Rehabilitating coral reefs is the main priority in many countries as climate change continues to destroy and kill corals. Due to climate change, ocean heating and acidification from dissolved carbon dioxide have resulted in widespread coral bleaching, particularly in Australia’s Great Barrier Reef. Bleaching occurs when coral turns white due to changes in ocean temperatures. While bleaching itself doesn’t kill, it weakens corals, making them more susceptible to disease and death.
The UN’s International Panel on Climate Change predicts that coral reefs will decline by 70% to 90% in the next couple of decades and by 99% if global warming reaches 2 degrees Celsius above pre-industrial levels. Despite efforts to prevent this from happening, reports showed that tropical sea surface temperatures have increased by more than 1 degree Fahrenheit in recent decades. There’s also a significant increase in marine heatwaves. These changes are responsible for mass bleaching events such as the one that devastated the Great Barrier Reef in 2016.
Recently, Australia's Great Barrier Reef suffered its most widespread coral bleaching on record. This occurred as February brought the highest monthly sea temperatures on the Great Barrier Reef since the country began keeping records in 1900. According to Phys.org, an internet news portal that provides the latest news on science, a recent comprehensive survey found record sea temperatures had caused the third mass bleaching of the 2,300-kilometre (1,400-mile) reef system in just five years.
"We surveyed 1,036 reefs from the air during the last two weeks in March to measure the extent and severity of coral bleaching throughout the Barrier Reef region. For the first time, severe bleaching has struck all three regions of the Great Barrier Reef –- the northern, central and now large parts of the southern sectors,” Terry Hughes, professor at James Cook University, said.
Coral Diet Can Underpin Bleaching Susceptibility
Unhealthy reefs threaten not only the organisms that inhabit them but also the livelihoods of the people who depend on them. They provide a home for thousands of marine species and help people’s livelihoods. The world’s reefs are valued in the tens to hundreds of billions of dollars annually. The Great Barrier Reef, for instance, contributes $3.84 billion to Australia’s economy.
While current reports of mass bleaching events provide little reason to hope, experts still pursue studies to save coral reefs from vanishing. "I believe there is hope that they will be able to identify corals that may withstand climate change. The question becomes if they would be able to replenish and restore coral to the same extent that the ecosystem exists today. Coral restoration is a slow and time-consuming process,” Renee Setter, a biogeographer at the University of Hawaii Manoa, said.
Aside from coral restoration, coral helps themselves from surviving the devastating impacts of climate change through their diet. A recent study published in Science Advances accurately predicted how long corals could withstand elevated temperatures without bleaching. According to Oceanographic, a bi-monthly marine lifestyle magazine with a focus on ocean conservation, exploration and more, researchers have developed a new method for determining what corals eat. They also showed that reliance on certain nutritional sources underpins their bleaching susceptibility in heating oceans.
In the study, the researchers compared the stable isotope "fingerprint" of hundreds of corals collected in Hong Kong to that of their associated algae. They discovered two things: some corals have isotopic fingerprints that match that of their algae while other corals have fingerprints distinct from their algae. These results show how they will change as climate change progresses. Corals are dependent on photosynthesis bleach faster while predatory corals can withstand warming temperatures longer.
"The results of our study help predict which coral species are more likely to survive as oceans warm. Unfortunately, what we found is that the most susceptible species are those that are commonly used in coral reef restoration efforts. To ensure the long-term success of reef rehabilitation, restoration initiatives should shift their focus to bleaching-resistant species," Dr. David Baker, Associate Professor of School of Biological Sciences, said.
The researchers hope that the study will help scientists, conservationists and policymakers anticipate how coral reef ecosystems will change as a result of global heating. However, the team clarified that while the coral’s diet can protect them from bleaching, it will not last long. "Capturing a lot of food doesn't save corals from bleaching. It just buys them a little more time—time that they desperately need,” lead author Dr. Inga Conti-Jerpe said.
Helping the World’s Reefs
While coral reefs can at some point protect themselves from bleaching, efforts should still be created to save them. A 2019 study published in Nature Climate Change revealed that the best way to protect corals threatened by climate change is to conserve a wide range of their habitats. Co-author Malin Pinsky, an associate professor in the Department of Ecology, Evolution, and Natural Resources at Rutgers University-New Brunswick, stated that the best strategies in saving the corals conserve a wide diversity of sites instead of conserving just the cold places with corals.
According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the researchers evaluated a range of potential conservation strategies and found that conserving many different kinds of reefs would work best. These strategies include those that conserved sites suitable for corals to move to in the future; conserved sites with large populations of certain species; protected sites where existing coral populations appeared to be "preadapted" to future conditions; conserved the smallest populations; or protected reef sites chosen at random.
"Corals are facing a gauntlet over the coming years and decades from warming oceans, but we found that reef conservation, in general, can really boost corals' ability to evolve and cope with these changes. There is strength in diversity, even when it comes to corals. We need to think not only about saving the cooler places, where corals can best survive in the future, but also the hot places that already have heat-resistant corals. It's about protecting a diversity of habitats, which scientists hadn't fully appreciated before,” Pinsky said.
While these efforts to save particular reefs are offering some hope, scientists said that these solutions are only a stop-gap. “Unless we curb carbon emissions, none of this is going to make any difference whatsoever,” Iliana Baums, a molecular ecologist at Pennsylvania State University (Penn State) in University Park, said.