Coral reefs are some of the most diverse ecosystems in the world, housing tens of thousands of marine species. About one-third of all marine fish species live part of their lives on coral reefs. Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine water that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support and...
Coral reefs are some of the most diverse ecosystems in the world, housing tens of thousands of marine species. About one-third of all marine fish species live part of their lives on coral reefs. Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine water that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support and protect the coral polyps. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Often called "rainforests of the sea", shallow coral reefs form some of the most diverse ecosystems on Earth and in Maldives. They occupy less than 0.1% of the world's ocean surface, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Paradoxically, coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water corals also exist on smaller scales in other areas. Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection. The annual global economic value of coral reefs is estimated between US$30–375 billion. However, coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature. They are under threat from climate change, oceanic acidification, blast fishing, cyanide fishing for aquarium fish, sunscreen use, overuse of reef resources, and harmful land-use practices, including urban and agricultural runoff and water pollution, which can harm reefs by encouraging excess algal growth.
Tropical coral reefs are very productive ecosystems. Not only are do they support enormous biodiversity, they are also of immense value to humankind.
Latest estimates suggest coral reefs provide millions of dollar each year in goods and services, including:
FISHERIES - Coral reefs are vital to the world’s fisheries. They form the nurseries for about a quarter of the ocean's fish, and thus provide revenue for local communities as well as national and international fishing fleets. An estimated one billion people have some dependence on coral reefs for food and income from fishing. If properly managed, reefs can yield around 15 tonnes of fish and other seafood per square kilometre each year.
TOURISM - Tourism revenues generated by coral reefs are also significant. For example, according to a report by the Key West chamber of commerce, tourists visiting the Florida Keys in the US generate at least US$3 billion dollars in annual income, while Australia’s Great Barrier Reef generates well over US$1 billion per year. Sustainably manged coral reef-based tourism can also provide significant alternative or additional sources of income to poorer coastal communities in developing countries.
COSTAL PROTECTION - Coral reefs break the power of the waves during storms, hurricanes, typhoons, and even tsumanis. By helping to prevent coastal erosion, flooding, and loss of property on the shore, the reefs save billions of dollars each year in terms of reduced insurance and reconstruction costs and reduced need to build costly coastal defences - not to mention the reduced human cost of destruction and displacement.
SOURCE OF MEDICAL ADVANCES - We can also expect coral reef species to contribute to future medical advances. Already coral reef organisms are being used in treatments for diseases like cancer and HIV. Just as with tropical forests, we may continue to find the answers to medical problems in the coral reefs - so long as we can keep them healthy.
INTRINSIC VALUE - For many coastal societies around the world, coral reefs and their inhabitants are intricately woven into cultural tradtions. For these people - as well as for those who have floated with a mask and snorkel, immersed themselves in the three dimensional wonderland of a scuba dive, or experienced these habitats through media and books - a world without coral reefs would be an infinitely poorer place.
Despite the importance of coral reefs, these wildlife habitats are imperiled throughout the world. A recent report estimated that 75 percent of remaining coral reefs are currently threatened, and many have already been lost. Even some of the most remote and pristine reefs are losing species.
WARMING WATERS - Although there are many problems facing reefs today, rising seawater temperature as a result of climate change is one of the most serious causes of stress to corals throughout the world. When temperatures are too high, the relationship between corals and their symbiotic microalgae breaks down. The algae are what give corals some of their bright colors, so when this happens, corals appear white or "bleached." Just one degree above the typical summer max is enough to bleach many corals. If the temperature is too high for too long, corals and their microalgae are unable to recover. Over the past 30 years, bleaching has become more frequent, more intense, and more widespread. This has led to massive die offs of corals throughout the world. Warmer ocean temperatures cause even more problems when it comes to disease – high temperatures allow corals to become sick more easily, and allow disease-causing organisms to grow faster. There is a huge array of different diseases in corals. Most of them are named after how they change a sick coral’s appearance, like black band, white band, white spot and purple blotch diseases.
OCEAN ACIDIFICATION - As more carbon dioxide (CO2) is released into the atmosphere, it also has adverse effects on the oceans. Recently, ocean acidification has emerged as another potentially serious threat to coral reefs. Seawater absorbs some of the excess CO2 from the atmosphere, causing the oceans to become more acidic. As a result, the oceans’ acidity has increased by 25 percent over the past 200 years. These acidic conditions dissolve coral skeletons, which make up the structure of the reef, and make it more difficult for corals to grow. If left unchecked, scientists estimate that the oceans could become 150 percent more acidic by the end of this century, making it very hard for corals to grow at all.
CARELESS TOURISM - Careless boating, diving, snorkeling, and fishing happens around the world, with people touching reefs, stirring up sediment, collecting coral, and dropping anchors on reefs. Some tourist resorts and infrastructure have been built directly on top of reefs, and some resorts empty their sewage or other wastes directly into water surrounding coral reefs.
POLLUTION - Urban and industrial waste, sewage, agrochemicals, and oil pollution are poisoning reefs. These toxins are dumped directly into the ocean or carried by river systems from sources upstream. Some pollutants, such as sewage and runoff from farming, increase the level of nitrogen in seawater, causing an overgrowth of algae, which 'smothers' reefs by cutting off their sunlight.
SEDIMENTATION - Erosion caused by construction (both along coasts and inland), mining, logging, and farming is leading to increased sediment in rivers. This ends up in the ocean, where it can 'smother' corals by depriving them of the light needed to survive. The destruction of mangrove forests, which normally trap large amounts of sediment, is exacerbating the problem.
CORAL MINING - Live coral is removed from reefs for use as bricks, road-fill, or cement for new buildings. Corals are also sold as souvenirs to tourists and to exporters who don't know or don't care about the longer term damage done, and harvested for the live rock trade.
DESTRUCTIVE FISHING PRACTICES - These include cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami (banging on the reef with sticks). Bottom-trawling is one of the greatest threats to cold-water coral reefs.
OVERFISHING - This affects the ecological balance of coral reef communities, warping the food chain and causing effects far beyond the directly overfished population.