After decades of searching, scientists have filmed a cuttlefish battle for dominance in the wild – and it's brutal.

Image: Brown Digital Repository/YouTube

The dramatic scene unfolded back in 2011 in the Aegan Sea off the coast of Turkey, and (as most love triangles do) it started rather innocently.

A male-female pair of common cuttlefish (Sepia officinalis) were seen swimming together after some tentacled sexy time, with the male hovering above his recent mate. Things took a grisly turn, however, when a second male joined the fray.

As the interloper moved ever closer to the female, the original male defended his lady with a show of cuttlefish bravado: stiff arms, dilated pupils and flashes of aggressive zebra colouration. 


"They have a whole repertoire of behaviors that they use to signal to each other, and we're just barely starting to understand some of them," says Brown University ecologist Dr Justine Allen, who led a recent study on the behaviour. "Most of these battles are beautiful, stunning skin displays. It's a vicious war of colors."

Only this one didn't stop at "fist pump, push-up, chapstick." It got physical – and fast.  

The approaching male swooped in and managed to push off his opponent. But having already planted his seed, male number one wasn't giving up. In a flash, the pair erupted into a rough-and-tumble tussle of ink-squirting, biting and grappling. 

The ferocity of the encounter surprised Allen and her colleagues because cuttlefish – being squishy creatures – tend to avoid altercations that could damage their skin. These animals rely on tiny, pigment-filled organs in the skin called chromatophores to achieve their incredible camouflage. Any scarring incurred during a battle could put the cuttlefish at risk.

Rough sex is pretty standard in the ocean (just take a look at these grey reef sharks) and seasoned aquarists have observed similar interactions in captivity, but never at this intensity. 

Co-author Dr Roger Hanlon, a senior researcher at Brown University's Marine Biological Laboratory, found the slow buildup of this particular courtship clash intriguing. He notes that it seems to fit the "mutual assessment" model of game theory, meaning that individuals size-up their opponents' abilities, and compare them to their own, before choosing to brawl or bail.

"This was a totally serendipitous video sequence that I had been searching for nonstop for 20 years," he says. 

Cephalopods have long been praised for their brain power, so it's not entirely surprising that common cuttlefish and their kin may be able to choose their opponents wisely. In fact, this has already been proposed in closely-related species, like Australia's giant cuttlefish (Sepia apama).

In the end, the original male managed to stave off his challenger with a dizzying barrel roll. And according to Allen, he returned to guard his female shortly after.

The team hopes to document more of these tentacle tussles in the future, to paint a clearer picture of how they play out. 


Top header image: Joachim S. Müller