2013/03/01 by Adrian Burton · 1 citation
Agricultural and Biological Sciences · #Cephalopods and Marine Biology
paper · pdf · doi:10.1890/1540-9295-11.2.112
openalex publication_date 2013/03/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/15
The deadly cold deep of Antarctica's Southern Ocean is where you must look to find Mesonychoteuthis hamiltoni, the colossal squid. Weighing in at around 500 kg, it makes the slightly longer giant squid (Architeuthis dux), which may only pack around 300 kg into its 13-m “tip-to-toe” length, look like a runt. The colossal squid's arms and club-ended tentacles are equipped with hooks that dig into its prey. Those on the tentacles can even swivel through 360°; when the colossal squid grabs something, it doesn't mean to let go. Yet even this largest of all invertebrates falls prey to marauding sperm whales. It therefore needs a defense and, just like any other squid, it produces ink. Anyone who has been “inked” by a cephalopod can tell you what a good defense it is; you are blinded for no more than an instant, yet the animal is gone. But what good is dark ink in the black depths of the sea? Some cephalopods may produce ink that acts as a chemical deterrent against certain predators, but the evidence hardly extends to all species. Might the colossal squid therefore produce some form of luminescent ink that shines in the darkness, leaving its predators blinded by the light? Such a proposal has been put forth by the Museum of New Zealand in its Colossal Squid Exhibition, where the largest M hamiltoni ever captured remains on display until August of this year (see http://squid.tepapa.govt.nz/exhibition). A firefly squid lighting up the sea. The idea is not as wacky as it might at first sound. About two-thirds of all squid genera have bioluminescent members. Some produce light from specialized groups of cells arranged around their bodies. Those of the 7-cm-long firefly squid Watasenia scintillans shine so brightly that they produce a dazzling display of mating season marine fireworks. Every spring, Japanese fishermen set off in search of the amorous creatures in Toyama Bay, their nets lighting up in a darting neon-blue spectacle as the squid are hauled in. The much larger Dana octopus squid (Taningia danae) has similar photophores – but 5 cm or so in length – and has been filmed flashing light to apparently blind its prey and maybe to attract mates. The deep-sea vampire squid, Vampyroteuthis infernalis, also uses light organs on the tips of its arms, perhaps to distract predators away from its body. They can even release a light-emitting cloud into the water if their owner becomes particularly alarmed. Other species make use of symbiotic bioluminescent bacterial colonies that can be covered and uncovered like signaling lamps. For example, the Hawaiian bobtail squid (Euprymna scolopes) has teamed up with the bacterium Vibrio fischeri, and at night produces a soft glow that allows it to blend in with the moonlight filtering down from above, making it invisible to predators and prey below. It is the tiny odd bobtail squid, Heteroteuthis dispar, however, that has taken bacterial lighting to spectacular limits. When scared, it can squirt bacteria-lit mucus out of its siphon, producing a screen of defensive bioluminescence akin to a luminous ink cloud. So what about the colossal squid's ink? Is it really luminescent? Well, maybe not. “[This is] speculation, and not based on anatomical evidence”, admits Bruce Marshall, Mollusc Collection Manager at the Museum of New Zealand. “[If it has] luminescent ink, it might be used to confuse predators in the darkness of the deep sea.” But sperm whales hunt by sonar; how a glowing inky cloud could help a squid that's been pinpointed by a sound wave is not entirely clear. Hold back that disappointment, though, for M hamiltoni does come with a bioluminescent surprise. Its forward-facing, beachball-size eyes – the largest in all the animal kingdom – each contain a (possibly) bacteria-driven light organ several centimeters long, a discovery made during an examination of the exhibition's 495-kg prize specimen. It's speculated that these organs might light up those huge eyes like glowing orbs, the beams illuminating prey as if in a car's headlights. If true, coming face to face with such a behemoth, its glowing optics focused on you and its hooked tentacles ready to strike, must be among the greatest terrors of the abyss. Regular squid ink can, of course, take on an importance beyond that of a cephalopod's defense. Where I live, in Spain, it's used to make chipirones en su tinta – squid in their own ink. Squid caps are stuffed with chopped eggs, ham, and breadcrumbs, or even pâté, and, after browning in olive oil, are cooked in a thick onion, tomato, red pepper, carrot, wine, and garlic sauce, all tinted deep black with squid ink. It's delicious – although the first time you see the dish the ink can still repel you. Epicureans, however, may want to imagine how a glowing plate of squid served in its own luminescence might look!