Previous researchers have examined the contents of vampire squids’ stomachs with inconclusive results. 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.
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 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.
The organic detritus that forms the bulk of the vampire squid's diet are not particularly nutritious. 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.
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. Hoving explains, "Because of its unique adaptations, the vampire squid is able to permanently and successfully inhabit the center of the oxygen minimum zone, an otherwise hostile environment where the vampire squid's predators are few, and its food is abundant."
Even though Hoving and Robison's research shows that the vampire squid is a "detritivore" rather than an active predator, its sinister appearance and stealthy habits will no doubt continue to fascinate both researchers and the general public.