By Anna Cummins, Ben Westcott
Back-to-back bleaching in 2016 and 2017 has devastated 1,500 kilometers of this UNESCO World Heritage Site, several Australian scientists warned CNN on Monday.
Before 2016, only two bleaching events had been recorded on the Great Barrier Reef in the past two decades: 1998 and 2002.
This is the first time that two discolorations have occurred so close to each other. "I was surprised that I had to get on a plane again this year to assess recent damage," said James Kerry of James Cook University.
Last year's bleaching, the worst in history, mostly affected the northern part of the reef, while this year's bleaching has impacted the midsection, according to scientists from the ARC Center of Excellence for the Study of Coral Reefs.
The lower third of the reef is now the only section that has escaped significant discoloration.
"The central section of the reef now shows the same degree of bleaching as in the north," says Kerry. “By examining those reefs this year we can tell how low the coral cover was. It was shocking to see the consequences of last year's whitening. "
Damage from Cyclone Debbie, which hit Queensland last March, compounded the problem. "The storm did a lot of damage to the coral," explains Kerry.
Threat number one
Coral bleaching - or bleaching - is a reaction to stress that occurs when ocean temperatures rise, driving out the algae that grow inside the coral, bleaching it, and suppressing its main source of energy. It is directly related to global warming.
The bleaching does not immediately kill the corals, because if temperatures drop, the algae can recolonize that space. But if the temperatures remain high, the corals end up dying, which means the elimination of the natural habitat of many marine species.
Australian Environment and Energy Minister Josh Frydenberg said in a statement that climate change was the "number one threat" to his country's Great Barrier Reef.
"For this reason, the Australian government has launched an unprecedented effort to invest more than 2,000 Australian dollars (1,500 million US dollars) in the Arrecife 2050 plan," said the minister.
Kerry explains that a two or three degree rise in temperature above the average maximum for "three or four weeks" is enough to push corals out of their comfort zone.
"When it's very hot for that length of time, corals don't just bleach, they die off quickly," adds Kerry. "I think that's what happened, based on what I saw from the air and what I saw last year."
An ecosystem in danger
Australia's Great Barrier Reef is home to the largest collection of coral reefs in the world, with about 400 types of coral and 1,500 species of fish. It is also home to other endangered species, including the great green sea turtle and the dugong.
The Reef reports about $ 3.7 billion to the Australian economy each year, through fishing and tourism.
About 275 million people around the world depend directly on reefs for their source of livelihood. Reefs also make up about a quarter of the world's fish population, according to the UN.