Cuttlefish evolved 21 million years ago, which is plenty of time to develop special skills, like a natural camouflage that instantly transforms their colors and patterns. Humans are still discovering new powers held by these sea chameleons.
A study published in the Journal of Experimental Biology (paywall) on Jan. 11 reveals that cuttlefish can hear infrasound, which is sound at extremely low frequencies—far below the 20 Hz, or cycles per second, that humans hear—and they rely on this exceptional auditory skill to stay safe. They are so attuned to sound that they can anticipate an impending predator’s arrival based on particle changes in water flow, and escape using jet propulsion.
After observing cuttlefish’s movements in the wild, and remarking that the creatures seemed to swoop out of the way of prey, the researchers decided to test whether cuttlefish rely on sound for survival. “It is impossible to eat something underwater without creating a hydrodynamic disturbance,” lead researcher Maria Wilson told the Company of Biologists, which publishes several biological journals, in a statement on the study. The disturbance takes the form of tiny particle changes in water flow; those particle changes makes sounds at extremely low frequencies.
So, the researchers tested how cuttlefish in a lab responded to water-flow disturbances at three different frequencies: 3 Hz, 5 Hz, and 9 Hz. They also tested the fish under three different conditions: in a darkened tank, a lit tank, and finally, in a lit tank with a screen displaying the cuttlefish’s typical prey—shrimp—after 24 hours without food. These distinct conditions allowed researchers to differentiate between visual, sensory, and auditory responses to disturbances in water flow, and to measure whether cuttlefish might risk danger when hungry and in hunting mode.
They discovered that cuttlefish did in fact hear the low-frequency sounds of water-flow disruptions—the sort that a predator would make when approaching. And when the cuttlefish in the lab tests heard the “predator” coming, they pressed water out of a cavity in their mantle, propelling them away at high speed. That is, if they weren’t distracted.
Hungry cuttlefish watching shrimp on the tank’s screen were engaged with the video, sometimes to their detriment. When preoccupied by technology’s wonders, the cuttlefish didn’t pay attention to danger signals until they became more powerful.
One of the nine juvenile cuttlefish tested also displayed a sense of humor—or justice. Cephalopds are called tintenfisch (“ink fish”) in German; one of the cuttlefish squirted ink in Wilson’s face when she tried to take the sea creature out of its tank. “Almost as if it did it on purpose,” she says.
Jokes aside, Wilson worries that cuttlefish are at risk. Human activity in the world’s waters creates a constant low “fog of noise” that masks sounds these ancient cephalopods have long relied upon to survive.