Disarming deep-sea tactics
Baku, July 31 (AZERTAC). Many deep-sea squid dispel an ink cloud to flee a predator, but one species goes a step farther: It ensures a getaway by counterattacking and then ditching the tips of its arms. These detached bits can continue to twitch and emit bioluminescent light—likely providing a vital distraction. By catching this strange maneuver on camera, scientists have established Octopoteuthis deletron as the only known squid to drop portions of its arms in self-defense, much as lizards drop their tails before escaping.
O. deletron inhabits depths of 500 to 600 meters. Little is known about the biology of these gelatinous deep-dwellers, but recently they have begun to yield their secrets—including some bizarre mating behavior—thanks to powerful video cameras mounted on robotic submersibles operated by researchers at Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California.
Viewing some of this footage, Stephanie Bush, a postdoctoral fellow at the University of Rhode Island, Kingston, noticed many individuals with arms of different lengths, and suspected that these cephalopods lost their arms during an attack. To investigate, Bush collaborated with researchers at MBARI. With a bit of luck, the team found squid off the coast of California, and tried poking them with the control arm of the submersible. The creatures attacked the vehicle but never held on, perhaps because they couldn`t grip its smooth metal surface, Bush says. Eventually, the researchers resorted to attaching the bottle-brush they used to wash their laboratory glassware to the submersible. When they nudged the next squid they encountered, the squid attacked the brush and immediately left behind parts of two arms. Fortunately the team caught the action with a high-resolution camera (see video). As the scientists erupted into cheers in the control room, Bush says she wondered why she hadn`t tried this earlier.
Not all individuals were so hasty to drop their arm tips—it often took several provocations, but squid always struck back before ditching their arm tips, Bush reports this month in Marine Ecology Progress Series. This distracting counterattack and the subsequent loss of limbs has been documented only in some crabs, Bush says. When she prodded seven other squid species from similar depths in Monterey Bay, none sacrificed their arms.
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