Multi‐Actor Networks for Monitoring the Invasive Atlantic Blue Crab in Support of Social–Ecological Conservation in the French Mediterranean

ABSTRACT Early observations and adequate monitoring of non‐indigenous species are of paramount importance for conservation, as biological invasions are among the top five drivers for declines in biodiversity. This case study focuses on the Atlantic blue crab ( Callinectes sapidus ), which has unexpectedly become invasive since 2020 in French Mediterranean coastal lagoons. We analyse the development of its multi‐actor monitoring, in which local actors mobilise multiple techniques to produce diversified knowledge, driven by both scientific and political considerations. We examine how the diversification of techniques shapes biodiversity monitoring practices, in order to understand why, despite successive innovations, novel techniques for monitoring aquatic species do not replace former techniques but rather accumulate and complement each other. We used qualitative methods combining multi‐sited observation and 33 semi‐structured interviews with scientists, fishers and public policy stakeholders to identify the drivers and barriers to multi‐actor monitoring. On the one hand, multi‐actor monitoring is facilitated by a strong alignment of aquatic conservation and socio‐economic objectives for managing the Atlantic blue crab. This allows the exchange of environmental knowledge and technical know‐how among stakeholders, therefore fostering their autonomy for implementing monitoring initiatives and subsequent adaptive management measures. On the other hand, several barriers hinder long‐term engagement in multi‐actor monitoring, as producing environmental data implies an unequal division of labour depending on geographical and social position. Placed in the context of the Europeanisation of environmental conservation policy, these results offer a more nuanced perspective on the thesis that standardising monitoring at the supranational level would lead to a decline in the diversity of local knowledge about nature.