Coral Reefs
Coral
reefs are the ocean’s most diverse and complex ecosystems, supporting 25% of
all marine life, including 800 species of reef-building corals and more than
one million animal and plant species. They are close relatives of sea anemones
and jellyfish, as each coral is a colony consisting of many individual sea
anemone-like polyps that are all interconnected.
Tropical coral reefs found in warm, clear water at relatively shallow depths are intricately patterned carpets of life growing on foundations formed primarily by calcium carbonate exoskeletons and coralline algae. These structures fuse over time, enlarging the reef and creating countless nooks and crannies. As the reef grows, species from nearly every major taxonomic group cover every square inch of these tightly integrated systems, providing food and shelter to a spectacular variety of fish species, including many of commercial value.
‘Hard’ corals use calcium carbonate from seawater to synthesize a hard, mineral protective shell around each polyp. These exoskeletons, along with shells formed by coralline algae, mollusks and tubeworms, spicules made by sponges, and shells of other calcifying species form the structural foundation of coral reefs. Corals catch plankton with their tentacles, but most of their nutrition comes from photosynthetic algae that live in their tissues, using the coral’s waste products for their own nutrition and feeding the corals with sugars and other nutritious compounds that leak through their cell membranes.
Deep water reefs, formed by large, long-lived but fragile, soft corals are also architecturally and ecologically complex and teem with life, but lack a calcium carbonate foundation. Though beyond the reach of sunlight, underwater lights reveal them to be nearly as beautiful and colorful as their tropical counterparts.
The condition of coral reefs is important to the Ocean Health Index because healthy reefs provide many benefits to people, including food, natural products, coastal protection from storms, jobs and revenue, tourism and recreation, biodiversity and others.
60% of reefs are already seriously damaged by local sources such as overfishing, destructive fishing, anchor damage, coral bleaching, coral mining, sedimentation, pollution, and disease. When these types of human threats are combined with the influence of rising ocean temperatures, 75% of reefs are threatened (Burke et al, 2011).
Tropical coral reefs found in warm, clear water at relatively shallow depths are intricately patterned carpets of life growing on foundations formed primarily by calcium carbonate exoskeletons and coralline algae. These structures fuse over time, enlarging the reef and creating countless nooks and crannies. As the reef grows, species from nearly every major taxonomic group cover every square inch of these tightly integrated systems, providing food and shelter to a spectacular variety of fish species, including many of commercial value.
‘Hard’ corals use calcium carbonate from seawater to synthesize a hard, mineral protective shell around each polyp. These exoskeletons, along with shells formed by coralline algae, mollusks and tubeworms, spicules made by sponges, and shells of other calcifying species form the structural foundation of coral reefs. Corals catch plankton with their tentacles, but most of their nutrition comes from photosynthetic algae that live in their tissues, using the coral’s waste products for their own nutrition and feeding the corals with sugars and other nutritious compounds that leak through their cell membranes.
Deep water reefs, formed by large, long-lived but fragile, soft corals are also architecturally and ecologically complex and teem with life, but lack a calcium carbonate foundation. Though beyond the reach of sunlight, underwater lights reveal them to be nearly as beautiful and colorful as their tropical counterparts.
The condition of coral reefs is important to the Ocean Health Index because healthy reefs provide many benefits to people, including food, natural products, coastal protection from storms, jobs and revenue, tourism and recreation, biodiversity and others.
60% of reefs are already seriously damaged by local sources such as overfishing, destructive fishing, anchor damage, coral bleaching, coral mining, sedimentation, pollution, and disease. When these types of human threats are combined with the influence of rising ocean temperatures, 75% of reefs are threatened (Burke et al, 2011).
Major Sources Of Damage To Coral Reefs
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Which Goals Does This Affect?
How Was It Measured?
The extent of coral reefs are derived from the 500m resolution dataset developed for Reefs at Risk Revisited (Burke et al. 2011), in conjunction with a re-sampled version of the Ocean Health Index EEZ regions. The condition of reefs was estimated using data for percentage cover by live coral determined from 12,634 surveys conducted from 1975-2006 and summarized by Bruno and Selig (2007) and Schutte et al. (2010).
What Are The Impacts?
ECOLOGICAL IMPACT
Corals
that are exposed to elevated sea surface temperatures expel the symbiotic
photosynthetic algae responsible for their nutrition and coloration
[zooxanthelle] in a process known as coral bleaching. Corals can recover from
occasional bleaching, but not from repeated bleaching. Increases in sea-surface
temperature of about 1-3 °C are projected to result in more frequent coral
bleaching events and widespread mortality (IPCC 2007).
Elevated sea surface temperatures cause increased damage to reefs from breakage as storm frequency and intensity increase.
