Vampire squids have a reproductive strategy unlike any other soft-bodied cephalopod, scientists have discovered.
In a chance discovery, researchers realised that many of the female vampire squid specimens held at the Santa Barbara Museum of Natural History had spawned but did not have any riper or developing eggs and were in a phase of reproductive resting.
While all other known squids reproduce once late in their lives – vampire squids instead appear to alternate between reproductive and resting phases, with multiple spawning more commonly seen in fish.
Vampire squids live life at a very slow pace at depths of between 500 and 3,000m. They tend to float, rather than swim, and live on a low calorie diet of zooplankton and detritus. They also need very little oxygen to survive.
The creature was initially misidentified as an octopus when it was described in 1903. It has a webbing of skin connecting its eight arms and globular red or blue eyes. The name vampire comes from its dark colour and red eyes, not because it feeds on blood.
Their name Vampyroteuthis infernalis translates to vampire squid from Hell.
Publishing their findings in the Cell Press journal Current Biology, the authors believe it is their lifestyles that have led to this unique reproductive strategy.
"Their slow mode of life seems insufficient to support one big reproductive event, unlike other coleoid cephalopods," study author Henk-Jan Hoving. "Perhaps it is therefore that vampire squid return to a gonadal resting phase after spawning, and presumably start accumulating energy for a new reproductive cycle."
Researchers have now characterised the reproductive status of more than 40 vampire squid females. One of the females that was in a reproductive resting phase had released at least 3,800 eggs, yet had 6,500 more viable oocytes for the future – the authors say this likely suggests she had spawned at least 38 times (assuming an average batch is 100 eggs) and that she had another 65 spawning sessions to go.
"With the ability to inhabit low oxygen environments, where predators are fewer, vampire squid may benefit from increased adult survival rates, allowing for multiple reproductive cycles at low reproductive cost," the authors wrote.
Researchers also said their discovery shows just how little we know about creatures from the deep.
Hoving said: "We need to enhance our knowledge of deep-sea pelagic organisms and the system they are part of, since the pelagic deep sea is the largest living space on the planet. A better understanding of this unique marine ecosystem will eventually allow for better development of management and conservation strategies."