Coral reef A fringing reef forms around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast
Coral Sea whitetip reef shark ("Triaenodon obesus", 21%), silvertip shark ("Carcharhinus albimarginatus", 10%), tiger shark ("Galeocerdo cuvier", <1%) and great hammerhead ("Sphyrna mokarran", <1%). The interaction rate (free diving) at the Coral Sea reefs ranged from a few to 26 sharks per hour. The rare "Etmopterus dislineatus" shark species is endemic to the central part of the Coral Sea. It has been observed at depths of 590–700 m on or near the continental slope. The coastal areas of the Coral Sea were populated at least 40,000 years ago by prehistoric people descending through the northern islands. Those Aboriginal tribes have been dispersed