While preserving our coastal ecosystems, in a context of growing anthropogenic pressures (renewable marine energy plants, marine aggregates extraction, fishing, ...), appears as a major social challenge, little is known about the mechanisms leading to ecosystem restoration. Yet, marine environmental management policies, implemented at the European or national level, recommend to focus on mitigation measures (avoiding, reducing and offsetting effects), while considering the cumulative impacts of all human activities. To provide relevant answers in terms of ecosystem management, scientific programs have to focus on defining ecological thresholds that would guarantee the resilience of a given ecosystem. A better understanding of the interaction between pressures, ecosystem functioning and resilience is needed to succeed.

The extraction of marine aggregates is one of the main activities that have been carried out for many years in the coastal area. France is currently the 5th European country in terms of the annual volumes of extracted aggregates (ICES WGEXT annual report 2018). However, the extraction projects are very often controversial, particularly because of its effects (destruction of benthos, creation of a turbid plume, etc.) and potential impacts on environments (habitat modifications, disturbance of the sediment dynamics and effect on coastline migration...). Although the direct effects of extractions have been well described (Dalfsen et al., 2000; Birchenough et al., 2010; Degrendele et al. , 2010; Froján et al., 2011; Hussin et al., 2012; de Backer et al., 2014; de Jong et al., 2014; de Jong et al., 2015; Waye-Barker et al., 2015; Cooper and Barry, 2017; Desprez, 2000; Desprez et al., 2009; Le Bot et al., 2010; Duclos et al., 2013), only a few studies have focused on the resilience of extraction sites after cessation of the operations (Kenny et al., 1994; Boyd et al., 2004; Cooper et al., 200 ; Foden et al., 2009; Frojàn et al., 2011; Desprez, 2000; Le Bot et al., 2010).

The extraction site of Le Pilier (located off the Loire estuary) has been operated between 1986 and 2017. During this period, more than 40 Mm3 of sand and gravel were collected. The extractions led to the creation of a pit of almost 2.5 km² reaching a maximum of 7-8 m depth. The environmental monitoring carried out in accordance with regulations has shown changes in the nature of the superficial sediments. In some places, deeper coarser sediments are now exposed due to the removal of the finer superficial sediments, while in contrast other areas now evidence finer sediments, contributing to a change in benthic community. This site is one of the first large-scale extraction site closed to extraction, and therefore no further extraction will be carried out. Therefore, the site seems particularly well suited to start a scientific research program focusing on the resilience of a site under anthropogenic pressure. During the scientific cruise, biological and physical proxies of the system will be monitored in order to investigate the interaction between ecosystem functioning and resilience.