In the midst of a frosty Arctic winter, marine biologist Andy Juhl led a team from Columbia University’s Earth Institute on snowmobiles out over the frozen Chukchi sea. There they drilled holes through the ice, several feet thick, and dropped a submersible down into the frigid environment and take a peek at what lies beneath.
As George Dvorsky reports for Gizmodo, what they found delighted them: a jellyfish.
Until now, scientists believed that the creatures spent the winter in polyp form—bulbous masses that cling to surfaces and release bell-shaped jellies in the Spring. But the translucent critter, Chrysaora melanaster, shows that the jellies can overwinter in the waters off the coast of northern Alaska—an environment previously believed to be too harsh for adult jellies to survive. The scientists described their find in a new study, published in the journal Marine Ecology.
C. melanaster, also known as the "northern sea nettle," is one of the Arctic's largest jellyfish. Their voluminous bells can grow up to a foot or more across and their tentacles and ruffle-like string of "lips" stretch behind them for nearly ten feet. The jellies thrive in the cold Arctic waters, but until this latest study, researchers had yet to find evidence that they could remain in this environment over the course of the harsh winters.
Though their presence might seem surprising, as the researchers write in their study, the sea ice might protect the jellyfish from turbulent storms while the cold would slow their metabolism, allowing them to survive on little food throughout the winter. According to the Census of Marine Life, Chrysaora melanaster jellies feed on large zooplankton, small fish, copepods, and even other jellies.
In the video, the creature can be seen dragging across the seafloor, which might not appear like a thriving environment in the peak of winter. But as the researchers note, the Arctic seas support a surprising amount of winter food, namely ice algae, which grow inside and along the bottom of sea ice and eventually sink to the bottom, providing a base for the food chain.
Even so, the researchers note that reduced food supplies don't stop these resourceful creatures, which can regrow their gonads once food availability increases. This means that even if food is short, these overwintering jellies will likely still be capable of reproduction come spring.
"Thus, overwintering could be an effective strategy for individuals with the potential to mature to consume the abundant zooplankton food available in spring and increase their sexual reproductive output," the researchers write.
Knowing that these creatures can survive the winter under sea ice will help scientists better understand jellyfish population dynamics, which greatly vary from year to year, Dvorsky writes. Some years there are hardly any, while other years they are so common that fishing nets are choked with them.
These swings in jellyfish populations don't just plague Alaska. One particularly dramatic bloom in the Mediterranean this summer prompted a researcher from Italy’s Institute of Sciences of Food Production, Antonella Leone, to try to get locals to eat them. She hopes to curb their numbers as warmer waters spur populations to grow “gelatinous generation after gelatinous generation,” Jason Horowitz reported for The New York Times earlier this year.
The latest study is not necessarily an indicator of changes in climate, but suggests that the northern sea nettle could be sensitive to future shifts in sea ice—just like the polar bears and walruses we commonly think of struggling to adapt to the changing Arctic.
As Juhl and his colleagues write, it’s especially important to understand these dynamics now, "as coastal Arctic seas become more open to transportation, commercial fishing, oil and gas exploration, and other forms of commercial exploitation." These ventures could affect not just the furry creatures roaming above the ice, but the gelatinous ones sliding along below.