The subtle lives of deep sea squid
Monstrous squid with crushing tentacles have been a part of pop culture in many parts of the world for many decades, a trend recently helped along with internet sensationalist posts about the colossal squid (Mesonychiteuthis hamiltoni), depicting this innocent mollusc as a voracious whale sized predator. In reality of course, the colossal squid is a much smaller than advertised little understood squid with a slow life style that would see it struggle with even the meekest of whales. Still, weighing in at 500kg and with hooks on the tips of its tentacles instead of suckers, it would not be advised to get in the water with one (see the video below to get an idea of what they really look like). Those squid more commonly seen in the public eye such as the giant and colossal squid and the notoriously ferocious humbolt squid, are all reasonably similar in body shape, and all employ a similar hunting strategy. That is to say; rush forwards quickly and grip potential prey in powerful tentacles. They are ambush predators capable of short bursts of speed like fleshy, boneless jaguars of the deep. However, while these powerful muscle cars of the squid world bathe unknowingly in the limelight of human attention, there are squid lurking in the deep sea who prefer to take a more subtle approach to hunting.
Fishing in the deep.
Grimalditeuthis bonplandi is a species of mostly transparent deep sea squid with rather dainty arms. This in itself is nothing unusual, however, what got scientists really curious, were its two, hugely elongated tentacles (squid have eight arms and two tentacles) and the bizarre fins that are found on the end of them. In most squid then tentacles have clubs covered in suckers or hooks at the end, this allows them to reach out long distances from the body and grab prey, which is then brought back into reach of the shorter and more powerful arms. In the case of G. bonplandi however, its tentacles are gelatinous, clearly too thin and weak to attempt this, and the purpose of the fins on either side of the clubs had scientists stumped for decades.
It is only recently with the development of submersibles and remote operated vehicles that the use of these tentacles has finally been discovered. While they lack the grasping power of many other species of squid, the thin tentacles are difficult for potential prey to detect, and the fins on either side of the club allow the squid to “swim” the clubs forwards through undulations of the fins, similar to the manner a sting ray undulates its pectoral fins to glide through the water. The undulating movement of these fins acts like a lure to small fish, and G. bonplandi can simply draw this lure through the water column, bringing its prey ever closer and closer towards its mouth. In this manner, the little squid can fish the deep seas without having to use strength and power to pursue prey. Although this species has been known to science since 1839, it was only in 2013 that this discovery was made.
The deep sea trawl.
While G. bonplandi could be likened to a traditional fisherman with rod and line, there exists and even stranger squid that could be more closely likened to an industrial fishing operation. The big fin squid belonging to the genus Magnapinidae are quite unlike any other squid, possessing enormous fins on either side of their mantle, and extremely long arms and tentacles (both of which are the same length) that are often seen hanging vertically downwards at the end of strange “elbows” which are themselves held at right angles to the body. The whole appearance puts one in mind of a distinctly alien creature. Given that their appearance and physiology is so different compared to other squid, it is assumed that their feeding methods will be equally as different.
Unfortunately, these species are incredibly poorly understood, the only images that exist come from deep sea ROV’s, and often document fleeting encounters with these enigmatic giants. However, based on observations it is currently theorized that, by using its “elbows” to increase the spread of its limbs, it is capable of simply drifting through the water column, catching any small organisms in a net of sticky tentacles. Almost totally unknown to science, encounters with these animals have increased since the development of reliable submersibles and underwater imaging equipment Alternatively, the extremely long tentacles may be able to fill the space around it, acting as an early warning system for detecting either predators or prey. This hypothesis is based on the behaviour observed in the few encounters that humanity has had with living individuals . In an interaction with the ROV Tiburon a big fin squid was observed trailing the ends of its tentacles over the sea floor, and other encounters have noted that the tentacles are very sticky, being covered in thousands of minute suckers which cause them to stick to ROV’s easily. Compared to the lone fisherman of G. bonplandi, the Magnapinidae Could be likened to a large open water long lining operation, with multiple lines (or limbs in this case) that will capture anything they come into contact with that is to weak to escape.
These two examples both appear to have developed in a very different way to many shallow water squid, one that allows them to survive in the food scarce environment of the deep sea. The slow movements of the big fin squid are a world apart from the rapid jet propulsion seen in it’s shallow water cousins, and both G. bonplandi and the Magnapinidae have hunting strategies that exert minimal energy in acquiring food. Whats more is that it seem unlikely that these could be the only species of squid employing novel hunting strategies in the deep sea, and further study could reveal ever more intriguing life styles. What is clear is that there is still so much to be learnt about these these fascinating animals found in earths own final frontier.