BY ALPER ÖZKAN (MSN/PhD)
d_ozkan@ug.bilkent.edu.tr
I now recall that I had promised a column on squid some time ago, so here it is.
While octopi are geared toward stealth and dexterity, their ten-limbed counterparts are all about speed and offense, their bodies streamlined for rapid movement in water—or air, as some surface squid can spread their fins and tentacles to glide for considerable distances. (This maneuver is typically used to flee from a predator, but it has recently been discovered that needlefish dive into water to strike their prey from a blind spot; one wonders if other fish and squid can pull that off as well.) Their limbs, too, reflect their habits: while the sucker-lined arms of octopodes evolved for the fine manipulation of objects and can easily slip through cracks in the exoskeletons of well-armored prey, squid tentacles shoot through the water at blinding speeds to strike at unwary fish, their tips armed with hooks to better dig into their soft flesh. Their hunting methods aren’t limited to mindless slash-and-bash, however: cephalopods as a group are amazingly intelligent animals, and some use a considerable amount of guile to lure and attack their prey.
One such tactic lies in surprise—a difficult prospect in the deep sea, where many animals possess advanced sensory systems to avoid being sneaked up on. But Taningia, the giant octopus squid, turns these very systems against their owners: just prior to its strike, the squid flashes the light organs on its arms, momentarily dazing its prey to ensure a clean kill. Others use their photophores to draw prey within their reach, capturing would-be predators that mistake the luminescent arms for small deep-sea animals—a similar behavior is exhibited by Grimalditeuthis, whose tentacles possess neither hooks nor photophores, but do bear fin-like membranes that can be waved around to attract curious prey. Still others may alternate their tactics: the Humboldt squid typically catches its prey by striking at it with its tentacles, but can also snare nearby fish by forming a cage with its arms; cuttlefish (which are closely related to squid) will strike directly at fish and shrimp, but attack crabs from the back to avoid potential retribution from their claws. (Humboldt squid, by the way, are swarm animals that are playful when not feeding and diabolically aggressive when they are—they are known to eat their own wounded kin.)
While all squid (and indeed all cephalopods, with the exception of the vampire squid, which mostly feeds on marine snow) are predatory, they are by no means invulnerable to other predators—indeed, many fall prey to bigger fish and squid, and must defend themselves to avoid that fate. As with many other animals, they can leverage their offense as a defense: a tentacleful of hooks and suckers can make a predator decide that it will be better off seeking prey elsewhere, and some squid can even sacrifice an arm to wrestle with an attacker while they make their escape. Their visual acuity, photophore arrays and color-changing capabilities also allow many cephalopods to surprise predators with a sudden flash of light or change of color, and their intelligence allows them to decide on the right signal for the right predator. Cuttlefish, for example, will display visual warning signals when confronted by a sea bass, which hunts by sight, but never do so against crabs, which couldn’t care less what their prey looks like.
Fancier defense systems are found in deep-sea squid (what else?), and especially in Histioteuthis, which are commonly called cockeyed squid because of their greatly mismatched eyes—one is normal by cephalopod standards, but the other is bloated to twice the ordinary size and placed on a telescope-like support mechanism. This giant eye is generally turned upward, allowing the squid to watch for potential predators, while the smaller, “normal” eye is used for the area below and around the squid. My favorite defensive trick, though, belongs to the vampire squid (which is not a true squid, being aligned more closely with octopodes). This remarkably lazy inhabitant of the deep sea considers itself above such base actions as fleeing, and when confronted by a stronger foe, will flash the lights on its arms…and progressively shrink them in size, giving the impression that it’s swimming away at flank speed, while the animal is in fact doing anything but.
As anyone who knows me will attest, the vampire squid is my spirit animal, and I pride myself in my ability to pull off a variation of that decoy trick—mostly to get some time to sleep. (I will omit the details for now, since I am still a graduate student, and revealing it will do me no good…let’s just say that Sun Jian tried it once, just before his last charge.)
If that fails, I also vomit luminescent ink when threatened.