Vampire squid can live nearly two miles beneath the surface, so much less is known about them than shallower squid. In the new study, researchers examined specimens of the species from the Santa Barbara Museum of Natural History to learn more about their feeding and spawning habits.
Other cephalopods (with the exception of nautiluses) produce all their eggs at once. They may spawn at intervals, but the eggs themselves are created in one go. And once their single reproductive cycle is complete, the female is done.
But vampire squid who had spawned previously still had the capacity to make more eggs.
"They seemed to be in a sort of resting phase," study author Henk-Jan Hoving of the GEOMAR Helmholtz Centre for Ocean Research Kiel said. "There were clearly multiple reproductive cycles occurring."
The findings are an indication of how little we know about deep-water creatures and their life-cycles, Hoving said.
"It shows that there’s a diversity," he said, "and it may indicate that the pace of life is slower than what we know for shallow-water cephalopods, which are known to grow very fast. Age and longevity are important parameters for us to understand how animals live their lives and how their ecosystems work."
Hoving believes that vampire squids might have their slow metabolisms to thank for their reproductive uniqueness. Unlike many cephalopods, they don't actively hunt for food. They rely on tiny particles of plankton and marine snow, and consume far fewer calories than species near the surface. They probably lack the energy to release fertile eggs all in one go, but their slow pace may also keep them alive longer.
This isn't the first sign that deep-sea cephalopods may live longer than their shallow-water counterparts, who tend to have life spans of around two years at most. In a previous study by one of Hoving's co-authors, a deep-sea octopus was observed brooding her eggs for a full four years — longer than anyone thought an octopus could even live.
"In that case, they actually had a direct observation showing that these animals can live longer," Hoving said. "But here, based on the reproductive pattern, we're hypothesizing that the same might be true."
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