The aim of the project is a comparative study of the 'structural' biodiversity and the causal factors by which it is induced and regulated. Present environmental factors and historical background (phylogeny of the biota and geographic evolution of the locality) are indeed main causes of the biodiversity observed today. We therefore plan to study the biodiversity in coastal ecosystems and estuaries in tropical and subtropical areas. Lagoons and estuaries are very productive ecosystems with a major impact on the functioning of open sea ecosystems and important for human activities. On the other hand, (sub)tropical areas are known to yield the highest biodiversity on which very few information is available. Moreover, semi-closed systems are very suitable to study speciation phenomena such as gene flow interruption and the origin of endemisms.