Florida Keys coral reef

Category: Marine and Oceanic Biomes.

Geographic Location: North America.

Summary: North America's only coral barrier reef features a rich biota; its attractiveness to human activities must be balanced against the limits and requirements for the health of the habitat.

The Florida Keys is a 158-mile (254-kilometer) chain of keys or islands that begins south of Miami on the Florida mainland, and ends at the Dry Tortugas group at the westernmost tip of the chain. About 6 miles (10 kilometers) offshore, and paralleling the keys, is North America's only coral barrier reef: a natural wonder that supports tourism and commercial fishing industries even as it has declined in terms of ecosystem health. There are few if any other coral reefs in the world so close to such a heavily populated area. The barrier reef here extends 220 miles (354 kilometers) from North Key Largo to the Dry Tortugas.

Biologic Diversity

Coral reefs are among the most biodiverse ecosystems, rivaling even the tropical rainforests. The Florida Keys Coral Reef biome is home to over 80 species of corals and 600 species of fish. This interdependent ecosystem boasts stony and soft corals, fish, sponges, anemones, jellyfish, snails, crabs, lobsters, rays, eels, conch, sea turtles, dolphins, and seabirds among its richness. Together with mangroves and seagrass beds, one-third of Florida's threatened and endangered species call the reef home.

The Florida Keys coral barrier reef is characterized by spur and groove formations, or linear coral formations flanked by sand channels, in waters 3 feet to more than 100 feet (1 meter to more than 30 meters) deep. Patch reefs also grow in shallow waters on both sides of the keys. Typical stony coral types include brain, star, staghorn, elkhorn, and pillar. These reef-building creatures create rigid limestone exoskeletons, or corallites, that protect the living polyp within.

Soft corals, or gorgonians—such as sea fans, sea whips, and sea rods—are also abundant in this biome. These filter feeders sway with the ocean currents; they lack an exoskeleton, although they contain tough and spiky skelites that give them rigidity and help them anchor to and build up reefs.

Common reef fish here include edible species such as grouper, yellowtail snapper, grunt, hogfish, and barracuda. Tropical fish are numerous, among them angelfish, beau gregory, blue tang, butterfly fish, cowfish, damselfish, drum, parrotfish, porcupine fish, sergeant major, trunkfish, and trumpetfish.

Living Animals

Corals are comprised of millions of tiny animals, coral polyps, that form massive colonies. They grow by producing buds that create new layers above the skeletons of older ones. Corals also reproduce during an annual spawning event that occurs in August after the full moon in the Florida Keys. Polyps eject sperm, and others eject eggs into the water that join and then eventually recruit on hard substrate to form new colonies. Corals grow slowly—typically, a half-inch (13 millimeters) per year. One exception is elkhorn, a branching coral that grows up to 6 inches (152 millimeters) every year. Once abundant in the Florida Keys, elkhorn is now an endangered species.

Corals are scientifically classified in the phylum Cnidaria. They are characterized by their tentacles, with nematocysts or stinging cells to feed and defend themselves; a central digestive cavity for food; and radial symmetry. Coral polyps extend their tentacles at night to feed, especially on zooplankton, while during the day, the polyps retract.

Zooxanthellae is an algae that lives within the coral in a symbiotic relationship, giving it color and using photosynthesis to produce 90 percent of the food for the coral while assimilating waste products. Corals require clear, clean, tropical waters with temperatures of 75–85 degrees F (24–29 degrees C). Growth stops when temperatures exceed 90 degrees F (32 degrees C). They also have trouble when temperatures drop below 64 degrees F (18 degrees C) for any extended length of time.

Ancient Reef Events

The Florida Keys were formed over an extended geologic time period. The Lower Florida Keys, from Big Pine Key to Key West, is a zone comprised of ancient coral reefs, shifting sand shoals, and tidal sandbars. During the period 125,000–200,000 years ago, these sandbars were shaped by tidal currents flowing between Florida Bay and the Atlantic Ocean. (The Middle and Upper Keys, from Big Pine Key to Key Largo, were formed by corals and calcareous algae.)

Sea level was 20 to 50 feet (6 to 15 meters) higher than now, and most of present-day Florida was under water. The water started dropping 100,000 years ago, down to 300 feet (91 meters) below present levels, causing the corals to die, and creating coral rock. Gradual erosion from air, sun, wind, rain, and wave action solidified the sand shoals and flattened the reefs to slope down toward receding sea levels.

