Corals are small, sedentary marine animals that occur in dense colonies in warm shallow waters of oceans. Reef-building corals are scattered throughout the tropical and subtropical western Atlantic and Indo-Pacific oceans, generally between 30 degrees North and 30 degrees South latitudes.
Coral reefs are formed by the skeleton remains of many generations of stony
corals. Massive reef structures are built over thousands of years by tiny coral polyps
aided by minute algae (zooxanthellae) that live in their tissues, calcifying algae, and
other organisms that secrete calcium carbonate and adhesives. Reef- building corals are
generally found at depths of less than 46 m, where there is sunlight and clear water
through which the sunlight penetrates better. Reef-building corals, along with the algae,
require warm ocean temperatures (2028° C) and are therefore found along the eastern
shores of major land masses where the water is warmer. These reefs are amongst the
earths oldest living communities of plants and animals. They vary in shape, size and
Coral reefs are sometimes referred to as tropical rainforests of the deep since they are one of the most diverse, productive, and beautiful marine ecosystems in the world. The extraordinary diversity of reefs makes them biologically important and, like rainforests, they have provided valuable scientific insights into the nature of underwater ecology. It is a diverse collection of species that interact with each other and the physical environment. The sun is the initial source of energy for this ecosystem. They are considered to be one of the most sensitive to any change. When they are environmentally stressed they lose much of the algae that gives them the colour along with other pigments. When this happens the corals appear white in colour and are referred to as bleached.
Excessive growth and accumulation of phytoplankton and seaweed would be detrimental to coral vitality and diversity, and low nutrient conditions are needed to prevent this. Diverse and abundant populations of grazing fish and invertebrates also keep the growth down.
The coral reef ecosystem is a diverse collection of species that interact with each other and the physical environment. The numerous species residing and depending on coral reefs represent a bank containing the genetic diversity necessary for adaptation to changes in the environment. Sponges have been an important part of the coral reef ecosystem. Sea anemones provide shelter to the fish and other creatures in the reefs. Fishes play a vital role in the reef's food web, acting as both predators and prey. Bryozoans are microscopic invertebrates that form branching colonies over coral skeletons and reef debris, cementing the reef structure.
The reef is also home to a variety of worms, shrimps, crabs, lobsters, starfish, sea cucumbers, and sea urchins. Octopuses, squids, clams, scallops, marine snails, and also some species of sharks, skates, and rays live on or near the reef. Some sea turtles frequent reef areas. Green, loggerhead, and hawksbill sea turtles live in the warm waters of the Great Barrier Reef.
The crown of thorns, a starfish, is a well- known predator of coral. Large numbers of these starfish can devastate reefs, leaving behind only the calcium carbonate skeletons. Parrotfish use chisel-like teeth to nibble on hard corals and eat the algae within the coral. Eels are one of the reef's largest predators and feed on the small fishes, octopuses, shrimps, and crabs.
Types of reefs
There are three types of reefs: the fringing reef, the barrier reef, and the atoll.
Importance of corals and coral reefs
While coral reefs are sensitive to environmental changes, they appear to be able to recover effectively from physical disturbance or temporary pollution events provided the water quality is generally high. For example, the corals in Kaneohe Bay, Hawaii, for the most part recovered from severe overgrowth of algae after sewage inputs were diverted away from the Bay.
The world has woken up to the magnitude of the problem and has taken steps to halt this degradation of one of the richest eco systems.
The Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES, has classified many corals as threatened species.
The establishment of marine sanctuaries or preserves may help ensure the availability of this ecosystem in the years to come. The Great Barrier Reef Marine Park was established in 1975 and is the largest project undertaken to preserve the coral reef in the world. Initiatives for the preservation of coral reefs in India have been undertaken on a large scale in the Wandur Marine National Park in the Andaman Nicobar islands. People on their part can play a role in preventing this depletion. Corals should not be collected, either alive or dead. All waste should be treated before it is released into the sea and no waste is to be dumped directly into the water. Once this awareness is built in the people the well being of these reefs can be ensured
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