Octopus Researchers Crack Mystery of Meeting Place

Two miles below the surface of the ocean some 80 miles off central California sits the world's largest known assembly of octopuses. This "octopus garden," featuring thousands of the typically solitary mollusks, stunned researchers who discovered it on the foothills of an inactive underwater volcano in 2018. It was "one of those really special moments" where "you recognize immediately the magnitude" of what you've found, San Jose State University invertebrate biologist Amanda Kahn, an expedition member, tells the New York Times. Still, it took many years of study to understand the gathering of pearl octopuses. In a study published Wednesday in Science Advances, researchers reveal the site to be a mating and breeding ground, where embryos enjoy a huge advantage.

A "shimmering" indicated the cool ocean water was mixing with warm water from what turned out to be a hydrothermal spring. In this spot, where many female octopuses were brooding, the water temperature was around 52 degrees Fahrenheit, compared to 35 degrees in the surrounding area. At near-freezing temperatures, pearl octopus eggs would take five to 10 years to hatch due to slower rates of embryonic growth, per the Times. But in the warmer water, researchers found eggs hatched in less than two years on average, twice as fast as expected, per the Washington Post. The shorter development period likely boosts reproductive success, limiting the time predators have to feast on the eggs and ensuring mother octopuses are around for protection.

Female octopuses stay with their eggs but spend all their energy tending to them. They go without eating and typically die around the time the eggs hatch. The team counted 6,000 octopuses in an area that size of a few football fields, more than 80% of which were nesting females, but believe there could be as many as 20,000. Though special, the octopus garden isn't an anomaly. Five miles away, the research team found another nursery near thermal springs. And in June, other researchers confirmed the discovery of yet another nursery near thermal springs off Costa Rica. The team now aims to understand how octopuses know about these hotspots, speculating that the mollusks might be returning to reproduce in the same places they were born. (More octopus stories.)