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Glass sponges take advantage of clear 'skies'

Quick adaptation In the freezing waters around Antarctica, pale sponges made of glass have spread rapidly across the seafloor as surface ice disappeared, German and Swedish researchers report.

Glass sponges are a group of long-lived, cup-shaped animals with skeletons made of silica, a major component of glass.

They once dominated the sea floor, but today the only place they are found in large numbers is in the Antarctic, explains Professor Claudio Richter, a marine biologist from the Germany's Alfred Wegener Institute for Polar and Marine Research.

"The sponges are large and vase-shaped and much of their bodies is made up of glass," says Richter, who co-authored a report on the sponges in the latest issue of the journal Current Biology.

"Not solid glass, but rather glass of a structure reminiscent of glass padding or mineral wool."

In the Antarctic, the sponges live in water that is below freezing (0°C), where for most of the year there is too little light to sustain the production of phytoplankton which forms the basis of the Antarctic food web.

Richter and his colleagues have been studying these creatures in the ocean that was once covered by the Larsen Ice Shelf, a thick floating ice platform that extended along part of the east coast of the Antarctic Peninsula.

"The permanent cover of the Larsen ice shelf severely limited life on the seafloor to an impoverished fauna reminiscent of the deep sea," says Richter.

However in recent decades, regional warming along the Antarctic Peninsula has caused the Larsen shelf to disintegrate, allowing seasonal blooms of the plankton to feed the wider food-chain.

Considering how cold the water is in this region, and the relative scarcity of food, the researchers had expected marine life to respond slowly to these environmental changes, Richter explains.

But after studying glass sponges in this area in 2007 and again in 2011 using a remotely operated underwater vehicle, researchers unexpectedly found that their abundance had increased dramatically.

"To our surprise, the sponge doubled their biomass and tripled their densities in only four years. This suggests that glass sponges are very efficient in using the scarce resources and can reproduce very fast."

Although there are many questions still to answer about these enigmatic organisms, the results are providing clues about how living ecosystems respond to environmental changes, Richter says. His team plans to keep going back to this polar site, to see what might happen next.

"We know now that not only the abiotic environment can change dramatically, [but] also the biota are changing, and they are changing fast."

"Whether or not they can keep pace with the abiotic changes is difficult to predict," he adds. "This is why it is important to follow these changes over time. This is an international effort, to which Australia is also contributing."