Coral changing color under the effects of a bacterial infection known as the white plague.

(Hunter Nolen/Florida Department of Environmental Protection)

At a Glance

The disease has affected at least 20South Florida coral species from the Middle Keys through Palm Beach County.Tissue loss disease is a bacterial infection that is often confused with coral bleaching.Corals already under stress from the same conditions that result in coral bleaching make them more susceptible to diseases.

A coral bacterial disease attacking reefs off Florida's southern coast has become the most extensive outbreak ever, a scientist says.

Greta Aeby, an assistant researcher at the University of Hawaii's Marine Disease Research Lab and a coral disease ecologist studying the disease at theSmithsonian Marine Station in FortPierce, Florida, told weather.com the "tissue loss disease" that is attacking Florida's reefsbegan in the Miami-Dade area in 2014 and has spread north into Martin County to the northern-most reefs and south down into the Keys.

Previously known as the "white plague," the disease expanded into the Lower Keys down to Looe Key this year.

According to information Aeby provided from the Florida Department ofEnvironmental Protection, nearly half, or 150 square miles, of Florida's reefs have been affected, and at least 20 of South Florida's 45 coral species from the Middle Keys through Palm Beach County have been infected with the disease that can mimic coral bleaching.

"When the coral gets sick, the animal (coral polyp) dies and sloughs off the colony leaving the white, bare skeleton behind which is quickly covered in sediment and other stuff," Aeby said.

According to the state agency, the tissue loss disease is a bacterial pathogen that is often confused with coral bleaching, whichisa stress reaction to a variety of factorsincludingnutrient pollution from runoff, dredging, which creates a lot of sediment, and heat stress from climate-driven warming seas.

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Tissue loss disease, on the other hand, is a that can spread from reef to reef. Corals already under stress from the same conditions that result in coral bleaching can make them more susceptible to diseases.

"Florida's coral reefs have been suffering from land-based sources of pollution (sewage, sedimentation, agricultural run-off) for decades and have been on the decline," Aeby said. "By 2002, one study reported losses of coral cover at some sites in the Florida Keys of 61 percent.And that was 16 years ago. So is the current outbreak connected to warming seas?Well, the main problem is the chronic stress humans are putting these corals under so when warming seas occur they don't have the energy to fight back."

Aeby added that the outbreak occurredafter two consecutive local stress events: dredging in the Miami areafollowed by a bleaching event.

"Perhaps if the corals had been in decent condition to start with, this disease outbreak might not have occurred," Aeby noted.

Earlier this year, William Precht,director of marine and coastal programs for the Miami consulting firm Dial Cordy and Associates, told WMNF that at least three species are nearly extinct.

“We lost 98 percent of the brain coral, Meandrina meandrites," he said in April. "We lost 97 percent of this starlet coral,Dichocoenia stokesi,and 93 percent of the large-grooved brain coral and so on and so on ... when you go out and swim on the reefs of Miami-Dade County today, it would be a very rare chance encounter that you would see some of these three or four species … which is really catastrophic."

Aeby says the situation is dire for Florida reefs.

"The reefs have already sustained a lot of coral mortality from this disease outbreak; and they had already lost so much coral from poor environmental conditions, other disease outbreaks, hurricanes andpast bleaching events," she said. "It does not look good for Florida's reefs."

Aeby said their only chance is the success of numerous agencies and universities, who are working together to come up with aplan to slow down the disease and mitigate it, as needed.

"Florida will become a model system on how to respond to massive coral disease outbreaks and it is hoped that other regions will recognize the threats from disease, especially tissue loss diseases, and proactively take steps to guard against this," Aeby said.