Twenty types of coral said to be at increased risk due to climate change have been listed as threatened species by the federal government.

As oceans become warmer and more acidic, the coral species have been damaged by climate change "but not to the point that they are endangered yet," said David Bernhart of the National Oceanic and Atmospheric Administration, as quoted by the Associated Press.

Global warming is also believed to be a factor in promoting the devastating bleaching disease among coral, which can lead to reduced growth and even total colony death.

Five of the species newly listed as threatened live off the Atlantic and Gulf of Mexico coasts of Florida, Puerto Rico and the Virgin Islands, while the other 15 inhabit the Pacific Ocean close to Guam and American Samoa.

Experts have been looking for ways to protect coral species, which create vital fish habitats and also protect against land erosion.

"There is a growing body of expert scientists talking about a risk of mass extinction in the sea and on land," said Elliott Norse, founder and chief scientist of the Marine Conservation Institute of Seattle, according to the AP. Coral "are organisms on the front line of anything that humans do" when it comes to the possibility of being harvested or damaged.

The NOAA initially sought to protect 66 species as threatened but announced only 20 on Wednesday.

Besides providing a habitat for ocean creatures and improving water quality, coral reefs shield at least 100 million people from rising ocean levels and protect against land erosion, according to a study recently published in the journal Nature Communications.

For the project, a research team examined 27 previous studies of coral reefs worldwide and discovered that coral reefs subdue the energy of waves by an average of 97 percent.

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