Recent reports from the Global Coral Reef Monitoring Network (GCRMN), Reef Check, and many other projects indicate that coral reefs are under considerable stress and are experiencing considerable damage. Coral reefs have been resilient ecosystems since the Mesozoic (about 200 million years ago), surviving major environmental events such as ice ages, meteor strikes, and large changes in solar activity. Notwithstanding these events, coral reefs have recovered to form the extensive reefs we see today, although recovery may have taken thousands to hundreds-of-thousands of years. For example, during the last ice age (end of the Pleistocene) sea levels fell by over 100 m, killing all existing coral reefs, but corals continued to grow on continental margins and seamounts. When sea levels started to rise 10,000 years ago, corals invaded continental shelves and island slopes and, over the last 6000 years of relatively stable sea level, have been forming new reefs. Coral reefs also have the capacity to regenerate rapidly after catastrophic tropical storms, plagues of the coral-eating crown-of-thorns starfish, and severe bleaching. Recovery often takes 15 to 20 years. However, over the past 50 years, there have been major increases in stresses to coral reefs from direct and indirect human activities. These stresses are threatening the existence of reefs in some areas, and will diminish the value of reefs in other areas. Fortunately the corals on vast areas of remote reefs are unlikely to be severely affected. The same cannot be said about valuable reef fisheries resources.

The major stresses to reefs are storms and waves, particularly tropical storms and cyclones (called hurricanes in the Atlantic; cyclones in the south Pacific and Indian Oceans; and typhoons in the north Pacific). These cause major intermittent damage to reefs, particularly to those reefs that rarely experience these storms. For example, Guam in the northwest Pacific is hit by one typhoon a year on average, such that the corals are stunted and robust; whereas reefs in the eastern Pacific, such as in French Polynesia and the southern Caribbean, rarely experience such storms, with the result that strong waves from the infrequent storms smash the fragile coral communities.

Freshwater runoff damages reefs in semi-enclosed bays and lagoons of the larger Pacific islands (e.g. Kaneohe Bay in Hawaii) by lowering salinity and depositing large amounts of sediments and nutrients. Reefs are also damaged by volcanic activity (earthquakes, volcanic lava flows, severe uplifting) in the Pacific, for example in Vanautu, the Solomons, Papua New Guinea, the Philippines and Indonesia. Coral bleaching has been particularly notable recently, and particularly damaging from 1997 to 1998. While bleaching is a response by corals to many stresses, the recent apparent increase in incidence and severity may be a foretaste of global climate change (see below).

The major biological stresses on reefs are predation by the crown-of-thorns starfish, and diseases. Starfish plagues can outbreak on reefs in the Pacific and Indian Oceans, and often reappear at 12 to 20 year intervals. In the Caribbean, coral diseases have been particularly devastating in some areas. There is now considerable speculation that the incidence of both these stresses has been exacerbated by human activities.

Increases in human populations and economic activity in the tropics over the past 50 years have resulted in increasing pressures on adjacent reefs. The major damaging factors to reef corals are: pollution from excess sediment and nutrients because of poor land-use practices on high islands, agriculture, industries, urban sewage and over-fishing. The major stress to remote reefs is from over-fishing, particularly the use of destructive methods in the Indo-Pacific over the past 10 to 20 years. In 1997, the first GCRMN/Reef Check global coral reef survey revealed that most reefs show clear evidence of local extinction of species, and obvious damage from blast and poison fishing in the West Pacific. The value of, and demand for, reef fisheries products has increased rapidly, particularly for export to east Asia. The surveys showed that key indicator species, such as giant clams, lobsters, sea cucumbers, pearl shell and trochus, and reef sharks have been removed. Now high-priced fish such as grouper, humphead wrasse, snappers, and parrot fish are being removed from reefs throughout the Indo-Pacific through the use of fine-mesh gill nets and traps, dynamite (usually home-made), and poisons, such as cyanide and bleach. Subsistence fishing is depleting fish stocks in the Caribbean, particularly through the use of fine-mesh traps and nets.

The first and second global GCRMN/Reef Check surveys showed that most of the world’s reef corals are in good to excellent condition, because they are either remote from human populations, or are under good management, such as the Great Barrier Reef. But these surveys also showed that management in most marine parks is failing to stop the loss of high-value, edible species, and that greater attention is needed to improve management. The ecological balance in many of the world’s best reefs has been altered by the removal of high-value organisms.

A recent estimate by the World Resources Institute in Washington suggested that as many as 56% of the world’s reefs are threatened. Finally, there are those reefs that have been severely damaged or destroyed. Approximately 10% of the world’s reefs fit into this category, being mined for sand and rock, reclaimed for development (particularly for airports), or have been buried under sediment washing into the sea from inappropriate land use.

Fortunately most reefs have a high capacity for recovery, and if pressures are reduced or removed, many damaged reefs will rebound to a healthy status.

