Scientists say although many of the reefs are badly damaged, corals have evolved to cope with tsunamis and other natural disasters. Photo / AP

Scientists say although many of the reefs are badly damaged, corals have evolved to cope with tsunamis and other natural disasters. Photo / AP

Scientists surveying American Samoa's coral reefs say the September 29 tsunami obliterated some corals and damaged others to the point that they may not recover.

Researchers say more assessments will be needed to get a full sense of how the disaster affected coral in the United States territory.

But in at least one area, the damage was so severe, and the affected area in such bad shape before the tsunamis, that the coral may never return.

There's an additional threat the surviving coral may suffer secondary damage weeks after the tsunamis if waves drag heavy debris from people's wave-wrecked homes - such as refrigerators, tin roofs and other objects - across the reefs.

Mounds of household goods dislodged by the giant waves are still sitting in the water off devastated villages.

Corals, which are colonies formed by small, fragile animals called polyps, provide vital habitats for fish, sea slugs, prawns, sea worms and many other marine species that find food and take shelter among the reefs.

This makes measuring the extent of the tsunami damage important for understanding the disaster's effect on the broader environment.

Tsunamis generated by an 8.3-magnitude earthquake killed at least 32 people in American Samoa. About 150 were killed in nearby Samoa and Tonga.

A team led by Douglas Fenner, a coral reef monitoring ecologist with American Samoa's Department of Marine and Wildlife Resources, has surveyed about 20 sites around the territory so far. The condition of the coral examined ranged from untouched to destroyed. Several spots lost 20 to 30 per cent of their coral.

Fenner also found unblemished reef next to corals that were wiped out.

That was the case near Leone, a town where at least 10 people died and dozens of homes were destroyed.

He first saw that delicate corals to the village's left were in perfect shape.

"Then I got right in front of the village and man, the coral had just been broken to bits," Fenner said.

Paul Brown, a marine ecologist with the National Park Service, said the reef off Faga'alu - an urbanised area near Pago Pago, the capital - was in poor shape even before the tsunamis hit.

Years of pollution and sediment in the area's runoff had led to poor water quality offshore, deprived corals of the sunlight they needed to grow and smothered the reef.