About 130 kilometers southwest of Monterey, California, a low ridge on the flank of an extinct underwater volcano called Davidson Seamount holds one of the densest gatherings of octopuses ever documented. The site, which researchers at the Monterey Bay Aquarium Research Institute named the Octopus Garden, sits 3,200 meters, or roughly 10,500 feet, beneath the surface of the Pacific, deep enough that sunlight never reaches it and the water hovers barely above freezing.
A single high-resolution video census of the site counted 5,718 octopuses packed into a 2.5-hectare patch of seafloor, and MBARI scientists estimate the full nesting ground, which spans roughly 1.29 square miles, holds more than 20,000 individuals at any given time. Senior scientist Jim Barry has called it the largest known aggregation of octopuses anywhere on Earth, deep-sea or shallow.
Streams of octopuses in the dark
The garden was found almost by accident. In October 2018, an expedition run by NOAA’s Monterey Bay National Marine Sanctuary and the Ocean Exploration Trust sent the remotely operated vehicle aboard the research vessel Nautilus across a stretch of seafloor near Davidson Seamount. Pilots noticed water shimmering above a crevice, a visual signature of warmer fluid mixing with the near-freezing water column, and steered closer to investigate.
What they found, according to Scientific American’s account of the discovery, was a single octopus pair at first, then “streams of 20 or more octopuses nestled in crevices” along the rock face, each female curled protectively over a clutch of eggs. Follow-up dives by MBARI’s ROV Doc Ricketts confirmed the pattern extended across a much larger area of the ridge.
A patch of warmth in the near-freezing dark
The ambient water around Davidson Seamount sits at about 1.6 degrees Celsius, or 34.9 degrees Fahrenheit, cold enough that biological processes generally slow to a crawl. But inside the rock crevices where the octopuses nest, instruments recorded temperatures reaching nearly 11 degrees Celsius, or about 51.8 degrees Fahrenheit, fed by warm fluid seeping up through fractures in the extinct volcano.
The pattern was not incidental. Female pearl octopuses, Muusoctopus robustus, were consistently found clustered in the warmest available crevices rather than distributed evenly across the ridge, a finding the research team published in Science Advances in August 2023 under the title “Abyssal hydrothermal springs — cryptic incubators for brooding octopus.” The paper’s authors, led by Barry, framed the warm seeps as a previously undocumented feature of deep-sea octopus reproduction.
Why warmth speeds up an octopus egg
Octopuses, like other cephalopods, are ectotherms: their metabolic rate, and the pace of embryonic development inside their eggs, tracks the temperature of the surrounding water rather than being internally regulated. In the near-freezing water typical of the abyssal seafloor, that relationship works against a brooding octopus. Based on comparative data from other cold-water octopus species, MBARI researchers estimated that eggs at Davidson Seamount’s ambient temperature would need somewhere in the range of five to eight years, “if not longer,” to develop and hatch.
Eggs nested in the warm seep crevices, by contrast, were observed hatching in under two years. Researchers describe the seep water as accelerating the octopuses’ metabolism and, in turn, the biochemical pace of embryonic growth, sharply cutting the length of time a clutch of eggs remains exposed to seafloor predators. That five-to-eight-year baseline is a comparative estimate, not a measurement taken at the same site without the warm water — a distinction MBARI’s own reporting on the 2023 findings makes explicit. The underlying biology, temperature-dependent metabolism in cold-blooded animals, is well established in cephalopods generally, but the exact hatching timeline this specific population would face without the seeps has not been directly observed.
Watching the same mothers for three years
Confirming any of this required more than a single dive. MBARI’s monitoring program returned to the site repeatedly over roughly three years, using a 4K camera mounted on Doc Ricketts to photograph individual brooding females closely enough to recognize them again on later visits, by scars and other distinguishing marks on their skin. That let researchers track how long specific mothers stayed with a given clutch and roughly when eggs disappeared, presumably after hatching.
Temperature and oxygen sensors placed directly in nesting crevices supplied the seep-water readings that anchored the mechanism, while a purpose-built census system counted and mapped nests across the core of the site. Some questions remain open, including exactly how the octopuses initially locate suitable warm crevices before settling in to brood. Barry has pointed to the practical stakes of the work beyond the biology itself, telling MBARI that the findings help give resource managers the information they need to weigh protections for deep-sea habitat like this one, which sits within the Monterey Bay National Marine Sanctuary.
Not the only warm nursery in the deep
Davidson Seamount’s garden is striking for its size, but it is not unique. Researchers have documented comparable warm-seep octopus nurseries at Dorado Outcrop off Costa Rica and near Vancouver Island in British Columbia, according to Scientific American’s reporting on the broader pattern. In each case, brooding octopuses appear to seek out localized geothermal warmth on the otherwise cold seafloor, suggesting the behavior may be more widespread among deep-sea octopus species than a single California site would imply.
That pattern raises the possibility that geologically active seafloor terrain — seamounts, ridges and other features prone to fluid seepage — plays a functional role in where certain octopus populations choose to reproduce. It may not simply reflect where researchers have happened to look most closely.
Returning with sharper eyes in 2026
MBARI’s work at the site did not end with the 2023 paper. In early August 2026, a ten-day expedition aboard the research vessel David Packard, again using ROV Doc Ricketts, returned to map the Octopus Garden with a new instrument called the Low-Altitude Survey System, which combines multibeam sonar, laser-based lidar and stereo photography to build centimeter-scale maps of the seafloor, according to a report on the expedition.
The team repeated survey lines first run in 2021 to track how the site has changed over time and expanded coverage into new sections of the ridge, while also testing automated software designed to detect and count animals in the resulting imagery. The same expedition ran the new mapping system at a second chemosynthetic site, Tubeworm Slump in Monterey Canyon, for the first time. The ongoing monitoring underscores that the Octopus Garden remains an active research site, not a one-time discovery. Scientists are still working out how many octopuses actually nest there and how the population shifts from year to year.