How do starfish keep cool when mercury rises? They shift heat to arms

Science Now

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

At the hub of the sea creatures’ arms is the central disk, which holds the animals’ heart, stomach and central nervous system.

If this disk’s temperature rises above 35 degrees Celsius, such as at low tide, when the animal may be isolated from cool ocean water, the starfish dies.

To figure out how starfish stay cool, scientists collected 70 ochre starfish from the California coast and placed them under heat lamps to simulate potentially lethal low-tide heat exposure at temperatures ranging from 26 to 42 degrees.

About one-third of the starfish died when their central disk temperatures reached 35 degrees, the team reported online in the Journal of Experimental Biology. Researchers found that the arms of surviving starfish were a few degrees warmer than the disk, suggesting the animals shunted heat into their extremities.

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