Yet another marvel of planet Earth has been revealed by — well, Planet Earth.
The hit BBC series with Sir David Attenborough recently shed light on the largest wild congregation of octopuses the world has ever seen.
It’s called the “Octopus Garden,” and some 20,000 pearl octopuses gather there to raise their young. If they’re trying to find a quiet neighborhood to settle down in, the location is understandable. It’s near the Davidson Seamount, an undersea mountain about three kilometers deep off the California coast.
Image: MBARI
“That life is there at all is amazing,” producer and director Will Ridgeon, who spent two years filming the octopuses alongisde the Monterey Bay Aquarium Research Institute (MBARI) in California, told the BBC.
The fact that there’s so much of it is beyond precedent. Octopuses are solitary by reputation and even tend to cannibalize each other in close quarters. But the Octopus Garden’s population seemed to defy that behavior.
“The question was, why there?” asked MBARI senior scientist Jim Barry.
Octopuses all the same age
To find out, they set up exhaustive surveillance over the approximately 2.5-hectare site. Shooting with an unmanned submersible, they first stitched together high-resolution photos to count the specimens. Then they set up time lapse cameras around the seabed. This helped them keep track of the animals’ activity for months without missing a beat.
The team recorded surprising findings.
They first noted that all 20,000 octopuses seemed to be about the same age. They spotted few, if any, young or adolescent octopuses — only fully-grown adults. The vast majority were female.
Even though it’s called the “Garden,” the site more than likely functions as a nursery, the BBC reported. To that end, the researchers found evidence that indicates that brooding females are using thermal vents at the site to speed up development of their young. Warmer temperatures help octopuses reach maturity faster. The longer their eggs rest on the seafloor, the longer they’re exposed to scavengers.
Eggs take two years to hatch
Pearl octopus females settle in for the long haul regardless. It takes about 1.8 years for their clutches of about 60 eggs to hatch. During that time, they don’t move.
“Once you plant your eggs on the rock, that’s it –- you’re stuck with that site,” said Barry. The mothers spend the entire time fighting off predators and generally guarding their clutch.
Amazingly, it would likely take a decade or more for the Octopus Garden eggs to hatch without the thermal springs.
Hatchlings measure around five centimeters across, which is big for a young octopus. At the end of the Planet Earth segment, they swarm away from the Octopus Garden toward ambiguous futures in the ocean.
Eight-legged circle of life
Sadly, though, it’s curtains for their mothers.
“These mums are fierce defenders of their brood, while they’re just withering away,” Barry told the BBC.
Shortly after their offspring depart, each one dies. “On-screen, we see the females’ eyes glaze over and their bodies become wrinkled,” the BBC reported.
Of course, nothing is wasted in nature. The deep-sea predators and scavengers the mothers spent years warding off soon descend on their remains.
It’s a typical full-circle arc for a Planet Earth spotlight. While the BBC has finished its filming at the location, Barry will continue his studies.
Among the big questions: Where do the hatchling octopuses go, and what keeps them coming back to the Garden?
“Are the octopuses locked into this form of breeding in warm sites, or can they still breed elsewhere at cooler, ambient temperatures? Is there fidelity to a particular nest site? Do they come back to the site they were born?” he asked. “We’ll definitely keep going back.”
