Scientists work together to solve a coral disease mystery in Florida Keys National Marine Sanctuary

By Elizabeth Weinberg

August 2018

The Florida Keys are known for their lush coral reefs and incredible biodiversity. Protected by Florida Keys National Marine Sanctuary, the Keys support more than 6,000 species of plants, fishes, and invertebrates – including more than 65 species of stony corals. But in the past few years, something has been targeting these corals.

scientist diving near coral
Scientists document stony coral tissue loss disease as it infects nearly two dozen stony coral species on the Florida Reef Tract. Photo: Nick Zachar/NOAA

In September 2014, researchers began noticing that certain stony corals along the Florida Reef Tract weren’t doing well. The Florida Reef Tract stretches approximately 360 miles in an arc along the Florida Keys and southeastern Florida. Off Virginia Key, in Miami-Dade County, corals were showing "small circular or irregular patches of white, exposed skeleton devoid of tissue," explains Dr. Andy Bruckner, research coordinator for Florida Keys National Marine Sanctuary. From there, the tissue would slough off, leaving the stark white skeleton exposed until algae colonized it. The disease, he explains, "radiates across the colony and outward."

This spells trouble for the reefs, and for the creatures and people who depend on them. The reefs of the Florida Keys provide food and recreational opportunities for residents and vacationers alike, and they can protect coastal communities since they serve as a buffer for hurricanes and other storms. So as Joanna Walczak, southeast regional administrator at the Florida Department of Environmental Protection puts it, "this is an all hands on deck situation, requiring an unprecedented effort and response."

Partners from universities, nonprofits, and government agencies have joined Florida Keys National Marine Sanctuary and the Florida Department of Environmental Protection to understand the disease and how it can be stopped. "This collaborative response effort is vitally important," says Sarah Fangman, Florida Keys National Marine Sanctuary superintendent. "The broad knowledge provided by all our partners working together has resulted in the development of a variety of interventions." Together, these partners hope to develop an effective treatment.

graphic showing the spread of the disease along the florida reef tract
Stony coral tissue loss disease has spread quickly since it was first identified in 2014. Image: Florida Department of Environmental Protection

An unprecedented ailment

From time to time, corals – like any other animal – become susceptible to diseases and pathogens. But stony coral tissue loss disease is proving to be unprecedented in terms of its range, duration, and deadliness for corals.

Since 2014, the disease has spread over 150 square miles, and nearly half of the stony coral species found on the Florida Reef Tract have been affected. That includes the primary reef-building species in Florida Keys National Marine Sanctuary, as well as five species that are listed under the Endangered Species Act. And this disease is often deadly, with a mortality rate of 66 to 100 percent. Once a coral begins to lose living tissue, it’s likely that the colony will die within weeks to months. The cause of the disease is still unknown, but evidence points to a bacterial pathogen that is transmitted by touch and water circulation.

Not all reef-building corals are susceptible. Two of the most-recognized and also among the most endangered species – staghorn and elkhorn coral – are not impacted. Additionally, not all susceptible species within the disease zone are affected, suggesting some may be more resilient.

three images showing the progression of the disease in a coral colony
Stony coral tissue loss disease progresses rapidly once stony corals are infected. This coral lost 60 percent of its living tissue over the course of roughly a month. Photos: Brian Reckenbeil/Florida Fish and Wildlife Conservation Commission

Collaboration is key

A disease like this requires a multi-pronged approach, with scientists working both to understand what the disease is and how they may be able to treat it. "NOAA scientists are working with partners to identify a pathogen that causes the tissue loss, better characterize transmission of the disease, and understand the patterns of spread throughout the reef and overall impacts of the disease," says Bruckner.

One step in the response is surveying: researchers need to know what kinds of corals are most affected by stony coral tissue loss disease and where affected corals are. Scientists are tracking where the disease is spreading, how many corals have been infected, how badly those corals are injured, and what impacts the disease is having on the broader ecosystem.

There is some good news. Coral is not a single animal, but rather a colony made up of thousands of identical, interconnected individuals. That means that if part of a colony dies, the parts that survive can continue growing.

Additionally, researchers are taking tissue samples to identify potential pathogens and how the disease is impacting corals. And by tracking environmental conditions like water temperature, water quality, and sedimentation, researchers hope to evaluate whether these factors may be influencing how susceptible to disease the Florida Keys corals are.

science diver surveying coral
A science diver surveys a patch reef in Florida Keys National Marine Sanctuary. Photo: Jim Abernethy

"Florida Keys National Marine Sanctuary scientists are also working collaboratively to develop effective treatments for infected corals to prevent the most important reef-building corals from dying," says Bruckner. Using antiseptics like chlorine and broad-spectrum antibiotics, scientists have been working to halt the spread of the disease. These measures are particularly crucial for corals like pillar coral, which is near extinction in Florida. With targeted delivery systems, these treatments should not impact the broader ecosystem, and researchers are carefully monitoring treatment sites.

