensitive to locally dominant predator species.

The findings are published in the journal Proceedings of the Royal Society B.