The Spectacular Strobe Squid

As drawn by author and artist Richard Ellis, the deep-sea squid Taningia danae is an especially adorable cephalopod. Depicted on page 151 of his book The Search for the Giant Squid, the squishy creature has big eyes and broad fins that would make Sister Bertrille envious. The squid almost looks like a Pokémon character, and certainly has a fitting name for the anime franchise – “Taningia, I choose you!”

But Taningia danae isn’t actually as cuddly as it looks in Ellis’ book. In addition to arrays of chitinous hooks lining the tentacles of this seven-foot squid, Taningia danae also possesses a pair of lemon-shaped organs on two tentacle tips that can be fired like strobe lights. This is a squid that dazzles before it kills.

Up until about twenty years ago, much of what squid experts knew about Taningia came from occasional specimens hauled up in fish nets and partially-digested individuals found in the guts of whales and other predators. Teuthologists – those scientists dedicated to the study of squid – knew more about what was eating Taningia than what the peculiar, eight-armed squid was hunting and how the squid did so. The squid’s pair of lightbulb-like organs were obviously light-producing structures called photophores, but no one really knew whether they actually emitted light or how the squid used them.

The fortuitous capture of a relatively small Taningia solved the mystery. In 1975 teuthologists Clyde Roper and Richard Young captured a roughly two-foot specimen off the coast of Hawaii and kept it alive long enough to place the animal in a shipboard aquarium. Curious to see if the supposed photophores really did emit light, the two scientists turned off the lights, and, as explained in a 1993 paper by Roper and colleague Michael Vecchione, “one observer slowly moved his hand around in the aquarium in an effort to stimulate a response.”

Whichever researcher trawled their hand around in the squid tank turned out to be a glutton for punishment. In the technical tone reserved for scientific papers, Roper explained that “two primary responses were evoked” – “coordinate flashes accompanied by an attack, grasping the researcher’s fingers and biting”, and “a bright flash followed by rapid retreat from the stimulus.” (Unfortunately there was no cephalopod equivalent of the Schmidt Sting Pain Index to gauge just how bad the bites felt.) The flash-and-bite technique was far more common, though, and Roper explained that “continuous stimulation” – such as pinching the captive squid’s fins – spurred the squid’s organs to glow for between one and seven seconds. All of which goes to show that sticking invertebrates in glass containers and poking them to see what they will do is a scientific technique employed by curious grade-schoolers and professional scientists alike.

The specimen of Taningia danae captured by Roper and Young. Not a happy squid. From Roper and Vecchione, 1993.

Based upon the captured squid’s behavior, it seemed that the flashes of light might act as a defense. “The bright, quick arm-tip flashes startled the observers”, Roper wrote in 1993, and this technique seemed like a good way to “startle, distract, and confuse an approaching predator.” Then again, the bright flashes did not do much to help the squid against sperm whales, sharks, and elephant seals – many Taningia specimens were recovered from the digestive flotsam and jetsam of these animals. Alternatively, Roper and Vecchione proposed that the flashes “may serve as an offensive behavior that disrupts defenses of prey.” Obviously the light organs could be used for both purposes – as Roper and Young learned the hard way in 1975 – but direct observation of the living animals in their deep sea haunts was needed to know for sure.

Marine biologists finally got their chance in 2005. In that year Japanese marine biologists Tsunemi Kubodera, Yasuhiro Koyama, and Kyoichi Mori recorded the first videos of Taningia danae hunting and feeding in the dark reaches of the sea near the Ogasawara Islands. Their report of the behaviors were published two years later in the Proceedings of the Royal Society B, and the accompanying videos of the squid darting about their natural habitat are mesmerizing. A small bait squid dangles from a hook – looking as if it is being buffeted by undersea winds – as spots of greenish-yellow light glow and fade around it. The Taningia themselves are nearly invisible in the dark, save for the lights that give away their presence.

Kubodera and colleagues were lucky enough to observe the strobe-light squid during twelve different deployments of their hi-def underwater camera rig, and all the encounters occurred between depths of 240 and 940 meters. The squid did not act the same way each time. Sometimes the squid would go after the bait that had been set, and other times they would attack the rig line, pole, or halogen lights that were part of the rig. The squid modified their strikes in the case of each target. When the squids attacked the halogen light, for example, they would rush in with their arms spread wide, but when the Taningia attacked the bait they spread their tentacles, flashed their photophores, spun around the bait, and sped off backwards with the morsel in their arms. (These squid lack the long, rubber-band-like tentacles used by other squid species to quickly snatch prey, and so must grab prey with their eight arms.)

That Taningia was such an active and acrobatic predator was somewhat surprising. Though Roper and Young found out first hand just how quick the squid can be, some marine biologists thought Taningia might be a relatively sluggish predator. The reason why has to do with how the Taningia – as well as other squid, like the famous giant squid – maintain neutral buoyancy in the water. Their secret is ammonia, but even though the compound helps big squid stay afloat in the water column without expending extra energy, the stuff is so prevalent in their flesh that, as Kubodera and co-authors point out, their bodies feel “flabby and soft to the touch.” Ammonia-rich squid where therefore cast as possible couch potatoes of the sea – lazy ambushers that quickly nabbed whatever unfortunate victims happened by – but the video of Taningia and recently-captured photos of giant squid show that these cephalopods are quick and agile hunters.

No big predators showed up to confirm what Roper and Vecchione had proposed about the flashes as a defense mechanism, but the several Taningia Kubodera and colleagues observed did more than pop their photophores just before charging the bait. In one case, a video shows a squid “wandering around the bait without attacking”, though exactly why the squid did this is unclear. Maybe, the biologists hypothesized, the squid was trying to somehow communicate with the double torch lights that formed part of the rig. Likewise, Kubodera and colleagues interpreted another incident – a two-second flash before an attack on the rig line – as an indication of uncertainty on the squid’s part. Given the difficulty of interpreting the intentions of other species, though, what the squids were signaling and why remains mysterious.

Taningia danae probably uses its impressive photophores for a variety of reasons. The squid flashes its bulbous light organs just before striking prey, before attacking threats, and may even use them to communicate with others of its own kind. In writing about this superb squid, though, I have to admit that Taningia danae reminds me of the ads for useless gags and other crap advertised in the back of comic books. I can imagine it there now, a poorly-drawn squid surrounded by gaping kids, in an ad proclaiming “Amaze Your Friends and Startle Your Enemies With the Spectacular Strobe Squid! *(Tank and squid food sold separately.)”

Top Video: A strobe squid – Taningia danae – circles a baited line and flashes its photophores. Video from the supplementary material of Kubodera et al., 2007.

References:

Ellis, R. 1998. The Search for the Giant Squid. Penguin: New York, pp. 150-152

Kubodera, T., & Mori, K. (2005). First-ever observations of a live giant squid in the wild Proceedings of the Royal Society B: Biological Sciences, 272 (1581), 2583-2586 DOI: 10.1098/rspb.2005.3158

Kubodera, T., Koyama, Y., & Mori, K. (2007). Observations of wild hunting behaviour and bioluminescence of a large deep-sea, eight-armed squid, Taningia danae Proceedings of the Royal Society B: Biological Sciences, 274 (1613), 1029-1034 DOI: 10.1098/rspb.2006.0236

Roper, C., and Vecchione, M. 1993. A geographic and taxonomic review of Taningia danae Joubin, 1931 (Cephalopoda: Octopoteuthidae), with new records and observations on bioluminescene, in Okutani, T., O’Dor, R., and Kubodera, T. (eds.) Recent Advances in Fisheries Biology. Tokai University Press: Tokyo. pp. 441-456

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