Visitors to the tropical coral reefs are stunned by their beauty and biodiversity. Whether you are an aquarium enthusiast, a diver, naturalist, professional biologist, underwater photographer or tourist, the colorful life of these shallow underwater gardens thrills you.
Coral reefs are of utmost importance to people. Nearly 500 million people depend on coral reefs for food, coastal protection and tourism income, and about 30 million of the poorest people on Earth depend entirely on coral reefs for food. In addition, coral reef sites are special or holy places for some local people; for example, local people of East African coast settlements have strong cultural and religious ties to marine environments where they have carried out traditional fishing for hundreds of years. Consequently, there are several reasons to protect the coral reefs. The tropical coral reefs are among the most endangered ecosystems on our planet.
More than 240 contributors for 98 countries published a 580-page report, the full report can be downloaded from the Australian Institute of Marine Science (AIMS) at www.aims.gov.au. This article gives a brief overview of the major problems stressing the coral reefs.
There is little doubt that we — the humans — are directly involved in destroying the reefs. Although the corals have had to cope with natural forces for millions of years, it is human activities that kill the reefs.
Post The 1998-Bleaching Event
Coral bleaching (which involves the actual whitening of coral) occurs when symbiotic zooxanthellae are lost or there is a decrease in photosynthetic pigments in the zooxanthellae (Buckheim, 1998). It is wise to look back to 1998 when the global bleaching event happened. This was a “once-in-a-millennium” event. Hard and soft corals were affected in widely separate parts of the world, and much of it coincided with a large El Niño event, which immediately switched over to a strong La Niña. In some regions and countries, such as in Palau and other parts of Micronesia, the results were especially catastrophic. Here, more than 50 percent of the corals were killed, including some colonies more than 1,000 years old. These were some of the oldest organisms living on Earth, and it is therefore needless to say what a disaster the bleaching created. In some locations, nearly all of the fast-growing staghorn corals (Acropora) died. There were no historical experiences or reference of similar events. Since 1998, there have been more localized bleaching events in 2000 and 2003 that have caused damage to reefs (e.g., the 2003 event in the Caribbean and the Gulf of Mexico).
El Niño/La Niña, which caused the 1998 global coral bleaching event, killed about 16 percent of the world’s coral reefs, and of these, about 40 percent has recovered. The total of permanently destroyed reefs in 2004 was about 20 percent, which is an increase of 9 percent compared to 2000. This corresponds to more than 25 square kilometers. Even worse, 24 percent of the living reefs are under imminent risk of being destroyed, with another 26 percent under long-term threat of collapsing.
The Arabian and Persian Gulf, East Africa (including Kenya, Tanzania and Mosambique), southwest Indian Ocean, South Asia (such as Bangladesh, India and Maldives) and Southeast Asia (including Indonesia and the Philippines) are some of the regions under the greatest threat. These areas contain roughly 127 square kilometers of reefs, where about 48 square kilometers (38 percent) have been destroyed.
The report states:
There are few encouraging signs for reefs in the high biodiversity areas of Southeast Asia and the Indian Ocean, where human pressures continue to increase on coral reef; whereas reefs in the Pacific and around Australia remain quite healthy.
And the report does not give very promising predictions for the future, saying:
Increasing sea surface temperatures and CO2 concentrations provide clear evidence of global climate change in the tropics, and current predictions are that the extreme events of 1998 will become more common in the next 50 years….
The report goes on to say that global bleaching will not be an infrequent event occurring once every thousand years or so, but instead will be a regular event.
Reefs of the Caribbean and western Atlantic have also suffered and declined severely over the past years. The region has undergone bleaching events from 1983-2000, with 1998 as the most serious year. The major cause is high temperatures above 84 degrees Fahrenheit (29 degrees Celsius) for a long period of time.
Analyses of coral reefs in the wider Caribbean region confirm major reef declines, and they do not resemble the reefs of 30 years ago. Coral cover on many Caribbean reefs has declined by up to 80 percent; however, there are some encouraging signs of recovery.
