The central question presented in these pages is:

How the geomorphologic characteristics of atolls influence their lagoon functioning? 

Indeed, there are more than 400 atolls in the world displaying a high morphological diversity. Their size range from more than 1000 km² to less than one km², with emerged land surfaces high or low. Some of the lagoon are largely open to the ocean by deep passage or submerged reef flat, others are closed, with no or very low renewing of waters. These differences in residence time of oceanic oceanic waters inside the lagoons could have an important effect on the quality of lagoonal waters and planktonic and benthic communities. To try to answer the central question, the IRD TYPATOLL program has studied 12 atolls selected in the Central Tuamotu in function of their morphology. We present here some of the main results.