The coral die-off was indentified though monitoring by marine ecologists from the Wildlife Conservation Society based at New York's Bronx Zoo, Australia's James Cook University and Indonesia's Syiah Kuala University in Banda Aceh.
Following up on local reports of coral bleaching in the waters off the northern tip of the Indonesian island of Sumatra, the scientists determined from field studies completed in early August that 80 percent of some species have bleached and died since the initial assessment in May and more colonies are expected to die within the next few months.
Normal coral in the waters off Indonesia's Aceh province (Photos courtesy WCS)
Bleaching is a whitening of corals that occurs when colorful algae living within coral tissues are expelled. It is an indication of stress caused by environmental triggers such as sea surface temperature fluctuations.
The scientists say this event is the result of a rise in sea surface temperatures in the Andaman Sea - an area that includes the coasts of Myanmar, Thailand, the Andaman and Nicobar islands, and northwestern Indonesia.
The U.S. National Oceanic and Atmospheric Administration's Coral Hotspots website shows temperatures in the region peaked in late May, when the temperature reached 34 degrees Celsius (93 degrees Fahrenheit) - four degrees Celsius (7.2 degrees F.) higher than long term averages for the area.
"This is a tragedy not only for some of the world's most biodiverse coral reefs, but also for people in the region, many of whom are extremely impoverished and depend on these reefs for their food and livelihoods," said WCS Marine Program Director Dr. Caleb McClennen.
"Immediate and intensive management will be required to try and help these reefs, their fisheries and the entire ecosystem recover and adapt. However, coral reefs cannot be protected from the warming ocean temperatures brought on by a changing climate by local actions alone," said Dr. McClennen.
On Friday NOAA reported that global sea surface temperatures are still climbing. The combined global land and ocean surface temperature made this July the second warmest on record, behind 1998, and the warmest averaged January - July on record, the U.S. agency said.
The worldwide ocean surface temperature was 0.54 degrees C (0.97 degrees F) above the 20th century average of 61.5 degrees F (16.4 degrees C) and the fifth warmest July on record. Although the warmth was most pronounced in the Atlantic Ocean, the general trend affects the corals of the Andaman Sea.
"It's a disappointing development particularly in light of the fact that these same corals proved resilient to other disruptions to this ecosystem, including the Indian Ocean tsunami of 2004," said WCS Indonesia Marine Program Director Dr. Stuart Campbell.
Surveys conducted in the wake of the Indian Ocean tsunami revealed that the many reefs surrounding Aceh were largely unaffected by this massive disturbance.
Bleached coral off the coast of Aceh Province. Stressed by rising ocean temperatures, the coral has expelled its algae.
Scientists found that reefs damaged by poor land use and destructive fishing prior to the tsunami had recovered due to improved management. Government and community-managed areas in the region have been remarkably successful at maintaining fish biomass despite ongoing access to the reefs.
But the bleaching and mortality this year have reversed this recovery and will have a profound effect on reef fisheries, the researchers say.
NOAA indicates warming has affected the entire Andaman Sea and beyond. Similar mass bleaching events in 2010 have now been recorded in Sri Lanka, Thailand, Malaysia and many parts of Indonesia.
"If a similar degree of mortality is apparent at other sites in the Andaman Sea this will be the worst bleaching event ever recorded in the region," said Dr. Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies at James Cook University. "The destruction of these upstream reefs means recovery is likely to take much longer than before."
NOAA reported Friday that the combined global land and ocean surface temperature made this July the second warmest on record, behind 1998, and the warmest averaged January-July on record.
The global average land surface temperature for July and January - July was warmest on record.
The global ocean surface temperature for July was the fifth warmest, and for January - July 2010 was the second warmest on record, behind 1998.
Dr. McClennan warned, "This is another unfortunate reminder that international efforts to curb the causes and effects of climate change must be made if these sensitive ecosystems and the vulnerable human communities around the world that depend on them are to adapt and endure."
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