Environmental Science (2+1)

ii. Coral Reefs

• Coral reefs are widely distributed in warm shallow waters. They can be found as barriers along continents (e.g., the Great Barrier Reef of Australia), fringing islands, and atolls. Naturally, the dominant organisms in coral reefs are corals. Corals are interesting since they consist of both algae (zooanthellae) and tissues of animal polyp. Since reef waters tend to be nutritionally poor, corals obtain nutrients through the algae via photosynthesis and also by extending tentacles to obtain plankton from the water. Besides corals, the fauna include several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars.


• Coral reefs are made up of calcareous skeletal remains and secretion of corals and certain algae. They are confined largely to the warm waters of the pacific and Indian oceans. The reef building corals grow best in waters having an average annual temperature of about 24 ◦C at a depth of about 40-50 meters with salinity of 35 g per litre. They cannot grow in fresh or turbid waters or in highly saline lagoons.


• Corals build protective shells of calcium carbonate around their bodies, which after their death, sink and accumulate on the sea bottom. Coral families usually produce forms that resemble branching trees or shrubs. In due course, the inner spaces between the branching coralline structures are filled up by the deposition of calcium carbonate either by lime secreting organism or by debris brought by sea waves.