During a glacial period 15,000 years ago, sea level rose again. It stabilized 5,000 years ago, and corals started growing on former reefs. Today, those ancient reefs and sand shoals provide the foundation for land and reefs alike in the Florida Keys.

Interdependent Ecosystem

The ecosystems of the Florida Keys Coral Reef biome include biota in habitats within and around the reefs, mangroves, and seagrasses—each of which depends on the others. Mangroves are salt-tolerant trees that stabilize the shoreline and provide habitat and a nesting area for seabirds. Their roots are nurseries for sea life that migrates to the reef. Mangroves trap and produce nutrients, filter land-based pollutants, and provide an important sink for carbon dioxide. This region has three species of mangroves: white, black, and red. The seaward side is dominated by red mangroves.

Red mangroves have two types of branching aerial roots: prop roots that develop from the trunk, and drop roots that develop from branches. Breathing pores called lenticel deliver oxygen from above the water surface to submerged roots. Red mangroves are salt excluders; they inhibit salt absorption through their roots. To reproduce, a fertilized flower develops into an embryo, then an elongated seed or propagule falls into the water and floats vertically until it roots in sediment. Black and white mangroves follow a similar pattern, but with differently shaped propagules.

Black mangroves occur shoreward of red mangroves. Their leaf undersides are covered with excreted salt crystals. These mangroves produce pneumatophores—small, pencil-like vertical roots—that extend through the ground, enabling the trees to obtain oxygen from air.

White mangroves, the smallest of the three types, grow above the high-tide mark on dry ground. The leaves are thick, rounded at both ends, and the same color on both sides. Their root system resembles that of terrestrial trees, and they extrude salt crystals at the leaf base. These mangroves are protected by state law, but all species are threatened by global warming as well as by human-induced deforestation.

Protected Status

Because of its accessibility from the continental United States, the coral reefs of the Florida Keys have become one of the world's most heavily visited reef, attracting millions of divers, snorkelers, photographers, ecotourists, and fishermen annually. It is one of the world's biggest dive destination, with the most charter boats, combined with Florida's largest commercial spiny-lobster and stone-crab fishery. Key West, the most populated key, typically hosts more cruise-ship guests than any other site in North America. Many of those guests visit the reef.

In recognition of the reef's value, Looe Key and Key Largo National Marine Sanctuaries were created and then expanded in 1990 to form the Florida Keys National Marine Sanctuary, encompassing 2,800 square nautical miles (9,616 square kilometers). Management of state and federal waters is shared by the National Oceanic and Atmospheric Administration (NOAA) and the State of Florida. The sanctuary implemented a zoned management system to reduce user conflicts. Some reefs are off-limits, and fishing is restricted. Special rules apply in Sanctuary Preservation Areas, and a Sanctuary Advisory Council provides citizen input. These sanctuaries also have a water-quality-protection program headed by the US Environmental Protection Agency (EPA), which launched a coral-reef monitoring program. Keys environmental centers encourage reef-friendly actions, but physical effects still occur from heavy use.

Reef Mooring Buoys

One seemingly simple—but highly effective—preservation method is the reef mooring buoy, which relieves boaters from having to drop anchor on the fragile coral. Sanctuary biologist John Halas and then-US Geologic Survey geologist Harold Hudson together designed the reef mooring buoy. The idea began with the holes left when geologists extract small cores of fossilized coral to study growth circles; these holes provide perfect foundations for a mooring. To create a reef-mooring buoy, a stainless-steel eyebolt is inserted into one of these holes and then packed with hydraulic cement or epoxy. After the cement or epoxy cures, a downline with a buoy and pickup line are attached to the eyebolt. Boaters retrieve the floating pickup line to secure their positions on the reef. In the 2010s, there were more than 490 reef-mooring buoys throughout the Florida Keys reef system, and the design has been exported to reefs worldwide.

