Coral is threatened by global warming

I.t no news that coral reefs are in hot water. Corals, which are sedentary animals related to sea anemones, contain algae in their tissues, which provide them with food and attractive colors for tourists. But when the temperature rises, the photosynthetic mechanisms of these algae fail. Instead of molecular oxygen, the usual waste product of photosynthesis, they begin to generate highly reactive and thus toxic oxygen-rich compounds such as peroxides. If they do this excessively, the hosts expel them by bleaching the appropriate corals.

Bleached corals may linger for a while, but have no nutrients for their symbionts, they are vulnerable to disease. Eventually, if the temperature does not drop so much that the algae can be reused, they die.

And the world is getting warmer. As a result, the number of corals in it has decreased since 1980 by 30-50%.

At the local level, things can be even more dramatic. In just three years (between 2015 and 2018) Australia’s Great Barrier Reef has lost more than 30% of its coral due to deaths from bleaching. Surveys conducted in March this year showed that another Barrier Reef whitening event is now underway. This case is particularly alarming because it is the first to take place during the Pacific Cold War called La Niña, not during its opposite warming, El Niño, or the intermediate period in between.

These losses affect not only tourists. Coral reefs are important parts of the world ecology. They contain a third of multicellular marine species, including many commercially important fish. They also provide free shore protection. Cities like Cancun, Honolulu and Miami are counting on them to keep the waves at bay. According to a study published in 2014 by Robert Costanza, an economist at University College London, such benefits amount to up to $ 10 trillion a year. Thus, the preservation of reefs has practical and aesthetic significance. So something needs to be done to stop the heat-induced bleaching.

One approach is to identify species that are already heat-resistant and transfer them to reefs that are at risk. Some of the most impressive examples of heat-resistant corals come from places in the Gulf of Aqaba on the northern tip of the Red Sea, which is one of the hottest places on the planet. Several species of coral found here can withstand the heat, leading to massive bleaching elsewhere. A study published in 2021 by Romain Savary of the Swiss Federal Institute of Technology in Lausanne found that a specific reef builder called the Red Sea Stylophora pistillate was able to withstand rising temperatures above 5 ° C, above the 27 ° C at which it normally lives – more than expected by Earth this century.

It is expected that similar foci of heat resistance will appear elsewhere. Ann Cohen of the Woods Hole Oceanographic Institute, Massachusetts, is in charge of a recently launched project aimed at identifying “superriffs” of this kind around the world. Using a mix of genetic analysis and hydrological modeling, it seeks to find reefs that are heat-resistant and genetically diverse, and thus potentially capable of restoring former glory to neighboring bleached sites. It then hopes to expand the protection of these reefs to increase their chances of survival as heat-resistant resources in the future.

However, the evolution of heat resistance is not just a matter of geography. It has also been found worldwide in corals living on the cheek behind jaws with more vulnerable specimens. This indicates a complex origin. Christian Woolstra of the University of Constanta in Germany (who is also a co-author of Dr. Savar’s work) is leading a project aimed at identifying critical parts of the coral genome.

Some don’t like hot

To do this, he exposes a series of corals to a strong blast of heat to see how they behave. While this 18-hour stress test is known as cbass (Automated stress system for bleaching corals), can not cover all the effects of long-term bleaching, he hopes that the most resistant to bleaching corals, however, will show their courage in it.

Having determined which corals are resistant, the next step is to search for genes or genetic variants that are common to such corals but absent in others. Dr. Woolstra’s initial research led him to believe that only a few genes would indeed be responsible. And while some will be geographically specific, he expects others to be found around the world.

Further evidence also points in this direction. In 2020, Philip Cleves of Stanford University published a paper that showed that knocking out one particular gene in a species called Acropora millepora significantly reduces its ability to withstand heat. If such resistance genes could be cataloged and their presence detected in this area, it would allow researchers to identify elastic corals much faster than cbass can. This can be done using either some easily detected biochemical implications of their presence (a so-called biomarker), or one of a new generation of handheld devices for sequencing genes that are now coming to market.

