Article: Sato, Noriyosi, et al. “Japanese pygmy squid (Idiosepius paradoxus) use ink for predation as well as for defence.” Marine Biology 163.3 (2016): 1-5.
Squid are, no doubt, fascinating and mysterious creatures. Think about it, one of the largest creatures on earth, the Giant Squid, has rarely ever been seen alive. Squid can also camouflage, using pigmented cells called chromatophores, to blend in with their background and hide from predators (Fig. 1). Even squid that are seen can shoot out a cloud of ink and vanish within seconds (Fig. 2). The fact that squid produce and use ink has been known for quite sometime. Most squid that live in the photic zones of the oceans, those receiving light, have ink-producing sacs. It is well established that squid use ink for defense, to avoid predation. Since ink takes a lot of energy to produce, it is only used as a secondary defense, the primary defense being their keen ability to camouflage themselves. Squids are known to use their ink defensively in two different ways: first, they may use it as a decoy to attract their predators, or second, they may use it as a “smokescreen” and hide behind it.
As there is a lot left to learn and understand about squid, scientists continue to study aspects of their physiology, behavior, and ecology. In studying predator-prey dynamics and feeding behavior in squid, researchers in Japan recently observed something unexpected. Their study species of squid was not using their ink for defense but was using their ink for something else – catching prey. This was a first, so what did they find out?
Researchers were investigating predation and feeding in the Japanese pygmy squid (Idiosepius paradoxus) (Fig. 3). Squid were collected from seagrass meadows off the coast of Japan and brought back to be acclimated to lab conditions. Predation was tested by offering squid one of three common prey items, all species of shrimp of various sizes, found in their native habitat. It was during these tests that researchers discovered something quite interesting.
Overall, 322 predation events were observed and recorded. Overwhelmingly, most predation events were pretty standard, with the squid capturing their prey using normal methods. But researchers did observe 17 instances (of the 322 total) in which the squid used ink to aide their effort. Remember, using ink as a predation tool has never been observed in squid, so while 17 seems like a pretty low number, these are likely the first 17 instances ever recorded (Fig. 4). If you are curious as to how this actually works, check out this great video put together by New Scientist which shows the predation in action!
Interestingly, squid only used ink in predation when going after the two larger prey items, and was never observed to use ink in preying on the smallest prey, which turned out to be the most common prey. Surprisingly, the researchers noted that using ink didn’t increase the success of their predation and capture rates were essentially the same for squid using ink and not using ink. They found that ink could be used as a predatory aide in two ways, first squid could use it as a “smokescreen” the same way they use it in escaping predation, but rather than fleeing behind it, they use it to hide before launching through it to attack their prey (Fig. 5). Second, squid could use the ink cloud as a decoy that would distract prey so that they could blindside them.
Researchers here were able to document a novel use of ink clouds, where instead of using ink to escape being eaten, they are using ink to help themselves eat. Seeing as squid traditionally use ink defensively, there are cues in the ink that attract predators, allowing the squid to escape. This cue associated with the ink could help explain why ink was used in such a small percentage of predation events by squid. When squid are focused on hunting, if they use ink to help them hunt they may be attracting unwanted predators. Clearly, there is a lot left to learn about squid, as researchers here found that these creatures have figured out ways to make the most of their abilities. At this point, it is likely that by the time the ink dries on this predatory aide, squid will have shown us something else to get excited about!
Postdoctoral Researcher, Claremont McKenna College
I am currently a postdoc at Keck Sciences, Claremont McKenna College. I work with Dr. Sarah Gilman, measuring and modeling energy budgets in intertidal species. I am a climate scientist and marine community ecologist and my PhD (University of Rhode Island) focused on how ocean acidification and eutrophication, alters coastal trophic interactions and species assemblages.
I love bad jokes and good beer.