Coral Reefs

Direct human activities are a major threat to coral reefs. Many of these threats can be small-scale or localised but they reduce the resilience of the reefs making them more susceptible to climate change and resulting diseases. The main anthropogenic pressures are:

• Over-fishing and destructive fishing practises - harvesting of fish and invertebrates beyond sustainable limits, and the use of destructive fishing methods in developing countries such as blast and cyanide fishing that destroy coral reef habitat. As human populations increase and national economies grow, there is a parallel increase in the demand for seafood. The net effect of over-fishing is that coral reefs are far more susceptible to overgrowth by macro-algae, plagues of coral predators, and probably increases in coral disease. There is also direct physical damage to the reefs from anchors, nets, traps and often devastation from the use of explosives used to stun fish. Unless fishing pressure can be significantly reduced many coral reef fisheries are likely to collapse.


• Sedimentation – sediment run-off from the land due to poor land use, development and deforestation, and benthic dredging. Sediment clouds the water column reducing light penetration which is necessary for photosynthesis by the coral's zooxanthellae. Sediment settling on the coral reefs can also smother corals and other sessile organisms, and increase the rates of disease and bio erosion.


• Eutrophication and chemical pollution - Most coral reefs near areas of human population suffer degradation through nutrient pollution from fertilizer run off from agricultural land, untreated sewage, animal husbandry and industry. Excess nutrients in the water encourage the growth of macro-algae, particularly when herbivores populations, mainly fish and sea urchins, are reduced, resulting in the macro-algae out-competing coral for space on the reef.


• Habitat loss from unsustainable development - Coastal development and land reclamation are increasing in many countries with coral reefs. Coastal habitats are destroyed or degraded and there are corresponding increased levels of siltation and pollution. Mining of coral reef rock and sand is also and threat in some areas.


• Coral trade: It is estimated that between 11 and 12 million pieces of live coral are traded globally each year. Included in this number are approximately 140 species of hard coral. Despite quotas and trade regulation by CITES it is unknown if these species are being harvested sustainably. The harvest of wild coral may lead to population declines and the techniques used to collect coral may cause physical damage to the reef and other species of coral that are not targeted for collection. The main exporter of live coral is Indonesia with the USA and EU the biggest importers of live coral.