Cuttlefish hearing – in living color

Sepia latimanus (Reef_cuttlefish), Wikimedia, by Nick Hobgood Cuttlefish are perhaps one of the more complicated critters you’re likely to encounter. Related to the squids and the octopus they have many of the same highly visual adaptation of being able to rapidly change color and even textures of their skin in exceedingly complex ways. Given the complexity and rapidity of these changes it has been suggested that the changes are more than just simple expressions of fear, anger, or lust; they may contain more complex communications.

They mimic shapes and colors in ways that are handy for camouflage, but they also mimic shapes and colors of other animals for who knows what reason… humor perhaps? It also turns out that unlike their apparently deaf cousins, the octopus, the cuttlefish are hearing animals.

Aran Mooney at Woods Hole Oceanographic Institute (WHOI) is finding the color and shape-morphing behavior convenient in testing hearing thresholds. In most “operant conditioning” tests animal subjects need to be trained to respond to stimuli and then run through a threshold testing regime. Thus can take a lot of time – even with subjects as smart as cuttlefish. But cuttlefish display subtle color changes, and “twitching” predictably to sound stimulus indicative of stress levels. This takes the training requirement out of the loop.

This video of the WHOI work is at the extreme end of the testing. Cuttlefish “ink and jet” to escape when mortally threatened. (Being exposed to this nasty sound, I’d do much the same.) This brings us around to why all of this is important. Hansjoerg P. Kunc et.al played environmental sounds to the cuttlefish and found that when exposed to shipping noise they displayed color changes and physical motions indicative of stress, which they did not display when played the natural sounds of waves crashing.

It is not surprising that any hearing animal could distinguish the difference between shipping noise and waves. And while there is no reason a cuttlefish should be specifically fearful of ships, there is a reason they might be stressed out by unnatural sounds.

Knowing that stress compromises the health and breeding fitness of these cephalopods points to a larger and more nuanced concern that we should have when introducing unnatural sounds into productive marine habitats.