Mass
coral bleaching now affecting half of Australia's Great Barrier Reef
Climate
change and strong El Niño cause hundreds of kilometres of reef to
bleach, as higher temperatures stress the coral
Michael Slezak
Monday 11 April 2016
03.00 BST
The mass coral
bleaching event smashing the Great Barrier Reef has severely affected
more than half its length and caused patches of bleaching in most
areas, according to scientists conducting an extensive aerial survey
of the damage.
“The good news
with my last flight is that I found 50 reefs that weren’t bleached,
so that may be the southern boundary,” said Terry Hughes from James
Cook University. Hughes is the head of the national coral bleaching
task force, which has been conducting flights over the length of the
reef, mapping bleached areas and recording the severity of the
damage.
Climate change and a
strong El Niño have caused hundreds of kilometres of the reef to
bleach, as the higher water temperatures stress the coral, and they
expel their symbiotic algae. If the bleaching is bad enough, or the
temperatures remain high for long enough, the corals die, putting the
future of reefs at risk.
The mass bleaching
on the Great Barrier Reef is part of what the US National
Oceanographic and Atmospheric Administration has called the third
global bleaching event – the first occurred in 1998.
Initial reports
suggested only the most northern and remote areas of the Great
Barrier Reef were bleaching, but as aerial surveys have continued,
scientists have struggled to find a southern boundary.
The latest find of a
stretch of unaffected reefs around Mackay was a small piece of good
news, Hughes said.
But he said its
significane would be unclear until reefs further south were examined.
“It may be a false
southern boundary,” Hughes said. The reefs around Mackay have
unusually large tides, which might have pulled in cooler water and
saved the coral there.
So far, the surveys
reveal there are severely bleached reefs almost as far south as
Cairns, and patchy bleaching almost to Mackay.
Morgan Pratchett
from James Cook University said there was some bleaching even further
south. “There is reasonable levels of bleaching as far south as the
Keppels, which is even more than we suspected initially,” Pratchett
said.
Hughes planned to
fly over another 150 reefs, creating a total of about 900 surveyed.
Only then will the group have a complete picture of how bad the
bleaching is.
The next step will
be to examine how much of that bleached coral has died. “If the
corals are severely bleached, then a lot will die. If they are
lightly bleached, which is the case with a lot of reefs south of
Townsville, then they’ll regain their colour over the next couple
of months and there won’t be much mortality,” Hughes said.
Two weeks ago, the
Great Barrier Reef Marine Park Authority reported half the coral in
the northern parts of the reef were dead. Hughes said that was
consistent with reports from divers north of Port Douglas.
Hughes said this was
by far the worst bleaching event to have hit the Great Barrier Reef.
He said it was three to four times worse than in 1998 or the second
great bleaching in 2002.
Last year, the Great
Barrier Reef narrowly escaped being listed as “in danger” by
Unesco, even though environmental groups said it clearly met the
criteria.
Hughes said the
“outstanding universal value” of the reef was now “severely
compromised”.
Ariane Wilkinson, a
lawyer at Environmental Justice Australia, said the bleaching might
cause Unesco to reconsider its decision.
“[Unesco] weren’t
scheduled to examine the reef this year but in light of the terrible
bleaching it is entirely possible that they may decide to look at the
reef,” she said.
“If the World
Heritage system is to have any value, it must address the most
serious threats to the most iconic examples of world heritage,” she
said. “If any site falls into this category, it is the ... Great
Barrier Reef.”
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