From The Expert: How Heat Waves Kill Coral Reefs

Coral reefs: bright, colorful and teeming with sea creatures who call them home. They might just be among the most beautiful and life-filled natural habitats we can find.

But now, they’re bleaching, dying, becoming sick and losing their ability to create a space for marine life to thrive.

The world's oceans are experiencing a drastic shift in reef health, with coral bleaching events now occurring five times more frequently than they did just a few decades ago, according to weather.com meteorologist Jennifer Gray.

This rapid acceleration poses a severe threat to global marine ecosystems, as corals are absolutely critical to ocean health. 

In fact, thousands of species — representing 25% of all marine life — depend directly on coral reefs to survive.

Beyond their ecological importance, reefs serve as a vital shield for human infrastructure, preventing 97% of wave activity from hitting coastlines and protecting the homes of people, too. They're also an important source of food for humans, providing about 10% of the fish caught worldwide.

How Coral Becomes Bleached

The primary driver behind this escalating crisis is global heat. Because the Earth's oceans absorb 90% of the excess heat stored in the atmosphere, ocean temperatures are steadily rising, according to Gray.

Corals rely on a delicate, symbiotic relationship with a specific type of algae that lives on them, which acts as the coral's main food source. 

However, this bond is easily broken. A temperature increase of only 1°C is enough to stress the coral and trigger a bleaching event.

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Once a coral becomes stressed by temperature shifts or other environmental factors, the algae leave, depriving it of its primary food source.

"Now once the coral becomes stressed, it becomes very pale, white and very susceptible to disease and death,” Gray said.

Other Culprits

While rising global temperatures are a primary concern, scientists emphasize that warm water is not the only culprit behind reef degradation. Corals are highly sensitive to a variety of environmental shocks:

• Extreme Cold: In January 2010, corals in the Florida Keys suffered a massive bleaching event when water temperatures dropped an astonishing 10 degrees.
• Weather and Pollution: Excessive rainfall can wash heavy drainage and pollutants directly into the ocean, disrupting the marine environment.
• Environmental Shifts: Severe changes in water chemistry, more sunlight than normal, and even low tides for excessive periods of time can all cause corals to bleach.

A Shift in the Science: Finding Resilience

Despite the compounding threats, the focus of the scientific community is shifting toward active intervention. 

"At the end of the day, climate change is about mitigation," Gray said.

Decades ago, conventional wisdom dictated that human hands should stay off the reefs. Today, modern science is completely overturning those old assumptions.

(MORE: Baby Corals Get Second Chance On Great Barrier Reef)

Organizations and scientists are now tracking down the most resilient corals — those that manage to survive extreme temperature stressors. Scientists are harvesting these resilient strains, breeding and growing them in specialized coral nurseries, and then strategically planting them back onto the damaged reefs.

“And it's actually working,” Gray said. “Decades ago, we thought that you couldn't touch the corals, they'll die, it takes forever for coral to grow — but now we're seeing different science.”

weather.com content writer Ada Wood enjoys exploring the stories that science and climate teach us about our natural world and how it influences the way we live in it.