Red Sea Corals may be Resilient to Climate Change

In recent decades, many coral reefs around the world have been suffering tremendous damages as a result of global climate change. Climbing greenhouse gas emissions do not only cause a rise in average global temperature and more extreme weather events but also cause the oceans to become warmer and more acidic. What follows are mass bleaching events like those that wreaked havoc on the Great Barrier Reef (GBR) in Australia between 2016 and 2017. At that time 30 percent of the shallow water corals in the North and another 22 percent further South were irrecoverably destroyed.

However, in the Gulf of Aqaba/Eilat, the situation seems to be somewhat different: research has shown that the coral reefs of the northern Red Sea are unusually resilient to climatic changes, and are likely to survive even harsher conditions in the future. Israeli scientists agree the coral reef of Eilat, the northernmost coral reef in the world, is unique and needs to be protected and preserved.

Recently, it was found that the northern Red Sea corals are not only adaptable to changing environmental conditions but also continue to produce offspring at the same rate and quality, which could ensure reef survival for many years to come, provided we humans do not interfere.

A shelter from bleaching

Climate change engenders two specific phenomena which affect the health and survivability of coral reefs worldwide: warming seawater temperatures and acidification. The existence of corals is made possible through symbiosis - cooperative interactions between the coral organism itself and a symbiotic species of algae called zooxanthellae, which live within the coral tissue and give it its color. These algae perform photosynthesis, during which sugars are formed, and carbon is fixed, some of which is transferred to the coral and utilized for building its limestone skeleton. The algae, on their part, take advantage of the waste materials that are expelled from the coral cells and receive protection inside of the coral tissue.

When the water temperature rises one or one and a half degree Celsius above the average summer temperature for several weeks in a row, the algae might abandon the coral tissue, rendering it transparent and the underlying white skeleton visible, a phenomenon known as coral bleaching. When this happens, the coral loses its primary source of energy supply, which can result in its death (some of the corals may survive and recover after the temperature drop). The deterioration of a coral reef following a mass bleaching event undermines the complex ecosystem it supports and may lead to widespread and permanent damage of the reef's biodiversity, including fish, invertebrates and other animals.

At the same time, high concentrations of human-made carbon dioxide emitted into the atmosphere dissolve in seawater, alter its chemistry and cause an increase in acidity. A coral skeleton is made up of many thin layers of calcium carbonate, which slowly deposit throughout many decades. This process depends on the chemical composition of the water. High levels of acidity can impair the deposition and demand greater energy investment from the coral, which comes at the expense of growth rate and reproduction.

In recent decades the phenomenon of bleaching has become very common. The Great Barrier Reef in Australia suffered the most severe bleaching between 2016 and 2017 when at least 50 percent of the regions coral reefs were affected. Nonetheless, there are areas in the world where no coral bleaching has been observed so far, one of which is the Northern Red Sea. Damages seen in the majority of reefs around the world cannot be found in the corals in Eilat even after exposure to extreme stress situations. Researchers believe coral survival in the Gulf may be attributed to a series of evolutionary processes which took place in the region, allowing corals to survive even when water temperatures rise by up to five degrees Celsius above average summer maximum temperatures.

Producing offspring even under harsh conditions

The resilience of coral reefs in Eilat to high temperatures and increased acidity is a significant finding, but the ability of the corals to survive in the future depends on both their genetic flexibility and adaptation to the changing habitat. In other words, for the prolonged existence of the corals in the coming decades, they must continue to reproduce without their offspring being harmed by the harsher conditions of their environment.

A new study conducted by Prof. Maoz Fine of the Faculty of Life Sciences at Bar-Ilan University, together with researchers at the Interuniversity Institute of Marine Sciences in Eilat and researchers from Switzerland and Holland, examined whether the parent generation of corals exposed to elevated temperatures and  higher acidity (conditions expected to prevail at the end of the 21st century and even later) affects the offspring - the "Carryover effect."

For this purpose, the researchers collected parent colonies of the species Stylophora pistillata, a common coral in the Gulf of Aqaba/Eilat, and exposed them to elevated water temperatures and increased acidity levels (pH 0.4 units lower than current seawater acidity and water temperature 5°C higher). By doing so, the scientist simulated the conditions that are expected to occur in the region towards the end of the century, during the breeding season of the corals.

The study examined many physiological parameters of adult corals and their offspring, as well as the number of offspring who managed to settle (to find their place on a hard bed). 

"In our study, we found that extreme temperatures and acidic conditions do not affect the coral offspring - neither in the reproductive stage nor in the breeding stage. In other words, those periods, in which corals are most sensitive to extreme conditions, do not constitute a 'bottleneck' for the effects of temperature or high acidity," says Fine. 

Mitigation is still vital

Although coral reefs in the Gulf of Aqaba/Eilat seem more resilient to the effects of climate change than other reefs elsewhere in the world, their survival depends heavily on human activity. "We have completed experimental simulations for future conditions and also for much more extreme circumstances," Fine says. "Along the Red Sea, there is a very long stretch of coral reef, straddling right next to the shore which is very much affected by development and pollution happening on the coast. Therefore, it is important to find immediate and tangible solutions to enable coral reef survival in the region”, Fine stresses.

Disturbances affecting the reef may not only result from global climatic influences but from local aspects. Among those are agricultural runoff, sewage, oil spills, discharge of marine aquaculture wastes and light pollution which harms the coral's biological clock and interferes with their reproduction, Fine adds.

According to Fine and a series of research studies, the protection of the coral reefs in Eilat is critical not only due to its direct ecological and economic relevance but because it might be a potential sanctuary for other corals from the effects of climate change in the near future.

Earlier this year, an article published by Prof. Fine and a group of researchers from various universities discussed the challenges of the conservation of the Red Sea and its species. It proposes solutions from multiple fields, such as increasing the number of protected areas while limiting the number of divers permitted to the natural reef each year and directing them to other sites instead (artificial reefs and sunken ships). 

At the same time, awareness campaigns would have to give divers and swimmers a better understanding as to the importance and sensitivity of corals. The article also suggested regulatory measures by imposing various governmental restrictions on development projects near the reef. 

Through awareness and education as well as determined enforcement, it may be possible to safeguard the continued existence of this unique natural treasure that lives and thrives in the Red Sea. 

Source: ZAVIT - Science and Environment News Agency