Most islands in the Tropics and Subtropics are surrounded by coral reefs that are inhabited by many kinds of organisms. However, the environmental conditions to which coral reefs around the world are exposed have been declining in recent decades. Coral reefs are utilized not only as tourism resources, but also as fishing grounds. The conservation of coral reefs is now. an urgent issue. Coral reef ecosystems have been damaged by numerous factors, such as unusually high temperatures, outbreaks of corallivore organisms, sedimentation, eutrophication, and pollution. The latter 3 factors have a strong correlation with tropical agriculture. In this paper, case studies of the effects of agriculture on coral reefs are introduced, and countermeasures to reduce the impact of agriculture on the coral ecosystem are discussed.