The Reefs at Risk project also gives alarming estimates for this region, such as threats caused by coral disease and increasing water temperatures. It also mentions the following:
• Human activities put 64 percent of Caribbean coral reefs at risk.
• Thirty-three percent of Caribbean reefs are at risk due to costal developments.
• Thirty-five percent of the reefs are at risk because of land-based pollution and run-off.
• Overfishing threatens 60 percent of Caribbean reefs.
The conclusion is rather drastic with respect to the wider Caribbean and the reefs of the nearby Atlantic region. Here, there is an estimated decline of coral cover on many reefs from about 50 percent 25 years ago to about 10 percent in 2004. The decline is especially evident with respect to elkhorn species (Acropora cervicornis and A. plamata), and is caused by the same problems as for other regions of the world.
The number of diseases affecting coral reefs has increased considerably during the last years. As of 2004, there were 29 described coral diseases affecting more than 150 species on tropical coral reefs. The western Atlantic (including the Caribbean) and the Red Sea are the regions hardest hit.
Diseases have the potential to cause severe declines in coral populations as happened in the Caribbean with staghorn corals in the 1970s and 1990s. Stress to the corals lowers their resistance to diseases. The increasing number of coral diseases might therefore be linked to human pressures and global climate changes.
Crown Of Thorns Starfish (COTS) Outbreaks
The outbreak of the crown-of-thorns starfish (Acanthaster planci) is well-known to reef scientists, as well as aquarium enthusiasts, and has been a major issue on the Great Barrier Reef and other Indo-Pacific coral reefs for more than 40 years. During spawning, one single starfish can release as many as 50 million eggs per season, which gives this species a much higher fertility than other starfish. The invasion of Acanthaster on reefs causes disaster. These sea stars feed exclusively on stony coral polyps. Graveyards of white skeletons of stony corals are left behind where the coral-killing starfish has been.
The reason for COTS outbreaks remains uncertain, but there is much data that supports a theory that the survival of the starfish larva is linked to the amount of phytoplankton in the water. The amount of phytoplankton is linked to the run-off of nutrient-rich sediments, which has increased steadily during the last decades (Dr. Glenn Death, AIMS, personal communication). If this theory holds, it means that even COTS outbreak is indirectly caused by human activities.
The 2004 Tsunami
Another catastrophe having an impact on reefs was the disastrous tsunami that happened on December 26, 2004, radiating in the Indian Ocean from a major earthquake off Sumatra and from secondary earthquakes throughout the Andaman and Nicobar Islands. The tsunami resulted in more than 250,000 people killed or missing, and caused massive destruction to coastal resources and infrastructure. The tsunami also affected coral reefs in the Indian Ocean, but the damage was patchy and largely dependent on local environmental conditions.
Most of the damage to coral reefs resulted from sediment and rubble washed off of the land. The reefs of eastern Indonesia, Thailand, the Andaman and Nicobar Islands, and Sri Lanka suffered the most. Wilkinson (2004) estimates that most reefs will need 5 to 10 years to fully recover, provided that effective management is implemented. Yet human activities (e.g., pollution, overfishing, sediment run-off) are far more damaging to Indian Ocean reefs than the effects from the 2004 tsunami.
Norwegian Deep Sea Bioherms
Deep water coral reefs (bioherms) built by the nonphotosynthetic stony coral Lophelia pertusa, have been known for centuries from Norwegian fjords (inlets between cliffs or slopes) and the continental shelf. The coral was first mentioned in a publication by Erik Pontoppidan in 1752. It is, however, not until recently that we came to realize how widespread and large the reefs can be. Some of the structures composed by many individual reefs are several kilometres long and up to 35 meters high. With a growth rate of less than 1 centimeter per year, they represent the oldest living organisms in Norway.
Even these indispensable deep water reefs are threatened. Fish gather in great numbers around bioherms, which means that the deep water reefs become attractive sites for fishing boats. Trawling and other methods of fishing have damaged between 30 and 50 percent of the total coral area in Norwegian waters.
