MBARI researchers filmed a giant "seven‑arm" octopus nearly half a mile beneath Monterey Bay, marking the fourth sighting by the team in about 40 years. The ROV footage, recorded on Nov. 6 at roughly 700 meters (2,300 feet), shows the octopus holding and eating a bioluminescent red helmet jellyfish. The sighting confirms earlier evidence that Haliphron atlanticus feeds on gelatinous prey and highlights how males conceal a specialized reproductive arm, creating the appearance of seven arms.
Rare Deep-Sea Encounter: Giant 'Seven‑Arm' Octopus Filmed Holding Bioluminescent Jellyfish Off California
Nearly half a mile beneath the surface of Monterey Bay, California, researchers from the Monterey Bay Aquarium Research Institute (MBARI) captured rare footage of a giant “seven‑arm” octopus clutching and eating a bioluminescent red helmet jellyfish. This marks only the fourth time the same research team has observed the species in roughly four decades.
The footage, taken by a remotely operated vehicle (ROV) on Nov. 6, was recorded at about 700 meters (roughly 2,300 feet) below sea level—inside the ocean’s so‑called twilight zone. The sighting reinforced earlier observations that these octopuses include gelatinous animals in their diet: the team’s previous encounter also involved the octopus holding part of a jellyfish.
"To be able to confirm our first observation with this new sighting was informative because this octopus was holding a different, deeper‑living type of jellyfish than we’d seen before," said Steven Haddock, a senior scientist at MBARI and a member of the team that observed the animal.
Known scientifically as Haliphron atlanticus, the so‑called seven‑arm octopus actually has eight arms. Males commonly conceal a specialized eighth arm—the hectocotylus—which is used to transfer sperm during mating, giving the appearance of only seven appendages. Females grow much larger than males, reaching as much as 13 feet in length and weighing up to 165 pounds, according to MBARI.
MBARI scientists noted that it is remarkable one of the ocean’s largest known octopus species reaches such sizes while subsisting largely on gelatinous prey. Observations like this help researchers compare diet and behavior across depths and better understand life in poorly explored deep‑sea environments.
Why it matters: Each confirmed sighting provides valuable behavioral and ecological data about a rare deep‑sea species, improves our knowledge of the twilight‑zone food web, and demonstrates the power of ROVs and long‑term monitoring in revealing hidden ocean life.
This story originally appeared in the Los Angeles Times. Footage and reporting were provided by MBARI.
