Rare footage captures giant jellyfish living under Arctic ice

Scientists spotted this huge jellyfish (<em>Chrysaora melanaster</em>) dragging a crustacean with one of its tentacles under the sea ice covering the Chukchi Sea off the north coast of Alaska. (Andrew Juhl and Craig Aumack)

Biologists who explore the Alaskan Arctic ecosystem aren't just interested in polar bears. Some are also captivated by the "gelatinous species" hidden below the ice.

Now, scientists have published rare footage of one of the Arctic's largest jellyfish drifting beneath the sea ice near Utqiaġvik, also known as Barrow, off the north coast of Alaska.

Such videos aren't easy to get. From May to June each year between 2011 and 2014, the team of researchers drove onto the frozen Chukchi Sea with snowmobiles, sometimes nearly 2 miles (3 kilometers) from shore, and drilled holes into the thick sea ice. They sent a camera-equipped underwater vehicle into the water to have a look at the seafloor. [See Amazing Images of Jellyfish Swarms]

The scientists captured footage of algae, crustaceans and several species of comb jellies (also know as ctenophores) under the ice. But the big surprise was finding adults of a species of jellyfish known as Chrysaora melanaster. The bell of this type of jellyfish can reach 24 inches (60 centimeters) across, with its two dozen or so tentacles extending up to nearly 10 feet (3 meters), according to the Census of Marine Life. The researchers counted 55 of these jellyfish, all of which appeared healthy and in their adult, or medusa, stage. They were often dragging their long tentacles along the seafloor, likely trying to pick up food —with some apparent success. At least one of the jellyfish was seen carrying an isopod, a type of crustacean.

The presence of adult jellyfish during the late spring and early summer suggests these C. melanaster medusas can survive the Arctic winter, according to the research published in the journal Marine Ecology Progress Series on Oct. 23. Like most jellyfish, this species was thought to live for only a few months. And scientists thought the species survived the winter only in the polyp stage of their life cycle. (Bottom-dwelling polyps settle on rocks or other surfaces and produce baby jellyfish in the spring.)

"Life under sea ice is like living in a refrigerator—everything slows down," study co-author Andy Juhl, a marine biologist at Columbia University's Lamont-Doherty Earth Observatory, told his department's blog. Juhl and his colleagues think that thick sea ice in winter helps protect the medusas from rough seas, while the low temperatures help slow their metabolism so they don't need much food to survive.

"We believe that the prevalence of jellyfish and ctenophores living through the winter is greater than generally appreciated," the researchers wrote.

The Arctic has been experiencing record-low levels of sea ice in recent years due to climate change. The authors of the new study noted that jellyfish populations could be more sensitive to these changes than scientists had thought.

"Understanding the implications of changing sea-ice conditions will become increasingly important as coastal Arctic seas become more open to transportation, commercial fishing, oil and gas exploration, and other forms of commercial exploitation," Juhl and his colleagues wrote.

Original article on Live Science.