Location of the Octopus Garden off the Central California coast
The Octopus Garden is located 3,200 meters (10,500 feet) below the ocean’s surface on a small hill near the base of Davidson Seamount, an inactive volcano 130 kilometers (80 miles) southwest of Monterey, California. Illustration: Madeline Go/MBARI, ArcGIS Online/Esri

In 2018, researchers from NOAA’s Monterey Bay National Marine Sanctuary and Nautilus Live observed thousands of octopus nesting on the deep seafloor off the Central California coast. The discovery of the “Octopus Garden” captured the curiosity of millions of people around the world, including MBARI scientists. For three years, MBARI and our collaborators used high-tech tools to monitor the Octopus Garden and learn exactly why this site is so attractive for deep-sea octopus.

Our work has confirmed that pearl octopus (Muusoctopus robustus) migrate to the Octopus Garden to mate and nest. The Octopus Garden is one of a handful of known deep-sea octopus nurseries. At this nursery, warmth from deep-sea thermal springs accelerates the development of octopus eggs.

The Octopus Garden is the largest known aggregation of octopus on the planet—using an innovative sensor suite designed by engineers in MBARI’s Seafloor Mapping Lab we counted more than 6,000 octopus in a portion of the site and expect there may be 20,000 or more at this nursery.

The ambient water temperature around the Octopus Garden is 1.6 degrees Celsius (about 35 degrees Fahrenheit). However, within the cracks and crevices where octopus nest, the water temperature reaches nearly 11 degrees Celsius (about 51 degrees Fahrenheit). 

At the near-freezing temperatures of the abyss, we would expect pearl octopus eggs to take five to eight years, if not longer, to hatch. Surprisingly, the eggs here hatched in less than two years. Warmth from thermal springs increased the metabolism of female octopus and their broods, reducing the time required for incubation. The shorter brood period greatly reduces the risk that developing octopus embryos will be injured or eaten by predators. Nesting in warmer water boosts the reproductive success of the pearl octopus, better ensuring the offspring’s survival.

The thermal springs at the Octopus Garden are part of a ridge flank hydrothermal system. Here, water percolating beneath the seafloor picks up heat from Earth’s mantle before it’s channeled out through volcanic rock outcrops like Davidson Seamount. These systems have become an emerging focus in seafloor geology, though only a few have been discovered so far.

A photomosaic assembled from photos taken during low-altitude surveys with an underwater robot. Several pale octopus are visible nesting in two crevices along the black, rocky seafloor at the top left and the right of the photo. Other marine life, including pale orange sea anemones, are also visible.
Visual surveys of the center of the Octopus Garden revealed nearly 6,000 nesting pearl octopus (Muusoctopus robustus). Researchers estimate there may be more than 20,000 total nests at the site. Image: © 2021 MBARI

Unlike hydrothermal vents, which form at ridge crests and belch plumes of hot water that are detectable hundreds of meters above the bottom, thermal springs on ridge flanks are cryptic. These springs seep warm water that dissipates only meters above the bottom, making them exceedingly difficult to find and only visible by a slight shimmer in the water.

Our yearlong recordings from thermal springs at the Octopus Garden demonstrate these may be stable environments, with the potential to release warm fluids for thousands of years. Such stability benefits not only pearl octopus, but also the community of life that thrives alongside the nesting mothers.

The recent discoveries of octopus nurseries off the Pacific coast of Costa Rica, also near hydrothermal springs, suggest these areas may be more common than previously thought. It also highlights that hydrothermal springs may be vital biological hotspots.

Davidson Seamount and the Octopus Garden are protected as part of Monterey Bay National Marine Sanctuary. Previous MBARI expeditions to Davidson Seamount in 2002 and 2006 revealed the stunning community of life on its rocky slopes. MBARI’s images and video of beautiful deep-sea corals, vibrant sponges, and curious fishes engaged and inspired audiences worldwide. Ocean champions spoke up to protect this unique, and still untouched, ocean wilderness. In 2008, resource managers expanded the Monterey Bay National Marine Sanctuary to include Davidson Seamount.

The deep sea is not immune to threats like fishing, pollution, and climate change. By documenting deep-sea biodiversity and identifying hotspots of life on the ocean floor, MBARI scientists are gathering important information that resource managers can use to guide protections for the deep sea and its inhabitants.

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Barry, J.P., S.Y. Litvin, A. DeVogelaere, D.W. Caress, C.F. Lovera, A.S. Kahn, E.J. Burton, C. King, J.B. Paduan, C.G. Wheat, F. Girard, S. Sudek, A.M. Hartwell, A.D. Sherman, P.R. McGill, A. Schnittger, J.R. Voight, and E.J. Martin. 2023. Abyssal hydrothermal springs—Cryptic incubators for brooding octopus. Science Advances, 9(34): 1–13. science.org/doi/10.1126/sciadv.adg3247

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