Ecosystems: Coral Reefs

kelp forest
There are more than 6,000 species of plants and animals in the waters of the Florida Keys, and many of these can be found on the reefs. (Photo credit: Mike White)

Florida Keys National Marine Sanctuary

Location: Florida's coral reef tract extends from Fowey Rocks near Miami to the Dry Tortugas. It parallels the emergent Keys for 356 km. All but the northern most extent of the reef tract lies within the sanctuary boundaries. There are various reef types with some existing near the shore while others are found over 10 km offshore.

Reef Structure and Physical Features: The Florida reef tract is the most extensive living coral barrier reef system in North American waters and the third largest system in the world. The reef tract has a distinct profile along most of its length, with depths decreasing seaward of Hawk Channel toward the reef tract. Scattered dead coral outcroppings supporting sparse hardbottom biota are dispersed in seagrass beds, marking the landward edge of the bank reef community. Just seaward is a discontinuous band of offshore patch reefs that parallel the Keys and comprise the first major habitat encountered in a seaward progression toward the reef tract. The topographic relief of patch reefs varies depending on their proximity to the more seaward back reef and bank reef communities. Sediment accumulation landward and behind some bank reefs is rapid, and may have an effect on the relief of offshore patch reefs.

A back reef or reef flat (i.e., a shallow water habitat dominated by turtle grass and manatee grass, with scattered coral heads and small patch reefs) separates the offshore patch reefs from the bank reefs. Bank reefs are considered unique due to the presence of elkhorn coral (Acropora palmata), coral zonation by depth, and seawardly oriented spur-and-groove formations. These formations give the reefs three-dimensional relief and contribute to their complexity. Many of these reefs are found 4.6 to 6 m below the surface.

Seaward of the bank reefs are deeper intermediate reef communities. This habitat, which forms the majority of available reef substrate along the reef tract, begins at an approximate depth of 10 m and extends out to a depth of approximately 19 to 21 m. The slope is gradual, decreasing only about 11 m over 1 km. The reef is composed of a drowned spur-and-groove system exhibiting low-profile coral spurs.

At about 20 m, the intermediate reef begins to slope at a greater angle, and a deep reef habitat is formed descending to about 30 m. At the deepest margin of the deep reef habitat, the reef terminates into soft sand/mud substrate. This extends seaward, gradually sloping until it reaches a deeper reef community approximately 1 km from the base of the deep reef called the outlier reef.

Coral Species and Cover: A survey at Looe Key, one of the more diverse reefs in the Florida Keys, reported 63 taxa of stony corals, 42 species of octocorals, and two species of fire coral. Stony corals and octocorals dominate offshore patch reef habitat. Massive corals include: Montastrea faveolata, Montastrea cavernosa, Solenastrea bournoni, Dendrogyra cylindrus, and giant brain coral. Millepora complanata, Acropora palmata, boulder corals, head corals, and soft corals are typical on the bank reef. Boulder corals are most prominent on the intermediate reef where colonies of Porites are sometimes over 1 m in diameter. Platelike growth forms of Agaricia agaricites, Montastrea faveolata, Montastrea cavernosa, and Madracis mirabilis and deepwater octocorals such as Ellisella barbadensis and Iciligorgia schrammi are common on the deep and outlier reefs.

Other Fauna and Flora: Over 500 fish species have been recorded in the sanctuary. Queen and horse conch are found occasionally on seagrass and sand areas. The spiny lobster, snow crab, echinoderms, Caribbean manatee, American crocodile, and leatherback, loggerhead, Kemp's ridley, and green sea turtles may occur. Seagrass communities surround the offshore patch reefs. Dominant plants of the fore reef include encrusting red algae of the genera Lithothamnium, Goniolithon, and Peyssonellia. Halimeda opuntia and Dictyota species occur on the fore reef and the intermediate reef.

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Revised July 31, 2017 by Sanctuaries Web Team | Contact Us | Web Site Owner: National Ocean Service
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