The shape of reef corals is affected by light level1,2 and by wave stress3,4, leading to the well-known zonation of coral form associations with exposure and depth3-6. Growth form also seems to be constrained by geometric factors2,7,8. Similarly, coral calcification rate, of importance both for coral form and for net reef growth, is light dependant9,10, and may be affected by other factors such as wave stress and sediment flux. Here the growth structure of raised Pleistocene reefs in New Guinea, of both fringing and barrier types, is explained in terms of variations of coral framework growth rate across the reef profile. A model for growth rate in terms of wave stress, light level and other variables is outlined, first by examining the effects of these factors on coral form and diversity.