Climate change

Retreating Antarctic Ice 

Fuels Surprising Glass 

Sponge Invasion

Wired,

11 July, 2013

In the frigid, inky ocean depths beneath permanent ice shelves, life tends to move pretty slowly. But a recent expedition to the seafloor under a newly thawed Antarctic ice sheet has revealed an unexpected invertebrate invasion. Some of Earth’s strangest species, a group of ghostly pale sponges made of glass, have set up shop there in a hurry, upending much of what scientists know about these exotic creatures.

Thanks to changes in this ecosystem brought on by a warming climate, these gardens of glass sponges have sprouted up in only a few years, a veritable population explosion for species once thought to take decades or centuries to spread. It suggests that glass sponges could find themselves squarely on the winner’s podium when it comes to climate change.

In 2011, a team led by researchers from the Alfred Wegener Institute for Polar and Marine Research completed a new census of glass sponge growth on the seafloor underneath the Larsen Ice Shelf in Antarctica’s Weddell Sea, following up on a similar survey done in 2007. Their surprising results were published today in Current Biology.

Glass sponges like those found in the western Weddell Sea are not well studied because they live in deep water beneath polar ice sheets. Ironically, surveys in this area are only possible today because two-thirds of the Larsen Ice Shelf no longer exists, disintegrating without warning in 1995 and 2002.

Navigating the German research icebreaking vessel Polarstern through the icy waters there, the team was able to carefully pilot their remotely operated vehicle (ROV) along the same path studied in 2007. Their cameras got an unprecedented view of the same seafloor at two different points in tim

To their surprise, large numbers of glass sponges had taken up residence on the seafloor in just a few years. Occasional observations had suggested that glass sponges are capable of short growth spurts, but the consensus held that these species multiplied on the timescales of redwoods, not weeds. This new research provides the strongest evidence yet that glass sponges are capable of rapidly reproducing and colonizing large areas of seafloor in short amounts of time, although the reasons why remain uncertain.

Claudio Richter, an author of the new study, has one theory. He thinks the thawing of the Larsen ice shelves has created a veritable feast in this extreme environment. The newly exposed ocean exposed a fresh habitat for sun-loving phytoplankton near the surface. Although these blooms are small and sporadic compared to those seen elsewhere, Richter explains that a rain of algae and phytoplankton can reach all the way down to the seabed 300 meters below the surface, where glass sponges are bathed in complete darkness. More plankton alone is not enough to explain the accelerated growth, though. These deep water residents are picky eaters.

Marine ecologist Paul Dayton, who was not involved in the study, spent decades studying glass sponges at the Scripps Institute of Oceanography. He says they depend primarily on only the smallest species of plankton and aquatic microbes for food. With the ice shelf gone, Dayton speculates that bacteria were swept up from the ocean floor, providing a boost in the specific prey the sponges required.

Glass sponges are one of the oldest examples of complex life that survive today. These long-living, cold-water invertebrates trace their evolutionary history back more than 550 million years, predating the so-called Cambrian explosion when most of today’s animal lineages originated. Today, most of the complex species alive in pre-Cambrian times exist only as fossils, yet somehow this family of ancient ocean-dwellers lives on in the flesh. The oxymoronic glass sponge gets its name from the surprising material they use to build their skeletons. Instead of the calcium-based structures that support organisms like coral and vertebrates, glass sponges extract silicon from sea water to erect elegant glass lattices, able to withstand the crushing pressures present hundreds of meters below the surface.