Astonishingly, the oceans have absorbed thus far 90% of the excess heat generated by human-caused global warming, according to the Special Report on the Ocean and Cryosphere in a Changing Climate by the Intergovernmental Panel on Climate Change. And even if emissions are drastically reduced, the oceans will continue to warm at an alarming rate for decades. This is because human-produced carbon dioxide emitted into the atmosphere raises the water temperature and acidity. This change in environmental conditions stresses coral polyps and causes them to lose photosynthesizing zooxanthellae algae that live in the polyps’ tissues. The symbiotic relationship between polyps and algae “provides the coral with a substantial ecological advantage in generally nutrient-poor tropical oceans” [1].

And yet, despite sea temperatures rising faster in the Gulf of Eilat/Aqaba than the global average rate, the coral reef of the northernmost point of the Red Sea exhibit remarkable resistance and seems immune to the effects of global warming.

A significant natural selection event during the last ice age is one of the reasons for the northern Red Sea coral’s resilience. When glaciers retreated, reefs moved in to recolonize the southern part of the sea through a relatively narrow Bab el Mandeb strait and the Gulf of Aden and only those that could withstand the heat matured and migrated north. All these corals evolutionarily selected for heat resistance live now well below their thermal threshold, making the Gulf of Aqaba a refuge for robust corals.

The research conducted in Eilat suggests that while resilience ranged between the northernmost Red Sea corals tested, some could easily tolerate and thrive with an increase of 4-5 degrees Celsius above the current summer maximum. And in extreme cases, even up to 7 degrees Celsius.

Coral reefs in other parts of the world do not have the same biological capacity to endure, a 1-2C increase above the maximum summer temperature would typically induce coral mass bleaching event – breakdown of the nutritional photo-symbiosis with intracellular algae.

What’s particularly interesting with Red Sea coral is that their symbiotic algae, in some instances, have doubled the amount of oxygen produced and increased primary productivity by 51% with the increased sea temperature. That means that these corals show resilience and appear to do better in warmer waters.

At the current pace of global warming, we’re on track to increase ocean surface temperatures by 2-3C or more by the end of the century, putting most of the world’s reefs at immediate risk. So scientists from the I.U.I. in Eilat are trying to understand the biological capacity of the northernmost Red Sea corals to live at higher temperatures, hoping this knowledge could help reefs elsewhere in the world.

Although the coral reef in Eilat is perhaps capable of withstanding climate change, it is also under threat from many other anthropogenic factors – large-scale development, over-tourism, boat traffic, fish farming, waste runoffs into the sea and light pollution.

Even though climate change and rising ocean temperatures are global issues, our individual actions can make a difference for our local marine ecosystems. In 2018, Hawaii, for example, banned the use of chemical sunscreens thought to endanger coral health. Likewise, people everywhere can reduce their use of single-use plastics, which degrade into micro-particles that make their way into the sea, where stressed corals can consume them.

Reef death carries severe consequences for wildlife and the livelihoods of millions of people who fish, work in tourism, live on coral-covered islands, or rely on reefs to protect them from coastal erosion.

There’s a glimmer of hope that this surviving coral reef could be used as a blueprint for an entirely new climate-resilient ecosystem.


[1] – Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification
Thomas Krueger, Noa Horwitz, Julia Bodin, Maria-Evangelia Giovani, Stéphane Escrig, Anders Meibom and Maoz Fine
https://royalsocietypublishing.org/doi/full/10.1098/rsos.170038

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