'Coral reefs' are
aragonite structures produced by living organisms, found in shallow, tropical marine waters with little to no nutrients in the water. High nutrient levels such as that found in runoff from agricultural areas can harm the reef by encouraging the growth of
algae.
[1] In most reefs, the predominant organisms are stony
corals, colonial cnidarians that secrete an exoskeleton of
calcium carbonate (limestone). The accumulation of skeletal material, broken and piled up by wave action and
bioeroders, produces a massive calcareous formation that supports the living corals and a great variety of other animal and plant life. Although corals are found both in temperate and tropical waters, reefs are formed only in a zone extending at most from 30°N to 30°S of the equator; the reef-forming corals do not grow at depths of over 30 m (100 ft) or where the water temperature falls below 16 °C (72 °F).
Biology
Anatomy of a coral polyp.
The building blocks of coral reefs are the generations of reef-building
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 fish (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 [i.e zooxanthelate,filamentous algae] are important contributors to the structure of the reef 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 also to the structural integrity of the reef.
Reef-building or hermatypir corals are only found in the
photic zone (above 50 m 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. Corals can get up to 90% of their nutrients from their zooxanthellae symbionts.
[2]
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 hardy 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.
Formations
Diagram of a fringing coral reef.
Fringing reef off the coast of Eilat, Israel.
Coral reefs can take a variety of forms, defined in 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 that is directly attached to a shore or borders it with an intervening shallow channel or lagoon.
★ 'Barrier reef' – reef separated from a mainland or island shore by a deep
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 extending all the way around a lagoon without a central island; see
atoll.
★ 'Bank Reef' – Bank reefs are larger than patch reefs and are linear or semi-circular in outline.
Distribution
Locations of coral reefs.
Coral reefs are estimated to cover 284,300 square kilometres, with the
Indo-Pacific region (including the
Red Sea,
Indian Ocean,
Southeast Asia and the
Pacific) accounting for 91.9% of the total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including
Australia accounts for 40.8%.
Atlantic and
Caribbean coral reefs only account for 7.6% 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). They are also restricted along the coast around north-eastern
South America and
Bangladesh due to the release of vast quantities of freshwater from the
Amazon and
Ganges Rivers respectively.
Famous coral reefs and reef areas of the world include:
★ The
Great Barrier Reef - largest coral reef system in the world,
Queensland, Australia;
★ The
Belize Barrier Reef - second largest in the world, Belize,
Central America; and
★ The
Red Sea Coral Reef - located off the coast of Egypt and Saudi Arabia.
★
Pulley Ridge - deepest photosynthetic coral reef,
Florida
★ Many of the numerous reefs found scattered over the
Maldives
Ecology and biodiversity
Coral reefs support an extraordinary
biodiversity; although they are located in nutrient-poor tropical waters. The process of
nutrient cycling 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),
molluscs (including
cephalopods),
echinoderms (including
starfish, 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 molluscs, and
Sipunculans. Those settling on the reef include many other species, particularly crustaceans and
Polychaete worms (Nybakken, 1997).
Due to their vast biodiversity, many governments world-wide take measures to protect their coral reefs. In Australia, the Great Barrier Reef is protected by the
Great Barrier Reef Marine Park Authority, and is the subject of many plans and pieces of legislation, including a
Biodiversity Action Plan.
Algae and coral reef
Researchers have found evidence of algae dominance in locations of healthy coral reefs. In surveys done around largely uninhabited US Pacific islands, algae consists of a large percentage of the surveyed coral locations.
[3] The algae population consists of turf algae,
coralline algae, and
macroalgae.
Threats
Human activity continues to represent the single greatest threat to coral reefs living in Earth's
oceans. In particular,
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. Hughes, et al, (2003), writes 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".
Currently researchers are working to determine the degree various factors impact the reef systems. The list of factors is long but includes the oceans acting as a
carbon dioxide sink, changes in
Earth's atmosphere,
ultraviolet light,
ocean acidification, biological
virus, impacts of
dust storms carrying agents to far flung reef systems, various pollutants, impacts of
algal blooms and others... Reefs are threatened well beyond coastal areas and so the problem is broader than factors from land development and pollution though those are too causing considerable damage.
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. Both the loss of wetlands and mangrove habitats are considered to be significant factors affecting
water quality on inshore reefs.
