Red Sea coral reefs at risk of bleaching if temperature drops – study

Written by on April 20, 2021

Coral living in the Northern Red Sea and the Gulf of Aqaba are at risk of bleaching if the water temperature drops, new research has shown.

A joint collaboration between Bar-Ilan University’s Mina and Everard Goodman Faculty of Life Sciences and the Interuniversity Institute for Marine Science in Eilat and published in journal PeerJ, tested coral in a lower temperature in controlled experiments to determine whether they would be affected.

Bleaching is the process whereby coral, one of the most diverse ecosystems on the planet, are affected by a change in temperature and expel the algae living inside their tissue, causing them to turn white.

Previous research from Professor Maoz Fine of Bar-Ilan University and his team proved that the coral reefs of Israel’s shores showed a high tolerance to an increase in the temperature of the seawater in comparison to other reefs around the world, research that could have valuable consequences with global warming and rises in sea temperature.

Using a Red Sea Simulator System to expose coral to higher temperatures expected to occur with global warming, Fine and his team originally found that the coral coped well with the warmer water. However, with experts predicting the Red Sea entering a cooler period, the results show how much just a slight drop can cause damage to a vast ecosystem.


“Whilst we have repeatedly demonstrated the high temperature tolerance of coral on the shallow reefs in Eilat, we wanted to test the possibility that this exceptional heat tolerance comes with the trade-off of being cold-sensitive,” said Dr. Jessica Bellworthy, who conducted her doctoral research in Fine’s department.

“Indeed we found that exposure to cold water periods causes a physiological response akin to bleaching.”

The team demonstrated after a particularly cold winter in Israel that even a 1°C drop in the average temperature can result in a physiological stress response similar to that seen in other coral under heat stress.

This has proven just how close the Red Sea’s corals live to their lower temperature threshold.

The research showed that the damaged, cooler coral did not die and in fact returned to their previous state. They were then tested again at a higher temperature to see whether the cold stress had had any effect.

“It was an important discovery for us to understand that even those individuals that suffered the cold winter stress, still did not bleach at the high temperatures,” Bellworthy said.  

Scientists have estimated that between 70 to 90% of all coral reefs will disappear by mid-century, primarily as a result of climate change and pollution, so the unique properties of the Gulf of Aqaba’s coral could provide vital information into helping preserve other reefs around the world. 

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