Eilat coral reefs are being 'starved' by high water temperatures

The reefs in Eilat displayed widespread bleaching, a phenomenon in which the symbiosis between coral and algae fails, typically due to high water temperatures.

By DR ASSAF ZELVONI NOVEMBER 6, 2024 10:56

Coral reef in Eilat (photo credit: NATURE AND PARKS AUTHORITY)

In August 2024, corals on Eilat's reefs began showing signs of bleaching due to a high increase in seawater temperatures. 

According to Dr. Assaf Zebuloni, an ecologist with the Nature and Parks Authority, the corals are experiencing severe starvation.

By mid-August, the reefs in Eilat displayed widespread bleaching—a phenomenon where symbiosis between coral and algae fails, typically due to high water temperatures. This breakdown forces algae, crucial for coral sustenance, to leave the coral tissues, rendering the corals vulnerable.

The corals depend on their relationship with algae as a primary energy source. Once the algae are expelled, the coral’s white skeleton becomes visible through its transparent tissue, creating the bleaching effect.

At the onset of bleaching, the coral remains alive but starves. If temperatures do not return to normal, the coral could die. Besides warming, other factors—such as infections and water quality issues—further weaken the corals’ resilience.

Coral reef in Eilat (credit: NATURE AND PARKS AUTHORITY)

Warmer temperatures

Historically, the corals of the Gulf of Eilat have exhibited a unique natural resilience to rising temperatures and bleaching. This resilience is attributed to a selection process that has occurred over thousands of years in the Bab al-Mandab Straits, where only heat-resistant coral genotypes enter the Red Sea. 

While the Gulf of Eilat has milder temperatures, its corals descended from these resilient genotypes.

Until 2024, Eilat's corals had largely resisted bleaching. This year, however, was exceptionally warm.

Data from the Eilat Bay National Monitoring Program indicate a peak seawater temperature of 31.9°C on August 4, with daily temperatures exceeding 30°C from July 12 to September 12. 

Over this period, the average maximum temperature was 30.4°C. Additionally, weak summer winds and stagnant air conditions prevented water mixing and evaporation, creating an unusually warm surface layer.

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On August 12, reports surfaced of Millepora dichotoma (fire coral) bleaching, and since then, over ten coral species and sea anemones have exhibited bleaching. Ongoing surveys are assessing the scope of this event and tracking coral recovery or mortality rates.

Challenges to Resilience

Although Eilat’s corals are highly resilient, this year’s extreme temperatures have pushed the reef system to a critical threshold. The 2024 summer heat combined with nutrient-rich discharge into the northern Gulf from desalination processes and aquaculture facilities poses an additional risk. 

The nitrogen discharge is at 26 tons annually, exceeding the recommended threshold of 22 tons. This nutrient enrichment, when combined with rising temperatures, significantly heightens the risk of severe bleaching events.

Another concern is the presence of pollutants in Eilat's coral reefs, including substances from commonly used medications, which may further harm the coral's resilience.