Pollution and sedimentation

Some of the biggest problems facing the coral reefs come from the land. Corals are threatened by pollution in many forms, including oil slicks, sediments, fertilizers, pesticides and other chemicals, heavy metals, and garbage. A nasty cocktail of chemicals is carried in the rivers and even in pipes, and winds up near the coral reefs. Human sewage, one of the most common problems for the reefs, encourages the growth of certain types of large algae or seaweed. These grow much better than the corals and can smother or kill them by shading them out of existence.

Deforestation and Sedimentation
In many parts of the world people are chopping down forests and plowing up the land. A great deal of soil is being washed off the land, into the rivers and from the rivers to the sea. When there is a lot of mud in the water it cuts out the light. This mud or “sediment” sinks down and creates muddy ooze on the bottom of the ocean. Corals need bright clear waters to get the sunlight they need, and also hard surfaces to grow on. This sediment stops new corals from growing, and can smother and suffocate the existing corals.