Bleaching emerges as major coral threat

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The phenomenon of coral bleaching is emerging as the leading threat to coral reefs in the Andaman Sea, just as they recovered from the effects of last December’s tsunami, marine biologists warned.

”Marine scientists are no longer worried about the impact of the tsunami on coral reefs, which have recovered rapidly over the past six months,” said Ukkrit Satapoomin of the Phuket Marine Biological Centre (PMBC).

”But we are concerned that the recovering reefs could be killed by the bleaching phenomenon which began in May 2005,” he told a meeting of leading marine biologists on the post-tsunami marine ecosystem.

The PMBC comes under the Ministry of Natural Resources and the Environment.

Scientists believe the main cause of coral bleaching is the warming of the oceans, which forces zooxanthallae, an algae which coexists with the coral and gives it colour, to extract itself from the coral’s shell.

Many coral reefs in the Andaman Sea have now turned a pale yellow, pink or white colour and have gradually died off.

Mr Ukkrit said the destructive impact of the tsunami on the reefs was far less than has been caused by coral bleaching, which has become an annual event in Thai waters over recent years.

According to a study on the impact of the tsunami on the marine ecosystem, jointly conducted by the PMBC and marine biologists from nine universities, the overall extent of coral reef damage caused by the tsunami was far less than had been expected. Only 5% of the seagrass bed in the Andaman Sea was affected by the tsunami, it noted.

From a total of 174 sites representing the principal area of coral reef in the Andaman Sea, up to 60% were either untouched, or had suffered very little damage. Only 23 sites were severely damaged, which meant that more than 50% of the coral had been damaged.

The Dec 26 tsunami caused coral reefs to turn over, break and collapse on sliding sandy slopes. Some was smothered by sand sediment or covered with debris or garbage generated by the tsunami.

Ranong, the west coast of Phangnga, Koh Phi Phi, Surin and the Similan Islands suffered particularly badly from the effects of the tsunami on their coral populations.

Some coral lines in these areas were also found to have been infected by diseases which could not be identified. They are thought to have been generated by the discharge of wastewater.

The researchers noted that the massive clean-up and coral recovery operations carried out by state agencies and volunteer divers had contributed to the rapid restoration of coral reefs and seagrass beds. Most of the staghorn coral wrecked during the tsunami has already regenerated fresh branches that are up to 5-6 cm in length.

Shettapong Meksumpun, of Kasetsart University’s faculty of fisheries, said a recent survey he had conducted of coral reefs off Ranong province had found that a wide range of reefs had been badly hit by coral bleaching. The seawater temperature in the area was between 31-32C, which was extremely high, he said.

”Coral bleaching is caused by rising sea temperatures, but scientists are still searching for the cause of unusually high sea temperatures. We are also studying whether or not it is a result of the tsunami.”

Niphon Phongsuwan, PMBC’s coral expert, meanwhile, called on the National Park, Wildlife and Plant Conservation Department to impose a ban on tourism in severely-damaged diving sites before the high season begins at the end of November.

”This recovery period is … crucial for the survival of reefs damaged in the tsunami. Any activity that may disturb the recovery must be strictly prohibited,” he said.

Kasetsart University marine biologist Thon Thamrongnawasawat proposed that diving sites at Torilla island in Mu Koh Surin marine national park, Koh Koa in Mu Koh Similan, Koh Pai near Phi Phi island, and Koh Rok off Krabi province be closed to allow for coral rehabilitation.

Source: Bangkok Post