BANGKOK, Thailand - Southeast Asia's tsunami-ravaged coral reefs have bounced back with surprising speed, according to a study released yesterday, four years after the deadly waves hit.

The findings came as communities across the Indian Ocean remembered with prayers, songs and tears the disaster that struck Dec. 26, 2004. About 230,000 were killed in a dozen countries when a magnitude-9.0 earthquake triggered the tsunami.

Surveys of coral reefs after the tsunami showed that up to one-third were damaged, and experts predicted it would take a decade for them to recover fully.

Scientists from the New York-based Wildlife Conservation Society, working with the Indonesian government and the Australian Research Council Centre of Excellence for Coral Reef Studies, said their examination of 60 sites on 497 miles of coastline along Indonesia's Aceh province showed the reefs were bouncing back.

"On the fourth anniversary of the tsunami, this is a great story of ecosystem resilience and recovery," said Stuart Campbell, coordinator of the Wildlife Conservation Society's Indonesia Marine Program.

"Our scientific monitoring is showing rapid growth of young corals in areas where the tsunami caused damage, and also the return of new generations of corals in areas previously damaged by destructive fishing," Campbell said in a statement.

Healthy coral reefs are economic engines for Acehnese communities, Campbell added, supplying fish to eat and sell as well as tourism dollars from recreational diving.

The tsunami decimated coastlines across the Indian Ocean, wiping out villages, killing entire families, and crippling the economies in parts of Indonesia, Sri Lanka and Thailand.

The United Nations estimated that Aceh alone lost $332.4 million from the damage to its reefs.

But four years on, the multibillion-dollar rebuilding process is almost complete, with more than 120,000 homes built in Aceh and the reconstruction of tourist hotels and restaurants along Thailand's Andaman coast.

Thousands gathered yesterday to celebrate the progress but also to remember the dead and reflect on a tragedy that turned their lives upside down.

"I don't think people will ever forget the tsunami. It changed a lot of people's lives," said Alisara Na-Takuatung, a local Phuket radio disc jockey who took part in a ceremony on Thailand's Patong beach attended by 200 people.

About 50 Buddhist monks prayed while schoolchildren played traditional Thai instruments.

"I know people who lost their husbands, their kids," Na-Takuatung said. "Those people won't forget about the tsunami. They will see it as a lesson. You think about what you can do for others."

Ibrahim Musa, 42, a civil servant who lost his family, joined thousands in a prayer service in Aceh province.

"Even after four years, I cannot forget how I lost hold of my wife and baby," he said. "I have tried in vain to look for them for three years. Now I have no choice but to accept their departure as destiny."

Siti Hasnaini, 40, who still lives with her two sons and husband in a temporary shelter in Aceh, prayed for "my daughter, who was washed away with my house."

In India, where thousands also perished, interfaith prayers and a moment of silence were held.

The Sri Lankan government declared two minutes of silence for the 35,000 killed there as well as other victims of natural disasters.

The healing embraced by those devastated by the tsunami has extended to the reefs, with communities responding to calls to protect them from illegal fishing, pollution and coastal development.

Campbell said citizens had been particularly responsive in Aceh, where fishermen have stopped using illegal techniques like dynamite, and villagers have transplanted corals into areas that were hardest hit.