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How do starfish keep their cool?

To survive excessively warm water, some starfish seem to transfer heat from their core into their arms. (ISTOCKPHOTO)
How starfish keep cool in the heat

Dogs pant. Humans sweat. But how do starfish keep from overheating?

At the hub of a sea creature’s five (or more) arms is the central disk, which holds the animal’s heart, stomach and central nervous system. If this disk’s temperature rises above 95 degrees (such as at low tide, when the animal may be isolated from cool ocean water), the starfish dies.

To figure out how the animal stays cool, scientists collected 70 ochre starfish (Pisaster ochraceus) from the California coast and placed them under heat lamps to simulate potentially lethal low-tide heat exposure at temperatures ranging from 79 to 108 degrees. About one-third of the starfish died when their central disk temperatures reached 95 degrees, the team reports online in the Journal of Experimental Biology.

Researchers found that the arms of surviving starfish were a few degrees warmer than the disk, as warm as 102 degrees, suggesting that the animals shunted heat into their extremities.

The strategy is not without a cost, however. In the days following the experiment, 16 of the surviving starfish severed their heat-damaged arms, which are costly to regrow.

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