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Great Barrier Reef is facing death as bleaching continues for a second year

It is the world’s largest living structure, and two-thirds of it has been damaged since last spring.

Bleached coral in the Great Barrier Reef

The Great Barrier Reef of Australia passed away in 2016 after a long illness. It was 25 million years old.

— Rowan Jacobsen in Outside magazine.

Health bulletins from Australia’s Great Barrier Reef, the world’s largest living structure, have grown increasingly dire over the past year as a consequence of a huge bleaching event last spring.

This weekend brought more bad news: A fresh aerial survey establishes that a second major bleaching is under way this spring, marking the first time this system has experienced such events in two successive years.

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The damage now extends to at least two-thirds of the individual reefs making up the system, which follows the Coral Sea coastline of Queensland for about 1,400 miles in northeast Australia.

Last year, mostly the northern portions suffered; this year extended the damage into the middle reaches; only the southernmost reaches remain unscathed.

Given the scope of the damage, and the minimum 10-year recovery period, it now seems possible that Outside magazine’s much-mocked “obituary” from last October, quoted above, was merely premature. Especially since the agreed-upon main driver, global warming, isn’t going to abate anytime soon.

Already you can find scientists referring to the Great Barrier Reef — sprawling over an underwater territory roughly the size of Finland, and visible from space — as the world’s largest dying structure.

Tiny cornerstones of huge importance

Coral reefs hold much appeal for tourists, especially those toting snorkels and scuba tanks, but they are generally underappreciated for their importance to the world’s ocean ecosystems. Their contributions are way out of proportion to their tiny physical size — considerably less than 1 percent of the world’s sea floor.

Most of the life in a coral reef is minute to microscopic, consisting of critters called polyps that live within shells of calcium carbonate, and harbor colonies of colorful algae in a mutually beneficial relationship.

Water too warm causes polyps to eject the algae, which kills the polyps, turns the algae to fish food, and leaves behind the branching white skeletons we carelessly call “coral.”

But ocean life surrounding and dependent on the reef is large and vast, from many commercially important fish species down through a cascade of mollusks, crustaceans and invertebrates so diverse it may comprise one-quarter of all marine species.

And the reefs are fragile. Always vulnerable to hurricane damage and a few predators, they have been pressured in the industrial age by shoreline development, overfishing,  pollution discharges and tainted runoff.

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A strong El Niño event can do considerable harm by inducing a regional rise in seawater temperatures, but large bleaching events of the kind the Great Barrier Reef is experiencing go back only 19 years,  according the Coral Reef Watch project operated by the U.S. National Oceanic and Atmospheric Administration.

That’s because ocean temperatures have been rising steadily, amplifying the El Niño effect into the force that drove major bleaching events in 1998, 2002 and 2016 (1998 saw bleaching that killed 15 percent of corals worldwide).

But 2017 is not an El Niño year. It’s more like the new normal.

No help from cyclone

There was hope last month that Cyclone Debbie, in addition to damaging reef areas in north Queensland, might also deliver some benefit in the form of cooler seawater. But Terry Hughes, who runs the Australian Research Council’s Centre of Excellence for Coral Reef Studies, said recently that the storm had “come a month too late and in the wrong place” to help.

This year’s bleaching results from seawater temperatures that began rising into the danger zone in February and peaked a couple of weeks ago; the ultimate extent won’t be known until the cycle has run its course later this spring.

Meanwhile, NOAA’s Coral Reef Watch is paying close attention to other areas that have experienced back-to-back bleaching years since the middle of 2014 — so far including, just in U.S. waters, reefs in Hawaii, Florida, Guam and the Northern Mariana Islands.

Among the best journalism on the new findings from Great Barrier Reef appeared Monday in Yale Environment 360, which published a long Q&A with Terry Hughes. Some key excerpts, starting with a description of the intensity of the annual aerial survey, made during a two-week period after the bleaching is first evident but before the dead coral gets covered up with seaweed:

I personally have spent eight days flying in a small plane and helicopter, covering in all about 5,000 miles in the air. We fly very low and as slowly as we can over individual reefs. Last year, we surveyed more than 1,000 of the Great Barrier Reef’s nearly 3,000 reefs. It is incredibly challenging and emotionally exhausting to fly for hours over, say, 200 reefs in the worst-affected area, where reef after reef is 60 to 80, or more than 80, percent bleached.

When I show the aerial clips of our survey during public lectures, the room goes silent. People are truly shocked and horrified by the extent of the damage. I’ve had people in the front rows of my lectures crying.

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The phenomenon that we are seeing now is a very modern issue for reefs. Until an El Niño event in 1982-83, mass bleaching at the scale of, say, the Caribbean basin or the Western Pacific or the Indian Ocean was unheard of. The first completely global bleaching event was in 1998. That was a wake-up call for people here in Australia, because that was the first time ever that the Great Barrier Reef had bleached.

I did my Ph.D. at Johns Hopkins University in Baltimore looking at Jamaican coral reefs. Caribbean reefs became degraded much earlier than elsewhere due to runoff following land clearing, mostly for sugar cane, and they are also very heavily fished. So there are few fish left, which means that when the coral die, they are rapidly covered with seaweed rather than with new corals — because there are not enough herbivores, like fish or sea urchins, to eat the seaweed.

Tragically, the Great Barrier Reef is rapidly catching up with the Caribbean.

‘We are running out of time’

The reality is that La Niña years [of cyclical cooling] now are warmer than El Niño years were say 25, 30 years ago, due to global warming….  So we are on a trajectory toward more, and more frequent, mass bleaching events. And the gap between these recurring events is getting shorter and shorter — tragically we have had no gap at all between 2016 and 2017…. I would argue that we are running out of time.

Some scientists are already looking to direct manipulation of the reefs through introduction of heat-tolerant coral species. But Hughes is not particularly sanguine.

The idea is you raise coral in an aquarium at elevated temperatures so they are adapted to those temperatures, and then you put them out into the wild and over time they infiltrate into the wild population and replace the more susceptible individuals in that population.

I have a problem with the scale of that because the size of the wild populations is vast, and adding, say, 1,000 aquarium-bred individuals into the wild is not going to make a significant difference to the gene pool.

An interesting, detailed examination of this “unnatural selection” strategy appeared in the New Yorker about a year ago, under the byline of Elizabeth Kolbert (who, by the way, is lecturing on global extinction on Thursday at the University of Minnesota.)