Underwater robots discover giant egg-brooding squid in deep sea

During an expedition to the Gulf of California in 2015, MBARI researchers encountered a squid brooding exceptionally large eggs. New research suggests this may represent a previously unknown species in the family Gonatidae. Credit: MBARI.

The deep sea is Earth’s largest living space, but many of its inhabitants remain a mystery.

Advanced underwater robots from the Monterey Bay Aquarium Research Institute (MBARI) are helping scientists explore these hidden depths.

In 2015, during an expedition to Mexico’s Gulf of California, MBARI’s remotely operated vehicle (ROV) Doc Ricketts made an incredible discovery—a mother squid cradling a cluster of eggs.

These eggs were twice the size of those previously seen in other deep-sea squids.

Researchers from MBARI, GEOMAR’s Helmholtz Center for Ocean Research Kiel, and the University of South Florida reviewed the footage and examined similar squids collected on previous expeditions.

They determined that this squid likely represents a new species in the Gonatidae family, known for brooding giant eggs.

Their findings were published in the journal Ecology.

“Squid are crucial in the ocean—they’re fierce predators and a vital food source for many animals, including humans,” said Henk-Jan Hoving, lead author of the study and head of the deep-sea biology working group at GEOMAR.

“Advanced underwater robots help us uncover fascinating new information about deep-sea squids.”

Most deep-sea squids remain poorly understood, particularly their mature females and spawned eggs. While maternal care is common among octopuses, only a few squids are known to brood their eggs.

Typically, squids leave their eggs attached to the seafloor or release floating egg masses, requiring little post-spawning care. In contrast, brooding squids, like the one observed, do not eat while carrying their eggs and die after the eggs hatch.

This sacrifice improves the chances of their offspring’s survival.

MBARI researchers were the first to observe brooding behavior in deep-sea squids. Over 37 years, their ROVs have recorded 17 observations of brooding squids, including the black-eyed squid (Gonatus onyx) and other Gonatus species, as well as the deep-sea squid Bathyteuthis.

The squid found in the Gulf of California, however, stood out due to its exceptionally large eggs.

“The deep sea is the largest living space on Earth, and there’s still so much to discover,” said Steven Haddock, MBARI Senior Scientist and chief scientist during the expedition. “This encounter with a squid brooding giant eggs highlights the diversity of adaptations in deep-sea life.”

By analyzing video footage and studying similar specimens, the team identified this squid as an undescribed species in the Gonatidae family.

The eggs were approximately 11.6 millimeters (about half an inch) in diameter, compared to the usual six millimeters (about a quarter of an inch) seen in other Gonatus squids.

Additionally, this squid was brooding far fewer eggs—about 30 to 40—compared to up to 3,000 eggs in other Gonatus species.

Producing large eggs may be beneficial in the deep sea’s stable environment, allowing for higher investment in fewer offspring with a better chance of survival.

This strategy has been observed in other deep-sea cephalopods, such as the warty deep-sea octopus and the pearl octopus.

The research team estimated that these giant eggs might take one to four years to develop, longer than the entire life cycle of most shallow-water squids. Deep-sea squids are vital in ocean food webs, preying on fish and invertebrates and serving as food for large fish, sharks, whales, dolphins, seals, and seabirds.

Despite their importance, much remains unknown about the reproductive biology and natural history of deep-sea squids. MBARI scientists and their collaborators continue to explore and answer fundamental questions about these mysterious creatures.