Scientists have also created gene banks for pillar corals, and are working to expand this effort to other species. These banks preserve key genetic individuals of these species so that later, when a treatment has been found for the disease or it has subsided naturally, the corals could be propagated and transplanted along the reef. These and other experimental techniques may help preserve the reef in the face of this disease. "Restoration of the most resilient species of corals and the strongest genetic individuals of these species will be key to the future of reefs here in Florida," says Fangman.

scientist creating a trench filled with epoxy on a coral colony
A scientist creates a trench filled with chlorinated epoxy to treat a colony of mountainous star coral (Orbicella faveolata) impacted by stony coral tissue loss disease. Photo: Brian Walker/Nova Southeastern University

How you can help

It’s not just trained scientists who are on the scene: citizen scientists have also been helping with data collection. Volunteers with the Southeast Florida Action Network (SEAFAN) and Community-based Observation of Coastal Ecosystems and Assessment Network (C-OCEAN) have helped track healthy and unhealthy corals throughout South Florida. Anyone diving or snorkeling in the Keys can use SEAFAN, the state’s reporting tool, to describe what they are seeing and upload images.

Although some coral species within Florida Keys National Marine Sanctuary are suffering, the sanctuary remains an incredible place to visit and explore. The reefs still have many healthy corals and other marine life such as reef fish, sharks, turtles, and rays. When you visit, you can help corals maintain their resilience with just a few small actions. "All of us can be part of the solution and help shape a better future for the reefs of Florida," says Fangman.

When boating, use mooring buoys to avoid anchoring on and injuring coral structures. Make sure to pack out your trash: marine debris can hurt marine life and impact habitats. Using reef-friendly sunscreens that do not contain oxybenzone and avobenzone can also help. These compounds are lethal to coral reproduction even in very small amounts, so check your sunscreen’s ingredients list to make sure you’re not bringing toxins into the coral reef environment.

If you live in Florida, you can also help by reducing runoff into storm and wastewater drains. Plant rain gardens that capture runoff and allow it to filter naturally through the soil; design your yard with permeable surfaces like bricks, gravel, and mulch instead of asphalt or concrete; and consider installing a rain barrel to capture rainfall for later use. These actions keep fertilizers, pesticides, debris, and loose soil from draining into our ocean, where they can negatively impact wildlife like corals.

graphic showing land-based threats to coral colonies
By reducing land-based pollution, we can increase coral reef resilience in the face of this disease. Image: NOAA

If you’re a diver, you can play a direct role in helping to control the spread of this disease. Because this disease is likely spread by touch and water flow, cleaning your gear is essential. Be sure to properly dispose of your cleaning solution; never pour it back into the ocean.

While diving, practicing proper reef etiquette can also help. Make sure you’re not dragging your gear, and keep your buoyancy in mind. Knocking against the reef or touching corals can damage them, and risks transferring the disease from one colony to another.

Want to get more involved with protecting our coral reef? Join citizen science efforts like SEAFAN and C-OCEAN to document what you see when you visit your sanctuary. With a tourism-based economy where the majority of jobs in the Florida Keys are tied to the marine ecosystem, this coral disease outbreak affects residents and visitors alike.

"I believe that once people understand the seriousness of this issue, they’ll want to be involved, whether that is participating in marine debris cleanups, using reef-safe sunscreen and reducing runoff, or reporting coral condition for investigation," says Fangman.

Hope for the corals

Since this disease was first identified in 2014, scientists have diligently worked to respond to it and protect the coral reef habitat of South Florida. Still, it will likely take years to determine the exact cause of the disease. In the meantime, addressing other known coral stressors may help the corals’ ability to recover. Poor water quality, large amounts of sediment in the water, pollution, and other factors can make it more difficult for corals to survive. Mitigating these factors gives corals a better shot at fighting this infection.

Coral reefs, like those in Florida Keys National Marine Sanctuary, are among the most biologically-diverse, culturally-significant, and economically-valuable ecosystems on Earth. Stony coral tissue loss disease endangers industries and recreational opportunities like recreational fishing and scuba diving, and supporting the health of the Keys supports the health of these industries. By working together, we can help protect these magnificent reefs for generations to come.

cleaner gobies swimming over star coral
Cleaner gobies swim over star coral in Florida Keys National Marine Sanctuary. Photo: Steve Miller

Partners currently involved in the response effort include Broward County, Coral Restoration Foundation, Cry of the Water, Florida Aquarium, Florida Atlantic University, Florida Department of Environmental Protection (Florida Coastal Office, Florida Parks Service), Florida Fish and Wildlife Conservation Commission (Fish and Wildlife Research Institute), Florida Institute of Technology, Florida International University, George Mason University, Keys Marine Laboratory, Martin County, Miami-Dade County, Mote Marine Laboratory, NOAA (Coral Reef Conservation Program, National Centers for Coastal Ocean Science, Florida Keys National Marine Sanctuary), National Park Service (Biscayne National Park, Dry Tortugas National Park, South Florida/Caribbean Network), Nova Southeastern University/National Coral Reef Institute, Palm Beach County, Palm Beach County Reef Rescue, Southeast Florida Coral Reef Initiative, Smithsonian Institution, The Nature Conservancy, United States Geological Survey (National Wildlife Health Center), University of Florida, University of Miami Rosenstiel School of Marine and Atmospheric Science, and the University of South Florida.

Elizabeth Weinberg is the social media coordinator and writer/editor for NOAA’s Office of National Marine Sanctuaries.