Mass bleaching has killed 35 percent of the coral in the Great Barrier Reef in Australia, the world’s largest coral system, according to a report released on Monday.
Experts from James Cook University’s ARC Centre of Excellence for Coral Reef Studies made analyses by air and submarine of the impact of bleaching in the ecosystem, which stretches 2,300 km off the country’s northeastern coast, EFE news reported.
Corals have a special symbiotic relationship with the microscopic algae called zooxanthellae, which provides them with oxygen and a portion of the organic compounds produced through photosynthesis.
When subjected to environmental stress, many coral reefs expel their zooxanthellae en masse, and coral polyps are left without pigmentation appearing almost transparent on the white skeleton of the animal, a phenomenon known as bleaching.
Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues.
Results indicated that the worst affected area is located off the coast of Townsville and Papua New Guinea, while in the region located south of Cairns, the average mortality is 5 percent.
“Fortunately, on reefs south of Cairns, our underwater surveys are also revealing that more than 95 percent of the corals have survived, and we expect these more mildly bleached corals to regain their normal colour over the next few months,” Mia Hoogenboom of James Cook University said in a statement.
The researchers also found that in Kimberley, north of Cairns, 80 percent of the coral has been severely affected by bleaching and at least 15 percent have died.
The director of the reef studies centre, Terry Hughes, said this year is the “third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we’ve measured before.”
Hughes explained that the three events of coral bleaching that occurred in the last 18 years coincide with the one degree Celsius rise in temperature above that recorded in the pre-industrial period.
In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centred around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.
Not all bleaching events are due to warm water. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death.
The health of the Great Barrier Reef, home to 400 types of coral, 1,500 species of fish and 4,000 types of molluscs, began deteriorating in the 1990s owing to warming sea water and an increase in its acidity through the increased presence of carbon dioxide in the atmosphere.