2023 Annual Report
Several pale purple octopus nesting in between greenish black boulders. This screen capture from underwater video shows brooding octopus oriented upside down with their arms and suckers exposed. Several pale orange sea anemones are interspersed among the nesting octopus.

For three years, MBARI and collaborators monitored the Octopus Garden with high-tech tools. The team learned that large numbers of pearl octopus (Muusoctopus robustus) gather at this site to mate and nest. Image: © 2022 MBARI

Revealing the secrets of a deep-sea octopus nursery

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 why this site is so attractive for deep-sea octopus. In 2023, the team of researchers from MBARI, NOAA's Monterey Bay National Marine Sanctuary, Moss Landing Marine Laboratories, the University of Alaska Fairbanks, the University of New Hampshire, and the Field Museum published their findings detailing why deep-sea octopus migrate to the Octopus Garden to mate and nest.

At this nursery, warmth from deep-sea thermal springs accelerates the development of octopus eggs. Scientists believe the shorter brooding period increases a hatchling octopus’ odds for survival. The Octopus Garden is the largest known aggregation of octopus on the planet—researchers counted more than 6,000 octopus in a portion of the site and estimate there may be 20,000 or more at this nursery.

A topographic map showing part of the Central California coastline in pale gray, brown, and green on the right and the eastern Pacific Ocean on the left in three shades of blue representing depth gradients. Three white dots and accompanying text labels mark the locations for San Francisco, Monterey, and MBARI’s research facilities in Moss Landing, California. At the bottom center of the map, labels call out the location of Davidson Seamount and the Octopus Garden in white text.
Davidson Seamount is an inactive volcano located 130 kilometers (80 miles) southwest of Monterey, California. The Octopus Garden is located 3,200 meters (10,500 feet) below the ocean’s surface on a small hill near the base of the seamount. Illustration by Madeline Go/MBARI, basemap created via ArcGIS Online, sources: Esri, USGS | Esri, GEBCO, DeLorme, NaturalVue | California State Parks, Esri, HERE, Garmin, SafeGraph, FAO, METI/NASA, USGS, Bureau of Land Management, EPA, NPS

The Octopus Garden is located 3,200 meters (10,500 feet, or about two miles) below the ocean's surface on a small hill near the base of Davidson Seamount, an inactive underwater volcano 130 kilometers (80 miles) southwest of Monterey, California. The site is full of Muusoctopus robustus—a species MBARI researchers nicknamed the pearl octopus because from a distance, nesting individuals look like opalescent pearls on the seafloor.

Most of the octopus were oriented upside down, with their inverted arms folded around their bodies. This posture was an indication of pearl octopus mothers protecting, or brooding, their eggs. The pearl octopus is a pale purple species about the size of a grapefruit that occurs in the northeastern Pacific Ocean from Oregon to Baja California. MBARI has observed this species at depths of 2,300 to 3,600 meters (7,500 to 11,800 feet).

The deep sea is one of the most challenging environments for science and technology. The expertise of the MBARI team—the scientists, the engineers, pilots of our submersible vehicles, and crew of our research vessels—was integral to studying this hotspot of life two miles below the surface. Leveraging decades of experience in deep-sea exploration, the team developed and deployed instruments to study the Octopus Garden without disturbing the nesting mothers.

Our remotely operated vehicle (ROV) Doc Ricketts—controlled by scientists and submersible pilots aboard the research vessel Western Flyer—allowed researchers to observe nesting octopus with a suite of scientific instruments.

High-definition and 4K video revealed the behavior of brooding pearl octopus and their neighbors. Advanced instruments measured the environmental conditions within their nests, including temperature and oxygen levels. An innovative, custom-built mapping system took a census of octopus nests at the heart of the nursery. A time-lapse camera collected long-term observations of the octopus’ behavior and changes in the community between research expeditions.

The researchers examined a trove of data to learn why such large numbers of pearl octopus are attracted to this location. The presence of adult male and female octopus, developing eggs, and octopus hatchlings indicated that the site is used exclusively for reproduction. The team did not observe any intermediate-sized individuals or any evidence of feeding. Pearl octopus gather at this site solely to mate and nest.

When researchers from NOAA and Nautilus Live first discovered the Octopus Garden, they observed “shimmering” waters. This phenomenon occurs when warm and cool waters mix, suggesting the region had previously unknown thermal springs. Further investigation by MBARI researchers and their collaborators confirmed octopus nests are clustered in crevices bathed by hydrothermal springs where warmer waters flow out of the seafloor.

The ambient water temperature at 3,200 meters (10,500 feet) deep is 1.6 degrees Celsius (about 35 degrees Fahrenheit). However, the water temperature within the cracks and crevices at the Octopus Garden reaches nearly 11 degrees Celsius (about 51 degrees Fahrenheit).

