Environmental and trophic drivers on growth and shell properties in wild and farmed mussel Mytilus galloprovincialis

We investigated environmental drivers of growth and shell properties in wild and farmed Mytilus galloprovincialis along the north–central Adriatic coast (Rimini, Senigallia, and Giulianova) through seasonal sampling at artificial reefs and mussel farms. Physical, chemical, and biological parameters of the water column were integrated with biometric, physiological, molecular, and skeletal analyses, including shell porosity and bulk density of mussels to evaluate mussel responses to spatial and seasonal variability. Condition index (CI) revealed significant spatial and seasonal differences and was best explained by trophic factors, particularly dinoflagellate abundance and the small phytoplankton (<5 μm) fraction, indicating the importance of food availability and quality for physiological conditions. In contrast, skeletal properties responded primarily to salinity, pCO₂, particulate inorganic matter, and small-size phytoplankton, highlighting cumulative environmental effects on calcification. Random Forest models identified different sets of environmental drivers for CI and shell traits, suggesting partially independent environmental regulation of somatic growth and calcification. Seasonal patterns seemed to reveal trade-offs between tissue growth and skeletal investment, with higher shell porosity during winter under enhanced growth conditions and denser shells during warmer months. Differences between farmed and wild mussels further demonstrated the role of ecological context in shaping shell structural variability. These findings provided a basis for improving site selection and monitoring shell quality in Adriatic mussel aquaculture and, thereby, contributing to the sustainable management of this important species for the ecology and economy in the Adriatic area.