Coral Reefs

Coral reefs are thalassic structures formed as a result of deposition of calcium carbonate, secreted from various species of tiny aquatic animals called corals, over the course of hundreds of years. Coral reefs are part of a diverse and complex marine ecosystem, serving as a habitat to a variety of marine organisms, accounting for around 25% of all marine species. They thrive in shallow, clear water in warm tropical/sub-tropical climate, generally located around 30⁰N and 30⁰ S of the equator, around the globe. The bio-diversity of the reefs makes them a marine treasure. Healthy coral ecosystems provide vital ecosystem services to tourism, fisheries and coastline protection, and are of great medicinal value. Coral reefs are sensitive to changes in their environment. Changes in the temperature or salinity of the sea water, pollution and sedimentation pose potential threats to this valuable ecosystem. Efforts are underway for conservation of the “rainforest of the sea”, so, they thrive for generations to come.


Composition and Process of Formation

Corals are part of a diverse group of aquatic animals, belonging to the phylum cnidaria. Corals live in colonies of thousands of genetically identical polyps which grow in numbers by budding. Coral reefs are created by reef building hard corals. Hard corals absorb calcium from the sea water and secrete a calcium carbonate skeleton from their basal plates, which forms the substratum of the polyp colony. It is these hard skeletal secretions that compound to form large structures called coral reefs, over a period of thousands of years. The continuous secretion of calcium carbonate exoskeleton by the corals adds to the size of the coral reefs. However, rates of growth of reefs vary, depending on the species of corals and environmental factors. Corals are “zoned”, according to their respective species, in the reef structure. Corals share a symbiotic relationship with the single-celled algae called Zooxanthellae. The algae dwell inside the coral polyp, providing the corals with food through the process of photosynthesis, deriving shelter and the light required for photosynthesis, in return. Zooxanthellae also lend the vibrant colors to corals. Reef building corals are found in clear, shallow water in warm tropical climates, where they get plenty of light for photosynthesis. It is noteworthy that coral reefs are home to diverse groups of organisms, which depend on the reef for food and protection, contributing to its bio-diversity. The mélange of organisms residing in coral reefs include, crustaceans like shrimp, molluscs like oysters , echinoderms like star fish, various sponges, other cnidarians like sea anemones and various species of fish. The coral reef ecosystem also includes Mangrove trees and sea grasses. The salt-resistant Mangrove trees with submerged roots act as a breeding ground for marine life- forms, while preventing coastal erosion. They also filter pollutant and provide nutrients. Sea grasses prevent sea-bed erosion and provide oxygen to marine organisms.

Types and Geographical Distribution of Coral Reefs

Coral reefs are classified into three broad categories, based on their structural and morphological differences. Fringing reefs are the most common structural forms among the coral reefs. They form close to the shore and project towards the sea. Fringing reefs are sometimes separated from the coast by narrow water channels. Young and evolving fringing reefs are known as apron reefs. Fringing reefs are most common in Hawaii and the Caribbean regions. Barrier reefs grow farther away from the shore. They are extensive linear structural patterns, occurring parallel to the shore. They are demarcated from the shore by wider water bodies with considerable depth. They create a “barrier” to navigation by touching the water's surface at shallow points. The 1200 miles long, Great Barrier Reef in Australia, is the world's largest barrier reef and the largest living structure on Earth - a home to diverse species, including pre-historic turtles and crocodiles. Large Barrier reefs are also found off New Caledonia's north east coast. In the Caribbean region, they are found off the coast of Belize and off the north coast of Providencia. Atolls are located in the middle of the sea. They are generally circular or oval in structure, with a central lagoon. According to Darwin's theory, atolls emerge as a result of subsidence of volcanic islands, with fringing reefs surrounding the extinct volcanic island creating a lagoon in the middle. Atolls are the end-result of a gradual process of metamorphosis. In the South Pacific, atolls are most common in the Marshall Islands, Micronesia, the Cook Islands and French Polynesia. In the Indian Ocean, atolls occur in the Maldives, theChagos, and the Cocos island groups and the Seychelles. Overall, the coral reefs are prominent in the Indo-Pacific region, including the Indian Ocean, the western Pacific, the tropical western Atlantic region including Florida, the Bahamas and the Caribbean Sea, and the Red Sea region.


