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Bourton 2009

Created By: Sarah Butler
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One starfish has a remarkable strategy to avoid overheating in the sun, scientists have discovered.

The starfish [9] pumps itself up with cold seawater to lower its body temperature when exposed to the sun at low tide.

It is equivalent to a person drinking seven litres of water before heading into the midday sun, scientists say.

However, global climate change may drastically interfere with this vital mechanism by increasing sea temperatures, the researchers warn.

The ochre starfish or sea star (Pisaster ochraceus) is found in the intertidal zone along the Pacific North American coast. 
 It mainly feeds on mussels while underwater. During low tide it is exposed to the air and cannot move until it is submerged again at high tide.

When exposed to the warm sun at low tide, the ochre starfish can suffer heat stress.

Now scientists based in California, US reveal how it manages this excess heat in the journal American Naturalist.

Pump up the volume

"We have discovered a quite novel thermoregulation strategy in the animal kingdom," says Dr Sylvain Pincebourde, formerly of the University of South Carolina, Columbia but now at the François Rabelais University in Tours, France.

"We found that the weight of the sea stars increased during the days after exposure to high temperature at low tide."

"The sea stars were not allowed to feed. So this increase can be explained only by an increase in seawater uptake. When sucking up water, the body mass of a sea star increases," he says.

The increase in body mass allows the starfish to be buffered against environmental temperature changes in the subsequent low tide.

"Because its body mass is now higher, body temperature increases more slowly," Dr Pincebourde explains.

"The thermoregulatory strategy we have revealed in our study indicates that the sea star is well adapted to such a variable environment."
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