Résumé
This paper presents the first study examining the relationship between angiosperms, their associated bivalves, and environmental conditions, with the aim of assessing the health of the El Mellah lagoon. The study was conducted monthly throughout 2019 at three stations selected for their continental and marine influences. The seagrass beds exhibit remarkable abundance, with biomass reaching up to 1313.32 ± 132.73 g DW m⁻² in September. The biomass of Zostera noltei is positively correlated with temperature, while that of Ruppia maritima is positively correlated with salinity. Bivalve density in El Mellah follows the variation in seagrass bed biomass. The densities of the native bivalve Loripes orbiculatus and the invasive species Arcuatula senhousia increase with both the aboveground and belowground biomass of Z. noltei, as well as with temperature. This suggests the existence of a tripartite mutualism between seagrass beds, lucinid bivalves, and their sulphide oxidising gill symbionts. These findings highlight the importance of investigating the factors influencing the mutualistic relationship between seagrasses and lucinid bivalves in the El Mellah lagoon, not only to improve the long-term success of seagrass restoration but also to strengthen their resilience to climate change.