Tropical Oceans
Threats to Coral Reefs

Human Contact Touching Reefs, even slightly, can harm them. Boats and dropped anchors can cause severe damage to these fragile ecosystems. Frequent human contact kills the reefs over time. 
Runoff Water Silt from eroded soil in runoff water can block sunlight. Without sunlight, photosynthesis does not occur and reefs gradually die. 
Sewage Untreated or improperly treated sewage promotes the growth of algae, which harms coral reefs. 
Cyanide Fishing Some fishermen stun fish by squirting cyanide, a very toxic poison, into reef areas where fish seek refuge. The poison does not kill, but disorients the fish in the coral where they hide. 

The fisherman then rip apart the reefs with crowbars to capture the fish. In addition, cyanide kills coral polyps and the symbiotic algae and other small organisms necessary for healthy reefs. Cyanide fishing is common in the South Pacific and Southeast Asia. 

Fertilizers & Pollution Fertilizer runoff, pesticides and other chemicals can poison reefs. 
Blast Fishing Shock waves from blast fishing can destroy coral reefs. 

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