It is the calcified remains of polyps that create the platforms to keep the living descendants in shallow, sunlit waters. Reef systems are perfect climate indicators. The polyps need lots of water movement, shallow, warm water no less than 20C and no greater than 30C, salty water that is low in nutrients and plenty of sunlight. They are incredibly sensitive to changes in these factors and in climate, probably being among the first to suffer from global warming and phenomena such as El Nino. Healthy reef is a myriad of colourful cities one could imagine as far distant worlds, and home to hundreds of species of brightly coloured tropical fish.
Dead coral is bleached white, stressed to death by environmental factors.
Fortunately there is virtually no dead coral present on the Great Barrier Reef, perhaps at least partly because since the 1970s the reef and the Whitsundays have been protected by Australian law. Only and handful of resorts have been allowed to develop in the Whitsundays and even there, careful maintenance of the environment is a requirement to preserve the whole ecosystem of islands and reefs. There are some 350 species of coral over 345 square kilometres. Hardy Reef, Heart Reef, Hook Reef, Line Reef, Sinker Reef. At Hardy Reef a floating platform facility offers diving for beginners through to the experienced.