Coral reef

Some of the biodiversity of a coral reef.

A coral reef is a type of biotic reef that develops in tropical waters by the growth of coralline algae, hermatypic corals, and other marine organisms. Coral reefs are typically massive biogenic formations of calcium carbonate (limestone) that is deposited within or around the bodies of the inhabitants of the reef as skeletal material. This material gradually accumulates as debris and/or is knitted together by the continued growth of the attached forms living on the reef.

Coral Reef Biology

The building blocks of coral reefs are the skeletons of generations of reef-building algae, corals, and other organisms that are composed of calcium carbonate. For example, as a coral head grows, it lays down a skeletal structure encasing each new polyp. Waves, grazing fishes (such as parrotfish), sea urchins, sponges, and other forces and organisms break down the coral skeletons into fragments that settle into spaces in the reef structure. Many other organisms living in the reef community contribute their skeletal calcium carbonate in the same manner. Coralline algae are actually the main contributors to the structure, at least in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae contribute to reef-building by depositing limestone in sheets over the surface of the reef and thereby contributing to the structural integrity of the reef. Many coralline algae species form nodules, or develop on the surface of fragments, enlarging these. The crust-forming species protect coral reefs by withstanding and mitigating wave pressures that would destroy most corals. This crust often forms a protective ridge on the outer edge of a reef (reef crest or reef margin), particularly in the Pacific (Castro and Huber, 2000; Nybakken, 1997).

Reef-building or hermatypic corals are only found in the photic zone (above 50m depth), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. The coral polyps do not photosynthesize, but have a symbiotic relationship with single-celled algae called zooxanthellae; these algal cells within the tissues of the coral polyps carry out photosynthesis and produce excess organic nutrients that are then used by the coral polyps. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Indeed, the relationship is responsible for coral reefs in the sense that without their symbionts, coral growth would be too slow for the corals to form impressive reef structures.

Although corals are found growing in most areas of a healthy coral reef, the elevation of the reef flat relative to sea level (and considering tidal range) imposes significant constraints on coral growth. In general, only a small number of coral species can thrive on the reef flat, and these cannot grow above a certain height because the polyps can withstand only limited exposure to the air at low tide. Of course some reef flats carry a meter or so of water over the surface, and then coral growth can be prolific. It is the upward growth of coralline algae on the outer part of the reef flat that ultimately results in an overall rise in the surface elevation of a reef, which typically slopes gently downward in towards the shore or lagoon and very steeply downward in the seaward direction. Prolific growth of these algae is a response to water motion bringing in inorganic nutrients and removing waste products. The damaging effects of exposure at low tide on the algae is ameliorated somewhat by constantly breaking waves on the reef edge. Nonetheless, it is the case that mature reefs are in equilibrium with both sea level and wave regime with respect to their elevation, and excess production of limestone moves away from the margin to expand the reef laterally and fill in low areas.

The more prolific growths of corals are to be found in water deeper than where the bottom is exposed at low tides: on the frontal reef slope (forereef), in lagoons, and along reef channels that bisect the flat. Under conditions of clear, moving seawater, corals provide the bulk of the skeletal material comprising the reef and the structural complexity that results in a high diversity of reef associated fishes and invertebrates.

Coral Reef Formations

Diagram of a fringing coral reef.

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.

World-wide distribution of reefs

Locations of coral 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 total (Spalding et al., 2001).

Coral reefs are either restricted or absent from along 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). Corals are also restricted from off the coastline of South Asia from Pakistan to Bangladesh (Spalding et al., 2001).

Famous coral reefs and reef areas of the world include:

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

Ecology and biodiversity

Coral reefs support an extraordinary amount of biodiversity, although located in nutrient-poor tropical waters. The process of nutrient recycling between corals, zooxanthellae, and other reef organisms provides an explanation for why coral reefs flourish in these waters: recycling ensures that fewer nutrients are needed overall to support the community. Cyanobacteria also provide soluble nitrates for the coral reef through the process of nitrogen fixation. Corals absorb nutrients, including inorganic nitrogen and phosphorus, directly from the water, and they feed upon zooplankton that are carried past the polyps by water motion (Castro and Huber, 2000). Thus, primary productivity on a coral reef is very high. Producers in coral reef communities include the symbiotic zooxanthellae, coralline algae, and various seaweeds, especially small types called turf algae, although scientists disagree about the importance of these particular organisms (Castro and Huber, 2000).

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

Reefs are also home to a large variety of other organisms, including sponges, Cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, spiny lobsters and crabs), mollusks (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. A few of these varied species feed directly on corals, while others graze on algae on the reef and participate in complex food webs (Castro and Huber, 2000; Spalding et al., 2001).

