ABSTRACT
The position of estuaries, deltas and lagoons in coastal areas at the interface of marine and riverine infl uences, results in highly variable environmental and ecological conditions that shift over both space and time. In addition, the effects of global change also have a tremendous impact on these ecosystems. The health and conservation of these environments is one of the biggest challenges facing humanity and, in order to achieve integrated management, scientists, ecologists and managers need to select relevant indicators which could be used as tracers for the state of coastal areas. These indicators are generally chosen from living species or physico-chemical parameters or a combination of both. Among the fi sh species living in estuaries, very few occupy these ecosystems in more than one oceanic region, but there is one particular species among the mullets, the fl athead mullet Mugil cephalus which is found worldwide in almost all tropical, subtropical and warm temperate coastal zones. This fi sh is able to live in widely different habitats, but the mechanisms which drive the life cycle of M. cephalus are poorly known or have been studied separately in each area.
