Florida Reef


The Florida Reef is the only living coral barrier reef in the continental United States. It lies a few miles seaward of the Florida Keys, is about 4 miles wide and extends along the depth contour from Fowey Rocks just east of Soldier Key to just south of the Marquesas Keys. The system encompasses more than 6,000 individual reefs. Florida waters are home to over 500 marine fish and mammal species along with more than 45 species of stony corals and 35 species of octocorals.

Geography

The barrier reef tract forms a great arc, concentric with the Florida Keys, with the northern end, in Biscayne National Park, oriented north-south and the western end, south of the Marquesas Keys, oriented east-west. The rest of the reef outside Biscayne National Park lies within John Pennekamp Coral Reef State Park and the Florida Keys National Marine Sanctuary. Coral reefs are also found in Dry Tortugas National Park west of the Marquesas Keys. The reefs are 5,000 to 7,000 years old, having developed since sea levels rose following the Wisconsinan glaciation.
Isolated coral patch reefs occur northward from Biscayne National Park as far north as Stuart, in Martin County. In 2024, Florida created the Kristin Jacob Coral Aquatic Preserve to protect the reefs north of Biscayne National Park. The reefs north of Fowey Rocks are non-accreting relicts, with three reef lines. The outer reef line grew from about 10,200 BP until about 8,000 BP. The middle reef line grew from about 6,000 BP until about 3,700 BP. The inner reef line ceased growing about 6,000 BP.
The densest and most spectacular reefs, along with the highest water clarity, are found to the seaward of Key Largo and Elliott Key where the two long keys help protect the reefs from the effects of water exchange with Florida Bay, Biscayne Bay, Card Sound and Barnes Sound. The bays and sounds tend to have lower salinity, higher turbidity and wider temperature variations than the water in the open ocean. Channels between the Keys allow brackish water from the bays to flow onto the reefs, limiting their growth. Microstructural abnormalities in large benthic foraminifera from the Florida Keys indicate carbonate chemistry stress that is also consistent with long-term environmental decline on the reef tract A 2024 study found that the best habitat for Acropora palmata restoration occurs in areas with low chlorophyll‑a levels, moderate wave exposure, and stable salinity, including Biscayne Bay, the Upper Keys, western‑lower Keys, and Dry Tortugas, while conditions in the middle Keys are generally less suitable.

Reef structure and communities

The Florida Reef consists of two ridges separated from the Florida Keys by the Hawk Channel. Closest to the Keys is a sand ridge called White Bank, covered by large beds of sea grass, with patch reefs scattered across it. Further out to sea on the edge of the Florida Straits is the second ridge forming the outer reefs, covered by reefs and hard banks composed of coral rubble and sand.
Almost 1,400 species of marine plants and animals, including more than 40 species of stony corals and 500 species of fish, live on the Florida Reef. The Florida Reef lies close to the northern limit for tropical corals, but the species diversity on the reef is comparable to that of reef systems in the Caribbean Sea.
The Florida Museum of Natural History defines three communities on the Florida reefs. The hardbottom community lies closest to the Florida Keys and consists primarily of algae, sea fans and stony corals growing on limestone rock that has a thin covering of sand. The stony corals in hardbottom communities include smooth starlet coral, mustard hill coral, golfball coral, elliptical star coral and common brain coral. Hardbottom provides habitat for anemones, mollusks, crabs, spiny lobsters, seastars, sea cucumbers, tunicates and various fish, including grunts, snappers, groupers, Atlantic blue tang, Ocean surgeon and Great barracuda.
File:Montastraea annularis Molasses reef FL.jpg|thumb|Boulder star coral on Molasses Reef
Second is the patch reef community. Patch reefs form in shallow water, some in Hawk Channel and some on the outer reef, but mainly on White Bank between Hawk Channel and the outer reefs. Patch reefs start from corals growing on a hard bottom, but grow upward as new corals establish themselves on the skeletons of dead corals. Most of the structure of patch reefs is formed from star and brain corals. Other corals attach wherever there is an opening. Patch reefs may grow up to the surface of the water, and spread outwards. Dome-type patch reefs, found in Hawk Channel and on White Bank, are round or elliptical, and are generally less than three meters high, but may reach up to nine meters high. Dome-type patch reefs are surrounded by sand which is kept clear due to browsing by long-spined sea urchins and grass-eating fish. Linear-type patch reefs are found on the outer reefs, and are linear or curved. They occur in single or multiple rows, trending the same direction as the bank reefs on the outer reefs. Linear-type patch reefs often include elkhorn coral, which is rare on the dome-type patch reefs. As dead coral skeletons age and are weakened by the activities of boring sponges, worms, and mollusks and by wave action, parts of a patch reef may collapse. Patch reefs provide habitat for spiny lobsters and for many species of fish, including Bluehead wrasse, damselfish, Ocean surgeon, French and queen angelfish, white, caesar and spanish grunts, yellowtail and other snappers, redband and stoplight parrotfish, sergeant major, tomtate, trumpetfish, filefish, groupers, snappers, bar jack, great barracuda, pufferfish, squirrelfish, cardinalfish, and green morays.
Third is the bank reef community. Bank reefs are larger than patch reefs and are found on the outer reefs. Bank reefs consist of three zones. The reef flat is closest to the keys, and consists of coralline algae growing on fragments of coral skeletons. Further out to sea are the spur and groove formations, low ridges of coral separated by channels with sand bottoms. The shallowest parts of the spurs support fire corals and zoanthids. Starting at five or six feet deep, Elkhorn, star, and brain corals are the most important members of the community. Various types of gorgonians are also common. Beyond the spur and groove zone is the forereef, which slopes down to the deeps. The upper forereef is dominated by star coral. At greater depths plate-like corals dominate, and then as the available light fades, sponges and non-reef building corals become common. Bank reefs provide habitat for various fishes, including French angelfish, blue and queen parrotfish, Queen triggerfish, rock beauties, Goatfish, porkfish and snappers. The sand found around and in the Florida Reef is composed of shell, coral skeleton and limestone fragments.
In 2025, large‑scale planting of nursery‑grown corals began in the Florida Keys, aiming to expand restoration.These efforts involve growing corals in protected nursery environments until they are strong enough to be transplanted into degraded reef areas. Sediment analyses over time show a shift on the Florida Reef Tract, with coral debris tripling in the Middle Keys over a 37-year period, indicating major changes in reef framework production.
Other common species of hard coral found on the Florida Reef include Ivory Bush Coral, which is the dominant coral in the patch reefs along the Florida coast north of the Florida Keys, staghorn coral, lettuce coral, grooved brain coral, boulder star coral, great star coral, clubbed finger coral and massive starlet coral.

