The seagrass Posidonia oceanica is essential for the Mediterranean marine ecosystems, but human activities have led to its decline. This project, conducted by engineering students in collaboration with SARTI Research Group at the Polytechnic University of Catalonia, aims to develop cost-effective methods for replanting P. oceanica. The team designed new chalk substrates for seedling growth, using virtual simulations and field tests near Vilanova I la Geltrú to evaluate their effectiveness. The final design of the chalk substrate features elliptical and cylindrical shapes, optimized for stability and ease of production. These substrates, connected by bamboo frames and secured with hemp fiber ropes, provide a sustainable and biodegradable solution for replanting. Virtual simulations using OrcaFlex helped refine the design by testing its behaviour under various environmental conditions. Initial results were promising, with substrates remaining stable and supporting seedling growth. The project emphasizes sustainable material use, with life cycle analyses confirming the environmental benefits of chalk and bamboo.