Coral bleaching once more centre stage

Posted: 15 July 2008

During the 9th International Coral Reef Symposium (ICRS) in Bali, Indonesia, coral bleaching was one of the main topics discussed by experts. Now, eight years later, coral bleaching has again taken centre stage in the current Florida symposium - the 11th after the Okinawa symposium in 2004. Coral bleaching, like global warming, is a phenomenon that can no longer be ignored.

In 2005, the world experienced the hottest year, which exceeded the previous nine record years, including 1998. The warm water temperatures caused large-scaled coral bleaching as "a stress response."

"Bleached coral were effectively starving and susceptible to other stresses including diseases," wrote Dr. Clive Wilkinson and Dr. David Souter in their executive summary for the newly-released, Status of Caribbean Coral Reefs After Bleaching and Hurricanes in 2005. "As a result, many coral reefs died."

Bleached corals, Great Barrier Reef
Bleached corals, Great Barrier Reef
Bleached corals on southern Great Barrier Reef. Photo © Ove Hoegh-Guldberg, University of Queensland
In Brazil, the first coral bleaching was reported "but it was minor." In June, bleaching reports came in from Colombia and Puerto Rico. By July, the bleaching extended to Belize, Mexico and the US Virgin Islands, where it affected "between 25 per cent to 45 per cent of coral colonies."

By August, mass coral bleaching were reported from Florida, the Cayman Islands, the northern Dutch Antiles (St. Maarten, Saba. St. Eustatius), the French West Indies (Guadeloupe, Martinique, St. Bathelemy), Barbados, Jamaica and Cuba. "Bleaching in these countries was generally severe affecting 50 per cent to 90 per cent of coral colonies," Wilkinson and Souter wrote.

Corals grow in the warm waters, but many of them are near the limits of their tolerance for high temperatures. Bleaching is a breakdown of a "complex biological system" that corals have evolved in order to survive. Each coral formation is a colony of hundreds or thousands of tiny organisms (known as polyps) that jointly build a skeleton that forms the reef. The outside layer of each coral polyp is inhabited by tiny one-celled plants scientists called zooxanthellae. It is these organisms that give the coral its bright colors, and when expelled due to warmer water or some other stress, coral appears bleached (that is, go pale or snowy-white).

Poor recovery

Without zooxanthellae, the coral cannot survive for long. "Corals tend to die in great numbers immediately following coral bleaching events, which may stretch across thousands of square kilometres of ocean," explained Dr. Ove Hoegh-Guldberg, who has studied the phenomenon of coral bleaching since the early 1980s.

Damaged coral reef
Damaged coral reef
This reef shows signs of erosion and bleaching. Photo © Ove Hoegh-Guldberg, University of Queensland.
Their report on the Management of Bleached and Severely Damaged Coral Reefs traced coral bleaching as far back as 1870. However, since the 1980s, bleaching events have become more frequent, widespread and severe.

In a press conference, Dr. Douglas Fenner, a professor of the Johns Hopkins University, reported of "a widespread annual summer mass coral bleaching" happening in American Samoa since 2003.

"I have observed the phenomenon every summer in the last five years," he said. "A few of the corals died and some were close to death after the bleaching." Only a fraction survived.

What alarmed him is the fact that after the global mass coral bleaching that occurred in 1998 after the El Niño phenomenon, some coral reefs were able to recuperate. But with summer bleaching, there is no time the corals could recover. "The future (for coral reefs) does not look good," he warned.

Algal partners

But there are some good news. Dr. Andrew C. Baker, who has recently been awarded the prestigious 2008 Pew Fellowship in Marine Conservation, is planning to develop novel and groundbreaking techniques to enhance the thermal tolerance and help them survive dangerously warming oceans around the world.

Dr. Baker's initial breakthrough discovery that reef corals may be able to withstand climate change by switching algal partners was published in the journal Nature and hailed by Discover magazine as one of the "Top 100 Science Stories of 2001."

All over the world, coral reefs are facing death. Before it is too late for the world to wake up one day without coral reefs, Dr. Simon Donner urged that something must be done now. He compared the international community to that riding on a big ship like Titanic heading for oblivion.

"We have to do hit the break to slow down from moving to hit the iceberg," urged Dr. Donner, a Canadian scientist based at the University of British Columbia. "We have to find something to lessen the impact of coral bleaching and other stressors from destroying the coral reefs."

Henrylito Tacio is an award-winning journalist, based in the Philippines, and a contributing editor of this website. See more of his reports from the 11th International Coral Reef Symposium in the Coasts and Oceans section.