In addition, unless effective integrated coastal zone management is implemented, more than two-thirds of the world's coral reefs may become seriously depleted of corals and associated biota within two generations. Rapid population growth and migration to coastal areas where coral reef ecosystems occur exacerbate the problem. The resulting coastal congestion leads to increasing competition for limited resources, to increased coastal pollution, and to problems related to coastal construction. Technology also allows humans to exploit the reef with mechanical dredges, hydraulic suction, dynamiting, and large-scale poisoning. Millions of people depend on reefs for food and livelihood.
Reefs also create sheltered lagoons and protect coastlines and mangroves against wave damage.
Mangroves in turn protect reefs from sedimentation and eutrophication. Mangroves and seagrasses also play an important role in coastal protection and provide spawning and nursery areas for reef and offshore fishes. The economies of many atoll nations are based on marine resources. In the Pacific, over 2.5 million people live on islands built by or surrounded by coral reef ecosystems. Over 300,000 people live on coral islands in the Indian Ocean and many more in the Caribbean.