Scientists have confirmed that 67 percent of shallow-water corals of the Great Barrier Reef northern region had died in the past eight-night months. The reef’s southern area was able to survive the bleaching with minor damages while the central region, although it was also affected, did not show a significant damage as in the northern region of Great Barrier Reef. It will take between 10 to 15 years to recover the north of the reef.
The northern region had escaped two other bleachings in 1998 and 2002 but failed to do so in 2016. Two-thirds of the corals in the north of the Great Barrier Reef died, setting a record for the worst-ever bleaching event suffered by the Australian reef.
When surveying the extensive ecosystem, scientists found that not all the northern region was affected by the bleaching. The northern offshore corner of the Great Barrier Reef Marine Park showed that it managed to survive the damage and the loss of coral was lower than in other reefs of the area.
Between 2015 and 2016 heat stress from record high summer temperatures affected microscopic algae called zooxanthellae. The alga lives in the tissues of corals, and warm waters change them, turning them in white and eventually killing them. 2015 and 2016 have been recorded the hottest years due to global warming, being the first time that humans contribute to the loss of reefs around the world.
After bleaching, corals can recover and slowly regain the zooxanthellae they need to live if the temperatures decrease, otherwise, the reef dies.
This is not the first time the Great Barrier Reef is affected by a severe bleaching, but it is the first time it kills such an extension of corals. The first time the Australian reef significantly bleached was in 1998, and it happened again in 2002 without causing significant damages.
Mapping the Great Barrier Reef affected areas and assessing the possibilities of recovering
Scientists from the Australian Research Council (ARC) Centre of Excellence Coral Reef Studies did underwater surveys during March and April 2016, when the bleaching was at its peak. The same study was made again between October and November to compare data and see how bad the damage was. The northern region -from Port Douglas to Papua New Guinea- lost about 60 reefs.
Losses of corals ranged from 83-99 percent reports The Conversation in a collaborative article with David Wachenfeld, Director for Reef Recovery at the Great Barrier Reef Marine Park Authority. It was also found that bleaching and mortality decline with depth.
On average, 6 percent of bleached corals die in the central region and 1 percent in the South, said Professor Andrew Baird from the ARC Centre who led the November-October survey.
The Director of the ARC Centre stated that the last survey found that a large corridor of reefs in the north was not affected for the severe bleaching along the eastern edge of the continental shelf in the far north of the Great Barrier Reef.
In the east Torres Strait and outermost ribbon reef -also part of the northern region of the Great Barrier Reef- the survey spotted large swathe of reefs that escaped the damages of the bleaching. Nonetheless, 26 percent of the area shallow- water corals died.
It is believed that the eastern Torres Strait was able to survive the bleaching due to strong currents and upwelling of cooler water across the edge of the reef, protecting it from heat stress.
Corals in the central region are already recovering their color, and those who were not affected are in good condition. The last time this area was affected was by the Severe Tropical Cyclones Hamish and Yasi which occurred in 2009 and 2011 respectively.
The Great Barrier Reef bleaching outcomes: Tourism will not be affected
The reef will continue to be monitored to see the progress of the 2015-2016 bleaching effects. Scientists had already predicted that the Great Barrier Reef would suffer higher levels of damage, slower rates growth rates and lower rates of reproduction in the coming months.
If water temperatures cool down, the northern region could replace the dead corals by new ones in 10- 15 years. If temperatures continue to rise, a fourth severe bleaching could threaten the large reef.
The Australian tourism sector is relieved for the moment because the southern and central region were barely affected. Tourism on the Great Barrier Reef generates $5 billion in income each year and employs around 70 thousand people.
Professor Baird said that the patchiness of the bleaching situation allows Australians to continue to provide a world-class coral reef experience in the less affected areas.
The Great Barrier Reef is the largest reef in the world: It is greater than the Great Wall of China stretching for over 1,400 miles (2,300 kilometers) over an area of approximately 133 thousand square miles (344,400 square kilometers).
The Australian reef comprises over 300 individual systems and coral cays. The labroadcosystem is considered one of the seven wonders of the natural world.
Source: ARC Centre of Excellence