Mara Skadden knew something was wrong when the leaves suddenly turned yellow.
Hundreds of young mangrove trees at a Brevard County plant nursery that had looked healthy days earlier were droopy and weak.
Within days, Skadden said, nearly 400 died.
“It was very, very fast,” said Skadden, the director of science at the restoration nonprofit Marine Resources Council. “To be honest, I thought my plants weren’t getting enough nutrients. But the fact that they were dying at an unprecedented rate made me think something else was going on.”
She contacted researchers at the University of Central Florida, who took samples in February. The culprit, their analysis found, was a co*cktail of disease-causing fungi that scientists have identified in several countries across the globe, from Vietnam to Colombia.
In 2019, researchers found the pathogen in Miami mangrove trees, the first known report in the United States. Now, scientists are finding trees infected with the fungi along the Indian River Lagoon on Florida’s east coast, according to Melissa Deinys, a University of Central Florida research assistant who specializes in mangrove infections.
The pathogen may be more widespread than what current data shows because it can lie dormant in healthy trees. Deinys and her team have tested wild populations for the fungus species, and Florida’s wildlife agency said the university’s research team has found it in 80% of leaves tested in Southeast Florida.
Deinys said she also has received pictures of plants from Venice and the Panhandle that look infected, and reports from Sarasota make her think it’s likely in the Tampa Bay area, too.
In a mangrove tree, the fungi acts like chicken pox or shingles: It lurks until it’s stressed — then the symptoms begin. In the case of red, white and black mangrove species, that usually means curled leaves, dark spots, stem lesions and fallen leaves.
The fungus doesn’t mean wild mangroves will die, but it could start to kill the plants if they are already stressed, according to state wildlife spokesperson Jonathan Veach.
The disease could be yet another setback for a plant species that serves as Florida’s natural line of defense against sea-level rise, flooding and storm surge. In Florida, mangroves already face a range of threats, from habitat loss to hurricane damage.
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Explore all your optionsAs the burning of fossil fuels intensifies global climate change, scientists including Deinys say more climate-related stressors, like stronger hurricanes, could speed up mangrove die-offs if plants are infected with the pathogen.
“As the ecosystem starts changing, we need to change with it,” Deinys told a room full of scientists in Palm Bay on May 3 during a meeting about the mangrove fungi.
“As these diseases are becoming more prevalent … we need to start looking out for them and coming up with solutions. (Mangroves) take a long time to grow, and we don’t have a very long time to save them.”
Disease poses a threat. But likely not the biggest one.
One solution is already being tested.
In the weeks after the mangrove die-off at the Marine Resources Council’s nursery, the nonprofit entered into an agreement with the University of Central Florida to test a treatment, records show.
The treatment, a liquid concoction created by the university, essentially tricks the mangrove into sucking up microscopic particles that contain an anti-fungal treatment.
“It’s a treatment, not a cure,” Skadden said.
Florida’s Department of Agriculture and Consumer Services has approved the transfer of sick mangroves into a greenhouse for testing, according to Kathy Mears, who is the chief of staff for the agency’s commissioner, Wilton Simpson. That’s a signal to mangrove planters the treatment is on the state’s radar, and it is watching the pathogen’s potential spread.
The blend of fungal species causing the disease can likely be transmitted through air, water and insects, according to the Marine Resources Council. Younger plants are more susceptible than older mangroves. And the disease can infect other native, coastal Florida plants, including sea grapes and buttonwoods, Deinys said.
It’s still not clear why mangroves at the council’s plant nursery were susceptible to the pathogen.
Deinys thinks an insect may have triggered the pathogen to emerge, while Skadden suggests it could have been temperature or high winds.
Not all nurseries are showing signs of the pathogen. In West Palm Beach, for example, the conservation clothing company Mang houses about 26,000 mangrove plants for restoration projects.
Mang’s chief restoration officer, Keith Rossin, said he isn’t seeing widespread signs of the pathogen at the company’s nursery. Rossin attended the session May 3 and said, based on how easily the pathogen can spread, he’s confident it is already in other mangroves across the state.
Plant growers should focus on limiting stress on mangroves that can allow the pathogen to take over the plant, paying close attention on fostering healthy growing conditions in the wild, Rossin said. Poor water quality, human development, boat traffic and hurricanes can stress mangroves.
“Historically in Florida, humans have been the No. 1 cause for mangrove destruction,” Rossin said.
Lorae Simpson, a biologist who has studied mangroves for about 15 years, said while it’s important to monitor the pathogen’s spread, it probably won’t become the biggest mangrove killer in Florida. That will likely continue to be habitat degradation and destruction.
“It’s something to watch, but this isn’t going to kill all of our mangroves,” Simpson said. “In a healthy system, these plants can regulate the pathogen. That’s why it’s important for us (when restoring mangroves) to maintain diverse and resilient habitats.”
Mangroves under stress
Researchers are trying to piece together why the plants at the Palm Bay nursery died while others haven’t.
Plant pathogens can be common in the wild and in agricultural nurseries. Because they flare up when a plant is stressed, it can be difficult to pinpoint the cause of death when a plant shrivels and dies, Veach said.
The mangroves in Florida’s Indian River Lagoon are indeed under a lot of stress, according to Candy Feller, an insect and plant ecologist with the Smithsonian Institution. Feller has studied mangroves for decades and has witnessed their decline throughout Florida, she said.
In the 156-mile-long lagoon, nutrient pollution from fertilizer runoff, leaky septic tanks, Lake Okeechobee discharges and other pollutants have all created a difficult environment for mangroves to thrive, she said.
Because the pathogens can be carried between the wild and nurseries, they may hinder mangrove conservation and restoration efforts, Calvin Kang, a mangrove ecologist at the University of Florida, wrote in an email. More work needs to be done to determine how the fungi could respond to a planet warming from climate change, he said.
“Understanding how pathogens spread among mangrove populations and how to control them is crucial for safeguarding Florida’s mangrove coastline,” Kang said.
How you can help
Scientists are looking for more reports of this mangrove pathogen in the wild. If you see a tree that may be experiencing disease or showing symptoms, email the location and photographs to mangroveprotection@outlook.com
