The geography and natural resources of the Florida Keys make them among the most diverse of ecosystems in North America. The chain of over 1,700 islands that make up the archipelago of the Keys extends approximately 220 miles southwest along the southern tip of the Florida peninsula. As recently as 125,000 years ago, the islands themselves were actually part of a submerged coral reef. Today the exposed limestone bedrock supports a diverse sampling of plants and animals, including unique hardwood HAMMOCKS, numerous species of palms and more types of trees than can be found in all of Europe.

Stands of red, black and white MANGROVE trees are found throughout the islands. Mangroves are vital for the structural support that they provide for the shoreline, and the protection they provide to the thousands of marine creatures that seek refuge among their protective roots. In the waters surrounding the islands are distinct habitats that combine to form a marine ecosystem unlike any other in the continental United States. Attracting millions of visitors each year, these interdependent habitats are the SEAGRASSES, HARDBOTTOM, and CORAL REEFS.

In the shallow waters surrounding the islands are meadows of turtle, manatee and shoal SEAGRASSES. Seagrasses require ample amounts of sunlight. The depth at which they can be found is limited by the clarity of the water. Their blades help to maintain water clarity by trapping fine suspended particles and sediments. They stabilize the sea floor with their roots and rhizomes, in much the same way that grasses on land help to prevent soil erosion. Seagrass beds also serve as a host for encrusting organisms, and as a food source, safe haven and nursery for fish, shrimp, lobster and many other species of marine life. Seagrasses are a valuable part of South Florida’s marine environment, but they are disappearing at an alarming rate. Dredge and fill projects, degraded water quality and prop scars caused by inexperienced or careless boat operators are among the factors responsible for their marked decline.

Adjacent to the seagrass beds are the HARDBOTTOM communities, characterized by exposed or thinly covered bedrock or cemented sediment and rubble. These habitats are abundant in shallow waters. At first glance the hardbottom may look barren and lifeless compared to the reef. But this is not the case, as the thin sediment supports a wide variety of crabs, worms, brittle stars and other organisms, and the bedrock is home to a variety of soft corals, sponges and algae. Many fish, lobster and turtles commonly feed and find shelter in hardbottom areas, especially in the numerous solution holes that can be found there.

Of all the habitats found in the waters of South Florida, it is the CORAL REEFS that draw most visitors to the Keys. Lying an average of six miles offshore, ours is the only living barrier reef in continental North America, and the third largest barrier coral reef system in the world (Australia’s Great Barrier Reef is the largest, followed by the reefs of Belize in Central America). The reefs themselves are made up of colonies comprising thousands of tiny coral animals, called polyps, that live in a very delicate and balanced environment. Corals are invertebrates belonging to the phylum Cnidaria, along with their close relatives, the jellyfish, anemones and hydroids. There are more than 90 different species of coral in the waters of the Florida Keys, generally categorized as being either hard or soft.

Hard corals form the massive structures of the reef. Commonly seen types include the brain, elkhorn, staghorn, star and pillar corals. As coral polyps develop, they produce calcium carbonate. The excretion of this mineral by thousands of polyps, over hundreds of years, results in the large, hard reef structures that we see today. The colonies of soft corals, called gorgonians, contain more protein than minerals, and thus they can be seen swaying in the currents. Common soft corals in the Florida Keys include sea fans, whips, plumes and rods.

Coral polyps are basically colorless. The beautiful hues of orange, yellow, purple, green and pink that come to mind when divers think of the reef are actually caused by different types of algae; minute plants that live within the coral. One type of algae is especially important to coral growth. Living a symbiotic existence within the actual tissue of the polyps are zooxanthellae. These microscopic plant cells convert sunlight into energy, giving off oxygen that nourishes their coral hosts. The polyps, in turn, provide protection and nutrition to support the zooxanthallae.

All corals are fragile, and require a very specific aquatic environment in which to live. There must be the right balance of warm water, sunlight, salinity, nutrients and gentle wave action in order for them to thrive. It is important for divers to realize that only the very surface of the coral heads are alive, and that they are very vulnerable. Their mucous and mineral coverings offer little protection against physical contact, and they are extremely susceptible to stress from disease and pollution. Most corals are slow growing; a broken piece of coral may take decades to grow back.