Thursday, December 24, 2015

Murky water might actually help bleached corals--how weird is that?

Okay, this is just weird--something we think is bad turns out to be good.

(Image: Bleached Seriatopora coral colonies in the Philippines. The shaded one at lower right has retained some pigmented algae and will survive, the central one in full sun has severely bleached and will die. Credit: Robert van Woesik/Florida Institute of Technology.)

We know that overwarm water can cause coral bleaching, and if it lasts a long time it can kill corals.

And we know that turbidity in the water can smother corals and block sunlight their symbiotic algae need to survive.

But here’s some research that turbidity can protect corals from warming—including some of the coral populations of the Northwestern Hawaiian Islands.

Researchers Chris Cacciapaglia and Robert van Woesik, of the Florida Institute of Technology, thought that sediment in the water might shade corals, and help protect them—the way a hat or an umbrella protects you from sunburn—by physically blocking solar radiation.

“We hypothesized that some turbid nearshore environments may act as climate-change refuges, shading corals from the harmful interaction between high sea-surface temperatures and high irradiance,” they write in an article in the journal Global Change Biolog.

The article is entitled : “Climate-change refugia: shading reef corals by turbidity.” 

While many have focused on the water temperature, the Florida scientists say it’s the combination of high temperature and the brightness of the sunlight—irradiance--that cause damage to corals.

They looked at similar reefs, where some were in clear water and nearby ones in cloudy water. And they found that the corals in mildly cloudy water survived better than those blasted by the full power of both heat and light.

“Protecting the turbid nearshore refuges identified in this study, particularly in the northwestern Hawaiian Islands, the northern Philippines, the Ryukyu Islands (Japan), eastern Vietnam, western and eastern Australia, New Caledonia, the northern Red Sea, and the Arabian Gulf, should become part of a judicious global strategy for reef-coral persistence under climate change,” they wrote.

It may seem counterintuitive to protect areas with cloudy water, but at least to some degree, that might protect some oft he corals, the authors write.

“We’ve identified refuges from climate change, where naturally turbid environments will reduce the temperature stress predicted for 2100,” Cacciapaglia said in a press release.

© Jan TenBruggencate 2015

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