Threats to coral reefs

Threats to Coral Reefs
Human Contact
Touching coral reefs even slightly, can harm them.If ships or boats dropped anchors on them it can cause severe damage to these fragile ecosystems. Frequent human contact can also kills the reefs over time.
Runoff Water
slits from eroded soil in runoff water can block sunlight. Without this sunlight, photosynthesis cannot ccur and the reefs gradually die.
Sewage
Untreated or improperly treated sewage promotes the growth of algae, which cause harms to the coral reefs
Cyanide Fishing
Some fishermen stun fishes by squirting cyanide, a very toxic poison, into reef areas where fishes seek refuge. The poison does not kill, but disorients the fishes in the coral where they hide. The fisherman then rip apart the reefs with crowbars to capture the fishes. In addition, cyanide kills coral polyps , the symbiotic algae and other small organisms necessary for healthy reefs. Cyanide fishing is most common in the South Pacific and Southeast Asia.
Destructive fishing practices
These include cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami (banging on the reef with sticks). Bottom-trawling is one of the greatest threats to cold-water coral reefs.
Careless tourism
Careless tourism example: Careless boating, diving, snorkeling and fishing happens around the world, with people touching reefs, collecting corals and dropping anchors on reefs. Some tourist resorts and infrastructure have been also built directly on top of reefs, and some resorts empty their sewage or other wastes directly into water which is surrounded by coral reefs.
Pollution
Urban and industrial waste, sewage, agrochemicals, and oil pollution are poisoning the reefs. These are dumped directly into the ocean or carried by river systems from sources upstream. Some pollutants, such as sewage and runoff from farming, increase the level of nitrogen in the seawater, causing an overgrowth of algae cutting off the coral's sunlight.
Sedimentation
Erosion caused by construction by both along coasts and inland mining, logging, and farming is leading to increased sediment in rivers. This ends up in the ocean, where it can 'smother' corals by depriving them of the light they need to survive. The destruction of mangrove forests, which normally trap large amounts of sediment, is exacerbating the problem.
Coral mining
Live corals are removed from reefs for use as bricks, road-fill, or cement for new buildings. Corals are also sold as souvenirs to tourists and to exporters who don't know or don't care about the longer term damage done, and harvested for the live rock trade.
Climate change
Corals cannot survive if the water temperature where they live in is not suitable or is too high for them to live in. Global warming has already led to increased levels of coral bleaching, and this is predicted to increase in frequency and severity in the coming decades.