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When scientists drilled a half-mile-long (900 meters) hole into an Antarctic ice shelf, they found something surprising: a rock covered with unknown animals on the seafloor below.
In fact, the scientists weren't looking for marine life at all; they were geologists planning to gather sediment samples from the ocean floor. They'd set up camp on the Filchner-Ronne Ice Shelf, a large body of floating ice in the southeastern Weddell Sea, where they spent many hours shoveling snow and using hot water to bore a narrow hole through the ice. With the hole complete, they lowered a camera with their sediment corer, to scope out the seafloor more than 1,000 feet (300 m) below the bottom of the shelf.
They hoped to hit mud, "but instead, they hit a rock. And that's incredibly bad luck for them," said Huw Griffiths, a marine biogeographer with the British Antarctic Survey. However, the team later showed their video footage to Griffiths, and though the rock blocked their path to the sediment, the camera picked up something Griffiths never expected to see: a community of sponges and other unknown filter feeders clinging to the stone.
"It's a place where, essentially, we didn't expect this kind of community to live at all," Griffiths said. Some of the creatures had squat, round bodies, while others had thin stalks that stretched into the surrounding water; parts of the rock were also coated in a thin layer of fuzz, which could possibly contain tiny, thread like organisms.
"This is showing us that life is more resilient, and more robust, than we ever could have expected, if it can put up with these conditions," said Griffiths, who, along with his colleagues, published a paper about the serendipitous discovery Feb. 15 in the journal Frontiers in Marine Science.
Other animals have been discovered beneath Antarctic ice shelves in the past, but those included mobile animals such as fish and arthropods, a group of invertebrates that includes crustaceans, Griffiths said. Besides the occasional jellyfish, which can get swept beneath the ice by ocean currents, the only animals seen in the frigid, pitch-black water were those that actively moved around to gather food, he said.
But stationary filter-feeding animals, like sponges and corals, remain fixed in one spot and sustain themselves on food that happens to float by. Tiny phytoplankton — microscopic marine algae — serve as a huge source of nutrients for entire marine ecosystems, including these filter feeders, and the phytoplankton rely on sunshine for photosynthesis.
In the context of ice shelves, the nearest source of sunshine lies in the open water atthe edge of the shelf; intuitively, you wouldn't expect sponges to grow far from that edge, because few phytoplankton would be likely to reach them.
But lo and behold, several species of stationary filter feeders showed up on this rock, located 160 miles (260 kilometers) from the edge of the Filchner-Ronne Ice Shelf. What's more, due to the pattern of ocean currents in the area, any phytoplankton that the animals could feed on would first be swept farther away and then loop back under the ice shelf. In other words, the food would "have to come the long way around to get to these animals," Griffiths said.
Following the ocean currents, the sponges are about 370 to 930 miles (600 to 1,500 km) away from the nearest sources of fresh phytoplankton, Griffiths said. Much of this available food might be eaten by other animals or else sink to the ocean floor, as some phytoplankton die along the way, he said. And yet, against all odds, the newfound sponges still have enough fuel to grow.
"For me, that's really exciting, because these animals must be getting enough food from somewhere," Griffiths said. This raises a multitude of questions about how much food the creatures need to survive, whether their metabolism slows or stops when food becomes scarce and whether they gather extra fuel in away we don't yet understand, he said.
So far,everything the scientists know about these creatures comes from less than aminute of video footage. Studying the animals further will present a huge challenge, since no research vessel can get close to them, Griffiths said."We're going to have to develop technologies and things that can go and do that for us on their own," he said.
These tools might include miniature underwater vehicles that can be operated remotely or run autonomously; the vehicles would have to fit through narrow boreholes, hesaid. The robots could gather sediment and water samples that scientists could then examine for nutrients and DNA. The robots could also collect tiny samples of the sponges themselves; however, given that the ecosystem may be rare, scientists will have to figure out how to do so without disrupting the surrounding environment, Griffiths noted.
That raisesan other huge question: How many other rocks are teeming with undiscovered life beneath the Antarctic ice? In total, ice shelves cover about 580,000 square miles (1.5 million square km) — an area about twice the size of Texas — of the Antarctic continental shelf, according to a statement from Frontiers in Marine Science. But in terms of the seafloor beneath, scientists have photographed only the equivalent of one tennis court, Griffiths said.
Having barely glimpsed this mysterious ecosystem, scientists can't yet fully understand how threats such as climate change might impact the unique species living there, or how losing any of these species might affect the overall environment,Griffiths said.
"Two ice shelves collapsed in Antarctica in my lifetime. How many unique species... have we already lost, without even knowing we'd lost them?" Griffiths said, referring to the Wilkins and Larsen ice shelves. "Although this ice shelf we're studying is a lot more stable than those that collapsed, it's still going to be vulnerable to climate change."
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