Red Sea Corals Laugh Off Global Warming but Suffer in Cold Snaps

Climate change is causing extreme weather: The Red Sea coral is resilient to heat but ironically, it bleaches in the cold

Ruth Schuster
Ruth Schuster
A diver swimming above a coral reef in the Red Sea, offshore of the King Abdullah University of Science and Technology near the city of Jedda.
A diver swimming above a coral reef in the Red Sea, offshore of the King Abdullah University of Science and Technology near the city of Jedda.Credit: LUCAS JACKSON/REUTERS
Ruth Schuster
Ruth Schuster

Ironically, the Red Sea corals touted as the most likely to survive global warming turn out to have a problem with climate change, and it isn’t the heat. Up to a point, of course. It’s the cold.

Climate change is characterized by weather extremes, we are discovering by the day. “Global warming” also involves relatively extreme cold snaps. The corals in the northern Red Sea can survive extraordinarily hot water temperatures as much as 7 degrees (!) Celsius (12.6 degrees Fahrenheit) above their average range, Prof. Maoz Fine of Bar-Ilan University, Ramat Gan, tells Haaretz – temperatures at which other corals would roast.

Hence the hypothesis that the Red Sea corals will be the last ones standing, as it were, in this time of climate change. But if the water temperature drops a mere 1 degree below its winter average, it turns out the poor things bleach, Fine and Dr. Jessica Bellworthy write in Science Daily.

Bleaching means they lose the symbiotic algae on which they depend.

In fact, it turns out the Red Sea corals are surviving close to their tolerance of chill.

Fish swimming above a coral reef in the Red Sea, offshore of the King Abdullah University of Science and Technology near the city of Jedda.Credit: LUCAS JACKSON/REUTERS

This discovery, Fine explains, further validates their theory that the Red Sea corals underwent evolutionary adaptation to very hot water. Examination of the breadth of their thermal tolerance shows that Red Sea corals trend strongly to heat tolerance, at the expense of low temperature tolerance.

Why would that be? Because the Red Sea is like an all-but-closed saline lake, fed exclusively by warm surface water leaking through the Bab el-Mandeb strait.

A little bit colder now

Meanwhile, based on long-term planetary cycles, researchers at the King Abdullah University of Saudi Arabia predict in Geophysical Research Letters that the Red Sea region could enter a cooling phase, some decades into the future.

Why? Because of the Atlantic Multidecadal Oscillation, which among other things will cool the surface of the Red Sea, according to their models. Sounds lovely.

Fish swimming near a coral reef in the Red Sea off the coast of Eilat.Credit: TOM SHLESINGER / Reuters

The Earth is on the worst-case trajectory as greenhouse gas emissions relentlessly continue to climb, together with the hot air emitted by politicians. Some areas in the Middle East are already experiencing bouts of unsurvivable heat, decades earlier than had been expected.

But assuming their model is accurate – and that depends how good the data is, Fine points out (the GIGO principle) – how helpful could this be for us? And could this oscillation actually have enough of an effect to discombobulate the cold-sensitive Red Sea corals, under the scenario of climate change decades in our future?

Not at all, and no. Humankind may well have shown long-term planetary cycles who’s boss. The amplitude of the oscillation’s cooling will quite certainly get buried in the furnace of heat we are creating for ourselves.

In other words, there remains doubt about the Atlantic multidecadal oscillation model and its effect on the Red Sea region; there is zero doubt about climate change, Fine explains. Maybe the oscillation will mitigate it a bit, for a while.

In any case, even in the event of extreme weather causing the corals to shiver, they’ll get over it, Fine predicts.

Fish swimming amid the corals in the Red Sea. Credit: irisphoto1 / Shutterstock

It’s true that their toolbox is strongly oriented to high temperature, but first of all, the Gulf of Aqaba/Eilat is characterized by an extremely steep slope: cold water sinks to the bottom, while the corals live in shallow water, he explains.

Also, his lab’s research has shown that when these heat-resistant corals get cold and bleach, they don’t just roll over and die; they hang on and recover. Come the summer, they’re fine and dandy.

And if the summer is unusually hot even by the terms of the Red Sea area – as we said, these corals are resilient.

Corals elsewhere are facing double whammies of blisteringly cold winters and supercharged summers causing them to bleach twice yearly, which makes them vulnerable. Not the ones in Eilat. And their limit may be a vast seven degrees above the usual range, but climate change is heading that way and beyond.

While discussing corals, climate change and looming disaster, temperature isn’t the only danger climate change poses to coral. In Hawaii, extreme rainfall is creating a host of problems for the islands’ iconic reefs, as described in an article in Phys Org.

Fish swimming above a coral reef in the Red Sea, offshore of the King Abdullah University of Science and Technology near the city of Jedda.Credit: LUCAS JACKSON/REUTERS

One problem is that the rain is washing degraded land – thanks to deforestation, erosion et al – into the sea. The sediment both settles on the corals, which don’t appreciate it, and blocks sunlight when suspended in the water. Does coral need sunlight? The algae symbionts do… Also, the storms are washing sewage, fertilizer and other pollution into the sea. Human effluent is already killing off the state’s coral significantly, scientists say, a lot faster than the heat is.

Corals in the Gulf of Aqaba.Credit: Prof. Maoz Fine

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