[Science] In the Deep, Dark Sea, Corals Create Their Own Sunshine

[tao]

Echinophyllia sp., a deep water coral that produces fluorescent orange-red light. Credit E. Smith

 

Corals are pretty and colorful and fluorescent. They produce their vibrant colors because they don’t live alone, which is also what keeps them alive.

 

Over billions of years they’ve worked out a special arrangement with algae: Corals give them shelter and algae convert light into food for the corals. Corals do other things for the algae, too. Deep inside their tissue are little proteins that take the sun’s ultraviolet light and turn it into a glowing green sunscreen, shielding from the sun these corals that live just below the water’s surface.

 

The mouth region of the coral Lobophyllia hemprichii. Some corals that live well below the ocean’s surface produce light to drive photosynthesis for algae that live with them. Credit J. Wiedenmann

 

But deeper in the water, it’s dark and the little light that reaches that far down is only in the blue part of the spectrum. Somehow, there are corals that live up to hundreds of feet below the surface and also manage to glow burning hues of orange and red.

 

The reasons for this fluorescence have remained a mystery, until now: These deep-sea corals glow to get more sunlight, according to a study published on Wednesday in the journal Proceedings of the Royal Society B. Their proteins soak up the scarce light and shine it back out as red-orange light that penetrates deep inside their tissues where their microscopic roommates take up residence. This means there’s light for photosynthesis, and the algae creates energy and food for the coral.

 

“This is a strategy that some corals pursue to cope with the challenges of a low-light environment,” Prof. Joerg Wiedenmann, a biologist at the University of Southampton in Britain who led the study, wrote in an email. It’s quite an adaptation, with a brilliant byproduct.

 

A polyp of the coral Montastraea cavernosa. The proteins in some deep-sea corals soak up the scarce light and shine it back out as red-orange light. Credit J. Wiedenmann

 

The research could have implications for coral-reef conservation by highlighting how different species of coral adapt to various light conditions. For two decades scientists have considered the idea that deep-sea reefs might provide a safe haven for shallow-water corals during threatening times of extreme heat. The thought is that shallow coral larvae pulled down by currents could survive long enough to reproduce and send their offspring back near the surface when temperatures returned to normal.

 

But “the depth might not offer a convenient escape road,” said Dr. Wiedenmann. He said he worries that shallow-water corals may not be able to adapt to the little light down deep.

 

“We need to make sure that their homes in the shallows stay habitable,” he said.

 

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[Cereberus]

but it's sad that lots of the corals in the great barrier reef are being bleached

[tao]

12 hours ago, Cereberus said:

but it's sad that lots of the corals in the great barrier reef are being bleached

What is coral bleaching?

 

When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

 

Can coral survive a bleaching event? If the stress-caused bleaching is not severe, coral have been known to recover. If the algae loss is prolonged and the stress continues, coral eventually dies.

Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.

 

In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.

 

Not all bleaching events are due to warm water.

 

In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death. Water temperatures dropped 12.06 degrees Fahrenheit lower than the typical temperatures observed at this time of year. Researchers will evaluate if this cold-stress event will make corals more susceptible to disease in the same way that warmer waters impact corals.

 

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[Cereberus]

then what about acidification process?

http://www.teachoceanscience.net/teaching_resources/education_modules/coral_reefs_and_climate_change/how_does_climate_change_affect_coral_reefs/