[5]
Poor water quality has also been shown to encourage the spread of
infectious diseases among corals.
[6]
Copper, a common industrial pollutant, has been shown to interfere with the
life history and development of coral polyps.
[7]
Fish trade
The hobby of keeping saltwater aquaria has experienced an increase in world popularity since the 1990s. Beyond sales of aquaria, air pumps, food, medications and other supplies, the primary product of the aquarium industry is fish. However, the world market is limited in the diversity of collected species. For example, among 4000 coral reef fish species, only 200–300 are exploited. Selection of species results from a demand for fish being highly colorful and being able to be maintained and fed in aquaria. The last point is very important in the choice of imported species.
Although a few fish species (e.g. Pomacentridae) can be reproduced in aquaria, 95% of exploited fish are directly collected in the coral environment. Intense sampling of coral reef fish, especially in South-East Asia (including Indonesia and the Philippines), has caused great damage to the environment. 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%.
[8] In such
developing countries, a fisherman might resort to such unethical practices in order to prevent his or her family from starving.
Most, 80–90%, of aquarium fish exported from the Philippines are captured with
sodium cyanide. This toxic chemical is dissolved in sea water and released into fish shelters. It has a rapid narcotic effect on fish, which are then easily captured. However, most fish collected with cyanide die a few months after capture from extensive liver damage. Moreover, other fish species that are not interesting for the aquarium market also die in the field.
[9]
Dynamite fishing
Dynamite fishing is another extremely destructive method that fishermen use to harvest small fish. Sticks of dynamite, grenades, or home-made explosives are lit or activated and thrown in the water. Once the dynamite goes off the explosion brings about an underwater shockwave, causing the internal organs of fish to liquefy, killing them almost instantly. 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 not only kills the fish within the main blast area, but also claims the lives of many reef animals that are not edible or wanted. Also, many of the fish do not float to the surface to be collected, but sink to the bottom. The blast also kills the corals in the area, eliminating the very structure of the reef, destroying the habitat for fish and other animals important for the maintenance of a healthy reef. Areas that used to be full of coral become deserts, full of coral rubble, dead fish and little else after dynamite fishing.
Bleaching
Main articles: Coral bleaching
During the 1998 and 2004
El Niño weather phenomena, 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.
Ocean acidification
Main articles: Ocean acidification
The decreasing ocean surface pH is of increasing long-term concern for coral reefs.
[10]
Increased atmospheric CO
2 increases the amount of CO
2 dissolved in the oceans.
[11] Carbon dioxide gas dissolved in the ocean reacts with water to form
carbonic acid, resulting in
ocean acidification. Ocean surface pH is estimated to have decreased from approximately 8.25 to 8.14 since the beginning of the industrial era,
[Jacobson, M. Z. (2005). Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry. ''J. Geophys. Res. Atm.'' '110', D07302.] and it is estimated that it will drop by a further 0.3 - 0.4 units by 2100 as the ocean absorbs more anthropogenic CO
2.
[Orr, J. C. ''et al.'' (2005). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. ''Nature'' '437', 681-686.]. Under normal conditions, the conditions for calcium carbonate production are stable in surface waters since the carbonate ion is at
supersaturating concentrations. However, as ocean pH falls, so does the concentration of this ion, and when carbonate becomes under-saturated, structures made of calcium carbonate are vulnerable to dissolution. Research has already found that corals experience reduced calcification or enhanced dissolution when exposed to elevated CO
2[Gattuso, J.-P., Frankignoulle, M., Bourge, I., Romaine, S. and Buddemeier, R. W. (1998). Effect of calcium carbonate saturation of seawater on coral calcification. ''Glob. Planet. Change'' '18', 37-46.].
African dust outbreaks
Dust from the
Sahara moving around the southern periphery of the
subtropical ridge moves into the
Caribbean and
Florida during the warm season as the ridge builds and moves northward through the subtropical Atlantic. Since 1970, dust outbreaks have worsened due to periods of drought in Africa. There is a large variability in the dust transport to the Caribbean and Florida from year to year.
[12] Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s.
[13]
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 under way 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% of Indonesia’s coral reefs are in excellent condition, while 24% are in good condition, and approximately 70% are in poor to fair condition (2003
The Johns Hopkins University).
General estimates show approximately 10% of the coral reefs around the world are already dead.
