How are coral reefs threatened?

How are coral reefs threatened?
In 2001, according to the World Atlas of Coral Reefs published by the UN Environment Programme World Conservation Monitoring Centre, 58% of the world’s coral reefs are under threat from human activities.
For more information visit:
http://www.unep-wcmc.org/
http://www.icran.org/
http://www.coralreef.org/
portals.conservation.org

Some of the major threats are:
Marine pollution from commercial sea vessels
Commercial shipping illegally dumps waste materials at sea.
Ballast and fuel storage tanks are emptied at sea, releasing fuel, oil and other chemicals.
Anti-fouling paints leach toxic chemicals.
For more information visit: http://www.imo.org/

Sewage from land-based developments
Tourist developments have inappropriate water treatment and sanitation systems.
Raw sewage is often dumped directly into the sea via outflow pipes that insufficiently long to prevent the sewage from being brought back to shore.
Effluent release results in increased levels of nitrogen and phosphorous into the sea leading to eutrophication.

Sedimentation
Deforestation removes the root systems that anchor forest soils.
Heavy rains erode unstable soil, which is transported by rivers and streams towards the sea.
Mangrove removal leads to above normal levels of sedimentation smothering the reef system.
Root mats hold 99% of rainforest nutrients. When a rainforest is burned or cut down the nutrients are removed from the system creating unproductive soil.
The land is often abandoned and new areas cleared.
For more information visit:
http://www.aims.gov.au/
http://info.anu.edu.au/

Over fishing
Natural predator and prey species are lost.
The balance within the system is lost, usually with detrimental effects.
Destructive fishing practices

Dynamite and other explosive fishing methods destroy habitats and breeding sites.
Larger fish are stunned and removed by fishers, but many smaller or less desirable fish die and are left amongst the broken coral.

Coral mining
Coral is often mined for use as a building material in coastal town and tourist resort development.

Aquarium trade
1471 fish species are traded worldwide.
Many juvenile ‘aquarium sized’ fish are captured, sedated and shipped in plastic bags within polystyrene boxes. Most do not survive the long journey.
Future generations of potential breeding fish stocks are lost.
Only 1-10% of fish and less than 1% of coral species can be bred in captivity. This perpetuates the demand for wild animals.
Concern about over-exploitation has led the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to list many coral species on CITES Appendix II.
For more information see CITES

Souvenirs
Over 500 invertebrate species (other than coral) are traded as marine ornamentals.
Estimates place the value of marine ornamental trade at US $200-330 million/year.
Increased popularity of coral for use in jewellery is of particular concern as many are rare deep-water species.
Extraction involves destructive trawls and tangle-net dredges causing immense damage to the reef.
As yet, pink, gold and bamboo corals are not listed in CITES so trade is not adequately monitored.
For more information see CITES

Bleaching
Global warming and altered global climate patterns has increased the incidence of coral bleaching.
Bleaching arises from abnormally high sea temperatures inducing the coral polyps to expel their zooxanthellae removing the corals primary means of nutrient absorption and ultimately causing the death of the coral.
Sometimes corals recover their zooxanthellae and survive the event.
Prolonged stress from other factors such as salinity, ultraviolet light, sediment, or pollutants, means the corals are unable to cope and die.
Increased atmospheric carbon dioxide has further implications on coral growth as it affects the skeleton forming chemical reactions.
A link between temporary local hotspots and bleaching events has been identified. A series of monitoring systems identifying hotspots have been implemented using satellites, buoys and underwater sensors to assess sea surface temperatures.
In 1998, 75% of reefs were affected by bleaching related to global climate change, 16% died.
For more information see:

http://www.cites.org/
http://www.icriforum.org/
coralreefwatch.noaa.gov/satellite/index.html
www.reefbase.org/threats/thr_bleaching.asp
www.cordio.org/bleaching.asp