The reefs of Biscayne National Park are part of a 150-mile-long chain of coral reefs extending down through the lower Florida Keys and the Caribbean. The coral reef of the Florida Keys is North America's only living coral barrier reef and the third longest coral barrier reef in the world. The reefs provide habitat for fish, stony and soft corals, sponges, jellyfish, anemones, snails, crabs, lobsters, rays, moray eels, sea turtles, dolphins, sea birds, and other animals. Coral reefs are the most biologically diverse ecosystems in the world. They are home to more than 150 species of tropical fish and 50 species of coral, representing 80% of the coral species in the tropical western Atlantic. The coral reef ecosystem is a delicately balanced, interdependent marine environment composed of coral reefs, mangroves, and seagrasses. Along with hardwood hammocks, Florida's coral reefs are home to 1/3 of Florida's threatened and endangered species. The overall health of the reefs has decreased dramatically in the past 15 years. Among factors responsible for this decline are heavy use, physical damage from boats, careless divers and snorklers, fishing, habitat loss from coastal development, declining water quality, global climate change, and natural storm events.