Scientists studied 2,500 coral reefs to figure out how to save them

Updated 2103 GMT (0503 HKT) August 12, 2019

Photos: How are humans harming coral reefs?

Also known as "rainforests of the sea", coral reefs offer spectacular sights, as well as supporting wildlife, providing food, jobs and coastal protection for an estimated 500 million people.

But human activities are threatening their survival. Scroll through the gallery to see how our actions are putting coral reefs at risk.

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Rising temperatures: Man-made greenhouse gas emissions are making oceans warmer. <br />In hotter water, corals lose their algae coverings and turn white or "bleached". Bleached coral are not yet dead -- but without their algae they eventually starve.

Photos: How are humans harming coral reefs?

Rising temperatures: Man-made greenhouse gas emissions are making oceans warmer.
In hotter water, corals lose their algae coverings and turn white or "bleached". Bleached coral are not yet dead -- but without their algae they eventually starve.

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Photos: How are humans harming coral reefs?

Overfishing: The coral reef's inhabitants are its first line of defense. Fish eat some of the creatures that eat coral, while crabs and shrimp use their pincers to protect their coral homes. Fish also graze on seaweed and algae so that they don't grow to cover the reef.

Indiscriminate overfishing can disrupt these ecosystems, leaving the coral more vulnerable to predators. Fishing boat anchors can also scar and break the corals below.

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Photos: How are humans harming coral reefs?

Invasive species: Over the past 25 years, lionfish have colonized Atlantic coastal regions, from their native Indo-Pacific waters. It's thought they were released into the Atlantic by owners who no longer wanted them as aquarium pets.

With fewer natural predators, the species' new Atlantic populations are growing rapidly. They can eat and out-compete native coral reef creatures. Aquarium releases, aquaculture and fishing boats can all unwittingly introduce invasive species to delicate coral environments.

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Acidification: Seawater absorbs our carbon dioxide emissions, which makes the oceans more acidic. <br /><br />Corals, like many marine species, protect themselves with skeletons made from calcium carbonate. More acidic seawater makes it harder for corals to build new skeletons, and can even decompose existing skeletons. <br /><br />

Photos: How are humans harming coral reefs?

Acidification: Seawater absorbs our carbon dioxide emissions, which makes the oceans more acidic.

Corals, like many marine species, protect themselves with skeletons made from calcium carbonate. More acidic seawater makes it harder for corals to build new skeletons, and can even decompose existing skeletons.

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Pollution: Oil spills, septic waste and pesticides can also disrupt coral reef ecosystems. <br /><br />Researchers at the University of Queensland, Australia, found that when corals are exposed to chemical pollutants over long periods, their resilience to other stresses - including higher temperatures and ocean acidification - may also decrease.

Photos: How are humans harming coral reefs?

Pollution: Oil spills, septic waste and pesticides can also disrupt coral reef ecosystems.

Researchers at the University of Queensland, Australia, found that when corals are exposed to chemical pollutants over long periods, their resilience to other stresses - including higher temperatures and ocean acidification - may also decrease.

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(CNN)An international group of scientists has surveyed more than 2,500 coral reef systems across 44 countries to determine how to save them in the face of damage caused by climate change and humans, according to a new study.

A hundred scientists were involved in the survey that looked at coral abundance in the Indian and Pacific oceans. Many of the reef systems were found to be full of complex species that created distinctive structures and were functioning in spite of deadly marine heat waves in recent years.

Global warming is killing the Great Barrier Reef, study says

The study was published Monday in the journal Nature Ecology and Evolution.

"The good news is that functioning coral reefs still exist, and our study shows that it is not too late to save them," said Emily Darling, the lead author of the study and a Wildlife Conservation Society scientist leading the global coral reef monitoring program. "Safeguarding coral reefs into the future means protecting the world's last functioning reefs and recovering reefs impacted by climate change. But realistically -- on severely degraded reefs -- coastal societies will need to find new livelihoods for the future."

Heat stress affected many coral reefs during the El Niño event between 2014 and 2017. But 450 reefs in 22 countries survived in protective cool spots. The scientists believe those areas should be the focus of urgent protection and management efforts.

Previously, the Indo-Pacific reefs were also hit by mass coral bleaching and heat stress in 1983, 1998, 2005 and 2010, before the world's most intense, longest and largest bleaching event between 2014 and 2017.

Coral bleaching occurs when ocean temperatures rise and corals release the algae that lives in their tissues, causing them to turn white, according to the National Oceanic and Atmospheric Administration.

Corals in the waters of Borneo, Malaysia.