International study led by researchers from the Hebrew University reveals that Eilat corals survived four years of heat waves, including 30 DHW in the summer of 2024 – the highest in the world; spot bleaching observed for the first time in shallow waters
New research reveals that corals in the Gulf of Aqaba have withstood four consecutive and intensifying marine heatwaves, including the world’s most extreme event in 2024, without suffering mass bleaching – a resilience unmatched elsewhere. This is important because coral reefs around the world are collapsing under rising ocean temperatures, threatening ecosystems and human livelihoods. The Gulf of Aqaba may represent one of the Earth’s last natural refuges for reef survival, offering a crucial model for understanding resilience and underscoring the urgency to protect this unique ecosystem before it reaches its limits. New research reveals the resilience of Red Sea corals in the face of intensifying climate threats. This is according to a new study published in the scientific journal Science of the Total Environment .
While mass bleaching and even widespread coral mortality have been recorded in many parts of the world, in the Gulf of Eilat the corals examined remained relatively stable. The researchers, Naama-Rose Kochman and Maoz Fine, monitored colonies of five coral species throughout this period and found that the corals maintained their metabolic balance and the energy reserves they needed.
Unusual data in summer 2024
This summer, record temperatures of 32.6 degrees Celsius were measured – 3.4 degrees higher than the multi-year average. The heat wave lasted for 113 consecutive days, and the cumulative index called DHW – Degree Heating Weeks (cumulative heating weeks), 30 points were recorded. For comparison, values of 8 DHW are already considered in most areas as the limit beyond which mass bleaching and mortality occur. In the Gulf of Eilat, corals remained stable, an exceptional figure on a global scale.
Among the species examined, corals of the type Porites demonstrated the highest stability, reinforcing their status as a species of central importance for future reef restoration. Stylophora pistillata and-Pocillopora damicornis showed different adaptations but they also preserved their energy reserves. In contrast, Cyphastrea They demonstrated relative sensitivity, with a more than 50% decrease in the density of associated algae, although they recovered in the following months.
Alongside the encouraging findings, for the first time, spot bleaching was observed on the shallow reefs at a depth of less than five meters. The explanation for this lies in the combination of extreme heat, extremely strong radiation, and weak winds that reduced water mixing. This phenomenon is a warning sign that even this unique "thermal shelter" may reach the limits of its endurance.
Global significance
While about 44% of the world's coral species are considered endangered due to global warming, the study results illustrate the value of the Gulf of Eilat as a unique genetic reservoir that may aid in future reef restoration. However, the researchers emphasize that maintaining local conditions free from pollution and other pressures is critical, otherwise this comparative advantage will also be eroded.
Prof. Payne added: “These results highlight both the resilience and fragility of coral ecosystems. They highlight the urgent need In regional conservation policy To protect what may be the last thriving coral reef in the world."
Coral reefs are biodiversity hotspots that support millions of livelihoods, from fishing to coastal protection. However, marine heatwaves – prolonged periods of unusually warm sea surface temperatures – are now one of the leading causes of coral mortality worldwide.
The resilience of the Gulf of Aqaba corals offers a rare glimmer of hope. Scientists stress, however, that without rapid action on climate change and local protections, even this stronghold may not withstand future warming.
What is DHW?
DHW – Degree Heating Weeks It is a commonly used measure of thermal stress on corals. It is accumulated whenever the sea surface temperature is at least one degree above the local summer average temperature, and is measured over a 12-week period. For example, a temperature that is 2 degrees higher for four weeks would give a value of 8 DHW. This value is considered the threshold at which widespread coral bleaching begins.
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