In the ethereal blue glow of the water, a huge shape swept toward them. Around 30 feet long, with four billowing arms and a domed head, the creature was larger than the tourists’ personal submersible. This startling sight occurred hundreds of feet underwater off the coast of Antarctica’s Rongé Island.
When they returned to their Viking Expeditions cruise ship and showed photos to Daniel M. Moore, a marine biologist with Exeter University in the U.K., he knew they’d seen “something incredibly rare.”
As it turns out, these lucky travelers are among only a handful of people ever to lay eyes on the giant phantom jellyfish, or Stygiomedusa gigantea. Until that point, in January 2022, there had been only 126 recorded observations since the species was first described in 1910—including individuals caught in nets and footage captured by remotely operated underwater vehicles, or ROVs. Even scientists with the Monterey Bay Aquarium Research Institute, which has logged thousands of hours of submersible dives, have seen just nine.
Surprisingly, the first jellyfish sighting was not a one-off. Just a week later, in late January 2022, a different group of tourists also saw a phantom jellyfish, followed by one more, in mid-March. In the most recent tourist season, between October 2022 and January 2023, submersibles have spotted seven or eight more.
Part of the reason for the frequent encounters is that tourism expeditions in the Antarctic are increasingly offering personal submersibles to guests, says Moore, who is chief scientist for Viking Cruises, which runs the Antarctic expeditions.
Antarctic waters below 160 feet haven’t yet been well explored because they are so difficult and expensive to reach. Now, with private submersibles descending to around a thousand feet, you might be “the first human ever to see a particular patch of seabed,” he says. (Read more about the mesmerizing world of jellyfish.)
The 2022 encounters with giant phantom jellyfish are already changing what we know about this mystical deep-water species, Moore adds—particularly the breadth of its ocean habitat. Phantom jellyfish are usually found at nearly 22,000 feet, but these animals were swimming in waters of between 260 and 900 feet.
A deep-sea enigma
Scientists still know very little about these giant invertebrates, which dwell in the polar oceans' dark, cold midnight zone and are believed to use their undulating, ribbon-like arms to capture and prey on plankton and small fish.
One thing that's known for sure: It often has company. The phantom jellyfish has been observed with a small fish—called a pelagic brotula, or Thalassobathia pelagica—living alongside it. In this mutually beneficial relationship, the fish receives shelter and protection in return for keeping the jellyfish disease-free by eating any parasites that attach to it. (Read about a rare deep-sea jellyfish that resembles a plastic bag.)
As for why the large jellyfish are showing up in shallower Antarctic waters, Moore speculates they could be carried by currents, or perhaps come up from the depths to expose themselves to the sun to rid themselves of any additional parasites.
A win for science
Personal submersibles are free-roaming vehicles that hold a pilot and six guests. They’re outfitted with probes and sophisticated cameras, allowing guests to take photos and video.
Moore, who led a recent study about the research potential of private submersibles in the journal Polar Research, calls the phenomenon “extreme citizen science.”
Paris Stefanoudis, a marine biologist at the University of Oxford, adds a key benefit of submersibles is allowing people to “look at environments firsthand, rather than just viewing a screen,” as they would with an ROV. (Read about a pioneering ROV that could improve ocean exploration.)
But submersible research has an obvious drawback—the cost. Such cruise expeditions are priced at tens of thousands of dollars a person, making them available to a very small group of individuals, says Stefanoudis, who wasn’t involved in the research. While there are many pros, he says, “You have to face that fact: Not everyone can use [or afford] them.”
Yet Stefanoudis agrees submersibles could provide scientists more data about little-seen ocean creatures. In particular, he’s interested in learning more about the phantom jellyfish’s geographical distribution and how it lives within its environment.
Involving members of the public has benefits, too, since they become more aware of threatened ecosystems and inspired to protect them. All in all, he says, “it’s a win for science."