Hitting the limits of Israel’s coral reef resilience?

Nature has a way of healing itself, but have we reached the limit of coral reef resilience in the Red Sea?

The stunning coral reefs just off the coast of Eilat, Israel's southernmost city, have been under threat for many years due to pollution and other environmental factors. However, now extensive signs of “bleaching” have appeared after an unusually hot summer, from which the corals may never recover, according to ecologist Dr. Assaf Zebuloni of the Israel Nature and Parks Authority.

Coral bleaching is primarily caused by high sea temperatures and results in the breakdown of algae, which leaves coral tissue vulnerable and at risk of dying completely. The symbiosis between coral and algae breaks down under excessive heat, a catastrophic event for the coral, as algae serve as a vital source of energy and protection.

When the algae disappear, only the coral's white skeleton remains, visible through its transparent tissue, which is why the phenomenon is described as “bleaching.” Without the algae, the coral begins to starve and will eventually die unless temperatures return to cooler levels.

Technically speaking, Coral Guardian explained that when stressed by poor water quality and too much heat, “coral will no longer recognize the zooxanthella as its symbiote. In this case, the symbiosis between corals and their zooxanthellae stops, leading to the loss of these micro-algae and a rapid bleaching of the coral host.” 

Although the Red Sea is surprisingly cool given the scorching heat in Eilat, this summer it was even warmer than usual. The Eilat Bay National Monitoring Program showed that the seawater temperature reached 31.9°C on Aug. 4 and that it hadn’t fallen below 30°C from July 12 to Sept. 12.

A lack of air movement also prevented evaporation and water mixing which resulted in an unusually warm surface layer. Zebuloni warned in mid-August that coral reefs in Eilat were displaying widespread bleaching. 

In addition to the hot summer temperatures, the Red Sea has also been subject to pollution from desalination processes and local aquaculture facilities. Currently, 26 tons of nitrogen discharge enter the Red Sea each year from these plants, compared to the recommended maximum of 22 tons. 

Damage to coral reefs is often a result of compounded stressors, such as the type of pollution caused by industrial processes, common medications entering the water, overfishing and rising temperatures.

The coral reefs currently under the greatest threat are found in Australia, Indonesia, the Pacific Ocean, Hawaii and the Caribbean according to earth.org, but bleaching has recently been recorded in over ten coral species and sea anemones in the Red Sea, including the Millepora dichotoma (fire coral). The situation is being carefully monitored.

Nature’s ability to adapt and survive is remarkable, and we have seen unusually resilient types of coral entering the Gulf of Eilat.

A report from The Jerusalem Post attributes the Red Sea coral's unique ability to withstand rising temperatures and bleaching to a "selection process in the Bab al-Mandab Strait" that has occurred over millennia, allowing only heat-resistant coral genotypes to enter the sea. However, even these hardy corals are now struggling to cope with the increasing environmental stresses.

Experts from Coral Guardian warn that about 90% of the world’s coral reefs could disappear by 2050, and that over 70% are directly and immediately threatened by local and global pressures.