This deep-sea squid jettisons arms as a defensive tactic

University of Rhode Island researchers have observed a never-before-seen defensive strategy used by a small species of deep-sea squid.

Indeed, the foot-long octopus squid (Octopoteuthis deletron) found deep in the northeast Pacific Ocean counter-attacks a predator – and then leaves the tips of its arms attached to the assailant.

According to Stephanie Bush, the bioluminescent tips continue to twitch and glow, effectively creating a diversion that enables the squid to escape from predators.

“If a predator is trying to attack them, they may dig the hooks on their arms into the predator’s skin. Then the squid jets away and leaves its arm tips stuck to the predator,” explained Bush. “The wriggling, bioluminescing arms might give the predator pause enough to allow the squid to get away.”

While Bush was a graduate researcher working with the Midwater Ecology Lab at the Monterey Bay Aquarium Research Institute, she observed that numerous octopus squid boasted arms of different lengths. 

Scientists had speculated that they may release their arms, just as lizards can release their tails when attacked, but no one had actually seen it happen. 

However, using a remotely operated vehicle in the Monterey Bay Submarine Canyon off the coast of California, Bush was able to poke the squid with a bottlebrush.

“The very first time we tried it, the squid spread its arms wide and it was lighting up like fireworks,” she said. “It then came forward and grabbed the bottlebrush and jetted backwards, leaving two arms on the bottlebrush. We think the hooks on its arms latched onto the bristles of the brush, and that was enough for the arms to just pop off.”

As expected, the squid are capable of re-growing their missing arms.

“There is definitely an energy cost associated with this behavior, but the cost is less than being dead,” Bush said.

In additional experiments, Bush determined that certain octopus squid appeared hesitant to sacrifice their limbs, but some did so after being prodded several times. When she similarly provoked seven other squid species, none dropped their arm tips.

Bush’s research on squid began in 2003 when she decided to investigate the assumptions that some scientists had made about deep-sea animals.

“Scientists had assumed that squid living in the deep-sea would not release ink as a defensive measure, but all the species I’ve observed did release ink. They assumed that because they’re in the dark all day every day that they’re not doing the same things that shallow water squids are doing.

“They also assumed that deep-sea squid don’t change color because of the dark, but they do. They’re a really abundant species in the Gulf, so presumably if they are that abundant, they must be feeding on lots of different things and there must be lots of things feeding on them. They could be very important to the health of the ecosystem,” she added.