Individual reefs

Notable individual reefs in the Florida reef system include:
  • 9-foot Stake
  • Alligator Reef
  • Ajax Reef
  • Carysfort Reef
  • Cheeca Rocks
  • Coffins Patch
  • Conch Reef
  • Crocker Reef
  • Davis Reef
  • Dry Rocks
  • Eastern Dry Rocks
  • Eastern Sambo
  • French Reef
  • Grecian Rocks
  • Hen and Chickens
  • Looe Key
  • Marker 32
  • Molasses Reef
  • Newfound Harbor Key
  • Pacific Reef
  • Pickles Reef
  • Rock Key
  • Sand Key
  • Snapper Ledge
  • Sombrero Key
  • Tennessee Reef
  • The Elbow
  • Turtle Reef
  • Western Sambo

    Threats to the reefs

Coral reefs are among the most biologically diverse ecosystems on the planet, supporting approximately 4,000 species of fish and 800 species of hard coral per unit area, more than any other marine habitat. Their ongoing global decline affects ecological balance, as well as the social, cultural, and economic health of human communities. In Florida, coral reefs face several stressors, including overfishing, disease, rapid coastal development, and climate change. As of the late 2010s, scientists with the National Oceanic and Atmospheric Administration estimated that only about 2% of Florida's original coral cover remained, following decades of cumulative stress from pollution, overfishing, disease, and climate change. Animals known as polyps, which create the fundamental structure of a reef, die from ingesting tiny bits of trash floating throughout the ocean called microplastics. Overfishing is also threatening reef fish populations, which feed on the algae that will smother corals. Fluctuating ocean temperatures caused by global warming presents the largest threat to coral reefs.The sudden warming or cooling of the water stresses the corals, causing them to lose their nutrients and turn white, a process known as bleaching. With the destruction of these complex yet fragile ecosystems comes a wide range of global consequences such as extinction of marine species, endangerment to the fishing industries, and severe coastal erosion. Elevated nutrient enrichment and altered freshwater inputs, particularly from historical water-management practices affecting Florida Bay, have contributed to algal overgrowth and declining coral health on the Florida Reef Tract.
In common with coral reefs throughout the Caribbean and the world, the Florida Reef exhibits some signs of stress and deterioration. Precht and Miller state that the numbers of Elkhorn and Staghorn corals are declining to an extent that is unprecedented in several thousand years. Between 1981 and 1986, Staghorn corals declined by 96% at Molasses Reef. Between 1983 and 2000 at Looe Key, Elkhorn corals declined by 93% and Staghorn corals by 98%. A joint reef monitoring program conducted by the United States Environmental Protection Agency, Florida Marine Research Institute and National Oceanic and Atmospheric Administration recorded a loss of 6% to 10% living corals at 40 sampling stations from 1996 to 2000. Long-term monitoring of Florida's coral reefs has shown that stony coral recovery has been minimal in many regions, with some areas exhibiting no measurable regrowth for over 15 years due to repeated disturbances and chronic stressors.
Elevated temperatures can damage coral reefs, causing coral bleaching. The first recorded bleaching incident on the Florida Reef was in 1973. Incidents of bleaching have become more frequent in recent decades, in correlation with a rise in sea surface temperatures. In July 2023, recordbreaking early and rapid warming resulted in widespread coral bleaching and death. Rescue efforts, such as relocating corals to tanks or to deeper waters have helped some bleached corals recover. Oceanographer Jamison Grove at the NOAA stated that these efforts must be accompanied by reductions in greenhouse gas emission to save the reef. The Florida Aquarium and Florida Fish and Wildlife Conservation Commission have tested a protective device known as the "Coral Defender", which shields young corals from predatory fish and invertebrates. Early trials suggest that the device can significantly improve survival rates for nursery‑reared corals once they are placed in existing reefs. White band disease has also adversely affected corals on the Florida Reef. While hurricanes often can cause localized damage to Elkhorn and Staghorn corals, Precht and Miller state that the severe and widespread loss of those corals on the Florida Reef cannot be attributed to hurricane damage. In addition to coral loss, the degradation of Florida's reefs has led to the flattening of reef structures and a decline in fish populations, particularly in areas near intense coastal development, as the loss of habitat affects reef fish that rely on coral for food, shelter, and reproduction. Other possible causes of the losses of corals on the Florida Reef include epizootic diseases, eutrophication, predation, sedimentation, overfishing, ship