More than 90 percent of Australia’s Great Barrier Reef has been hit by mass coral bleaching, a new survey shows. While bleached corals are not dying, they stop growing at a normal rate and cease being a valuable natural habitat for other marine species.
According to data released by the National Coral Bleaching Taskforce, 93 percent of the Great Barrier Reef is affected by bleaching. Coral bleaching is a direct consequence of climate change and happens when corals expel the algae living inside, the flagellate protozoa, which sustain corals by providing them with food. The phenomenon happens when the corals are exposed to stressful conditions, such as temperature variations of even a few degrees above normal ones.
The result of coral bleaching is devastating, as it leads to loss of habitat for many of the organisms living in coral reefs. Stretching over 1,400 miles, Australia’s Great Barrier Reef is the world’s largest coral reef system. However, according to a 2012 survey, it has lost half its surface, compared to 1985. Now, due to the mass coral bleaching event affecting it, the Great Barrier Reef has slowed down its growth. According to scientists, bleached corals do not die off completely, but dramatically slow down their growth rate and resume the normal growth pace only then the protozoa return.
While all corals are vulnerable to rises in water temperatures of even one degree Celsius, not all respond the same way. Studies show that Porites, a type of stony coral, for example, are more resistant to temperature variations, while smaller, polyp stone corals such as Acropora are much more sensitive.
University of Queensland’s Professor Justin Marshall likened the current mass coral bleaching event to an environmental disaster, the biggest ever affecting Australia. According to him, coral bleaching events and man-induced climate change are “irrevocably” linked. As a result of the current event, considered the longest the planet’s coral reefs have ever been exposed to, a large part of them will be lost. Referring to the state of the Great Barrier Reef, Marshall concluded that, although regrowth is possible, the reef system will not return to the state it was in just six months ago in his lifetime. Coral regrowth is similar to that of a forest, however, in the case of corals regeneration depends on a multitude of factors which cannot be controlled, the most important one being water temperatures.
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