90% of coral reefs could disappear by 2050.
Discover why
Why are corals threatened?
Coral reefs are damaged due to an accumulation of threats resulting from human activities. Overfishing, pollution and coastal development are at the top of the list of chronic stressors. Others are dredged or sandblasted for their limestone or to improve access and navigational safety.
In addition, long-term global changes (rising sea temperatures and CO2 levels), storms, earthquakes and volcanic eruptions also affect coral reefs.
Coral bleaching
Following a stress that can be caused by various factors, coral will no longer recognize the zooxanthella as its symbiote. In this case, the symbiosis between corals and their zooxanthellae stops, leading to the loss of these micro-algae and a rapid bleaching of the coral host.
Ocean warming
Ocean warming is the main factor in coral bleaching.
Ocean surface water temperature has increased by an average of 0.5°C since 1860. The IPCC predicts an increase in average air temperature of 1.5°C by 2030 to 2050. The surface waters of the oceans will therefore continue to warm.
If ocean surface temperatures continue to rise, the frequency and severity of coral bleaching will also increase, likely affecting the ability of coral reefs to adapt and provide most of the services we demand of them.
Ocean acidification
Carbon dioxide in the atmosphere is absorbed by the ocean. This causes the ocean’s pH to drop, leading to ocean acidification. This decrease in pH has negative consequences, especially for oceanic carbonate organisms such as coral reefs. This phenomenon reduces their ability to build their skeletons, making them much more vulnerable to erosion.
Rising sea levels
According to the IPCC, observations made since 1961 show that the average temperature of the oceans has increased, even at great depths, and that the ocean has absorbed more than 80% of additional heat in the climate system. This warming is causing sea levels to rise and is creating problems for coastal areas.
Ocean warmingOcean acidificationRising sea levels
Ocean warming is the main factor in coral bleaching.
Ocean surface water temperature has increased by an average of 0.5°C since 1860. The IPCC predicts an increase in average air temperature of 1.5°C by 2030 to 2050. The surface waters of the oceans will therefore continue to warm.
If ocean surface temperatures continue to rise, the frequency and severity of coral bleaching will also increase, likely affecting the ability of coral reefs to adapt and provide most of the services we demand of them.
Carbon dioxide in the atmosphere is absorbed by the ocean. This causes the ocean’s pH to drop, leading to ocean acidification. This decrease in pH has negative consequences, especially for oceanic carbonate organisms such as coral reefs. This phenomenon reduces their ability to build their skeletons, making them much more vulnerable to erosion.
According to the IPCC, observations made since 1961 show that the average temperature of the oceans has increased, even at great depths, and that the ocean has absorbed more than 80% of additional heat in the climate system. This warming is causing sea levels to rise and is creating problems for coastal areas.
Overfishing
The increased demand for fish has led to overfishing of reef species. Overfishing of certain species can easily affect the ecological balance and biodiversity of the reef. For example, overfishing of herbivorous fish can lead to high levels of algal growth that can suffocate coral.
Destructive fishing methods
Fishing with dynamite and cyanide makes the fish easier to catch. These practices cannot target one species in particular, they destroy everything and permanently so where they are used. Damaging coral reefs has consequences for the entire reef ecosystem, and thus has an immediate impact on the livelihood of related fishermen.
Unsustainable tourism
Tourism generates large amounts of income for host countries. When unregulated, the pressures of tourism can cause damage to the surrounding environment: careless divers, badly placed boat anchors, hotels discharging untreated wastewater (polluting the water, creating sedimentation, while encouraging the growth of algae that compete with corals).
Pollution
Pollution from land-based human activities, when transported by rivers into coastal waters, can damage coral reefs. Nutrient enrichment (eutrophication) promotes the development of algae. Macro-algae then colonize the substrates used by coral larvae. If these algae proliferate, the reef cannot regenerate and this situation is usually irreversible. Whether it is plastic or chemical, pollution has severe consequences on marine ecosystems, which find it difficult to recover.
Trade for aquariums
It is estimated that nearly 20 million tropical fish and 12 million hard corals worldwide are sold annually, the vast majority to private individuals (UN, 2003). The vast majority of marine aquariums are supplied with species caught in the wild. Threats from this trade include the use of cyanide for collection, over-exploitation of target organisms, and high levels of mortality associated with poor maintenance and shipping practices.
Coral diseases
Over the past 10 years, the incidence of diseases developed in corals appears to have increased dramatically, contributing to the deterioration of coral reef communities around the world.
Crédit photo : NOAA.
Invasive species
Species, like the Acanthaster planci, that, due to human activity, have been moved, intentionally or unintentionally, to areas where they do not naturally exist are called “invasive species“. This is often due to a lack of predators and parasites that play a regulatory role. These species can then multiply rapidly by radically modifying the ecosystem. The damage caused by these species can be devastating: alteration of ecosystem dynamics, loss of biodiversity, reduction of ecosystem resilience and loss of resources.
