Coral reef: Encyclopedia - Coral reef

Coral reef

A coral reef is a type of biotic reef that develops in tropical waters by reef-building, or hermatypic, corals. Coral reefs are formed of large amounts of calcium carbonate (limestone) that is deposited by corals and other organisms. Coral reefs come in a variety of forms, and provide a habitat for an amazing variety of organisms.

Coral reef - Coral Reef Biology

The building blocks of coral reefs are the skeletons of generations of reef-building hard corals, which are composed of calcium carbonate. As each coral 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 (Castro and Huber 2000, p. 276-278).

Reef-building corals are only found in the photic zone (<50m), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. The corals themselves do not photosynthesize, but instead live in symbiosis with zooxanthellae, single-celled algae that photosynthesize and produce excess nutrients that are used by the corals. Because of this, coral reefs also grow much faster in clear water, which absorbs less light.

Reefs may also be built or contributed to by calcareous algae, especially (although not entirely) species of red algae. These algae contribute to reef-building by depositing a great deal of limestone in hard sheets over the surface of the reef, as well as cementing together various pieces of limestone, and thus contributing to reef growth. This crust helps protect coral reefs by withstanding and mitigating wave pressure that would destroy corals. This crust often form a protective ridge on the outer edge of many reefs, particularly in the Pacific (Castro and Huber p. 280, Nybakken 1997 p. 363).

Coral reef - Coral Reef Formations

Coral reefs can 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.

Coral reef - World-wide distribution of reefs

Coral reefs are estimated to cover 284,300 square kilometers, with the Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) accounting for 91.9 percent of the total. Southeast Asia accounts for 32.3 percent of that figure, while the Pacific including Australia accounts for 40.8 percent. Atlantic and Caribbean coral reefs only account for 7.6 percent of the world's total (Spalding et al 2001, p. 17).

Coral reefs are either restricted or absent from the west coast of the Americas, as well as the west coast of Africa. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (Nybakken 1997 p. 339). Corals are also restricted from the coastline of South Asia from Pakistan to Bangladesh (Spalding et al. 2001, p. 18).

Famous coral reefs around the world include:

• Great Barrier Reef - largest coral reef in the world, Queensland, Australia
• Barrier Reef of Belize, second largest in the world, Belize, Central America

Coral reef - Ecology and biodiversity

Coral reefs support an extraordinary ammount of biodiversity, despite often being located in nutrient-poor tropical waters. The process of nutrient recycling between corals, zooxanthellae, and other reef organisms helps provide an explanation for why coral reefs can survive in these waters, since recycling ensures that fewer nutrients are needed overall to support the community. Cyanobacteria also provide nutrients for the coral reef through nitrogen fixation. Corals also absorb nutrients, including nitrogen and phosphorus, directly from the water, and they also eat zooplankton that are carried in (Castro and Huber p. 290).

Thus, primary productivity on coral reefs is very high. Producers in coral reef communities include the symbiotic zooxanthellae and seaweeds, especially small types called turf algae, although scientists disagree about the importance of these particular organisms (Castro and Huber p. 291).

Coral reefs are home to a variety of tropical or reef fish, such as the well-known colorful parrotfishes, angelfishes, damselfishes and butterflyfishes. Other fish groups include groupers, snappers, grunts and wrasses. Over 4,000 species of fish inhabit coral reefs (Spalding et al. 2001, p. 40).

Reefs are also home to a variety of other organisms, including sponges, Cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, spiny lobsters and crabs), molluscs (including cephalopods), echinoderms (including starfish, sea stars, sea urchins and sea cucumbers), sea squirts, sea turtles and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins being the main group. Some of these varied species feed directly on corals, while others graze on algae and seaweeds on the reef (Castro and Huber 2000, p. 295-297, Spalding et al. 2001, p. 31-44).

A number of invertebrates, or cryptofauna, inhabit the coral substrate itself, either boring into the limestone surface of the reef or living in pre-existing holes and crevices. Those animals boring into the rock include sponges, bivalve mollusks, and Sipunculans. Those settling on the reef include many other species, particularly crustaceans and Polychaete worms (Nybakken 1997, p. 373).

Coral reef - Threats to Reefs

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. Physical destruction of reefs due to boat and shipping traffic is also a problem. The live food fish trade has also been implicated as a driver of decline due to the use of cyanide in the capture of fish. Finally, high water temperatures, due to weather phenomena such as El Nino or global warming, can cause coral bleaching. According to The Nature Conservancy organization, if destruction increases at the current rate, 70% of the world’s coral reefs will have disappeared within our life times.

Land development and pollution

High levels of land development can threaten the survival of coral reefs. Within the last 20 years, 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.

Live reef fish trade

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. (Barber and Pratt, 1-2) 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 them.

