What is a Coral Reef?
There Are More Kinds of Life on a Coral Reef Than Anywhere Else on the Planet
Coral reefs are the most biologically diverse marine eco-systems on earth, rivaled only by the tropical rainforests on land. That means there are more kinds of life on a coral reef than anywhere else on the planet. Coral reefs occupy less than one quarter of one percent of the earth's marine environment, yet they are home to more than a quarter of all known fish species. They are delicately balanced marine environments that rely upon the interaction of hard and soft corals, sponges, anemones, snails, rays, fish, crabs, lobsters, turtles, dolphins and other sea life.
Corals grow over geologic time and have been in existence at least 200 million years, some scientists say 400 million years. Corals reached their current level of diversity 50 million years ago.
What is a coral reef made of?
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 excretes a calcereous exo-skeleton and lives in a symbiotic relationship with a host algae, zooxanthellae, that gives the coral its color. Zooxanthellae takes in carbon dioxide, process is 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 visible from outer space.
Corals are divided into two kinds and both are stationary on the ocean bottom. Hard corals such as brain, star, staghorn, elkhorn and pillar corals have rigid exoskeletons, or corallites, that protect their soft delicate bodies. They form the main structure of a coral reef. Gorgonians, or soft corals, such as sea fans, sea whips, and sea rods, sway with the currents and lack an exoskeleton. They are filter feeders and help improve water quality.
Hard & Soft Corals
Coral Reefs Depend Upon Mangroves and Sea Grasses
Coral reefs are part of a delicate marine ecosystem that also includes mangroves and seagrasses; each depends upon the other to survive.
Mangroves are salt-tolerant trees with submerged roots that are a nursery and breeding ground for birds and most of the marine life that later migrates to the reef. Many species of fish are bred in the mangroves and then move to the seagrasses for their juvenile stage. Mangroves trap and produce nutrients for food and habitat, stabilize the shoreline, and filter pollutants from the landbase.
Seagrasses are flowering marine plants that are an important part of the food web. They provide food and habitat for turtles, manatees, many fish, filter-feeding organisms and foraging sealife such as sea urchins and sea cucumbers. And of course sea turtles depend upon turtle grass. Seagrasses are a nursery and breeding ground for pink shrimp, lobster, snapper and other sealife. They filter the water of sediments, release oxygen and stabilize the ocean bottom, improving water quality for corals and other marinelife.
Coral reefs deserve protection for their intrinsic natural value. In addition, the economic, tourism, fishing and recreational resources of tropical areas around the world depend upon healthy coral reef ecosystems. Barrier coral reefs protect shorelines from erosion and storm damage. The food, tourism revenue, coastal protection and new medications that reefs provide are worth about hundreds of billions of dollars each year.