Increasing concentrations of carbon dioxide in the atmosphere cause increased concentrations in surface waters, leading to ocean acidification (lowered pH). Acidification decreases the availability of calcium carbonate, making it harder for corals and other calcifying organisms to form their shells; it also dissolves existing shells.
By the end of the century, it is predicted that ocean pH will drop from its current value of about 8.1 by as much as 0.4 units; by 2050, conditions will not be sufficient for the formation of calcium carbonate (Hoegh-Guldberg et al. 2007).
Coral reefs that have been overfished can cause ecosystem structure to shift as fish populations decline. This can result in increases in disease and take-over by coral predators and aggressive algal species.
Overfishing threatens more than 70% of coral reefs in the Caribbean (Burke et al. 2011).
Hard corals develop and grow at a very slow rate, which does not allow for easy recovery when they are physically damaged by hurricanes, shipwrecks or anchors. Branching hard corals can recover more easily, but they are more susceptible to breakage by storms or physical contact.
Elevated sea surface temperatures cause increased damage to reefs from breakage as storm frequency and intensity increase.
Increasing concentrations of carbon dioxide in the atmosphere cause increased concentrations in surface waters, leading to ocean acidification (lowered pH). Acidification decreases the availability of calcium carbonate, making it harder for corals and other calcifying organisms to form their shells; it also dissolves existing shells.
By the end of the century, it is predicted that ocean pH will drop from its current value of about 8.1 by as much as 0.4 units; by 2050, conditions will not be sufficient for the formation of calcium carbonate (Hoegh-Guldberg et al. 2007).
Coral reefs that have been overfished can cause ecosystem structure to shift as fish populations decline. This can result in increases in disease and take-over by coral predators and aggressive algal species.
Overfishing threatens more than 70% of coral reefs in the Caribbean (Burke et al. 2011).
Hard corals develop and grow at a very slow rate, which does not allow for easy recovery when they are physically damaged by hurricanes, shipwrecks or anchors. Branching hard corals can recover more easily, but they are more susceptible to breakage by storms or physical contact.
HUMAN HEALTH IMPACT
Corals
and affiliated sponges contain bioactive chemical compounds that can be useful as
cancer and virus-fighting drugs. For example, AZT, a compound generated by a
Caribbean reef sponge, is an antiretroviral drug that effectively slows the
spread of the HIV virus.
ECONOMIC IMPACT
Almost
500 million people depend on coral reefs for coastal protection, food, and
tourism income (Wilkinson, 2008).
Coral reefs help protect shorelines from storm damage and can absorb 70-90% of wave energy.
The economic benefit of reef protection can be substantial. A proposed wastewater treatment facility in the Florida Keys that would cost US $60-70 million to build and US $4 million annually to operate and maintain would lead to an estimated US $700 million benefit in Net Present Value (NPV) from reef ecosystem services and other reef industries (Cesar et al. 2003).
Total net benefits from coral reef shoreline protection are estimated at US $9 billion globally (Cesar et al. 2003).
Reef fisheries generate large potential net benefits and are relied upon by many for livelihoods and food; unsustainable fishing practices can have a severe impact upon reef-dependent economies.
Total net benefit of coral reefs to fisheries: US $5.7 billion (Cesar, Burke, and Pet-Soede, 2003).
Reef tourism provides long-term benefits although upfront costs to prevent reef degradation may initially be high.
Costs of coral bleaching to tourism in Net Present Value (NPV) is estimated at $10 - $40 billion (Cesar, Burke, and Pet-Soede, 2003)
Coral reefs help protect shorelines from storm damage and can absorb 70-90% of wave energy.
The economic benefit of reef protection can be substantial. A proposed wastewater treatment facility in the Florida Keys that would cost US $60-70 million to build and US $4 million annually to operate and maintain would lead to an estimated US $700 million benefit in Net Present Value (NPV) from reef ecosystem services and other reef industries (Cesar et al. 2003).
Total net benefits from coral reef shoreline protection are estimated at US $9 billion globally (Cesar et al. 2003).
Reef fisheries generate large potential net benefits and are relied upon by many for livelihoods and food; unsustainable fishing practices can have a severe impact upon reef-dependent economies.
Total net benefit of coral reefs to fisheries: US $5.7 billion (Cesar, Burke, and Pet-Soede, 2003).
Reef tourism provides long-term benefits although upfront costs to prevent reef degradation may initially be high.
Costs of coral bleaching to tourism in Net Present Value (NPV) is estimated at $10 - $40 billion (Cesar, Burke, and Pet-Soede, 2003)
What Has Been Done?
