Comparative assessment of transplantation methods and donor sources for the restoration of Posidonia oceanica meadows.

The restoration of coastal ecosystems, especially seagrass meadows, has become a key priority to support the recovery of ecosystem services. In the Mediterranean Basin, although many projects have been carried out to restore Posidonia oceanica meadows over the past 50 years, major knowledge gaps persist. This study is the first to simultaneously compare two donor sources, storm fragments versus donor meadow cuttings, and three sustainable transplantation methods. This three-year experiment involved transplanting 693 cuttings using three distinct transplantation methods (iron staples, coconut fiber mats, and BESE elements) in shallow (20 m) and deep (28 m) dead matte areas of Calvi Bay (Corsica, NW Mediterranean). Performance was assessed through survival, shoot production, leaf and root morphological traits, with particular attention given to root systems development, a critical but often overlooked component in seagrass restoration studies. Storm-fragments performed comparably to donor meadow cuttings, supporting their use as a sustainable, non-destructive source of planting material. Among transplantation methods, iron staples led to the best performance across survival, root development, and cost-efficiency. BESE elements ensured high survival but limited root development, while coconut fiber mats performed poorly overall. Despite encouraging survival rates (>80 % under optimal conditions), significant differences in leaf and root traits remained between transplants and natural meadows after 36 months, suggesting incomplete ecological recovery. This comparative approach provides a critical first benchmark for evaluating the feasibility, performance, and economic viability of different restoration techniques in P. oceanica meadows.