The MAGMA cruises were carried out in the West Gironde Mud Patch (WGMP) on the RV Côtes de la Manche over two different seasons: MAGMA-1 (April-May 2021) and MAGMA-2 (October-November 2021). The WGMP is located in the Bay of Biscay off the Gironde estuary. These cruises are key components of the MAGMA project cofunded by LabEx COTE in the framework of the Cluster of Excellence of the University of Bordeaux, the Region Nouvelle-Aquitaine and the Office Français de la Biodiversité. The results should enable to define a strategy to optimize the future monitoring programs of offshore marine habitat (e.g; WGMP ) that will be implemented by the Marine Strategy Framework Directive (MSFD). For doing this, experts associated with different french research organizations (Universities, IFREMER, CNRS) covering a large spectrum of environmental sciences have been gathered on research vessels of the French oceanographic fleet to :

1. Improve our understanding of the structure and the biogeochemical and ecological functioning of the WGMP by relating the temporal changes in the spatial structuring of the descriptors and benthic processes with the hydrological regime of the Gironde and local hydrodynamics (LEG-1);
2. Continue our research effort for a better understanding of the link between biodiversity and biogeochemical processes that control the functioning of its benthic habitat (LEG-1); the MAGMA campagns are continuing the work carried out since 2016 (see JERICObent, DOI:10.18142/284);
3. Assess the particles transfer from the mouth of the Gironde Estuary to the WGMP, and changes in the reactivity of key chemicals during this transfer (LEG-2);
4. Investigate the existence of spatiotemporal changes of contamination and toxicity levels in surface sediments (LEG-1), and assess the link between the sediment contamination and the amount accumulated in benthic macro/megafauna with different feeding modes (LEG-2), and their final transfer to predatory fish (the common sole; LEG-3) to assess the transfer capacity of (in)organic contaminants within the food web;
5. Identify the relationships between early alert biomarkers (eg cellular respiration, detoxication, DNA repair) and classical biomarkers (eg DNA alterations, reproductive stage, growth) at the cellular/individual level for the common sole and the key specie of benthic fauna (LEG-2 et LEG-3).

The MAGMA cruises have allowed : (1) to improve our understanding of the structure and functioning of the WGMP, (2) to cross the evaluations of the environmental quality status of this mudflat obtained from different MSFD descriptors, and (3) to define an optimized environmental monitoring strategy of the WGMP by the Marine Strategy Framework Directive.