Coral Reef Case Studies
Although the pressures affecting coral reefs are numerous and
challenging, there are many examples of ways that these can be successfully
addressed. Encouraging examples from 16 countries are available on the Reef
Resilience Web site.
CI
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Conservation International [CI]: Socioeconomic Conditions along the World’s Tropical Coasts: 2008
Synthesizes the latest knowledge regarding people and reefs based on
socioeconomic monitoring around the world.
Coral Reef Alliance [CORAL]
An
international NGO founded to support local projects that benefit coral reefs
and surrounding communities.
Global Coral Reef Monitoring Network [GCRMN]
GCRMN works to improve coral reef conservation
and management efforts and synthesizes the latest ecological and socioeconomic
monitoring results into a biannual publication, Status of Coral Reefs of the World
International Coral Reef Initiative [ICRI]
A
partnership between non-government organizations, governments and other
international organizations, that works to implement international conventions
and agreements.
International Coral Reef Action Network [ICRAN]
A
network of science and conservation organizations that use scientific knowledge
to conserve reefs on a global scale.
Reef Base: A Global Information System for Coral Reefs
A
source for coral reef data, publications, maps, and other resources from around
the world hosted by World Fish Center
Reef Environmental Education Foundation [REEF]
A foundation that preserves marines environments
by educating and enabling divers and other people interested in ocean
conservation to perform volunteer reef surveys.
Science to Action: Coral Health Index: Measuring Coral Community Health
A
guidebook to evaluating coral health and understanding impacts
Science to Action: Economic Values of Coral Reefs, Mangroves, and Seagrasses
A
Global Compilation provides the latest statistics on the economic values of
tropical marine resources
Science to Action: Living with the Sea
Local
efforts buffer effects of global change: explains the benefits of protecting
reefs at a local level.
World Resources Institute [WRI]: Reefs at Risk Revisited
A
booklet detailing spatial and statistical data on current threats to coral
reefs.
World Atlas of Coral Reefs
A
detailed assessment of the distribution and status of coral reefs
Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC.
Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC.
References
Barber, Charles Victor, Pratt, Vaughan
R. 1997. Sullied Seas: Strategies for Combating Cyanide Fishing in Southeast
Asia and Beyond. World Resources
Institute, Washington, DC.
Bryant, D., Burke, L., McManus, John & Spalding, Mark Reefs at Risk: A Map-Based Indicator of Threats to the World’s Coral Reefs. 60 (World Resources Institute: Washington D.C., 1998).
Bruno, J. F. & Selig, E. R. Regional Decline of Coral Cover in the Indo-Pacific: Timing, Extent, and Subregional Comparisons. PLoS ONE 2, e711 (2007).
Burke, Lauretta & Maidens, J. Reefs at Risk in the Caribean. 84 (World Resources Institute: Washington D.C., 2004).
Burke, Lauretta, Reytar, Katie, Spalding, Mark & Perry, Allison Reefs at Risk Revisited. 130 (World Resources Institute: Washington D.C., 2011).
Burke, Lauretta, Selig, Liz & Spalding, Mark Reefs at Risk in Southeast Asia. 76 (World Resources Institute: Washington D.C., 2002).
Burkepile, D. E. & Hay, M. E. Herbivore species richness and feeding complementarity affect community structure and function on a coral reef. PNAS 105, 16201–16206 (2008).
Hoegh-Guldberg, O. et al. Coral Reefs Under Rapid Climate Change and Ocean Acidification. Science 318, 1737–1742 (2007).
Sandin, S. A. et al. Baselines and Degradation of Coral Reefs in the Northern Line Islands. PLoS ONE 3, e1548 (2008).
Schutte, V. G. W., Selig, E. R. & Bruno, J. F. Regional spatio-temporal trends in Caribbean coral reef benthic communities. Mar Ecol Prog Ser 402, 115–122 (2010).
Spalding, M., Ravilious, C., Green,
E.P. (2001). World Atlas of Coral Reefs.
Prepared at the UNEP World Conservation Monitoring Centre. Berkley,
CA: University of California Press
Wells, S. In the front line. Shoreline protection and other ecosystem services from mangroves and coral reefs. (UNEP-WCMC: Cambridge, UK, 2006).
Vargas-Ángel, B., Looney, E. E., Vetter, O. J. & Coccagna, E. F. Severe, Widespread El Nino Associated Coral Bleaching in the US Phoenix Islands. Bulletin of Marine Science 87, 623–638 (2011).
Wilkinson, C Status of Coral Reefs of the World: 2008. 296 (Global Coral Reef Monitoring Network and Reef and Rainforest Research Center: Townsville, Australia, 2008).
PHOTO(S): © Keith A. Ellenbogen