After five years, scientists have solved the mystery of the octopus garden.
Octopuses off California's coast gather in herds around hidden deep-sea vents to mate and lay eggs.
They use the heat from the vents to speed up their reproductive cycle and get an evolutionary edge.
Parting the black blanket of the deep sea with the headlights of their submarine, scientists stumbled upon a mystery — 6,000 octopuses, stacked in rows along jagged stabs of sea rock, glittering like pearls. That was five years ago.
The scientists nicknamed it an octopus garden, and as far as anyone knows, it's the largest gathering of pearl octopuses ever seen, said Jim Berry, a marine ecologist at the Monterey Bay Aquarium Research Institute.
The team estimates the total population could exceed 20,000 octopuses.
"It's just an astounding scene. And then immediately, you wonder, why are they there," Berry told Insider. Especially since this type of octopus is usually solitary.
Berry said it was quickly obvious that the octopuses were breeding, but it took longer for him and his collaborators to determine why they might have picked that location.
An evolutionary edge
Normally, deep sea octopuses have to work really hard to reproduce. The cold temperatures and harsh conditions make the octopus eggs take four years to hatch, Berry said.
But the octopuses that made their nursery here cut that time in half, taking roughly two years to reproduce.
The scientists think that the cephalopods are using the warmer waters to speed up their egg maturation and the rocky walls as a place to store them, Berry and his colleagues report in a study published in Science Advances.
These two advantages mean that the octopuses were able to reproduce faster, and easier, Berry added.
"It's really tough to make a living in the deep sea. And these octopuses have found a way to find thermal springs so that they can improve their reproductive success," he said.
The octopus garden of death and birth
When the garden was first discovered, Berry was immediately interested.
In fourteen dives over five years Berry and the team, with their uncrewed submarine, saw adult male and female octopuses, their eggs, and their corpses.
Because crucially, and cruelly, pearl octopuses die shortly after they reproduce. That means ocean scavengers also frequent the area, picking through the remains of the late parents. This makes the site a place for death and rebirth.
So the octopuses found a special spot reserved for those epic moments at the bookends of life. The rest of their life, you'll find them drifting amongst the muddy bottoms of the deep sea, scavenging, the study said.
More ingenious cephalopods may exist
This site, called the Davidson Seamount, is an extinct underwater volcano that sits about 10,500 feet underwater 80 miles southwest of Monterey, California.
Prior to 2018, the researchers didn't even know there were volcanic vents in the area, Berry said.
Humans have only charted about 5% of the ocean, UNESCO estimates. So, there could be many other ingenious pods of cephalopods doing similar things across the sea, Berry said.
This is why it's crucial to take care of our oceans before we impact them in ways that forever change their unique environments, he said.
"As we explore more of the deep sea, we find more and more that it's not just a homogeneous, deep, sort of mud-covered pit. There are special places that play a large role in either the geology or the biology or ecology of different areas."
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