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+ Alteration of coastal habitats for urban development: mangrove deforestation and dredging, draining, or filling in coastal wetlands all affect water quality.

+ Tourism and recreation: careless divers break coral, kick up sand, feed fish, and remove specimens; careless boaters drop and drag anchors across fragile coral, leak oil, and dump garbage.

Corals have been hit by diseases. Since the 1970s, Florida’s corals have been struck by an unprecedented number of diseases: white pox, black band, yellow band, white band, white death, and white plague. Outbreaks are more frequent, more intense, and wider ranging than ever before. Many of these diseases are new to science and their causes are unknown.

The diseases might result from a bacterial or fungal infection from the Pacific Ocean introduced to the Atlantic through bilge water of ships crossing the Panama Canal, or from animals or other materials carried from the Pacific.

Unlike Pacific species, Atlantic corals have no immunity to these pathogens. Poor water quality could also be causing disease. The fungus Aspergillus is thought to be transferred by land runoff into Florida Bay and infecting corals directly. Diseased fish swimming on the reefs may also be contributing. Airborne contaminants could also be a culprit. At first it was thought to be sewage flowing through porous limestone from the Keys that was infecting coral reefs miles offshore. Scientists then began wondering why the same diseases infected coral reefs in remote areas of the Caribbean. They now suspects that red, iron-rich African dust borne by transatlantic trade winds are carrying bacterial spores to reefs, and correlations between dust and disease outbreaks are presently being studied. The iron also stimulates algal growth, which is bad for reefs (see explanation earlier).

Other environmental factors could be causing harm. Hurricanes and storms also damage reefs and devastate coastal areas. While large waves cause severe short-term damage to reefs, recovery is rapid, and part of a cycle of disturbance and recovery that helps shape healthy coral reefs. When the reef is already stressed by pollution or overfishing, though, it may not be able to recover from storm damage.

In the early 1980s, a mysterious epidemic killed almost all the long-spined black sea urchins in the Caribbean and South Atlantic. The “sheep” of the reef, the urchins grazed on the seaweed that competes with corals for space. Whether attributable to global warming, or urban runoff, warmer water affects reef chemistry. For example, it can lead to overproduction of oxygen by zooxanthellae, which damages the polyps. Rising water temperatures also mean a rise in sea levels. Because algae and reef-building corals need sunlight for photosynthesis, the reef must grow relatively near the ocean’s surface to survive (generally within thirty meters). This means that a rapid rise in sea level could “drown” corals that don’t grow fast enough.

One widespread symptom of systems under stress is coral bleaching, which takes place when the microscopic algae that lives inside the coral polyps are expelled. With the loss of these photosynthetic algae, corals lose their coloration and rapidly turn white. Within a number of weeks, the coral animals die and the “bleached” reef is sterilised and no longer regenerates.

The causes of coral bleaching are uncertain, but one possibility is the rise in sea surface temperatures. Tropical seawater is generally very stable in its temperature, rarely rising above 31 degrees Celsius. However, within the last ten years, those maximum temperatures have been exceeded frequently and they’ve stayed hot for a long time, a change drastic enough to kill the algae. (Water that is too cold can also damage reefs.) Corals may be an early warning sign for global warming. Recently, many reefs around the world have bleached several times, most often when local water temperatures were unusually high. Parts of these reefs are now dying. At least one species of coral may have already become extinct due to bleaching.

The Florida Keys Reef Monitoring Project is designed to assess the health of the reefs in the 2800-square-mile Florida Keys National Marine Sanctuary. A three-scientist team (Jim Porter, Phil Dustan and Walter Japp) designed and implemented the coral reef part of the program. Fortunately, they combine over sixty years of experience, because the question the study asks–”Are the reefs changing?”- is a complicated one. It’s grounded not just in reef ecology but in population biology, which involves sophisticated mathematical analysis of the equilibrium between births and deaths in a community of organisms. One hundred and sixty-eight monitoring stations were established in 1996 and the first assessment was conducted in 1997; there will be at least four more. The project’s primary focus is on overall water quality. Parallel studies are examining the health of fish and of sea grass communities. The purpose of the survey is to figure out what’s causing the reef decline in the hopes that it can be arrested and prevented.

The best way to determine the health of corals is to monitor over time to see whether the corals are growing or staying the same or possibly even dying. That’s done by taking a series of still life pictures and a series of Hi8 videos, over time, in exactly the same locations. Forty-two reefs were chosen, each with four video units consisting of two stainless steel survey

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