October 28, 2009

Starfish Species Survives In The Sunlight

Scientists have discovered that one species of starfish has a remarkable strategy to avoid overheating in the sun, BBC News reported.

Experts say the ochre starfish or sea star (Pisaster ochraceus) pumps itself up with cold seawater to lower its body temperature when exposed to the sun at low tide, something scientists say is equivalent to a person drinking seven liters of water before heading into the midday sun.

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

The starfish is mostly found in the intertidal zone along the Pacific North American coast, where they mainly feeds on mussels while underwater.

But during low tide they are exposed to the air and cannot move until being submerged again at high tide. The ochre starfish can suffer heat stress when exposed to the warm sun at low tide.

U.S. researchers, writing in the journal American Naturalist, have now revealed how the species manages this excess heat.

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

The team found that the weight of the sea stars increased during the days after exposure to high temperature at low tide, making them unable 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 said.

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

The team of researchers made their discovery by studying the starfish in an aquarium, and replicating tides and environmental conditions.

For the study, they employed heat lamps to adjust the aerial temperature and an infrared camera to measure body temperature. They then weighed the starfish to estimate the amount of body fluids. The amount of water the starfish were able to store in just a few days surprised the scientists.

Pincebourde said it was like if humans decided to suck up more than 15 pounds of cold water in the morning to prepare for the high temperatures at noon.

The team also noted the degree of control the starfish had, as the quantity of stored water allowed a decrease of almost 4°C in excess body temperature, which is enough to avoid reaching dangerous body temperatures.

But this novel strategy may have limitations in a rapidly changing world, Pincebourde warned.

"This discovery is quite important for us to formulate expectations on what could be the impact of climate change on the sea star," he said.

He explained that as oceans warm together with air temperature, the thermoregulatory mechanism used by the starfish would cease to work.

However, the efficiency of this thermoregulation strategy therefore might be annihilated by ocean warming, since the colder the sea water, the more the starfish is able to lower its body temperature.

"Sea stars will reach more frequently high aerial body temperatures, leading to higher mortality rates."


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