Life in the Octopus Garden: What We Can Learn from the Mysterious Nurseries of the Deep Sea

Saturday - September 16 2023, 20:08 UTC - 1 year ago

The Octopus Garden off Monterey, California, is an underwater mountain where thousands of pearl octopuses (Muusoctopus robustus) have been discovered breeding. Warmer temperatures near these thermal springs is speeding up embryo development for octopuses, allowing them to survive better and even move into colder climates. Through research, scientists have been able to identify how to protect these nurseries and successfully understand the behavior of cephalopods.

Two miles below the ocean surface off Monterey, California, warm water percolates from the seafloor at the base of an underwater mountain. It’s a magical place, especially if you’re an octopus. In 2018, one of us, Amanda Kahn, was aboard the research vessel E/V Nautilus when scientists discovered the "Octopus Garden." Thousands of pearl octopuses (Muusoctopus robustus) were curled up into individual balls in lines and clumps .

As Nautilus Live streamed the expedition online, the world got to share the excitement of the discovery. We now know why these amazing creatures gather at this and other underwater warm springs. In a new study involving scientists from several fields, we explain why octopuses migrate to the Octopus Garden. It’s both a mating site and a nursery where newborn octopuses develop faster than expected, giving them the best shot at survival in the deep, cold sea .

Life in the Octopus GardenFemale octopuses seek out rocky cracks and crevices where warm water seeps from the rocks. There, they vigilantly guard their broods. Subsisting off their energy reserves alone, these mothers will never eat again. Like most cephalopods, they make the ultimate sacrifice for their offspring and die after their eggs hatch. The Octopus Garden, at the base of Davidson Seamount about 80 miles (130 kilometers) southwest of Monterey, California, is the largest of a handful of octopus nurseries recently discovered in the Eastern Pacific .

Many have been found near hydrothermal springs where warm water seeps from the seafloor. We wanted to know what makes these environments so appealing for nesting octopuses. To solve this mystery, we assembled geologists, biologists and engineers. Using Monterey Bay Aquarium Research Institute’s deep-sea robots and sensors, we studied and mapped the Octopus Garden during several visits over three years to examine the links between thermal springs and breeding success for pearl octopuses .

We found nearly 6,000 nests in a 6-acre (2.5-hectare) area, suggesting more than 20,000 octopuses occupy this site. A time-lapse camera that kept watch over a group of nesting mothers for six months opened a window into the dynamic life in the Octopus Garden. We witnessed male octopuses approaching and mating with females. We cheered for the successful emergence of hatchlings, which looked like translucent miniatures of their parents .

And we mourned the deaths of mothers and their broods. When a nest became empty, it was quickly filled by a different octopus mother. We saw that nothing went to waste at the Octopus Garden. Dead octopuses provided a vital food source for a host of scavengers, like sea anemones and snails. Warmer water speeds up embryo developmentA new generation of octopuses must overcome at least two hurdles before hatching .

First, they must develop from egg to hatchling. They start as opaque, sausage-shaped eggs cemented to the rocks. Over time, tiny black eyes, then eight little arms grow visible through the egg capsule. Second, crucially, they must not succumb to external threats, including predators, injuries and infections. The longer the incubation period, the greater the likelihood of dying from disease or being eaten .

We studied the intricacies of octopus egg development by submerging octopus mothers in tanks containing water at different temperatures. Pearl octopuses can survive and maintain activity at water temperatures as low as 4°C, far lower than most deep-sea creatures can tolerate. We found that, as suspected, embryos develop faster in warmer water: At 20° and above, hatching can occur in 40 days. Most octopus nurseries occur at water temperatures ranging from 20–24°C — these shallower sites enjoy cooler water than other thermal springs, suggesting they offer protection from temperature extremes .

But we were surprised to discover that hatching occurred significantly faster at temperatures up to 28°C. This suggests that, while the ocean warms, octopuses may be able to move farther up the slopes of seamounts to find life-sustaining warmer water in colder climates. We hope that by understanding the biology and behavior of the mother octopuses, we can learn to identify and protect deep-sea nurseries .

The intriguing discovery of the Octopus Garden contributes to the growing body of evidence that universally, cephalopods are the shortest lived marine mammals—and some of the most fascinating.