Environmental drivers influencing fattening and calcification processes of wild and farmed mussels in the Adriatic Sea

Mussels (Mytilus galloprovincialis) are the most important species for Italian shellfish market. The production mainly comes from sea-farms and wild populations of the northwestern (NW) Adriatic Sea. In recent years, both farmed and wild mussels have experienced meat loss and increased shell fragility, which negatively affects their quality and market value. Since farming techniques have remained mostly unchanged, and wild populations show similar affections, environmental factors are likely contributing to these effects. The main goals of this PRIN-PNRR ENDRIMUS Project are to identify key environmental and biological factors affecting the quality of farmed and wild mussels along a latitudinal gradient on the Adriatic coast, to provide farmers insights for the future development of mussel farms. Environmental analyses showed a salinity gradient toward the south, while other factors (temperature, total alkalinity) and chemistry carbonate parameters resulted homogeneous along the coast. Nutrient concentrations also showed a decreasing gradient toward south during the winter period while during spring season nutrient concentrations appeared more homogeneous across all investigated areas. Moreover, a decreasing trend in chlorophyll a was observed towards south. The abundance of target phytoplankton groups in mussel tissues reflected the expected phytoplankton assemblages. All mussel samples contained seeds, with the settlement season extending until spring when specimens of 2-4 mm total length (TL) were found. Shells of the farmed mussels showed to be more porous and less dense compared to the wild ones, while mechanical properties (like the resistance to fracture) resulted homogenous across sites and between farmed and wild mussels. These are preliminary results obtained by seasonal campaigns in the NW Adriatic Sea aim to contribute in understanding this complex phenomenon affecting Adriatic mussels.