Reefs at Risk

4. The threats and the causes

Critical and threatened coral reefs of the world

The dangers facing coral reefs all result from global changes.

The dangers facing coral reefs today have more than one cause, but they all result from global changes.

One of the major factors is demographic: rapid population growth found in tropical developing countries and migration to coastal areas where coral reefs are located, result in increasing pressure on coastal resources.

Another major factor in recent coral reef decline has been technological development. Pre-industrial peoples took material and resources from reefs with minimal impact on the environment. Mechanical dredges or hydraulic suction devices, dynamiting and large-scale poisoning of reefs to collect fish, produce "the 4 Ds" of coral reef impact: damage, degradation, depletion, and destruction.

Population growth and technology: operating together these two factors account for the major causes of coral reef decline - excessive domestic and agricultural waste pouring into ocean waters, poor land-use practices that increase sedimentation of rivers and then of reefs, and over-exploitation of reef resources, often in combination with practices such as harvesting with dynamite. and poison; all degrade reefs.

Domestic, agricultural and industrial wastes are discharged into coastal waters in many countries. Apart from the pollution and risks to human health created by such wastes, nutrient-rich waters diminish rather than increase the health of coral reefs. Deforestation, over-grazing, and poor land-use practices, often far inland, are leading to massive soil erosion and siltation of rivers and washing large loads of sediment onto coral reefs.

Destructive fishing techniques have now lasted for so long they are considered part of the traditional culture.

Because reefs have such high species diversity, overfishing may not be noticed until depletion of resources is relatively advanced. Fish stocks have certainly declined markedly in many reef areas, particularly close to centres of human population in developing countries. Landings of many fish species are continuing to decrease and it takes much more energy and effort to catch the fish in many areas. Average and maximum sizes have diminished, and the mix of species in the catch has changed. As early as 1959 in Jamaica, for example, fish catches in coral reef waters contained only juvenile fish.

in some areas fishermen say they have been forced by the decline in catches to use destructive techniques to get enough fish to feed their families and make a living. These practices, which have now lasted several decades, are today considered part of the "traditional" culture. Dynamite fishing is illegal in the Philippines but is still commonly practised in some areas.

The over fishing of some species has other effects which accelerate the degradation of coral reefs. Removing fish and other grazers of reef algae such as molluscs from the system allows the algae to compete with, the corals for substrate. Jamaica provides an example of the devastating effect that can result. A hurricane hit this Caribbean island in 1980 causing severe destruction of corals. The normal recovery process was impeded by a second event. The major algal grazer on these reefs, a long-spined sea urchin, was wiped out by disease. This allowed the macro-algae to smother juvenile corals trying to settle. Coral cover dropped from 50-70% to under 5%, and 10 years afterwards, there is still no sign of recovery.

Tourism can only be environmentally friendly to reefs when carefully controlled.

Particularly in Southeast Asia, export of reef fish to Japan, Taiwan, Hong Kong and Singapore is contributing to overfishing. Taiwanese harvesting of the giant clams Tridacna spp. has led to population crashes and local extinction on isolated reefs. Tobacco and soap may also be killing giant clams. In the Philippines many tridacnid clam species have become locally extinct. The main cause is the trade in shells, frequently sold to tourists as ashtrays and soap dishes. This country probably remains the major exporter of coral reef curios, though largely prohibited within the country and by the states where tourists import them. Giant clams have recently been added to the list of species covered by the Convention on International Trade in Endangered Species (CITES) as a means of reducing the trade.

Collecting aquarium fish and live corals for European and North American markets has developed into another lucrative but damaging industry. The techniques used in harvesting fish for this trade are often destructive, killing organisms not intended for collection. Cyanide is widely used to force fish out from the coral and stun them so that they can be easily captured. Probably more than 50% of the fish collected in this way die before reaching the retail market.

Tourism can be an environmentally friendly way of generating income from coral reefs, but only when resort development and operation are carefully controlled. Unlimited collecting, sport fishing and accidental damage by waders, swimmers and boat anchors can all degrade the reefs that earn the tourist dollars. Allowing sewage and other wastes from tourist facilities to pollute reef areas, or siting resorts so that beach erosion increases, can be even more degrading to the health of the reef than the direct damage caused by visitors.

