Stony Coral Tissue Loss Disease FAQ
Beginning in fall 2014, an outbreak of the previously undescribed stony coral tissue loss disease started near Virginia Key, Miami. It spread north and south to impact nearly all of Florida’s Coral Reef and remains active to this day. By 2017 the disease had spread to the northern end of the reefs in Martin County, and by 2020 had reached southwest past Key West into the Marquesas. In May 2021 the disease was documented within Dry Tortugas National Park. While past outbreaks of other diseases have subsided during the cooler winter months, this disease has continued with no indication of seasonality and without any interruption from Hurricane Irma or other storm events.
As of mid-2021 most of the 330-mile Florida’s Coral Reef has been affected – over 109,700 acres from Martin County to the Lower Florida Keys. The western boundary of the disease front is currently in the southeast portion of Dry Tortugas National Park. Very little of Florida’s Coral Reef remains unimpacted (last updated June 2021).
Based on the area affected and the known density of corals across the habitats in this area, it is estimated that tens of millions of reef-building (i.e. stony) coral colonies have been killed.
Studies have shown the disease can be transmitted through the water column, from one coral touching another, or potentially through coral predators like butterflyfish and snails. The spread of the disease was relatively fast – up to 300 feet per day. The disease traveled with water currents and rode the Gulf Stream north, and in countercurrent coastal eddies south into Biscayne National Park and the Florida Keys. The disease moved generally in a linear fashion, although in the Florida Keys offshore reefs were infected before nearshore reefs.
Because scientists still aren’t sure what is causing the disease, it’s impossible to know how long it takes a coral to get infected after being exposed. The disease first impacts the coral on the cellular level before creating the visible lesions that are the hallmark of this disease. Once disease signs are observed on a colony, the more susceptible species are killed within weeks to months depending on the size of the colony; less susceptible species may succumb in months or a year. Once a coral is infected survival depends on the species – for some species like brain or maze corals, nearly all adult corals will likely die; for others like the star corals about half of the adult corals will die. Some colonies have also been successful in fighting off the disease with only partial colony mortality. Their ability to survive the disease with only partial mortality depends on the coral species.
Intervention efforts – actively finding ways to stop the disease on coral colonies - have also been successful in stopping or slowing the disease spread on specific coral colonies. Repeatedly treating infected corals with antibiotic paste has saved many corals throughout southeast Florida and the Florida Keys. The antibiotic paste is applied along the edge of disease lesions, sometimes with “fire breaks” between diseased and healthy tissue created with an underwater angle grinder. For a great story map about Intervention efforts, please see https://floridadep.gov/rcp/coral/content/reconnaissance-and-intervention-coral-disease-response-team.
Nearly half of Florida’s 50 stony coral species can be impacted by this disease. Among the most impacted species are those in the Meandrinidae and Faviidae families – the Endangered Species Act listed species Dendrogyra cylindrus (pillar coral), Dichocoenia stokesii (elliptical star coral), Meandrina meandrites (maze coral), Colpophyllia natans (boulder brain coral), Eusmilia fastigiata (smooth flower coral), and the brain corals in the Pseudodiploria and Diploria genera. These species are one of the first to succumb to SCTLD on an impacted reef and almost 100% of the adult colonies will die. Many of the species strongly impacted by coral are large reef-building species that are very important for reef structure. The loss of these species is changing the face of the reefs in the Florida Keys.
How coral species respond to the disease differs by 1) how early a coral starts exhibiting symptoms after the disease is found on the reef, 2) how fast the disease moves across a coral colony, and 3) how likely a coral from this species is likely to die.
Asterisks indicate a species listed under the Endangered Species Act.
Highly susceptible species (the first species to show symptoms on the reef; fast progression across the colony with 1 week to 2 months until death; high mortality):
Colpophyllia natans (Boulder brain coral)
Dendrogyra cylindrus (Pillar coral)*
Dichocoenia stokesii (Elliptical star coral)
Diploria labyrinthiformis (Grooved brain coral)
Eusmilia fastigiata (Smooth flower coral)
Meandrina meandrites (Maze coral)
Pseudodiploria strigosa (Symmetrical brain coral)
Pseudodiploria clivosa (Knobby brain coral)
Intermediately susceptible (start exhibiting symptoms about a month after highly susceptible species; slower progression over the colonies with months to years before death; lower mortality rate):
Montastraea cavernosa (Great star coral)
Orbicella annularis (Lobed star coral)*
Orbicella faveolata (Mountainous star coral)*
Orbicella franksi (Boulder star coral)*
Siderastrea siderea Massive starlet coral)
Solenastrea bournoni (Smooth star coral)
Stephanocoenia intersepta (Blushing star coral)
Unknown susceptibility (not enough data to categorize):
Agaricia agaricites (Lettuce coral)
Agaricia fragilis (Fragile saucer coral)
Favia fragum (Golfball coral)
Helioseris cucullata (Sunray lettuce coral)
Isophyllia rigida (Rough star coral)
Isophyllia sinuosa (Sinuous cactus coral)
Madracis arenterna (Pencil coral)
Mussa angulosa (Spiny flower coral)
Mycetophyllia spp. (Cactus corals)*
Scolymia spp. (Disk corals)
Corals not found on this list are rarely or never infected – including the ESA-listed Acroporids Acropora cervicornis (staghorn coral) and A. palmata (elkhorn coral).
