Coral reefs are dying on a massive scale around the world, driven by climate change. The planet’s largest reef, Australia’s Great Barrier Reef, has only a third of its 2,300-kilometer ecosystem left unscathed by bleaching, which happens when colored algae are ejected by the coral and their normal symbiosis breaks down.
However, corals in the Gulf of Aqaba in the northern Red Sea are particularly resistant to the effects of global warming and ocean acidification.
That is the encouraging finding of a study recently published in the journal Royal Society Open Science by scientists in Lausanne, Switzerland, and from Bar-Ilan University and the InterUniversity Institute of Marine Sciences in Israel.
Because the Gulf of Aqaba is a unique coral refuge, its corals may provide the key to understanding the biological mechanism that leads to thermal resistance, or the weakness that underlies wide-scale bleaching. It is also hoped that the Gulf of Aqaba reefs could be used to re-seed deteriorated reefs in the Red Sea and perhaps even around the world.
The scientists performed the first-ever detailed physiological assessment of corals taken from the Gulf of Aqaba after exposure to stressful conditions over a six-week period. Surprisingly, the corals did not bleach and in fact most of the measured variables actually improved, suggesting that these corals might thrive in higher temperatures and are better prepared for predicted ocean warming.
At the InterUniversity Institute for Marine Sciences in Eilat, scientists exposed corals of the species Stylophora pistillata, collected from the Gulf of Aqaba, to water temperatures and acidification. The conditions resemble the summer conditions of a future ocean in this region if local ocean warming continues at its current rate of approximately 0.4-0.5°C per decade.
An overall health check of all the major physiological functions of the corals – including energy metabolism, ability to build a skeleton, and nutrient exchange at the molecular level between corals and algae — were barely affected by the harsh experimental treatment.
Pre-acclimated to thermal tolerance
The coral species Stylophora pistillata occurs in other regions of the world, yet does not necessarily demonstrate thermal resistance beyond the Gulf of Aqaba.
“Corals in the Gulf of Aqaba are pre-acclimated to thermal tolerance due to the special geography and recent history of the Red Sea,” said Prof. Maoz Fine of Bar-Ilan University’s Mina and Everard Goodman Faculty of Life Sciences and the InterUniversity Institute of Marine Sciences.
At the end of the last ice age, corals started recolonizing the Red Sea from the Indian Ocean to its south. The thermal bottleneck at the southern entrance with summer water temperatures rising to 30-32°C provided a selective barrier, allowing only highly resistant individuals to move north.
Ironically, this heat-resistant founding population encountered much cooler waters once reaching the northern end, where the Gulf of Aqaba is located.
Based on this history, the study hypothesized that these corals might be able to better cope with ocean warming, considering that they not only descended from a heat-selected founding population, but they also started their warming trajectory from a lower temperature, compared to their counterparts in the central and southern Red Sea.
The researchers cautioned that the corals from the Gulf of Aqaba remain vulnerable to other stresses, such as pollution. “Local disturbances such as oil pollution, nutrients from fish farms, and herbicides from gardening may reduce the exceptionally high tolerance of the Gulf of Aqaba reefs,” said Fine.
The study’s authors urged the countries around the Gulf of Aqaba – Saudi Arabia, Egypt, Jordan and Israel – to get together and create a strong protection environmental program for the coral reef “because it might very well be one of the last reefs standing at the end of this century.”