The Red Sea reefs are only affected in a minor way by human disturbances. Consequently the reefs are in near-pristine condition, and few threats loom on the horizon. Reefs on the Arabian Sea coast are heavily influenced by cool upwellings, which limit coral growth and favour the growth of large algae. But these reefs are only marginally affected by human activities, and remain in good condition. The shallow fringing reefs in the Arabian Gulf are impacted by high sediment runoff, and large fluctuations in temperature and salinity, hence they are not well developed. Also they have been severely impacted by coral bleaching in recent years. There is little active coral-reef management in the region, however, there are projects to increase management capacity and conserve some valuable reefs. An imminent threat to these reef systems is oil pollution from increasing tanker traffic.

The status of reefs ranges from those in virtually pristine condition, such as the atolls in mid-ocean, to reefs that are heavily impacted by human activities, such as those fringing the coasts of East Africa and Madagascar. Extensive clearing of land and forests in Kenya, Tanzania, and Madagascar has led to excessive sediment runoff, which has damaged many reefs. In addition, there is over-fishing, including the use of explosives, so that these reefs are in medium to poor condition. Some reefs on Mauritius have been impacted by sediment runoff from sugar-cane farming, and by over-fishing, whereas the reefs of the Comoros and Seychelles are mostly in good to very good condition, except immediately adjacent to large population centres. Reef management is not well developed, and fisheries and coastal development are poorly regulated. Rapidly increasing populations and tourism are contributing to reef destruction. Recently there has been significant progress in reef management in the Seychelles, Mauritius, Kenya, and Tanzania, particularly in establishing marine protected areas for tourism. Efforts at increasing community-level management are proving successful in some areas of Kenya and Tanzania.

The coral reefs of south Asia vary considerably. In the Maldives, Laccadive/Lakshadweep and Chagos atolls the status of the oceanic reefs is very good, and virtually undisturbed reefs fringe the Andaman and Nicobar Islands. In contrast, the fringing reefs and patch reefs off India and Sri Lanka are predominantly in poor condition, and increased sedimentation, pollution, coral mining, and intensive fishing, including for the aquarium industry, are major problems. Tourism is now the mainstay of the economy in the Maldives, and is increasing in Sri Lanka and the Andaman Islands. Virtually all reefs in South Asia (except Chagos) have suffered major damage from coral bleaching in 1998. Environmental awareness is increasing, and reef management is gradually improving.

Approximately 30% of the coral reefs of the world are in southeast Asia, the global centre of biodiversity for hard corals and many other reef animals and plants. But the populations and economies of the region are growing rapidly, mainly in coastal areas, and the result is non-sustainable use and degradation of many reefs, particularly those close to major populations. Some remote reefs may still be healthy, but fishers are moving throughout the region, taking fish by destructive means, especially cyanide. The demand for healthy reefs for tourism may increase reef conservation because tourism can generate long-term sustainable income if managed carefully. Many reefs have been monitored and show a steady decline in live coral cover over the last 15 years. As a response, more marine protected areas have been gazetted, but less than 10% are well managed. Although awareness of the importance of reefs is increasing, recent economic problems will mean that reef conservation may take a lower priority.

The major stresses to Australian reefs are natural, such as cyclones, coral bleaching, and crown-of-thorns starfish. Human stresses are minimal, except on some reefs close to the land, because population density is low, the economic status is high, and fishing pressure is low. Major research is underway to ensure that fishing is sustainable for target species, for total catch, and for reef health. All Australian reefs are efficiently managed, local support for reef management is strong, and compliance is achieved more by education and involvement than by enforcement.

The bulk of the Great Barrier Reef is in good condition because most of it is remote from land influences, but inner shelf reefs may have suffered impacts resulting from increased sediment and nutrient runoff caused by cattle grazing and sugar-cane farming. However the farming industry is working out of both self-interest and concern for the environment to reduce the impacts of sediment and nutrient runoff. All tourist resorts are now required to treat sewage to avoid any runoff, and to manage the areas of reefs that they use.

Reefs off Western Australia are in good health as they are generally not impacted by land influences, and no impacts have been attributed to petroleum exploration or fishing. There is strong recognition by government that the tourism and resource values of coral reefs are particularly high, which means that reef management receives sufficient attention.

Reefs of China, Japan, and Taiwan are normally impacted by typhoons and crown-of-thorns starfish, and recently have been severely damaged by sediment, pollution, and over-fishing, including blast and cyanide fishing. Reefs of the Marianas have likewise deteriorated and both coral and fish populations have reduced. However, the reefs of Palau, the Federated States of Micronesia, and the Marshall Islands are in good health, except those around population centres where there is sediment and nutrient pollution. The traditional low-level fishing activity has increased dramatically in response to enormous demand from Asia and America. Giant clams, sea cucumbers, trochus shells, lobsters, and top quality fish are often severely depleted, even on remote reefs. Reef conservation is inadequate, although management is improving in all countries. However, far greater efforts are required to arrest the continuing trend of reef degradation.