groundings, anchor dragging, commercial lobster and crab traps moved by storms, pollution, development on the Keys, growing numbers of visitors to the Keys and the reefs and the growth of seaweed on the coral. In January 2010, the Florida Reef Tract experienced an extreme cold-water anomaly in which temperatures fell below 16 degrees C, which resulted in greater coral tissue morality than prior years. In recent years, considerable effort has been made to make corals resilient to rising temperatures. Researchers from the Florida Aquarium and the University of South Florida are collaborating on a new initiative to protect the Florida Keys' coral reefs. More than 1,000 juvenile elkhorn corals that have been genetically modified to resist environmental stress are being planted at seven locations in the Florida Keys. Before being planted, they are housed in specialized tanks to acclimate to the ocean's temperature. Only a few percentage may survive, but those that do can develop further in the future, according to Cindy Lewis, director of the Keys Marine Laboratory. NOAA's Mission: Iconic Reefs, aims to restore approximately three million square feet of coral habitat across seven key reef sites in the Florida Keys National Marine Sanctuary by the year 2040. The project includes large‑scale coral planting, removal of harmful algae, and long‑term monitoring to ensure restored areas continue to thrive in the future.
The long-spined sea urchin, which browses on seaweed on and around reefs, was sharply reduced in numbers on the Florida Reef in the 1980s. While populations of this sea urchin have somewhat recovered elsewhere, its numbers are still very low on most of the Florida Reef, with the exception of the Dry Tortugas. As a consequence, there has been no effective check of the growth of seaweed on reef corals. However, the severe die-off of Elkhorn and Staghorn corals occurred before the die-off of the sea urchins, so that the proliferation of seaweed following the loss of the sea urchins was not the cause of the die-off of the corals, but may be retarding recovery by the corals.
Researchers studying Florida's coral reefs have found that juvenile coral populations remain low even in areas where conditions appear suitable for growth. A major factor contributing to this is the widespread presence of thick, sandy algae mats, particularly in flat reef zones. These mats trap sand and form dense layers that make it difficult for young corals to attach and survive. Although fish that feed on algae are abundant and usually help maintain reef health by controlling harmful algae, they cannot remove the LSAT because the underlying silt blocks light and reduces oxygen levels, creating unfavorable conditions for coral larvae to settle. Furthermore, only certain algae species, such as crustose coralline algae, support coral recruitment, but these beneficial algae are scarce in these degraded reefs. Other algae types, like Dictyota, do not aid coral growth and may even hinder it. Recent ecological surveys show that following major disturbances, juvenile coral assemblages on the Florida Reef Tract exhibit a shift toward higher octocoral recruitment relative to stony corals. Studies of reef-building corals have shown that bacterial communities in Montastraea annularis can vary significantly across small spatial scales, which suggests complex microbial drivers of coral health and stress response Research in 2024 identified specific environmental factors that predict where Coral restoration is most likely to succeed. Applying these findings can help conservationists focus their efforts on areas with conditions most favorable for coral growth in turn, improving restoration success rates
Another threat to the Florida Reef is the ongoing rise in sea level. The sea level has risen almost six inches at Key West since 1913, and one foot since 1850. This rise in sea level increases the volume of water in Florida Bay significantly, and increases the exchange of water between the Bay and the water over the reefs. The lower salinity, higher turbidity and more variable temperature of the water from Florida Bay adversely affects the reefs. A continued rise in sea level would likely intensify the effect.
A perceived deterioration of the reefs became a concern in the 1950s. Early attempts to protect the reefs led to the establishment in 1960 of a protected area that became John Pennekamp Coral Reef State Park. The creation of Biscayne National Monument in 1968 protected the northern part of the Florida Reef. In 1990 the Florida Keys National Marine Sanctuary was established, bringing all of the Florida reef into federal or state protection.
Coral reproduction on the Florida Reef has drastically declined, with many species failing to produce new offspring in the wild due to low population density, disease, and environmental stress.