"If this disease is as damaging as it appears it is, it might be prudent to try to control it," she said. But first, scientists will have to find out what's causing it.

The table coral affected is known to science as Acropora cytherea. It can form broad, oval platforms as much as 6 feet across. The species is not found in the main Hawaiian Islands.

Aeby said she took samples from the corals to be studied in laboratories. It's not known whether "white syndrome" is a bacterial or viral disease, or comes from some other source.

Aeby said she is satisfied that the coral death is not associated with reef animals that feed on corals.

White and brown patches on Northwestern Hawaiian Islands corals show signs of the mysterious "white syndrome" first noticed in 2003. Greta Smith Aeby

Aeby said the disease is spreading fast, particularly at French Frigate Shoals, where the state's largest beds of table coral are found. She saw none of it when she dove there in 2002.

"This is not a subtle disease. I was looking for disease that year and I didn't see it," she said.

She located a single diseased coral in 2003 and three in 2004. She returned this week from a monthlong research trip through the islands with the new NOAA ship Hi'ialakai, and found that five of six sites she checked there had the disease. She established permanent markers at the locations so she can return to the same coral heads in coming years to view their progress.

"We need answers," she said. "Does the disease progress and kill the corals? Does the coral stop it? Is water temperature or some other environmental factor associated with it?"

Aeby also is watching another oddity observed during the research voyage: certain corals were suffering bleaching. Reef corals under stress often eject the internal algae that help feed them and also give them their color. Without the algae, the corals weaken and can die if conditions don't change to allow the algae to repopulate the coral polyps.

There was a severe bleaching event in Northwestern Hawaiian Island corals in 2002, when warm temperatures, sunny days and calm winds heated the atoll waters during the late summer. This year's event is much less severe, but Aeby said it's worrisome that it was occurring in May when waters normally are well within the corals' normal temperature range.

"I didn't anticipate bleaching at all because the water was cold, but we have installed water temperature recorders, so we should be able to track changes in the future," she said.

Randy Kosaki, chief scientist on the Hi'ialakai's recent voyage, said that most previous research trips have been in the early fall, and that one of the reasons for this year's trip was to view the condition of the reefs during a different time of the year.

"It was a very minor bleaching event, but we were surprised to see it at this time of the year. But part of the reason for this cruise was to look at things temporally out of synch with what we normally do," Kosaki said.