Marine pollution originates from a variety of sources, many of which are land-based. Organic pollution, often in the form of fertilizer run-off or sewage, results in excess nutrient loads to the sea. This may lead to increased algal growth, which can outcompete corals for light and nutrients. When algal blooms die, they can smother a reef in the same way that sediment does. Chemical pollution also has a significant detrimental effect on coral reef health.
Humans overexploit the reef environment directly in many ways.
Unfortunately, this tends to target specific species, which can disrupt the food chain . Some fishermen use dynamite to stun the fish so that they can gather them up easily. This often accounts for whole shoals of fish dying, and can damage coral reefs extensively. Other destructive fishing practices such as cyanide fishing are also common in South East Asia. Reefs are also exploited for the aquarium and curio trades which are growing rapidly internationally.