Outstanding climate resistant corals could be lost to local pollution

By Jessica Bellworthy

We have lost an estimated 50% of the world’s coral reefs in the last 30 years and their greatest threat is climate change. However, the first experiment of my PhD reached an unusual but encouraging conclusion; long term exposure of corals to extreme warming (6 weeks at + 5ºC) resulted in few significant changes in their physiology (Bellworthy and Fine 2017). That’s a deviation from the doom and gloom coral bleaching story often told in recent years. How can it be that such extreme temperatures do not result in severe bleaching or even death?

The Red Sea Simulator flow- through experimental system in Eilat, Israel.

One hypothesis comes from my supervisor, Prof. Maoz Fine, from Bar Ilan University, Israel. We study the corals at the northern most tip of the Red Sea, in the Gulf of Aqaba. Maoz suggests that since in order to enter the Red Sea, all coral larvae must pass the super-heated region at the southern-most point (Bab el-Mendeb) this acts as a thermally selective barrier, allowing only the very thermally tolerant organisms inside (Fine et al. 2013).

At this barrier, temperatures can reach 36 ºC. Hence, corals which have found their way to the Northern Red Sea, where maximum temperatures are 27 ºC, live well below their thermal maximum. In fact, by conducting experiments in the Red Sea Simulator mesocosm (Bellworthy and Fine 2018), we have found that when we increase the water temperature by 1 – 2 ºC, as predicted by future climate change scenarios, corals actually perform better through increased photosynthetic efficiency and greater net photosynthesis (Krueger et al. 2017).

This means that the Northern Red Sea region has been proposed as a potential refugium for corals in the face of climate change.

However the most recent paper we published shows that this evolutionary resistance would be compromised by increased nutrients in the water, known as eutrophication (Hall et al. 2018). The most significant declines in coral physiology occur when nitrate and phosphate are added to the water. Worst of all, this change to the normally clear, nutrient poor waters in this region, cause the coral to lose their resistance to ocean warming and acidification.

Unfortunately, there is a risk of this becoming a reality for the Gulf of Aqaba. The shoreline is bordered by Israel, Egypt, Jordan, and Saudi Arabia; four highly populated countries. Each has its own development plans; desalinization plants, fish farms, urbanization, all of which can impact water quality when waste water reaches the sea. Any one poor management decision can affect the whole region, so a coordinated international effort is required. The challenge is that these country’s’ political relationships are tense, to say the least. Therefore, it will take a big effort, serious discussions, and likely an outside neutral country to act as a mediator to ensure the protection of these reefs.

We must act to limit the local impacts to the Red Sea reefs in order to safe-guard this region as a coral climate change refugium.

My Ph.D. involves plenty of dive time, collecting samples from the Eilat reefs to assess coral health.


Bellworthy J, Fine M (2017) Beyond peak summer temperatures, branching corals in the Gulf of Aqaba are resilient to thermal stress but sensitive to high light. Coral Reefs, 36: 1071-1082

Bellworthy J, Fine M (2018) The Red Sea Simulator: a high precision climate change mesocosm with automated monitoring for the long-term study of coral reef organisms. Limnology and Oceanography: Methods, doi: 10.1002/lom3.10250

Fine M, Gildor H, Genin A (2013) A coral reef refuge in the Red Sea. Global Change Biology, 12: 3640-3647

Hall ER, Muller EM, Goulet T, Bellworthy J, Ritchie KB, Fine M (2018) Eutrophication may compromise the resilience of the Red Sea coral Stylophora pistillata to global change. Marine Pollution Bulletin, 131: 701-711

Krueger T, Horwitz N, Bodin J, Giovani ME, Escrig S, Meibom A, Fine M (2017) Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification. Royal Society Open Science, doi: 10.1098/rsos.170038

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