A postdoctoral researcher at the University of Rhode Island has observed a never-before-seen defensive¹ strategy used by a small species of deep-sea squid in which the animal counter-attacks a predator² and then leaves the tips of its arms attached to the predator as a distraction³. Stephanie Bush said that when the foot-long octopus⁴ squid (Octopoteuthis deletron) found deep in the northeast Pacific Ocean "jettisons⁵ its arms" in self-defense, the bioluminescent（生物性发光的） tips continue to twitch⁶ and glow, creating a diversion that enables the squid to escape from predators⁷.

 

"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 wriggling⁸（蠕动） , bioluminescing arms might give the predator pause enough to allow the squid to get away."

 

The discovery was published in the July issue of the journal Marine⁹ Ecology Progress Series.

 

While Bush was a graduate researcher working with the Midwater Ecology Lab at the Monterey Bay Aquarium¹⁰ Research Institute, she observed that many octopus squid had arms of different lengths. Scientists had speculated that they may release their arms, just as lizards¹¹ can release their tails when attacked, but no one had seen it happen. Using a remotely operated vehicle in the Monterey Bay Submarine Canyon¹² off the coast of California, Bush poked¹³ at a squid with a bottlebrush.

 

"The very first time we tried it, the squid spread its arms wide and it was lighting¹⁴ up like fireworks," she said. "It then came forward and grabbed the bottlebrush and jetted backwards¹⁵, leaving two arms on the bottlebrush. We think the hooks on its arms latched¹⁶ onto the bristles¹⁷（猪鬃） of the brush, and that was enough for the arms to just pop off."

 

The squid are able to re-grow their missing arms.

 

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

 

In further experiments, Bush found that some octopus squid appeared hesitant to sacrifice their limbs, but some did so after being prodded¹⁸ several times. When she provoked seven other squid species similarly, none dropped their arm tips.

 

Bush's research on squid began in 2003 when she decided¹⁹ 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," she said. "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."

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