Physiological and biochemical indicators of Posidonia oceanica transplantation success

Evaluating the success of Posidonia oceanica transplantation is challenging due to the species' slow growth and delayed structural responses. This three-year study in Calvi Bay (Corsica) examined how transplantation method (iron staples, coconut fiber mats, BESE elements), donor source (donor meadow vs. storm-fragments), transplantation depth (20 m vs. 28 m) and time post transplantation influence the physiological and biochemical parameters of transplanted cuttings. Plant responses were assessed through photosynthetic activity, leaf elemental concentrations (C, N, P, S), and rhizome carbohydrate reserves. Transplanting depth and transplantation method had limited effects on the measured parameters. The transplanting method, influencing root development, suggests distinct strategies for resource acquisition without altering physiological parameters. In contrast, donor source emerged as the main driver of variability: cuttings from donor meadows consistently showed higher nitrogen and phosphorus concentrations, lower C:N ratios, and faster convergence towards natural meadow trait profiles than storm-fragments. Multivariate analyses revealed early convergence between donor meadow cuttings and natural meadows, whereas storm-fragments remained distinct. By 36 months, both donor types again diverged from reference conditions. These results demonstrate the value of trait-based approaches, particularly eco-physiological indicators, as sensitive, early measures of transplantation success, complementing traditional structural metrics. We recommend including C, N, P, and starch concentrations as key biochemical indicators in restoration monitoring programs, as they provide integrative and early signals of seagrass metabolic status and recovery potential. Full convergence with reference meadows appears to be a long-term process, emphasizing the importance of extended monitoring and careful donor selection to improve seagrass restoration outcomes.