A coral colony usually consists of thousands of little coral animals, or polyps, as seen in this picture. Each polyp is like a tiny anemone (or jellyfish on its back) which secretes a calcium carbonate, or limestone skeleton on/in which it lives. A colony may begin with just one polyp, to stretch over many metres in diameter as it grows, adding more and more polyps. Coral polyps, like anemones and jellyfish, are typically partially carnivorous, feeding on any small particle that is floating on the water and brushes against its tentacles. Corals also have microscopic algal cells living within their tissues called zooxanthellae. These algae take the metabolic waste products of the coral as fertilizer, combine them with light (like any other plant) and produce enough food for both the algae and the polyp. The algae gets food and protection within the polyp, and the polyp gets food from the algae. In this way, the polyp is able to recycle food within itself, being efficient enough to thrive in the nutrient poor waters of the tropical oceans. Coral reefs are in fact one of the most productive natural communities on earth, occurring in clear, shallow tropical waters around the world.

A reef provides food and habitat for fish and also protects the shoreline from erosion. Coral reefs, when healthy, are continually growing, forever strengthening this protective barrier. Reefs protect shallower inshore habitats such as sea grass beds and mangrove systems from incoming waves, and the mangrove systems and sea grass beds protect the reefs from coastal stresses such as excessive nutrients and muddy water. It's all a big system working together.

A common type of asexual reproduction in corals is by fragmentation. After a storm strong enough to break off pieces of coral, any pieces that land on a suitable substrate may begin to grow and produce a new colony. This type of reproduction is common in branching corals like Acropora cervicornis and A. Palmata. A large patch of these species may be all of one genotype, or clones of the same colony broken up. A positive correlation has been found between fragment size and survival: small pieces rarely survive.

Many coral species mass spawn. Within a 2-hour period (and often a lot shorter- a few minutes) all the coral from one or several species release their eggs and sperm at the same time. This occurs in species of Montastraea (boulder coral), and in other genera such as Montipora, Platygra, Favia and Favites (smaller coral species). In some Montastraea and Acropora (branching corals) species, the eggs and sperm are released in a sack. The sack is larger then the egg and sperm would be on their own, and are thus less likely to be eaten by predators, including other filter feeders or corals. They float to the surface where they separate, and there fertilization takes place. The zygote (fertilized egg) develops into a larvae called a planula, which attaches itself to a suitable substrate (rocky bottom) and grows into a new coral colony.

Intra species mass spawning is common, but raises the possibility of hybridisation (cross breeding) by congeneric species. Usually these hybrids won't survive, but Acropora prolifora (Fused Staghorn coral) is a hybrid of A. palmata (Elkhorn) and A.cervicornis (Staghorn) coral which does.

After a mass spawning event, the water feels greasy on the surface, and often has a sickly sweet smell.

The ways in which these diseases are transmitted are unknown. White pox is thought to be caused by a bacteria present in the human gut, and is present in untreated sewage. White band is often associated with "Farmer Fish": the little, aggressive damsel fish species who vigorously hold territories in which they "farm" their favourite algae. They nibble at the branching coral to kill the polyps, then farm their algae on the dead parts. White Band is thought to be spread in part on the fishes lips or teeth, as the disease helps the fish to kill, and then farm, the coral.

Corals under stress are more likely to be infected by any disease. WIth Black Band, one notes higher rates of infection in very warm waters. Seasonal temperatures affect the spread, as also will any anthropogenic warming of water temperatures.

The exact mechanism by which corals bleach or the trigger that induces bleaching is unknown. However, there are a number of hypotheses that attempt to answer this question. Laboratory experiments have shown that the zooxanthellae are released into the gut of the polyp and then are expelled from the polyp through the mouth. However this has not been observed in nature. Another hypothesis is that stressed corals give algae fewer nutrients and thus the algae leave the polyp. Algae may produce oxide toxicity under stress, and these toxins may affect the polyps.

A coral colony or polyp can withstand a couple of weeks of bleaching, after which it may die. If the stress goes away before this time, the coral will simply collect and grow new zooxanthellae, regain its colour and go on.