Coral Reef Task Force
In recent years, many environmental and protective organizations, databases and Internet sites have appeared — all with a common goal to preserve and monitor coral reefs. One of these is the Coral Reef Task Force (CRTF), established in June 1998, by Presidential Executive Order 13089. On their Internet, site it says, “Our mission is to lead, coordinate, and strengthen U.S. government actions to better preserve and protect coral reef ecosystems.”
The CRTF is responsible for overseeing implementation of the Executive Order, and developing and implementing coordinated efforts to map and monitor United States coral reefs. Additionally, they research the causes and solutions to coral reef degradation, implement strategies to promote conservation and sustainable use of coral reefs internationally, and reduce and mitigate coral reef degradation from pollution, overfishing and other causes.
In 2000, the Task Force developed the National Action Plan for Coral Reef Conservation, the first comprehensive U.S. strategy to conserve coral reefs. The plan outlines 13 integrated conservation strategies within two fundamental themes to address the most pressing challenges facing reefs today. To help implement the National Action Plan, the Task Force has launched a variety of initiatives and provides a forum for supporting collaborative action of its members and partner organizations.
In 2003, CRTF called for a report characterizing the condition of shallow water coral reef ecosystems in the U.S. and Pacific Freely Associated States (Republic of the Marshall Islands, Federated States of Micronesia and the Republic of Palau). The report was compiled by Center for Coastal Monitoring and Assessment (CCMA) through the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Conservation Program.
The latest news on the organization’s website links to reports from CRTF meeting in Palau, November 2005. The purpose of this meeting was to learn about and take action on key issues related to coral reef conservation in the Pacific region. The U.S. Coral Reef Task Force and other organizations devoted to protecting the coral reefs of the world are highly needed. It is we humans who are causing trouble for nature’s richest marine ecosystems, and we must act to reestablish balance.
Top Threats To Reefs
Like many other habitats, coral reefs face many dangers in today’s world, many of the problems being caused by humans. The factors are many, but include:
Global and environmental problems. These include diseases affecting corals, as well as bleaching. In addition, calcification of corals and other animals living on reefs is decreasing, due to higher carbon dioxide levels.
Problems related to human activities. This refers to run-off, overfishing and the expansion of industry and other developments on the coast.
Government and political factors. Problems in this area include absence of coral reef management and protection, and lack of resources for reef protection.
(Data based on Wilkinson, 2004)
Australian Institute of Marine Science (AIMS). http://www.aims.gov.au/
Buckheim, J. “Coral Reef Bleaching.” Odyssey Expeditions. www.marinebiology.org/coralbleaching.htm
Coral Reef Task Force. http://www.coralreef.gov/
Fenner, B. 2003. “Hard Coral Species Diversity on Great Barrier Reef and Osprey Reef Sites Visited by the Undersea Explorer.” Coral Sea Conservation online document. www.coralseadiving.com/corals/coral_report_Nov2003.htm
Global Coral Reef Monitoring Network (GCRMN). http://www.gcrmn.org/
National Oceanic and Atmospheric Administration (NOAA). http://www.coralreef.noaa.gov/
On Norwegian Deep Water Bioherms. www.imr.no/coral/index.php
Reef Base. http://www.reefbase.org/
Spalding, M.D., C. Ravilious, and E. P. Green. 2001. World Atlas of Coral Reefs. University of Califronia Press. Los Angeles, California. 424 pp.
Wilkinson, C., D. Souter and J. Goldberg (eds.). 2006. Status of Coral Reefs in Tsunami Affected Countries: 2005. Australian Institute of Marine Science. Townsville, Queensland, Australia. 154 pp.
Wilkinson, C. (ed.). 2004. Status of Coral Reefs of the World: 2004 (Volume 1). Australian Institute of Marine Science, Townsville, Queensland, Australia. 301 pp.
Wilkinson, C. (ed.). 2004. Status of Coral Reefs of the World: 2004 (Volume 2). Australian Institute of Marine Science, Townsville, Queensland, Australia. 557 pp.
World Resource Institute. http://reefsatrisk.wri.org/