BANGKOK, Aug. 18 (Xinhuanet) -- Last year's tsunami had limited impact on coral reefs in the Andaman Sea, which is now more threatened by bleaching phenomenon, said Thai marine officials.

    "Marine scientists are no longer worried about the impact of the tsunami on coral reefs, which have recovered rapidly over the past six months," Bangkok Post on Thursday quoted marine official Ukkrit Satapoomin as saying.

    The overall extent of coral reef damage caused by the tsunami was far less than had been expected, said Ukkrit from Phuket Marine Biological Center under the Thai Ministry of Natural Resources and the Environment.

    Only five percent of the seagrass bed in the Andaman Sea was affected by the tsunami, according to a study, jointly conducted by the Phuket Marine Biological Center and marine biologists from nine Thai universities.

    From a total of 174 sites representing the principal area of coral reef in the region, up to 60 percent were either untouched, or had suffered very little damage.

    Only 23 sites were severely damaged, which meant that more than 50 percent of the coral had been damaged.

    Massive clean-up and coral recovery operations carried out after the tsunami proved to be effective for the restoration of coral reefs in the Andaman Sea.

    The Andaman Sea lying along Thailand's western coast is home toseveral coral reef sites, such as Phi Phi Island, Similan Islands and Surin Islands. All are famous diving sites for tourists.

    However, coral reefs at these sites are threatened by coral bleaching phenomenon.

    "We are concerned that the recovering reefs could be killed by the bleaching phenomenon which began in May 2005," said Ukkrit.

    The coral bleaching phenomenon have become an annual event for the Andaman Sea in the recent years.

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

    Warming of the oceans is believed to be main cause of bleachingphenomenon, during which an algae coexisting with the coral and giving it color is forced by higher water temperature to extract itself from the coral's shell.

    Certain areas of the Andaman Sea have been tested of an abnormal high ocean temperature of between 31-32 Celsius degrees, said marine scientists from the universities.

    Scientists have yet to find the reason of the higher ocean temperature.

    In 1998, an El Nino global coral bleaching event caused deaths of many coral reefs, a disaster occurring only once in 1,000 years,said the head of the World Conservation Union (IUCN) Global MarineProgram.

    The world largest conservation group IUCN also warned that the extreme events of 1998 will become a more regular event in the next 50 years. Enditem