Warm Oceans, Climate Change Bleaching Coral Of Its Vibrant Color — Why That Matters

The world’s coral reefs are quickly succumbing to the planet’s third bleaching event, a phenomenon that leeches away their vibrant color and eventually kills what have been called the ocean’s rainforests.

A deadly combination of El Nino, global warming, and a warm “blob” in the Pacific is being blamed for coral bleaching, which began last year near Guam and the Northern Mariana Islands and spread across the Pacific to Hawaii.

The prognosis for U.S reefs is dire: 95 percent may be bleached this year, and 60 percent of those will be hit so hard they’ll die, the Washington Post reported.

Why is this important? U.S. reefs have significant economic benefits, including for tourism, and their value totals $2.4 billion. Worldwide, they provide food and livelihood to 500 million people. And though they cover only 0.1 percent of the ocean’s area, they are the epicenter of its life. A million species live on coral, including one of every four fish; two-thirds of those species are mysteries to science.

“(They) are the underwater equivalent of rainforests, and by removing the corals, you remove the trees of that underwater world,” said scientist Richard Vevers.

So what exactly is coral bleaching? It’s intimately related to temperature, and the combination of El Nino, global warming, and that blob have made the oceans very warm. It only takes one degree higher than normal for about a couple months for it to start, and this occurs because the organisms didn’t evolve to live in warm waters for long periods of time.

This causes stress, and, as a result, they expel the algae that gives them both their color and nutrients. Without these, bleaching occurs, and they become very vulnerable. They can handle it in the short term, but not in the long term.

“[This is] the largest and most pervasive threats to coral reefs around the world,” Mark Eakin, NOAA‘s Coral Reef Watch coordinator, told Discovery News.

The longer the temperature stress goes on and the more severe it is, the more likely coral is to die.

This year’s bleaching is expected to last into 2016, and it started in 2014. By the end of it, 4,5000 square miles of coral could die — or 5 percent. A coral bleaching in 1998 was much worse than that, but if it goes on for two years, this one could be much worse.

That year was the planet’s first global coral bleaching and was caused by a record El Nino; the second one happened in 2010. Each were one-year events.

According to NOAA, last year witnessed one of the worst bleaching events — and only the second near the Hawaiian Islands. It devastated the protected Papahānaumokuākea Marine National Monument, killing some coral.

“[It] was the worst our scientists have seen,” said scientist Randy Kosaki. “Almost one and a half square miles of reef bleached last year and are now completely dead.”

The phenomenon is now being spotted in the Caribbean and the Indian Ocean, as well as reefs in the U.S. One the coral dies, it may be up to 20 years before they bounce back, and many species are now being hit every five years. Some of the reefs being hit by bleaching and killed are hundreds of years old.

Only local protection and concerted efforts to dial back global warming by curbing carbon dioxide emissions can help save the reefs, said expert Nancy Knowlton with the Smithsonian.

And this third bleaching event is happening to some reefs that are already under stress.

“No reefs that experience unusually warm waters are likely to escape unscathed, but reefs already suffering from overfishing and pollution may have a particularly rough time recovering, based on what we have learned from past bleaching events.”

[Photos Courtesy welcomia, Tischenko Irina