The Fragile Beauty of Coral Reefs
Swarms of anthias shelter near coral outcroppings and feed in the passing current. Fiji.
Tropical reefs form on the seafloor in shallow waters if there is enough light for the growth of coral. These animals are made up of a hard rocklike skeleton covered by a fleshy exterior, or polyp. The skeleton is made up of calcium carbonate which is secreted by the polyp. Each new generation of coral grows on top of the exoskeletons of the previous generation so that over time a reef is formed. Reefs can grow upwards at rates of 1 to 100 cm per year forming huge structures over incredibly long periods of time making them the largest and oldest living systems on earth. For example, the 1,250 mile Great Barrier Reef was formed over five million years ago.