Report: Coral bleaching, disease link closer than thought

UM researcher discovers new information

The same oceanic temperature shifts that created Hurricane Katrina in 2005 also caused warm water to settle over parts of the Florida Keys, triggering mass coral bleaching that affected up to 90 percent of reef cover in the area.

Now, a study led by a University of Miami professor who studied the waters before, during and after Katrina has found that bleaching can make corals more susceptible to disease and, in turn, coral disease can exacerbate the negative effects of bleaching.

A paper in the October issue of the journal Ecology shows that when they occur together, this combination of afflictions causes greater harm to corals than either does on its own.

“Traditionally, scientists have attributed coral declines after mass bleaching events to the bleaching alone,” said Marilyn Brandt, a post-doctoral researcher at the UM’s Rosenstiel School of Marine and Atmospheric Science and the lead author on the paper.

“This study shows that the interplay between diseases and bleaching can play a much larger role than we realized.”

Brandt and her colleagues examined coral colonies in the Florida Keys before, during and after Hurricane Katrina to determine the relationship between bleaching and coral disease.

The researchers found that the coral diseases they saw were related to bleaching, but in different ways. The prevalence of white plague disease increased during the bleaching, which Brandt said may have to do with increased susceptibility to the disease.

Because diseases happen on a much finer scale than mass bleaching events, Brandt suggests that management of coral ecosystems should involve more frequent monitoring to determine the underlying causes of coral damage.

“Understanding how these different stressors interact can help explain the mortality pattern we see after large-scale bleaching events,” Brandt said. “If we understand what’s causing the mortality, we can institute control measures that are more specific to the causes.”