Coral bleaching

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.

Destruction worldwide

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).

Coral reef - Protection and restoration of reefs

The coral reefs of the Indonesian islands are the most diverse in the world as well as one of the most difficult natural phenomenons to restore. In 1991 Indonesian and Philippine governments made a move to decentralize the capacities of enforcement authorities with regards to coastal management. This led to a lack of national support and funding and a great challenge for smaller sectors in facing the destruction of Southeast Asian coral reefs (Courtney 42). Though in 2002, 18% of the regions reefs were officially destroyed and 85% were called threatened, efforts for restoration are becoming more evident. Some of these efforts include creating isolated marine sanctuaries, transplantation of reefs, forms of electrolysis to advance growth and restrictions on harmful fishing techniques. Along with being labor intensive and hard to enforce, these efforts are extremely expensive; the US is estimated to spend $100 million or more.

An ill-balanced economic concept has occurred in Indonesian and Philippine waters with coral reefs. A predicted net benefit of coral reef fisheries is 2.4 US billion a year throughout Southeast Asian locations, while poverty levels are at an extreme high. As outside sources provide supplies for illegal coral/fish harvesting, rural fishermen decline to these methods in order to simply battle against starvation. The cycle of destruction becomes perpetual.

Marine Protected Areas

The concept of Marine Protected Areas (MPAs) has been introduced in Southeast Asia and elsewhere around the world to attempt to promote responsible fishery management and habitat protection. Much like the designation of national parks and wild life refuges, potentially damaging extraction activities are prohibited. The objectives of MPAs are both social and biological. Some of these include restoration of coral reefs, aesthetic maintenance, increased and protected biodiversity, and economic benefits. Conflicts surrounding MPAs involve lack of participation, clashing views and perceptions of effectiveness, and funding.

It is estimated that about 60% of the world’s reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in Southeast Asia, where an enormous 80% of reefs are considered endangered. One method of coastal reef management that has become increasingly prominent is the implementation of marine protected areas (MPAs). Indonesia currently has nine MPAs, claiming a total 41,129 squared kilometers of coastal are to be under protection. A study done on one of the more recently established MPAs in Indonesia showed the need for co-management when it comes to the success of managing MPAs. This collaborative approach emphasizes the cooperation and partnership between parties at the national, provincial, and local community level.

The coral reefs in the Philippines and Indonesia are disappearing rapidly due to dynamite and cyanide fishing. Between 1966 and 1986 the productivity of coral reefs in the Philippines dropped by one-third as the national population doubled (State of the Reefs). In Indonesia as well, over eighty percent of the coral reefs are under threat (The Jakarta Post). These two locations are home to the world's most diverse range of corals. If the rate of destruction does not diminish, seventy percent of all the world's coral reefs will be gone in the next twenty-five to forty years (the Philippines). Fortunately, efforts, such as Marine Protected Areas, are being made to promote coral reef restoration.

The Marine Aquarium Council (MAC), an international, not-for-profit organization that works to bring responsibility and sustainability to the aquarium fish trade industry, is also concerned with very specific human practices that bring harm and destruction to the coral reefs. Such concerns include the use of cyanide to stun and collect the fish, poor handling and husbandry practices, stock depletion, limited government regulation and reef management and lack of reliable data about the industry. A ban on the aquarium industry would create a loss of income to communities, as well as an increase in the illegal trade industry. MAC encompasses a large network of researchers, industry operators and conservationists to ensure objective solutions that can benefit the industry and the environment. Hughes, et al, acknowledges that “with increased human population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially. For example, markets for fishes and other natural resources have become global, supplying demand for reef resources far removed from their tropical sources” (Science 2003). MAC believes that there is a sustainable and responsible way to meet the demands of the industry by creating international standards and certification schemes to inform and educate consumers, collectors and retailers on the importance of sustaining healthy coral reef habitats. For more information, see MAC's website.

Coral reef - Artificial Reefs

Various efforts are being made to grow coral reefs and coral, a difficult task; they are fragile, react to small changes in their biological environment.

Coral reefs are being grown using a process called "mineral accretion". Applying a low voltage to a metallic structure causes limestone to build on the metal, upon which baby coral can attach, settle and feed. This greatly speeds the coral reef growth process. The voltage is low enough that it can easily generated by floating solar panels or from the waves. A coalition of scientists known as the Global Coral Reef Alliance, GCRA, has been growing coral reefs, as well as teaching the techniques. Numerous photos of the results are available at their website.

See also

• Coral
• Reef
• Atoll
• Southeast Asia coral reefs
• Marine conservation
• Diving locations
• Great Barrier Reef
• Project AWARE

Adapted from the Wikipedia article "Coral reef", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki