Months of extreme heat have turned thousands of kilometres of pristine habitat into an endless watery graveyard.
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So what happens without this pre-stress “practice run”?
“To see the reefs change this dramatically in just a few months is shocking”, says Baum. Without this protection, coral is more susceptible to rough weather and disease. “What we’ll see is an accumulation of one big stress”.
Corals are fascinating organisms. That could make this year’s damage even greater than predicted, and spells trouble for the hundreds of marine species that depend on the reef for food and shelter. Unfortunately, corals are also extremely sensitive to environmental disturbance, which has made them become a poster-child for the impacts of industrial society.
In Australia alone, some scientists estimate that 1,000 kilometers (620 miles) of the Great Barrier Reef face a major bleaching event.
With a 2-degree temperature rise, more than 80 per cent of reefs would be directly exposed to bleaching events, he said.
“Mortality appears to increase with the intensity of the bleaching event, which is determined by how much and for how long temperatures remain above the maximum mean summer temperatures”, reported the Australian Government Bureau of Meteorology. We’re now in the midst of another mass die-off, and this one’s shaping up to be far worse.
They found that corals within the reef, over time, have developed a tolerance mechanism which allows them to adapt to sharp increases in sea temperatures without bleaching occuring. And according to a recent NOAA analysis, the bleaching could continue through early 2017.
Not only has some parts of the reef lost its attraction, but hundreds of fish species could lose their livelihoods, including the yellow clown goby, also known as Okinawa goby, which feeds on corals.
A severely bleached patch of coral.
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Many fear an increase in coal production will lead to more run-off pollution on the Great Barrier Reef and higher temperatures due to carbon dioxide released into the air. Three quarters of all thermal stress events, the researchers found, were preceded by a period of slightly elevated temperatures – a so-called “protective trajectory”. However, when water temperatures rise, the coral expels the algae, revealing its white skeleton and typically ending in death. The results were dramatic. These physiological differences were paralleled by genetic changes, with corals under the single and repetitive bleaching scenarios showing gene expression profiles consistent with heat stress. The 2050 plan set goals to manage the protection of the Great Barrier Reef and to keep it off of the UNESCO World Heritage Committee’s endangered list.
Bleaching left devastation at the Airport Reef in American Samoa last summer.
If these predictions are born out, coral cover in the Great Barrier Reef could dwindle to less than 5 per cent by the end of the century.
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The future is not looking bright. And when this cycle occurred – warm, cooler again, then very warm – the researchers found that corals had a mechanism to protect themselves. “The disheartening thing is that our model shows that in the future the proportion of events with that protective [warming period] will be reduced”. The researchers say they’ll need to study that next.