A pale purple octopus nesting in a rocky crevice. This screen capture from underwater video shows a female octopus oriented upside down with her arms and suckers exposed. Underneath the octopus are several pale white, sausage-shaped eggs. Many pale snails are clustered around the octopus on the greenish black rock.
At the Octopus Garden, pearl octopus (Muusoctopus robustus) mothers nest in rocky crevices bathed by hydrothermal springs. The warmer water accelerates the development of octopus eggs. Image: © 2020 MBARI

Octopuses are ectothermic, or cold-blooded, animals. The frigid temperatures of the deep sea slow their metabolism as well as their rate of embryonic development. Deep-sea octopuses have very long incubation periods compared to their relatives inhabiting warmer shallow seas. Past experiments have measured egg incubation time for a number of octopus species in habitats and locations around the world. Comparing those brood periods clearly demonstrates how temperature affects the rate of embryo development—the colder the water, the slower the embryos grow.

At the near-freezing temperatures of the abyss, researchers expected pearl octopus eggs to take five to eight years, if not longer, to hatch. The higher resolution of the 4K camera on MBARI’s ROV Doc Ricketts provided a close-up look at nesting mothers. Scars and other distinguishing features of individual octopus moms allowed the team to monitor the development of their broods. Surprisingly, the eggs 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.

Researchers believe the shorter brood period in warmer waters greatly reduces the risk that developing octopus embryos will be injured or eaten by predators, resulting in more eggs hatching viably. Thus, nesting in warmer water boosts the reproductive success of the pearl octopus, better ensuring the offspring’s survival.

The deep sea is one of the harshest environments on Earth, yet animals have evolved clever ways to cope with frigid temperatures, perpetual darkness, and extreme pressure. The percentage of a mother’s eggs that survives and hatches is expected to decrease with very long brooding periods. By nesting at hydrothermal springs, octopus moms give their offspring a leg up.

The massive number of octopus in one area attracts both predators and scavengers. Like most other cephalopods, pearl octopus die after they reproduce. Dead octopus at the Octopus Garden provide a bounty for scavengers. A rich community of invertebrates lives alongside the nesting females, undoubtedly feeding on spent adult octopus carcasses, unhatched eggs, and even the vulnerable hatchlings.

Many questions still remain about the Octopus Garden, including where pearl octopus go after hatching, how this octopus species became adapted to breeding in thermal springs, how adult octopus find the thermal springs, what advantage individuals breeding in these hydrothermal springs have over those that breed elsewhere, and how common hydrothermal springs are in the deep sea.

A pale purple octopus with a round body, black eyes, and eight thin arms sitting on the deep seafloor. This screen capture from underwater video shows an animal perched on a rock covered in fine brown sediment. Its body is pointed to the back and its arms are curled around the front. At the top right, a black canister holding a light is illuminating the octopus, casting shadows behind the octopus and creating a vignette effect with the edges of the frame left in dark shadows.
MBARI’s advanced deep-sea technology helped bring the Octopus Garden to life in Planet Earth III, an eight-part global series produced by BBC Studios Natural History Unit. Image: © 2021 MBARI

The footage collected by the ROV Doc Ricketts provided valuable research data, as well as an opportunity to share the story of the Octopus Garden with the world.

MBARI collaborated with the BBC Studios Natural History Unit to share the story of these deep-sea octopus moms with global audiences as part of the landmark new series, Planet Earth III.

Over two years and five expeditions, BBC Studios Natural History Unit filmmakers accompanied MBARI’s Benthic Biology and Ecology Team to the Octopus Garden to capture the events unfolding at the nursery. Stunning closeups of the brooding mothers personalize an animal that might otherwise be unfamiliar to viewers. The slow pulse of a siphon, the glimpse of an inky purple eye, and the mesmerizing movement of arms gently caressing pearlescent eggs—all these behaviors paint a picture of the last, long, laborious act these mothers perform to best ensure their young ones’ survival.

MBARI’s education and outreach efforts, including our collaborations with media partners, help raise awareness about the importance of ocean health. In Planet Earth III, the simultaneous fragility and resilience of nature take the spotlight. As human activity changes our planet at an unprecedented rate, we hope meeting the amazing animals of the deep inspires responsible stewardship of marine animals and environments.

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

“MBARI research is providing the critical information that resource managers need to enact protections for deep-sea animals and habitats.”
—Senior Scientist Jim Barry

For more than two decades, researchers from MBARI and NOAA have collaborated to study Davidson Seamount. Since the first expedition to the seamount in 2002, NOAA has leveraged MBARI expertise in marine geology and benthic biology and ecology to develop a comprehensive research program that aims to understand the community of life on and around this special habitat. Now, Davidson Seamount is considered one of the best-studied and most well-protected seamounts in the world.

Several pale purple octopus nesting in between greenish-brown boulders. This screen capture from underwater video shows octopus oriented upside down with their arms and suckers exposed. Several pale orange sea anemones are interspersed among the nesting octopus, including a large peach-colored anemone in the center and a large pale-orange flytrap anemone on the left. On the right is a pale purple octopus moving along the rocks.
Biological hotspots like the Octopus Garden teem with life and need our protection. Sharing images and video of deep-sea animals and environments can inspire stewardship of these living treasures. Image: © 2021 MBARI

Davidson Seamount and its 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.

As the imprint of human activities reaches deeper into ocean ecosystems, we need to protect the many other biological treasures that remain undiscovered.

Our work at the Octopus Garden was funded as part of the David and Lucile Packard Foundation’s long-term support of MBARI’s advances in ocean research and technology.

Research Publication:

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: eadg324. doi.org/10.1126/sciadv.adg3247

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