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Coral bleaching is a big problem for marine ecosystems. Here's why. by Alix Hines
Science

WATCH  |  Coral bleaching is a big problem for marine ecosystems. Here's why. 

Australia's Great Barrier Reef is experiencing its second year in a row of mass coral bleaching, according to the Australian government's Great Barrier Reef Marine Park Authority

Bleaching events occur when corals are exposed to warmer ocean temperatures than they're used to for an extended period of time. That causes the algae that live within the coral, which gives them their color, to be expelled from the coral. 

What's left is the clear tissue over the skeleton of the coral, which makes it appear white. 

Infographic courtesy of NOAA


Bleaching events don't actually kill coral, but it does put them under more stress, which makes them more susceptible to dying, explained Jennifer Koss, the director of the National Oceanic and Atmospheric Administrations's (NOAA) Coral Reef Conservation Program.

"The tissue that’s still there is living and if temperatures come back down soon enough, those corals can re-recruit those algae and recover from the bleaching event," Koss said.

Why is this bad? 

Coral reefs cover less than one percent of the ocean's floor, but provide homes for nearly one million species of fish, invertebrates and algae, according to the National Park Service.

Gabby Ahmadia, a senior marine scientist at the World Wildlife Fund (WWF), explained that losing those coral reefs can disrupt the marine ecosystem. 

"So think of it like apartment buildings, when those apartment buildings go away, you don’t really have a place to live and so we lose a lot of that life," Ahmadia said. 

Corals are also really beneficial to humans. 

"We depend on them for the food, recreation, tourism -- there are a lot of pharmaceuticals that are derived from coral reef areas," Koss explained. "And just the physical presence of a coral reef protects fragile coastlines." 

What causes coral bleaching? 

Increased ocean temperature caused by climate change is the leading cause of coral bleaching, but runoff, overexposure to sunlight and extreme low tides can also cause bleaching events. 

Research in the journal Archives of Environmental Contamination and Toxicology indicates that certain chemicals in sunscreen can also damage coral reefs. 

That's a big deal because the report also notes that between 6,000 and 14,000 tons of sunscreen end up in the global coral reef system annually.

Hawaiian state senator Will Espero recently proposed a bill that would ban the sale of sunscreens containing oxybenzone and octinoxate across the islands, Fox News reports. These chemicals can awaken coral viruses and can cause coral bleaching. 

Sunscreens with titanium oxide or zinc oxide contain natural mineral ingredients, which have been deemed "reef friendly."

This is absolutely not normal. I think it’s the first time it’s ever been recorded. So this is very scary, it’s unprecedented.

Gabby Ahmadia

Both Ahmadia and Koss noted that the back-to-back coral bleaching events in the Great Barrier Reef aren't a normal occurrence. 

They added that the best way to prevent coral bleaching events is to be conscientious of what you do.  

Here are some practical ways you can protect coral reefs (Infographic courtesy of NOAA)