Published: Fri, April 20, 2018
Medicine | By Daryl Nelson

Great Barrier Reef was devastated by warming waters in 2016, 2017

Great Barrier Reef was devastated by warming waters in 2016, 2017

An extended heatwave in 2016, researchers report in the journal Nature, has killed almost a third of the Great Barrier Reef's corals.

Professor Terry Hughes, Director of the ARC Coral CoE, said that while coral has the ability to survive and "regain their colour" after higher water temperatures, this did not happen after 2016.

The extent of the coral die-offs in 2016 - and another severe bleaching event in 2017 - had already been known to scientists, but the new research chronicled specifically how rising temperatures had affected different reef species and the reef's ecological health at large.

The study, published online in the Nature journal today, examined the link between heat exposure and coral survival along the 2,300km length of the Great Barrier Reef following last year's heatwave. The existing scientific understanding was that bleached corals - which depend on symbiotic zooxanthellae algae for nutrition and their bright colors - die slowly. The first event hit the northern third of the reef the hardest, while the second did more damage in the middle third. Without the algae, the coral dies and seaweeds take over. However, with the 2016 heatwave, Hughes said, "That's not what we found".

Combined, he said, the back-to-back bleaching events killed one in every two corals in the Great Barrier Reef.

"They cooked because the temperatures were so extreme", he said, referring to temperature-sensitive species of corals which began to die nearly immediately when water temperatures rose.

In many areas of the reef, there was a reduction in the diversity of coral species: shifting from the dominance of fast-growing species like tabular coral to simpler, slower growing varieties. The research team observed "markedly divergent responses to heat stress". The die-off of staghorn corals in the 2016 bleaching event impacted 29 percent of the 3,863 reefs that comprise the Great Barrier Reef system. "On the other hand, the so-called losers [had] mortality rates of 90 percent or more in the worst-affected portion of the reef", Hughes told ABC News.

Shohei Ohtani Struggles with Blister, Suffers First Bump in the Road
In his two innings of work, the 23-year-old surrendered three runs and four hits while struggling with his control. Corbin (3-0) gave up a walk and a two-out, eighth-inning single while pitching his first career complete game.

The events have radically changed the cocktail of coral species living on hundreds of reefs within the greater system, said Andrew Baird, another study author from Coral CoE at Australia's James Cook University.

"Mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining", he said.

Australia's Great Barrier Reef has lost more than half its coral cover in the past 27 years due to storms, poisonous starfish and bleaching linked to climate change. "We need to focus urgently on protecting the glass that's still half-full, by helping these survivors to recover", Hughes said in a statement. Study authors stat that the increasing prevalence of post-bleaching mass mortality of corals is a radical shift in the disturbance regimes of tropical reefs.

Water temperatures along the reef rose 1C above the average caused by a combination of climate change and the El Nino weather cycle.

"If we fail to curb climate change, and global temperatures rise far above 2 degrees Celsius [above preindustrial levels], we will lose the benefits they provide to hundreds of millions of people", Hughes said.

If the targets in the Paris agreement are met, the reef will survive as "a mixture of heat-tolerant [corals], and the ones that can bounce back".

Like this: