Coral Reef

It is a type of biotic reef developing in tropical waters. Although corals are major contributors to the overall framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault by ocean waves are calcareous algae, especially, although not entirely, species of red algae.

Water temperature of 20–28 °C (68–82 °F) is an optimal range for proper growth and health of coral reefs. Coral reefs are found in all oceans of the world, except the Arctic Ocean, generally between the Tropic of Cancer and the Tropic of Capricorn, because reef-building corals live in these waters. Reef-building corals are found mainly in the photic zone (<50m), where the sunlight reaches the ground and offers the corals enough energy. The corals themselves do not photosynthesise, but they live in a symbiotic relationship with types of microscopic algae that photosynthesise for them. Because of this, coral reefs also grow much faster in clear water, which absorbs less light.

Such reefs take a variety of forms, defined as the following:

* Apron reef — short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.

* Fringing reef — reef extending directly out from a shoreline, and more or less following the trend of the shore.

* Barrier reef — reef separated from a mainland or island shore by a lagoon; see Great Barrier Reef.

* Patch reef — an isolated, often circular reef, usually within a lagoon or embayment.

* Ribbon reef — long, narrow, somewhat winding reef, usually associated with an atoll lagoon.

* Table reef — isolated reef, approaching an atoll type, but without a lagoon.

* Atoll reef — a more or less circular or continuous barrier reef surrounding a lagoon without a central island; see atoll.

Importance of Coral Reefs
Coral reefs provide a natural habitat and massive protection for different species of fish. They are not plants; they are living organisms that provide an environment for fishes to breed. Without them, fish in the ocean are homeless. According to professor Christie’s lecture, corals are colonial organisms that need to be exposed to sun, in order for them to grow. The corals also influence the amount of carbon dioxide in the ocean, because coral polyps, which are tiny invertebrates (cnidarians) that look like upside-down jellyfish, fix carbon dioxide to form limestone. This is a major process that acts as a 'carbon sink' for excess carbon dioxide in the atmosphere, as well as maintaining an environment of exceptionally high biodiversity despite relatively poor nutrient availability.

Biology
See also: Coral
The building block of coral reefs are the skeletons of generations of hard corals, composed of calcium carbonate. As each polyp dies, it leaves behind its skeletal structure, upon which the next generation of polyps grow, enlarging the reef. Grazing fish (such as parrotfish), sea urchins, sponges and other organisms break down the coral skeletons into fine fragments, which settle into spaces in the reef structure.

Coral reefs are among the most diverse and productive biological communities on Earth. The reef structure provides habitat and shelter to a wide variety of marine plants and animals - it is estimated that a quarter of marine life lives in or around coral reefs. Additionally, corals act as water filters, increasing water quality in the vicinity of the reef. Offshore, the reef structure acts as a breakwater, protecting coastlines from ocean waves. The wide variety of flora and fauna has turned some coral reefs and the islands and coastal areas near them into popular tourist attractions.

Deep water reefs
In December 2004, United States Geological Survey (USGS) researchers announced the confirmation of the discovery of the deepest coral reef ever found in the United States. The reef is in the Pulley Ridge area, a north-south-trending drowned barrier island, more than 60 miles (100 km) long, approximately 40 miles (70 km) west of Dry Tortugas National Park. It is up to three miles wide and about 20 miles long (5 km wide and 30 km long), and located at a depth that ranges from 200 to 250 feet (60 to 80 m). Unlike most coral reefs, which tend to grow vertically, Pulley Ridge coral grows flat, an adaptation to the limited penetration of light at that depth to increase surface area exposed to sunlight.

Similar deep reefs occur in other parts of the world, e.g. the Mingulay reef complex and the Darwin Mounds located off the west of Scotland in about 150 metres of water.

Threats to Reefs

Coral Reef bioerosion

Bioerosion (coral damage) such as this may be caused by coral bleaching.
Humans continue to represent the single biggest threat to coral reefs. In particular, land-based pollution and over-fishing are the most serious threats to these ecosystems. The live food fish trade has been implicated as one driver of decline due to the use of cyanide in the capture of fish. Rising water temperatures produce toxins in the coral tissue, due to bleaching.

High levels of land development have also been threatening the survival of coral reefs. Within the last 20 years, the once thick mangrove forests, which absorb massive amounts of nutrients from runoff caused by farming and the construction of roads, buildings, ports, channels, and harbors, are being destroyed. Nutrient-rich water causes algae to thrive in coastal areas in suffocating amounts, also known as algal blooms.

Due to the increased demand for live reef fish in North America and Europe, the use of cyanide fishing has increased in the Indo- Pacific region. 85% of the of the world’s aquarium fish are caught in this region and almost all of them are caught using cyanide. Cyanide is used to stun the fish, in order to easily capture them for trade. It is detrimental to the organs of fish, which would explain the 90% mortality rate of cyanide captured fish. Cyanide is also very destructive to the surrounding coral reef ecosystems. It kills corals and other reef invertebrates. Corals are also harmed by the poor harvesting practices of the live fish trade. Fishermen sometimes pound on the reef with crowbars and rocks to scare fish into nets or pry corals apart to retrieve stunned fish.

A major catalyst of cyanide fishing is poverty within fishing communities. In areas like the Philippines where cyanide is regularly used to catch live aquarium fish, the percentage of the population below the poverty line is 40%[2]. In such developing countries, a fisherman might resort to such unethical practices in order to prevent his or her family from starving.

Dynamite fishing is another extremely destructive method that fishermen use to harvest small fish. The procedure of dynamite fishing starts with a bottle that is filled with explosives made of potassium nitrate, once the dynamite goes off the explosion brings about an underwater shockwave causing the swim bladders of fish to burst making them float to the top. A second blast is often set off after the first to kill any larger predators that are attracted to the initial kill of the smaller fish. This method of fishing does not only kill small fish but also claims the lives of many reef animals that are not edible or wanted, such as the coral itself. Areas that used to be full of coral now are like desert sand, no sign of coral or any other reef animals that used to inhabit it.

During the 1998 and 2004 El Niño weather phenomenons, in which sea surface temperatures rose well above normal, many tropical coral reefs were bleached or killed. Some recovery has been noted in more remote locations, but global warming could negate some of this recovery in the future. Toxins in the tissue are produced when the water temperatures climb, causing coral bleaching. However, Ben McNeil of the University of New South Wales hypothesises that reefs are not in decline, and may exceed pre-industrial levels by as much as 35 percent by 2100, especially because of the positive influence of global warming. However, growth in some reefs due to global warming is expected to be offset by declines in other reefs, due to the comfortable temperature range for a coral being close to the temperature at which they bleach.

In general, Southeast Asia coral reefs are at risk from damaging fishing practices (such as cyanide and blast fishing), overfishing, sedimentation, and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas, are underway to protect these reefs.Indonesia has nearly 33,000 square miles of coral reefs. Its waters are home to a third of the world’s total corals and a quarter of its fish species. Coral reefs of Indonesia are located in the heart of the Coral Triangle and have been victim to destructive fishing, unregulated tourism, and bleaching due to climatic changes. Many of the diverse coral reefs are being smothered by sediment and poisoned from cyanide fishing and organic pollution. Data from 414 reef monitoring stations throughout Indonesia in 2000 found that only 6 percent of Indonesia’s coral reefs are in excellent condition, 24 percent are in good condition, and approximately 70 percent are in poor to fair condition (2003 The Johns Hopkins University). According to The Nature Conservancy organization, if the destruction increases at the current rate, 70% of the world’s coral reefs will have disappeared within our life times

See Also
* Coral
* Reef
* Atoll
* Southeast Asia coral reefs
* Marine conservation
* Diving locations
* Great Barrier Reef

See also:
• Australia
• Belize
• Nassau Grouper

• This article is licensed under the GNU Free Documentation License.
• It uses material from the Wikipedia article "Coral Reef".