Corals are underwater animals that live in a mutually beneficial relationship with the algae Zooxanthellae, which provides them with food, oxygen, waste filtration, and about 90 percent of their energy. Individual corals — soft translucent polyps — live and add on to the calcium carbonate exoskeletons of their ancestors, forming coral reefs one tiny exoskeleton at a time.

About 500 million people depend on fishing stock and tourism opportunities provided by coral reefs, which also keep coastal communities safe by acting as natural barriers absorbing the force of waves and storm surges. Many people get their primary source of protein from reef fish like the coral trout, which is being affected by bleaching events faced by Australia’s Great Barrier Reef.

Coral bleaching is the complete whitening of corals when their vibrant colors fade from expelling the Zooxanthellae living in their tissue due to stressful conditions in the ocean environment, such as low tides, changes in temperature, light and nutrients.

#ClimateChange is the leading cause of coral bleaching, making entire reef ecosystems deteriorate. An assessment of 1,800 reefs in 41 countries published in April 2020 found that only 5 percent of reefs “were able to provide all of their lucrative byproducts, such as healthy fish stocks and biodiversity,” National Geographic reports.

Coral reefs, also known as underwater rainforests, support some of the most biodiverse ecosystems, providing shelter, spawning grounds and protection from predators. About 4,000 fish species and a fourth of marine life such as sea turtles, crabs, sea birds depend on reefs at some point of their existence. Collapsing reef ecosystems may lead to the extinction of at-risk species.

For the past 50 years, oceans have been absorbing over 90 percent of the heat trapped by greenhouse gases in the atmosphere produced by humans burning fossil fuels. Oceans are warming up 40 percent faster than was estimated six years ago, New York Times reports.

Although corals can survive bleaching, they’re more susceptible to diseases and mortality without Zooxanthellae and once corals die, reefs rarely return. Without a combination of long-term cuts in emissions and short term interventions, most reefs could die by 2050.