giant phantom jelly
© ROV SuBastian / Schmidt Ocean InstituteA giant phantom jelly documented by a recent deep-sea expedition.
During an expedition off the coast of Argentina, scientists saw something unexpected. In December, they spied a rare jellyfish roughly the length of a school bus, known as the giant phantom jelly, wading through Atlantic waters at about 820 feet below the surface.

"There was a mixture of excitement and disbelief," says María Emilia Bravo, a marine biologist at the University of Buenos Aires in Argentina and the expedition's chief scientist, to Alexa Robles-Gil at the New York Times. "Its ethereal and delicate presence in such an extreme environment was deeply surprising."

The researchers stumbled upon the massive jellyfish while using a remotely operated vehicle (ROV) called SuBastian on an expedition spanning Argentina's entire coast. Unlike some jellyfish, giant phantom jellies lack stinging tentacles. Instead, they use ribbon-like arms to grab prey, typically plankton or small fish, and pull them into their mouths.

The gargantuan creatures can reach lengths of 33 feet and have bells more than 3 feet wide. But despite their massive size, the elusive creatures have been spotted only about 120 times since the first specimen was collected in 1899. That's because they prefer to lurk in the "midnight zone," a part of the ocean ranging from 3,300 to 13,100 feet deep, that is shrouded in complete darkness.


Thanks to ROVs, scientists are finally getting a good look at the animals. "Up until recently, nobody was able to actually see it in its natural habitat and in its full glory," says Steve Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute who was not involved in the expedition, to the Times. Scientists at the institute have previously spotted the rare jellies off the California coast.

The main goal of the Argentinian voyage, operated by the Schmidt Ocean Institute, was to locate cold seeps. These are areas of the ocean floor where chemicals such as methane and hydrogen sulfide escape from cracks and serve as energy for microbes, forming the foundation of the marine food web. While operating the ROV from a ship, the researchers found one active seep measuring just under half a square mile, per a statement.

The team also uncovered a surprising amount of biodiversity. They discovered the largest known Bathelia candida coral reef, which, at 0.15 square miles, is almost the size of Vatican City. It was located about 370 miles farther south than its known range.

Additionally, the researchers spotted a whale carcass on the seafloor about 12,800 feet below the surface, marking Argentina's first deep-water whale fall. These remains can create complex temporary ecosystems that provide food and shelter for deep-sea animals and other organisms.
Did you know? How whale falls help other creatures

Different marine communities benefit from the various stages of a whale carcass' degradation. Scavenger species quickly pick off soft tissue in just a few months. Organic debris adds to the sediments for a year or more. And the skeleton can provide structures and nutrients for invertebrates for years to decades.
What's more, the team documented 28 potential new species, including worms, sea urchins, corals, sea snails and sea anemones.

"We were not expecting to see this level of biodiversity in the Argentine deep sea and are so excited to see it teeming with life," Bravo says in the statement. "Seeing all the biodiversity, ecosystem functions and connectivity unfolding together was incredible. We opened a window into our country's biodiversity only to find there are so many more windows left to be opened."