Coral reefs have the most biodiverse ecosystems known to man. They support a huge number of marine species and are a valuable source of income and food for many coastal communities around the world.
However, close to 60% percent of them are on the verge of extinction owing to anthropogenic and natural threats to coral reefs.
Anthropogenic/Human-caused Threats to Coral Reefs
These include pollution, overfishing, destructive fishing, intrusive aquarium trade and coral mining. Pollution is one of the top most dangerous threats to marine life as a whole. Land-based runoffs and pollutant discharges are a product of coastal development, sewage treatment plant operations, agricultural and deforestation activities as well as dredging.
The runoffs usually contain chemicals all of which eventually end up in water bodies. Oil spills can inhibit the spawning and the reproductive processes of corals. Sewage and runoff from farming activities causes a rise of nitrogen levels in seawater and consequently an excessive algae growth.
The algae grow on the surface blocking the coral from getting sunlight. Sediment from mining, construction, farming and logging activities also ends up in oceans where it smothers coral reefs, depriving them of the much needed sunlight exposure.
Fishing techniques like blast/dynamite fishing, muro-ami fishing and cyanide fishing are very destructive towards coral reefs. In fact these methods can stress the corals to the extent of expelling their algae and thus leading to bleaching.
Cyanide fishing kills the coral polyps and has affected several reef habitats in over 15 countries worldwide. Deep water trawling involves dragging a fish net along the sea bed and in the process damaging corals. Reckless dropping of anchors and lines is also a great problem to these habitats. Other people may collect corals for aquarium and curio trades or for construction purposes. Overfishing also destabilizes the ecological balance in the various coral reef habitats.
Climate change is a human-caused issue that has led to the continued rise in sea temperatures. Warm waters usually expel the photosynthesis-enabling algae leaving the coral more susceptible to diseases.
The rise in temperature is the number one reason for current mass bleaching (coral die-off) on the Great Barrier Reef. Continued carbon dioxide emissions into the atmosphere increase the acidity levels in water bodies. The acidic conditions in turn dissolve the coral outer structure and thus comprising the reef.
Natural Threats to Coral Reefs
These dangers include coral disease, weather-related effects and sea predators. Responses to biological stresses like fungi, viruses and bacteria or non-biological stresses like a rise in sea temperature, UV radiation and pollutants may trigger coral diseases.
Strong waves from cyclones and hurricanes can break corals into fragments, however destruction of a whole colony is not common. Prolonged low tides may leave shallow water coral heads exposed to harsh ultraviolet radiation and thus damaging the coral’s tissues. Increased biological and non-biological stresses like a rise in temperature or salinity may force the corals to expel their algae out leading to bleaching.
The crown-of-thorns starfish, snails, fish, barnacles and marine worms all prey on the soft inner linings of coral polyps.
The balance of nature ensures that coral reefs will recover from any natural occurrence, and thus it is the anthropogenic threats to corals that will force them into extinction.