Coral Reef Bleaching Is Happening So Frequently That Full Recoveries Are Now Impossible

Heron Island, within the Great Barrier Reef, can ber seen here surrounded by Wistari coral reef. JPL/NASA

Robin Andrews 05 Jan 2018, 18:04

There’s no two ways about it: The world’s coral reefs are being annihilated by climate change. Adding insult to injury, a new study in Science has found that coral bleaching is happening way more often than it used to.

Around the time of the early 1980s, coral bleaching events occurred once every 25 to 30 years. An analysis of 100 coral reefs spread across the globe revealed that this recurrence rate is now once every 5.9 years in 2016.

The authors explain that “tropical reef systems are transitioning to a new era in which the interval between recurrent bouts of coral bleaching is too short for a full recovery of mature assemblages.”

Of the reefs sampled, 300 bleaching episodes were considered to be severe, which means that 30 percent or more corals were drained of their hues on a scale of tens or even hundreds of kilometers. Another 312 were denoted to be moderate, which is when 30 percent or less of corals have been bleached.

Of the 100 coral reefs, only six escaped severe bleaching.

“We have known for quite a long time now that bleaching events are becoming more frequent and intense and that a global coral reef crisis is underway,” study co-author Dr Verena Schoepf, a research fellow and program co-leader at the ARC Centre of Excellence for Coral Reef Studies, told IFLScience.

“In fact, this has been predicted quite a while ago but back then, scientists were still hoping that this may have been an overly pessimistic outlook.”

“So while our study has confirmed what we already knew in a general sense, crunching the actual numbers and seeing that reefs are running out of time to recover from recurrent bleaching – and that none of the 100 reefs that we examined have remained free of any bleaching since 1980 – was heartbreaking.”

The international research endeavor was led by the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University, and it’s another unwelcome melancholy narrative about the state of our oceans. It follows hot on the heels of a separate study that found that our oceans are also being rapidly deoxygenated.

The full recovery of mature coral reefs, post-bleaching, is now not possible. q phla/Flickr; CC BY 2.0

Coral bleaching, in case you’re not aware, is a visual representation of the collapse of coral reefs.

Corals, those huddled marine invertebrates, create their calcium carbonate-rich castles around them for protection. At the same time, microscopic algae live within the corals’ tissues.

It’s a mutualistic relationship: The algae is protected by the coral, and the coral feeds on the leftovers from the algae when they photosynthesize. Aesthetically speaking, the algae give the coral reefs their incredible color.

That’s why, when water temperatures get out of an optimum range – too hot or too cold – the corals become stressed and their algae are expelled. During such a “bleaching” event, the colors drain from the corals, which are left vulnerable to attack, disease, or starvation. If they cannot recover, they die.

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