The Great Barrier Reef’s coral is dying, and it may never be the same again.
Last month, as historically high ocean temperatures bathed the waters around the Great Barrier Reef, the Australian government raised the coral bleaching threat to the highest level possible.
On an aerial reconnaissance trip from Cairns to Papua New Guinea, researchers observed the parts of the reef that are supposed to be the most pristine and vibrant. What they saw was chilling.
“This has been the saddest research trip of my life,” said Prof. Terry Hughes, convener of the National Coral Bleaching Taskforce. “Almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef. We flew for 4000km in the most pristine parts of the Great Barrier Reef and saw only four reefs that had no bleaching. The severity is much greater than in earlier bleaching events in 2002 or 1998.”
The northern sections of the reef had, during previous bleaching events, survived relatively unscathed compared to the rest of the reef. In fact, scientists saw the north as a sort of genetic seed bank that could help re-seed the decimated reefs that bleached elsewhere. With this widespread warming, that hope is somewhat dashed, and experts say the Great Barrier Reef will not recover for decades or more, assuming waters don’t get too much warmer.
The southern parts of the reef had stayed slightly cooler during this event, thanks to substantial cloud cover in previous weeks. But any hope that the south had escaped serious bleaching was dashed last week, when scientists reported the results of extensive aerial surveys which found that only 7 percent of the Great Barrier Reef (GBR) has avoided bleaching.
This is the longest bleaching event in recorded history — almost two years at this point, with little sign of stopping. This is dangerous because it gives the coral no time for respite.
This is a relatively new phenomenon; over the last several hundred years, there is only evidence for these kinds of mass bleaching events in the late 20th century. Pacific Ocean water temperatures rise in a kind of pulse during a strong El Niño. These temperature spikes can cause coral bleaching events in the Pacific, but due to steady background global warming caused by human greenhouse gas pollution, they have become more frequent. The results can be catastrophic for the reef, which is in danger of losing its UNESCO World Heritage Site status from this bleaching threat and because of the approval of a nearby coal mine.
“Tragically, this is the most remote part of the Reef, and its remoteness has protected it from most human pressures: but not climate change”, said Andrew Baird, a professor with the ARC Centre of Excellence for Coral Reef Studies, who spent weeks at sea confirming the aerial results with underwater surveys. “North of Port Douglas, we’re already measuring an average of close to 50 percent mortality of bleached corals. At some reefs, the final death toll is likely to exceed 90 percent.”
Coral is an animal that lives symbiotically with a plant-like organism in the reef structures familiar to snorkelers and Finding Nemo enthusiasts. The animal part is an invertebrate polyp which comprises the structure of the coral, while the plant part is the colorful photosynthetic algae which lives in the structure. The algae supplies oxygen to the coral polyps, and the corals’ hard skeletons help protect the algae. When abnormal environmental conditions occur, such as high water temperatures, the algae turns toxic and the coral expels it. This leaves just the animal part of the coral behind, and it turns white — or bleaches. If the environmental conditions stay abnormal for long enough, the coral may die.
The algae can recolonize the corals if temperatures drop quickly enough, allowing the corals to recover. It’s not as though reefs haven’t experienced bleaching events before, but in the past, there have been slow periods of oceanic temperature increases prior to El Niño events which often allow the reef to survive, according to a recent study. The study, published in the journal Science, found that it will likely get a lot harder for coral reefs like the GBR as greenhouse gas emissions rise and the oceans warm. The slow periods of temperature increase give the reefs a chance to “practice” surviving in hotter water. It’s like training to run a marathon, an analogy the researchers use often. Running a marathon without practice often spells doom for the runner, and so does surviving a temperature spike without prior mild warming for coral reefs.
The researchers’ study confirmed this, and also looked at what will happen to these practice runs under future emissions scenarios.
“Our finding is that coral bleaching stress going into the future is predicted to not only become more frequent but also to have more severe impacts because of the shift away from the protective trajectory,” Scott Heron, a NOAA coral reef scientist and an author of the study, told ThinkProgress. The “protective trajectory” Heron mentions is the “practice run” that will disappear when baseline water temperatures rise 0.5 degrees C.
Heron said that while there are natural ocean temperature cycles, like El Niño, “climate change is increasing the baseline about which those natural variabilities occur.” This will drastically change reefs on the Great Barrier Reef.
This constantly high ocean temperature scenario, likely to happen in 40 years under current emissions trajectories, will stress the reefs. Paired with the spikes, reefs are in serious trouble.
“These results are timely given the bleaching currently occurring on the [Great Barrier Reef] that is being assessed by the Australian National Coral Bleaching Taskforce and, indeed, bleaching occurring on other coral reefs around the world,” said Heron.
Under lower emissions scenarios, the researchers found that average reefs within the larger Great Barrier Reef have decent odds to survive. This is all the more reason to drastically cut emissions, say reef experts.
“Say you fall asleep in your car on the highway, and you wake up and find yourself driving at 60, 70 miles an hour into a brick wall,” said David Wachenfeld, the Great Barrier Reef Marine Park Authority’s director of reef recovery, to National Geographic.
“You wouldn’t think, ‘Hmm, how hard do I have to stamp on the brake pedal before I hit the wall?’ You’d just brake as hard as you can.”
Heron said that he and fellow researchers were in the process of looking at whether this same protective mechanism is present in other reef locations around the globe.
It isn’t just hotter-than-normal temperatures that stress coral. One third of the carbon dioxide that humans emit goes directly into the ocean. This makes the water more acidic: ocean acidification has been found to limit the growth of coral.
Globally, reef cover has dropped by half over the last 30 years, according to a WWF report last year. The world’s reefs could disappear completely by 2050. The report singled out climate change and overfishing as the main culprits. And it’s not just aquatic tourists who will suffer — 850 million people around the world depend on reefs for their food security.
Some Australian scientists became so frustrated with their local Queensland papers failing to properly cover the bleaching crisis they published a full-page ad in region’s largest paper last week. They explained the problem and called for “the end of the fossil fuel era,” starting with a rapid coal phase-out.
There is little reef managers and advocates can do to help the reefs make it through this bleaching event. There is no technological, chemical, or biological therapy or prophylactic for coral bleaching. Cutting carbon emissions to attempt to lessening the human causes of global warming is the main solution to this horrible problem.
Scientists can also help reef managers to anticipate which reefs will be most likely to face future stress. For the first time, researchers at Northwestern University found a way to provide a “global index” of the coral species most at-risk of bleaching damage or death. Another new database helpfully organizes research on traits that could help scientists explain why some species are more vulnerable than others.
Heron said that management agencies can then hope to make regulatory decisions to ameliorate stress on the Great Barrier Reef from human activity and water pollution, for instance. Indeed, about half of the reef is protected from fishing, and scientists found the coral there was healthier and less bleached than the unprotected areas.
These smaller decisions can help, but the massive bleaching event happening now is so extreme and wide-ranging it’s even decimating reefs in the largest atoll in the world. Kiritimati Atoll is isolated and very few people live or travel there compared to the GBR — yet it has lost at least 80 percent of its coral, with another 15 percent severely bleached.
Some corals survive bleaching events, and scientists don’t entirely know why. Researchers like Ruth Gates, of Hawaii’s Gates Coral Lab, have been looking into the qualities and circumstances that separate the hardy survivors from the bleached dead. Most researchers, however, say addressing the root causes of the myriad stressors killing reefs around the world is paramount, and that begins with emitting less greenhouse gas pollution.