Overall, we are seeing a sharp decline in the population of the susceptible species. In fact, larger colonies of some of the highly and intermediately susceptible species have disappeared entirely from certain reef sites. However, no coral except the pillar coral has completely disappeared from wide areas of Florida’s Coral Reef, and smaller individuals of all coral species remain largely unaffected by the disease.
Research led by FWC scientists had shown that corals first show symptoms internally, with no outward signs of the disease. The beneficial algae that lives in coral tissues and gives them their color – zooxanthellae – are the first to succumb to the disease. Nearby coral tissue cells start to rupture and die and this mortality can be seen by the naked eye when cell death reaches the outer edge of the polyps.
Stony coral tissue loss disease symptoms look different depending on the coral species, but tissue loss happens in all species. Tissue loss often appears on the edge of a colony first. It then spreads out radially from that initial point – and multiple infection points can happen on the same coral. These lesions can eventually fuse together as they move across the colony (e). Some species are completely overcome in a few weeks; in others it takes months or years to completely die. In some species, a band of bleached tissue separates the recently dead area from the rest of the colony (e). In still other species, the coral may discolor first, turning purple, before any outwardly evident tissue loss occurs (b).
In some species, the tissue loss moves across the colony fast. In this case, there will be wide areas of freshly exposed skeleton which is stark white (a, d). In other species, the tissue loss occurs more slowly, allowing time for turf algae to colonize the areas of skeleton that died weeks prior (e). The width of older dead skeleton vs recently dead skeleton tells scientists how fast the disease is moving across the colony. Lesions can have sharp (c) and/or irregular (d) borders of living coral tissue.
Coral bleaching and stony coral tissue loss disease are not the same thing. While bleaching is a stress response to higher water temperatures, coral diseases are generally caused by another organism – like bacteria, viruses, or fungi. Although we still don’t know for sure what pathogen is behind the stony coral tissue loss disease, bacteria is involved either as part of the primary or secondary infection.
Bleaching is usually a response to warm water. Corals have a mutually beneficial, or symbiotic, relationship with a type of algae known as zooxanthellae. Zooxanthellae live inside the coral and provide them with energy derived from photosynthesis, and the coral provides the algae with shelter. However, corals can tolerate only a relatively narrow temperature range and prefer water between 73-84 degrees, and water temperatures over 86 degrees or under 64 degrees can become stressful and eventually fatal for coral. When the water gets too warm, zooxanthellae release compounds to deal with the heat stress that are harmful to the coral, causing the coral to expel their zooxanthellae. Because these algae are what gives coral their color, when they are expelled it leaves the coral tissue colorless, giving them a “bleached” look. Although the coral is still alive, just colorless, they will eventually die from starvation if the zooxanthellae does not return.
Recently, massive, region-wide bleaching events have become more common in Florida. Six extensive coral bleaching events have affected the entire reef tract since 1987, with substantial mass coral mortality occurring during the global bleaching events of 1997/1998 and 2014/2015. Even beyond these major bleaching episodes, some level of bleaching is occurring nearly every year in the Florida Keys.
Although the stony coral tissue loss disease outbreak started in the same year as the 2014/2015 global bleaching event, scientists do not think temperature plays a large role in the spread of this disease. Research by FWC scientists have shown that the spread of the disease is independent of season or water temperature. However, high water temperatures and other stressors, like pollution and dredging activities, can weaken coral’s immune systems and leave them open to further illnesses, such as stony coral tissue loss disease.
Coral and disease scientists are studying tissue samples (just like a biopsy) to try to identify potential pathogens. Unfortunately, the disease agent(s) has not yet been positively identified, although recent research has indicated that bacteria within the groups Rhodobacterales or Rhizobiales may be the culprit. Another line of evidence pointing to a bacterial pathogen is that antibiotics have been effective in combating disease progression. However, it’s possible that bacteria is secondary to the true cause of the disease. Additionally, rather than a distinct disease agent, multiple factors or pathogens can contribute to coral disease, making the definitive causes of any coral disease outbreak challenging to determine. Investigation into the potential causes of the stony coral tissue loss disease outbreak is ongoing.
