Many different organisms, including mollusks, sponges, and worms, help shape reefs, but hard corals and various algae are the major architects. In effect, the corals build limestone, because their skeletons are made of Calcium Carbonate. The skeletons deposited by these corals and other organisms accumulate, along with sand and other debris, to form the backbone of the reef. Over tens of thousands of years, chemical and mechanical changes turn the reef into true rock.

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.

• Avoid shallow coral reefs when trawling. Hooks can scar and injure the coral, and leave live coral vulnerable to infection by microscopic organisms.

Poor water quality affects other parts of the coastal ecosystem. Coastal ecosystems act as buffers between land and sea, reducing negative impacts in both directions. When stressed, they are less effective. There are three key environments in Florida that are intimately related. First of all, the mangroves along the shore, secondly, the grass beds in shallow water, and finally, the coral reefs at the edge of the shelf. Water flows through this system, and the health of each system determines the health of the next. Every time somebody cuts down mangroves, it affects the sea grass beds somewhat further off shore. Every time a sea grass bed is destroyed, it affects the coral reef even further off shore. So all these interconnected habitats need to be preserved as a whole. Increased nutrients in the water were blamed for a major sea grass die-off in the bay in 1987, further stressing the reefs.

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.

• 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.

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