Endangered Ecosystem

The Florida Keys reef is a fragile ecosystem that requires clean, clear waters. In the 1990s, a spate of new coral diseases and algae blooms appeared, resulting in extensive coral and seagrass loss. As ocean waters clouded, photosynthesis was difficult, and nuisance algae outcompeted corals and seagrasses. The source of the water-quality decline was traced to high nutrients—nitrogen and phosphates—found in wastewater, storm water, and agricultural runoff from Florida Bay. Reef Relief, a nonprofit organization dedicated to improving and protecting coral reef ecosystems, began monitoring Key West reefs and alerting scientists, who then pioneered much research into coral diseases. In 2014, an unnamed coral disease was discovered to be spreading along the Florida's coral reef tract; the disease spread to the Florida Keys coral reef in 2017. The coral illness was later called stony coral tissue loss disease, and by 2022, had spread to reefs in the Caribbean.

The city of Key West led efforts to improve water quality by upgrading sewage treatment to advanced nutrient-stripping levels and then upgraded storm water. A keys-wide No Discharge Zone was adopted, and numerous pump-out facilities plus mobile pump-out boats became available to boaters. The Everglades Restoration plan recognized the need for improved water quality for the downstream reefs. Nonetheless, in the 2010s, conditions were significantly reduced from the gin-clear waters and vibrant coral reefs of the past.

Additional threats emerged. Climate change has raised water temperatures, which has increased coral bleaching, disease vulnerability, and fish die-offs at shallow keys reefs. Fishing has also harmed the reef. In 2022, it was estimated that 98 percent of the original coral covering the reef had been lost. To restore the reef, scientists have established offshore coral nurseries. Once the coral has grown large enough, divers will transfer it to the reef, where it should permanent fuse. However, scientists caution that the process is very slow-going.

Local, national, and international efforts are directed into preserving the coral reefs in the Florida Keys and elsewhere. Millions of people visit and enjoy them each year. At risk are the local tourism and fishing economies that provide healthy revenue, high property values, and quality of life for residents of the Florida Keys. But most at risk is the biologic diversity of life itself.

Bibliography

Filosa, Gwen. "A Killer Coral Disease is Spreading toward Key West Reefs, Researcher Says." Miami Herald, 19 June 2018, www.miamiherald.com/news/local/community/florida-keys/article213461714.html. Accessed 29 June 2018.

"Florida." Coral Reef Information System, National Oceanic and Atmospheric Administration, 28 June 2017, www.coris.noaa.gov/portals/florida.html. Accessed 5 Oct. 2017.

"Florida's Coral Reefs." Florida Department of Environmental Protection, State of Florida, 25 July 2016, www.dep.state.fl.us/coastal/habitats/coral/. Accessed 5 Oct. 2017.

Humann, Paul and Ned DeLoach. Reef Coral Identification—Florida Caribbean Bahamas. Eugene, OR: New World Publications, 2002.

Lindwall, Courtney. "The Mission to Save Florida's Reefs." NRDC, 23 Sept. 2021, www.nrdc.org/stories/mission-save-floridas-reefs. Accessed 4 Aug. 2022.

Mooney, Chris, and Tim Meko. "The Race to Save Florida's Devastated Coral Reef from Global Warming." The Washington Post, 25 June 2017, www.washingtonpost.com/graphics/2017/business/environment/florida-reef/?utm‗term=.f4a6a5157faf. Accessed 5 Oct. 2017.

Lucas, Tim. "Local Interventions Boost Coral's Resilience to Bleaching." Nicholas School of the Environment, Duke University, 18 June 2018, nicholas.duke.edu/about/news/local-interventions-boost-corals-resilience-bleaching. Accessed 29 June 2018.

Parker, Laura. "Florida's Coral Reef is Disintegrating." National Geographic, 2 May 2016, news.nationalgeographic.com/2016/05/160502-reef-florida-acidification-fish-miami/. Accessed 5 Oct. 2017.

Porter, James and Karen Porter, eds. The Everglades, Florida Bay and Coral Reefs of the Florida Keys, An Ecosystem Sourcebook. Boca Raton, FL: CRC Press, 2001.

"Stony Coral Tissue Loss Disease Response." Florida Department of Environmental Protection, 15 June 2022, floridadep.gov/rcp/coral/content/stony-coral-tissue-loss-disease-response. Accessed 4 Aug. 2022.

The Royal Society of London. Ocean Acidification Due to Increasing Atmospheric Carbon Dioxide. Cardiff, UK: The Clyvedon Press, 2005.