2010, an article in Rolling Stone likened the investment bank Goldman Sachs to “a great vampire squid wrapped around the face of humanity, relentlessly jamming its blood funnel into anything that smells like money. “The creature it was referring to does exist – it’s not a true squid, but one of their close relatives. But despite its terrifying name and appearance, it’s not a vampire. It doesn’t suck blood. It doesn’t have a “blood funnel”.
In fact, thanks to newly published observations, we now know that the vampire squid is a garbage-eater. It extends living fishing lines from its body to snag a rain of rubbish falling from the surface, getting fat on a menu of faeces and corpses.
The Goldman Sachs metaphor still works, doesn’t it?
The vampire squid belongs to the cephalopods, the group that includes squid, octopuses and cuttlefish. But it’s an evolutionary relict that appeared well before any of these more familiar animals. Its body is gelatinous and blood-coloured as if the internal organ of a larger animal had broken free. It swims with two wing-like flaps, sees with opal-blue eyes, and lights up the surrounding water with flashing organs found all over its body, and especially at the tips of its arms.
Two of these arms have been modified into white thin filaments, which coil up into special pockets, and can extend to 8 times the animal’s length. The other eight arms are connected by a cloak-like web that can be inverted over the vampire squid’s body to reveal a muddy charcoal interior, lined with fleshy spines. You can see where the name comes from.
The vampire squid lives all over the world, but we know very little about what it does. That’s partly because it lives at incredible depths – 600 to 900 metres below the surface, in pitch blackness. This level is known as the oxygen minimum zone (OMZ) and unlike the vampire squid, it’s well-named. While a few animals thrive here, most are choked off by the lack of oxygen.
The vampire squid copes by having an incredibly slow metabolism, blood proteins that hug oxygen molecules with an unyielding grip, and a body that so closely matches the density of water that it neither floats nor sinks. It rarely wastes energy on unnecessary movements. It simply hangs in the darkness.
But even though it lives life in the slow lane, the vampire squid needs food, and that’s in short supply in the oxygen minimum zone. What does it eat? To find out, Hendrik Hoving and Bruce Robison from the Monterey Bay Aquarium Research Institute (MBARI) analysed footage of 170 vampire squids, taken over the last decade by the institute’s submersibles.
The videos, along with feeding experiments on captive vampire squids, revealed that they use their filaments like mobile spider webs. They extend these into the surrounding water to ensnare particles of food falling from above. The filaments are covered in tiny hairs, probably for catching these particles. They also have neurons that connect to a particularly large part of the creature’s brain, presumably so it can sense what’s stuck to its fishing lines.
When the time is right, it retracts the filaments, transfers the food to its other arms, and coats them in mucus secreted from its arm tips. It then conveys these delicious balls of mucus-bound detritus into its mouth, possibly with the help of the spines within its cloak.
This strategy is very different to that of other cephalopods, most of which are active hunters that attack and kill their food. Vampire squids are definitely not that, as Hoving and Robison confirmed by checking the stomachs of captured specimens. They found eggs, algae, pellets of faeces, bits of jelly, crustacean body parts—antennae, eyes, some shells, whole copeopods—and flesh from another deep-sea squid. In both kind and quantity, these remnants don’t reflect the diet of a hunter.
Instead, Hoving and Robison think that the vampire squid is mainly a ‘detritivore’ – a rubbish-eater. With few predators in the oxygen minimum zone, it can afford to sacrifice powerful swimming muscles or a high metabolism. Instead, it leads a relatively passive lifestyle, collecting the plentiful snowing debris with its two modified arms. With these adaptations, it can greatly extend the reach of its mouth, while its body—and its life—literally hangs in the balance.
Reference: Hoving & Robsion. 2012. Vampire squid: detritivores in the oxygen minimum zone. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2012.1357
All images from Hoving and Robison. Copyright MBARI