August 5, 2012
Deep-sea Squid Will Detach Its Arms As Defensive Tactic
redOrbit Staff & Wire Reports - Your Universe Online
A defensive strategy, never seen before, being 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 diversion has been observed by a postdoctoral researcher at the University of Rhode Island.
When the foot-long octopus squid (Octopoteuthis deletron) found deep in the northeast Pacific Ocean "jettisons its arms" in self-defense, the bioluminescent ends continue to shudder and glow which creates a diversion so that the squid can flee from its predators, according to Stephanie Bush.
"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."
The discovery was published in the journal 'Marine Ecology Progress Series' July issue.
While Bush was working with the Midwater Ecology Lab at the Monterey Bay Aquarium Research Institute as a graduate researcher, she observed that many octopus squid had arms of different lengths. It had not been observed yet, but scientists thought that they may release their arms, just as lizards can release their tails when attacked. Bush poked at a squid with a bottlebrush using a remotely operated vehicle (ROV) in the Monterey Bay Submarine Canyon off the coast of California.
"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."
The squid´s missing arms then re-grew.
"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 of the octopus squid appeared hesitant to give up their limbs, but after being prodded several times some did. When she provoked seven other squid species similarly, none dropped their arm tips. Bush decided to investigate the assumptions that some scientists had made about deep-sea animals and began her research in 2003.
"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."
The main focus for the URI scientist's current research is on a tiny squid that lives in the Gulf of California that migrates every day from the deep in the ocean where there is little oxygen to the surface waters to feed. She is looking at their oxygen consumption rates and how rising water temperatures will affect their survival.
"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," Bush said. "They could be very important to the health of the ecosystem."