Pacific Warty Octopuses Get Wartier the Deeper They Live and Scientists Don't Know Why

Scientists have discovered that Pacific warty octopuses get wartier the deeper they live—but they don't know why. These pink octopuses are found at depths ranging from 3,600 to 9,000 feet, but they are so different in appearance that until recently researchers thought they may well be different species.

To find out, Janet Voight, associate curator of zoology at the Field Museum, Illinois, and colleagues collected dozens of specimens from different depths all of which had been classified as belonging to the species Graneledone pacifica.

Voight told Newsweek these octopuses are often seen during dives to these deep parts of the sea—and are often spotted at a hydrothermal vent in the Northeast Pacific. Hydrothermal vents are openings on the sea floor where hot, mineral rich water mixes with the cold ocean.

"I started studying these octopus to figure out if the ones from near the hydrothermal vent were different from those elsewhere, but I could not identify any character that separated them," she said. "At one point it seemed many animals near vents were distinct [species], but it turned out not to be so in this case."

Researchers counted the number of warts each octopus had on its back and head, as well as the number of suckers it had on each arm. Those collected at shallower depths were found to be larger, with smoother pink skin. The deeper they got, the smaller and wartier the octopuses were.

However, analysis of their DNA showed little difference between the different octopuses collected—strongly indicating they all belong to the same species. The findings are published in the Bulletin of Marine Science.

Voight said she became interested in the octopuses because these relatively large predators have ended up living in the deep ocean, where little prey is available. What advantage wartier skin would be to an octopus living 9,000 feet below the surface is unclear, she added.

"We still don't know [why they are wartier]," Voight said. "Because there is only light from bioluminescence at these depths, it doesn't seem [that] it could be camouflage. I am working with a colleague now to document what [the warts] are made of—maybe that will give us a clue."

In a statement, Voight said being able to identify species from the deep sea is hugely important in understanding this habitat. "There's still just so much we don't know about the deep sea," she said. "We need to be able to understand the information that's becoming available from ROV footage. And we can only do it by knowing what the animals look like."