Serving as home to 30% of all marine life, coral reefs are the ocean's rainforests. In terms of economic growth, they sustain almost a billion people all over the world. Climate change, on the other hand, puts coral reef ecosystems in jeopardy.
rofessor Christian Voolstra of the University of Konstanz and an international group of experts describe how to extend and harvest natural adaptive processes to increase the resilience of corals and the reef ecosystems they build in an article published in the current issue of the online journal Nature Reviews Earth & Environment.
Natural Heat Tolerance
To increase corals' natural heat tolerance, the researchers recommend applying nature-based techniques and creating related methods. In some ways, the goal is to give a toolkit of strategies that will allow corals to assist themselves.
Under climate change, corals' historically tight adaption to their surrounding climate is their Achilles heel. Even reducing global warming to 1.5 degrees Celsius will not be enough to safeguard coral reefs. This is because corals are so well acclimated to their surroundings that even a slight increase in temperature can negatively influence them.
An excellent example is coral bleaching, a sign and indicator of a broken symbiosis between corals and their necessary photosynthetic algae. "We have to do something," the study's participants insist emphatically.
"We advocate for a strategy based on the concept that "nature knows best." What strategies have corals devised to enhance their stress tolerance, how can we research them, and how can we put them to the greatest possible use?" The tasks are described by Voolstra, Professor of Genetic Adaptation in Aquatic Systems at the University of Konstanz.
Because the same bleached corals are utilized, restoring coral reefs by fragmenting corals to produce new colonies has not shown to be very successful.
As a result, it's just a matter of time before these corals bleach and dies during the next heat wave. As a result, the researchers are focusing on ways that might help regenerated coral survive longer.
Finding a Different Material
Choosing better source material is one possibility. However, not all corals are equally sensitive to environmental changes. There are reefs with very resistant corals, for example, that keep their characteristics when utilized as a material for colony restoration.
Voolstra's research group developed the fast test CBASS ("Coral Bleaching Automated Stress System") to assess the heat tolerance of corals to identify such species. Voolstra recently used this test during a field study in the Red Sea. "Even within the same reef, we noticed a huge natural range of extremely resistant and very vulnerable colonies," adds Voolstra.
Another way to improve restoration is to condition the corals to make them more resistant. By progressively delivering a low amount of stress to very young corals, or coral larvae, the process of "environmental hardening" exposes them to tougher environmental circumstances.
These "primed" corals are better prepared to deal with real-world stress circumstances, as has already been demonstrated. Therefore, one line of study focuses on establishing whether environmental events and places have previously taught corals to thrive in increasingly severe environments. Colonies along the shore, for example, are subjected to extreme temperature swings since the ocean is warmer during the day and cooler at night in such areas. The corals become more robust as a result of this.
Furthermore, because corals and their related algae live in symbiosis as so-called holobionts, this symbiosis may be utilized to improve coral stress tolerance. There are variations in stress resistance among various algae species linked with corals, for example. Free-swimming coral larvae are rarely linked with algae in their early stages of life.
Finally, mutualistic bacteria can be transferred from a resilient coral to a vulnerable coral to improve heat tolerance. This can be done by moving the microbiome of better, stress-resistant corals onto vulnerable corals or by giving a probiotic cocktail made up of a combination of cultivated, beneficial bacteria isolated from especially resistant colonies.
Researchers were able to show that using a probiotic treatment reduced the mortality of corals under acute heat stress by 40% in the long term in the study "Coral microbiome manipulation elicits metabolic and genetic restructuring to mitigate heat stress and evade mortality," in which Voolstra also participated.
A Crucial Note
It's crucial to note that no artificial or foreign genetic material is used in this type of manipulation, unlike genetic alterations. "It is tough to anticipate the impacts of foreign genetic material in complex ecosystems, particularly in microbes that have concise reproduction periods and are thus able to spread and develop fast," Voolstra said of genetic modification to rescue reefs.
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