I also noticed that corals do not die as they grow, which is what most books on the subject teach. They just keep on dividing and then the colony grows in size but the coral stays alive. Thus the colony still contains the same DNA as the original polyp that was spawned perhaps thousands of years ago.
I don't know why some scientists say that corals die and new ones "move into" their empty skeletons. Once the coral dies the remaining skeleton grows over with algae. Granted, new spawned corals can still settle on it but it may be a different species altogether.