Vampire Squid: Demons of the Deep
The Vampire Squid, Vampyroteuthis infernalis is literally translated to mean the vampire squid from hell. Found in the temperate and tropical waters of the Pacific, Atlantic and Indian oceans, the Vampire squid has frightened sailors and confused scientists. On the Valdivia Expedition in 1903, the first specimens were collected and the Vampire squid was misidentified as a member of the octopuses. In actuality the Vampire squid is neither a squid nor an octopus, in fact sharing characteristics between both groups, with its unique retractile sensory filaments justifying its placement in to its own order, Vampyromorphida.
The Vampire squid received its unfortunate and misleading name due to its large red eyes; a result of depressurisation bursting the blood vessels within its eyes, its black cloak-like webbing and the dangerous looking spines on the inside of the tentacles. Unlike its namesake, the Vampire squid has been found to feed upon marine snow, detritus from the upper ocean containing prawns, copepods, cnidarians and other small invertebrates. This is done through the unique feeding method where two long filamentous strands are used to catch the marine snow before dragging it through its arms covering the snow in mucus before bringing it to its mouth to be eaten.
The Vampire squid is the only known member of this order and as such is classed as a phylogenetic relic with all other species of this order being extinct. It is thus known as a living fossil, and studies have shown it to have remained unchanged for millions of years. The Vampire squid has a maximum body length of approximately 30cm and can vary in colour from black to red. Its eyes are proportionally very large measuring 2.5cm in diameter.
The Vampire squid is found at depths between 600 and 1200 metres in the aphotic zone, where little to no light penetrates. A result of the low light means that no photosynthesising organisms like phytoplankton can be found leading to an area containing very few prey items or nutrients in the water.
The Vampire squid lives in the oxygen minimum zone, an area where the saturation of oxygen is too low to support the metabolism of most complex organisms. This hypoxic zone is a result of high productivity in the photic zone depleting the oxygen levels.
As a result of the low nutrient availability in the deep ocean the Vampire squid has evolved several ways to survive. Firstly it lives a slow pelagic lifestyle. By using its fins to move instead of jet propulsion like most cephalopods, energy is conserved. The lack of available nutrients has also resulted in its small size, and a low metabolic rate. The mass specific metabolism rate is the lowest of all the deep sea cephalopods, this means that the Vampire squid can go long periods of time without feeding, a useful advantage when the food it consumes is low in energy and difficult to find.
The lack of available oxygen has been circumvented through the use of haemocyanin in the blood. This respiratory pigment has a high affinity for oxygen giving the Vampire squid blue blood whilst also binding and transporting oxygen more effectively than in other cephalopods. Vampire squids also have a very large surface area on their gills which aids the uptake of oxygen from very low saturated waters.
The Vampire squid has a very weak musculature but maintain a high agility and buoyancy through the use of statocysts and ammonium-rich gelatinous tissues that closely match the density of the surrounding liquid. The haemocyanin in the blood is also neutrally buoyant, reducing energy expenditure for swimming.
The Vampire squid lacks the stereotypical ink sacs of other squids and octopus. Instead when the Vampire squid is threatened it adopts what is known as the pineapple posture. It will raise its tentacles up and outwards wrapping them around its body turning itself inside out exposing many little spiny projections.
Vampire squid also possess several bioluminescent displays, which are believed to be incorporated into anti-predation behaviour. It is thought that when in the “pineapple posture” they wave their tentacles around with the tips lit to disorientate predators, tricking them in to being unable to pinpoint their exact location. If the Vampire squid is highly agitated then it can resort to creating a sticky web of bioluminescent mucus from the arm tips. This can last up to 10 minutes and is presumed to daze predators long enough for the Vampire squid to disappear in to the inky blackness without having to travel far or fast. However the production of mucus is energetically very costly and as such the Vampire squid will only use this strategy if it is feeling very agitated.