Thau lagoon (south of France) is one of the largest Mediterranean coastal lagoons (Fig. 1). It supports many ecosystem services such as shellfish farming, whose production reaches 10 000 tons a year. Since the 1960s, the increase of anthropogenic inputs, linked to the exponential growth of human population (Fig. 2), have resulted in contaminations of shellfish farming and the eutrophication of Thau lagoon, with significant ecological and socio-economic impacts (Mongruel et al. 2013). Since the 1970s and the late 2000s, the considerable efforts made to water depuration systems on the watershed have induced a significant decrease of nutrient inputs (Fig. 2), and have gradually led to a good environmental status of the lagoon according to the Water Framework Directive (WFD). Dissolved Inorganic Phosphorus (DIP) concentrations were reduced by 99% from 1972 to 2016, moving from bad to high WFD ecological status (Fig. 3). Dissolved inorganic nitrogen, total phosphorus and nitrogen decreased and corresponded to high status from 1999 to 2016 (Derolez et al., 2017).

Simultaneously with the restoration of the lagoon ecosystem, fishermen and shellfish farmers experienced changes in their professional activities related to recent residential and touristic attractiveness of the area. Facing difficulties in their economic sector, they also worry about the potential limiting capacity of the ecosystem.