As a result of human activities, many coral reefs suffer chronic stress. Waste disposal, pollution, sedimentation, overfishing, coral mining, tourism and curio collection: all combine to degrade and threaten the ecological collapse of an estimated 30% of the world's reefs within two decades.

The new factor: global climate change

Lately another factor has entered on the scene: global climate change. According to the best available predictions of scientists, the next century will bring higher world temperatures and a rate of change in climate greater than we have seen for more than 6000 years. Other predicted results include an accelerated rise in sea-level, while cyclonic storms and floods could become more frequent in some places. Ocean circulation patterns may alter, and even the chemistry of sea-water might change because of higher concentrations of carbon dioxide.

What will be the effect on coral reefs and the people who depend on them?

A Global Task Team of experts sponsored by the United Nations Environment Programme (UNEP), the Intergovernmental Oceanographic Commission (IOC) of UNESCO (the United Nations Educational, Scientific and Cultural organisation), and the Association of South Pacific Environmental Institutions (ASPEI) looked at the situation and prospects. Working together with the World Meteorological Organisation (WMO) and IUCN-The World Conservation Union, the Task Team has produced a report which reviews the possible impacts of climate change and sea-level rise on coral reefs.

The new factor: global climate change

Lately another factor has entered on the scene: global climate change. According to the best available predictions of scientists, the next century will bring higher world temperatures and a rate of change in climate greater than we have seen for more than 6000 years. Other predicted results include an accelerated rise in sea-level, while cyclonic storms and floods could become more frequent in some places. Ocean circulation patterns may alter, and even the chemistry of sea-water might change because of higher concentrations of carbon dioxide.

What will be the effect on coral reefs and the people who depend on them?

A Global Task Team of experts sponsored by the United Nations Environment Programme (UNEP), the Intergovernmental Oceanographic Commission (IOC) of UNESCO (the United Nations Educational, Scientific and Cultural organisation), and the Association of South Pacific Environmental Institutions (ASPEI) looked at the situation and prospects. Working together with the World Meteorological Organisation (WMO) and IUCN-The World Conservation Union, the Task Team has produced a report which reviews the possible impacts of climate change and sea-level rise on coral reefs.

Crinoid, black coral and fish in reefs of Irian Jaya, Indonesia. Changes in temperature and frequency of storms could affect such reef organisms.

Photo: WWF / Rod Salm

Black coral and fish in reefs of Irian Jaya

Acropora coral and fish at Pase Hays, New Caledonia. Harvesting of giant clams in the Pacific has led to local extinction.

Photo: WWF / Thierry Petit / BIOS

Acropora coral and fish at Pase Hays, New Caledonia

The scientists warn: "The condition of many of the world's coral reefs has reached a crisis point. (... ) Global climate change may directly impose new stresses on reefs, or it may interact synergistically with other more direct human pressures to cause added and Accelerated environmental damage. These [climate change] effects could accelerate the current rate of coral reef degradation in areas already stressed."

Global climate change, the Task Team said, may not pose an immediate threat to the existence of reefs worldwide, but locally the impact may vary from disastrous to benign. Some reefs may be destroyed, others badly affected, while some could even experience more vigorous growth in the medium term.

150,000 years of climate change

Climate change is the only potential threat on the horizon for those reefs remote from large human populations.

For the next 10-40 years, local stresses from human sources are a greater threat to most reefs than climate change. On the other hand, the long-term threat from climate change and sea-level rise may make reef islands uninhabitable. This long-term threat may be of greater significance to the human populations than the short-term problems of these islands.

The scientists point out: "Climate change is the only potential threat on the horizon for those reefs remote from large human populations in the central Pacific and Indian Oceans and along much of the Australian Great Barrier Reef."

The menace hanging over these reefs is as dangerous as the threat facing coral systems close to human populations: "The more remote reefs have the important potential to serve as refuges for coral reef biodiversity," the Global Task Team observes. "Their health and preservation are important to the ecosystem on a global scale."

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March 30, 2010