Advanced underwater robots discover deep-sea squid hatching giant eggs

The deep sea is the largest living space on Earth, but many animals and habitats located far below the ocean’s surface remain shrouded in mystery. MBARI’s advanced underwater robots, including remotely operated vehicles (ROVs), help study life in the deep ocean.

During an expedition to Mexico’s Gulf of California in 2015, MBARI’s ROV Doc Ricketts encountered a mother squid cradling a cluster of eggs. MBARI researchers had previously observed deep-sea squid incubating their eggs, but this observation was striking because the eggs were twice the size of those of other deep-sea squid incubating.

A team of researchers from MBARI, GEOMAR’s Helmholtz Center for Ocean Research in Kiel and the University of South Florida carried out a meticulous review of the ROV’s images and examined similar-looking squid specimens collected during previous expeditions to the Gulf of California.

The team determined that this individual likely represents an unknown species in the Gonatidae family that incubates giant eggs. The researchers shared their findings in Ecology.

“Squid play an important role in the ocean – they are fierce predators and a vital food source for many animals, even humans – but we still have much to learn about the squid that live in the deep sea. Advanced underwater robots are helping us better understand the lives of deep-sea squid, revealing fascinating new information about their biology and behavior, each new observation is another piece of the puzzle,” said Henk-Jan Hoving, former researcher postdoctoral fellow at MBARI who now leads GEOMAR’s in-depth marine biology working group and was the lead author of this new study.

Scientists still have many unanswered questions about the lives of deep-sea squid. For the majority of deep-sea squid, researchers have never observed mature females or their eggs laid.

Although maternal care is common among octopuses, brooding has only been observed in a handful of squid. Most squid species leave clusters of eggs attached to the seafloor or release neutrally buoyant egg masses containing thousands of eggs that drift through the water column. These reproductive strategies require relatively little effort compared to caring for the eggs after laying.

“Brooding takes a lot out of a mother squid. She doesn’t eat while carrying her eggs and eventually dies after her eggs hatch. But her sacrifice improves her offspring’s chances of survival. It’s only “one of many remarkable adaptations that can help cephalopods survive in the deep sea,” Hoving explained.

MBARI researchers were the first to observe the brooding behavior of a deep-sea squid. During 37 years of deep-sea exploration, MBARI’s ROVs have recorded 17 sightings of hatching squid. These include multiple observations of brooding black-eyed squid (Gonatus onyx) and other hooked squid (Gonatus sp.) that are difficult to identify to species from video alone, as well as the large squid Bathyteuthis funds. But the squid observed in the Gulf of California left its mark on researchers.

“The seabed is the largest habitable space on Earth and there is still much to discover. Our unexpected encounter with a squid hatching giant eggs caught the attention of everyone in the ship’s control room. This remarkable observation highlights the diversity of ways animals adapt to the unique challenges of life in the deep,” said MBARI Principal Scientist Steven Haddock, who was the lead scientist on the expedition that encountered this brooding squid.

By analyzing the video footage and studying specimens of similar-looking squid collected during previous expeditions to the Gulf of California, the research team determined that it was likely an undescribed species of the family Gonatidae.

It was the large size of this squid’s eggs – about 11.6 millimeters (about half an inch) in diameter – that caught the research team’s attention. Previous observations of hatching Gonatus squid reported eggs half the size, with a maximum diameter of just six millimeters (about a quarter of an inch).

The squid observed in the Gulf of California also incubated significantly fewer eggs than other Gonatus squid. Researchers estimated that it carried between 30 and 40 eggs, while Gonatus squid observed in the past incubated up to 3,000 eggs at a time.

Producing many small eggs is beneficial in environments where food is limited and/or predation is high. In these environments, a larger number of offspring provides a greater chance that at least some will survive.

Giant eggs may be more beneficial in the more stable and predictable conditions of deep water, allowing greater investment in fewer offspring with a better chance of survival. This has been observed in other deep-sea cephalopods, including the deep-sea warty octopus (Graneledone sp.) and the beaded octopus (Muusoctopus Robustus).

Extrapolating from data reported by other scientists on egg development rates, the research team estimated that the eggs of this new deep-sea squid could take one to four years to develop, which is longer than the complete life cycle of most shallow-water squid.

Deep-sea squid play a vital role in ocean food webs. They are predators that feed on fish and invertebrates in the intervening waters and, in turn, are eaten by large fish, sharks, whales, dolphins, seals and seabirds. Deep-sea squid make up a large part of the diet of commercially important fish such as tuna, swordfish and billfish.

Despite their ecological and economic importance, we still know very little about the reproductive biology and natural history of deep-sea squid. MBARI scientists and their collaborators answer fundamental questions about the biology of deep-sea cephalopods.