Corals inflate to escape the sand

8 February 2012 Last updated at 03:38 By Victoria Gill Science reporter, BBC Nature

Footage captured over 20 hours shows the coral inflating and deflating to throw off sand

Coral might appear solid and inanimate, but surprising new footage of a mushroom coral inflating itself to escape a sandy burial has brought the organism to life.

A scientist from the University of Queensland used timelapse photography to capture the footage.

It was already known that the species could release itself from the sandy seabed, but it was not clear how.

Since corals move so slowly, time-lapse imagery was used to find out.

Dr Pim Bongaerts captured the footage and published his findings in the journal Coral Reef.

As sandy sediments shift on the seabed, corals need to breathe and prevent themselves from being smothered.

"Sedimentation presents a major threat for corals, as they can become covered in a layer of sand from which they are unable to escape," explained Dr Bongaerts.

To find out how mushroom corals - a particularly mobile family of corals - did this, the researcher brought specimens into the lab and put them in aquaria in order to film the process.

"I covered the corals in sediment and, from that moment on, started photographing them every 10 seconds for 20 hours," Dr Bongaerts said.

Unlike many of the more familiar branching and "staghorn-type" corals, mushroom corals have a relatively thick layer of fleshy tissue on top of their tough calcium carbonate skeleton.

Dr Bongaerts explained: "Many of them live on the sand bed and have quite a unique lifestyle.

"Most corals are attached to the limestone substrate that makes up the reef, but mushroom corals can actively move around and find themselves better habitats."

Inflate and deflate

To move around, the corals "inflate and deflate" parts of their body. And, as the footage that Dr Bongaerts captured showed, they use a similar technique to free themselves from a covering of sand.

"The corals inflate and deflate their entire body in a series of rhythmic pulses," said Dr Bongaerts, "which allows them to effectively shed the sediment in a matter of hours.

"It's so crazy to see; it looks like another type of creature entirely."

He says that the idea of using time-lapse came from watching natural history documentaries.

"People often don't have the concept that corals are animals," he said. "But this really brings them to life."

"It's surprising that they're capable of such controlled movements."

Source: http://www.bbc.co.uk/nature/16843053

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