Coral Reef Status and Threats

The latest estimates (2004) of The Global Coral Reef Monitoring Network (GCRMN), globally states that 20% of the coral reefs are regarded as effectively lost globally (which means damaged beyond repair). Another 24% of the remaining reefs are at critical status (high to very high threat of destruction, if we do nothing), and only 50% are currently classified as low risk.⁵

The majority of reef loss or damage is not deliberate. Coral reefs are being degraded by an accumulation of stresses arising from human activities. In simple terms, stresses can be grouped by the actions of people extracting material from, and placing materials upon, coral reefs. Over-fishing, pollution and coastal development top the list of chronic stressors. However, long term changes in the oceans and atmosphere (rising sea temperatures and rising levels of CO2 that will reduce coral calcification), and acute stresses from highly variable seasons, severe storms, earthquakes and volcanic eruptions also affect reefs.

In many situations chronic stresses are overwhelming the resilience (or the capacity for self-repair) of reef communities. Some coral reefs are covered with sand, rock and concrete to make cheap land and stimulate economic development. Others are dredged or blasted for their limestone or to improve navigational access and safety.

Currently, the stresses of greatest concern are:

Over-fishing and destructive fishing methods

Aggressive intensity and fishing methods hurt coral reefs, especially in south and southeast Asia, where fishermen commonly dynamite reefs and inject cyanide into the water. Both these methods stun the fish, making them easier to catch. The fishermen say they have no other option if they are to compete with trawlers and overcome a smaller supply of fish because of previous over-fishing. Some estimates indicate that 90 percent of the coral reefs in the Philippines have been harmed so much that they probably can't recover.

Dynamiting and poisoning reefs are blatant approaches. Less obvious is the damage caused by over-fishing. This is a problem in many parts of the world. Many people know the problems that cod and salmon fishermen have faced with a smaller supply of fish. However, over-fishing of certain species near coral reefs can easily affect the reef's ecological balance and biodiversity. For example, over-fishing of herbivorous fish can also lead to high levels of algal growth.

One method to reduce over-fishing and destructive fishing methods is the implementation of Marine Protected Areas (MPAs)⁶ , in order to promote responsible fishery management and habitat protection. Much like the designation of national parks and wildlife refuges, potentially damaging extraction activities are prohibited. The objectives of MPAs are both social and biological, including restoration of coral reefs, aesthetic maintenance, increased and protected biodiversity, and economic benefits.⁷

Coral Bleaching

Coral bleaching occurs when the symbiosis between corals and their symbiotic zooxanthellae breaks down. This results in the loss of the brown symbionts and a rapid whitening of the coral host (thus the term "bleaching")⁸. This is a stress response by the coral host. If the temperature decreases, the stressed coral can recover; if it persists, the affected colony can die.

The impacts from coral bleaching are becoming global in scale, and are increasing in frequency and intensity. Mass coral bleaching generally happens when temperatures around coral reefs exceed 1oC above the an area's historical norm for 4 or more weeks. Sea surface temperature increases have been strongly associated with El Niño weather patterns. However, light intensity (during doldrum (i.e. flat calm) conditions) also plays a critical role in trigger the bleaching response. If temperatures climb to more than 20 C for similar or longer periods, coral mortalities following bleaching increase.

Mass coral bleaching was not documented in the scientific literature before 1979; however, significant mass bleaching events have since been reported in 1982⁹, 1987, 1992 and the strongest sea surface warming event ever recorded occurred in 1998, where an estimated 46% of corals in the western Indian Ocean were heavily impacted or died. In 2005, sea surface temperatures in the Caribbean were the highest reported in more than 100 years, and there was also significant coral bleaching following this warming. And in 2007, coral bleaching is being reported in several locations around the world.

The onset of coral disease has been shown to spread following coral bleaching events, so the evidence of a connection between warmer-than-normal water and coral disease is growing stronger. If sea surface temperatures continue to rise, then the frequency and severity of coral bleaching will also increase, likely affecting the ability of coral reefs, as we have known them, to adapt and to provide many of the services (such as shoreline protection, and fisheries) that people rely upon.

Global warming has other impacts on reefs as well, and some of these may be even more damaging to reefs than bleaching. Ocean acidification results from global warming, and when the pH of seawater drops, corals and other calcareous organisms are impeded in their ability to lay down calcium carbonate skeletons (see Ocean Acidification, W2O Ocean Observer archives).

Land development and pollution

Extensive and poorly managed land development can threaten coral reefs. Within the last 20 years, once prolific mangrove forests, which absorb massive amounts of nutrients and sediment from runoff caused by farming and construction of roads, buildings, ports, channels, and harbors, are being destroyed. Nutrient-rich water causes fleshy algae and phytoplankton to thrive in coastal areas in suffocating amounts known as algal blooms. Coral reefs are biological assemblages adapted to waters with low nutrient content, and the addition of nutrients favors species that disrupt the balance of the reef communities. Both the loss of wetlands and mangrove habitats are considered to be significant factors affecting water quality on inshore reefs. Poor water quality is suspected (and is currently being investigated) as a facilitator in the spread of infectious diseases among corals.¹⁰

And, as if this were not enough, coral reefs are suffering from the paradoxical situation that we are loving reefs to death. Visitors to reefs add stresses, in some cases tipping the balance such that immune-suppressed corals become suspectible to further disease spread and die. In addition, the marine souvenir and curio trade is responsible for the denuding of reefs all around the world – corals are taken for jewelry and as live rock for aquaria, and reef fishes and other organisms are sold in preserved form in trinket shops and alive in pet shops. According to the U.S. Coral Reef Action Plan, the U.S. is the world’s largest importer of ornamental coral reef species, and as such has a critical responsibility to address degradation of coral reef ecosystems that may arise from destructive collection practices and unsustainable trade. The U.S. has banned the use of most destructive fishing practices, and collection of stony corals and live rock are prohibited in most federal, state and territorial waters.¹¹ However, unenlightened U.S. tourists join tourists from many other parts of the globe to buy reef souvenirs, unwittingly contributing to the dramatic decline of reefs around the world.