A study reveals a seafloor once covered by ice supporting a booming population… (Current Biology )
“Speedy” might sound like an odd adjective to describe a sponge, but researchers have discovered a fast-growing community of marine sponges off the eastern coast of the Antarctic Peninsula. Their findings, published Thursday in the journal Current Biology, challenge the hypothesis that Antarctic life responds slowly to climate change.
Severe cold and scarce food in the Antarctic led many scientists to believe that its inhabitants responded to climate change at a glacial pace, said Laura Fillinger, a biologist at the Alfred Wegener Institute in Bremerhaven, Germany, and the study’s lead author. But the collapse of a giant ice shelf — one of many in the area in recent decades, attributed to rapid regional warming — has revealed a seafloor supporting a booming population of glass sponges.
Despite a patchy food supply and water temperatures measuring a frigid 2 degrees Celsius, the creatures’ size and abundance doubled — and their numbers tripled — in four years, the authors wrote.
"This is much faster than any one of us would have thought possible,” Fillinger said.
Glass sponges are vase-shaped organisms that can grow up to 6 feet in size. True to their name, they’re made of a mineral component of glass called silica, “reminiscent of glass padding or mineral wool,” said Alfred Wegener Institute marine biologist and study coauthor Claudio Richter.
So far, scientists have thought that glass sponges grew slowly and lived a long time – 10,000 years, according to some estimates, Fillinger said. But her team’s findings have cast doubt on whether these filter feeders “are really that sluggish and old.”
The glass sponge explosion was due partly to the collapse of the Larsen A ice shelf in 1995, after a storm. The breakup of the shelf, which took more than 10 years, affected an area of more than 770 square miles.
In 2007, the team visited the site and used an underwater robot equipped with a video camera to investigate how the ice shelf collapse had affected life on the seafloor. They surveyed the site again in 2011 to see what had changed. (View video of the glass sponges here.)
The researchers were surprised by the sponges’ explosive growth after four years, Fillinger said.
Exactly why these glass sponges enjoyed such a boom is still uncertain, although the researchers think that after Larsen A collapsed, areas of the seabed that were once shrouded in darkness then saw sunlight for part of the year, supporting a seasonal bloom of phytoplankton, the bottom of the marine food chain, though blooms only occurred in two of the four years.
These findings offer a more dynamic picture of seafloor communities, even under extreme Antarctic conditions, Fillinger said. Only four years before, sea squirts had dominated the area. The study results also suggest that these sponges “may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats,” the authors wrote.
As glass sponges fill the remaining seafloor space, a diverse, steady-state “climax community” could form, Fillinger added, although it may happen within years or decades, rather than centuries, as previously thought.
The authors write that “glass sponges may find themselves on the winners’ side of climate change” if ice shelf disintegration continues, but they can’t say for sure. Predicting climate change’s effects on Antarctic life is difficult because of the complexity of species interactions and their effects, Fillinger said.
On the one hand, climate change might have a positive effect — opening up space once covered by ice shelves could, for example, enhance phytoplankton growth and the runoff of silicon, which glass sponges use to build their skeletons.
“But there are many unknowns: how may sponge predators, competitors and/or pathogens react?” Fillinger said. Although the team saw hardly any of the snails and starfish that prey on glass sponges, that doesn’t rule out the possibility that these predators will eventually follow suit.
“Could these indirect negative effects outweigh the positive effects? With so many unknowns, we can only guess,” Fillinger said.
The team plans to check on the site again in a few years. They’re also planning to use tools they’ve developed for their underwater robot to learn more about glass sponges, studying, for example, their diet and how they’re able to survive the food-scarce Antarctic winter.
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