During high tide, sea stars are completely submerged in cool seawater, but at low tide, they reside on rocky shorelines in the hot sun. Somehow, sea stars survive the rapid changes in temperature that come with the tidal changes, and a recent study suggests how they do this: They use their bodies to soak up cool water during high tide to use later during low tide to keep them cool. This strategy has never been observed before in the animal kingdom.
Sylvain Pincebourde of Francois Rabelais University in Tours, France, and his team believed that it had something to do with fluid-filled cavities in the arms of sea stars. So he and his team simulated tidal patterns in aquariums with sea stars. Heat lamps controlled temperature, and some stars experienced hotter temperatures than others. The stars exposed to higher temperatures at low tide had higher body mass after the high tide that followed. Since the stars had not eaten, the increased mass could only have come from soaking up water.
“This reservoir of cool water keeps the sea star from overheating when the tide recedes again the next day, a process called ‘thermal inertia,’” Pincebourde said.
Coauthor of the study Brian Helmuth of the University of South Carolina at Columbia said, “It would be as if humans were able to look at a weather forecast, decide it was going to be hot tomorrow, and then in preparation suck up 15 or more pounds of water into our bodies.”