Coral Reefs

Coral Reefs. . , Coral Reefs are the most biologically diverse marine eco-system on earth rivaled only by the tropical rainforests on land. Corals grow over geologic time and have been in existence for nearly 200 million years. Corals reached their current level of diversity 50 million years ago. The delicately balanced marine environment of the coral reefs relies on the interaction of hard and soft corals, sponges, anemones, snails, rays, crabs, lobsters, turtles, dolphins and other sea life.

A coral reef is composed of thin plates or layers of calcium carbonate secreted over thousands of years by billions of tiny soft-bodied animals called coral polyps. It takes years for some corals to grow an inch and they range in size from a pinhead to a foot in length. Each polyp secretes a calcareous exoskeleton and lives in a symbiotic relationship with a host alga, zooxanthellae, which gives the coral its color. Zooxanthellae takes in carbon dioxide, processing through photosynthesis, and then gives off oxygen as a by-product that is used by the host polyp. Millions of polyps grow on top of the limestone remains of former colonies to create the massive reefs, yet these tiny animals form the only natural formation.

Corals are divided into two types and both are stationary on the ocean floor. Hard corals such as the brain, star, staghorn, elkhorn, and pillar corals have rigid exoskeletons, or corallites, that protect their soft delicate bodies. Gorgonians, or soft corals, such as sea fans, sea whips, and sea rods, sway with the currents and lack an exoskeleton.