Reefs at Risk

Cyclone Yasi, as big as Katrina, and one of the strongest cyclones in a century, swept across the Great Barrier Reef and on into Queensland on Feb 2. A coral reef has little defense against such a storm.

Crossing the unusually warm Coral Sea before it got to the reef, it grew in strength to Category 5 – just as Katrina grew to Category 5 when it blew across the warm Gulf of Mexico. The Coral Sea has in fact never been warmer, a product of the impact of the current La Nina and the long-term warming of the ocean.

Cyclone Yasi, Category 5, about to hit Queensland on Feb 2 (

Because of the warmer surface waters, this has been another bad year of global coral bleaching on reefs from the Indian Ocean, Thailand, the Maldives, and the Caribbean, probably as bad as 1998, certainly worse than 2002 or 2005. Global bleaching events such as these used to occur every hundred or a thousand years. No longer.

Coral bleaching occurs when water temperatures get too warm and symbiotic algae called zooxanthellae are expelled (

Corals live very close to their upper lethal temperature limits, and a rise in surface temperatures of just 1-2 degrees centigrade is enough to cause extensive coral bleaching. Following the global bleaching of 1998, about 15% of corals failed to recover. We’ll see soon enough how much recovery occurs from the global bleaching of this last year.

At the same time, as atmospheric carbon levels continue to rise, the oceans are becoming more acidic. This is the greatest threat of all: at some point calcareous skeletons of corals will no longer form and the reefs will crumble. Only a reduction in atmospheric levels of CO2 will prevent this, and we all know now how unlikely that is.

As atmospheric CO2 rises, so does the amount of CO2 dissolved in sea water, and the pH gradually drops, making sea water more acidic (

Coral reef scientists around the globe have been warning us for some years that coral reefs are not going to survive global warming. The warnings have now escalated. The World Resources Institute, along with the Nature Conservancy and a diversity of coral reef monitoring organizations, has just published “Reefs at Risk Revisited”, updating its last report of 1998. Local and global stresses now threaten 75% of reefs. Without action on our part, by 2030 that will be 90%, and by 2050, all of them.

Of course, efforts to protect the reefs from overfishing, destructive fishing, pollution, and coastal development are all worthwhile, allowing the corals to be as resistant as possible to the serious global stresses of warming temperatures, coral bleaching, and ocean acidification. But there probably isn’t a single coral reef scientist left who thinks there will still be reefs in existence for our grandchildren to see.

What will the world look like without reefs? This isn’t hard to imagine – we need only go to many parts of the Caribbean and snorkel or dive around reefs that now are dead and crumbling rubble, covered with macroalgae.

A Caribbean coral reef reduced to rubble, abandoned by most fish and all scuba divers (

The costs are huge. A coral reef dies, and those who depend on it leave or die with it – reef fish and their prey and predators, scuba diving operations, recreational visitors, community fishermen, everything is lost. Vulnerable tropical countries, most of them island nations, are now advised to reduce their dependence on coral reefs, and ‘build adaptive capacity’.

We don’t know if life is abundant or rare in the universe, but we can make some reasonable guesses. With 100 billion galaxies, each with its trillion or so stars, life is probably not unusual. But it is probably bacteria-like rather than multicellular, for after all that’s what life on our own very benign planet looked like for a couple of billion years or more.

Stromatolites are mounds of cyanobacteria and look like rocks. They dominated life on Earth for about two billion years. Life on other planets may be no more complex. (

Complex ecosystems like those we find on Earth may be extraordinarily unusual across the universe. And even if complex life has evolved elsewhere, it will be different, contingent on the interacting pressures and planetary events of their own systems. Coral reefs evolved here, on Earth, and probably nowhere else.

Other ecosystems may survive these perilous times through adaptation, resilience, and migration to different latitudes. But not coral reefs. We’ve become familiar, even comfortable, with the extinction of particular species. But the extinction of an ecosystem? That is something very different.

There are no words that I know of to express the depth of such a loss. It is a loss to our universe.

Great Barrier Reef. See it while it's still there. (

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