Even if we manage to find out all the genetic complexity of heat resistance, other mysteries will remain. Some corals are able to survive the heat that kills their next of kin as well as their unrelated neighbors. This has led to the suggestion that heat resistance can also be imparted to corals by symbiotic organisms – either by individual types of their accompanying algae, or perhaps by the bacteria that together make up their “microbiome”.

Both in terms of corals and in terms of algae, it would be wise for coral symbionts to develop more robust photosynthetic mechanisms that do not behave at high temperatures. Probably, given the time and continuation of global warming, this will happen naturally. But it could help the process. Indeed, in an article published in 2020, a group led by Madeleine van Oppen of the University of Melbourne showed that a significant difference can be made in the production of algae active oxygen-rich compounds in just four years of selective breeding for heat tolerance.

Even if algae cannot be exploited in this way, there may be other microscopic organisms living in the coral. Microbiomes – groups of bacteria, fungi and viruses that coexist with most animals, especially in their intestines – are now taken seriously as physiological factors. The human microbiome has been with varying degrees of plausibility associated with conditions ranging from obesity to Alzheimer’s, and gut microbes are essential for the digestive processes of animals as diverse as cattle and termites. There is no reason for corals to be exempt from their influence.

Raquel Peishot of King Abdullah University of Science and Technology in Saudi Arabia is investigating the issue in collaboration with Dr. Woolstray. In previous experiments, she and her team isolated several microbes common to resistant corals and then grafted them into dozens of unstable varieties in which they are absent. Survival of vaccinated corals at 4 ° C was 40% higher than that of unvaccinated corals.

Whatever mix of genetics and microbes is needed for resilience, each of these factors offers its next steps. If genetics is key, then corals with appropriate genes can be prioritized by conservationists, transplanted to new sites, or stimulated to more productive reproduction, possibly by crossing different heat-resistant strains. If the microbiome is responsible for this, you can develop probiotic injections. That would be exciting. Breeding for heat resistance would take generations. Injecting probiotics can change the outlook of a coral head doomed here and now. Some experiments even suggest that individual corals may be “hardened” to adapt to warmer climates over their lifetime and then may pass this strength on to offspring through a process called epigenetic heritage that allows certain acquired characteristics to be passed on from generation. or two through mechanisms that control gene expression.

The last possibility is the use of genetic tricks crispr-Cas9 DNA editing or similar techniques for inserting or modifying heat resistance genes. This approach is being studied by Dr. Cleves, although he does not yet intend to conduct his experiments outside the laboratory. The prospect of holding them on the reef remains controversial, as it would mean releasing genetically modified organisms into the wild. But as the planet continues to heat up, he believes there may come a time when conservationists will have no alternative. Also, it may be faster than trying to achieve similar results by crossing.

Know your enemy

The immediate priority, however, is a better understanding of what is available. That means doing a few things. These include creating standard tests for heat resistance so that species from different locations can be compared; study resistant corals to see which biomarkers they share; crossing resistant corals to find any undesirable characteristics that are inherited along with heat resistance; and plumbing transformational potential probiotics.

Further challenges await those seeking to turn such observations into practical effects. The first is scale. The Great Barrier Reef is, however, the largest target, the size of Italy. On the contrary, the multi-hectare restoration project will currently be considered ambitious, so the first targets are likely to be reefs of high value as tourist attractions or natural marine defenses.

In the long run, automated distributors of coral larvae or probiotic bacteria that promote resilience can help. So it would be possible to identify reefs, which due to local currents play a major role in the spread of larvae to other places – because it may be the most useful place to start. For Dr. Cohen, a set of these natural knots will be crucial for engineering change in fairly large areas. “We have to let nature do its job,” she says, “because only nature can do it on the scale needed.”

Source link