Dying coral 'a wake-up call'
By Jan TenBruggencate
Advertiser Science Writer
A malady is killing off a small proportion of the table corals at French Frigate Shoals, a situation that has reef scientists wary.
Greta Aeby
The disease — or rather what coral experts believe is likely a disease — looks very much like something seen on Australian reefs, where it is called "white" syndrome. When it attacks, the light brownish-yellow color of live coral is replaced by the blinding white of unprotected coral skeletons. And if enough time passes, the dead coral is colonized by aggressive algae.
The white growths are tumors on a table coral at French Frigate Shoals. Scientists do not know the cause.
"The main point this Acropora outbreak tells me is that disease outbreaks can occur on Hawaiian reefs. Since, Hawai'i's reef are comparatively healthier than other systems, such as in Florida, we can be proactive and enact changes to ensure that our reefs remain that way," said coral researcher Greta Aeby, with the state Division of Aquatic Resources.
Aeby said she studied the same reefs in 2002 and saw no sign of the disease. This year, she and Fish and Wildlife Service reef expert Jim Maragos, working independently, saw it in several locations.
But so little is known about disease processes in the Hawaiian archipelago that researchers are unwilling to make too much of the finding.
"It may be that these things we see have always been there," said Jean Kenyon, a marine ecologist with the National Marine Fisheries Service's coral reef ecosystem investigation program.
However, experience in Florida waters, notably around the Florida Keys, suggests that coral disease has expanded aggressively in lock step with increased human activity there, although it isn't entirely clear whether that involves humans physically bringing new disease organisms into an area, or polluting its waters with fertilizer, mud and other materials, or through dredging or other actions.
The field of coral research is in its infancy, Aeby said. Scientists are reporting changes in the reefs they monitor but don't always know what the changes mean. The situation is even more clouded on the reefs of the Northwestern Hawaiian Islands because research there began only within the past few years.
"Before 2002, nobody had looked at disease on the Northwestern Hawaiian Islands at all. In 2002, I saw normal, low levels of potential diseases across populations of corals," but nothing that looked out of the ordinary, she said. She did notice an occasional tumor growing on table corals.
But this year, she noted something new.
On isolated populations of table corals, there was evidence of massive tissue loss, with only skeleton left behind. It appeared to be quite distinct from the tumors, although one colony had both tumors and the white splotches.
"The pattern of tissue loss seemed to spread out from the center of the colony," she said.
No one has yet done the laboratory tests that might identify a disease organism, and it's not clear whether it would be immediately recognized if tests were done.
"Very few of the things that cause coral disease have been discovered," Aeby said.
The "white" disease only appears to occur on the table coral Acropora cytherea, which is common on the reefs at French Frigate Shoals, but is not found in the main Hawaiian Islands.
Aeby said the disease does not appear to be associated with areas that suffered coral bleaching last year — perhaps because of unusually warm water temperatures on the reefs. It does appear to occur in area where the table corals are extremely dense.
"These are large, mature corals, and I don't know where it's going. This is a wake-up call to take care of these reefs. They are not immune from harm," despite being distant from the main Hawaiian Islands, she said.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