[14][15]Problems range from
environmental effects of fishing techniques, described above, to
ocean acidification.
[10] Coral bleaching is another manifestation of the problem and is showing up in reefs across the planet.
Protection and restoration
Inhabitants of Ahus Island,
Manus Province,
Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. While line fishing is permitted, net and spear fishing are restricted based on cultural traditions. The result is that both the
biomass and individual fish sizes are significantly larger in these areas than in places where fishing is completely unrestricted (Cinner et al. 2005).
[17]
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.
Marine Protected Areas
One method of coastal reef management that has become increasingly prominent is the implementation of
Marine Protected Areas (MPAs). MPAs have 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, including 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.
Indonesia currently has nine MPAs, claiming a total 41,129 square kilometres of coastal waters 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).
See also
★
Coral
★
Coral bleaching
★
Coral rag
★
Black band disease
★
Marine conservation
★
Project AWARE
★
Coral Reef Alliance
★
White band disease
References
1. Corals reveal impact of land use
2. A Reef Manager’s Guide to Coral Bleaching, , , , Great Barrier Reef Marine Park Authority,, , 1 876945 40 0
3.
4. Bioerosion: an essential, and often overlooked, aspect of reef ecology Ryan Holl
5. Industries, Land Use and Water Quality in the Great Barrier Reef Catchment - Key Points Australian Government Productivity Commission
6. Sewage nutrients fuel coral disease Rachel Nowak
7. Copper decimates coral reef spawning Emma Young
8. CIA - The World Factbook -- Philippines
9. David LECCHINI, Sandrine POLTI, Yohei NAKAMURA, Pascal MOSCONI, Makoto TSUCHIYA, Georges REMOISSENET, Serge PLANES (2006) "New perspectives on aquarium fish trade" Fisheries Science 72 (1), 40–47
10. Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006, Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research, NSF, NOAA, & USGS, 88 pp.
11. The Ocean and the Carbon Cycle
12. Usinfo.state.gov. Study Says African Dust Affects Climate in U.S., Caribbean. Retrieved on 2007-06-10.
13. U. S. Geological Survey. Coral Mortality and African Dust. Retrieved on 2007-06-10.
14. Save Our Seas, 1997 Summer Newsletter, Dr. Cindy Hunter and Dr. Alan Friedlander
15. Tun, K., L.M. Chou, A. Cabanban, V.S. Tuan, Philreefs, T. Yeemin, Suharsono, K.Sour, and D. Lane, 2004, p:235-276 in C. Wilkinson (ed.), Status of Coral Reefs of the world: 2004.
16. Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006, Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research, NSF, NOAA, & USGS, 88 pp.
17. Coral Reef Management, Papua New Guinea
General 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.
★ Cinner, J. et al. (2005). Conservation and community benefits from traditional coral reef management at Ahus Island, Papua New Guinea. Conservation Biology 19 (6), 1714-1723
★
CIA - World Factbook -- Philippines
★ 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
★
Encyclopedia of Earth - Coral reef
★
ARC Centre of Excelence in Coral Reef Studies
★
Coral reef facts from
The Nature Conservancy
★
NOAA's Coral-List Listserver for Coral Reef Information and News
★
NOAA's Coral Reef Conservation Program
★
NOAA's Coral Reef Information System
★
NOAA Report: The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2005
★
ReefBase: A Global Information System on Coral Reefs
★
National Coral Reef Institute Nova Southeastern University
★
Global Coral Reef Alliance
★
Global Coral Reef Monitoring Network
★
Marine Aquarium Council
★
NCORE National Center for Coral Reef Research University of Miami
★
The Coral Reef Alliance (CORAL) - Working Together to Keep Coral Reefs Alive
★
Science and Management of Coral Reefs in the South China Sea and Gulf of Thailand
★
A special report on the plight of the planet's coral reefs—and how you can help—from ''Mother Jones'' magazine
★
Coral reefs – their distribution and origin
★
The Reef Ball Foundation website
★
A guide to finding sources and literature about coral reefs
★
CORAMM - Coral Risk Assessment, Monitoring and Modelling. European project investigating potential impacts on cold water coral reef health.
★
The EU HERMES( Hotspot Ecosystem Research on the Margins of European Seas) project webpage gives a good introduction to cold water corals.
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