Threats to Coral Reefs

The bio-diversity and ecosystem services rendered by the coral reefs make them an asset for all of humanity. Healthy reefs cater to food and recreational needs of human being, making them a commercial hot spot, furnishing huge profits to tourism and hospitality industries. In developing countries, coral reefs serve as food sources for tens of millions of people. However, they are very sensitive to changes in their environment. Various natural and human-induced environmental “stresses” pose a potential threat to the survival of the biologically-rich, yet vulnerable coral reefs. Some natural “stresses” to coral reefs include hurricanes, marine predators and diseases. Weather-related changes, such as, increases in temperature of the sea water, increased salinity, and decreased sea levels, primarily due to the El-Niño effect, adversely affect the coral communities. However, coral reefs are more tolerant to natural stresses. The human-induced stresses wreak havoc on the coral reefs, endangering their very survival. Human-induced threats include harmful fishing practices, such as, cyanide fishing and blast fishing which poison the reef ecosystem, with pernicious impact on the coral reefs. Further, overfishing disturbs the ecological balance of the coral reefs, removing their key species. Pollutants and sewage carried to the ocean, increase the nutrient-level of the sea water, making them a fertile breeding ground for “coral-competitors”, consequently, narrowing their “domain”. Sediment-runoff from terrestrial activities, such as, construction and farming threatens the very survival of corals, by blocking sunlight. Tourists and scuba-divers may inadvertently damage the coral reefs by touching them, and taking coral “souvenirs” home. Careless tourism practices, such as building resorts right on the coral reefs and emptying sewage around them, spell disaster for the coral reefs. Coral mining, where coral reefs are scraped away, to be used in construction of roads or building has a deadly effect on the coral reefs. Global warming compounds these problems by increasing the temperature of sea water.

Protecting the Coral Reefs

There is an emerging partnership between organizations around the world to check human-induced stresses and their repercussions on the coral reef ecosystem. The world wide fund for nature (WWF) has been working towards coral reef protection since the 1970's. The Coral Triangle Initiative Leader's Declaration, by the 6 coral triangle nations, aims to protect the coral reef ecosystem in the coral triangle region, comprised of Malaysia, Indonesia, Philippines, Solomon Islands, Papua New Guinea and Timor Leste. This region is the epicenter of marine biodiversity. Coral and mangrove protection initiatives have been introduced in every continent. The Marine Turtle Conservation Act passed by the US has created a fund for the protection of marine turtles, with a considerable portion earmarked for the conservation of coral reef ecosystem. WWF has devised a zoning plan for Australia's Great Barrier Reef marine park, inaugurating a network of marine highly protected areas. Another major victory for WWF was the European Union's regulation on the elimination of trawling, around UK's Darwin mounds, protecting the cold-water reef from their lethal effects. The implementation of European Union's Habitats and Birds directives imply the protection of coral habitats in the European seas, as well. The United Nations Environmental program's (UNEP) coral partnership Unit (CPU) and The International Coral Reef Initiative (ICRI) are working in tandem with WWF to forge international co-operation on conservation of coral reefs and mangrove ecosystems, through various treaties, agreements and multilateral partnerships. The various agencies and programs of United Nations facilitate data monitoring, overlook appropriate funding, restrict intrusive trading, and aim at reversing bio-diversity loss through Sustainable Ocean Initiative, for protection and conservation of coral reefs. Protection of coral reefs is essential as they are of “outstanding human value” as natural heritage sites.


A clown fish on a coral reef.


The pristine beauty and biodiversity of the coral reef ecosystem makes them an economic, social and environmental asset. Coral reefs are hot spots for tourism and fisheries, as also for recreational activities, such as, snorkeling and scuba diving. Hotels, restaurants and other businesses around the coral reefs also reap the benefits of their ecosystem services. The coral reef ecosystem, therefore, provides food and jobs to millions of people living close to the coral reefs. Coral reefs are of medicinal value, as well. Their biodiversity is facilitating research towards the discovery of medicines for the treatment of chronic diseases. Since, coral reefs are sensitive to the littlest changes in their environment, their health is an excellent indicator of the water quality. The coral reefs also protect the shores from coastal erosion and minimize the impact of cyclones by guarding human life and property. However, coral reefs are fragile ecosystems with high sensitivity to environmental stresses. Human induced stresses such as anthropogenic pollutants and sedimentation is perilous to the survival of these living structures. The social, economic and environmental value of coral reefs have united the global community in their concerted efforts towards the conservation and protection of these biologically rich yet, endangered living structures, through multilateral agreements and effective management of the coral reef ecosystems.


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