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Sharing the Coast

Coral Coasts Ecosystems

Coral reefs are massive calcareous rock structures that are slowly secreted by simple colonial animals that live as a thin layer on the rock surface. The living organisms continually build new structures on top of old, extending the reefs seaward toward deeper water and upward toward the surface.

Reef-building corals have algae living in their tissues in a symbiotic relationship. The algae supplies food to the coral, and the coral supplies shelter and metabolic wastes as nutrients to the algae. These reef-building corals are limited by water temperature to the tropical latitudes.

Coral reefs rival tropical rainforests as being among the most complex communities on earth. Rock-producing reef communities are some of the most ancient life forms found in the fossil record. At least 100,000 species have been named and described, but the total number inhabiting the world's reefs may exceed one million.

A portion of the Florida Reef Tract extends along the eastern coast of Florida in the Atlantic Ocean. The reefs in this region include hardbottom habitats, inner reefs, middle reefs, and outer reefs.

Hardbottom areas host abundant macroalgae, octocoral, stony coral, and sponges. Seaward of the hardbottom, inner reefs typically crest in 3-4 meters of water. The substrate for inner reefs consists of material from relict limestone and worm reefs. Macroalgae and small octocorals characterize these habitats.

Middle reefs crest in about 6-8 meters of water, and they have high concentrations of octocorals. Many stony corals are also present in this ecosystem, such as great star coral (Montastaea cavernosa) and massive starlet coral (Siderastrea sidereal). Outer reefs feature higher relief than preceding reefs, and they crest in 15-21 meters of water. Outer reefs contain the highest diversity and abundance of fixed(sessile) reef species. Octocorals, large barrel sponges, and stony corals are common to these reef ecosystems.

The Florida Keys are surrounded by reefs that extend west to the Tortugas Banks. Three habitats are found in the Florida Keys: hardbottom, patch reefs and bank reefs. Hardbottom is the most extensive habitat; it consists of rock colonized by calcifying algae, sponges, octocorals and stony corals.

Patch reefs are dominated by stony corals, particularly boulder star coral (Montastraea annularis). These habitats are concentrated in north Key Largo, near Elliott key, and in Hawk Channel between Marathon Key and Key West. Farther seaward, bank reefs feature ridges and channels built by elkhorn coral (Acropora palmata). Also known as the forereef, this habitat is a popular destination for snorkelers and scuba divers.

West of the Florida Keys lie the Tortugas Banks, which developed on Pleistocene-era karst limestone. The most common coral species in this ecosystem is Montrastraea cavernosa. Although coral species diversity is low in the area, it supports a major fishery that is dependent on the reef ecosystem.

Off the west coast of Florida in the Gulf of Mexico is the West Florida Shelf, which supports scattered reef ecosystems. The rock substrates in places such as Pulley Ridge and the Florida Middle Grounds have been colonized by Scleractinian corals, octocorals, black corals and sponges. Communities of diverse marine organisms rely on these ecosystems, and a number of these locations have been designated as Marine Protected Areas or Habitat Areas of Particular Concern by the Gulf of Mexico Fisheries Management Council.

Because of its geographical isolation, the Hawaiian Archipelago features high rates of endemism in reef organisms, meaning many species are found nowhere else on earth. This condition is common in both the main Hawaiian Islands and the Northwestern Hawaiian Islands (NWHI).

Reef ecosystems around the eight main Hawaiian Islands include non-structural reef communities, fringing reefs and barrier reefs. Over 400 species of algae have been identified in these ecosystems. The highest levels of coral species diversity are located at the islands of Oahu and Hawaii. There is also rich biodiversity of invertebrate organisms throughout the main Hawaiian Islands, including over 1,000 species of mollusks.

The NWHI comprise the older portion of the Hawaiian Archipelago. This area consists of mostly uninhabited islands, atolls, and shoals stretching for thousands of kilometers northwest of the main Hawaiian Islands. The NWHI is extremely remote, and consequently it hosts a unique and mostly undisturbed reef ecosystem. In addition to corals and algae, these reefs include sharks, sea turtles and monk seals. Many rare and endangered species are present in these reefs. The NWHI is one of the last reef ecosystems in the world to be virtually unaltered by man's activities.

Coral Reef Near Hawaii

Coral Reef Near Hawaii
Source:National Oceanic & Atmospheric Adminstration (NOAA)

Coral Coast Ecosystems

Corals are highly sensitive to increases in temperature, exhibiting a stress response known as coral bleaching. In 1998, a global mass bleaching caused extensive mortalities in many areas.

Atlantic Reef Ecosystems

Inner, middle and outer reefs run roughly parallel to each other offshore of southeastern Florida. They are separated by sand flats.

Gulf Reef Ecosystems

The warm waters of the Gulfstream current, the broad continental shelf and the absence of major rivers created ideal conditions for reef formation near Florida.

Hawaiian Reef Ecosystems

Coral reefs in the main Hawaiian Islands and the NWHI were mostly unaffected by the mass bleaching that took place worldwide in 1998. Their location near deep ocean waters is thought to be a factor in their protection from this event.