Reef-building corals grow in size by increasing the amount of carbonate calcium in their skeleton and adding new living tissue to cover the larger skeleton. Under ideal conditions, some species of coral form boulders which can be taller than an adult human. This process takes decades as boulder-type corals grow less than one centimeter per year. Thinner, branching corals grow as quickly as ten centimeters per year, but are easily broken in strong storms or as a result of human impact. The age of corals can be determined by examining coral growth rings, similar to counting rings in the trunk of a tree, or through the use of radioisotopes.

The Tortugas

Coral can reproduce asexually or sexually. Asexual reproduction occurs when a portion of living tissue buds off or when part of the colony is broken away from the parent colony, neither of these instances allows for genetic recombination. Sexual reproduction is the combination of egg and sperm to form larvae. These larvae are planktonic and exist in the water column until they settle onto an appropriate substrate and metamorphosize into a single coral polyp. The single polyp will then grow into a colony.

Coral spawning is a spectacular event and one means of sexual reproduction that occurs in the Florida Keys on an annual basis. Corals have been observed releasing their gametes into the water column five to eight days after the August full moon over the past four years. This type of broadcast spawning has been known to occur on Pacific reefs, but it was not observed in the north Atlantic until 1990.

Coral reefs are generally classified into three types: barrier reefs, fringing reefs, and atolls. Barrier reefs and atolls are both characterized by a lagoon that is protected on the seaward side by the reef. Barrier reefs occur in association with continental land masses, whereas atolls are coral reefs that form atop submarine volcanoes. Fringing reefs are considered immature because they have not yet formed a lagoon in the backreef. Under less than ideal conditions, coral also exists in small communities or patch reefs.

Plating Corals in the Tortugas

The degree of exposure and the amount of wave action is important in determining reef structure and this structure varies between reefs. However, most reefs have a number of general features including the back reef, reef flat, reef crest, and forereef. The deeper forereef often consists of large and deep surge channels at right angles to the shoreline. This is referred to as spur and groove topography with the groove being the surge channels and the spur being formed by massive reef-building corals between the channels. Species richness peaks in this zone of the reef. The maximum depth for actively growing coral and algae is approximately 70m.

Soft corals are predominant organisms on Key's reefs. The waving forests of sea whips and sea fans are a uniquely Caribbean feature, and are not found on reefs in the Pacific and Indian Oceans. Soft corals differ from reef-building corals in that their polyps have eight tentacles instead of six, their skeletons are flexible, protein-like cores not calcium carbonate, and they are found primarily on the forereef in deeper waters. Similar to reef-building corals, they have zooxanthellae within their tissue.

The rigidity of coral reefs helps protect the shoreline from destructive tropical storm waves. Reefs provide habitats for hundreds of species of marine organisms including commercially important finfish and shellfish. SCUBA diving, snorkeling, and sport fishing dominate the Keys' economy, producing millions of dollars annually in revenue for local businesses. Ecologically speaking, coral reefs are diverse places, containing 22 of the 23 animal phyla found on the planet. Symbiotic relationships are common and add to the complexity of species interactions. Coral reefs are among the most productive habitats, producing 2,000 decagrams of carbon per square meter per year, and the oldest, 400 million years.

The deterioration of the marine environment in the Keys is no longer a matter of debate. There is a decline of healthy corals, an invasion by algae into seagrass beds and reefs, a decline in certain fisheries, an increase of coral diseases and coral bleaching. In Florida Bay, reduced freshwater flow has resulted in an increase in plankton blooms, sponge and seagrass die-offs, and fish kills.

Storms, heat waves and other natural events can be blamed for some of the deterioration, but the activities of people are also responsible. Over three million people visit the Keys annually, 70 percent of whom visit the Sanctuary. Over 80,000 people reside in the Keys full time. There are significant direct and indirect effects from the high levels of use of Sanctuary resources resulting from residents and tourists. The damage done by people hinders the ability of marine life to recover from naturally occurring stresses. Human impacts can be separated into direct and indirect impacts.

Direct human impacts. The most visible and familiar physical damage results from the carelessness or, on occasion, the deliberate recklessness of ship captains, boaters, divers, fishermen, snorkelers and beachgoers. In the period between 1980 and 1993, approximately 500 vessels were reported aground in the Looe Key and Key Largo Sanctuaries. But in the one year between July 1993 and June 1994, 500 groundings were documented in the Florida Keys NMS. These groundings have a cumulative effect on the resources. Over 19 acres of coral reef habitat has been damaged or destroyed by large ship groundings. Over 30,000 acres of seagrasses have been damaged by boat propellers. Direct impacts to resources also result from careless divers and snorkelers standing on coral, improperly placed anchors, and destructive fishing methods.

Indirect human impacts. The nutrification of nearshore waters is a documented problem in the Sanctuary. A major source of excess nutrients is sewage- from 200 sewage treatment plants, 22,000 septic tanks, 5,000 cesspools and 139 marinas harboring over 15,000 boats. These nutrients are carried through the region by more than 700 canals and channels. Removing nitrogen and phosphorous from wastewater requires a technology that, at present, is lacking from sewage treatment facilities in the Keys. References: Levinton, J.S. 1982. Marine Ecology. Prentice-Hall: Englewood Cliffs, New Jersey. Thurman, H.V., H.H. Webber. 1984. Marine Biology. Charles E. Merrill Publishing Company: Columbus, Ohio.

Links to other web sites dealing with coral reefs

Coral Monitoring in the EPA Water Quality Protection Program