Coral reef to form fringing reefs, and can eventually grow become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs
Coral Sea tissue. An individual adult can eat up to 6 m of reef per year. In 2000, an outbreak of crown-of-thorns starfish contributed to a loss of 66% of live coral cover on sampled reefs. Changes in water quality and overfishing of natural predators, such as the Giant Triton, may have contributed to an increase in the number of crown-of-thorns starfish. There are at least 30 species of whales, dolphins, and porpoises, including the dwarf minke whale, Indo-Pacific humpback dolphin, humpback whale and dugongs. Six species of sea turtles breed on the GBR – the green sea turtle, leatherback sea turtle,