Drifting in the deep ocean, the vampire squid (Vampyroteuthis infernalis) possesses characteristics of both octopuses and squid. Despite its intimidating name, the vampire squid is not a blood-sucking predator. Researchers have uncovered the secrets of what and how this mysterious creature eats, revealing a unique feeding strategy adapted to the extreme environment it inhabits.
Habitat and Adaptations to the Deep Sea
Vampire squid are found worldwide in temperate and tropical deep-water zones at depths of 600 to 1200 m (1958 to 3937 ft). This is the oxygen minimum layer (OML), where there may be less than 5 percent oxygen saturation and little or no light. The water temperature at those depths is very cold, 2-6o C (35.6 to 42.8 o F). Most cephalopods cannot go below 50 percent oxygen saturation. To cope with this environment, they use hemocyanin (copper-based blue blood) that binds oxygen very well, and they have a large gill surface area to absorb oxygen.
The vampire squid's gelatinous body is colored jet black to pale reddish, depending on location and light conditions. It has eight arms that are connected by webbing and each is lined with rows of fleshy cirri (spine-like projections). The distal portion of each arm has suckers. The eyes are large and globular and colored red or blue depending on lighting. Mature adults have a pair of small fins projecting from sides of body furthest from eyes. Beaks, located in the center of the circle of arms, are white. Two pouches containing the tactile filaments are concealed within the webbing between the first and second pairs of arms. These filaments can be extended up to at least twice whole body length. The body surface is covered in poorly developed photophores (light producing organs).
To survive in the OML (oxygen minimum layer) of the deep ocean, the vampire squid has a very slow metabolism that causes it to need little oxygen to survive. The body of a vampire squid contain statoliths (from the Greek for balancing stones), that keep it neutrally buoyant.
Unique Feeding Mechanism: Not a Predator, but a Detritivore
Vampire squid are detritivores, the only known living cephalopod that does not catch and eat live animals for food. Instead, they feed on "marine snow", detritus that consists of bits of dead planktonic creatures and fecal pellets. This was not always known, and for many years it was a mystery to marine biologists how and what they eat. Previous researchers have examined the contents of vampire squids’ stomachs with inconclusive results.
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V. infernalis - which is related to octopuses and squid - has eight arms and, instead of the feeding tentacles used by squid to capture prey, has two long, retractile filaments. Hendrik Hoving and Bruce Robison at the Monterey Bay Aquarium Research Institute in Moss Landing, California, studied the feeding behaviour of V. infernalis using deep-sea video recordings, lab feeding studies and morphological examinations. Nature 490, 8 (2012).
The scientists observed that some of the vampire squid appeared to be using the filaments to collect marine snow. The scientists came up with a hypothesis that the vampire squid were catching marine snow to eat it (a hypothesis is a guess based on facts that explains a mystery). They tested this hypothesis by looking at what was in the stomachs of recently dead vampire squid (as well as doing a few other experiments; you can read the description of everything they did here). They discovered vampire squid had indeed been eating “the remains of gelatinous zooplankton, discarded larvacean houses, crustacean remains, diatoms and faecal pellets.” “Faecal pellets” is a more polite and scientific way of saying “poop.” Also, “faecal” is the British spelling. The American spelling is “fecal” as in “feces”. “Remains” is a polite way to say “dead stuff.” In other words, they were definitely eating marine snow.
They drift along with one filament deployed until contact with food is made, then swim around the food until it is caught. This frame grab from underwater video shows a vampire squid in a typical feeding position, drifting horizontally in the deep sea with one of its filaments extended.
The Discovery of the Vampire Squid's Diet
About 100 years ago, marine biologists hauled the first vampire squid up from the depths of the sea. Since that time, perhaps a dozen scientific papers have been published on this mysterious animal, but no one has been able to figure out exactly what it eats. Hoving looked carefully at 23 hours of footage taken by MBARI remotely operated vehicles (ROVs) of vampire squids filmed over the past 25 years. The scientists discovered that vampire squids use two long filaments that extend from their bodies to capture “marine snow” that drifts at these depths.
