These octopuses get wartier the deeper they live in the ocean

When comparing the octopuses, scientists noticed that some bore many large warts, while others showed no variation or bumps in their skin. But their DNA was the same. Their study was published Tuesday on World Octopus Day in the Bulletin of Marine Science journal.

"If I had only two of these animals that looked very different, I would say, 'Well, they're different species, for sure.' But variation inside animal species can sometimes fool you," says Janet Voight, lead study author and associate curator of zoology at the Field Museum in Chicago. "That's why we need to look at multiple specimens of species to see, does that first reaction based on two specimens make sense?"

While studying the octopuses, the scientists counted the suckers they had on each arm as well as the number of warts, if they had any. They tracked this information alongside where they found the octopuses.

The deeper in the ocean the octopuses lived, the wartier they were. The octopuses living at shallow depths had smooth skin. But that wasn't the only difference. The octopuses living on the ocean floor were also smaller and didn't have as many suckers on their arms. Scientists determined that the environment influences the appearance of the octopus.

The scientists aren't sure why living in the deep sea would cause bumpier skin.

As for the size difference, the researchers believe it has to do with food availability.

"There's less food as you get deeper in the ocean. So these animals have to work harder to find food to eat. And that means at the end of their lives, they'll be smaller than animals who have more food. If you're a female who's going to lay eggs at the end of your life, maybe your eggs will be smaller," Voight said.

Male octopuses transfer sperm packets using a modified arm. The octopuses deeper in the ocean had a much smaller special arm. This could lead to smaller octopuses being born.

"The octopus hatchlings in shallower water, only 3,660 feet, are bigger," Voight said. "Their eggs had more yolk. As the embryos grew, they developed farther inside the egg than the ones from 9,000 feet, who were developing in smaller eggs. They had less energy to fuel their growth before they left the egg, so they made fewer suckers."

The findings have implications for how climate change could affect octopuses and their food supply, showing how much influence environment and food have over one species.

In order to study the octopuses, the researchers used deep sea, remotely operated vehicles called ROVs.

And understanding that specimens of a species can look different helps researchers identify the diverse and strange life found on the ocean floor.

"There's still just so much we don't know about the deep sea," Voight 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."