Coral reefs are dying from natural causes and from the effects of human activity: - - - Harmful fishing practices such as the use of dynamite and cyanide to catch fish. These destroy both the habitat for fish and the biodiversity that is necessary for maintenance of a healthy reef. Overfishing removes species such as the sea snail which keep predators that eat corals on the control. There is selective removal of species for the ornamental trade. The destruction of mangrove forests that serves as nurseries for reef species and reduce the run-off of pollutants. Mangrove forests are removed to make way for the growing of rice, palm oil, and the production of pond streams for the world market. Climate change is the greatest global threat to coral reef ecosystems. The Earth's atmosphere and ocean are warming, and these changes are primarily due to greenhouse gases derived from human activities. As temperatures rise, coral bleaching and death of corals are becoming more frequent.