Coral Thrive in Cold Water, Die in Warm

It is the first study ever to address how coral reefs react to a colder climate change. Many studies have been done about the effect of a warming climate change on coral reefs.
Those studies have shown that coral reefs eventually die in environments with increased heating.

“The reason why it’s important to look at that aspect is [because] when you do research on climate change, most areas on earth warm up but some areas cool down,” Deheyn said.

Each study lasted three weeks. Roth and Deheyn worked in the Scripps experimental aquarium. They placed coral in water kept at 5 degrees warmer and water kept at 5 degrees cooler than normal.

There were three conditions of water: warm at 26 degrees Celsius (normal temperature for corals), very warm at 31 degrees Celsius and cold at 21 degrees Celsius. The corals were kept in individual jars because the scientists wanted to ensure that if a coral’s stress response could be accurately isolated.

The researchers found that in the first week that the corals liked the warmer environment better.

“They were like, ‘Oh this is no big deal, you know I can deal with warmer temperature,’” Deheyn said. “But then after a week their health declined very, very rapidly and they bleached and eventually they were close to dying by three weeks.”

The warmer environment sped up the corals’ metabolism and enzymes. This situation was not sustainable because enzymes could not keep up with the sped-up conditions. The enzymes began to break down and the algae living in the corals left.

Corals have a symbiotic relationship with algae. Most of the energy the coral receive is from symbiosis. When a coral undergoes stress, the stress is transferred to the algae, often causing algae to leave the coral. “Bleaching” occurs when algae leave coral because the coral turns white. The colder environment was hard on the coral in the first week. The corals were not growing and their metabolisms were lower.
 
“We thought those would eventually die first,” Deheyn said. “But after a week they stabilized and they started to adapt and thrive again in colder conditions.” Deheyn and Roth do not know the exact cause for the corals surviving in colder temperatures but they have a few theories: They think the cold tolerance means that the coral enzymes and the source of the energy slows down the metabolism of the organism, whereas in the warmer temperatures the enzymes work too fast and create stress for the corals.
 
“The pure mechanism of why it happens — it’s species specific,” Deheyn said. “It’s something that is worth investigating, but is probably due to the limits of terminal tolerance from the enzymes that made the corals.”

Roth is now based at Lawrence Berkeley National Laboratory. Deheyn said that he will continue to study corals.

“I was inspired to look at the affect of other stressors on corals,” Deheyn said. “We now work, for example, on the effect of metals on corals which are perimeters that also are important for the coral reefs.”

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