September 27, 2012
Not So Sinister After All, Vampire Squid Only Consume Marine Snow
April Flowers for redOrbit.com - Your Universe Online
Though the vampire squid was first discovered about 100 years ago, and a dozen scientific papers have been published, marine biologists have not been able to find out what the creature eats.
A new study, led by the Monterrey Bay Aquarium Research Institute (MBARI), shows that unlike its relatives the octopus and squid, which eat live prey, the vampire squid uses two thread-like filaments to capture bits of organic debris that sink down from the ocean surface into the deep sea.
The vampire squid is the stuff nightmares are made of with its dark red body, huge blue eyes and a cloak like web that stretches between its eight arms. The animal, Vampyroteuthis infernalis (vampire squid from hell), lives in the deep sea, and when threatened turns inside out, exposing rows of wicked looking "cirri." All of that is misleading, however, as the squid is a soft-bodied, passive creature about the size, shape and color of a football. The squid lives in the deep waters of all the world's ocean basins; a living fossil at depths where oxygen and predators are scarce. As the sole species of the Order Vampyromopha, the squid lives between 2,000 and 3,000 feet below the surface of the ocean.
Previously, researchers have tried to understand the eating habits by catching vampire squid in nets, hauling them to the surface, and examining stomach contents, which were generally inconclusive. The stomachs contained bits and pieces of tiny shrimp-like animals, microscopic algae, and lots of slimy goo.
MBARI Postdoctoral Fellow Henk-Jan Hoving and Senior Scientist Bruce Robison found that vampire squid eat mostly "marine snow" — a mixture of dead bodies, poop and snot. The dead bodies are those of microscopic algae that live closer to the surface, but whose bodies sink after death. The fecal matter is from small, shrimp-like animals such as copepods or krill, and the snot is debris from gelatinous animals called larvaceans, which filter and consume marine snow using mucus nets.
The study, published in the Proceedings of the Royal Society B: Biological Sciences, looked not only at the stomach-contents of vampire squid from museum collections, but also utilized the MBARI's remotely operated vehicles (ROVs) to collect live vampire squids and study their feeding habits in the laboratory. The team also examined squid arms and feeding filaments under scanning and optical electron microscopes.
Hoving and Robison were able to keep vampire squid alive in the laboratory for months at a time, and discovered that if small bits and pieces of microscopic animals were placed in the squid's tank, the food particles would stick to one of the string-like filaments that the animal sometimes extended. The squid would draw the filament through its arms to remove the food and coat it in mucus, then transfer the globs to its mouth and eat.
Using MBARI's video annotation and reference system (VARS), the scientists found every ROV dive for the last 25 years that had encountered a vampire squid. Hoving watched these 170 video clips (over 23 hours of footage) to look for more clues to what and how the animals eat.
The video clips show that the vampire squid often drives motionless in the water with one of the thin filaments extending like a fishing line. The filaments are up to 8 times longer than the animal's body, and in many cases Hoving saw marine snow sticking to it. Hoving saw the vampire squid repeat the maneuvers observed in the laboratory, drawing the filament through the arms, moving the globs to the mouth and eating.
The squid were examined microscopically, and the researchers learned that the squid's suckers are covered with cells that produce mucus, which the animal uses to glue together bits of marine snow. The filaments are covered with tiny hairs and a net of sensory nerves, making them extremely sensitive to touch.
"The suckers in vampire squid do not seem to have the sucking capacity as found in other cephalopods," he continued. "The suckers on the distal parts of the arms release mucus and they probably wrap the collected food in mucus, forming a food bolus, which is transported via fingerlike projections on the inside of the web to the mouth. Then the food bolus is ingested by the beak."
When stomach contents were examined, the researchers did not see bones or pieces of individual animals that would indicate the squids had been eating live prey. They mostly saw amorphous bits of crustaceans that sometimes hitchhike on sinking mucus nets or clumps of the marine snow.
The study concluded that, "the vampire squid's filament is likely a multifunctional organ that is deployed to detect and capture detrital matter but at the same time may detect the presence of predators and perhaps small living prey."
The squid complement their meager diets with extremely energy-efficient lifestyles and unique adaptations. With neutrally buoyant bodies, they don´t have to expend energy to stay at a particular depth. They also don´t have to expend energy swimming after their food, they just simply extend their filaments to collect food drifting past.
Escaping predators doesn't take much energy either, as the squid live at oxygen deprived depths where most other animals can't survive. Luckily, these oxygen deprived zones are usually beneath an area with an abundance of life that creates lots of marine snow.
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."
Richard Young, a biological oceanographer from the University of Hawaii, called the discovery spectacular.
"Vampire squid have always had these really funny long things that stick out of their body, and scientists like me had no idea what they were used for. Now we know," he said, adding that this "is one peculiar critter. I would be shocked if any other marine organism ate in such a way."