A number of invertebrates, collectively called cryptofauna, inhabit the coral rock substrate itself, either boring into the limestone surface or living in pre-existing voids 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).

Threats to Reefs

Bioerosion (coral damage) such as this may be caused by coral bleaching. [1]

Humans continue to represent the single greatest 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 been implicated as a driver of decline due to the use of cyanide and other chemicals in the capture of small fishes. Finally, above normal water temperatures, due to climate phenomena such as El Niño and global warming, can cause coral bleaching. According to The Nature Conservancy, if destruction increases at the current rate, 70% of the world’s coral reefs will have disappeared within 50 years. This loss would be an economic disaster for peoples living in the tropics.

Land development and pollution

Extensive and poorly managed land development can threaten the survival of coral reefs. Within the last 20 years, once prolific mangrove forests, which absorb massive amounts of nutrients and sediment from runoff caused by farming and construction of roads, buildings, ports, channels, and harbors, are being destroyed. Nutrient-rich water causes fleshy algae and phytoplankton to thrive in coastal areas in suffocating amounts known as algal blooms. Coral reefs are biological assemblages adapted to waters with low nutrient content, and the addition of nutrients favors species that disrupt the balance of the reef communities.

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 Asian coral reefs are at risk from damaging fishing practices (such as cyanide and blast fishing), overfishing, sedimentation, pollution and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas are underway to protect these reefs. Indonesia, for example 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. Indonesia's coral reefs are located in the heart of the Coral Triangle and have been victim to destructive fishing, unregulated tourism, and bleaching due to climatic changes. Data from 414 reef monitoring stations throughout Indonesia in 2000 found that only 6 percent of Indonesia’s coral reefs are in excellent condition, while 24 percent are in good condition, and approximately 70 percent are in poor to fair condition (2003 The Johns Hopkins University).

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) is an international, not-for-profit organization that works to bring responsibility and sustainability to the aquarium fish trade industry concerned with industry practices that bring harm to coral reefs. Such concerns include the use of cyanide to stun and collect fish, poor handling and husbandry practices, wild stock depletion, limited government regulation and management of natural resources, and lack of reliable data about the industry. A ban on collecting organisms from reefs for the aquarium industry would create a loss of income to communities, and possibly an increase in illegal trade. 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, (2003), 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". MAC supports the concept 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 environments.

See also

• Artificial reef
• Atoll
• Coral
• Great Barrier Reef
• Marine conservation
• Project AWARE
• Reef
• Southeast Asia coral reefs

References

• Barber, Charles V. and Vaughan R. Pratt. 1998. Poison and Profit: Cyanide Fishing in the Indo-Pacific. Environment, Heldref Publications.
• Butler, Steven. 1996. "Rod? Reel? Dynamite? A tough-love aid program takes aim at the devastation of the coral reefs". U.S. News and World Report, 25 November 1996.
• Castro, Peter and Michael Huber. 2000. Marine Biology. 3rd ed. Boston: McGraw-Hill.
• Christie, P. 2005a. University of Washington, Lecture. 18 May 2005.
• Christie, P. 2005b. University of Washington, Lecture. 4 May 2005.
• CIA - World Factbook -- Philippines [3]
• Clifton, Julian. 2003. Prospects for Co-Management in Indonesia's Marine Protected Areas. Marine Policy, 27(5): 389-395.
• Courtney, Catherine and Alan White. 2000. Integrated Coastal Management in the Philippines. Coastal Management; Taylor and Francis.
• Fox, Helen. 2005. Experimental Assessment of Coral Reef Rehabilitation Following Blast Fishing. The Nature Conservancy Coastal and Marine Indonesia Program. Blackwell Publishers Ltd, Feb 2005.
• Gjertsen, Heidi. 2004. Can Habitat Protection Lead to Improvements in Human Well-Being? Evidence from Marine Protected Areas in the Philippines.
• Hughes, et al. 2003. Climate Change, Human Impacts, and the Resilience of Coral Reefs. Science. Vol 301 15 August 2003
• Martin, Glen. 2002. "The depths of destruction Dynamite fishing ravages Philippines' precious coral reefs". San Francisco Chronicle, 30 May 2002
• Nybakken, James. 1997. Marine Biology: An Ecological Approach. 4th ed. Menlo Park, CA: Addison Wesley.
• Sadovy, Y.J. Ecological Issues and the Trades in Live Reef Fishes, Part 1
• USEPA.
• Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC.

External links

• Global Coral
• Marine Aquarium Council
• NCORE National Center for Coral Reef Research University of Miami
• Reef Management