Florida's Reefs

Healthy reefscape showing typical reef diversity with both hard and soft corals. Photo courtesy of NOAA.

Mixed school of blue-striped grunts and schoolmaster snapper. Photo courtesy of NOAA.

The Florida Keys reef tract is the most extensive living coral reef system in North American waters and the third largest barrier reef in the world. It is located parallel to the Florida Keys in the Atlantic Ocean, approximately 6 miles from the shore in waters that typically range from 15 to 30 feet deep. The reef tract starts near Miami and extends south and west to the Dry Tortugas, about 67 miles west of Key West. Patch reefs continue north through the Palm Beaches. Florida's reefs contain approximately 65 species of corals and include more than 80 percent of all the coral reef species in the tropical Western Atlantic.

Coral reefs are complex and diverse ecosystems found in the tropics and subtropics where environmental conditions are relatively constant. Reefs are composed of colonies of coral polyps and other organisms that, given enough time and favorable environmental conditions, develop into a rigid, wave-resistant, three-dimensional limestone structure (made of calcium carbonate) in shallow water. After thousands of years, these structures become "underwater cities." Besides corals, algae and sponges use the physical structure of the reef as a foundation for their growth. Coral reef ecosystems contain 22 of the 23 animal phyla found on the planet and are among the most productive habitats, producing 2,000 decagrams of carbon per square meter per year.

Importance of Coral Reefs

Coral reefs provide numerous critical ecological and economic functions, including:

• Habitat. Coral reefs serve as habitat, food source, and breeding territory for numerous species of plants and animals, including some endangered and threatened species such as marine turtles and queen conch. These animals rely on the small holes and crevices provided by the reef for food and protection from predators and strong wave activity.
• Fisheries. Coral reefs support recreational and commercial fisheries that depend on healthy reef communities. More than 500 species of fish live in the Florida Keys National Marine Sanctuary (FKNMS), including grouper, snook, and snapper.
• Tourism. Coral reefs support recreational fishing, diving, and snorkeling in FKNMS. Each year millions of people visit the Florida Keys and partake in these activities, contributing hundreds of millions of dollars to the local economy.
• Storm protection. Coral reefs function as storm barriers, breaking up large waves prior to their crashing on shore and thus protecting adjacent coastline.
• Biodiversity. Coral reefs host the greatest biological diversity of any marine ecosystem.
• Bioprospecting. Natural compounds from coral reef organisms have been used to develop pharmaceuticals.

Types of Coral Reef Habitats in FKNMS

• Inshore patch reef. These small, scattered reefs usually consist of large boulder corals, often surrounded by a barren halo of sand created by fish and invertebrates that graze on the surrounding seagrasses.
• Midchannel reef. Reefs in this area are usually hidden by Hawk Channel, the deeper body of water that separates the Florida Keys from the main reef tract. Corals in this reef rise up to 15 feet from the bottom and provide an important refuge for fish and invertebrates during different stages of their life cycles.
• Offshore patch reef. These reefs are located along the seaward edge of Hawk Channel, parallel to the outer reef tract. This diverse habitat is made of tall soft corals and abundant stony corals.
• Reef flat (back reef). This refuge from wind and waves is protected on the seaward side by a ridge of coral rubble. Shallow seagrasses, sand patches, and scattered coral outcroppings provide habitat for many organisms that prefer this sheltered environment.
• Fore reef. High-profile slopes and ledges of living and fossilized corals, separated by deep sand channels, form coral fingers referred to as spur-and-groove formations. An area of extensive coral growth, the fore reef includes the reef crest, a shallow zone frequently exposed to extreme conditions such as low tides or breaking waves.
• Intermediate to deep reef. The gradually sloping intermediate reef is a highly diverse, low-profile spur-and-groove coral reef system. The deep reef occurs in some locations where the intermediate reef drops off abruptly to the sand bottom.

Threats to Coral Reefs

Storms, heat waves, severe cold fronts, and other natural events cause some decline of healthy corals, but human activities are also responsible. Significant direct and indirect effects result from the high levels of use of FKNMS resources by residents and tourists. These impacts include ship groundings and acts of negligence by dive operators and other humans. The nitrification of nearshore waters is another problem in FKNMS, and sewage leaking from inefficient septic systems is a major source of excess nutrients. These nutrients are carried through the region by more than 700 channels and canals.