Wing-Chi Poon

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ScienceShot: How Starfish Sweat

Dogs pant. Humans sweat. But how do starfish keep from overheating? At the hub of a sea creature's five arms (or more, in some species) is the central disk, which holds the animal's heart, stomach, and central nervous system. If this disk's temperature rises above 35°C (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 26°C to 42° C. About one-third of the starfish died when their central disk temperatures reached 35°C, the team reports online today 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 39°, 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 own heat-damaged arms, which are costly to regrow.

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