CORAL GROWTH

How long does it take for coral to grow?

Corals grow at different rates, depending on water temperature, salinity, turbulence, and the availability of food. The massive corals are the slowest growing species, adding between 5 and 25 millimeters (.2 inches to an 1 inch) per year to their length. Branching and Staghorn corals (middle photo) can grow much faster, adding as much as 20 centimeters (8 inches) to their branches each year.

Coral polyps eat in two different ways, depending on their species. Many coral polyps are nourished in a unique way by a tiny algae called zooxanthellae (pronounced zo-zan-THEL-ee). These algae live within coral polyps, using sunlight to make sugar for energy, just like plants. Zooxanthellae process the polyp's wastes to retain important nutrients and in turn provide the polyp with oxygen. Meanwhile, the coral polyps provide the algae with carbon dioxide and a safe, protected home. Zooxanthellae living within the tissue of hard corals can supply them with up to 98 percent of their nutritional needs.

Another way that corals eat is by catching tiny floating animals known as zooplankton. At night the polyps come out of their skeletons to feed, making the reef look like a "wall of mouths". The polyps stretch out their long, stinging tentacles to capture the zooplankton that are floating by. The captured plankton are then put into the polyps' mouths and digested in their stomachs.

How do corals get their shape?

The variety of shapes and sizes of coral colonies largely depends on their species. Some form hard, pointed shapes, while others form soft, rounded shapes. The shape of coral colonies also depends on the location of the coral. For example, where there are strong waves corals tend to grow into robust mounds or flattened shapes. In more sheltered areas the same species may grow in more intricate shapes such as delicate branching patterns.