By Jan TenBruggencate
Advertiser Columnist

Tropical corals may be more sensitive to disease when water temperatures rise, according to a Cornell researcher who works in tropical waters.

Drew Harvell, a professor of marine ecology, said she specializes in a specific fungal disease, Aspergillus sydowii, that attacks certain fan corals. A fungus of the same genus is known to attack humans, and shows up particularly as a lung infection in people with suppressed immune systems.

"We're pursuing the immune resistance of corals" and studying the possibility that the apparent increase in aspergillosis in corals could be associated with changes in the environment, which may damage coral immune response.

She said this fungal disease is a useful one for researchers, because it is one of the few coral diseases that can be grown and studied in laboratory tanks. One of her research associates is testing corals at different temperatures in the lab by inoculating them with aspergillus spores and studying whether they are damaged.

"We've had a lot of outbreaks in the last decade, and most scientists feel that the rate of coral disease is much higher than it was previously. But we don't have good baselines, so it's hard to say how much higher it is than it was," Harvell said.

There are several environmental factors that could be putting corals under stress. Among them are increased sedimentation and increased nutrient levels from runoff from the land. Diseases may also be spread from the land through runoff. Oceanic aquaculture can spread disease to wild species as well, she said.

But one of the fascinating areas of research is whether the warming of the world's climate, which has already affected many coral reefs in the form of coral bleaching, may be damaging corals in other ways, including reducing their ability to fight off opportunistic diseases.

Researchers already know that corals have a limited temperature range. It only needs to get a couple of degrees warmer than their standard high temperature, and they enter a stress stage in which the single-celled algae that live within reef-building corals are ejected. The corals live in symbiosis with the algae, each helping meet the other's food needs.

Since the algae give corals their color, the stressed corals can appear pale or "bleached" after such events. If the water stays hot enough long enough, corals can die.

"In a way, corals are the canaries in the coal mine for global warming," Harvell said.

Harvell and her husband, Cornell oceanographer Chuck Greene, will give a free lecture on global warming's impact on corals and on trends in oceanography at 7 p.m. Thursday at the Ohana Keauhou Beach Resort on the Big Island.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Contact him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.