Deep-sea Octopus Squid Leaves Its Arms Behind as Escape Tactic

Posted on August 4, 2012

Stephanie Bush, a postdoctoral researcher at the University of Rhode Island, observed a never-before-seen defensive strategy used by a small species of deep-sea squid in which the animal counter-attacks a predator and then leaves the tips of its arms attached to the predator as a distraction. The squid are able to re-grow their missing arms.

Stephanie Bush says that when the foot-long octopus squid (Octopoteuthis deletron) "jettisons its arms" in self-defense, the bioluminescent tips continue to twitch and glow, creating a diversion that enables the squid to escape from predators. The octopus squid is found deep in the northeast Pacific Ocean.

Here the squid leaves a couple tentacles behind after a battle with a bottlebrush. Take a look:

While Bush was a graduate researcher working with the Midwater Ecology Lab at the Monterey Bay Aquarium Research Institute, she observed that many octopus squid had arms of different lengths. Scientists had speculated that they may release their arms, just as lizards can release part of their tails when attacked, but no one had seen it happen. Using a remotely operated vehicle in the Monterey Bay Submarine Canyon off the coast of California, Bush poked at a squid with a bottlebrush.

Bush says, "The very first time we tried it, the squid spread its arms wide and it was lighting up like fireworks. 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."

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

Bush says, "There is definitely an energy cost associated with this behavior, but the cost is less than being dead."

A paper about the discovery was published here the July issue of the journal Marine Ecology Progress Series.

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