About 99% of all southwest and east Pacific reefs are remote from urban pollution and sediment degradation, and structurally they remain in good to excellent condition. Reefs near large towns provide benefits in subsistence fishing, recreation, tourism, and shoreline protection, but these reefs are being chronically degraded. There is often significant over-fishing, and giant clams, sea cucumbers, and trochus shells are now rare. Sharks and lobsters have been removed from most remote reefs. This is an increasing trend, and involves cyanide and dynamite fishing for Asian markets. The largest natural threats are from storms and strong wave action, along with crown-of-thorns starfish. Concern is increasing about global climate change, coral bleaching, and stronger El Niño events. Rising sea levels will damage the shores of high islands that are rapidly subsiding, and may destroy low coral islands and jeopardise their island cultures. Management is required to reduce or divert increasing population pressures, and integrate traditional management of reef resources into ‘modern’ methods.

The Pacific coast reefs of Central America are small, have low diversity, and are being heavily impacted by natural and human pressures. Previous large-scale damage from crown-of-thorns starfish and El Niño bleaching is being compounded by sediment runoff from poor land-use practices. The reefs are remote from external sources of coral larvae, are continually stressed by cold upwellings, and damaged by bio-eroding animals; their potential for natural recovery is very poor. There is little active conservation and very few reefs are protected.

Caribbean reefs off Belize and well offshore to the south have high biodiversity and are in good to excellent condition. Most reefs were heavily damaged by coral bleaching, diseases, and death of the long-spined sea-urchin, but recovery has been good to patchy. Recovery had been poor on reefs being polluted by increased sediment and nutrient runoff resulting from poor land use, and where reefs were over-fished, for example the reefs off southern Panama. The severe coral bleaching of many reefs which started in mid-1998 continues, and there is major mortality. Hurricanes also pose a significant threat to reefs north of 15oN. Many of the marine protected areas exist only on paper, but a major project (Mesoamerican Barrier Reef Initiative) aims to increase monitoring and management of reef resources.

Most reefs in the northern Caribbean are in fair to relatively good condition, with a few degraded reefs. Some reefs are limited by natural conditions, including hurricanes, and human pressures vary from very high (e.g. off Haiti, and Veracruz in Mexico), to low (e.g. Flower Garden Banks, parts of the Bahamian and Cuban archipelagos). Coral diseases, such as white-band disease, have reduced coral cover on many reefs and the death of the algal-grazing urchin, Diadema antillarum, has resulted in proliferation of fleshy algae, particularly near sources of pollution and in highly fished areas. Stocks of reef fish also vary with socioeconomic conditions and the level of effective management. People are becoming more aware of the ecological and socioeconomic values of reefs, and conservation and sustainable management efforts are increasing.

Awareness of the need for reef conservation is particularly high on Bonaire and the Cayman Islands because reef tourism is a dominant part of the economy. These reefs are essentially healthy with few pressures. However, off the mainland (Colombia and Venezuela) and on Jamaica, reefs have been damaged so that there are fewer fish, more algae, and less coral cover, and current conservation efforts are insufficient to prevent ongoing damage from sediment, nutrient pollution, and over-fishing. Corals have also suffered from bleaching, diseases, and Diadema die-off. Cayman and Bonaire have well-developed reef management strategies, which are being used as examples for the rest of the Caribbean.

The Lesser Antilles include high volcanic islands with very narrow continental shelves, and some low coral islands with wider shelves. There are some excellent coral reefs, which are normally stressed by sediment runoff from heavy rains, and by hurricanes. Recently, coral bleaching, coral diseases, tourism, and fishing pressure have resulted in some degradation in many areas, but there are few long-term studies to determine the status of reefs or the trends in their condition. The number of reefs under active and effective management has increased, and the need for better management is being recognised. Community-based management on St Lucia may prove to be a model for the region.

There has been unprecedented bleaching of hard and soft corals throughout the coral reefs of the world from mid-1997 to late-1998. Information is coming in daily via the internet and from GCRMN and Reef Check teams. Much of the bleaching coincided with a large El Niño event, followed by a strong La Niña, but bleaching in other areas appears uncorrelated. Four overlapping levels of bleaching are apparent:

Bleaching and mortality were most pronounced in shallow water (less than 15 m) and particularly affected staghorn and plate Acropora and other fast growing corals. Many of the massive, slow-growing species bleached, but many recovered within 1 or 2 months. The consensus is that this is the most severe bleaching event ever observed, although in this case there were also more people looking specifically for bleaching following internet advice of the location of above average sea-surface temperatures. More observations and monitoring are required to determine whether bleached corals will recover (or die), and whether damaged reefs have the potential to ‘bounce back’. More importantly, there is a need for continued observations to determine whether this is a rare, severe event, or part of a pattern of increasing disturbance associated with global climate change.