SANTA BARBARA, CALIFORNIA—Though the average patron will never find it, a massive collection of one of Earth’s most mysterious deep-sea animals lives cataloged in a lab at the Santa Barbara Museum of Natural History. Jars stuffed with gelatinous appendages line the shelves of one room from floor to ceiling, and murky eyes peer unseeingly through their alcohol preservative. The label on the shelf reads Vampyroteuthis infernalis.
Ordinarily, there is no light—from the sun or the overhead museum fluorescents—in the habitat of the vampire squid. The 30-cm-long animal lives 500 to 3000 meters below the ocean’s surface, in a zone where oxygen is low and photons are rare. To survive the choking darkness, according to a new study, the squid has evolved a reproduction strategy unlike any of its kin—one that has extended its time on Earth.
“The study has given us a brand-new way of understanding how some cephalopods reproduce, and also has given us the first insight into what the possible life span of this animal might be,” says Kathrin Bolstad, a teuthologist at the Auckland University of Technology in New Zealand who was not involved in the work. “Every little tiny piece of the puzzle about deep-sea animals that we can put together is a fantastic advance.”
Despite its name, the vampire squid is not an aggressive predator, nor does it feed on blood. It glides slowly through the depths, feeding on detritus and plankton. “It has a slow pace of life,” says Henk-Jan Hoving, a marine biologist at the Helmholtz Centre for Ocean Research in Kiel, Germany. Hoving has been studying squid for more than a decade and discovered the museum’s cache of preserved vampire squid while researching what the animals eat. He noticed that the collection contained a large number of females that might allow him to unravel the specifics of the mysterious squid’s reproductive strategy.
Two vampire squids preserved in alcohol at the Santa Barbara Museum of Natural History.
His research, published today in Current Biology, suggests that unlike most cephalopods, vampire squid undergo multiple reproductive cycles during their lifetime. This contrasts dramatically with other squid and octopuses, which reproduce in one spectacular event and then die shortly thereafter. Multiple spawning events may better suit this squid’s low-energy lifestyle. “I don’t think this slow pace of life allows one big reproductive spawning event,” Hoving says.
For the new study, Hoving and colleagues dissected 47 females. Similar to humans, squid egg cells mature in the ovary and are supported by a shell of cells known as a follicle. The immature egg cell is eventually released during ovulation, but the follicles are left behind. Fortunately for the team, the ovary reabsorbs these postovulatory follicles quite slowly in vampire squid, allowing the researchers to count and characterize different batches of eggs produced by the mature females.
Using the follicles to reconstruct the vampire squids’ spawning history allowed researchers to make several surprising discoveries. First, unlike any other squid, the vampire has a gonadal resting phase, meaning there are times when the ovary has no growing or ripe egg cells. The authors suspect that the resting period between egg batches enables the females to store up enough energy to start a new reproductive cycle. Furthermore, it appears that developing eggs can be reabsorbed into the ovary to save energy if times are particularly lean.
The insight into the squids’ reproductive lives has also helped Hoving and his team refine their estimates for how long the creatures might live. The largest female in the museum’s collection was estimated to have spawned 38 times and contained enough reproductive cells for another 65 rounds. “If we assume 38–100 spawning events … the duration of the adult stage is at least 3–8 years in this specimen, with the total life span exceeding these numbers,” the authors write. Such longevity would dwarf the vampire’s shallow water relatives, which usually only live between 6 and 18 months. Bolstad affirms that the study “has given us the first insight into what the possible life span of this animal might be.”
There are, however, a lot of unknowns that need to be answered before the life span can be confirmed with more certainty. Researchers still don’t know how long it takes a follicle to be reabsorbed completely. Nor do they know how long gonadal resting phase between spawning events last or how long it takes an egg to reach maturity. “It would be nice to keep animals in the lab alive for as long as possible to try to figure out how fast they grow,” Hoving says.
Regrettably, the study was unable to identify any trends in when or where the spawning takes place. So as tantalizing as it might be to imagine hordes of vampire squid gathering to reproduce at specific locations in the pitch-black darkness, any such discovery will have to wait—but waiting is probably what the vampire squid does best.