Great Barrier Reef's northern part is experiencing the worst coral bleaching, an aerial survey revealed.

About 500 coral reefs from Papua New Guinea to Cairns were found to be experiencing intense coral bleaching. The aerial survey led by Prof. Terry Hughes of the National Coral Bleaching Taskforce revealed that a vast majority of the coral reef has reached the most severe bleaching category.

"Almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef," Hughes shared.

His team flew over 400 kilometers (249 miles) in the most unspoiled parts of the reef and found that only four reefs are not affected by the bleaching.

Hughes said that this present bleaching is much worse than the bleaching events of 1998 and 2002.

"We haven't yet found the southern limit of the bleaching," Hughes shared. "We'll be conducting further aerial surveys this week in the central Great Barrier Reef to identify where it stops." The professor shared his concerns about the extent of the damage to the reefs.

If the extensive bleaching can be seen from the air, experts believe that damage should also be studied from the surface. At present, a number of research vessels and island research stations are also looking at the extent of coral bleaching via in-water research. The team is also looking at the species of corals that are affected by the bleaching.

"Scientists in the water are already reporting up to 50 percent mortality of bleached corals," said Hughes. "But it's still too early to tell just what the overall outcome will be."

James Kerry, National Coral Bleaching Taskforce Project Manager, shared that greater bleaching are more apparent in the massive corals.

"The fact that these hardy species have also turned white shows just how severe summer conditions have become on the northern GBR," Kerry lamented.

The National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch Coordinator, Dr. Mark Eakin said that Australia may lose half of the country's healthiest corals.

"It's the worst bleaching ever seen on what was the healthiest part of the Great Barrier Reef," Eakin said. "This won't be the end of the GBR but it is a huge amount of damage. The problem is that it can take decades for reefs to recover from bleaching this bad and severe bleaching is becoming much more frequent and more severe."

Richard Vevers, CEO of Ocean Agency, who is working with Google in taking high-resolution underwater survey of the damaged reefs in the world, said that the damage to the GBR is devastating that the reefs may have not be able to recover before the next one hits.

The team will continue to carry out underwater surveys in the coming months to further identify the impact of the mass coral bleaching.

This massive coral bleaching, according to marine biologists and oceanographers, is part of the longest ever recorded global coral bleaching as climate change continue to heat up warm waters.

This event is not exclusive to the GBR. Eakin shared that Florida was hit by coral bleaching for two years.

"Right now there is bleaching across half the southern hemisphere - literally! It spans from the coast of Tanzania in the west to French Polynesia in the east," Eakin added.

Experts believe that the massive bleaching is secondary to climate change and the effects of El Niño.

Abnormal environmental conditions like intensified sea temperatures cause corals to release small photosynthetic algae called "zooxanthellae." As the algae is expelled the once colorful algae turns white as if it was "bleached."

If the temperature drops, coral bleaching can still be reversed if the algae are able to recolonize the zooxanthellae. If not, the coral can die.

The latest coral bleaching is only one of the concerns of experts about the Great Barrier Reef as it continues to be greatly affected by severe pollution in the area. The presence of Crown of Thorns Starfish (CoTS) known to cause reef destruction is highly associated with high levels of inorganic nitrogen.

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