Coral disease investigations are tremendously complicated. Many factors contribute to disease rather than a single cause, so the definitive causes may remain largely unknown for years. Marine disease can even be driven entirely by changes in the environment. This makes it incredibly difficult to identify which bacteria, viruses, and fungi are involved and the role of environmental factors.
Starting from square one - Additionally, while human health and disease management have advanced rapidly in recent years, knowledge about coral diseases and control options are far less advanced. Looking at the microbiome of a coral – the tiny community of bacteria, fungi, algae, and other small critters that live in and around coral – is critically important in being able to identify disease pathogens. Although microbiome data has been collected for corals infected with this disease, we unfortunately have little data from before the outbreak happened to compare such findings to.
Despite the complications inherent with coral disease investigations, significant progress in stony coral tissue loss disease knowledge and treatment has been made. The tools and strategies being developed to study this disease can benefit other coral and marine disease research in the future.
Since 2015, the Florida Department of Environmental Protection (DEP) has led the coordination of numerous partners in an open and collaborative multi-faceted disease investigation and response effort. Partners include federal, state and local governments, universities, nongovernmental organizations, and the South Florida community. The FWC Coral Research Program became involved when it was evident the disease outbreak was spreading rapidly beyond its origination point in Miami. In Fall 2015, FWC started collecting tissue samples from infected corals to investigate what was causing the disease and how coral tissue was changing in response to it. In Summer 2016 the disease was found by the FWC Coral Reef Evaluation and Monitoring Project in the Upper Florida Keys. The reefs were surveyed and samples of diseased and seemingly healthy corals were collected at Grecian Rocks. In April 2017 divers collected additional tissue samples from Martin County and two sites in the Middle Florida Keys.
In 2018, the multi-agency response got more organized - ten teams were established to make sure all aspects of the disease response are being tackled. This includes research into the disease, tracking where the disease front is, treating sick corals, coral rescue, coral restoration trials, communications and outreach, and sharing information and research with other Caribbean countries experiencing stony coral tissue loss disease outbreaks. More than $16 million worth of projects have been funded to research and combat the disease, thousands of corals have been treated with antibiotic paste, and thousands more have been rescued from the reefs and kept safe in aquaria until the disease subsides. For more information on this massive collaborative effort, please see https://floridadep.gov/rcp/coral/content/stony-coral-tissue-loss-disease-response.
Since 2018, FWC has spearheaded the Coral Rescue Project, an ambitious plan to save Florida corals from the disease. Corals were moved from the reef and taken to aquaria around the country until the disease has subsided and it’s safe to release them and their offspring back into the wild. Learn more about the Coral Rescue Project.
For more information on Disease Response, please visit the Stony Coral Tissue Loss Disease page and select the “Disease Response” tab..
The FWC, Florida Department of Environmental Protection (DEP), U.S. National Parks Service (NPS) and U.S. National Oceanic and Atmospheric Administration (NOAA) are working with dozens of partners from federal, state and local agencies, non-governmental organizations, universities, and members of the community to research and respond to this problem. Partners currently include but are not limited to:
- Association of Zoos and Aquariums
- Broward County Environmental Protection and Growth Management Department
- Coral Restoration Foundation
- S. Environmental Protection Agency
- Florida Aquarium
- Florida Atlantic University - Harbor Branch Oceanographic Institute
- Florida Department of Environmental Protection - Office of Resilience and Coastal Protection, Florida Parks Service
- Florida Fish and Wildlife Conservation Commission - Fish and Wildlife Research Institute
- Florida Institute of Technology
- Florida International University
- Florida Keys Community College
- FORCE BLUE, Inc.
- Friends of Our Florida Reefs
- George Mason University
- Keys Marine Laboratory
- Martin County Public Works
- Miami-Dade County Division of Environmental Management
- Monroe County
- Mote Marine Laboratory
- National Oceanic and Atmospheric, Administration - Coral Reef Conservation Program, National Marine Fisheries Service, Coral Disease and Health Consortium, Florida Keys National Marine Sanctuary
- National Park Service - Biscayne National Park, Dry Tortugas National Park, South Florida/Caribbean Inventory and Monitoring Network
- National Science Foundation
- Nova Southeastern University - Halmos College of Natural Sciences and Oceanography, National Coral Reef Institute
- Oregon State University
- Palm Beach County Division of Environmental Resource Management
- South Florida Regional Planning Council
- Southeast Florida Coral Reef Initiative
- Smithsonian Institution
- The Nature Conservancy
- Treasure Coast Regional Planning Council
- United States U.S. Geological Survey - National Wildlife Health Center
- University of Florida
- University of Hawaii
- University of Miami - Rosenstiel School of Marine and Atmospheric Science
- University of South Florida
Absolutely! While the condition is urgent and timing is of the essence, it isn’t too late to save Florida’s incredibly important coral ecosystems. Even on reefs that have been within the disease outbreak area for years, there are many survivors, including colonies of some of the most impacted species. Given their incredible resilience and survival against multiple stressors over the years, these corals may be among the most important corals in the world for future restoration efforts.
