Coral Reef Degradation

coral reef pic
Figure 1 Diverse Coral on the Great Barrier Reef. Photograph taken by David Doubilet ( Accessed 19/12/13.

Degradation of coral reefs is becoming a growing problem; coral are part of the Phylum Cnidaria and are a varied group of animals, most of which live in colonies and create a diverse ecosystem in the form of coral reefs. These ecosystems can be found worldwide, mainly 30° North or South of the Equator (Spalding et al., 2001) shown in Figure 2 ( Accessed 19/12/13). This is due to the unique symbiotic relationship between coral and zooxanthellae, which is dependent on availability of light, ocean temperature and the alkalinity of the ocean (Gattuso et al., 1999; Kleypas et al., 1999).

Map of coral distribution
Figure 2 The global distribution of Coral Reefs ( Accessed 19/12/13)
Coral bleaching 1
Figure 3 Coral bleaching has taken place and the white calcium carbonate skeleton is revealed.. (Photo: A. Bruckner) (Bruckner, 2001)

Coral have a hard calcium carbonate skeleton that protects their tissues, these tissues are inhabited by photosynthetic micro-organisms, zooxanthellae. The coral rely on zooxanthellae which fix carbon and provide them with energy whilst the coral simultaneously provides the zooxanthellae with protection and nutrients (Kaiser et al., 2011).  The calcium carbonate skeleton makes the coral appear structurally strong, however today coral reefs are threatened by a number of physical and human activities. Up to 30% of coral reefs are already severely damaged and it is predicted that by 2030 up to 60% of these will be lost (Wilkinson, 2002).

There are a number of threats that cause stress to coral reefs, these include diseases, overfishing, tourism, storms and other weather processes such as hurricanes. However, the impacts of climate change are a growing threat that will continue into the future and will be a focal point in the investigation of coral reef degradation. Climate change is a process caused by the release of carbon dioxide into the atmosphere; as the atmosphere warms, global ocean temperatures increase. The ocean also acts as a carbon sink, the increasing levels of carbon dioxide cause an increase in ocean acidification. This combined with a rise in global ocean temperatures causes a large amount of stress to the corals, which results in coral bleaching shown in Figure 3 (Bruckner, 2001) and Figure 4 ( Accessed 19/12/13).  A rise in ocean temperature by 1°C can exceed the corals thermal threshold; once their thermal limit is breached the coral quickly expel the zooxanthellae from their tissues due to the environmental stress (Hoegh-Guldberg, 1999). This reveals their calcium carbonate skeleton which make them appear white in colour, as seen in Figures 3 and 4. If the coral is not then inhabited by another algae with a higher tolerance level, it will eventually die due to the absence of nutrients provided by the symbiotic zooxanthellae. With human activity believed to be enhancing climate change through the continuation of increasing CO₂ emissions, the frequency of bleaching events is predicted to increase (Sheppard, 2003). It has been predicted that consequences of ocean warming and ocean acidification will lead to the loss of 95% of eastern Caribbean coral reefs by 2035 (Buddemeier et al., 2011). Therefore the need for conservation of reefs now is extremely important for sustainability in the future.

coral bleaching2
Figure 4 Photograph of Coral Bleaching showing the white calcium carbonate skeleton (Ove Hoegh-Guiderg/AFP/Getty Images) Accessed at:

Coral reefs are a valuable ecosystem that need to be preserved. Although they can be found worldwide they only make up <0.1% of the global ocean surface area. However, they are extremely rich in biodiversity with over a quarter of all fish species exploiting them and a much greater density of vertebrate species present than can be found in a rain forest (Kaiser et al., 2011). Furthermore they not only play an integral part to marine organisms but also impact greatly upon humans, providing massive economic benefits. For example the Great Barrier Reef provides tourism revenue of around $700 million each year for Australia (Spurgeon, 1992). They also provide social benefits in less economically developed countries. In such areas subsistence fishing is the main source of diet and income for local inhabitants of coastal regions (Kent, 1998). On a larger scale the fishing industry is reliant on coral reefs in many parts of the world such as Asia, Europe and the US to create a habitat for fish species that can be exploited. Therefore coral reef degradation will not only result in economic loss from decreased tourism but also from the reduction in fishing industries. It will cause social and ecological problems such as a reduction in fish available for people in less developed countries, and a decrease in the biodiversity of coral reefs. A reduction in biodiversity in one of the key ecosystems in the ocean would have adverse effects globally and for future generations thus making the conservation of coral reefs not only a priority, but also a necessity.


Bruckner, A.W. 2001. Coral health and mortalit: Recognizing signs of coral diseases and predators. In: Humann and Deloach (eds.), Reef Coral Identification. Jacksonville, FL: Florida Caribbean Bahamas New World Publications, Inc. pp. 240-271.

Buddemeier, R., Lane, D., Martinich, J. (2011) Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study. Climatic Change, 109, 375–397.

Gattuso, J.P., Allemande, D., Frankignoulle, M. (1999) Photosynthesis and calcification at cellular, organismal and community levels in coral reefs. A review of interactions and control by carbonate chemistry. American Zoologist, 39, 160-83.

Hoegh-Guldberg, O. (1999) Climate change, coral bleaching and the future of the world’s coral reefs. Marine and Freshwater Research, 50, 839-66.

Kaiser, M.J., Attrill, M.J., Jennings, S., Thomas, D.N., Barnes, D.K.A., Brierley, A.S., Hiddink, J.G., Kaartokallio, H., Polunin, N.V.C., Raffaelli,  D.G. (2011). Marine Ecology Processes, Systems and Impacts, 305-306.

Kaiser, M.J., Attrill, M.J., Jennings, S., Thomas, D.N., Barnes, D.K.A., Brierley, A.S., Hiddink, J.G., Kaartokallio, H., Polunin, N.V.C., Raffaelli,  D.G. (2011). Marine Ecology Processes, Systems and Impacts, 306.

Kent, G. (1998). Fisheries, food security and the poor. Food Policy. 22: 393-404.

Kleypas, J.A., McManus, J.W., Menez, L.A.B. (1999) Environmental limits to reef development: where do we draw the line? American Zoologist, 39, 146-59.

Sheppard, C.R.C. (2003). Predicted recurrences of mass coral mortality in the Indian Ocean. Nature 425: 294-297.

Spalding, M.D, Ravilious, C., Green, E.P. (2001). World Atlas of Coral Reefs. University of California Press, Berkeley.

Spurgeon, J.P.G. (1992). The economic valuation of coral reefs. Marine Pollution Bulletin 24: 529-36

Wilkinson, C., Ed., Status of Coral Reefs of the World (Australian Institute of Marine Science, Townsville, Australia, 2002)

Websites: (Accessed 19/12/13) (Accessed 19/12/13) (Accessed 19/12/13)

9 years ago

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