Remotely operated vehicles exploring the vast, mysterious depths of the ocean, have made a new discovery about the unique reproductive strategies of deep-sea squids. A team of scientists, led by Henk-Jan T. Hoving from the GEOMAR Helmholtz Centre for Ocean Research Kiel, along with collaborators from the Monterey Bay Aquarium Research Institute and the University of South Florida made a striking observation. They saw a female squid carrying exceptionally large eggs — twice as large as those of other known deep-sea squids.

In March 2015, a team running remotely operated vehicles (ROVs) in the Gulf of California, encountered a female squid at a depth of 2566 meters. Even by itself, this encounter would be pretty exciting. But this squid, likely belonging to the family Gonatidae, was carrying 30-40 large eggs.

The eggs, embedded in a small external egg sheet, had an average diameter of 11.2 mm. This may seem small (it’s just over 1 cm, or less than half an inch), but it’s significantly larger than typical squid eggs. In fact, this discovery is so surprising it raises numerous questions about the reproductive strategies of deep-sea squids.

Big squids, big eggs

The deep sea is a vast, mysterious place. Broadly defined as the water column below 200 meters, it’s an inhospitable and a largely unexplored frontier teeming with poorly understood biodiversity. Large mollusks, particularly squids, are some of the most intriguing creatures you can encounter in the deep sea.

These squids, often reaching impressive sizes, are adapted to the dark, cold, and high-pressure conditions of the deep ocean. They often showcase fascinating biological traits such as bioluminescence, elongated limbs, and specialized reproductive strategies. Scientists have proposed that their large size may be an evolutionary adaptation, allowing them to go longer in between meals, cover greater distances, and slow down their metabolism.

However, most deep-sea cephalopods are poorly understood. In fact, we’ve rarely observed most of them alive in their natural habitats. So, their reproductive biology is poorly documented. This is what drives researchers to embark on deep-sea explorations using advanced technology that doesn’t disturb the wildlife.

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

Self-sacrificing maternal love

For most female squids, laying eggs and caring for them are the last things they will do.

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

So how do the larger eggs help? Researchers aren’t exactly sure, but it must have something to do with improving survival rates.

This strategy contrasts with the reproductive tactics of squids in shallower, more variable environments, where spawning many small eggs over multiple events helps ensure some offspring survive despite fluctuating conditions. The stable deep-sea conditions allow for extended development times, which could span years. For instance, egg development in the deep-sea octopod Graneledone boreopacifica sometimes takes four years at low temperatures. Similar extended brooding times might apply to the newly observed squid species, although this is still speculative.

The observed squid also had far fewer eggs than most of its apparent relatives — just 30 to 40. Most squids lay thousands of eggs at a time. Laying a lot of eggs is typically useful in environments with a lot of predation or not-a-lot of food. Basically, you increase the chance that at leas some of the offspring are surviving. The opposite approach, with fewer, larger eggs, may be benefficial in areas where a higher investment in fewer offspring makes sense, ie where you don’t have a lot of predation, but the environment is challenging.

We don’t even know what species it is

The problem with this type of exploration is that it only offers a glimpse of the deep-sea environment. Researchers aren’t even sure what kind of squid it is.

The female squid likely belonging to the family Gonatidae, but they did not identify it as a known species. The squid did not match any existing taxonomic species descriptions, indicating that it is likely an undescribed species of Gonatidae. The researchers also had no samples to conduct genetic analysis, leaving the exact species identification unresolved. This just goes to show how much we still have yet to discover about these species.

Ultimately, the discovery of large eggs in a deep-sea squid highlights the importance of continued exploration of the deep ocean. Each new finding not only adds to our understanding of marine life but showcases some of the remarkable ways in which organisms adapt to their environments. Future research will aim to uncover more about the life cycles, reproductive strategies, and ecological roles of deep-sea cephalopods.

Journal Reference: Henk‐Jan T. Hoving et al, Giant eggs in a deep‐sea squid, Ecology (2024). DOI: 10.1002/ecy.4319