It is also worth noting that while roughly half of Florida’s coral species are impacted by this disease, half are not. Two species of great importance to the entire Atlantic/Caribbean basin –staghorn coral (Acropora cervicornis) and elkhorn coral (Acropora palmata) – are not known to be affected and are still the focus of the groundbreaking propagation and restoration efforts that make Florida a leader in coral reef restoration.
Our response to the disease has already saved thousands of corals through intervention and rescue efforts. Rescued corals are now within captive breeding programs, increasing the number of corals we can outplant back onto the reefs when the disease subsides. The collaborative efforts undertaken in Florida are now at the forefront of global disease research and response. The knowledge gained here will help save Florida’s coral reefs but will also be instrumental in informing coral disease outbreak response activities around the world – including the greater Caribbean as they battle their own outbreaks of the disease.
Still, the immediate intervention and rescue actions are strictly triage; those efforts alone won’t ensure long-term survival of our corals if we don’t address why they died in the first place. We urgently need to reduce local and regional stressors and reestablish the correct environmental conditions offshore so our reefs can be healthy again. Reducing land-based sources of pollution, unsustainable fishing practices, and eliminating impacts from vessel groundings, anchors and marine debris have long been advocated for by reef scientists and managers. Priority actions include, but are not limited to:
Reducing nutrient pollution (nitrogen and phosphorus) to coastal waters (e.g., upgrading urban wastewater and stormwater infrastructure).
Reducing algae by restoring herbivore populations and smart management of reef fish
Minimizing turbidity, sedimentation and direct physical injury associated with coastal construction.
Reducing impacts of climate change, including warming waters, extreme weather events, and ocean acidification.
Coral reefs are truly natural treasures. They are one of the most diverse and complex marine ecosystems on Earth. Florida’s Coral Reef stretches for more than 330 miles along Florida’s southeast coast from Martin County to the Dry Tortugas. As the only barrier reef in the continental U.S., it is the crown jewel of Florida’s coastal resources, and home to countless reef-building corals, soft corals, sponges, fish, algae, sea turtles, and invertebrates.
- Florida’s Coral Reef protects our beaches and coastlines by reducing impacts from direct wave action and flooding. This protects infrastructure and economic activity along our coasts.
- Healthy coral reefs dissipate 97% of wave energy that would otherwise erode beaches. The larger a coral is, the more it reduces wave energy, which helps protect coastlines and valuable infrastructure from big waves and storm surge.
- Annually, reefs in Florida protect more than 5,600 people and $675 million worth of property and economic activity from flooding.
- Losing 3 feet/1-meter of reef height, would expose 24,000 more people and $2.9 billion in property and economic activity to flooding.
- Check out The Nature Conservancy’s Mapping Ocean Wealth website and see just how much Florida’s reefs protect our shorelines.
- South Florida’s economy relies heavily on sharing it’s reefs and beaches with people from outside the state.
- Florida’s Coral Reef annually supports 71,000 full and part-time jobs and generates $6.3 billion in combined local sales and income associated with snorkeling, scuba diving, fishing, and more.
- Over 38 million people visit South Florida each year – a number equal to the population of California!
Fishing and Seafood
- Florida’s Coral Reef provides habitat for many marine species that are valuable to commercial and recreational fisheries.
- Florida has the largest recreational fishery in the country and the 2nd largest seafood industry. Recreational fishing trips have an economic impact of $9.2 billion and support 88,501 jobs. Commercial fishing provides 80 million pounds of commercial food fish landings worth over $222 million in dockside value (FWC).
- Florida’s Coral Reef serves as a frontier for biomedical research -- we have a medicine cabinet just offshore.
- Medicine developed from coral reef organisms are already on the market, including treatments to combat cancer, viruses, pain, and inflammation.
Culture and Aesthetics
- The futures of millions of people in Florida are tied to the future of coral reefs. Sandy coastlines, made possible in part by coral reefs, are vital to the Floridian way of life.
- Reefs are intrinsically linked to the cultural identity of many coastal communities and islanders, both here in Florida and beyond.
- In Florida, the Keys have inspired Jimmy Buffett songs, Hemingway novels, the plays of Tennessee Williams, and the poetry of Shel Silverstein.
- Also, it’s GORGEOUS!