Postdoctoral fellow Henk-Jan Hoving and senior scientist Bruce Robison, from The Monterey Bay Aquarium Research Institute, have discovered that vampire squids eat mostly "marine snow"-a mixture of dead bodies, faeces, and mucus which they collect with long filaments which extend up to 8 times as long as their bodies.
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Hoving and Robison collected living vampire squids and were able to keep them alive in the laboratory for months at a time. Hoving found that when pieces of microscopic animals were placed into a tank with a vampire squid, they would stick to one of the string-like filaments that the animal extends outward from its body.
The Process of Feeding on Marine Snow
If you were able to hangout deep in the ocean, you would notice that there were white flakes of stuff falling all around you. Though these white flakes look like snow (and are actually called "marine snow"), they are not crystals of ice like the stuff that covered my yard just a month ago (I live in Rochester, NY). They’re more like the fish food flakes you may have shaken into your home aquarium, except these flakes are not coming from someone shaking a giant can over the ocean. Marine snow flakes come from the bodies of fish, squid, sea turtles, plankton, and other living things near the surface.
Like you, ocean animals poop. Some of them also die every day, like when they get eaten. When an animal gets bitten, sometimes parts of it don’t quite make it into the predator’s mouth and fall out as crumbs. These bits of poop and dead stuff get pulled by gravity towards the bottom of the ocean, creating a blizzard of gently falling flakes of disgustingness that scientists call marine snow. “Disgustingness” is a human’s opinion, though, because poop and dead stuff contain calories and nutrients, which are what all living things need from their food. For a vampire squid, marine snow is super-abundant and nutritious free food that a vampire squid can snack on anytime it is hungry.
The vampire squid would then draw the filament through its arms, removing the particles from the filament and enveloping them in mucus. Finally, the squid would transfer the glob of mucus and particles to its mouth and consume it.
This close up view shows a vampire squid using its arms to scrape food off of one of its filaments. Under the microscope the researchers observed that mucus-producing cells cover the vampire squid's suckers, which the animal apparently uses to collect and glue together individual particles of marine snow. Other vampire squids had globs of marine snow and mucus dangling from their mouths.
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Nutritional Considerations and Energy Efficiency
The organic detritus that forms the bulk of the vampire squid's diet are not particularly nutritious. Hoving and Robison show that vampire squids eat mostly “marine snow”-a mixture of dead bodies, poop, and snot. As pure as marine snow may sound, it’s anything but. In reality, it includes animal feces, corpses and snot that sinks down from above.
However vampire squids complement their frugal diet with an extremely energy-efficient lifestyle and unique adaptations. Their bodies are neutrally buoyant, so they don't have to expend energy to stay at a particular depth, and they don't have to swim to find food, but simply extend their filaments to collect food that drifts past them. Their bodies are neutrally buoyant, so they don’t have to expend energy to stay at a particular depth.
Finally, vampire squids don't have to expend much energy avoiding predators either, as they live at depths where there is so little oxygen that few other animals can survive. Conveniently, these deep, low-oxygen zones are often found below where there is an abundance of life near the sea surface, which creates lots of marine snow for vampire squids to eat.
Reproduction and Development
V. infernalis has no defined breeding season and eggs are found all year. Males insert a sperm packet into the mantles of a female, where it is stored until needed. Fertilized eggs, laid in small masses, average 3.3 mm (0.1 in) across newly laid and float around until they reach hatching size. The transparent hatchlings are about 8 mm (0.3 in) long at birth and closely resemble adults but lack webbing, have small eyes and short velar filaments. Hatchlings have one pair of swimming fins, but as they become juveniles they grow a second pair of fins. Once the second pair reaches full size, the first is reabsorbed. This type of metamorphosis is only found in Vampire Squid.
Defense Mechanisms
Having no ink sacs to use to obscure themselves from predators, the vampire squid draws its tentacles (arms) and webbing backwards up over body into the “pineapple” posture to protect itself. The inside of its mantle is very dark, making the squid invisible in the dark lightless ocean around it.