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Mysterious glass sponge communities thrive with melting of Antarctic ice shelf

By Catholic Online (NEWS CONSORTIUM)
July 12th, 2013
Catholic Online (www.catholic.org)

One invertebrate community on the ocean floor seems to be benefiting from climate change and the melting of glacial shelves. The mysterious, beautiful glass sponge has taken root on the ocean floor in the wake of the disintegration of the Larsen A ice shelf in Antarctica disintegrated 20 years ago. Glass sponges were originally believed to have taken long periods to take root, but with the sudden influx of entire communities being discovered, the life form may be one the few to benefit from climate change.

LOS ANGELES, CA (Catholic Online) - Populations of glass sponges, or Hexactinellida have tripled between 2007 and 2011, allowing them to completely take over the seafloor.

"The shelf broke off, split into tiny pieces and was gone in a couple of weeks," lead researcher Claudio Richter, a biologist at the Alfred Wegener Institute in Germany, says. "Now the benthos, which we believed would take decades or centuries to move and change, is transforming quickly in just a matter of years."

Scientists originally believed that seafloor communities were very poor as animals could only get food when strong currents brought it in, Richter says. The biologist likens the thick ice shelf to a large balcony attached to a house or building, blocking the sun, which gives organisms at the base of the marine food chain energy.

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"If you have a balcony that extends really far out, you would have a difficult time growing vegetables beneath it," Richter says.

Warming waters in Antarctica's Weddell Sea in 1995 caused the Larsen A ice shelf to give way. Sunlight bathed the surface waters afterwards, allowing phytoplankton and ice algae, fed by photosynthesis, to grow. This food was then passed down to the seafloor, helping sponges, sea squirts and other animals thrive.

Scientists in 2007 discovered communities of deep-sea invertebrates that are normally found at depths of 3,300 feet or more. Scientists also saw occasional small glass sponges and large populations of fast-growing sea squirts, which dominated the seafloor.

Returning to the area in 2011, Richter and his colleagues and maneuvered their ROV over the original area surveyed in 2007. The seafloor changed dramatically in just four years: Predatory species such as sea stars were scarce in both surveys, but glass sponges had taken over the seafloor. However, the pioneering species of sea squirts had all but disappeared.

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"The sponges are now three times more numerous and two times as big as before," Richter said. What's even more astounding, he adds, is that satellite images show the area was only productive (in terms of phytoplankton and algae growth) for two out of the four years between the two surveys.

Previous research previously suggested that hexactinellid species live long, slow lives. Other research suggests the animals have a very slow metabolism, allowing them to live for 10,000 years or more. Recent findings, taken together with other work, suggest that Antarctic glass sponges that have endured arrested growth for decades can undergo booming periods that allow them to quickly colonize new areas.

"It's a complex issue," Richter said. "It's difficult to predict the evolution of how things develop, but for now, the sponges seem to be gaining pace."

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